Nsn Egprs in Bsc

(E)GPRS in BSC

dn99565086Issue 6-0 en

# Nokia CorporationNokia Proprietary and Confidential

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2003319Nokia BSC/TCSM S11 Product Documentation

The information in this documentation is subject to change without notice and describes only theproduct defined in the introduction of this documentation. This documentation is intended for theuse of Nokia's customers only for the purposes of the agreement under which the documentationis submitted, and no part of it may be reproduced or transmitted in any form or means without theprior written permission of Nokia. The documentation has been prepared to be used byprofessional and properly trained personnel, and the customer assumes full responsibility whenusing it. Nokia welcomes customer comments as part of the process of continuous developmentand improvement of the documentation.

The information or statements given in this documentation concerning the suitability, capacity, orperformance of the mentioned hardware or software products cannot be considered binding butshall be defined in the agreement made between Nokia and the customer. However, Nokia hasmade all reasonable efforts to ensure that the instructions contained in the documentation areadequate and free of material errors and omissions. Nokia will, if necessary, explain issueswhich may not be covered by the documentation.

Nokia's liability for any errors in the documentation is limited to the documentary correction oferrors. NOKIA WILL NOT BE RESPONSIBLE IN ANY EVENT FOR ERRORS IN THISDOCUMENTATION OR FOR ANY DAMAGES, INCIDENTAL OR CONSEQUENTIAL(INCLUDING MONETARY LOSSES), that might arise from the use of this documentation or theinformation in it.

This documentation and the product it describes are considered protected by copyrightaccording to the applicable laws.

NOKIA logo is a registered trademark of Nokia Corporation.

Other product names mentioned in this documentation may be trademarks of their respectivecompanies, and they are mentioned for identification purposes only.

Copyright © Nokia Corporation 2003. All rights reserved.

2 (130) # Nokia CorporationNokia Proprietary and Confidential


(E)GPRS in BSC

Contents

Contents 3

List of tables 5

List of figures 6

Summary of changes 7

1 Overview of (E)GPRS in BSC 91.1 Software and hardware requirements of GPRS 131.1.1 Packet Control Unit (PCU) 141.1.2 Gb interface functionality 161.1.3 Additional hardware for GPRS needed by the other BSC models than

BSC3i 181.2 GPRS Interoperability 191.2.1 Interaction of GPRS with other BSC features 20

2 GPRS parameters in BSC 292.1 Radio Network parameters for GPRS 292.2 Dynamic Abis Pool Handling parameters 312.3 Radio Network parameters for EGPRS 322.4 Radio Network parameters for PBCCH/PCCCH 322.5 Radio Network parameters for Priority Based Scheduling 342.6 Radio Network parameters for GSM-WCDMA cell re-selection 342.7 PAFILE parameters 352.8 PRFILE parameters 35

3 GPRS statistics in BSC 393.1 GPRS-specific measurements 393.2 GPRS-related counters in other measurements 423.3 System level trace for GPRS in BSC 43

4 GPRS alarms in BSC 45

5 Radio network management for GPRS in BSC 475.1 Routing Area 475.2 PCU selection algorithm 505.3 Neighbouring cell 505.4 Packet control channels 51

6 Gb interface configuration and state management 536.1 The protocol stack of the Gb interface 536.2 Load sharing function 556.3 NS-VC management function 566.4 BVC management function 606.5 Recovery in restart and switchover 63

7 Dynamic Abis 65



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Contents

7.1 Dynamic Abis Pool management 657.2 EGPRS Dynamic Abis Pool connections 687.3 Capacity of Dynamic Abis 697.4 Error conditions in Dynamic Abis 727.5 Restrictions to Dynamic Abis 72

8 Radio resource management 778.1 Territory method 788.2 Circuit switched traffic channel allocation in GPRS territory 878.3 BTS selection for packet traffic 888.4 Quality of Service 898.5 Channel allocation and scheduling 918.6 Error situations in GPRS connections 96

9 GPRS radio connection control 979.1 Radio channel usage 979.2 Paging 999.3 Mobile terminated TBF (GPRS or EGPRS) 1029.4 Mobile originated TBF (GPRS or EGPRS) 1069.5 Suspend and resume GPRS 1149.6 Flush 1149.7 Cell selection and reselection 1159.8 Traffic administration 1159.9 Coding scheme selection in GPRS 1199.10 Coding scheme selection in EGPRS 1239.11 Power control 126

10 Limitations of the GPRS feature 129



(E)GPRS in BSC

List of tables

Table 1. NS-VC operational states 56

Table 2. BVC operational states 61

Table 3. Coding scheme. Need for master (M) and slave channels (S) on Abis(EDAP) 71

Table 4. Defining the margin of idle TCH/Fs 82

Table 5. Defining the margin of idle TCHs, % 85

Table 6. Supported Network Operation Modes 100

Table 7. EGPRS Coding Schemes 124



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List of tables

List of figures

Figure 1. BSS relation to the GPRS network 10

Figure 2. PCU connections to BTS and SGSN 16

Figure 3. Protocol stack of the Gb interface 16

Figure 4. Gb interface between the BSC and SGSN 18

Figure 5. Relationship of Routing Areas and PCUs 48

Figure 6. The protocol stack on the Gb interface 54

Figure 7. Territory method in BSC 79

Figure 8. GPRS territory upgrade when a time slot is cleared for GPRS use with anintra cell handover 81

Figure 9. PS page and CS page in GPRS 101

Figure 10. Uplink power control 127



(E)GPRS in BSC

Summary of changes

Summary of changes

Changes between document issues are cumulative. Therefore, the latest documentissue contains all changes made to previous issues.

Changes made between issues 06 and 05W

Added information about Extended Uplink TBF Mode and EGPRS PacketChannel Request on CCCH to chapter 9, GPRS radio connection control.

Added the number of PBCCH/PCCCH channels to the EDAP DSP calculationformulas in chapter 7, Dynamic Abis.

List of visible PRFILE parameters updated.

Document name changed to (E)GPRS in BSC.

Some layout changes.

Changes made between issues 05W and 05V

Added another PCU limitation.

Changes made between issues 05V and 05

A warning about sharing a Dynamic Abis Pool between more than one BCFcabinets added.

Information about BTS selection for packet traffic added.



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Summary of changes



(E)GPRS in BSC

1 Overview of (E)GPRS in BSC

The function of the following features in the BSC is described here: BSS9006:GPRS , BSS10083: EGPRS , BSS10074: Support of PCCCH /PBCCH,BSS10084: Quality of Service, BSS10045: Dynamic Abis allocation.

In the context of this description, the term 'GPRS' refers to both GPRS andEGPRS, unless otherwise stated.

This text is applicable for both ANSI and ETSI environments.

GPRS provides packet data radio access for GSM mobile phones. GPRS is welladapted to burst data applications, and it upgrades GSM data services to allow aninterface with Local Area Networks (LAN s), Wide Area Networks (WAN s), andthe Internet.

GPRS uses the radio interface efficiently in two ways. Firstly, it enables a fastmethod for reserving radio channels. Secondly, the benefit of GPRS is the sharingof resources with circuit switched connections. GPRS packets can be transmittedin the free periods between circuit switched calls. Furthermore, GPRS providesimmediate connectivity and high throughput.

On a general level, GPRS connections use the resources only for a short timewhen they are sending or receiving data. When the user is ready to receive newdata, the terminal sends a request, and resources are again reserved only for theduration of transmitting the request and initiating a second data transfer. The datato be transferred is encapsulated into short packets with a header containing theoriginating and destination address. No pre-set time slots are used. Instead,network capacity is allocated when needed and released when not needed. This iscalled statistical multiplexing, in contrast to static time division multiplexing,where time slots are reserved for one user for the length of the connection,regardless of whether it is used or not, as with PCM lines and GSM voice andcircuit switched data.

GPRS offers a very flexible range of bitrates, from less than 100 bit/s to over 100kbit/s. Applications that need less than one time slot benefit from GPRS's abilityto share one time slot among several users. Moreover, the high bitrates that GPRSprovides by using multiple time slots give short response times, even if a lot ofdata is transmitted.



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Overview of (E)GPRS in BSC

The main functions of the BSC with GPRS are to:

. manage GPRS-specific radio network configuration

. control access to GPRS radio resources

. share radio resources between GPRS and circuit switched use

. handle signalling between the MS, BTS and Serving GPRS Support Node(SGSN)

. transfer GPRS data.

The figure below illustrates the GPRS network and how the Base StationSubsystem is related to the core network.

Figure 1. BSS relation to the GPRS network

Enhanced Data Rates for Global Evolution (EDGE) provides services such asEnhanced GPRS (EGPRS) allowing higher data rates than GPRS configurations.The Nokia EDGE Solution includes EGPRS for the packet switched data.EGPRS uses nine modulation and coding schemes (MCS) which vary from 8.8kbps up to 59.2 kbps with one time slot in the radio interface.

Corporate Server

Localareanetwork

Router

HLR/AuC

MSC

BSCBTS

PSTN

Firewall

Firewall

Firewall

R/S

SMS-GMSC

EIR

IP SUBNETWORK155.222.33.XXX

Serving GPRSSupport Node(SGSN)

BorderGateway (BG)

Inter-PLMNBackbonenetwork

Point-To-MultipointServiceCenter(PTM SC)

Gateway GPRSSupport Node(GGSN)

SS7Network

GPRSINFRASTRUCTURE

Datanetwork(X.25)

Datanetwork(Internet)

Intra-PLMNbackbonenetwork(IP based)



(E)GPRS in BSC

Due to GPRS traffic increase, more capacity is needed for the packet commoncontrol signalling. This will bring dedicated CCCH capacity for GPRS services.The PCCCH comprises logical channels for packet common control signalling.

Basically all TBFs (in GPRS calls) have the same priority, that is, all users andall applications get the same service level. The needs of different applicationsdiffer and mechanisms to have separate service levels are required. ETSIspecifications define QoS functionality which gives the possibility to differentiateTBFs by delay, throughput and priority. Priority Based Scheduling is introducedas a first step towards QoS. With Priority Based Scheduling the operator can giveusers different priorities. Higher priority users will get better service than lowerpriority users. There will be no extra blocking to any user, only the experiencedservice quality changes.

Benefits for the operator

GPRS has minimal effects on the handling of circuit switched calls, but theinteroperability of existing circuit switched features needs to be taken intoconsideration (refer to Interoperability for more information). Nevertheless,GPRS does offer additional benefits for the operator:

. resources are better used, thus there is less idle time

. circuit switched traffic is prioritised, but quality is guaranteed by reservingtime slots only for GPRS traffic

. new services, applications, and business for the operator

. fast connection setup for end-users

. high bitrate in data bursts, up to 100 kbit/s (for end-users).

In addition to higher data rates than previous GPRS configurations, EGPRSfurthermore offers the operator the following benefits:

. Migration to wireless multimedia services. The operator could increasedata revenues by offering completely new types of attractive services toend-users.

. Fast network implementation. EDGE capability can be introducedincrementally in the network.

. Optimised network investment as GSM enhancement. Flexible datacapacity deployment where the demand is.



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More information about GPRS:

. GPRS parameters in BSC

- Radio Network parameters for GPRS

- Dynamic Abis Pool Handling parameters

- Radio Network parameters for EGPRS

- Radio Network parameters for PBCCH/PCCCH

- Radio Network parameters for Priority Based Scheduling

- PRFILE parameters

. GPRS statistics in BSC

- GPRS specific measurements

- GPRS related counters in other measurements

- System level trace for GPRS in BSC

. GPRS alarms in BSC

. Radio network management for GPRS in BSC

- Routing Area

- PCU selection algorithm

- Neighbouring cell

- Packet control channels

. Gb interface configuration and state management

- The protocol stack of the Gb interface

- Load sharing function

- NS-VC management function

- BVC management function

- Recovery in restart and switchover

. Dynamic Abis

- Dynamic Abis Pool management

- EGPRS Dynamic Abis Pool connections

- Capacity

- Error conditions in Dynamic Abis

- Restrictions to Dynamic Abis

. Radio resource management

- Territory method

- Circuit switched traffic channel allocation in GPRS territory

- Quality of service



(E)GPRS in BSC

- Channel allocation and scheduling

- Error situations in GPRS connection

. GPRS radio connection control

- Radio channel usage

- Paging

- Mobile terminated GPRS TBF

- Mobile originated GPRS TBF

- Suspend and resume GPRS

- Flush

- Cell selection and reselection

- Traffic administration

- Coding scheme selection in GPRS

- Coding scheme selection for EGPRS

- Power control

. Limitations of the GPRS feature

1.1 Software and hardware requirements of GPRS

The BSC software releases from S9 onwards support GPRS.

The hardware needed for GPRS to function in the BSC are Packet Control Unit(PCU), Gb interface functionality between the BSC and Serving GPRS SupportNode (SGSN), GSWB extension, and ET5C cartridge (optional).

In general, the BSC S10.5 network element HW supports all existingfunctionalities and their implementation principles. BSC S10.5 does not requireany cabling or cartridge changes to the basic configurations of BSCE, BSCi,BSC2E, BSC2A, BSC2i and BSC3i. All modifications to the HW cabling orcartridge are related to the optional EDGE feature.

By the implementation of EDGE (Enhanced Data Rates for Global Evolution) anew service such as Enhanced GPRS (EGPRS) can allow higher data rates thanGPRS configurations. EGPRS can be implemented for the BSC with S9 levelGPRS PCUs. However, a new configuration has been created for BSC2E/A andBSC2i, with the possibilitly to add a second PCU (PCU-S or PCU-T plug-in unit)per BCSU unit (8+1) to further increase the packet processing capacity. Theimplementation of a second PCU also requires a GSWB extension from 192 to256 PCMs. Correspondingly the number of ETs can be extended from 112 to 144in BSC2s.



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BSC3i has two PCU-B plug-in units in each BCSU that each contain two logicalPCUs. So in essence, BSC3i has four PCUs per BCSU.

Additional or optional hardware for EGPRS for BSC3i

. Two PCU-B plug-in units

Additional or optional hardware for EGPRS for other BSCs

. PCU-S or PCU-T PIU and DMCT2-S terminator if not already installed.

. Two additional ET5C-cartridges.

. Fourth SW64B PIU and the SWBUS4 connector to the GSWB.

. AS7-X replaces AS7-V and AS7-VA in new deliveries.

1.1.1 Packet Control Unit (PCU)

For GPRS the BSC needs the Packet Control Unit, which implements both theGb interface and RLC /MAC protocols in the BSS. The Nokia implementation ofthe PCU is in the BSC.

PCU functions

The PCU controls the GPRS radio resources and acts as the key unit in thefollowing procedures:

. GPRS radio resource allocation and management

. GPRS radio connection establishment and management

. data transfer

. coding scheme selection

. PCU statistics.

PCU capacity and connections

Two 2 Mbit/s PCM lines are connected through the GSWB to the Abis interface,and one 2 Mbit/s line to the Gb interface towards the SGSN. Each BCSU has tohave equal number of PCU(s), either one or two. Refer to Enabling GPRS in BSCfor instructions on how to equip and connect the PCU, and to PCU for moreinformation on the plug-in unit hardware.



(E)GPRS in BSC

One PCU can handle the GPRS traffic of 256 radio time slots, and the maximumnumber of connected traffic channels (16kbit/s) in GPRS use in a BSS is 2048(that is, 8 times 256) for BSCE and BSCi, 4096 (16 times 256) for BSC2A,BSC2E and BSC2i, and 6144 (24 times 256) for BSC3i. Furthermore, one PCUcan handle a maximum of 64 BTSs and 128 TRXs. This means that at least fouractive PCUs are required to handle the maximum number of BTSs (248) of oneBSC.

The EGPRS modifications have an effect on the PCU memory demand due to thelarger RLC data block size and possible use of large RLC window size. Once awindow size is selected for a given MS, it may be changed to a larger size but notto a smaller size, in order to prevent dropping data blocks from the window.Therefore, if a TBF is reallocated so that the number of allocated timeslots isreduced, the RLC window size may become larger than the maximum windowsize for the new resources.

There are some limitations to the PCU:

. in one PCU, only 16 DAPs can be created

. in one PCU there can be only 256 channels (including PBCCH/PCCCH +default GPRS + EDAP channels)

. having more than 204 EDAP channels in one PCU is not recommended(requires space for at least 1 master channel per 4 slave channels)

There are also some limitations to the radio network:

. the maximum number of DAPs is 470

. The theoretical maximum number of TRXs per DAP is 20. However, sinceTRXs using DAP resources must be allocated to the same Abis ETPCMline with EDAP, the maximum TRX count for a DAP is 12 in the ETSIenvironment and 8 in the ANSI environment.

. one EDGE synchronisation master channel per TRX must exist (EGPRSlimitation)

. the serving PCU must be the same for all the TRXs under one segment (formore information, see Restrictions to Dynamic Abis )

. If the parameter EGENA is set to Y, then the TRX has to be connected to anEDAP (An exception to this rule is when normal TRXs and EDGE TRXsare in the same cell. Then the parameter GTRX must be set to N in thenormal TRXs and the normal TRXs cannot be attached to the EDAP).



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Figure 2. PCU connections to BTS and SGSN

1.1.2 Gb interface functionality

The Gb interface is an open interface between the BSC and the SGSN. Theinterface consists of the Physical Layer, Network Service layer (NS), and theBase Station Subsystem GPRS Protocol (BSSGP). The layers are brieflydescribed here, but their functions are discussed in more detail in Gb interfaceconfiguration and state management .

Figure 3. Protocol stack of the Gb interface

SGSN

ETs

ETs

ET

DMC bus

PCU

GSWB

Packets in FR

AbisGb

FR: bearer channel + optionalload sharing redundant bearer (2 Mbit/s)

Packets inTRAU frames

4 Mbit/s internal PCM256 channels

SGSNGbBSS

L1

NS

BSSGP

RELAY

RLC

MAC

LLC

BSSGP

NS

L1



(E)GPRS in BSC

The BSSGP protocol functions are BSSGP protocol encoding and decoding,BSSGP virtual connection (BVC ) management, BSSGP data transfer, pagingsupport, and flow control support.

The Network Service Control is responsible for NS protocol encoding anddecoding, NS data transfer, NS Service Data Unit (NS SDU) transmission, uplinkcongestion control on Network Service Virtual Connection (NS-VC ), loadsharing between NS-VCs, NS-VC state management, and GPRS-specificaddressing, which maps cells to virtual connections.

The Frame Relay protocols provide a link layer access between the peer entities.Frame Relay offers permanent virtual circuits (PVC ) to transfer GPRS signallingand data between the BSC and SGSN.

The Gb interface may consist of direct point-to-point connections between theBSS and the SGSN, or an intermediate Frame Relay network may be placedbetween both ends of the Gb interface. In the case of an intermediate Frame Relaynetwork, both BSS and SGSN are treated as the user side of the user-to-networkinterface.

In FR, the physical link is provided by the Frame Relay Bearer channels. In theBSC this physical connection is a maximum of one 2 Mbit/s PCM for each activePCU. For load sharing and transmission security reasons, one PCU can have upto four Frame Relay Bearer channels that are routed to the SGSN throughdifferent transmission paths. This means that the GPRS traffic from one PCU canbe shared with a maximum of four physical PCM connections. The PCUs cannotbe multiplexed to use a common bearer.

The maximum combined Bearer Channel Access Rate in both the ETSI andANSI environments is 2048 kbit/s within a PCU. This can be achieved bycombining the different PCMs so that 32 subtimeslots are available for traffic.The step size is 64 kbit/s. The Committed Information Rate of Network ServiceVirtual Connections can be configured from 16 kbit/s up to the Access Rate of theBearer channel in 16 kbit/s steps.

In the Nokia implementation each PCU represents one and only one NetworkService Entity (NSE).



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Figure 4. Gb interface between the BSC and SGSN

For more information on the NS and BSSGP protocols, refer to BSC-SGSNInterface Specification, Network Service Protocol (NS) and BSC-SGSN InterfaceSpecification, BSS GPRS Protocol (BSSGP) .

The following references, on the other hand, will give you more information onthe configuring and handling of the Gb interface: Enabling GPRS in BSC , FrameRelay Bearer Channel Handling , and Frame Relay Parameter Handling .

1.1.3 Additional hardware for GPRS needed by the other BSC models thanBSC3i

GSWB extension (optional)

The PCU requires the GSWB extension (2 per BSC) for multiplexing the 256Abis sub-time-slots into it. The second PCU card for the BSC unit requires anextension of the GSWB with a third SW64B plug-in unit.

ET5C cartridge (optional)

Additional ET5C cartridges are optional as they are not needed for GPRS.However, they are needed to increase the PCMs from 80 to 112. In the S8optional upgrade to High Capacity BSC they have been added.

BCSU 0

GSWB

FR

PCU

ET

PCM-TSL

bearer channelID=1name=BSC1time slots:1-31access rate:1984 kbit/s

SGSN

BSC



(E)GPRS in BSC

AS7-X, Adapter for CCS7 signalling

The AS7-X is a multichannel signalling link terminal for data or signalling usingthe HDLC format. The capacity of the AS7-X is the same as the AS7-Vand AS7-VA. The memory architecture in AS7-X pre-processor units is based on theSRAM .

The capacity of the AS7-X is as follows:

. 16 CCS7 links, or

. 64 LAPD channels, or

. digital X.25

AS7-X replaces AS7-V and AS7-VA in new deliveries.

1.2 GPRS Interoperability

This section describes how the existing features of the BSC interact with GPRS.

System viewpoint

GPRS needs a number of new network elements and new functionalities.

The new network elements are Serving GPRS Support Nodes (SGSN), GatewayGPRS Support Nodes (GGSN), GPRS backbone, and the Point-to-multipointService Centre (PTM SC).

In addition, mobile stations need to be capable of handling GPRS traffic, andsoftware upgrades are required in BTSs, MSC/VLRs and HLRs, NMSs, and theBSCs. BSC releases from S9 onwards support GPRS.

On the functionality side GPRS requires the following:

. GPRS-specific mobility management, where the location of the MS ishandled separately by the SGSN and by the MSC/VLR even if somecooperation exists

. the network management must be capable of handling the GPRS-specificelements

. new security features for the GPRS backbone

. a new ciphering algorithm



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. a new radio interface (Um) for packet data traffic

. new MAP and GPRS-specific signalling.

For the full use of GPRS all these need to be taken into consideration. The lattertwo � radio interface and GPRS signalling � are relevant to the functioning ofthe BSC.

EGPRS requires the following new network elements and new functionalities:

. new EDGE-capable TRX

. new EDGE-capable MS

. software upgrade to BSC

EGPRS network elements

Nokia EDGE-capable TRXs for the Nokia MetroSite EDGE BTS and theUltraSite EDGE BTS are compatible with GSM TRXs. In addition to providingNokia EDGE services, Nokia EDGE TRXs are fully GSM-compatible andsupport GSM voice, data, HSCSD, GPRS and EGPRS. They are also backwardcompatible with all legacy GSM mobiles.

The Nokia Talk-family BTS site can be upgraded to Nokia EDGE functionalitywith the installation of a Nokia UltraSite EDGE BTS (housing Nokia EDGE-capable TRXs) on the site as an extension cabinet. Site compatibility is achievedwith the synchronisation of Nokia Talk-family BTS and Nokia UltraSite EDGEBTS and by using existing antenna and feeding structures. The synchronizedBTSs share a single BCCH (per sector) and function in the network as a singlecell. The site is then seen as one object by the NMS and the BSC (Multi BCFcontrol feature). In this configuration, the Nokia Talk-family TRXs support voice,9.6 kbits data, HSCSD and GPRS.

1.2.1 Interaction of GPRS with other BSC features

The implementation of GPRS causes changes to the following existing functionsof the BSC:

. the PCU plug-in unit is introduced in Hardware ConfigurationManagement

. GPRS-related radio network parameters are introduced in Radio NetworkConfiguration Management

. co-operation between circuit switched traffic and GPRS traffic is defined inRadio Channel Allocation



(E)GPRS in BSC

. GPRS traffic is monitored by GPRS-specific measurements and counters

. the serving PCU must be same for all the TRXs under one segment.

The implementation is described in detail in Radio network management forGPRS in BSC , Gb interface configuration and state management , Radioresource management , and GPRS radio connection control . GPRS statistics inBSC introduce the new GPRS measurements.

In the BSC the introduction of GPRS means dividing the radio resources �circuit switched and GPRS traffic� into two territories. This has an effect on theradio channel allocation features in which the BSC makes decisions based on theload of traffic. For some features only the resources of the circuit switchedterritory are included in the decisions. However, for most features also the trafficchannels in the GPRS territory need to be taken into consideration when the BSCdefines the traffic load, because radio time slots (RTSL) in the GPRS territorymay be allocated for circuit switched traffic if necessary. Only if there are radiotime slots that are permanently reserved for GPRS use (dedicated GPRSresources), these cannot be used for circuit switched calls and the BSC totallyexcludes these in its decisions on traffic load.

Extended Cell Range

Cell resources in the extended area of a cell are not used for GPRS.

Note

Packet control channels cannot be used with Extended Cell Range.

Frequency Hopping

In Baseband hopping radio time slot 0 belongs to a different hopping group fromother radio time slots of a TRX. This makes radio time slot 0 unusable formultislot connections. If Baseband hopping is employed in a BTS, radio time slot0 of any TRX in the BTS will not be used for GPRS.

Both RF and Baseband hopping are supported in EGPRS.

Optimisation of the MS Power Level

The BSC attempts to allocate the traffic channels within the circuit switchedterritory according to the interference level recommendation the BSC hascalculated, in order to allow the performing of optimisation of the MS powerlevel. When the BSC has to allocate a traffic channel for a circuit switchedrequest in the GPRS territory, the interference level recommendation is no longer



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the guiding factor. Now the first GPRS radio time slot beside the territory borderis taken regardless of its interference level being among the recommended ones ornot. Refer to Radio resource management for more information on the divisionof territories.

Intelligent Underlay-Overlay

Super-reuse frequencies are not supported for GPRS.

Dynamic Hot Spot

For the Dynamic Hot Spot feature also the possible traffic on the GPRS channelsis meaningful. The radio time slots in GPRS traffic are regarded as busy channelsin the algorithms of the Dynamic Hot Spot feature during traffic channelallocation. On the other hand, the BSC applies the Dynamic Hot Spot algorithmwhen it allocates radio time slots for GPRS use in case the radio time slots areabove and beyond the operator-defined GPRS territory. When allocating thedefault GPRS territory that the operator has defined with the parameter defaultGPRS capacity (CDEF) , the BSC does not apply the Dynamic Hot Spotalgorithm.

Dynamic SDCCH allocation

The BSC selects a traffic channel time slot to be reconfigured as a dynamicSDCCH time slot always within the circuit switched territory.

TRX prioritisation in TCH allocation

The operator can set the BCCH TRX or the non-BCCH TRXs as preferred for theGPRS territory with the parameter prefer BCCH frequency GPRS (BFG) .If no preference is indicated, then no prioritisation will be used between differentTRX types when forming the GPRS territory either.

Trunk reservation

In trunk reservation the BSC defines the number of idle traffic channels. The BSCadds together the number of idle traffic channels in the circuit switched territoryand the number of traffic channels in the radio time slots of the GPRS territory,excluding the ones that are in the radio time slots that the BSC has allocatedpermanently for GPRS.



(E)GPRS in BSC

TRX fault

When a TRX carrying traffic channels becomes faulty, the radio time slots on theTRX are blocked from use. The BSC releases the possible ongoing calls and thecall control resources. The BSC downgrades the traffic channels belonging to theGPRS territory in the faulty TRX from GPRS use. To replace the lost GPRScapacity the BSC determines the possibility of a GPRS territory upgrade inanother TRX. Refer to Radio resource management for more information onGPRS territory upgrades and downgrades.

If the faulty TRX functionality is reconfigured to another TRX in the cell, theGPRS-enabled TRX is also transferred to the new TRX.

If the faulty TRX is EDGE-capable, and GPRS in enabled in the TRX andEGPRS is enabled in the BTS, the system tries to reconfigure its functionality toanother EDGE-capable TRX in the BTS.

Resource indication to MSC

In general the BSC�s indication on the resources concerns traffic channels of aBTS excluding those allocated permanently to GPRS (dedicated GPRS channels).GPRS territory resources other than the dedicated ones are regarded as workingand idle resources.

Half Rate

Permanent type half rate time slots are not used for GPRS traffic. Thus it isrecommended not to configure permanent half rate time slots in TRXs that areplanned to be capable of GPRS.

When the BSC can select the channel rate (full rate or half rate) to be used for acircuit switched call based on the traffic load of the target BTS, the load limitsused in the procedure are calculated using the operator defined BSC and BTSparameters lower limit for HR TCH resources (HRL) , upper limitfor HR TCH resources (HRU) , lower limit for FR TCH resources(FRL) , and upper limit for FR TCH resources (FRU) . The BSCparameter CS TCH allocation calculation (CTC) defines how theGPRS territory is seen when the load limits are calculated. Depending on thevalue of CTC either only CS territory or both CS and GPRS territories(excluding the dedicated GPRS timeslots) are used to calculate the load limits.Additionally, with the CTC parameter the user can define whether the resourcesin GPRS territory are seen as idle resources or as occupied resources.

High Speed Circuit Switched Data (HSCSD)

If GPRS has been enabled in a BTS, the HSCSD-related load limits are calculatedbased on the existing HSCSD parameters and the following rules:



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. the number of working resources includes all the working TCH/Fresources of a BTS, excluding the ones that have been allocatedpermanently to GPRS

. the number of occupied TCH/F resources includes all the occupied TCH/Fs of the circuit switched territory, as well as the default GPRS territoryTCH/Fs, excluding the GPRS radio time slots defined as dedicated

. HSCSD parameter HSCSD cell load upper limit (HCU) isreplaced with the radio network GPRS parameter free TSL for CSdowngrade (CSD) if the latter is more restricting; thus the one is usedthat limits HSCSD traffic earlier.

The parameter free TSL for CS downgrade (CSD) defines a margin ofradio time slots that the BSC tries to preserve idle for circuit switched traffic bydowngrading the GPRS territory when necessary.

If HSCSD multislot allocation is denied based on the appropriate parameters, theBSC rejects the transparent HSCSD requests and serves the non-transparentHSCSD requests with one time slot.

If the time slot share in HSCSD allocation is not restricted, the transparentrequests are served preferably in the circuit switched territory, and only ifnecessary in the GPRS territory. If a transparent HSCSD call ends up in the GPRSterritory, the BSC does not try to move it elsewhere with an intra cell handover.Instead it tries to replace the lost GPRS capacity by extending the GPRS territoryon the circuit switched side of the territory border.

When the transparent HSCSD call inside the GPRS territory is later released, theBSC returns the released radio time slots back to GPRS use to keep the GPRSterritory continuous and undivided. Refer to Radio resource management formore information on how the resources form the territories.

The non-transparent HSCSD requests are always served in the circuit switchedterritory as long as there is at least one TCH/F available. A normal HSCSDupgrade procedure is applied later to fulfill the need of the non-transparentrequest, if the call starts with less channels than needed and allowed. In order forthe non-transparent call to get the needed number of time slots, the BSC starts anintra cell handover for suitable single slot calls beside the non-transparentHSCSD call. At the start of the handover, the BSC checks that a single slot callcan be moved to another radio time slot and that HSCSD upgrade is generallyallowed.



(E)GPRS in BSC

A non-transparent HSCSD call enters the GPRS territory only in case ofcongestion of the circuit switched territory. If multislot allocation was originallydefined as allowed, it will be applied also within the GPRS territory to serve thenon-transparent request. If the BTS load later decreases, so that an GPRS territoryupgrade becomes enabled, the non-transparent HSCSD call is handed over toanother location in the BTS so that the GPRS territory can be extended.

When deciding whether to downgrade an HSCSD call or the GPRS territory theBSC checks first if the margin of idle resources defined by the parameter freeTSL for CS downgrade (CSD) exists. If a sufficient margin exists, the BSCacts as without GPRS; that is, using the state information that the HSCSDparameters define for the BTS, the BSC performs an HSCSD downgrade ifnecessary. If the number of idle resources is below the parameter free TSL forCS downgrade (CSD) , then the actions proceed as follows:

. if there are GPRS radio time slots that are above and beyond the operatordefined default GPRS territory then these additional GPRS radio time slotsare the first target for the GPRS territory downgrade

. if there are no additional GPRS radio time slots, the BSC examines if thereare more HSCSD traffic channels than the parameter HSCSD TCHcapacity minimum (HTM) requires and if so, executes an HSCSDdowngrade

. if the minimum HSCSD capacity is not in use, then an GPRS territorydowngrade is made to maintain the margin defined by the parameter freeTSL for CS downgrade (CSD) .

As a TCH/F becomes free through a channel release, the BSC first examines theneed and possibility for an HSCSD upgrade. If the BSC starts no HSCSDupgrade, it further checks the need and possibility for an GPRS upgrade. TheGPRS territory can be upgraded although the parameter HSCSD TCH capacityminimum (HTM) is not in use and there are pending HSCSD connections in thecell. The parameter free TSL for CS upgrade (CSU) and the margin itdefines is the limiting factor for GPRS territory upgrade.

free TSL for CS upgrade (CSU) defines the number of radio time slotsthat has to remain idle in the circuit switched territory after the planned GPRSterritory upgrade has been performed.

Refer to Radio resource management for more information on GPRS territories,and HSCSD and 14.4 kbit/s Data Services in BSC for more information on theHSCSD feature.



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Radio Network Supervision

Actions of the radio network supervision do not apply for time slots that havebeen included in the GPRS territory. The only reasonable thing to monitor is theuplink interference on time slots in GPRS use.

Radio Network Supervision does not apply to the packet control channel.

BTS testing

BTS testing cannot be executed on the packet control channel.

Multi BCF Control, Common BCCH Control

The Multi BCF feature introduces a new radio network object called the Segment.Several BTS objects can belong to one Segment. Only one BTS object of theSegment can have a BCCH. The Segment can have BTS objects, which differ in:

. frequency band (GSM800, PGSM900, EGSM900, GSM1800, andGSM1900)

. power levels (Talk-family and UltraSite base stations)

. regular and super-reuse frequencies

. normal and extended cell radius frequencies

. EDGE capability.

TRXs inside a BTS object must have common capabilities. An exception to thisis that EDGE-capable and non-EDGE-capable TRXs can be configured to thesame BTS object. In this case, GPRS must be disabled in the non-EDGE-capableTRXs. GPRS territory can be defined to each BTS object separately. GPRS andEGPRS territories cannot both be defined to a BTS object at the same time.Super-reuse and extended cell radius frequencies are not supported in GPRS.

There is only one BCCH /CCCH and one or no PBCCH /PCCCH in oneSegment.

Note

The Operator must define GPRS territory to the BCCH frequency band in aCommon BCCH cell in which more than one frequency band is in use. Otherwisethe GPRS feature will not work properly in the cell. The reason for thisrequirement is that in cases when the MS RAC of the GPRS mobile is not known



(E)GPRS in BSC

by the BSC, the TBF must be allocated on the BCCH frequency band first.During the first TBF allocation, the GPRS mobile indicates its frequencycapability to the BSC. After that other frequency bands of the cell can be used forthe GPRS mobile accordingly.

Note

GPRS territory must be configured into the BCCH BTS of a segment with two ormore BTSs on the BCCH band if PBCCH is not used and BTS(s) containing Gpchannels are hopping.

This is due to the fact that without PBCCH, hopping frequency parameters areencoded to the Immediate Assignment on CCCH with indirect encoding. Whenthe allocated BTS is hopping, indirect encoding can only refer to the SystemInformation 13 message, which in the Nokia BSS contains GPRS MobileAllocation only for the BCCH BTS.

The limitation to use only indirect encoding with hopping frequency parametersin Immediate Assignment comes from the fact that Immediate Assignmentmessage segmentation is not supported in the Nokia BSS. The other two possiblehopping frequency encodings, direct 1 and 2, might use a large number of octetsfor the frequency hopping. Large sized frequency parameters cause controlmessage segmentation. Thus as Immediate Assignment segmentation is notsupported, direct 1 and 2 encoding cannot be used.

Therefore, in a segment where BCCH band Gp channels are on hopping BTS(s),the TBFs must initially be allocated to the BCCH BTS. Later, the TBFs may bereallocated to other BTSs as well. Further, if frequency hopping and EGPRS areused in a cell without PBCCH, the operator must configure EDGE territory to theBCCH BTS or to a non-hopping BTS.

See Common BCCH Control in BSC and Multi BCF Control in BSC for moreinformation on Multi BCF and Common BCCH.



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(E)GPRS in BSC

2 GPRS parameters in BSC

The GPRS-related parameters that the user can modify are created to theBSDATA, PRFILE and PAFILE. The parameters are listed and shortly describedhow they are related to GPRS. Refer to BSS Radio Network ParameterDictionary for more detailed information on the BSDATA parameters. Refer toPRFILE and FIFILE Parameter List for a more complete list and description ofthe PRFILE parameters. Refer to PAFILE Timer and Parameter List for a morecomplete list and description of the PAFILE parameters.

More information on GPRS in BSC:

Overview of (E)GPRS in BSC.

2.1 Radio Network parameters for GPRS

Base Transceiver Station parameters

. GPRS non BCCH layer rxlev upper limit (GPU)

. GPRS non BCCH layer rxlev lower limit (GPL)

. direct GPRS access threshold (DIRE)

. max GPRS capacity (CMAX)

. Routing Area Code (RAC)

. GPRS enable (GENA)

. network service entity identifier (NSEI)

. default GPRS capacity (CDEF)

. dedicated GPRS capacity (CDED)

. prefer BCCH frequency GPRS (BFG)

The following eight parameters were PRFILE parameters in S9:



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GPRS parameters in BSC

. DL adaption probability threshold (DLA)

. UL adaption probability threshold (ULA)

. DL BLER crosspoint for CS selection no hop (DLB)

. UL BLER crosspoint for CS selection no hop (ULB)

. DL BLER crosspoint for CS selection hop (DLBH)

. UL BLER crosspoint for CS selection hop (ULBH)

. coding scheme no hop (COD)

. coding scheme hop (CODH)

Adjacent Cell parameters

. adjacent GPRS enabled (AGENA)

GPRS NS Layer Handling parameters

. data link connection identifier (DLCI)

. committed information rate (CIR)

. network service virtual connection identifier (NSVCI)

. network service virtual connection name (NAME)

. network service entity identifier (NSEI)

. bearer channel identifier (BCI)

. bearer channel name (BCN)

Power Control Handling parameters

. binary representation ALPHA (ALPHA)

. binary representation TAU (GAMMA)

. idle mode signal strength filter period (IFP)

. transfer mode signal strength filter period (TFP)

TRX Handling parameters

. GPRS enabled TRX (GTRX)



(E)GPRS in BSC

Base Station Controller parameters

. GPRS territory update guard time (GTUGT)

. maximum number of DL TBF (MNDL)

. maximum number of UL TBF (MNUL)

. CS TCH allocate RTSL0 (CTR)

. CS TCH allocation calculation (CTC)

The following two parameters were UTPFIL parameters in S9:

. free TSL for CS downgrade (CSD)

. free TSL for CS upgrade (CSU)



2.2 Dynamic Abis Pool Handling parameters

. identification (ID)

. Abis interface ET-PCM number and first TSL of the pool(CRCT)

. pool size (SIZE)

. BCSU-unit which handles PCU (BCSU)

. PCU-unit which handles PCU PCMs (PCU)

. new first timeslot (NFT)

. new last timeslot (NLT)

. TRX(s) connected to pool(s) (TRXS)





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2.3 Radio Network parameters for EGPRS


. EGPRS enabled (EGENA)

. EGPRS link adaptation enabled (ELA)

. initial MCS for acknowledged mode (MCA)

. initial MCS for unacknowledged mode (MCU)

. maximum BLER in acknowledged mode (BLA)

. maximum BLER in unacknowledged mode (BLU)

. mean BEP offset GMSK (MBG)

. mean BEP offset 8PSK (MBP)

Power Control parameters

. bit error probability period (BEP)



2.4 Radio Network parameters for PBCCH/PCCCH


. GPRS not allowed access classes (GACC)

. GPRS cell barred (GBAR)

. GPRS rxlev access min (GRXP)

. GPRS MS txpwr max CCH (GTXP1)

. GPRS MS txpwr max CCH 1x00 (GTXP2)

. GPRS cell reselect hysteresis (GHYS)

. RA reselect hysteresis (RRH)

. C31 hysteresis (CHYS)

. C32 qual (QUAL)



(E)GPRS in BSC

. random access retry (RAR)

. reselection time (RES)

. priority class (PRC)

. HCS threshold (HCS)

. PBCCH blocks (PBB)

. PAGCH blocks (PAB)

. PRACH blocks (PRB)

. calculate minimum number of slots (CALC)

. GPRS number of slots spread trans (GSLO)

. GPRS max number of retransmission (GRET)

Adjacent Cell parameters

. GPRS rxlev access min (GRXP)

. GPRS MS txpwr max CCH (GTXP1)

. GPRS MS txpwr max CCH 1x00 (GTXP2)

. priority class (PRC)

. HCS signal level threshold (HCS)

. GPRS temporary offset (GTEO)

. GPRS penalty time (GPET)

. GPRS reselect offset (GREO)

. routing area code (RAC)

. GPRS cell barred (GBAR)





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2.5 Radio Network parameters for Priority BasedScheduling

Base Station Controller parameters

. DL high priority SSS (DHP)

. DL normal priority SSS (DNP)

. DL low priority SSS (DLP)

. UL priority 1 SSS (UP1)






2.6 Radio Network parameters for GSM-WCDMA cellre-selection

The dual mode GSM/WCDMA mobiles are divided into two categories: GPRS-capable and non-GPRS-capable mobiles. The following idle state parameters areonly used by GPRS-capable mobiles:

Base Tranceiver Station parameters

. GPRS threshold to search WCDMA RAN cells (QSRP)

. GPRS fdd cell reselect offset (GFDD)

. GPRS minimum fdd threshold (GFDM)

For more information on these parameters, see section Cell re-selection withGPRS capable mobiles in GSM-WCDMA Inter-System Handover.





(E)GPRS in BSC

2.7 PAFILE parameters

These parameters have no Q3 interface and are stored in PAFILE, not BSDATA:

. DRX TIMER MAX

. MSC RELEASE

. SGSN RELEASE



2.8 PRFILE parameters

The following parameters are related to the Gb interface configuration and statemanagement and the PCU, and to the MAC and RLC protocols (Abis interface):

. TNS_BLOCK

. TNS_RESET

. TNS_TEST

. TNS_ALIVE

. NS_BLOCK_RETRIES

. NS_UNBLOCK_RETRIES

. NS_ALIVE_RETRIES

. NS_RESET_RETRIES

. TGB_BLOCK

. TGB_RESET

. TGB_SUSPEND

. BVC_BLOCK_RETRIES

. BVC_UNBLOCK_RETRIES

. BVC_RESET_RETRIES

. SUSPEND_RETRIES

. EGPRS_DOWNLINK_PENALTY



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. EGPRS_DWNLINK_THRESHOLD

. EGPRS_RE_SEGMENTATION

. EGPRS_UPLINK_PENALTY

. EGPRS_UPLINK_THRESHOLD

. FC_B_MAX_TSL

. FC_B_MAX_TSL_EGPRS

. FC_MS_B_MAX_DEF

. FC_MS_B_MAX_DEF_EGPRS

. FC_MS_R_DEF

. FC_MS_R_DEF_EGPRS

. FC_MS_R_MIN

. FC_R_DIF_TRG_LIMIT

. FC_R_TSL

. FC_R_TSL_EGPRS

. GPRS_DOWNLINK_PENALTY

. GPRS_DOWNLINK_THRESHOLD

. GPRS_UPLINK_PENALTY

. GPRS_UPLINK_THRESHOLD

. MEMORY_OUT_FLAG_SUM

. PRE_EMPTIVE_TRANSMISSIO

. TBF_LOAD_GUARD_THRSHLD

. TBF_SIGNAL_GRD_THRSHLD

. TERRIT_BALANCE_THRSHLD

. TERRIT_UPD_GTIME_GPRS

. UPLNK_RX_LEV_FRG_FACTOR

. DL_TBF_RELEASE_DELAY

. UL_TBF_RELEASE_DELAY

. UL_TBF_REL_DELAY_EXT

. UL_TBF_SCHED_RATE_EXT



(E)GPRS in BSC





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(E)GPRS in BSC

3 GPRS statistics in BSC


. Overview of (E)GPRS in BSC.

3.1 GPRS-specific measurements

For GPRS statistics there are several measurements in the BSC. Some of theseprovide information about the basic functionality of GPRS and some are relatedto some specific GPRS feature.

Packet Control Unit Measurement

The measurement gives cell level information about the functions in the PacketControl Unit (PCU).

The PCU measurement focuses on handling of Temporary Block Flows (TBF ).The same time slots are carrying several interlaced TBFs simultaneously.

The counters of PCU measurement give information about the different phases ofTBF: allocation requests, establishments, reallocations and finally TBF releases.In each of these phases a set of counters is triggered. Most of the counters areprovided for uplink and downlink TBFs separately.

The counters triggered in TBF allocation are counting the number of TBFrequests for different numbers of TSLs (1-8). Respectively, there are counters fordifferent numbers of TSLs that have actually been allocated. The counters for thenumber of TBFs both in acknowledged and unacknowledged mode are triggeredwhen the TBF is established.

In TBF reallocation the resources used to carry the TBF are changed, for examplethe number of TSLs used is increased or decreased. In this phase the counters forthe number of reallocations and reallocation failures is triggered.

When TBF is finally released the counters for maximum and average TBFduration are updated. There are also counters for different release causes.



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GPRS statistics in BSC

PCU Measurement also contains counters for the number of RLC data blocksand indicated bad frames during the measurement period. These counters areavailable for different coding schemes in uplink and downlink separately.Another group of counters is provided for GPRS signalling transactions, such aspaging and immediate assignment as well as some failure situations.

The information is updated with the following protocols and functions: PCUFrame Handler, RLC/MAC , BSSGP and radio channel management.

For further information, see BSC Counters: Packet Control Unit Measurement .

Frame Relay Measurement

The measurement provides bearer channel and Permanent Virtual Connection(PVC ) -specific information on the proper working of the frame relay betweenthe PCU and the SGSN.

The bearer-specific counters give information about the frame errors and bearerstate changes between operational and unoperational states. The PVC-specificcounters provide information about the number of frames and amount of data senton each PVC, as well as the status information of each PVC.

For further information, see BSC Counters: Frame Relay Measurement .

RLC Blocks per TRX Measurement

This measurement provides TRX-specific information on data throughput(number of blocks and retransmitted blocks) quality based on the RLC/MACblocks. The information can be used for the parameterisation of TRX capacity.

The counters are updated by the PCU Frame Handler (PFH) protocol object.

For further information, see BSC Counters: RLC Blocks per TRX Measurement .

Dynamic Abis Measurement

The Dynamic Abis Measurement provides information on the usage of DynamicAbis Pool both in uplink and downlink directions. The counters count the averageand peak usage of EDAP, as well as the unsuccessful or inadequately served TBFschedulings in EGPRS territory due to EDAP capacity load.

This measurement is optional.

For further information, see BSC Counters: Dynamic Abis Measurement .



(E)GPRS in BSC

Coding Scheme Measurement

The modulation techniques of Enhanced GPRS (EGPRS) allow up to three timeshigher data rates per time slot compared to standard GPRS. This has beenachieved by introducing a new type of air interface modulation.

The Coding Scheme Measurement provides information about the amounts ofdata transferred to uplink and downlink directions using the different modulationand coding schemes (MCS) of the EGPRS. The transferred data is represented onthe RLC block level and the number of different types of failures as well as RLCblock retransmissions are also provided in separate counters. The object level ofthis measurement is the BTS and the modulation and coding schemes usedwithin.

This measurement is optional.

For further information, see BSC Counters: Coding Scheme Measurement .

Quality of Service Measurement

The Quality of Service (QoS) Measurement provides information about TBFallocations and their duration, number of transferred RLC blocks, droppedLLCPDUs and average DL flow rate for each priority class. Priority classes arebased on combinations of GPRS delay class and GPRS precedence class values,and they are used in priority-based scheduling. The object levels of thismeasurement are the different priority classes on each segment. There are fourpriority classes in the uplink direction and three priority classes in the downlinkdirection.

For further information, see BSC Counters: Quality of Service Measurement .

PBCCH Availability Measurement

The Packet Broadcast Control Channel (PBCCH ) is used for sending packet-data-specific system information in the downlink direction. The PCCCHcomprises logical channels for common control signaling which are used forpacket data in both directions:

. Packet Paging Channel (PPCH ): Used for paging an MS.

. Packet Random Access Channel (PRACH ).

. Packet Access Grant Channel (PAGCH ).

The multiframe structure for packet control channels consists of 52 TDMAframes, divided into 12 radio blocks (B0-B11).



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The counters in the measurement can be divided into two groups: uplink PCCCHload counters and downlink PCCCH load counters. The contents of the countersare related to channel availability and access.

For further information, see BSC Counters: PBCCH Availability Measurement .



3.2 GPRS-related counters in other measurements

In addition to GPRS-specific measurements, some new counters have been addedto the existing measurements.

Traffic Measurement

The new GPRS counters in Traffic Measurement are related to the GPRS territorymethod. In the territory method the size of the GPRS territory is changedaccording to load situation both on circuit switched as well as on the packetswitched side. The new counters give information about the GPRS upgrade anddowngrade requests, their reasons as well as the possible failure situations.

For further information, see BSC Counters: Traffic Measurement .

Resource Availability Measurement

The new GPRS counters in Resource Availability Measurement provideinformation about the average and peak size of the GPRS territory, i.e. thenumber of default and additional channels delivered for GPRS use. The averageand peak number of dedicated GPRS channels is given in their own counters, aswell as the average holding time of the additional GPRS channels and the numberof additional GPRS channel seizures. This information can be used to indicate theneed for added GPRS capacity and to verify the correct functionality of the GPRSterritory method.

For further information, see BSC Counters: Resource Availability Measurement .

Resource Access Measurement

The Resource Access measurement gives information about the paging load bothon the Gb interface and on the radio interface. There are counters for average andmaximum paging buffer occupancies as well as for the numbers of sent CS andPS paging commands.



(E)GPRS in BSC

For further information, see BSC Counters: Resource Access Measurement .

Handover Measurement

A new counter for intra cell handover attempts due to GPRS (HO ATT DUE TOGPRS) is added. This counter is triggered when an intra cell handover of circuit-switched calls is attempted, while an GPRS territory is upgraded. These CS callsare moved from the new GPRS territory to other available channels in the samecell. Note that this counter may be triggered also without actual GPRS traffic, ifthe GPRS territory mechanism is active.

For further information, see BSC Counters: Handover Measurement .

BSC Clear Code (PM) Measurement

A new counter for intra cell handovers due to GPRS (INTRA GPRS HO) isadded. This counter is triggered when an intra cell handover is successfully madeto the circuit-switched calls, while an GPRS territory is upgraded. These CS callsare moved from the new GPRS territory to other available channels in the samecell. Note that this counter may be triggered also without actual GPRS traffic, ifthe GPRS territory mechanism is active.

For further information, see BSC Counters: BSC Level Clear Code (PM)Measurement .



3.3 System level trace for GPRS in BSC

TBF Observation for GPRS Trace

Trace is already implemented in the GSM network, but the introduction of theGPRS service adds new network elements (SGSN, GGSN) and changes oldprinciples. Therefore, new tracing facilities are needed. Trace is a system levelfeature and in order to get the full advantage out of trace, it should beimplemented in all main network elements of the GPRS network: SGSN, GGSN,BSC, MSC/HLR and NMS.

TBF Observation for GPRS Trace is a part of the System Level Trace for theGPRS feature. It is implemented to expand the tracing capabilities to includepacket switched services. The trace facility enables customer administration andnetwork management to trace the activities of selected subscribers, which resultsin events occurring in the PLMN. The trace facility is a useful maintenance aid



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and a development tool, which can be used during system testing. In particular itmay be used in conjunction with test-MSs to ascertain the digital cell "footprint",the network integrity and also the network quality of service, as perceived in thePLMN. The network management can use the facility, for example, in connectionwith a customer complaint, a suspected equipment malfunction or if authoritiesrequest for a subscriber trace for example in an emergency situation.

The ETSI specifies the tracing facility for GSM, where it refers both to subscribertracing (activated using IMSI) and equipment tracing (activated using IMEI).Only subscriber tracing is supported in BSC. Subscriber tracing can be definedfor a certain subscriber in the HLR or in a specific SGSN. From the BSC point ofview the GPRS trace invocation always comes from the SGSN.

The SGSN invokes the trace by sending a BSSGB SGSN-INVOKE-TRACE(GSM 08.18) message to the BSS when SGSN trace becomes active or whenSGSN receives a trace request. When the BSC receives this message it startstracing. The BSS does not send an acknowledgement of the BSSGB message tothe SGSN. When trace is activated in the BSS and the traced subscriber performsactions causing an allocation of TBFs (Temporary Block Flow) in the BSS thetracing is started. Each TBF reallocation, MCS (Modulation and Coding Scheme)change and finally the TBF release is recorded and a trace record in the BSC isproduced. In the case of a handover between BSCs the tracing is deactivated inthe source side BSC and activated on the target side BSC by an SGSN-INVOKE-TRACE message from SGSN.

The records of GPRS trace in the BSC concentrate on observing two things:resource consumption by the subscriber during tracing and call-quality-relatedtransactions performed on this subscriber. The former includes allocations,reallocations and releases of Temporary Block Flows (TBF). The latter consists ofchanges in the used coding scheme and MS flow control.

The BSC sends the generated trace reports to Nokia NetAct. Trace reports arealso stored in observation files on the BSC's disk.

The System Level Trace for GPRS in the BSC is implemented as a newobservation type in the BSC. This observation cannot, however, be started orstopped by MML commands or from the NMS. The trace is handled only by theSGSN-INVOKE-TRACE messages from the SGSN. If start of this observationtype is tried (without trace) from NetAct, the BSC replies with an error status.

For further information, see BSC Counters: TBF Observation for GPRS Trace .





(E)GPRS in BSC

4 GPRS alarms in BSC

This section lists the main GPRS-related alarms. Keep in mind that many of theexisting alarms may also occur with the use of GPRS. Refer to Alarm ReferenceManuals for detailed alarm descriptions, work instructions, and cancellinginformation.

. 2114 FR VIRTUAL CONNECTION FAILED

. 2115 FR USER LINK INTEGRITY VERIFICATION FAILED

. 2117 FR TRUNK FAILED

. 2188 FR ACCESS DATA UPDATING FAILED

. 2189 COMMUNICATION FAILURE BETWEEN FR TERMINALAND FRCMAN

. 3019 NETWORK SERVICE ENTITY UNAVAILABLE

. 3020 NETWORK SERVICE VIRTUAL CONNECTIONUNAVAILABLE

. 3021 NETWORK SERVICE VIRTUAL CONNECTION UNBLOCKPROCEDURE FAILED

. 3022 NETWORK SERVICE VIRTUAL CONNECTION BLOCKPROCEDURE FAILED

. 3023 NETWORK SERVICE VIRTUAL CONNECTION RESETPROCEDURE FAILED

. 3024 NETWORK SERVICE ENTITY CONFIGURATIONMISMATCH

. 3025 NETWORK SERVICE VIRTUAL CONNECTION TESTPROCEDURE FAILED

. 3026 NETWORK SERVICE VIRTUAL CONNECTION PROTOCOLERROR

. 3027 UPLINK CONGESTION ON THE NETWORK SERVICEVIRTUAL CONNECTION



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GPRS alarms in BSC

. 3028 NETWORK SERVICE VIRTUAL CONNECTION IDENTIFIERUNKNOWN

. 3029 BSSGP VIRTUAL CONNECTION UNBLOCK PROCEDUREFAILED

. 3030 BSSGP VIRTUAL CONNECTION BLOCK PROCEDUREFAILED

. 3031 BSSGP VIRTUAL CONNECTION RESET PROCEDUREFAILED

. 3032 BSSGP VIRTUAL CONNECTION PROTOCOL ERROR

. 3033 UNKNOWN ROUTING AREA OR LOCATION AREA DURINGPAGING

. 3068 EGPRS DYNAMIC ABIS POOL FAILURE

. 3073 FAULTY PCUPCM TIMESLOTS IN PCU

. 3164 PCU PROCESSOR OVERLOAD ALARM

. 7724 CONFLICT BETWEEN BSS RADIO NETWORK DATABASEAND CALL CONTROL

. 7725 TRAFFIC CHANNEL ACTIVATION FAILURE

. 7730 CONFIGURATION OF BCF FAILED

. 7760 FAILURE IN PACKET SYSTEM INFORMATION SENDING





(E)GPRS in BSC

5 Radio network management for GPRS inBSC

For Radio Network Configuration Management the preconditions are that thePCU and Gb interface have been created and configured. In the case of FrameRelay, the user builds the Gb interface in two phases: first the Frame Relay bearerchannels are created, then the NS layer. The BSC then builds the BSSGP virtualconnection automatically when the user enables GPRS. Before enabling GPRSon a cell level, the user needs to create the Routing Area. Refer to GPRSHandling in BSC for detailed task instructions.



5.1 Routing Area

Mobility management in the GPRS network is handled in a similar way to theexisting GSM system. One or more cells form a Routing Area (RA ), which is asubset of one Location Area (LA). The Routing Area is unique within a LocationArea. As Routing Areas are served by SGSNs, it is important to keep in mind thenetwork configuration plan and what has been defined in the SGSN, beforeconfiguring the BSC side. One Routing Area is served by one SGSN.

When creating a Routing Area the user identifies the obligatory parametersmobile country code (MCC) , mobile network code (MNC) ,location area code (LAC) , and routing area code (RAC) . RoutingAreas are created in the BSDATA.

The MCC, MNC, LAC and RAC parameters constitute a routing areaidentification (RAI). In other words:

RAI = MCC+MNC+LAC+RAC



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Radio network management for GPRS in BSC

The Routing Area and the BTS are linked logically together by the RAI. RoutingAreas are used in the PCU selection algorithm which selects a serving PCU forthe cell when the operator enables the GPRS traffic in the cell.

Figure 5. Relationship of Routing Areas and PCUs

Optimal Routing Area size

Paging signalling to mobiles is sent, for example, over the whole Location Area/Routing Area. If a Packet Common Control Channel (PCCCH ) exists in the cell,it is used for paging from the SGSN. This means that one paging message overthe A interface and Gb interface is copied to all Abis links going to the CCCHTRX of the cells in the same paging area. An optimal Routing Area (RA) isbalanced between paging channel load and Routing Area updates. Refer to GPRSradio connection control for more information on paging.

If the Routing Area size is too large, paging channels and capacity will besaturated due to limited LAPD Abis or radio interface CCCH paging capacity.On the other hand, with a small Routing Area there will be a larger number ofRouting Area updates. Paging channel capacity is shared between the paging ofthe existing GSM users to the Location Areas (LA) and the GPRS users to theRouting Area. Based on the traffic behaviour of subscribers and the performanceof the network (in terms of paging success), it is possible to derive guidelinesregarding the maximum number of subscribers per LA/RA.

BTS

RA 2

RA n

BTS

BTS

BTS

BTS

BTS

BTS

RA 1

SGSN

BSCLA

PCU 1

PCU 0

PCU 2



(E)GPRS in BSC

The Routing Area dimensioning is similar to the dimensioning of the LocationArea of the existing GSM service. Routing Area dimensioning balances pagingtraffic from subscribers and the paging capacity offered by a given pagingchannel configuration. The number of pages that are sent by the BTS within anLA/RA indicates the number of mobile terminating calls that are being sent tosubscribers in the LA/RA. The paging demand thus depends on three factors:

. the number of mobile terminating calls

. the number of subscribers in the LA/RA

. paging parameters defined by the operator in the SGSN.

The higher the number of mobile terminating sessions for subscribers in theRouting Area, the higher the number of pages that have to be sent by the BTS inthe Routing Area. The success of paging, that is the number of times that a pagingmessage has to be resent before it is answered, also has a profound effect onpaging traffic. Paging traffic can thus be observed by means of:

. the number of pages per second per user

. the number of subscribers

. the paging success ratio.

The Nokia infrastructure allows a combined Routing Area and Location Areapaging by implementing the Gs interface between the SGSN and MSC/HLR. Anattached GPRS mobile must send a Routing Area Update to the SGSN each timeit changes Routing Area. The SGSN then forwards the relevant location areaupdate information to the MSC reducing the RACH and AGCH load. Theconclusion is that the signalling load is highly dependent on the parameters. Inthe same LA/RA, the paging load should be monitored.

Note

The smallest cell in the LA/RAwill set the paging channel limit where combinedchannel structure is in use. Combined channel structure is possible if the cell isGPRS enabled (Routing Area exists).





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5.2 PCU selection algorithm

The PCU selection algorithm in the BSC distributes GPRS traffic capacitybetween PCUs. Traffic is distributed on a cell level when the user enables GPRSin the cell. The algorithm then selects which PCU takes care of the traffic of acertain cell.

When GPRS is enabled, each cell is situated in a Routing Area. In the RadioNetwork, each Routing Area has its own object, to which the user defines theNetwork Service Entity Identifiers (NSEI ) serving the Routing Area. The NSEIsare further discussed in Gb interface configuration and state management . TheNokia implementation is such that one PCU corresponds to one NSEI, and thus itcan be said that the function of the PCU selection algorithm is to distribute GPRStraffic capacity between these NSEIs.

The algorithm locates the cells (BVCIs ) in the same BCF to the same NSEI. Thealgorithm also tries to locate the cells which have adjacencies between each otherto the same NSEI. If there are no NSEIs with the same BCF or with adjacenciesthen the algorithm selects the NSEI to which the smallest number of GPRScapable traffic channels, defined with the parameter max GPRS capacity(CMAX) , is attached. Traffic channels are counted on TRXs which are GPRSenabled but not extended or super-reuse TRXs. Only unlocked NSEIs areselected. The NSEI is unlocked when it has at least one of its NS-VCs unlocked.

If a Dynamic Abis Pool is defined for a TRX in a cell and when GPRS is enabledfor the cell, the same NSEI (PCU) is selected for the cell as for the Dynamic AbisPool. In this case the PCU selection algorithm is not used.

The NSEIs can also be selected manually. If manual selection is used the PCUselection algorithm is not used. For more information on manual selection refer toGPRS Handling in BSC and Base Transceiver Station Handling in BSC (EQ).



5.3 Neighbouring cell

Introduction of PBCCH makes it possible to have a separate neighbour cell listfor GPRS, enabling GPRS capable MSs to camp only on GPRS capable cells.Furthermore, the usage of C31 and C32 cell selection parameters sent onPBCCH allows GPRS prioritisation of certain cells or network layers.



(E)GPRS in BSC

The new cell re-selection procedure applies to the MSs attached to GPRS if aPBCCH exists in the serving cell. If the PBCCH is not allocated, then the MS willperform cell re-selection according to the C2 criteria. The following cell re-selection criteria are used for GPRS:

. The path loss criterion parameter C1 is used as a minimum signal levelcriterion for cell re-selection for GPRS in the same way as for GSM Idlemode.

. The signal level threshold criterion parameter (C31 ) for hierarchical cellstructures (HCS) is used to determine whether prioritized hierarchicalGPRS cell re-selection shall apply.

. The cell ranking criterion parameter (C32 ) is used to select cells amongthose with the same priority.

The cells to be monitored for cell re-selection are defined in the BA(GPRS) list,which is broadcast on PBCCH . If PBCCH does not exist, BA(GPRS) is equal toBA(BCCH ). A GPRS MS will not camp on a non-GPRS-capable cell, that is,BA(GPRS) is a subgroup of BA(BCCH). The BSC sends the neighbour cell listto the MS in a Packet System Information 3 (PSI3) message, and the 3Gneighbour cell list in a PSI3quater message.



5.4 Packet control channels

In general the packet control channel is configured in the cell with the sameprinciples as other time slot types. The restrictions on the location of channel are:

. The operator can define only one Packet Control Channel (MPBCCH) inthe cell and it must be located in the same TRX as the BCCH . The timeslot of MPBCCH can be from RTSL 1 to 6.

. MPBCCH contains the following logical channels: PBCCH + PCCCH +PTCCH. In the current implementation the MPBCCH does not carry datatraffic. The MPBCCH channel may be located outside the GPRS territory.

MPBCCH is hopping inside the hopping group to which the timeslot belongsaccording to the parameters defined for the hopping group. An MS attached toGPRS will not be required to monitor BCCH if a PBCCH exists. All systeminformation relevant for GPRS and some information relevant for circuit switched



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services is in this case broadcast on PBCCH. When PBCCH exists in the cell theoperator can define the GPRS capability of neighbour cells with the parameters inthe adjacent cell object. Cell-level parameters handle MS-controlled cell re-selection.

In cases where the PBCCH/PCCCH channel is allocated to an EDGE TRX it actsas an EGPRS Abis L1 synchronisation master channel for the GPRS channels ofthe BCCH TRX.

The operator should not create the PBCCH/PCCCH channel in network operationmode II, because CS paging will not work on PCCCH in network operation modeII.





(E)GPRS in BSC

6 Gb interface configuration and statemanagement

The BSC has the following functions in connection with the Gb interface:

. load sharing

. NS-VC management

. BVC management

. recovery.



6.1 The protocol stack of the Gb interface

The Gb interface has a protocol stack consisting of three layers: Physical Layer,Network Service Layer (NS) and the Base Station System GPRS Protocol(BSSGP).



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Gb interface configuration and state management

Figure 6. The protocol stack on the Gb interface

Network Service Virtual Connection (NS-VC)

NS-VCs are end-to-end virtual connections between the BSS and SGSN. Thephysical link in the Gb interface is the Frame Relay Bearer channel.

An NS-VC is the permanent virtual connection (PVC) and corresponds to theFrame Relay DLCI (Data Link Connection Identifier) together with the Bearerchannel identifier. Each NS-VC is identified by means of an NS-VCI (NetworkService Virtual Connection Identifier).

Network Service Virtual Connection Group (NSE)

NSE identifies a group of NS-VCs in the BSC. The NSEI is used by the BSC todetermine the NS-VC that provides service to a BSSGP Virtual connection (BVC). One NSE is configured between two peer NSs. At each side of the Gb interface,there is a one-to-one correspondence between a group of NS-VCs and an NSEI.The NSEI has an end-to-end significance across the Gb interface at NS level, butonly local significance at the BSSGP level. One NSE per PCU is supported andwithin one NSE a maximum of four NS-VCs are supported.

BSSGP Virtual Connection (BVC)

BVCs are communication paths between peer NS user entities on the BSSGPlevel. Each BVC is supported by one NSE and it is used to transport NetworkService Service Data Units (NS SDUs) between peer NS users.

Each BVC is identified by means of a BVCI which has end-to-end significanceacross the Gb interface. Each BVC is unique between two peer NSs.

SGSNGbBSS

L1

NS

BSSGP

RELAY

RLC

MAC

LLC

BSSGP

NS

L1



(E)GPRS in BSC

Within BSS the user identifies a cell uniquely by a BVCI. The BVCI value 0000(hex) is used for signalling and the value 0001 (hex) is reserved for point-to-multipoint (PTM). PTM is not supported. All other values can be used for cellidentifiers.

Link Selector Parameter (LSP)

All BSSGP UNITDATA PDUs related to an MS are passed to NS with the sameLSP. This preserves the order of BSSGP UNITDATA PDUs, since the LSP isalways mapped to the certain NS-VC. LSP has only local significance at each endof the Gb interface.

Permanent Virtual Connection (PVC)

See Network Service Virtual Connection (NS-VC) .



6.2 Load sharing function

The BSC's load sharing function distributes all uplink Network Service ServiceData Units (NS SDU s) among the unblocked NS-VCs within the NSE on the Gbinterface. The use of load sharing also provides the upper layer with seamlessservice upon failure or user intervention by reorganising the SDU traffic betweenthe unblocked NS-VCs. When creating the NS-VC the operator gives a CIRvalue (bit/s). Note that all NS-VC CIR values need to have the same value.

The reorganisation may disturb the order of transmitted SDUs. All NS SDUs tobe transmitted over the Gb interface towards the SGSN are passed from BSSGPto NS along with the Link Selector Parameter (LSP ). For each BVC, NS SDUswith the same LSP are sent on the same NS-VC, since the LSP is always mappedto a certain NS-VC. Thus, the load sharing function guarantees that, for eachBVC, the order of all NS SDUs marked with the same LSP value is preserved.

The load sharing functions of the BSC and SGSN are independent. Therefore,uplink and downlink NS SDUs may be transferred over different NS-VCs. SGSNdistributes downlink NS SDUs.





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6.3 NS-VC management function

The Network Service Virtual Connection (NS-VC) management function isresponsible for the blocking, unblocking, resetting, and testing of NS-VCs. NS-VC management procedures can be triggered by both the BSC and the SGSN.

Only one substate (BL-US, BL-SY or BL-RC) is valid at a time when an NS-VCis blocked. The BL-US state overrides both the BL-SY and BL-RC states. TheBL-SY state overrides the BL-RC state. The BL-RC state does not override anyother blocking state, so it is only possible when the NS-VC is unblocked. Anexception is when the NS-VC is in the BL-SY state and SGSN initiates an NS-RESET. Refer to NS-VC reset.

Table 1. NS-VC operational states

State Possible substates

Unblocked (WO-EX Available) BL-RC (unavailable by remote user)

Blocked BL-US (unavailable by useror BL-SY (unavailable bysystem) or BL-RC (unavailable by remote user)

NS-VC blocking

When an NS-VC is unavailable for BSSGP traffic, the NS-VC is marked asblocked by the BSC and the peer NS is informed by means of the blockingprocedure.

The BSC blocks an NS-VC when:

. the user locks the NS-VC, thus making it unavailable for BSSGP traffic;the cause sent to SGSN is "O & M intervention"; operational state is BL-US

. an NS-VC test fails; the cause sent to SGSN is "Transit network failure";operational state is BL-SY

. Frame Relay detects unavailability of a bearer or PVC; the cause sent toSGSN is "Transit network failure"; operational state is BL-SY

During user block the BSC marks the NS-VC as user blocked, informs peer NSs,and reorganises BSSGP traffic to use other unblocked NS-VCs of the NSE. User-triggered blocking is started only when the PVC or the bearer is available,otherwise the NS-VC is marked as user blocked and the block procedure isskipped. The BSC cancels any pending NS-VC management procedure andrelated alarm.



(E)GPRS in BSC

After NS-VC test failure the NS-VC is marked as system blocked, the BSC raisesthe alarm NETWORK SERVICE VIRTUAL CONNECTION TESTPROCEDURE FAILED (3025 ) and blocks the NS-VC towards the SGSNthrough any 'live' NS-VC within the NSE, blocked or unblocked. The BSC alsoinitiates the NS-VC reset procedure. BSSGP traffic is reorganized to use otherunblocked NS-VCs of the NSE. If the NS-VC is user blocked while reset isattempted, the reset is stopped, the user block is accepted and the state of the NS-VC is user blocked. The BSC cancels the NETWORK SERVICE VIRTUALCONNECTION TEST PROCEDURE FAILED (3025 ) alarm after the nextsuccessful test procedure on the NS-VC. If the NS-VC is already user blocked,the BSC does not change the NS-VC state, it sets no alarms, and sends no blockto the SGSN, but instead initiates the NS-VC reset procedure. After a successfulreset, the test procedure is continued. If the NS-VC reset procedure fails after allthe retries, no alarm is set.

After the BSC detects the unavailability of a PVC or a bearer, the related NS-VC(s) is marked as system blocked and the BSC blocks it towards the SGSN throughany 'live' NS-VC within the NSE, blocked or unblocked. The BSC sets theNETWORK SERVICE VIRTUAL CONNECTION UNAVAILABLE (3020 )alarm for the blocked NS-VC(s) and reorganises BSSGP traffic to use otherunblocked NS-VCs of the NSE. If the NS-VC(s) is already user blocked, whenthe unavailability of a PVC or bearer is detected, the BSC does not change thestate of the NS-VC(s), does not set an alarm, and does not send a block to theSGSN, but instead stops the NS-VC(s) test. If the NS-VC(s) is already systemblocked, the BSC actions are the same but it also stops a possible ongoing resetprocedure.

During an SGSN-initiated block, if the NS-VC is not user, system or remoteblocked, the BSC marks the NS-VC as remote blocked, reorganises BSSGPtraffic to use other unblocked NS-VCs of the NSE and sets the alarm NETWORKSERVICE VIRTUAL CONNECTION UNAVAILABLE (3020 ). If the NS-VC isuser, system or remote blocked, then the BSC does not change the NS-VC stateand acknowledges the received block back to the SGSN.

In all the above cases, if the blocked NS-VC is the last one in the NSE, it meansthat all BSSGP traffic to/from PCU-managed cells stops on the Gb interface, andthe BSC sends System Information messages to relevant cells indicating thatGPRS is disabled. The BSC sets the NETWORK SERVICE ENTITYUNAVAILABLE (3019 ) alarm when PVC/bearers are unavailable, the SGSNinitiates the block, or related BVCs are implicitly blocked.

NS-VC unblocking

When the NS-VC becomes available again for BSSGP traffic, the peer NS isinformed by means of the unblocking procedure, after which the NS-VC ismarked as unblocked by the BSC.



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The BSC unblocks an NS-VC after:

. user unlocks the NS-VC thus making it available for BSSGP traffic.

. the system initiates a NS-VC reset, for example after a test failed NS-VC isreset or after a reset of a NS-VC whose bearer is resumed as available forNS level.

During user unblock the BSC informs the peer NS and marks the NS-VC asunblocked after receiving an acknowledgement from the peer NS. New BSSGPtraffic now uses this new NS link (refer to Load sharing function ). User triggeredunblocking starts only when the PVC or the bearer is available, otherwise theBSC marks the NS-VC as system blocked and skips the unblock procedure. TheBSC sets the NETWORK SERVICE VIRTUAL CONNECTION UNBLOCKPROCEDURE FAILED (3021 ) alarm and marks the NS-VC unblock as pendinguntil NS-VC unblock can be performed and the alarm is cancelled by the BSC.

During system unblock the BSC cancels the NETWORK SERVICE VIRTUALCONNECTION UNAVAILABLE (3020 ) alarm. The BSC does not start systeminitiated unblock if the NS-VC is user blocked.

During SGSN initiated unblock, the BSC marks the NS-VC as unblocked andcancels the NETWORK SERVICE VIRTUAL CONNECTION UNAVAILABLE(3020 ) alarm if the NS-VC is not user or system blocked. If the NS-VC is userblocked, then the BSC is not able to unblock the NS-VC. The NS-VC remainsuser blocked and the BSC initiates the NS-VC blocking procedure by returningan NS-BLOCK PDU to the SGSN with the cause "O & M intervention". ThisNS-BLOCK PDU is sent on the NS-VC where the NS-UNBLOCK PDU wasreceived. If the NS-VC is system blocked with no BSC initiated unblockprocedure on, then the BSC is not able to unblock the NS-VC. The NS-VCremains system blocked and the BSC initiates the NS-VC reset procedure byreturning an NS-RESET PDU to the SGSN with the cause "PDU not compatiblewith the protocol state". If the NS-VC is system blocked with a BSC initiatedunblock procedure on, then the BSC acknowledges the received PDU back to theSGSN and it is interpreted as an acknowledgement for the sent NS-UNBLOCKPDU.

In all the above cases, if the unblocked NS-VC is the first one in the NSE, itmeans that BSSGP traffic to/from PCU-managed cells can start again on the Gbinterface, and the BSC sends System Information messages to relevant cellsindicating that GPRS is enabled. The BSC triggers the BVC reset procedure forsignalling BVC and cell-specific BVCs, and cancels the NETWORK SERVICEENTITY UNAVAILABLE (3019 ) alarm in cases of system unblock and SGSNinitiated unblock.

For more information refer to BSC-SGSN Interface Specification, NetworkService Protocol (NS) .



(E)GPRS in BSC

NS-VC reset

The NS-VC reset procedure is used to reset an NS-VC to a determined statebetween peer NSs.

The BSC resets an NS-VC after:

. the user sets up a new or modifies an existing NS-VC or unlocks an NS-VC; the cause sent to the SGSN is "O & M intervention"

. a system or BCSU restart; the cause sent to the SGSN is "Equipmentfailure" (see BCSU (PCU) restart )

. a periodic NS-VC test fails; the cause sent to the SGSN is "Transit networkfailure"

. Frame Relay detects an unavailability of a bearer; the cause sent to theSGSN is "Transit network failure".

During a reset triggered by user unblock, the BSC marks the NS-VC as systemblocked, informs the peer NS, and reorganises BSSGP traffic to use otherunblocked NS-VCs of the NSE. After a completed reset procedure, the BSC startsa test procedure (periodic testing) and after successful testing unblocks the NS-VC. The BSC starts a reset triggered by user unblock only when the PVC or thebearer is available, otherwise it marks the NS-VC as system blocked, skips thereset procedure, and sets the NETWORK SERVICE VIRTUAL CONNECTIONRESET PROCEDURE FAILED (3023 ) alarm. The BSC sets the NS-VC reset aspending until the NS-VC reset can be performed and then cancels the alarm.

During an SGSN-initiated reset, the BSC marks the NS-VC as remote blockedand sets the NETWORK SERVICE VIRTUAL CONNECTIONUNAVAILABLE (3020 ) alarm if the NS-VC is not user or remote blocked. If theNS-VC is user or remote blocked, then the BSC does not change the state, butacknowledges the received reset back to SGSN and initiates the test procedure. Ifthe NS-VC is system blocked, then the action depends on whether the NS-VCreset is ongoing or not. If the NS-VC reset is ongoing, then the received NS-RESET is interpreted as an acknowledgement and the BSC acknowledges it backto the SGSN and initiates the test procedure. If the NS-VC reset is stopped, thenthe BSC changes the NS-VC state to remote blocked (to get the NS-VC up duringSGSN initiated NS-VC unblock), acknowledges the received reset back to theSGSN, and initiates the test procedure.

In all the above cases, if the blocked NS-VC is the last one in the NSE, it meansthat all BSSGP traffic to/from PCU managed cells stops on the Gb interface, andthe BSC sends System Information messages to relevant cells indicating thatGPRS is disabled. The BSC sets the NETWORK SERVICE ENTITYUNAVAILABLE (3019 ) alarm in a SGSN initiated reset and blocks the relatedBVCs implicitly.



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NS-VC test

The NS-VC test procedure is used when the BSC checks that end-to-endcommunication exists between peer NSs on a given NS-VC. The user can definethe test procedure with the PRFILE parameter TNS_TEST . When end-to-endcommunication exists, the NS-VC is said to be "live", otherwise it is "dead". A"dead" NS-VC cannot be in the unblocked state, instead it is always marked asblocked and a reset procedure is initiated.

Both sides of the Gb interface may initiate the NS-VC test independently fromeach other. This procedure is initiated after successful completion of the resetprocedure, and is then periodically repeated. The test procedure runs onunblocked NS-VCs and also on user blocked and remote blocked NS-VCs, butnot on system blocked NS-VCs, except after NS-VC reset. The test procedure isstopped when the underlying bearer or PVC is unavailable.




6.4 BVC management function

The BVC management function is responsible for the blocking, unblocking andreset of BVCs. The BVC reset procedure can be triggered by both the BSC andthe SGSN, but BVC blocking and unblocking procedures can only be triggeredby the BSC.

The user can output the BVC operational state with the command EQO . Thepossible states are shown in the table below.



(E)GPRS in BSC

Table 2. BVC operational states

State Possible substate

Unblocked (WO-EX, available) BL-SY (unavailable by system)

unblocked

BVC conf lost

unknown

WO-EX The BVC is operational.

BL-SY The NSE is not functional, or a radio network object (a TRX.BST or BCF) is blocked so that the cell does not have GPRScapability.

unblocked Either GPRS has been enabled in the cell and the BVC hasbeen created in the SGSN, but the BVC's flow control is notyet operational, or the cell has no GPRS TSLs.

BVC conf lost The BVC has not been configured for the PCU, or theconfiguration has been lost from the PCU.

This situation can be resolved by disabling, and the re-enabling GPRS in the cell, or by executing BCSU switchover.

unknown The enquired BVCI is outside the allowed value range, or thePCU does not report the state of the BVC within the timelimit because of some fault situation. In the latter case the usershould check the status of the PCU.

BVC blocking and unblocking

BVC blocking is initiated by the BSC to remove a BVC from GPRS data use.

The BSC blocks a BVC after:

. a user disables GPRS in a cell, disables the last GPRS-supporting TRX in acell, blocks the BCCH TRX in a cell, or deletes a BVC by disabling GPRSin a cell; the cause sent to the SGSN is "O & M intervention"

. a user or system block of the last NS-VC of the NSE serving the BVC;related BVCs are locally blocked by the BSC, no indication is sent to theSGSN



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. SGSN initiates a BVC-RESET procedure (if necessary); the cause sent tothe SGSN is "BVCI-blocked"

. a cell level fault, for example at the beginning of site reset, BTS reset orTRX reset; the cause sent to the SGSN is "Equipment failure".

BVC unblocking is used only in an exceptional condition when the BSC receivesan unexpected BVC-BLOCK-ACK PDU relating to a BVC that is locallyunblocked. The BSC then unblocks the BVC with the BVC-UNBLOCK PDU.

For more information refer to BSC-SGSN Interface Specification, BSS GPRSProtocol (BSSGP) .

BVC reset

A BVC reset is initiated by the BSC to bring GPRS data into use in a BVC. BVCreset is used instead of BVC unblock because of the dynamic configuration ofBVCs in the SGSN.

The BSC resets a BVC after:

. the user enables GPRS in a cell, enables the first GPRS-supporting TRX ina cell, deblocks the BCCH TRX in a cell, or creates a BVC by enablingGPRS in a cell; the cause sent to the SGSN is "O & M intervention"

. a user or system unblock of the first NS-VC of the NSE serving the BVC(signalling BVC is reset first, then the rest); the cause sent to the SGSN is"Network service transmission capacity modified from zero kbit/s togreater than zero kbit/s"

. a cell restart, for example after site, BTS or TRX reset, when the restartedobject is working; the cause sent to the SGSN is "Equipment failure".

With the BVC reset the underlying network service must be available for use,otherwise the BSC marks the BVC as unblocked in order to get the BVC up andrunning when the NS-level becomes available again, skips the BVC resetprocedure, and sets the BSSGP VIRTUAL CONNECTION RESETPROCEDURE FAILED (3031 ) alarm. The BSC cancels the alarm after the nextsuccessful BVC block, unblock or reset.

For more information refer to BSC-SGSN Interface Specification, BSS GPRSProtocol (BSSGP) .





(E)GPRS in BSC

6.5 Recovery in restart and switchover

In a recovery situation the BCSU and PCU are always handled together as a pair.The diagnostics of the PCU is included in the diagnostics of the BCSU.Diagnostics is run automatically, but the operator may also start the diagnosticsroutine if needed.

BCSU (PCU) restart

If the Gb interface uses Frame Relay, after user or system initiated BCSU (PCU)restart, the BSC recreates the Gb interface on the restarted PCU right after FrameRelay level set-up. The PCU starts Frame Relay level periodic polling towardsthe SGSN. Spontaneous indications come from the SGSN to the BSC's PCU onFrame Relay level about bearer channel availability for NS-VCs.

First all NS-VCs are created, then all BVCs are created after cell-specific blockindications. The PCU maintains only user blocked information of NS-VCs. TheNS-VCs which have received DLCIs from the network are reset when the bearerchannel is available. The PCU sets others as pending and raises the NETWORKSERVICE VIRTUAL CONNECTION RESET PROCEDURE FAILED (3023 )alarm for each NS-VC.

The reset procedure is completed when the PCU receives a suitable DLCI fromthe network, and cancels the alarm. The PCU then initiates the test procedure onthe successfully reset NS-VCs, and after successful tests unblocks all tested NS-VCs, and resets the signalling BVC. After successful BVC reset the uplinkBSSGP data delivery is possible on that BVC. After an initial flow controlprocedure for the BVCs, also downlink BSSGP data delivery is possible on thatBVC. Flow control is discussed more in GPRS radio connection control .

BCSU (PCU) switchover

If the Gb interface uses Frame Relay, after BCSU (PCU) switchover (either useror system initiated), the BSC recreates the Gb interface on the target PCU rightafter Frame Relay level set-up. The Gb interface configuration is from the sourcePCU and the setting up of the Gb interface is similar to what was described in thesection BCSU (PCU) restart.

The BSC does not send NS level blocks from the source PCU in order not tointerrupt the BVC configurations of the SGSN.

Forced BCSU (PCU) switchover

The operation in a forced BCSU (PCU) switchover is very similar to theoperation in a BCSU (PCU) restart. The PCU releases all PCU PCM connectionsrelated to the restarted PCU. All GPRS data connections will drop after the PCUPCM connections are released.



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After the switchover � whether user or system initiated � the BSC unblocksTRXs and delivers new territory to the PCU.

Controlled BCSU (PCU) switchover

A controlled BCSU (PCU) switchover is always a user action given with anMML command. The user defines between which BCSUs the switchover ismade, and the system tries to make it. A controlled switchover may fail, forexample the system may cancel the switchover command if the execution couldlead to a situation where some of the circuit switched calls would drop. If theswitchover fails, the original working BCSU is restored back to the working state.

Note

Only GPRS data connections that are connected to the PCU are released.

In a successful switchover, the BSC moves the control of the working BCSU/PCU pair to the spare BCSU/PCU pair as in the forced switchover, but data iscopied only from the working BCSU to the spare BCSU. Because GPRS data isnot copied to the PCU, the PCU sees the data as lost and thus releases all its PCUPCM connections and unblocks its BTSs. The BSC resets the new spare PCU tothe working state, and defines its new GPRS territory.

If the switchover is cancelled for some reason, the original working PCU isrestored back to the working state, and the BSC resumes GPRS territoryupdatings. The BSC allows new GPRS connection setups in the old workingPCU again. After an unsuccessful switchover the PCU uses the same GPRSterritory as it had before the switchover. At the end of the switchover the sparePCU is restarted regardless of the switchover being successful or not.





(E)GPRS in BSC

7 Dynamic Abis

The increasing capacity demand of the services connected over EDGE sets newdemands for Abis interface transmission, as well. The Abis interface transmissionrequirement varies a lot depending on the call type used. It is not sensible toallocate fixed transmission capacity according to the highest possible data rate forevery traffic channel from the Abis interface but share common transmissionresources between several traffic channels.

The Dynamic Abis feature makes it possible to define common transmissionresources for EDGE capable TRXs situated in the same Abis ET-PCM. Thiscommon resource is called the Dynamic Abis Pool. There are fixedly allocatedtransmission resources for Abis signalling links and traffic channels in Abis ET-PCM as before but extra transmission resources needed for EGPRS calls arereserved from the dynamic Abis pool.

Refer to Dynamic Abis pool handling for operating instructions on how to handleDynamic Abis pools in the BSC.



7.1 Dynamic Abis Pool management

Dynamic Abis is an optional feature. However, the Dynamic Abis feature is amandatory feature to enable EGPRS support in the BSC and in the PCU. Ifdynamic Abis is used, the operator must define the pool to be used by the TRX. Itmust be located on the same PCM as TRXSIG and the fixed traffic timeslots.Dynamic Abis usage cannot be modified later. If the operator wants to change theTRX's usage of Dynamic Abis, the TRX must be deleted and created again. CScalls are handled as before. Abis capacity is allocated fixedly.



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Activating Dynamic Abis Pool for EGPRS use

The operator can allocate common transmission resources for EDGE capableTRXs from the Abis ET-PCM. This common resource is called the Dynamic AbisPool (DAP) and it is comprised of consecutive Abis ET-PCM timeslots. Therecan be several DAPs in one Abis ET-PCM but normally only one is needed. TheDAP has to be created before the EDGE TRXs using the DAP are created to theAbis ET-PCM.

When a DAP is created, the BSC reserves the corresponding block of timeslotsfrom the PCUPCM. These PCUPCM circuits are needed when DAP circuits areconnected to EGPRS use. The BSC downgrades all packet switched trafficchannels from the PCU and then upgrades these same traffic channels to packetswitched use again. This short interruption ensures that the BSC can find a blockof free timeslots from the PCUPCM and to ensure optimised PCU DSP resourceusage for each DAP connected to the PCU. Refer to Creating dynamic Abis poolfor operating instructions on how to handle Dynamic Abis pools in the BSC.

Dynamic Abis Pool modification

The operator can change the size of the Dynamic Abis Pool (DAP) by addingAbis ET-PCM timeslots to DAP, or by removing Abis ET-PCM timeslots fromDAP. The integrity of the DAP is kept up in these operations. This means thatnew Abis ET-PCM timeslots are added to either upper or lower edge of the DAPand Abis ET-PCM timeslots are removed from either upper or lower edge of theDAP.

When new Abis ET-PCM timeslots are added to DAP, BSC reserves acorresponding block of timeslots from PCUPCM. These PCUPCM circuits areneeded when DAP circuits are connected to EGPRS use. The BSC downgradesall packet switched traffic channels from PCU and then upgrades these sametraffic channels to packet switched use again. This short interruption ensures thatthe BSC can find a block of free timeslots from the PCUPCM and to ensureoptimised PCU DSP resource usage for each DAP connected to the PCU.

The operator can also change the controlling PCU of the DAP. When the DAP'sPCU is changed, the BSC downgrades all packet switched traffic channels fromboth the old and the new PCU and then upgrades these same traffic channels topacket switched use again. This short interruption ensures optimised PCU DSPresource usage for each DAP connected to those PCUs. If there are one or moreTRXs attached to that pool, the packet swithed channels of the segments of theTRXs are upgraded to the new PCU. Refer to Modifying Dynamic Abis pool foroperating instructions on how to handle Dynamic Abis pools in the BSC.



(E)GPRS in BSC

Dynamic Abis Pool deletion

The operator can delete Dynamic Abis Pool (DAP) when there are no TRXsattached to it. The BSC releases all resources reserved for the DAP when it isdeleted. The BSC downgrades all packet switched traffic channels from the PCUand then upgrades these same traffic channels to packet switched use again. Thisshort interruption ensures ensures optimised PCU DSP resource usage for eachother DAP connected to the PCU. Refer toDeleting Dynamic Abis pool foroperating instructions on how to handle Dynamic Abis pools in the BSC.

Dynamic Abis Pool circuit routings

Circuit routings are needed for Abis ET-PCM circuits to utilise the Dynamic Abisfeature in BSC. The BSC makes these routings automatically when DynamicAbis Pool (DAP) is created, modified or deleted.

The BSC adds Abis ET-PCM circuits to a circuit group named �ET-PCM� at thesame time as the Abis ET-PCM circuits are added to DAP. This prevents other useof these Abis ET-PCM circuits while they belong to the DAP. The ET-PCMcircuit group is common for all DAP circuits.

The BSC has also own circuit group for every DAP. These DAP circuit groupsare named to �DAPxxx�, where �xxx� indicates Dynamic Abis Pool number withthree digits. The DAP circuit group is specially designed for Dynamic Abis and itenables hunting and connection methods required by Dynamic Abis. The BSCadds DAP circuits to the DAP circuit group as one bit wide circuits which are inascending order according to timeslots and subtimeslot. The BSC changes statesof these circuits from BA to WO at the same time as the circuits are added tocircuit group.

Note

It is not allowed to make changes to DAP routings manually even if it is possiblewith MML commands provided by the DX200 platform. Removing DAProutings causes malfunction of the Dynamic Abis feature.





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7.2 EGPRS Dynamic Abis Pool connections

The BSC connects Dynamic Abis Pool circuits to EGPRS use. The DAP areaconnected to EGPRS use is called the EGPRS Dynamic Abis Pool (EDAP). Theprocedure where DAP circuits are connected to EGPRS use is called the EDAPupgrade procedure and the procedure where DAP circuits are removed fromEGPRS use is called the EDAP downgrade procedure. If GPRS service isprovided with an EDGE TRX, EDAP circuits may also be used for GPRS. InEDAP upgrade and downgrade the BSC downgrades all packet switched trafficchannels from the PCU and then upgrades these same traffic channels to packetswitched use again. This short interruption ensures optimised PCU DSP resourceusage for each DAP connected to the PCU.

EGPRS Dynamic Abis Pool upgrade

The BSC performs the EDAP upgrade procedure when:

1. the DAP is created

2. new circuits are added to the DAP

3. the PCU controlling the DAP is restarted

There are two phases in the EDAP upgrade procedure. In the first phase the BSCmakes connections between Abis ET-PCM circuits and PCUPCM circuits. In thesecond phase the BSC attaches DAP circuits to EDAP by informing the PCUabout mappings between the Abis ET-PCM circuits and the PCUPCM circuits.

The BSC connects DAP circuits to EDAP starting from the last circuit and thenconnecting the next circuit from the side of previous circuit as long as there arecircuits configured to EGPRS use. EDAP is always comprised of consecutiveDAP circuits. All the circuits belonging to the DAP are connected to the EDAP.

EGPRS Dynamic Abis Pool downgrade

The BSC starts the EDAP downgrade procedure when:

1. the DAP is deleted

2. circuits are removed from the DAP

There are two phases in the EDAP downgrade procedure. In the first phase theBSC detaches DAP circuits from the EDAP by informing the PCU about changedmappings between Abis ET-PCM circuits and PCUPCM circuits. In the secondphase the BSC releases connections between the Abis ET-PCM circuits and thePCUPCM circuits.



(E)GPRS in BSC

BCSU (PCU) restart

When the BCSU is restarted the BSC releases all EDAP connections related tothe BCSU. After the PCU becomes operational again, the BSC runs an upgradeprocedure for each EDAP controlled by the PCU. The PCU shares the DSPresources optimally for all the EDAPs when the BCSU (PCU) is restarted.

BCSU (PCU) switchover

If a switchover is made for the BCSU, the BSC releases all EDAP connectionsrelated to the old BCSU and then starts an upgrade procedure to recover theEDAP connections in the new BCSU. The PCU shares the DSP resourcesoptimally for all the EDAPs in BCSU (PCU) switchover.



7.3 Capacity of Dynamic Abis

The capacity of a specific EDAP depends on the total count of EDAPs in thePCU, on the EDAP size, on the number of EDGE TRXs and EGPRS channels/PDCHs connected to the EDAP, and on the modulation and coding schemes(MCS) used in data transmission. The MCSs that are used are selected by thePCU based on the radio link quality measurements and Link Adaptionalgorithms. Operator parameters for initial MCSs are also taken into accountwhen selecting an MCS for data transmission. However, Dynamic Abis capacity(EDAP size and available PCU DSP resources) also affects MCS usage and dueto this, Dynamic Abis and PCU capacity limitations are also taken into account inMCS selection.

Dynamic Abis counters monitor EDAP usage and Dynamic Abis limitations toTBF scheduling in the EGPRS territory. The following actions may have to beconsidered if the Dynamic Abis counters indicate problems in Dynamic Abisusage:

. increasing EDAP size

. decreasing the number of EDGE TRXs and/or EGPRS channels attachedto EDAP

. sharing the load between PCUs (moving an EDAP(s) and/or GPRSchannels from one PCU to another)

. decreasing the initial CS/MCS for TBFs, in DL and/or UL direction



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GPRS TBF

In the BSC there are separate territories for GPRS and EGPRS. In onther words,GPRS traffic primarily uses non-EDGE TRXs and EGPRS traffic uses EDGETRXs. In GPRS load situations or when a GPRS territory does not exist, it ispossible that GPRS traffic (GPRS TBFs) uses EGPRS capacity from the EGPRSterritory. Nokia supports only coding schemes CS-1 and CS-2 in standard GPRSservice. When a GPRS TBF is via GPRS territory (via a non-EDGE TRX), theCS-2 coding scheme needs only 16 kbit/s from Abis. When a GPRS TBF is viaEGPRS territory (via an EDGE TRX), the CS-2 coding scheme needs a 16 kbit/smaster Abis channel and one 16 kbit/s slave channel from the EDAP. This isbecause the EDGE TRX uses different TRAU formats and synchronizationschemes. This means that master Abis channels and EDAP resources are onlyused by the EGPRS territory. The EDAP is not used by the GPRS territory.

In case a 16 kbit/s slave channel for a GPRS TBF cannot be found, for exampledue to the EDAP load situation, CS-2 cannot be used. In the UL direction, theMS's transmission turn may have to be rejected. In the DL direction, CS-1 may beused instead of CS-2 in certain cases.

Otherwise GPRS release 1 procedures apply for GPRS.

EGPRS TBF

The GPRS RR procedures apply in EGPRS as well. The difference comes fromthe EGPRS's need for more than 16 kbit/s Abis channels. The master Abischannel is always linked to a PDTCH . The rest of the required Abis transmissionis allocated from the EDAP in 16-64 kbit/s blocks, depending on the codingscheme (MCS) used. The Dynamic Abis resource information and coding schemeis told to the BTS by inband signalling of the EGPRS Abis L1 in the PCU masterdata frame transferred on the master Abis channel PCU frame with everydownlink block. So there will be two new PCU frame formats: a PCU master dataframe for the master Abis channel and a PCU slave data frame for the EGPRSslave channel.

In case enough 16 kbit/s slave channels for the coding scheme (MCS) used by theEGPRS TBF cannot be found due to the EDAP load situation, the desired codingscheme cannot be used. In the UL direction, the MS's transmission turn may haveto be rejected. In the DL direction, a lower coding scheme may be used instead ofthe desired coding scheme in certain cases.



(E)GPRS in BSC

Table 3. Coding scheme. Need formaster (M) and slavechannels (S) on Abis(EDAP)

CS/MCS

Need for masterand slavechannels

CS1 M

CS2 M+S

MCS1 M

MCS2 M+S

MCS3 M+S

MCS4 M+S

MCS5 M+S

MCS6 M+ 2*S

MCS7 M+ 3*S

MCS8 M+ 4*S

MCS9 M+ 4*S

The Dynamic Abis feature introduces new statistics measurements and counters.The purpose of all measurements is to help the operator to monitor/control theusage of EDAPs and to give the operator better possibilities to configure/optimizefor example EDAP sizes. There are separate counters for both UL and DLmeasurements.

Note

However, EDAP size is the same for both DL and UL directions, so it is notpossible to set different EDAP sizes for DL and UL directions.

For further information on statistics related to Dynamic Abis, see BSC Counters:Dynamic Abis Measurement .



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7.4 Error conditions in Dynamic Abis

If the BSC cannot connect one DAP circuit to EDAP because of connectionfailure, the BSC sets the alarm EGPRS DYNAMIC ABIS POOL FAILURE(3068 ) and then attaches all successfully connected DAP circuits to EDAP.

The BSC sets the alarm EGPRS DYNAMIC ABIS POOL FAILURE (3068 ) ifan EDAP configuration update or an EDAP modification to PCU fails.

PCU capacity (for example, PCU DSP resource load for on-going EGPRS callsusing EDAP resources) may start limiting the EGPRS and GPRS RR procedures.It is possible that new GPRS TCHs cannot be added to the PCU.

If the BSC cannot attach DAP circuits to EDAP, the BSC sets the alarm EGPRSDYNAMIC ABIS POOL FAILURE (3068 ).



7.5 Restrictions to Dynamic Abis

Only Nokia UltraSite EDGE BTSs and Nokia MetroSite EDGE BTSs are able touse Dynamic Abis allocation. Furthermore, only EDGE capable TRXs (EDGETRX) are capable of using shared EGPRS Dynamic Abis Pool (EDAP) resources.

Internal PCU restrictions:



(E)GPRS in BSC

. A PCU has 16 DSP cores. One DSP core can handle only one EDAP, butone EDAP can be shared by several DSP cores. The maximum number ofEDAPs per PCU is 16.

. One DSP core can handle 0&20 channels (16 kbit/s) including activeEDAP channels, EGPRS channels, GPRS channels and PBCCH/PCCCHs. The maximum number of 16 kbit/s channels per PCU is 256.

. All EGPRS channels of one EDGE TRX must be handled in the DSP corethat handles the related EDAP. If the EDAP is handled by several DSPcores, the EGPRS channels of one EDGE TRX can be divided to severalDSP cores.

PCUPCM allocation restrictions:

. one EDAP cannot be divided to separate PCUPCMs

. Every EDGE TRX must have one synchronization master channel(SMCH). SMCHs are allocated from the beginning of PCUPCM 0 andthey are usually allocated to a different PCUPCM TSL than other EGPRSchannels in the same TRX.

. One PCUPCM TSL (64 kbit/s = 4 x 16 kbit/s subTSLs) must be handled inone DSP core.

A PCU shares DSP resources optimally for EDAPs when a new dynamic Abispool is created or an existing pool is deleted or modified. DSP resources are alsoshared after BCSU restart or switchover. A PCU shares all (working) DSP coresbetween all EDAP's connected to the PCU by using a PCU internal algorithm.PCU DSP resources for an individual EDAP depends on the total number ofEDAPs for the PCU and on EDAP-specific properties (EDAP size and attacheddefault EGPRS channel count). Because the following formulas use the EDAP-specific default EGPRS channel count, BCSU switchover is recommended whenthe default EGPRS channel count is changed, in order to maintain optimal PCUDSP resource sharing for EDAPs.

First the PCU calculates the ideal DSP core count for each EDAP:

, where

IdealDSPcoreCountForEDAP=EDAPsizeIn16kbit/sChannels + DefaultEGPRSchannels+ PBCCH_PCCCHs

20



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. EDAPsizeIn16kbit/sChannels is EDAP size in 16 kbit/s PCM subTSLs

. DefaultEGPRSChannels is the sum of default EGPRS channels of all theTRXs (BTSs) attached to the EDAP

. PBCCH_PCCCHs is the number of PBCCH/PCCCH channels

. 20 is the 16kbit/s channel handling capacity of a single PCU DSP core

The ideal DSP core count is rounded upwards.

For each EDAP, the PCU also calculates the EDAP DSP load based on the idealDSP core count for that EDAP:

If the sum of ideal DSP core counts for all EDAPs in the PCU differs from theavailable DSP core count, the PCU adjusts DSP resources for each EDAPaccording to the available DSP core count. If the sum of ideal DSP core countsfor all EDAPs in the PCU is less than the available DSP core count, then the extraDSP cores are allocated to the EDAPs, starting from the EDAP with the highestDSP EDAP load. If the sum of ideal DSP core counts for all EDAPs in the PCUis more than the available DSP core count, then the PCU decreases the DSP corecount for the EDAPs that have the lowest DSP EDAP loads until the sum ofallocated DSP core counts equals the available DSP cores. However, each EDAPgets at least one DSP core.

PCU DSP resources assigned to an EDAP may limit the usage of EDAPresources and PCU capacity for new GPRS channels.

A possible but bad configuration example:

. One EDAP containing 12 TSLs and 15 EDAPs containing 2 TSLs each areconfigured to one PCU. The first EDAP is handled in one DSP core, andthe EDAP has 48 channels. Only 16 EDAP channels of the first EDAP canbe used by 4 EGPRS channels.

Warning

WARNING: One EDAP resource should not be shared between several BCFcabinets. It may damage the TRX or DTRU hardware if the operator tries toshare EDAP between several cabinets.

DSP_EDAPload=EDAPsizeIn16kbit/sChannels + DefaultEGPRSchannels+ PBCCH_PCCCHs

IdealDSPcoreCountForEDAP



(E)GPRS in BSC





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(E)GPRS in BSC

8 Radio resource management

Channel allocation for GPRS data users is a two-phase procedure in the BSC.

In the first phase of the GPRS channel allocation the BSC defines the territory forGPRS, which means selecting the radio time slots that the BSC will use primarilyfor packet data traffic and therefore avoid in traffic channel allocation for circuitswitched services. The second phase includes the PCU activity during which thedifferent GPRS channels are assigned for GPRS TBFs within the radio time slotsof the GPRS territory.

The radio resource management function that allocates traffic channels for thecircuit switched calls is also responsible for the territory management and theresource share between the circuit switched services and GPRS. The PCU has itsown radio channel allocation that takes care of allocating channels for GPRSTBFs. Up to seven uplink GPRS TBFs can share the resources of a single radiotime slot. The uplink and downlink schedulings are independent of each other,and for downlink up to sixteen GPRS TBFs can share the resources of a singleradio time slot.

First the operator has to activate the GPRS feature in the BSC with the cell-specific parameter GPRS enable (GENA) and define which TRXs are capableof GPRS with the parameter GPRS enabled TRX (GTRX) . To activate theEGPRS feature, the operator uses the BTS-specific parameter EGPRS enable(EGENA) . The BTS can contain both EDGE-capable and non-EDGE-capableTRXs (HW), if GPRS is disabled in the non-EDGE-capable TRXs. The operatorneeds to define which TRXs are capable of EGPRS with the parameter GPRSenabled TRX (GTRX) .

Only after the BSC has an update on the BTS parameters and other parametersindicating GPRS usage, does it count the number of default and dedicated GPRStime slots in the BTS and selects a TRX where it starts to establish the GPRSterritory.

The BSC can upgrade or downgrade the number of radio resources allocated forGPRS use according to the varying needs of the circuit switched and GPRStraffic. These procedures are also explained in detail below.




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8.1 Territory method

The territory method is the same for GPRS and EGPRS.

The BSC divides radio resources semipermanently between circuit switchedservices and GPRS, thus forming two territories. The PCU uses the GPRSterritory resources. The initial territories are formed on a BTS-to-BTS basisaccording to the operator-defined parameters. The BSC can later broaden theGPRS territory based on the actual need and according to the requests of thePCU.

The circuit switched services have priority over GPRS in channel allocationwithin common resources. GPRS releases its resources as soon as they are neededfor circuit switched traffic.

Within a cell, all the Full Rate and Dual Rate traffic channels are GPRS capable.GPRS capacity can be divided into three types:

. default GPRS capacity

. dedicated GPRS capacity

. additional GPRS capacity.

GPRS has a predefined set of resources which it can utilise when the circuitswitched load allows. This is referred to as the default GPRS capacity. Part ofthese default traffic channels can be reserved solely for GPRS and this meansthey are blocked altogether from circuit switched use. This is referred to as thededicated GPRS capacity. The user can modify these two capacities by using therespective parameters default GPRS capacity (CDEF) and dedicatedGPRS capacity (CDED) .

Additional GPRS capacity is referred to with radio time slots that are above andbeyond the default GPRS capacity and that the BSC has allocated for GPRS useaccording to the requests of the PCU. GPRS territory size can be restricted by theuser-modifiable parameter max GPRS capacity (CMAX) . There is a GPRSterritory update guard time defining how often the PCU can request new radiotime slots for GPRS use.



(E)GPRS in BSC

Figure 7. Territory method in BSC

The BSC calculates these defined resources from percentages to concretenumbers of radio time slots based on the number of traffic channel radio timeslots (both blocked and working) capable of Full Rate traffic in the TRXs withGPRS enabled (set with the parameter GPRS enabled TRX (GTRX) ). Thesuper reuse TRXs in the Intelligent Underlay Overlay feature and the extendedarea TRXs in the Extended Range Cell feature are never included as availableresources in the GPRS territory calculation. The calculation is as follows:

. the product of default GPRS capacity (CDEF) parameter and thenumber of radio time slots is rounded down to a whole number.

. if default GPRS capacity (CDEF) parameter value is > 0 but therounded product equals 0, then the territory size 1 is used

. default GPRS capacity (CDEF) parameter minimum value is 1.

. max GPRS capacity (CMAX) parameter minimum value is 1 (range 1�100%).

The BSC starts to create the GPRS territory by first selecting the most suitableTRXs in the BTS according to its GPRS capability, TRX type, TRXconfiguration, and the actual traffic situation in the TRX.

The prefer BCCH frequency GPRS (BFG) parameter indicates if theBCCH-TRX is the first or the last choice for the GPRS territory or if it is handledequally with non-BCCH-TRXs.

TRX 1

TRX 2

BCCH

DefaultGPRS Capacity

DedicatedGPRSCapacity

AdditionalGPRSCapacity

Territory border moves based onCircuit Switched and GPRS traffic load

GPRSTerritory

CircuitSwitchedTerritory

MaxGPRSCapacity



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The best candidate for GPRS territory according to the traffic load is the TCHTRX that holds the most idle successive TCH/F time slots counted from the endof the TRX (time slot 7). The GPRS time slots are always allocated from TSL7towards TSL0 per TRX. The TRX containing permanent TCH/F time slots ispreferred to one with Dual Rate time slots to avoid wasting Half Rate capabilityin the GPRS territory. TRXs with permanent TCH/H time slots or multislotHSCSD calls are also avoided, if possible.

One TSL of an EDGE TRX works as a synchronisation master channel for theother EGPRS channels on the EGPRS territory. GPRS/EGPRS traffic is notpossible in an EDGE capable TRX without a synchronisation master channel.The synchronisation master channel has to be part of the EGPRS territory or, incase the PBCCH/PCCCH channel is allocated to an EDGE TRX, it acts as asynchronisation master channel for the EGPRS channels of the BCCH TRX.

Having defined the GPRS capacity share and having selected the best TRX forGPRS, the BSC next begins a GPRS territory upgrade procedure where itallocates the selected radio time slots of the TRX for GPRS use and informs thePCU.

GPRS territory upgrade

The BSC uses a GPRS territory upgrade procedure to allocate part of theresources for GPRS use. The BSC starts the GPRS territory upgrade procedurewhen the user enables GPRS in a BTS.

The number of time slots given for GPRS use is defined by the operator with theparameters dedicated GPRS capacity (CDED) , default GPRScapacity (CDEF) and max GPRS capacity . All the defined time slotscannot necessarily be delivered immediately due to the circuit switched trafficload of the BTS. However, the BSC fulfils the defined GPRS capacity as soon aspossible. After the default capacity (which includes also the dedicated part) hasbeen delivered, the PCU can request more resources for a GPRS territory upgradebased on the actual need caused by GPRS use.

Each GPRS territory upgrade concerns time slots of one TRX; thus an upgrade isa TRX-specific procedure. The BSC performs upgrades of continuous sets ofsuccessive time slots. Starting from the end of the first TRX in the GPRSterritory, the BSC includes in a GPRS territory upgrade the time slots accordingto need and availability.



(E)GPRS in BSC

If the GPRS territory cannot be extended to its full size due to a time slot beingoccupied by circuit switched traffic, an intra cell handover is started. The aim ofthe handover is to move the circuit switched call to another time slot and clear thetime slot for GPRS use (refer to the figure below). The BSC then continues withthe upgrading of the GPRS territory after the release of the source channel of thehandover. If the GPRS territory of a BTS needs more time slots than one TRXcan offer, the BSC selects a new TRX and starts to define the territory.

When the user enables GPRS in a cell, the BSC starts a handover to be able toallocate dedicated GPRS channels, even if the defined margin of idle time slots isnot met but there is at least one time slot available.

The BSC starts a handover to move a non-transparent multislot HSCSD call, butnot for a transparent multislot HSCSD call. For a transparent HSCSD call, theHSCSD time slots are left inside the GPRS territory, although not as actual GPRSchannels. The BSC extends the GPRS territory on the other side of the time slotsreserved for the transparent HSCSD call.

Figure 8. GPRS territory upgrade when a time slot is cleared for GPRS usewith an intra cell handover

Situations leading to the starting of a GPRS territory upgrade are related toconfiguration and traffic channel resource changes. When the user adds GPRScapable TRXs in a BTS, it results in an increase in the time slot share that shouldbe provided for GPRS traffic. The BSC starts the GPRS territory upgradeprocedure when:

= Circuit Switched territory

= GPRS territory

B S C C C C C

C

C

C C

C

C d d D D D

C C C C

C C C

C

GPRS territory upgrade

B = BCCH TSLS = SDCCH TSLC = Circuit Switched call

Default GPRS capacity (d)= 20%Dedicated GPRS capacity (D) = 10%



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. the user enables GPRS in a cell

. the user or BSC unblocks a GPRS enabled TRX thus enabling a pendingGPRS territory upgrade

. the user or BSC unblocks a radio time slot inside the GPRS territoryenabling it to be included in the GPRS territory

. the BSC releases a circuit switched TCH/F causing the number of idleresources in the BTS to increase above a margin that is required beforeGPRS territory upgrade can be started

. the BSC releases a circuit switched TCH/F beside the GPRS territoryborder (as a consequence of handover) so that the pending GPRS territoryupgrade can be performed

. the PCU requests a GPRS territory upgrade.

Other general conditions for a GPRS territory upgrade are:

. previous GPRS territory change in the BTS has been completed

. that there is a sufficient margin of idle TCH/Fs in the BTS

. that there are idle GPRS capable resources available in the BTS

. that there is available capacity in the PCU controlling the BTS.

The margin of idle TCH/Fs that is required as a condition for starting a GPRSterritory upgrade is defined by the BSC parameter free TSL for CS upgrade(CSU) . In fact, the parameter defines how many traffic channel radio time slotshave to be left free after the GPRS territory upgrade. When defining the margin, atwo-dimensional table is used. In the two-dimensional table the columns are fordifferent amounts of available resources (TRXs) in the BTS. The rows indicate aselected time period (seconds) during which probability for an expecteddowngrade is no more than 5%. The operator can modify the period with the BSCparameter CSU . The default value for the period length is 4 seconds.

Table 4. Defining the margin of idle TCH/Fs

T-R-Xs 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Ti-m-e0

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

1 0 1 1 1 2 2 2 2 2 2 3 3 3 3 3 3



(E)GPRS in BSC

Table 4. Defining the margin of idle TCH/Fs (cont.)

T-R-Xs 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

2 1 1 2 2 2 3 3 3 3 4 4 4 4 5 5 5

3 1 1 2 3 3 3 4 4 4 5 5 6 6 6 6 6

4 1 2 2 3 4 4 4 5 5 6 6 6 7 7 7 7

5 1 2 3 3 4 5 5 5 6 6 7 7 7 8 8 8

6 1 2 3 4 4 5 5 6 6 7 7 8 8 8 9 9

7 1 2 3 4 5 5 6 7 7 7 8 8 9 9 9 9

8 1 3 4 4 5 6 6 7 7 7 8 9 9 9 9 9

9 1 3 4 5 5 6 7 7 8 8 9 9 9 9 9 9

10 2 3 4 5 6 7 7 8 8 8 9 9 9 9 9 9

The user can define and modify with the parameter GPRS territory updateguard time (GTUGT) the guard time, which the PCU has to wait betweensuccessive requests for GPRS territory configuration updates. The BSC obeysthis guard time also when it performs GPRS territory upgrades to fulfil theoperator-defined default GPRS territory.

If the conditions required for a GPRS territory upgrade are not met at the time thePCU requests a GPRS territory upgrade, the BSC simply does nothing butupdates related statistics. There are three reasons for a GPRS territory upgraderequest being rejected: lack of GPRS radio resources, circuit switched traffic load,and the capacity limit of the PCU unit. In case the PCU asks for several time slotsin one request and only a part of the requested resources are available, a statisticscounter is updated.

In the GPRS territory upgrade, the BSC selects a free PCUDSP channel from thePCU and connects it to an Abis circuit. If an error occurs when connecting thePCUDSP circuit to the Abis circuit, the BSC cancels the upgrade and savesinformation on the detected fault. The BSC initiates a new GPRS territoryupgrade after a guard period.

If two successive connection failures of a PCUDSP circuit with different Abiscircuits occur, the BSC marks the PCUDSP channel as faulty and sets the alarmFAULTY PCUPCM TIMESLOTS IN PCU (3073 ).



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Additional GPRS territory upgrade

The need for additional GPRS channels is checked when a new TBF isestablished or an existing TBF is terminated. The PCU will request additionalchannels, if a GPRS territory contains less channels than could be allocated to amobile according to its multislot class, or if the average number of TBFs per TSLis more than 1.5 after the allocation of the new TBF (average TBF/TSL>1.5).These additional channels will be requested only if all GPRS default channels arealready in the GPRS territory.

The number of additional channels the PCU will request is the greater of thefollowing two numbers:

. The number of additional channels needed in the allocation according tothe MS's multislot class (this criterion is used only when the GPRSterritory contains fewer channels than the MS is capable of using), and

. The number of additional channels needed for the average number ofallocated TBFs per TSL to be 1(average TBF/TSL=1).

Examples:

1. The GPRS territory consists of one (default) channel and resources shouldbe allocated for a downlink TBF of a multislot class 4 mobile. The PCUwill first allocate one channel for the TBF and it will request for (at least) 2more channels, as the mobile is capable of using 3 downlink channels.When the PCU receives this additional capacity, the TBF will bereallocated to utilise all channels.

2. The GPRS territory consists of three channels (one default and twoadditional) and a mobile of multislot class 4 has a downlink TBF of threetimeslots (performing ftp for example). One of the additional channels istaken into CS use, the territory is decreased to two channels, and thedownlink TBF is reallocated to these channels. When the previouslyreserved channel is freed from the CS side, a territory upgrade would bepossible, but nothing happens (no upgrade of the territory), because thesystem only checks for need for upgrade when a new TBF is established.However, if the existing TBF is terminated and a new one is established orif the concurrent uplink TBF is terminated the need and possibility of theterritory upgrade is re-evaluated.

GPRS territory downgrade

The BSC uses a GPRS territory downgrade procedure when it needs to reduce theshare of time slots in the GPRS territory, for example when there is an increase inthe circuit switched traffic load.

The BSC starts a GPRS territory downgrade procedure when



(E)GPRS in BSC

. the user disables GPRS in a cell

. the user or BSC blocks the TRX that is carrying GPRS traffic

. the user or BSC blocks the time slot that is carrying GPRS traffic

. the user or BSC blocks circuit switched resources causing the number ofidle resources in the BTS to decrease below the required margin

. the BSC allocates a traffic channel for circuit switched use causing thenumber of idle resources in the BTS to decrease below the required margin

. the PCU requests for a GPRS territory downgrade

If the user or the BSC blocks the time slot that is carrying the synchronisationmaster channel, the BSC starts a GPRS territory downgrade procedure for allGPRS channels connected to that TRX.

The PCU initiates a GPRS territory downgrade procedure for additional typeGPRS radio time slots. This means that the PCU has requested these time slots forGPRS traffic in addition to the default capacity, but the need for additional timeslots has ceased. If the BSC cannot start a GPRS territory downgrade at the timethe PCU requests it, the PCU will have to request a downgrade again after theterritory update guard time has expired, if the need for the downgrade still exists.

The operator defines the margin of idle TCHs that the BSC tries to maintain freein a BTS for the incoming circuit switched resource requests using the parameterfree TSL for CS downgrade (CSD) . If the number of idle TCH resourcesin the circuit switched territory of the BTS decreases below the defined margin, aGPRS territory downgrade is started if possible. The definition of the margininvolves a two-dimensional table. One index of the table is the number of TRXsin the BTS. Another index of the table is the needed amount of idle TCHs. Actualtable items are percentage values indicating probability for TCH availabilityduring a one-second downgrade opreration with the selected resource criterion.Default probability 95% can be changed through the free TSL for CSdowngrade (CSD) parameter (CSD).

Table 5. Defining the margin of idle TCHs, %

T-R-Xs 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

T-C-H0

94 84 76 69 63 58 54 50 48 45 43 41 40 38 37 35

1 99 98 96 93 91 87 85 82 79 77 74 72 70 68 66 64



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Table 5. Defining the margin of idle TCHs, % (cont.)

T-R-Xs 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

2 10-0

99 99 99 98 97 96 94 93 92 90 89 87 86 84 83

3 10-0

99 99 99 98 98 97 97 96 95 94 94 93

4 10-0

99 99 99 99 99 98 98 98 97

5 10-0

10-0

99 99 99 99

6 10-0

10-0

10-0

7 10-0

10-0

8 10-0%

10-0%

10-0%

10-0%

9 10-0

100

Additional GPRS territory downgrade

Additional channels are taken into CS use whenever more channels are needed onthe CS side. The need for additional GPRS channels is always checked when anexisting TBF is terminated. The PCU will request the removal of additionalchannels, if the average TBFs per TLS is less than 0.5(average TBF/TSL<0.5).





(E)GPRS in BSC

8.2 Circuit switched traffic channel allocation in GPRSterritory

The BSC maintains a safety margin of idle traffic channels for circuit switchedtraffic by starting a GPRS territory downgrade when the number of free trafficchannels in the circuit switched territory of a BTS decreases below the limitdefined by the parameter free TSL for CS downgrade (CSD) . Dependingon the size of the margin and on the amount of traffic on the BTS, new circuitswitched traffic channel requests may come before the GPRS territory downgradeprocedure has been completed. During a sudden burst of traffic channel requests,the BSC may not be able to maintain the margin with the GPRS territorydowngrade procedure and the circuit switched territory may run out of idle trafficchannels.

If the circuit switched territory becomes congested, the BSC can allocate a trafficchannel for circuit switched use in the GPRS territory � if there is one notdedicated for GPRS. The BSC first releases the channel in GPRS use from thePCU and then activates it in the BTS for circuit switched use.

The BSC cannot allocate a traffic channel in the GPRS territory for circuitswitched use, if the radio time slot in question is involved in a GPRS territoryupgrade procedure that has not been completed yet. In this case the circuitswitched traffic channel request is put in queue to wait for the GPRS territoryupgrade to finish. This kind of queuing can be performed if the MSC allows it forthe request. Traffic channel queuing during GPRS territory upgrade does notrequire the normal queuing to be in use in the target BTS. The use of theparameter free TSL for CS upgrade (CSU) aims at avoiding collisionsbetween a GPRS territory upgrade and circuit switched requests.

Multislot traffic channel allocation for an HSCSD call within the GPRS territoryfollows the same principles as for single slot requests. A non-transparent HSCSDcall is placed inside the GPRS territory only in the case of total congestion of theCS territory. In that case the HSCSD call can have one or more TSLs dependingon the HSCSD parameters of the BTS in question. A transparent HSCSD call canbe allocated partly over the GPRS territory so that traffic channels for the call areallocated from both territories or the whole HSCSD call can be allocated over theGPRS territory.

BB Hopping BTS

The BSC parameter CS TCH allocate RTSL0 (CTR) defines the order ofpreference between the RTSL-0 hopping group and the default GPRS territory inCS TCH allocation. Value 0 of the parameter means that the default GPRSterritory timeslots are preferred in CS traffic channel allocation. If no free



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resources are available in the default GPRS territory, the RTSL-0 hopping groupis searched. Value 1 of the parameter means that the RTSL-0 hopping group ispreferred in CS traffic channel allocation. If no free resources are available in theRTSL-0 hopping group, the default GPRS territory is searched.

Load limit calculation

The BSC parameter CS TCH allocation calculation (CTC) defineshow the GPRS territory is seen when the load limits for CS TCH allocation arecalculated. Additionally, it defines whether the resources in the GPRS territoryare seen as idle resources or as occupied resources. Value 0 of the parametermeans that only the resources in the CS territory are taken into account in loadcalculations. Value 1 of the parameter means that both the CS territory resourcesand the GPRS territory resources (excluding the dedicated GPRS timeslots) aretaken into account, and the GPRS territory resources are seen as occupiedresources. Value 2 of the parameter means that both the CS territory resources andthe GPRS territory resources (excluding the dedicated GPRS timeslots) are takeninto account, and the GPRS territory resources are seen as idle resources.



8.3 BTS selection for packet traffic

Channel allocation goes through all the following steps, in the order presented, inevery allocation and reallocation instance. After every step, the list of valid BTSsis relayed to next step and the BTSs that did not meet the requirements arediscarded.

BTS selection in a segment without PBCCH/PCCCH

1. Mobile RAC (bands)

With RF hopping there has to be a packet territory in BCCH BTS or in anon-hopping BTS on BCCH band.

2. Check maximum TBF/TSL

3. Signal Level

. In case of initial allocation (DL signal level not known), DIRE isused for ruling out some BTSs. BTS with NBL value greater thanDIRE is ruled out.

. Reallocation based on signal level is trickered by ( RX_level(BCCH)-NBL<GPL )



(E)GPRS in BSC

. In reallocation between different valid BTSs, NBL is used forcomparing levels and ruling out BTSs. ( RX_level(BCCH)-NBL>GPU )

. In reallocation case, if no BTS fullfilling ( RX_level(BCCH)-NBL>GPU ) is found, the old BTS is selected.

4. Mobile capability (GPRS /EGPRS )

5. Load (Penalty,Qos)

BTS selection in a segment with PBCCH/PCCH

1. Mobile RAC (bands)

2. Check maximum TBF/TSL in BTS

3. Signal Level

. In case of initial allocation (DL signal level not known), DIRE isused for ruling out some BTSs. BTS with NBL value greater thanDIRE is ruled out.

. Reallocation based on signal level is trickered by:( RX_level(BCCH)-NBL<GPL )

. In reallocation between different valid BTSs, NBL is used forcomparing levels and ruling out BTSs. ( RX_level(BCCH)-NBL>GPU )

. In reallocation case, if no BTS fullfilling ( RX_level(BCCH)-NBL>GPU ) is found, the old BTS is selected.

4. Mobile capability (GPRS/EGPRS)

5. Load (Penalty,Qos)

In UL reallocation, the uplink RX level of the TBF in the serving BTS iscompared to GPL to check if the reallocation was triggered by a bad uplink RXlevel (uplink RX level < GPL). If the reallocation was due to bad uplink RXlevel, then the old serving BTS will be discarded in the very beginning.



8.4 Quality of Service

The concept of 'Priority Class' is introduced at system level. This is based oncombinations of GPRS Delay class and GPRS Precedence class values. Packetshaving higher 'Priority' are sent before those packets having lower 'Priority'.



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ETSI specifications define QoS functionality which gives the possibility todifferentiate TBFs by delay, throughput and priority. Priority Based Schedulingis introduced as a first step towards QoS. With Priority Based Scheduling theoperator can give users different priorities. Higher priority users will get betterservice than lower priority users. There will be no extra blocking to any user, onlythe experienced service quality changes.

The PCU receives the QoS information to be used in DLTBFs from the SGSN ina DL unitdata PDU. In case of UL TBF, the MS informs its radio priority in aPACKET CHANNEL REQUEST (PCR) or a PACKET RESOURCE REQUEST(PRR), and this is used for UL QoS.

In the UL direction, the PCU uses the radio priority received from the MS.Exceptions to this rule are one phase access and single block requests; in thesecases the PCU always uses Best Effort priority.

The PCU receives the QoS profile information element in the DL unitdata. ThisIE includes Precedence class information which indicates the priority of the PDU.

Each TBF allocated to a timeslot has a so-called latest (timeslot specific) servicetime. In each scheduling round (performed every 20ms), the TBF with the lowestservice time is selected and given a turn to send a radio block (provided that nocontrol blocks have to be sent). Also, the latest service time of the selected TBF isincremented by the scheduling step size of the TBF.

The sizes of the scheduling steps determine the handing out of radio resources: Ifseveral TBFs have been allocated to a timeslot, then the higher the schedulingstep size of the TBF, the less often it is selected and given a turn.

In release 1 scheduling step sizes are set to the same constant value for all TBFs.In the S10.5 release these depend on the priority class of the TBF. Each priorityclass has its own scheduling step size which is operator adjustable.

Priorities are also taken into account in allocations of TBFs. The allocationprocess tries to ensure that better priority TBFs do not gather into the same radiotimeslot.

Priority Based Scheduling in BSC is a standard feature and is always active in anactive PCU.

To get more detailed information about QoS in Gb, see BSC-SGSN interfacedescription; BSS GPRS protocol (BSSGP).





(E)GPRS in BSC

8.5 Channel allocation and scheduling

GPRS channels are allocated according to the following rules:

. downlink and uplink are separate resources

. multiple mobiles can share one traffic channel, but the traffic channel isdedicated to one MS at a time � this is referred to as temporary GPRSconnection block flow or Temporary Block Flow (TBF ) � meaning thatone MS is transmitting or receiving at a time; seven uplink and sixteendownlink TBFs can share the resources of a single time slot; the uplink anddownlink scheduling are independent

. channels allocated to a TBF must be allocated from the same TRX

. those traffic channels which give the maximum possible (priority based)capacity for the TBF are allocated within the limits of the multislot class ofthe mobile; exceptions are TBFs for which only one channel is allocated.

Temporary Block Flow (TBF) is explained in GPRS radio connection control .

The PCU determines the number of traffic channels that are needed and countsthe best throughput for that number of traffic channels. When the load of trafficchannel combinations is equal they are first compared by QoS load of thechannel, then by capacity type (additional < default < dedicated) and then by thePacket Associated Control Channel (PACCH ) load. The QoS load of a channel isdefined as a weighted sum of the TBFs in the channel. The weights usedcorrespond with the scheduling rate of the QoS class of TBFs in the channel. ThePACCH load is the number of TBFs using a certain TCH as PACCH. PACCH isdefined in more detail in GPRS radio connection control .

Higher priority TBFs will get more turns, therefore they will cause more load onthe channel.

Packet scheduling

Uplink and downlink scheduling are independent. The PCU can assign multipleMSs to the same uplink traffic channels. ETSI specifications allow the schedulingof uplink transmission turns to be done by three different Medium Access modes(MAC ): dynamic allocation, extended dynamic allocation and fixed allocation.The BSC releases from S9 on support dynamic allocation.



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In Dynamic allocation, the BSC gives the MS a USF value for each assignedtraffic channel in the assignment message. The MS monitors the downlink RadioLink Control (RLC) blocks on the traffic channels it has been assigned.Whenever the MS finds the USF value in the downlink RLC block, it may sendan uplink RLC block in the corresponding uplink frame. The scheduling of theRLC data block in each time slot is independent of other time slots. Radio LinkControl is defined in more detail in GPRS radio connection control .

Scheduling is based on a kind of weighted round robin method, which means thata higher priority (QoS) Temporary Block Flow (TBF) gets a bigger share of thePDTCHs allocated for it than a lower priority TBF. See Quality of service formore information on adjusting weight.

TBF allocation

After the BTS has been selected, QoS and TBF type are comparedsimultaneously. Different QoS classes result in different penalties for loadcomparing. Multiplexed and non-multiplexed TSLs are also prioritized by apenalty value. Among multiplexed TSLs, QoS is the selecting criteria.

If there are both GPRS and EGPRS TBFs allocated in the same BTS, the PCUtries to avoid allocating the GPRS and EGPRS TBFs into the same timeslotsbecause it would dramatically worsen the throughput of EGPRS TBFs.

Multiplexing, that is, allocating GPRS and EGPRS TBFs into the same timeslotsis avoided by the means of a channel allocator: when it is searching for a bestchannel configuration for a TBF, it 'sees' a penalty in those channel combinationsthat would increase multiplexing.

If we would like to allocate a new EGPRS TBF into a TRX, the channel allocatorwould see the TRX as follows: the timeslots where there are already some GPRSTBFs allocated would not look very attractive for this allocation, because theEGPRS TBF would not get a very good data rate in those timeslots but it wouldincrease multiplexing.

When optimum resources for a mobile are searched for from the GPRS territory,both UL and DL resources are evaluated and the decision for the allocation ismade depending on the amount of effective resources received in both directions.If a mobile is using only one direction (UL or DL), only the resources of thedirection used are evaluated. If the mobile being evaluated already has an existingTBF in one direction and it requires resources from the other direction, theevaluation of resources received is first done for the concurrent allocation andthen for different re-allocations and, if effective resources received in theconcurrent allocation are the same as with re-allocation, the concurrent allocationis preferred. In the evaluation of the resources, dedicated and default territoryareas are preferred, so if similar resources are found from the additional anddefault territory, resources from the default area will be allocated.



(E)GPRS in BSC

Examples:

1. The GPRS territory consists of three channels, and a MS of multislot class4 has a downlink TBF of three timeslots (performing ftp for example) andalso uses an uplink TBF of one timeslot to acknowledge the received data(Note: the UL TBF is not always present as it is not always needed). Asecond mobile of multislot class 4 requests UL resources. These will beallocated to it and the optimum resources are evaluated for the ULdirection only. As a result, the second MS will get its UL resource from achannel that is not used by the first mobile.

TSL 0 1 2 3 4 5 6 7

DEF DEF DEF

UL MS1 MS2

DL MS1 MS1 MS1

2. Continuing from the previous example, downlink resources are needed forthe second mobile. Available resources are evaluated for both directionsand the allocation is made in such a way that optimum resources are usedin both directions. Now the allocation depends on the resource usage ofMS1 in both UL and DL directions.

a. A concurrent allocation for the DLTBF is made for MS2 if MS1 hasan UL TBF in use when the DL TBF of MS2 is allocated. Theconcurrent allocation is made, because the reallocation does notprovide any better resources for MS2 in this phase.

TSL 0 1 2 3 4 5 6 7

DEF DEF DEF

UL MS1 MS2

DL MS1 MS1

MS2

MS1

MS2

As a result, MS1 has the resources of 3 effective timeslots (the totalsum of UL and DL resources) and MS2 has the resources of 2effective timeslots. If MS2 had been allocated in the same way asMS1 (with re-allocation), it would have resulted in both MSs having



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only 2 effective timeslots (the total sum of UL and DL resources).MS2 does not receive the maximum amount of timeslots in the DLdirection in this phase, but it will receive them later, when theterritory upgrade has been completed.

b. DL resources for MS2 are given with reallocation if MS1 does nothave a UL TBF in use when the DL TBF of MS2 is allocated. Thereallocation is made, because better resources are achieved with it.

TSL 0 1 2 3 4 5 6 7

DEF DEF DEF

UL MS2

DL MS1

MS2

MS1

MS2

MS1

MS2

In this allocation, MS1 has the resources of 1.5 effective timeslots(the total sum of UL and DL resources) and MS2 has the resourcesof 2.5 effective timeslots.

Then the PCU would request a territory upgrade according to the rulesexplained in the section additional GPRS territory upgrade (in case a, twochannels will be requested and in case b, three channels will be requested).

3. Continuing from the previous example. PCU has received the additionalcapacity it has requested and the reallocation of the TBF(s) will be made.As a result, the following allocations will be made:

a. Both mobiles will get 2.5 timeslots in the DL direction and 1timeslot in the UL direction.

TSL 0 1 2 3 4 5 6 7

ADD ADD DEF DEF DEF

UL MS2 MS1

DL MS2 MS2 MS1

MS2

MS1 MS1

b. Both mobiles will get 3 timeslots in the DL direction and 1 timeslotin the UL direction.

TSL 0 1 2 3 4 5 6 7



(E)GPRS in BSC

ADD ADD ADD DEF DEF DEF

UL MS2 MS1

DL MS2 MS2 MS2 MS1 MS1 MS1

After the TBF is created in a BTS

When a GPRS TBF is in a multiplexed TSL, it will constantly check:

1. if the channel is multiplexed

2. if it is the only GPRS TBF in the TSL thus causing multiplexing

3. if there are multiplexed channels where it is allowed to reallocate

The PCU will request for more additional channels, if a GPRS territory containsless channels than what could be allocated to a mobile according to its multislotclass. These additional channels will be requested only if all GPRS defaultchannels are already in the GPRS territory. The maximum number of GPRSchannels is limited by CMAX.

When ensuring the best quality and speed for end-users, planning may not rely onadditional channels in the dimensioning of the GPRS territory. The use ofadditional channels is less efficient compared to the default channels. The reasonfor this is that the additional channels (territory upgrade) are always requestedfrom circuit-switched (CS) territory and there is always some delay before thechannel is moved to the GPRS territory. For example, there can be a CS call in thetime slot, which is to be moved to the GPRS territory, and intracell handover isneeded before the territory upgrade can be completed.

Additional channels are taken into CS use whenever more channels are needed onthe CS side. The need for additional GPRS channels is always checked when anexisting TBF is terminated. The PCU will request the removal of additionalchannels, if the average TBF/TSL is less than 0.5 (average TBF/TSL<0.5). Thetarget in the downgrade is to achieve an average TBF/TSL equal to 1.

When there is a multiplexed downlink TBF for GPRS and EGPRS, the MCS islimited to 1-4 (GMSK) whenever there is a CS-coded uplink TBF in the TSL.Even if there is only an EGPRS TBF present, there will be a CS-1 coded DL-block every 360ms for syncronization purposes.





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8.6 Error situations in GPRS connections

When the PCU detects a synchronisation error between itself and the BTS, theBSC downgrades the related channels from GPRS use. The BSC upgrades theradio time slots back to GPRS use after a guard period.

The BSC sets the alarm TRAFFIC CHANNEL ACTIVATION FAILURE (7725 )if the Abis synchronisation for an GPRS traffic channel repeatedly fails. Thealarm is automatically cancelled when the synchronisation succeeds and thechannel is taken back into GPRS use.

The BSC sets the alarm FAILURE IN PACKET SYSTEM INFORMATIONSENDING (7760 ) if the Abis synchronisation for the PBCCH/PCCCH channelfails. The alarm is automatically cancelled when the synchronisation succeedsand the channel is taken back into use.





(E)GPRS in BSC

9 GPRS radio connection control

Radio channel usage when GPRS is in use is discussed in this chapter. The GPRSradio connection establishment (TBF establishment) and data transfer aredescribed from the point of view of a mobile terminating (MT) and mobileoriginating (MO) GPRS TBF. Paging is described in a section of its own. Thissection describes the BSC's functions in relation to suspend and resume, flush,and coding scheme selection, as well as traffic administration and power controlin GPRS. Cell selection and reselection is also defined.



9.1 Radio channel usage

ETSI specifications (05.02) define the possibility to use dedicated broadcast andcommon control channels for GPRS.

System information messages on BCCH

The support of GPRS is indicated in a SYSTEM_INFORMATION_TYPE_3message. GPRS-specific cell parameters are sent to the MS in aSYSTEM_INFORMATION_TYPE_13 message.

For more information refer to GSM Specification (04.18).

Common Control Channel signalling (CCCH)

The Common Control Channel signalling (CCCH ) is used for paging and uplinkand downlink temporary block flow (TBF ) setup if Packet Common ControlChannels (PCCCH ) are not available.

GPRS paging is made on the Paging Channel (PCH ). The MS initiates uplinkTBF establishment on the Random Access Channel (RACH ). The networkresponds to the MS on the Access Grant Channel (AGCH ). Network-initiatedTBF establishment is done on the AGCH.



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GPRS radio connection control

Packet Common Control Channel (PCCCH)

PCCCH comprises logical channels for common control signalling which areused for packet data in both directions. Packet Paging Channel (PPCH ) is used topage the MS, the Packet Random Access Channel (PRACH ) is used to requestradio resources, and the Packet Access Grant Channel (PAGCH ) is used toallocate radio resources.

Packet Broadcast Control Channel (PBCCH)

The PBCCH broadcasts Packet System Information. If the PBCCH is notallocated, the packet data specific system information is broadcast on the BCCH.BCCH/CCCH and PCCCH/PBCCH are mapped to separate timeslots. PCCCHand PBCCH use the same timeslot. For more information refer to GSMSpecification (04.60).

Packet Data Traffic Channel (PDTCHs)

The Packet Data Traffic Channel (PDTCH) is a channel allocated for datatransfer. It is temporarily dedicated to one MS. In the multislot operation, one MSmay use multiple PDTCHs in parallel for individual packet transfer. All PDTCHsare uni-directional, either uplink (PDTCH/U) for a mobile originated packettransfer or downlink (PDTCH/D) for a mobile terminated packet transfer.PDTCH/U and PDTCH/D can be assigned to an MS simultaneously. In the Nokiaimplementation, traffic channels belonging to a GPRS territory are PDTCHs andtraffic channels belonging to circuit switched territory are TCHs. The PCU useseach radio time slot which the BSC has allocated for the GPRS territory, as onePDTCH. GPRS Territories are described in Radio resource management .

Packet Associated Control Channel (PACCH)

The Packet Associated Control Channel (PACCH) conveys signallinginformation related to a given MS. The signalling information includes, forexample, acknowledgements and resource assignment and reassignmentmessages. One PACCH is associated to one or several traffic channels that areassigned to one MS. PACCH is a bi-directional channel. It can be allocated bothon the uplink and on the downlink regardless of whether the corresponding trafficchannel assignment is for uplink or downlink. Assigned traffic channels are usedfor PACCH for the direction the data is sent. For the opposite direction the MSmultislot capability has to be taken into account when allocating the PACCH.



(E)GPRS in BSC

Temporary Block Flow (TBF)

Temporary Block Flow (TBF) is a physical connection used by two radioresource entities to support the unidirectional transfer of Logical Link Control(LLC ) PDUs on packet data physical channels. The TBF is allocated radioresources on one or more PDTCHs and comprises a number of RLC /MACblocks carrying one or more LLC PDUs. A TBF is temporary and is maintainedonly for the duration of the data transfer. A TBF is identified by a TemporaryFlow Identity (TFI ).

Logical Link Control (LLC) and Radio Link Control (RLC)

The Logical Link Control (LLC) layer provides a highly reliable ciphered logicallink. LLC is independent of the underlying radio interface protocols in order toallow introduction of alternative GPRS radio solutions with minimum changes tothe NSS . LLC PDUs are sent between the MS and the SGSN.

The Radio Link Control (RLC) function provides a radio-solution-dependentreliable link. RLC blocks are sent between the MS and the BSC (PCU). There aretwo RLC modes: acknowledged and unacknowledged mode. The latter does nothave retransmission.

In downlink data transmission, the PCU receives LLC PDUs from the SGSN,segments them to the RLC blocks and sends the RLC blocks to the MS. The LLCPDU is buffered in the PCU until it has been sent to the MS or discarded.

In uplink data transmission, the PCU receives the RLC data blocks from the MSand reassembles them into LLC PDUs. When the LLC PDU is ready, the PCUsends it to the SGSN and releases it from the PCU buffer. The LLC PDUs have tobe sent to the SGSN in the order they were transmitted by the MS.



9.2 Paging

The network may provide co-ordination of paging for circuit switched servicesand GPRS depending on the network operation modes supported.

Network operation modes

The BSC supports network operation modes I and II. Mode I requires Gsinterface between the SGSN and MSC/HLR.



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In mode II circuit switched paging messages are transferred through the Ainterface from the MSC to the BSC. In mode I circuit switched paging messagesare routed through the Gb interface for GPRS-attached mobiles. GPRS pagesalways come from the SGSN through the Gb interface.

The network operation mode is indicated as system information to mobiles, and itmust be the same in each cell of a Routing Area. Based on the provided mode, anMS can choose (according to its capabilities) whether it attaches to GPRSservices or to non-GPRS services, or to both.

The operator should not create the PBCCH/PCCCH channel in network operationmode II, because CS paging will not work on PCCCH in network operation modeII.

Table 6. Supported Network Operation Modes

Mode Circuit PagingChannel

GPRS PagingChannel

Gs interface Paging co-ordination

I CCCH/PCCCH CCCH/PCCCH Yes Yes

I Packet DataChannel

N/A Yes Yes

II CCCH CCCH No No

GPRS paging

The SGSN initiates the GPRS paging process. It sends one or morePAGING_PS_PDUs messages to the BSC (PCU). These PDUs contain theinformation elements necessary for the BSS to initiate paging for an MS within agroup of cells at an appropriate time. The BSC translates the incoming GPRS andcircuit switched paging messages into one corresponding Abis paging messageper cell. A GPRS paging message is sent only to cells that support GPRSservices.

The paging area indicates the cells within which the BSC pages the MS and theycan be:

. all cells within the BSC

. all cells of the BSC within one Location Area

. all cells of the BSC within one Routing Area

. one cell (identified with a BSSGP virtual connection identifier (BVCI)).



(E)GPRS in BSC

A Routing Area, a Location Area, or a BSC area is associated with one or moreNSEIs (PCUs). If the cells in which to page the MS are served by several NSEIs,then the SGSN sends one paging message to each of these NSEIs.

The SGSN indicates the MS's IMSI and DRX parameters, which enables theBSS to derive the paging group. If the SGSN provides a P-TMSI , then the BSCuses it to address the MS. Otherwise IMSI is used to address the MS.

In GPRS paging the BSS forwards the PACKET_PAGING_REQUEST messagefrom the SGSN to the MS on the CCCH(s) or PCCCH. The MS's paging responseto the SGSN is handled in the PCU as any other uplink TBF.

For more information, refer to BSC-SGSN Interface Specification, BSS GPRSProtocol (BSSGP) .

Figure 9. PS page and CS page in GPRS

Note

RA0 is a routing area for cells that do not support GPRS.

Note

SGSN

PCUCell

DX

RA / LA / BSS

PCU sends pagingmessage if cell hasPCCCH channel

DX sends pagingmessage on CCCHchannel

DX sends pagingmessage in cellsthat have onlyCCCH channel. Ifthe page came withRA indication, DXalso sends paging incells in RA0

PCU sends pagingmessage in cellsthat have PCCCHchannel

If cell does nothave PCCCH,paging message issent to DX

Paging messageis always sent toDX

PCU DX



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Gs interface is obligatory in order to support CS paging.

Circuit switched paging via GPRS in network operation mode I

In order to initiate circuit-switched transmission between the MSC and the MS,the SGSN sends one or more PAGING CS PDUs to the BSC. These PDUscontain the information elements necessary for the BSS to initiate paging for anMS within a group of cells. The paging area is the same as in GPRS paging.

The SGSN indicates the MS's IMSI and DRX parameters, which enable the BSSto derive the paging group. If the SGSN provides the TMSI , then the BSC doesnot use the IMSI to address the MS. If a radio context identified by the TLLIexists within the BSS, then the paging message is directly sent to the MS onPACCH . If no radio context identified by the TLLI exists within the BSS, thenthe TMSI is used to address the MS. Otherwise IMSI is used to address the MS.

After the paging procedure, the circuit switched connection is set up as usual asdescribed in Basic Call .

If within the SGSN area there are cells that do not support GPRS services, thecells are grouped under a 'null RA'. The 'null RA' covers all the cells in theindicated paging area that do not support GPRS services. For example, if theSGSN indicates to the BSC to initiate paging for an MS within a Routing Areathe BSC sends one circuit switched paging message to all cells in the RoutingArea and one message to all the cells in the 'null RA'. The 'null RA' in this case isall the cells that do not support GPRS services in a Location Area derived fromthe Routing Area.

For more details about the paging message contents, refer to BSC-SGSN InterfaceSpecification, BSS GPRS Protocol (BSSGP) .



9.3 Mobile terminated TBF (GPRS or EGPRS)

When the SGSN knows the location of the MS, it can send LLCPDUs to thecorrect PCU. Each LLC PDU is encapsulated in one DL-UNITDATA PDU. TheSGSN indicates the cell identification in every DL-UNITDATA PDU. For moredetails about the downlink data message contents, refer to BSC-SGSN InterfaceSpecification, BSS GPRS Protocol (BSSGP) .



(E)GPRS in BSC

The PCU allocates one or more PDTCHs for the TBF, and indicates it and the TFIto the MS in the assignment message. The TBF establishment is done in one ofthe following ways:

. on PACCH; used when a concurrent UL TBF exists or when the timerT3192 is running in the MS

. on PCCCH; used when a PCCCH exists in the cell, and there is noconcurrent UL TBF and T3192 is not running

. on CCCH; used when there is no PCCCH in the cell, no concurrent ULTBF, and T3192 is not running

These alternatives are described in the following subchapters. The procedures arethe same for GPRS and EGPRS TBFs. The EGPRS-specific things are discussedin the chapter Finding an EGPRS-capable MS.

Downlink TBF establishment on CCCH

The PCU allocates one PDTCH for the TBF, and sends anIMMEDIATE_ASSIGNMENT message to the MS. The possible multislotallocation is done later and indicated to the MS by a reallocation message.

When the MS is ready to receive on PACCH, the PCU sends aPACKET_POLLING_REQUEST message to the MS and requests anacknowledgement. This is done in order to determine the initial Timing Advancefor the MS. If the channel configuration to be allocated for the downlink TBFconsists of only one channel already assigned to the MS, the PCU sends thePACKET_POWER_CONTROL/TIMING_ADVANCE message to the MS toindicate the Timing Advance value.

When multiple PDTCHs are allocated to the MS, the MS GPRS multislot classmust be taken into account. The MS GPRS multislot class is part of the MS RadioAccess Capability IE, which is included in the DL-UNITDATA_PDU message.The PCU sends the PACKET_DOWNLINK_ASSIGNMENT message, andgives the whole configuration together with the Timing Advance value to the MS.

In case there are no radio resources for the new TBF, the LLC PDU is discardedand the BSC sends a LLC-DISCARD message to the SGSN. The assignmentprocedure is guarded with two timers, one for resending theIMMEDIATE_ASSIGNMENT message and one for aborting the establishment.

Downlink TBF establishment on PCCCH

The PCU allocates one or more PDTCH for the TBF, and sends aPACKET_DOWNLINK_ASSIGNMENT message to the MS.



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When the MS is ready to receive on PACCH, the PCU sends aPACKET_POLLING_REQUEST message to the MS and requests anacknowledgement from the MS. Then the PCU sends thePACKET_POWER_CONTROL/TIMING_ADVANCE message to the MS toindicate the Timing Advance value.

Downlink TBF establishment when an uplink TBF exists

Downlink TBF establishment when an uplink TBF exists follows the sameprinciples as uplink TBF establishment when a downlink TBF exists. This isdiscussed more at the end of Mobile originated TBF .

The establishment is done with a PACKET_DOWNLINK_ASSIGNMENT orPACKET_TIMESLOT_RECONFIGURE message. The TBF mode (GPRS/EGPRS) is always the same as the mode of the existing UL TBF.

Downlink TBF establishment when timer T3192 is running and no UL TBFexists

When the DL TBF is released, the MS starts the timer T3192 and continuesmonitoring the PACCH of the released TBF until T3192 expires. During thetimer T3192 the PCU makes the establishment of a new DL TBF by sending aPACKET_DOWNLINK_ASSIGNMENT on the PACCH of the 'old' DL TBF.

Finding an EGPRS-capable MS (EGPRS downlink TBF establishment)

The DL-UNITDATA message from SGSN to PCU includes the MS RadioAccess Capability IE (RAC). If this optional field is missing only the BCCH bandcan be used for TBF establishment and only 1 PDTCH can be allocated for aGPRS-mode TBF. Multislot capability struct has the optional field EGPRSmultislot class. If this field is not present the MS is not EGPRS capable, and astandard GPRS TBF is established with GPRS multislot capabilities. If the field ispresent it defines the multislot capabilities of the MS when an EGPRS mode TBFis used. The GPRS multislot class is used, however, if the PCU allocates a TBFfor the MS in GPRS mode.

Downlink EGPRS-mode TBF establishment is done by including EGPRS-specific fields, for example EGPRS window size, to the assignment message. Theexistence of these fields defines the TBF mode.

An EGPRS-mode TBF is primarily allocated for an EGPRS capable MS (to anEDGE capable BTS). A GPRS-mode TBF can be allocated for an EGPRScapable MS to a non-EDGE capable BTS if:



(E)GPRS in BSC

. there are no EDGE capable BTSs in the segment, or

. the average TBF / TSL is more than or equal to the parameter indicatingthe threshold amount of TBFs in one TSL, defined in every EDGE capableBTS.

MS-specific flow control

Mobile specific flow control is part of the QoS solution in the PCU. This featureworks together with the SGSN to provide a steady data flow to the mobile fromthe network. Mobile specific flow control also ensures that if an MS has betterQoS, and therefore better transmission rate in radio interface (more air time), itwill also get more data from the SGSN. It is also an effective countermeasureagainst buffer overflows in the PCU. Mobile-specific flow control is done forevery MS that has a downlink TBF. There is no uplink flow control.

Data transfer

During the actual data transfer, the MS recognizes the transmitted Radio LinkControl (RLC ) blocks based on the TFI, which is included in every RLC blockheader. Each TBF has a transmit window, which is the maximum number ofunacknowledged RLC blocks at a time. The window size is 64 blocks in GPRSmode. In EGPRS mode the window size is larger than in GPRS and depends onthe amount of allocated timeslots.

The PCU can request the MS to send an (EGPRS)_PACKET_DOWNLINK_ACK/NACK message by setting a polling flag to theRLC data block header. The PCU can send further RLC data blocks along withthe acknowledgement procedure. If the PCU does not receive the (EGPRS)_PACKET_DOWNLINK_ACK/NACK message when polled, it increments acounter. After the counter reaches its maximum value of 8, the BSC considers theMS as lost, releases the downlink TBF and discards the LLC PDU from the PCUbuffer, The BSC signals this to the SGSN by setting the Radio Cause informationelement (IE) value to "radio contact lost with MS". This indicates to the SGSNthat attempts to communicate between the MS and the SGSN via the cell shouldbe suspended or abandoned. The BSC thus recommends the SGSN to stopsending LLC PDUs for the MS to the cell.

The counter is reset after each correctly received (EGPRS)_PACKET_DOWNLINK_ACK/NACK.

The PCU can change the downlink PDTCH configuration whenever needed bysending the MS_PACKET_DOWNLINK_ASSIGNMENT orPACKET_TIMESLOT_RECONFIGURE message. The reasons for thisreallocation may be a GPRS territory downgrade, uplink TBF establishment, or achange of requirements of the SGSN.



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If reallocation is impossible in the case of GPRS territory downgrade, the PCUmay release channels with a PDCH_RELEASE message.

The normal downlink TBF release is initiated by the PCU by setting a FinalBlock Indicator (FBI) bit in the last RLC block header. There may still be someretransmission after this, but the PCU releases the TBF and removes the LLCPDU from the PCU buffer when the MS sends the (EGPRS)_PACKET_DOWNLINK_ACK/NACK message with the Final Ack Indicatorbit on.

When the PCU has sent the last buffered LLC PDU to the MS, the PCU delaysthe release of the TBF (by 1 s by default). If there is no concurrent UL TBF,during the delay time DUMMY LLC PDUs are sent to the MS (with polling), inorder to allow the MS to request for a UL TBF. If the PCU receives more dataduring the delay time, the PCU cancels the delayed release and begins to sendRLC data blocks to the MS, in other words the same downlink TBF continuesnormally.



9.4 Mobile originated TBF (GPRS or EGPRS)

When the MS wants to send data or upper layer signalling messages to thenetwork, it requests the establishment of an uplink TBF from the BSC. There arethe following main alternatives for the TBF establishment:

. on PACCH; used when a concurrent DL TBF exists

. on PCCCH; used when a PCCCH exists in the cell and there is noconcurrent DL TBF

. on CCCH; used when there is no PCCCH in the cell and no concurrent DLTBF

Additionally, on CCCH and PCCCH there are different options for TBFestablishment, for example one phase access or two phase access, depending onthe needs for the data transfer. The PCU may force the MS to make a two phaseaccess, even if the MS requested some other access type, for instance if there isno room for the TBF in the BCCH band.

These alternatives are described in the following subchapters. The procedures aremainly the same for GPRS and EGPRS TBFs. The EGPRS-specific things arediscussed in separate chapters.



(E)GPRS in BSC

Random access on CCCH

The MS can send a CHANNEL_REQUEST message or anEGPRS_PACKET_CHANNEL_REQUEST (EPCR) message on CCCH(RACH). The EGPRS_PACKET_CHANNEL_REQUEST is supported onRACH, if the BTS supports it. In cells where EPCR is not supported, the MScannot tell its EGPRS capability in the CHANNEL_REQUEST message, and theMS must use two phase access when it wants to initiate an EGPRS TBF onCCCH . The BSC tells the MS in the SI13 GPRS Cell Options IE about theEPCR support.

One phase access on CCCH, GPRS

In a one phase access the MS sends a CHANNEL_REQUEST message with theestablishment cause 'one phase access'. The PCU allocates a PDTCH for therequest, and informs the MS in the IMMEDIATE_ASSIGNMENT messagealong with TFI and USF values. The MS sends its TLLI in the first data blocksand the one phase access is finalized when the PCU sends thePACKET_UPLINK_ACK/NACK message to the MS containing the TLLI(contention resolution).

If the PCU has no PDTCHs to allocate to the MS, it sends anIMMEDIATE_ASSIGNMENT_REJECT message to the MS. One phase accessis guarded by a timer in the PCU.

Two phase access on CCCH, GPRS

In a two phase access the MS sends a CHANNEL_REQUEST message with theestablishment cause 'single block access'. The PCU allocates one uplink block forthe request, schedules a certain radio interface TDMA frame number for theblock, and informs it to the MS in the IMMEDIATE_ASSIGNMENT message.

The MS then uses the allocated block to send a more accurate request to the PCUwith the PACKET_RESOURCE_REQUEST message. The PCU allocates theactual configuration for the uplink TBF according to the information received inthis message. When multiple PDTCHs are allocated to an MS, the MS GPRSmultislot class must be taken into account. The MS GPRS multislot class is a partof the MS Radio Access Capability IE, which is included in thePACKET_RESOURCE_REQUEST message. The PCU indicates the PDTCHconfiguration, USF value for each PDTCH, and the TFI to the MS in thePACKET_UPLINK_ASSIGNMENT message sent in the same time slot inwhich the single block was allocated, but the assigned PDTCH(s) may beelsewhere. The channel allocation in this second phase is independent of the firstphase, and if the PCU has no PDTCHs to allocate to the MS, it sends aPACKET_ACCESS_REJECT message to the MS. The second part of the twophase access is guarded with a timer in the PCU.



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The two phase access is finalized when the PCU receives the first block on theassigned PDTCH . The MS sends its TLLI in thePACKET_RESOURCE_REQUEST message, and the PCU includes it in thePACKET_UPLINK_ASSIGNMENT message to the MS (contention resolution).

Two phase access on CCCH, EGPRS (EPCR not supported)

PCU assigns one RLC block for an MS with the IMMEDIATE_ASSIGNMENTmessage. The frame number of the assigned block is told in the message. The MSsends a PACKET_RESOURCE_REQUEST message in the assigned block.There the PCU receives information about the MSs EGPRS capabilities (EGPRSmultislot capability and uplink 8PSK capability). When uplink TBFestablishment is done with a CHANNEL_REQUEST message, the MS mightonly be able to tell the RAC information from the band where the CCCH islocated.

The multislot capability struct has the optional field EGPRS multislot class. If thisfield is not present, the MS is not capable of EGPRS, and a standard GPRS TBFis established with GPRS multislot capabilities. If the field is present it defines themultislot capabilities of the MS when an EGPRS mode TBF is used. The GPRSmultislot class is used, however, if the PCU allocates a TBF for the MS in GPRSmode. The PCU allocates the PDTCHs for the TBF and sends aPACKET_UPLINK_ASSIGNMENT (PUA) message to the MS. The PUAincludes the following new fields:

. EGPRS Channel Coding Command IE, where the BSC tells the MS whatMCS it must use in uplink RLC blocks.

. Resegment IE, which determines whether the MS must use the same MCSin RLC data block retransmission as was used initially, or resegment theretransmitted RLC data block according to the commanded MCS.

. EGPRS Window Size IE, where the BSC tells what RLC window size theMS must use

One phase access on CCCH, EGPRS

One phase access with EPCR on CCCH is similar to the case 'One phase accesson PCCCH, EGPRS', with the following exceptions:

. The assignment information is sent to the MS with anIMMEDIATE_ASSIGNMENT message

. Only one PDTCH can be assigned

. Reallocation need is checked, when the establishment is completed



(E)GPRS in BSC

Two phase access on CCCH, EGPRS

Two phase access with EPCR on CCCH is similar to the case 'Two phase accesson PCCCH, EGPRS', with the following exception:

. The multi block assignment information is sent to the MS with anIMMEDIATE_ASSIGNMENT message

Short access on CCCH, EGPRS

Short access with EPCR on CCCH is similar to the case 'Short access on PCCCH,EGPRS', with the following exception:


Signalling access on CCCH, EGPRS

Signalling access with EPCR on CCCH is similar to the case 'Signalling accesson PCCCH, EGPRS', with the following exception:


Random access on PCCCH

The BSC tells the MS in the PSI1 GPRS Cell Options IE whether the MS can usethe EGPRS_PACKET_CHANNEL_ REQUEST (EPCR) message or ifonlyPACKET_CHANNEL_REQUEST (PCR) is supported. This depends onwhether the BTS supports EPCR or not.

An EGPRS capable MS mainly uses EPCR (on EGPRS cells) and a non-EGPRSMS uses PCR for the access. The access types One Phase Access, short accessand two phase access can be used both with PCR and EPCR. Both messages alsocontain access codes for signalling purposes. In EPCR the MS can inform itsuplink 8PSK capability by different training sequences.

One phase access on PCCCH, GPRS

The differences when one phase access is initiated on PRACH instead of onRACH are:



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. The initial message is PACKET_CHANNEL_REQUEST with access typeOne Phase Access Request.

. MS tells its multislot class and priority in thePACKET_CHANNEL_REQUEST . The multislot class informationenables multislot allocation in the case of one phase access also. Thepriority information is used in priority based scheduling.

. The assignment is done with the PACKET_UPLINK_ASSIGNMENTmessage

Short access on PCCCH, GPRS

This is a new establishment cause, which cannot be used in RACH. Thedifferences compared to one phase access on PCCCH are:

. The MS tells its priority and the number of blocks in thePACKET_CHANNEL_REQUEST . The number of blocks indicates thenumber of the RLC blocks the MS needs to send during the TBF. Thenumber of the RLC blocks can be 1 - 8.

. Only one PDCH is allocated.

Two phase access on PCCCH, GPRS

The differences when two phase access is initiated on PRACH instead of onRACH are:

. The initial message is PACKET_CHANNEL_REQUEST with access typeTwo Phase Access Request.

. The single block assignment is done with thePACKET_UPLINK_ASSIGNMENT message.

Signalling access on PCCCH, GPRS

The MS can request a signalling access with codes Page Response, Cell Updateor MM procedure in PCR. Only one PDTCH is allocated and the highest priorityis applied to the TBF scheduling. The establishment procedure is completed aswith 'One phase access on PCCCH, GPRS'.

One phase access on PCCCH, EGPRS

In one phase access using the EPCR message, the MS's multislot class isincluded. In addition, the training sequence indicates whether the MS supports8PSK modulation is uplink direction. If the mobile does not have 8PSKcapability in uplink, only EGPRS GMSK MCSs can be used in UL data transfer.The PCU allocates the PDTCHs for the TBF, selects the initial MCS and theEGPRS window size to be used in the uplink TBF and sends a



(E)GPRS in BSC

PACKET_UPLINK_ASSIGNMENT (PUA) message to the MS. When the BSCsends the PUA message it can poll RAC information, which includes the MS'smultislot capabilities and information about the supported frequency bands.When the cell supports several frequency bands, the RAC is requested for themall. The MS sends a PACKET_RESOURCE_REQUEST (PRR) message whereit has included the requested RAC information from at least the first requestedband. If all the requested RAC information doesn't fit in the PRR, the MS alsosends an ADDITIONAL_MS_RADIO_ACCESS_CAPABILITIES (ARAC)message where it tells the RAC of the other frequencies. Transmission turns tothat MS can be scheduled regardless of the PRR and ARAC polling. The MS usesthe two radio blocks assigned first for these signaling messages.

Two phase access on PCCCH, EGPRS

In PCCCH the BSC can request RAC information from several frequency bandsin the PACKET_UPLINK_ASSIGNMENT (PUA) message. When the cellsupports several frequency bands the RAC is requested from them all. The PUAcontains a multi block allocation, assigning a single block or two consecutiveblocks for the MS, depending on the requested RAC information. The MS sendsa PACKET_RESOURCE_REQUEST (PRR) message where it has included therequested RAC information at least from the first requested band. If all therequested RAC information doesn't fit in the PRR, the MS also sends anADDITIONAL_MS_RADIO_ACCESS_CAPABILITIES (ARAC) messagewhere it tells the RAC of the other frequencies.

Short access on PCCCH, EGPRS

The MS may request EGPRS Short Access with or without uplink 8PSKcapability if the amount of sent data is less or equal to 8 MCS-1 coded RLCblocks. The amount of blocks is told in theEGPRS_PACKET_CHANNEL_REQUEST message. Only one PDTCH isallocated for such a request and no RAC information is polled. The assignedPDTCH and MCS are told to the MS in the PACKET_UPLINK_ASSIGNMENTmessage. The short access is completed as the 'One phase access on PCCCH,EGPRS'.

Signalling access on PCCCH, EGPRS

The MS may request EGPRS Signalling Access with or without uplink 8PSKCapability. Only one PDTCH is allocated for the request and no RACinformation is polled. The highest priority is applied to the TBF scheduling. Theassigned PDTCH and MCS are told to the MS in thePACKET_UPLINK_ASSIGNMENT message. The signalling access iscompleted as the 'One phase access on PCCCH, EGPRS'.



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Data transfer

In uplink data transfer, the RLC data blocks are collected to the PCU buffer. TheTBF has a transmit window, which is the maximum number of unacknowledgedRLC blocks. The window size is 64 blocks in GPRS mode. In EGPRS mode thewindow size is larger than in GPRS and depends on the amount of allocatedtimeslots.

The PCU can schedule the MS to send further the RLC data blocks along with theacknowledgement procedure. The PCU can at any time send thePACKET_UPLINK_ACK/NACK message to the MS. ThePACKET_UPLINK_ACK/NACK message includes a bitmap which tells thecorrectly received blocks. The PCU can use the PACKET_UPLINK_ACK/NACK message for other purposes too, for example to change the codingscheme, which also affects the frequency of the acknowledgements.

The PCU has a counter to control the MS's ability to send RLC blocks in theframes it has been assigned by the USF values. The counter is always reset whenthe MS uses the frame it has been assigned to. If the counter reaches its maximumvalue of 15, the MS is considered lost and therefore the PCU releases the uplinkTBF.

The PCU delivers the LLCPDU with a UL-UNITDATA PDU to the SGSN.There is only one LLC PDU per UL-UNITDATA PDU. The underlying networkservice has to be available for the BSSGP level in order to deliver data to theSGSN. Otherwise the data is discarded and a counter is updated.

The PCU can change the uplink PDTCH configuration whenever needed bysending the MS a PACKET_UPLINK_ASSIGNMENT orPACKET_TIMESLOT_RECONFIGURE message. Reasons for reallocationmay be a GPRS territory downgrade, downlink TBF establishment, or a changeof an MS's requirements.

If reallocation during a downgrade is impossible, the PCU releases channels witha PDCH_RELEASE message to the MS. A normal uplink TBF release is madeby countdown, where the MS counts down the last RLC data blocks (15 or less)with the last block numbered 0. There may still be some retransmission, but whenthe PCU has received all the RLC data blocks correctly, it sends the LLC PDU tothe SGSN, and a PACKET_UPLINK_ACK/NACK message with final ackindicator to the MS. The MS responds with a PACKET_CONTROL_ACKmessage and the PCU releases the TBF.

If the MS supports Extended UL TBF Mode (indicated in MS RAC), the normaluplink release is delayed (by 1 s by default). Instead of sending aPACKET_UPLINK_ACK/NACK (final ack) immediately, the networkschedules USF turns to the MS during the delay, but with a lower rate as



(E)GPRS in BSC

normally. The MS sends a PACKET UPLINK DUMMY CONTROL BLOCK inthe scheduled block if it has no data to send. If the MS has got new data, it sendsan RLC data block, and after that the PCU cancels the delayed TBF release, andthe TBF continues with the normal scheduling rate.

Even if the MS doesn't support Extended UL TBF Mode, the PCU may delay theULTBF release (by 0.5s by default). This is done when there is no concurrent DLTBF for the same MS. The purpose of the delay is to speed up the possiblyfollowing DL TBF establishment. No USF turns are scheduled during this delay.

For more details about the uplink data message contents, refer to BSC-SGSNInterface Specification, BSS GPRS Protocol (BSSGP).

Uplink TBF establishment when downlink TBF exists

During a downlink TBF the MS can request resources for an uplink TBF byincluding a Channel Request Description IE in the (EGPRS)_PACKET_DOWNLINK_ACK/NACK message. The TBF mode (GPRS/EGPRS) of the new UL TBF is always the same as the mode of the existing DLTBF.

If there is no need to change the downlink PDTCH configuration, aPACKET_UPLINK_ASSIGNMENT message from the PCU to the MS containsthe uplink PDTCH configuration, USF values for each PDTCH, and TFI.

If the downlink PDTCH configuration is changed, for instance due to MSmultislot capability restrictions, the PACKET_TIMESLOT_RECONFIGUREmessage from the PCU informs the MS of both the uplink and downlink PDTCHconfigurations, USF values for the uplink PDTCHs, and the uplink and downlinkTFIs.

The establishment is ready when the PCU receives the first block on the assigneduplink PDTCHs. This establishment is also guarded by a timer in the PCU.

If the PACKET_UPLINK_ASSIGNMENT message fails, the uplink TBF isreleased. If the PACKET_TIMESLOT_RECONFIGURE message fails, bothdownlink and uplink TBFs are released.





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9.5 Suspend and resume GPRS

The GPRS suspension procedure enables the network to discontinue GPRSpacket flow in the downlink direction. Suspend is referred to as the situationwhich occurs when a circuit switched call interrupts a GPRS packet flow and theGPRS connection is thus discontinued or suspended.

The MS initiates the GPRS suspension procedure by sending aGPRS_SUSPENSION_REQUEST message to the BSC. The BSC sends theSUSPEND_PDU message to the SGSN. The SUSPEND_PDU messagecontains the TLLI and the Routing Area of the MS. The SGSN acknowledgeswith a SUSPEND-ACK PDU, which contains the TLLI, the Routing Area of theMS, and the Suspend Reference Number. The SGSN typically stops paging for asuspended mobile.

After the MS has released the circuit switched call, the resuming GPRS servicesrelies on the Routing Area Update Requests sent by the MS. This is because theBSC is not able to send any resume message to the SGSN because the BSC doesnot maintain a link between the circuit switched and GPRS connections.



9.6 Flush

The flush procedure is used, for example, when the MS has stopped data sendingin a given cell and has moved to another cell. The SGSN sends a FLUSH-LLPDU to the BSC to ensure that LLCPDUs queued for transmission in a cell foran MS are either deleted or transferred to the new cell.

The MS's TLLI indicates which mobile's data is in question and the BVCI (old)indicates the cell. The BSC deletes all buffered LLC PDUs in the cell and allcontexts for the MS. If an optional new cell, BVCI (new), is given, the BSCtransfers all buffered LLC PDUs to the new cell on the condition that both theBVCI (old) and the BVCI (new) are served by the same PCU and the sameRouting Area.

For more details on flush, refer to BSC-SGSN Interface Specification, BSS GPRSProtocol (BSSGP) .





(E)GPRS in BSC

9.7 Cell selection and reselection

In BSC S10 and subsequent releases, the MS controls cell selection andreselection. The following cell re-selection criteria are used for GPRS:

. The path loss criterion parameter C1 is used as a minimum signal levelcriterion for cell re-selection for GPRS in the same way as for GSM Idlemode.

. The signal level threshold criterion parameter C31 for hierarchical cellstructures (HCS) is used to determine whether prioritised hierarchicalGPRS and LSA cell re-selection shall apply.

. The cell ranking criterion parameter (C32) is used to select cells amongthose with the same priority.



9.8 Traffic administration

The BSC has many overload mechanisms to protect existing traffic flow and thusensure good quality for end-users.

The cause of an overload may be, for example, in the planning of the network andcapacity being too small in a particular area. In the case of overload, neithercircuit switched nor GPRS connections can be set up. The BCSU continuouslytries, however, to set up the GPRS connection, and the unit can in the worst casethus easily run itself into a state of malfunction. The BCSU cuts down the load byrejecting particular messages when the processor load or the link load exceeds thedefined load limit. Circuit switched calls are marked in the same way as GPRSconnections.

The load the BCSU can handle has been tested, but the user can determine GPRSusage and thus prevent the overload situations from happening. Refer to Flowand Overload Control and section BSS overload protection in BSS (BSC)Traffic Handling Capacity, Overload Protection and Network Planning for moreinformation on the BSC's overload control in general.

BCSU overload control

The BCSU has an overload control to protect itself against the processoroverloading and the TRXSIG link overloading.



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BCSU protection against excessive number of paging messages on the Gbinterface

The BCSU cuts down the load by rejecting particular messages when theprocessor load or the link load exceeds the defined load limit. The BCSU rejectsmessages which are sent in the downlink direction to the TRXSIG if needed.Each message sent to TRXSIG has a certain message group value. In case themessage buffers of an AS7 plug-in unit begin to fill up, the BCSU rejectsmessages based on the message group value.

The BCSU cuts down the load caused by GPRS and circuit switched pagingmessages sent by the SGSN. The load control is based on the number ofunhandled messages in the BCSU's message queue. The BCSU checks the countof unhandled messages in the message queue every time a new paging message isreceived. If the load limit is exceeded, the message is deleted.

BCSU protection against high GPRS RACH load

In the uplink direction the BCSU cuts down the load caused by GPRS randomaccesses. The BCSU rejects P-CHANNEL_REQUIRED messages received fromthe TRXSIG if the processor load exceeds the defined load limit. The load controlis based on the number of unhandled messages in the BCSU's message queue.The count of unhandled messages in the message queue is checked every time anew P-CHANNEL_REQUIRED message is received. If the load limit isexceeded, the BCSU deletes the message.

BVC flow control

The BVC flow control mechanism is based on the following:

. there is a downlink buffer in the BSC for each cell as identified by a BVCIon the Gb interface

. the BSC controls the transfer of BSSGP UNITDATA PDUs for both BVC-specific and MS-specific buffer sizes and buffer rates to the SGSN

. only downlink BSSGP UNITDATA PDU transfer to BSC is managed withflow control procedures; uplink flow control is not performed

. flow control is not performed for signalling.

The BSC sends a periodic BVC FLOW-CONTROL PDU to the SGSN afterevery BVC-RESET in order to start the downlink BSSGP data transfer. TheSGSN modifies its downlink transmission as instructed within 100 ms and alsoensures that it never transmits more data than can be accommodated within theBSC buffer for a BVC.



(E)GPRS in BSC

The BSC sends a periodic FLOW-CONTROL-BVC PDU to the SGSN everytime the TgbFlow timer expires, if the criteria for controlling flow still exists.When the BSC does not receive a confirmation to a FLOW-CONTROL PDU andthe reason for flow control still exists, the BSC triggers another FLOW-CONTROL PDU without waiting for the expiration of the TgbFlow timer. If noreason for flow control exists, the FLOW-CONTROL PDU is not triggered.

The BSC monitors the lifetime values of LLC PDUs and if the lifetime expiresbefore the PDU is sent, the PDU is deleted. The local deletion is signalled to theSGSN by LLC-DISCARDED PDU.

For more information on BVC flow control, refer to BSC-SGSN InterfaceSpecification, BSS GPRS Protocol (BSSGP) .

MS-specific flow control

Mobile-specific flow control is part of the QoS solution in the PCU. This featureworks together with the SGSN to provide a steady data flow to the mobile fromthe network. It is also an effective countermeasure against buffer overflows in thePCU.

The BSS performs BSSGP flow control for each BVC (cell) separately.Additionally it performs MS-specific flow control within each BVC.

The flow control mechanism manages the transfer of BSSGP UNITDATA PDUssent by the SGSN on the Gb interface to the BSS.

The BSS controls the flow of BSSGP UNITDATA PDUs to its BVC buffers byindicating to the SGSN the maximum allowed throughput in total for each BVC.The BSS controls the flow of BSSGP UNITDATA PDUs to the BVC buffer foran individual MS by indicating to the SGSN the maximum allowed throughputfor a certain TLLI .

The BSS controls the flow of BSSGP UNITDATA PDUs by transmitting FlowControl PDUs to the SGSN. Within one Flow Control PDU the BSS candetermine new flow control parameter values for one BVC or for one MS. Thereceived flow control parameter values are stored by the SGSN and thetransmission rate of the BSSGP UNITDATA PDUs is adjusted accordingly forthe specified BVC or MS. The frequency of Flow Control PDUs is limited by thespecifications.

The cell-based flow control was already implemented in S9. MS-specific flowcontrol was implemented in S10.5.



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Only DL-TBF data flows are managed by the flow control algorithm. If the BSSwould support the BSS Context for QoS, then all the flows having the AgregateBSS QoS Profile would be monitored by the flow control algorithm. In S10, BSSContext for QoS is not supported.

Sending Initial Flow Control Message

After the PCU has started up, it delivers an initial flow control parameter to theSGSN. The SGSN performs flow control on an individual MS using initial valuesuntil it receives a new flow control message from the BSSGP regarding that MS.

Managing MS Flow Control

The BSSGP keeps record of the received data per MS. It knows the bufferloading and leak rate of each MS, and compares that leak rate value to the leakrate value reported by the SGSN. Flow control messages are triggered when thedifference in the two leak rate values of one or more MSs increases to the limit ofthe flow-control-triggering PRFILE parameter FC_R_DIF_TRG_LIMIT .Sending MS flow control messages stops when the leak rate difference of all MSsdecreases to the limit of the flow control parameter FC_R_DIF_TRG_LIMIT .

When conditions exist for sending more than one flow control message, theBSSGP selects which flow will be controlled.

Selecting the flow to be controlled

The rate with which the BSSGP is allowed to send flow control messages islimited for each flow: after a BVC or MS-specific flow control PDU, the BSSGPmay send a new PDU specific to that same MS or BVC after C seconds(1s<C<10s). With one message the BSSGP can control only one flow, either aBVC flow or one MS-specific flow.

The BSSGP sends a flow control message with new flow control parametervalues for every flow whose leak rate difference exceeds the parameterFC_R_DIF_TRG_LIMIT . For BVC flow control, the message FLOW-CONTROL-BVC will be sent to the SGSN. Otherwise the message FLOW-CONTROL-MS will be sent. The SGSN acquits these with the messages FLOW-CONTROL-BVC-ACK and FLOW-CONTROL-MS-ACK . If the SGSN doesnot acquit the flow control message, and the condition which caused the sendingof the flow control message still exists, the BSSGP may retransmit the flowcontrol message immediately.



(E)GPRS in BSC

Uplink congestion control on NS-VC

The BSC uses a local congestion control procedure to adapt uplink NS-Unitdatatraffic to the NS-VCs according to their throughput. The BSC sends an NS-Unitdata, which passes the procedure, to the SGSN as long as the CIR of the NS-VC is not exceeded.

The BSC deletes any NS-Unitdata that do not pass the procedure. This updates acounter, and the BSC sets the UPLINK CONGESTION ON THE NETWORKSERVICE VIRTUAL CONNECTION alarm. The BSC cancels the alarm whenNS-Unitdata again pass the procedure.



9.9 Coding scheme selection in GPRS

Stealing bits in the channel coding (for more information see ETSI specificationon Channel Coding) are used to indicate the actual coding scheme (CS) which isused for each block sent between the BSC's PCU and the MS.

In downlink packet transfer the PCU selects the CS, and the code word for theselected CS is included in each RLC data block sent to the MS. If the PCUchanges the CS during one TBF reservation, it includes the new CS code word inthe blocks.

In uplink data transfer, the PCU informs the MS the initial CS to be used in eitherthe IMMEDIATE_ASSIGNMENT or PACKET_UPLINK_ASSIGNMENTmessage. The PCU can command the MS to change the CS by sending thePACKET_UPLINK_ACK/NACK message, which includes the Channel CodingCommand field. In retransmission the same CS has to be used as in the initialblock transmission.

Currently the coding schemes CS-1 and CS-2 are supported. The BSC levelparameters coding scheme no hop (COD) and coding scheme hop(CODH) define whether the fixed CS value (CS-1/CS-2) is used or if the codingscheme is changed dynamically according to the Link Adaptation algorithm. Inunacknowledged RLC mode CS-1 is always used regardless of the parametervalues. When the Link Adaptation algorithm is deployed, then the initial value forthe CS at the beginning of a TBF is CS-2.

For synchronisation purposes, the network sends at least one radio block usingCS-1 in the downlink direction every 360 milliseconds on every timeslot that haseither uplink or downlink TBFs.



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Link Adaptation algorithm

The Link Adaptation (LA) algorithm is used to select the optimum channelcoding scheme (CS-1 or CS-2) for a particular RLC connection and it is based ondetecting the occurred RLC block errors.

Essential for the LA algorithm is the crosspoint, where the two coding schemesgive the same bit rate. In terms of block error rate (BLER) the following equationholds at the crosspoint: 8.0 kbps * (1 - BLER_CP_CS1) = 12 kbps * (1 -BLER_CP_CS2) , where:

. 8.0 kbps is the theoretical maximum bit rate for CS-1

. 12.0 kbps is the theoretical maximum bit rate for CS-2

. BLER_CP_CS1 is the block error rate at the crosspoint when CS-1 is used

. BLER_CP_CS2 is the block error rate at the crosspoint when CS-2 is used

If CS-1 is used and if BLER is less than BLER_CP_CS1, then it would beadvantageous to change to CS-2. If CS-2 is used and if BLER is larger thanBLER_CP_CS2, then it would be advantageous to change to CS-1. Since CS-1 ismore robust than CS-2, BLER_CP_CS2 is larger than BLER_CP_CS1.

The crosspoint can be determined separately for UL and DL directions as well asfor frequency hopping (FH) and non-FH cases. For this purpose the followingBSC-level parameters are used by the LA algorithm:

. UL BLER crosspoint for CS selection hop (ULBH)

. DL BLER crosspoint for CS selection hop (DLBH)

. UL BLER crosspoint for CS selection no hop (ULB)

. DL BLER crosspoint for CS selection no hop (DLB)

The given parameters correspond to the BLER_CP_CS1 (see equation above).

During transmission, two counters are updated: N_Number gives the totalnumber of RLC data blocks and K_Number gives the number of corrupted RLCdata blocks that have been transmitted after the last link adaptation decision.

At certain intervals (in uplink transfer after approximately 10 transmitted RLCblocks, and in downlink after every PACKET_DL_ACK/NACK messagereception) the LA algorithm is run by performing two of the following (either 1and 2 or 3 and 4) statistical tests:

1.Current coding scheme is CS-1; change to CS-2?



(E)GPRS in BSC

Hypothesis: BLER > BLER_CP_CS1.

Reference case: N_Number of blocks have been transmitted with a constantBLER value of BLER_CP_CS1. In this reference case the number of erroneousblocks follow binomial distribution and the P-value gives the probability to get atmost K_Number of block errors out of N_Number of transmissions.

P-value =

If the P-value is less than a certain risk level (RL), the hypothesis can be rejectedwith (1-RL) confidence. If the hypothesis is rejected, it means that the referencecase would hardly give the observed measures with the given condition of BLER> BLER_CP_CS1. If this is the case, then it can be concluded that BLER <BLER_CP_CS1.

Action in case the hypothesis is rejected: Change to CS-2. Reset countersN_Number and K_Number.

Action in case the hypothesis is accepted: No actions.

2.Current coding scheme is CS-1; confirm CS-1?

Hypothesis: BLER < BLER_CP_CS1.

Reference case: N_Number of blocks have been transmitted with a constantBLER value of BLER_CP_CS1. In this reference case the number of erroneousblocks follow binomial distribution and the P-value gives the probability to get atleast K_Number of block errors out of N_Number of transmissions.

P-value =

If the P-value is less than a certain risk level, the hypothesis can be rejected with(1-RL) confidence. This means that the reference case would hardly give theobserved measures with the condition of BLER < BLER_CP_CS1. If this is thecase, then it can be concluded that BLER > BLER_CP_CS1.



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Action in case the hypothesis is rejected: Reset counters N_Number andK_Number (CS-1 is confirmed).


3.Current coding scheme is CS-2; change to CS-1?

Hypothesis: BLER < BLER_CP_CS2.

Reference case: N_Number of blocks have been transmitted with a constantBLER value of BLER_CP_CS2. In this reference case the number of erroneousblocks follow binomial distribution and the P-value gives the probability to get atleast K_Number of block errors out of N_Number of transmissions.

P-value =

If P-value is less than a certain risk level, the hypothesis can be rejected with (1-RL) confidence. This means that the reference case would hardly give theobserved measures with the condition of BLER < BLER_CP_CS2. If this is thecase, then it can be concluded that BLER > BLER_CP_CS2.

Action in case the hypothesis is rejected: Change to CS-1. Reset countersN_Number and K_Number.


4.Current coding scheme is CS-2; confirm CS-2?

Hypothesis: BLER > BLER_CP_CS2.

Reference case: N_Number of blocks have been transmitted with a constantBLER value of BLER_CP_CS2. In this reference case the number of erroneousblocks follow binomial distribution and the P-value gives the probability to get atmost K_Number of block errors out of N_Number of transmissions.

P-value =



(E)GPRS in BSC

If P-value is less than a certain risk level, the hypothesis can be rejected with (1-RL) confidence. This means that the reference case would hardly give theobserved measures with the condition of BLER > BLER_CP_CS2. If this is thecase, then it can be concluded that BLER < BLER_CP_CS2.

Action in case the hypothesis is rejected: Reset counters N_Number andK_Number (CS-2 is confirmed).


In practice the threshold K_Number values have been computed beforehand tolook-up tables indexed with respect to the N_Number and the link adaptationdecisions can be performed by simply comparing the observed K_Number withthe theshold K_Number values.

The Risk Level parameters (UL adaption probability threshold(ULA) and DL adaption probability threshold (DLA) ) describe theprobability with which the LA algorithm may make a wrong conclusion to rejecta given hypothesis. In other words, they determine the sensitivity of the LAalgorithm. The larger the risk level, the more quickly the LA algorithm is ablereact to changes in BLER by switching the coding scheme but on the other handthe reliability of the switching decision is lowered as the risk level is increased.

The PCU chooses a lower CS than what the Link Adaptation algorithm allows, ifthere is no room in the dynamic Abis pool for the higher CS allowed by the LA.



9.10 Coding scheme selection in EGPRS

In the EGPRS air interface, each radio block consists of four bursts, which are allmodulated either using Gaussian Minimum Shift Keying (GMSK) or Phase ShiftKeying (8-PSK). The modulation is blindly detected by the receiver usingtraining sequences. The radio blocks include a protected header, which has oneformat for GMSK and two formats for 8-PSK. The two formats of 8-PSK are



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differentiated from each other using stealing bits. The information on the usedmodulation and coding scheme (MCS) is then carried in the protected header. Thecoding schemes are listed in Table 1 and the exact formats are specified in theGSM Specification (05.03).

Table 7. EGPRS Coding Schemes

Name MCS-1 MCS-2 MCS-3 MCS-4 MCS-5 MCS-6 MCS-7 MCS-8 MCS-9

peakthrough-put(bps/time-slot)

8800 11200 14800 17600 22400 29600 44800 54400 59200

Modula-tion

GMSK GMSK GMSK GMSK 8�PSK 8�PSK 8�PSK 8�PSK 8�PSK

MCSfamily

C B A C B A B A A

Formatofprotec-tedheader

3 3 3 3 2 2 1 1 1

RLCBlocksin radioblock

1 1 1 1 1 1 2 2 2

In downlink packet transfer the PCU selects the MCS for each downlink radioblock within a TBF . Original transmissions may be performed in any MCS, butfor retransmissions of RLC blocks the coding scheme must be chosen to be thesame as the original one or in some cases it can be changed within an MCSfamily. The mechanisms used for the switch may include padding the block withdummy bits, and/or changing the number of RLC blocks in a radio block.

In the uplink the PCU commands the MS to use a certain MCS in thePACKET_UPLINK_ASSIGNMENT message and can change the commandedMCS in the PACKET_UPLINK_ACK/NACK orPACKET_TIMESLOT_RECONFIGURE message. The commanded MCS isused for all initial transmissions. Retransmissions of RLC blocks obey the samerestrictions as in the downlink, but the MCS selection is controlled by thecommanded MCS according to rules in the GSM Specification (04.60).



(E)GPRS in BSC

All the EGPRS coding schemes MCS-1...MCS-9 are supported with incrementalredundancy.

Initial MCS (MCS used before any measurement data is available) is controlledby the operator. Parameters Initial MCS for acknowledged mode (MCA)and Initial MCS for unacknowledged mode (MCU) are used for this.

For synchronisation purposes, the network sends at least one radio block usingCS-1 or MCS-1 in the downlink direction every 360 milliseconds on everytimeslot that has either uplink or downlink TBFs. If there are only EGPRS TBFson the timeslot, the synchronisation block is sent using MCS-1. If there are alsoGPRS TBFs on the timeslot, the synchronisation block is sent using CS-1.

EGPRS Link Adaptation Algorithm

For the acknowledged mode, the link adaptation algorithm is designed tooptimise channel throughput in different radio conditions. For theunacknowledged mode, the algorithm tries to keep below a specified Block ErrorRate (BLER ) limit. The algorithm is based on Bit Error Probability (BEP)measurements performed at the MS (downlink TBF) and the BTS (uplink TBF).BEP measurement consists of the mean and cv (= coefficient of variance =standard deviation / mean) of burstwise BEP, calculated over one radio block andaveraged using an exponentially-forgetting filter. Mean BEP is expressed using 5bits (range 0...31) and cv BEP using 3 bits (range 0...7). The operator can offsetthe reported mean BEP values using the parameters mean BEP offset GMSK(MBG) and mean BEP offset 8PSK (MBP) . The same offset is applied inboth directions (uplink and downlink).

The PCU chooses a lower MCS than what the Link Adaptation algorithm allows,if there is no room in the dynamic Abis pool for the higher MCS allowed by theLA.

Link Adaptation can be enabled and disabled with the parameter EGPRS linkadaptation enabled (ELA).

LA in the acknowledged mode

The algorithm includes an internal MCS selection table to select the MCS thatoptimises throughput based on the BEP measurements. Both mean BEP and cvBEP are used as inputs. Also the desired modulation is selected at this step, takinginto account the BEP values of both modulations.

In some cases, the MCS that has the highest throughput also has a relatively highBLER. In that case, although the throughput is high, there is also a high numberof retransmissions and therefore the requirement on receiver IR memory is highand the delay can be quite large. The operator has the possibility to limit theestimated BLER to a certain value. This value is controlled by the parameter



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maximum BLER in acknowledged mode (BLA) . The algorithm computesa BLER estimate for each MCS based on BEP measurements. Then the estimatesare compared to the BLER limit, and an MCS whose BLER is higher than thelimit is not allowed even if its estimated throughput is the highest one.

The algorithm also has an internal mechanism to take into account IR memoryoverflows of the MS.

For retransmissions, the algorithm preferably uses high coding schemes, so that ablock first transmitted in MCS-6 (MCS-5) is usually retransmitted in MCS-9(MCS-7). This gives up to 2 dB better throughput performance than plain MCS-6(MCS-5). If the BEP values are poor, then lower MCS's (MCS-5 and MCS-6) canbe used instead.

LA in the unacknowledged mode

The BEP measurements are used to calculate an estimate of the BLER for eachMCS. Then the highest MCS whose BLER is lower than the operator adjustedparameter maximum BLER in unacknowledged mode (BLU) is selected tobe used for the next transmissions.



9.11 Power control

GPRS power control consists of the uplink power control. Due to the data burstsin traffic, the power control is not as effective as for circuit switched traffic.Downlink power control will be supported in future BSC releases.

Power control is used for optimising the signal strength from MS to BTS. Theoperator can use the cell-specific parameters binary representationALPHA (ALPHA) and binary representation TAU (GAMMA) tooptimise the signal strength. The gamma parameter sets the minimum powerlevel, and the alpha parameter sets the slope for field strength effect to uplinkpower level.



(E)GPRS in BSC

Figure 10. Uplink power control



05101520253035

-45

-50

-55

-60

-65

-70

-75

-80

-85

-90

-95

-100

-105

-110

Signal Strength (dBm)

gamma_ch = 30 alfa = 0.8

gamma_ch = 20, alfa = 0.3

Uplink power control

MS Outpu tPower (dBm)



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(E)GPRS in BSC

10 Limitations of the GPRS feature

There are a number of limitations to the GPRS and EGPRS features. Thelimitations are gathered here to a list, with links to the relevant sections in thelibrary where they are covered more thoroughly.

. The Satellite Abis feature is not supported.

. The Nokia GPRS implementation only supports dynamic traffic channelallocation.

. GPRS territory cannot be configured in the extended range area of cells.

. Super-reuse frequencies are not supported for GPRS.

. If Baseband hopping is employed in a BTS, radio time slot 0 of any TRXin the BTS will not be used for GPRS.

. PCCCH cannot carry data traffic.

. BTS testing cannot be executed on the packet control channel.

. PCCCH and PBCCH must use the same timeslot, and be configured onthe BCCH TRX.

. PBCCH/PCCCH is not supported in Network Operation Mode II.

. Network operation mode III is not supported.

. Coding Scheme CS-1 is always used in unacknowledged RLC mode.

. Coding schemes CS-3 and CS-4 are not supported.

. The Network Controlled Cell Re-selection feature is not supported.

. The paging reorganisation feature is not supported.

. Only EDGE capable TRXs are capable of using shared EGPRS DynamicAbis Pool (EDAP) resources.

. There can be 16 EGPRS Dynamic Abis Pools per Packet Control Unit.

. One EDAP cannot be divided to separate PCUPCMs.



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Limitations of the GPRS feature

. One EDAP resource should not be shared between several BCF cabinets.It may damage the TRX or DTRU hardware if the operator tries to shareEDAP between several cabinets.

. The BSS does not restrict the use of 8PSK modulation on TSL7 of theBCCH TRX, using the highest output power. The maximum output poweris 2dB lower than with GMSK. This is fully compliant with 3GPP Rel 5.





(E)GPRS in BSC

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