HSCSD_NSN

GSM/EDGE BSS, Rel. RG20(BSS), Operating Documentation, Issue 04

Feature description

BSS7003 and BSS7037: HSCSD and 14.4 kbit/s Data Services in BSC

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Issue 9-0Approval Date 2010-04-26

Confidential

2 DN9813893Issue 9-0

BSS7003 and BSS7037: HSCSD and 14.4 kbit/s DataServices in BSC

Id:0900d8058072ae6aConfidential

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Table of contentsThis document has 56 pages.

Summary of changes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

1 Overview of HSCSD and 14.4 kbit/s Data Services in BSC . . . . . . . . . . 7

2 Technical description of HSCSD and 14.4 kbit/s Data Services in BSC . 9

3 Functionality of HSCSD and 14.4 kbit/s Data Services in BSC . . . . . . . 16

4 HSCSD and 14.4 kbit/s Data Services effects on interface procedures 274.1 HSCSD and 14.4 kbit/s Data Services effects on A interface procedures.

274.2 HSCSD and 14.4 kbit/s Data Services effects on the Abis interface proce-

dures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 324.3 HSCSD and 14.4 kbit/s Data Services effects on Radio interface proce-

dures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

5 Schemes in HSCSD and 14.4 kbit/s Data Services. . . . . . . . . . . . . . . . 35

6 User interface of HSCSD and 14.4 kbit/s Data Services . . . . . . . . . . . . 55

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List of figuresFigure 1 HSCSD network architecture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9Figure 2 Double slot operation in the radio interface . . . . . . . . . . . . . . . . . . . . . . 10Figure 3 Puncturing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11Figure 4 Example of Ater switching. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18Figure 5 Transmission example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19Figure 6 Ater TSL allocation example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20Figure 7 Ater TSL allocation example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21Figure 8 Ater TSL allocation example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22Figure 9 Channel type information element . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27Figure 10 Coding of data rate/transparency indicator field . . . . . . . . . . . . . . . . . . . 27Figure 11 Mobile-originated call setup, basic scheme . . . . . . . . . . . . . . . . . . . . . . 36Figure 12 Mobile-originated call setup, basic scheme . . . . . . . . . . . . . . . . . . . . . . 37Figure 13 Resource downgrade from 3+1 to 2+2 HSCSD configuration, basic

scheme . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39Figure 14 Resource upgrade from 2+2 to 3+1 HSCSD configuration, basic scheme.

40Figure 15 Resource upgrade from 2+2 to 3+1 HSCSD configuration, basic scheme.

41Figure 16 BSC internal inter-cell handover, basic scheme . . . . . . . . . . . . . . . . . . . 43Figure 17 External handover, basic scheme. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45Figure 18 External handover, basic scheme. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

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List of tablesTable 1 Data rates achieved by HSCSD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7Table 2 Different failure causes scenarios for in call modification . . . . . . . . . . . 13

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Summary of changes

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

Changes between issues 9-0 (2010/04/26, RG20(BSS)) and 8-0(2009/12/02, RG10(BSS))

Technical description of HSCSD and 14.4 kbit/s Data Services in BSC (2)

Added information on BSS21238:Merged PGSM900 and EGSM900 feature under Restrictions in the use of HSCSD and 14.4 kbit/s data services.

Added Restriction due to Packet abis and A over IP under In Call Modification Added sectionBSS21238:Merged PGSM900 and EGSM900, BSS21341: A over IP,

Transcoder in BSS and BSS21454: Packet Abis over IP/Ethernet and BSS21440: Packet Abis over TDM under Interworking with other functionalities

Changes made between issues 8-0 and 7-0The term circuit mode is replaced with the term circuit type throughout the document.

Chapter HSCSD and 14.4 kbit/s Data Services effects on interface procedures: new AMR-WB pools have been added and the definitions to circuit types has been modified.

Changes made between issues 7-0 and 6-0Editorial changes.

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Overview of HSCSD and 14.4 kbit/s Data Services inBSC

Id:0900d80580735035Confidential

1 Overview of HSCSD and 14.4 kbit/s Data Services in BSCHigh Speed Circuit Switched Data (HSCSD) and 14.4 kbit/s data services are system functionalitites in Nokia Siemens Networks DX 200 Base Station Controller (BSC) and TCSM.They have effects on the following network elements: the Mobile Switching Center (MSC), Base Transceiver Station (BTS), NetAct, the Mobile Station (MS) and NPS/X.

High Speed Circuit Switched Data (HSCSD)High speed circuit switched data provides accelerated data rates for end-user applica-tions. The current trend is for increased demand for high data rate applications such as the World Wide Web (WWW), file transfer and facsimile. HSCSD will facilitate the use of such applications.

The Base Station System (BSS) implementation is to reserve a multiple set of basic (cur-rent) resources for one high speed data call. The data rate and number of reserved time slots varies between one and a user application-defined maximum. The variable rate is needed, for example, for handovers to a new cell if the requested data rate cannot be given immediately. The BSS implementation of HSCSD supports simultaneous use of four time slots per one HSCSD call. The following table presents the corresponding maximum data rates with different channel codings:

Both asynchronous and synchronous bearer services and transparent and non-trans-parent transfer modes are supported. Transparent HSCSD uses fixed data rates throughout the call whereas non-transparent HSCSD is flexible and the data rate can be changed during the call for example due to the traffic situation. The radio interface is either symmetric or asymmetric depending on MS capability. However, the Abis inter-face and the A interface are always symmetric. In the A interface, HSCSD connections can be switched to one of the HSCSD supporting pools.

14.4 kbit/s data services14.4 kbit/s data services accelerates the standard 9.6 kbit/s user data rate with a single time slot to 14.4 kbit/s.

The use of 14.4 kbit/s data service reduces cell coverage. For example, if the current 9.6 kbit/s service has 90% coverage, the 14.4 kbit/s service will have about 84-87% cov-erage. The current threshold for power control represents the predicted border of the acceptable user data performance for the speech or 9.6 kbit/s data. This is not adequate for 14.4 kbit/s user data since 14.4 kbit/s channel coding can stand fewer errors. To maintain 14.4 kbit/s performance adequate, the RX_QUAL value has to be better and

RTSLs 9.6 kbit/s 14.4 kbit/s

1 9.6 kbit/s 14.4 kbit/s




Table 1 Data rates achieved by HSCSD

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Overview of HSCSD and 14.4 kbit/s Data Services in BSC

therefore the power increase has to be started at higher quality for 14.4 kbit/s calls than for other calls.

A threshold parameter pc lower thresholds qual144 Rx level (LQR), Px (LQP), Nx (LQN) is defined for triggering downlink and uplink power increase for 14.4 kbit/s connections. However, for optimal performance, channel coding is changed between 14.4 kbit/s and 9.6 kbit/s channel codings by the automatic link adaptation (ALA) procedure according to Mobile Station (MS) and Base Transceiver Station (BTS) power levels. The parameter power limit ALA (ALIM) determines the MS and BTS power levels when ALA is performed. ALA is applicable for non-transparent data con-nections.

14.4 kbit/s data service can be combined with HSCSD. In the A interface, 14.4 kbit/s data connection can be switched to one of the pools which support 14.4 kbit/s channel coding.

Related topics of HSCSD and 14.4 kbit/s Data Services in BSC

Technical description of HSCSD and 14.4 kbit/s Data Services in BSC Functionality of HSCSD and 14.4 kbit/s Data Services in BSC HSCSD and 14.4 kbit/s Data Services effects on interface procedures Schemes in HSCSD and 14.4 kbit/s Data Services User interface of HSCSD and 14.4 kbit/s Data ServicesOther related topics

Instruction Activating and Testing BSS7003 and BSS7037: HSCSD and 14.4 kbit/s Data

Services

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Technical description of HSCSD and 14.4 kbit/s DataServices in BSC

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2 Technical description of HSCSD and 14.4 kbit/s Data Services in BSCIn HSCSD, higher data rates can be offered using several full rate TCHs for one con-nection. Therefore, a functionality is needed in both the MS and the MSC to split data to be carried in several radio interface FR TCHs and then to be combined at the other end. For cellular operations, the HSCSD channels in the same connection are controlled as one radio link. For example, handovers are made simultaneously for all channels in one HSCSD connection. On the A interface, HSCSD channels are multiplexed to one 64 kbit/s circuit (see Figure HSCSD network architecture).

In the Ater interface, HSCSD calls use circuit pools supporting four and eight bit switch-ings. Support for cases when the A interface does not support the pool concept is also required.

Figure 1 HSCSD network architecture

The adaptation of the GSM transmission to other networks (for example, PSTN) is done by the Interworking Functions (IWF) in MSC. On the MS side, the Terminal Adaptation Function (TAF) performs the adaptation between the terminal equipment and the GSM radio transmission part.

Transparent (T) serviceIn transparent data services, the radio interface transmission scheme provides only forward error correction. The throughput between IWF and TAF is constant. In HSCSD, this means that the requested data rate has to be fulfilled from the call setup to the release of the call, including possible handovers during the call. Radio interface user rates are requested in T service (for example 4.8, 9.6 or 14.4 kbit/s). In HSCSD, the transparent service uses only bi-directional channels.

Non-transparent (NT) service and flexible channel allocationIn non-transparent data services the sent frames include redundancy bits to enable the receiver to detect remaining errors after forward error correction. With Radio Link Protocol (RLP), the receiver tests the correctness of the frame and if found not correct, sends a negative acknowledge message to the sender. The available throughput varies with the quality of the basic transmission but the quality of the sent data is excellent.

NT service makes it possible to use flexible radio interface data rates. For HSCSD, this means that reserved radio resources can also vary during a call. Depending on the avail-able resources, the HSCSD connection can occupy channels from one to a user-defined maximum number of channels. New procedures, resource upgrade and resource down-

MSAir i/f

TAF

BTSAbis i/f

BSCAter i/f

TCSM

1-4TCH/F

1-4TCH/F

max 1circuit

MSCA i/f

max 1circuit

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Technical description of HSCSD and 14.4 kbit/s Data Services in BSC

grade, are introduced in the BSC. Total radio interface data rates are requested in the NT service (for example 6.0, 12.0 or 14.5 kbit/s).

MS multislot capabilityThe number of channels for an HSCSD connection depends on how many channels the MS is able to receive or transmit and how fast it can perform the adaptations between operation modes. With the MS multislot capability, the BSC can determine the kind of HSCSD connections it can allocate for a certain MS. See 3GPP TS 45.002: Multiplexing and multiple access on the radio path.

The Type 1 MSS need time to adapt between different modes, so they can only either receive, send, or monitor the neighbor cell fields at a time. Transmitting and receiving in the same time slot is made possible by shifting the transmitting time slots (see the figure below).

Figure 2 Double slot operation in the radio interface

The allocated channel may be from non-consecutive time slots as long as the MS mul-tislot capability is taken into account. For type 1 MSS, it means that in practice consec-utive time slots almost always have to be allocated. Type 2 MSS can receive and transmit simultaneously, which makes radio channel allocation more flexible.

Radio interfaceIn a symmetric HSCSD connection, all the channels transfer data in both uplink and downlink directions. In order to enable greater data rates for type 1 MSS, it is possible to transmit in downlink direction with more channels than in uplink direction. Channels that transmit in both directions are called bi-directional channels and channels that transmit only in the downlink direction are called uni-directional channels.

At least one bi-directional channel is required for each HSCSD connection. In both sym-metric and asymmetric HSCSD configurations one bi-directional channel, the main channel, carries a Fast Associated Control Channel (FACCH) used for all the signalling not carried on the Slow Associated Control Channels (SACCH).

Individual signal level and quality reporting is used for all bi-directional channels. The quality measurements reported on the main channel are based on the worst downlink quality measured among the main and the uni-directional downlink time slots used.

14.4/14.5 kbit/s channel coding14.4/14.5 kbit/s is the data rate to be used over one full rate traffic channel (FR TCH). The 14.4/14.5 kbit/s radio interface rate is achieved by changing the puncturing scheme. By puncturing, a number of channel coding bits in 22.8 kbit/s frame is reduced by a pre-determined rule.

For more information, see 3GPP TS 45.003: Channel Coding.

MS RX 0 1 2 3 4 5 6 7 0 1

MS TX 5 6 7 0 1 2 3 4 5 6

Monitor

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Figure 3 Puncturing

14.4/14.5 kbit/s channel coding is more vulnerable to bad quality. For example, if the current 9.6/12.0 kbit/s service has 90% coverage, the 14.4/14.5 kbit/s service will have about 84-87% coverage. In the NT service, when the error rate for 14.5 kbit/s is unac-ceptable, the performance can significantly be improved by automatic link adaptation (ALA) function. In ALA, channel coding is changed between 14.5 kbit/s and 12.0 kbit/s.

Requirements for HSCSD and 14.4 kbit/s data services

BSC: At least S7-level software is required Only MSS of phase 2+ which have HSCSD or 14.4 kbit/s data service especially

implemented support HSCSD and 14.4 kbit/s data services.

Restrictions in the use of HSCSD and 14.4 kbit/s data services

HSCSD configurations of up to four FR TCHs are supported. The automatic link adaptation (ALA) procedure is not used in transparent (T)

service. 4.8/6.0 kbit/s channel coding is not supported in HSCSD connections. The resource upgrade and downgrade procedures are not used in T service. Change of main channels during the call is not supported. Non-consecutive channel allocations are not allocated for T requests. HSCSD is supported in a PGSM 900 - EGSM 900 BTS where the BCCH is on the

PGSM 900 frequency band only with the Merged PGSM900 and EGSM900 feature. For detail, see BSS21238: Merged PGSM 900 and EGSM 900.

Maximum HSCSD data ratesUp to four channels can be allocated for one HSCSD connection. 14.4/14.5 kbit/s is the maximum throughput for one channel. When the HSCSD and 14.4/14.5 kbit/s channel coding are used together, data rates of 57.6 kbit/s for transparent service and 58 kbit/s for non-transparent service are achieved.

Interworking with other functionalities

Frequency HoppingThe same frequency hopping sequence is used for all the channels in the HSCSD configuration. When base band frequency hopping is in use, HSCSD channels in the same configuration must be allocated from the same hopping group.For more information, see Frequency Hopping.

12.0 kbit/s 8 kbit/s

240 bits 244 bits 488 bits 456 bits

14.5 kbit/s 8 kbit/s

290 bits 294 bits 588 bits 456 bits

22.

22.

Block code240 + 4

Block code290 + 4

1/2 rateconvol.code

1/2 rateconvol.code

punctu-ring588-132

punctu-ring488-32

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Intelligent Underlay-Overlay (IUO)HSCSD radio resource allocation parameters are defined separately for the regular layer (see User interface of HSCSD and 14.4 kbit Data Services). Resource upgrades are not done in the regular frequency area.In a super-reuse layer, all the channels in HSCSD configuration must fulfil the inter-ference band recommendation defined by the BSC.For more information on IUO, see Intelligent Underlay-Overlay.

Trunk ReservationWhen the trunk reservation algorithm is applied non-transparent connections are started with one channel and the connection is

upgraded if possible. The trunk reservation algorithm is used for every channel allocation.

for transparent connections, the parameter number of free traffic channels (n) is modified:n = n - number of channels needed for T connection + 1

For more information, see Trunk Reservation. Queuing

Call setup or handover attempts in queue are preferred to upgrade pending HSCSD connections in channel allocation algorithm.Transparent HSCSD connections cannot enter a cell through queueing. Non-trans-parent HSCSD connections can have the first channel through queueing.For more information on queuing, see Radio Resource Pre-emption and Queuing.

Pre-emptionTransparent HSCSD connections cannot enter a cell by pre-emption. The pre-emption handover is not applied to transparent HSCSD connections.If the target of pre-emption is a non-transparent HSCSD connection with more than one channel, the handover or release is changed to a resource downgrade.Non-transparent HSCSD connections can enter a cell by pre-emption with only one channel.For more information on pre-emption, see Radio Resource Pre-emption and Queuing.

Extended Cell RangeHSCSD load is controlled separately in extended and normal areas. For more infor-mation, see Extended Cell Range.

FACCH Call SetupFACCH Call Setup is not made for transparent HSCSD connections requiring more than one channel. Non-transparent connection is started with one channel and the possibility to resource upgrade is checked after the assignment.For more information, see FACCH Call Set-up.

RX Quality and RX Level StatisticsUni-directional channels are taken into account by modifying the main channel incre-ment step. The main channel increment step is the number of unidirectional channels plus one. The counter to be incremented is defined by the quality or level of the main channel. For more information, see 14 RX Quality Statistics Measurement.

In Call ModificationIn call modification is not made for transparent connections requiring or using more than one channel. The BSC functions in the following way when the MSC allows changes during a non-transparent connection:

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speech to HSCSD: the connection is started with one channel and additional channels are allocated by the resource upgrade procedure if needed.

HSCSD to speech: the connection is downgraded to one channel before change of modes.

The BSC functions in the following way when the MSC does not allow changes during a non-transparent connection: speech to HSCSD: the connection is made with one channel, resource upgrade

is not possible. HSCSD to speech: the connection is downgraded to one channel before change

of modes.Restriction in In Call ModificationIn call modification from voice to data or vice-versa is not supported when packet abis is configured between BSC and BTS. It is also not supported in cases when AoIP is configured between BSC and MSS and transcoder (TC) resides in BSS. When MSS sends ASSIGNMENT REQUEST to BSC, the failure cause message for the different interface combinations is send in the ASSIGNMENT FAILURE message to MSS as given in Table 2.

traffic reason handoverTraffic reason handovers are made only to single slot connections and HSCSD con-nections requiring only one channel. For more information, see Traffic Reason Handover in BSC.

Power optimization in handoverOptimized power is defined by the channel triggering the handover and it is used for all time slots in HSCSD configuration. For more information on power optimization in handover, see RF Power Control and Handover Algorithm and Intelligent Underlay-Overlay.

Interference band recommendationThe interference band recommendation is defined by the channel triggering the handover and it is used for all time slots in HSCSD time slot allocations.For more information on interference band recommendation, see Radio Resource Pre-emption and Queuing

Abis type configured between BSC and BTS

A interface configured between BSC and MSS

Failure cause message

Legacy Abis AoIP TC in BSS Requested transcoding/rate adaption unavailable

Packet Abis AoIP TC in BSS Requested transcoding/rate adaption unavailable

Packet Abis AoTDM or Legacy A Requested terrestrial resource unavailable

Table 2 Different failure causes scenarios for in call modification

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RF Power Control and Handover Algorithm Intelligent Underlay-Overlay.

Dual band network operationSystem information messages Sys_Info_5, Sys_Info_5bis, Sys_Info_5ter and Sys_Info_6 are sent only in the main channel. For more information, see Dual Band Network Operation.

TRX locking with forced HO and save calls by forced HO prior to cell recoveryHandover is started only in the main HSCSD channel. The subchannels are then set free along with the main channel. For more information on TRX locking with forced handover (HO) and save calls by forced HO prior to cell recovery, see RF Power Control and Handover Algorithm.

RXLev Min AccessIf RXLev Min Access is activated in the BSC, the C/N based method for an HSCSD or single slot data call is used to determine whether TCH can be allocated according to the downlink RX level measured by MS.Different call types (EFR/FR, HR, AMR FR, AMR HR, and 14.4 data) require sepa-rately set C/N threshold values. These values determine the serving rxlevel needed for a data call.The EFR/FR C/N threshold value is used for 4.8 kbit/s and 9.6 kbit/s. The 14.4 C/N threshold value is used for 14.4 kbit/s coding.In case of Non-Transparent HSCSD or single slot call, the following rules are valid when selecting appropriate coding for channel allocation. Requested data rate and MS capabilities determine which codings are appropri-

ate (and in case of HSCSD data call; how many TSLs are needed). Available appropriate coding fulfilling the C/N threshold value is selected for

coding in channel allocation.If the appropriate available coding does not fulfil the required C/N threshold in a Transparent HSCSD or single slot call, the data call request is rejected.For more information, see RXLev Min Access in Radio Channel Allocation.

BSS21238: Merged PGSM 900 and EGSM 900HSCSD is supported in a PGSM 900 - EGSM 900 BTS where the BCCH is on the PGSM 900 frequency band only with the Merged PGSM900 and EGSM900 feature. For detail, see BSS21238: Merged PGSM 900 and EGSM 900.

BSS21341: A over IP, Transcoder in BSSHSCSD requires presence of TCSM entity in GERAN, that is, HSCSD is supported in case of A over IP when the transcoder is located in BSS. It requires the following circuit pools to be defined to Ater interface for multislot cases of two and four slot pools: Pool no 89 for 16kbps and 32 kbps HSCSD calls Pool no 90 for 64 kbps HSCSD calls.Pool no 90 is also used for 32kbps call HSCSD class which can be upgraded to a 64kbps call. The BSC find the Ater resource to support HSCSD calls. It also supports 16, 32 and 64kbit/s circuits in the Ater interface. HSCSD call requires the Rate Adaptation unit in the TRAU. TRAU is available only in the PCM over IP (PI) or PCM over TDM (PT) interface, hence for HSCSD calls only PI or PT A-Interface is used.

BSS21454: Packet Abis over IP/Ethernet and BSS21440: Packet Abis over TDM When either packet Abis over TDM or packet Abis over Ethernet is used, HSCSD is supported only with the AoIP (TC in BSS) and AoTDM (G.711), A interfaces options. Data transfer at user plane between BTS and ETPT/E in BSC happens via UDP-

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Radio Channel-ports of TCHs. Each TCH of a HSCSD call has its own port. UDP-Radio Channel-port identifies the radio timeslot and TRX of the data in multiplexed Abis u-plane UDP packet. In HSCSD call setup and channel configuration upgrade u-plane resources are allocated form ETPT/E and group switch. During HSCSD connection ETPT/E converts Abis u-plane packets to TRAU frames and sends them to Ater via group switch. ETPT/E also receives TRAU frames from group switch and converts them to Abis u-plane packets and sends them to BTS via UDP-Radio Channel-ports of the HSCSD connection.

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Functionality of HSCSD and 14.4 kbit/s Data Services in BSC

3 Functionality of HSCSD and 14.4 kbit/s Data Services in BSCThe following topics are covered below:

HSCSD call setup Radio resource allocation Channel configuration change The A and Ater interfaces Power control and handover algorithm in HSCSD and 14.4/14.5 kbit/s connections Handover signalling Start of ciphering in HSCSD HSCSD load controlHSCSD call setupParameters for an HSCSD call are negotiated by the MS and the MSC in the call setup phase. The BSC notices the HSCSD call in a Channel Type information element (IE) in an ASSIGNMENT REQUEST message received from the MSC. The channel type IE defines the requested data service type (Non-transparent/transparent), a required total data rate, maximum number of full rate traffic channels (FR TCH) and supported channel codings. The MS sends its multislot class information to the network using the early classmark sending procedure. These are the parameters for channel allocation procedure.

A separate channel activation is applied for all the HSCSD channels. One of the bi-direc-tional channels is a main signalling link which carries an FACCH used for all signalling not carried on the SACCH(s). The selected channel configuration is forwarded to the MS in an ASSIGNMENT COMMAND message. The MSC is informed of the chosen HSCSD configuration in an ASSIGNMENT COMPLETE message.

Radio resource allocationAn HSCSD call uses a multislot configuration consisting of one or several FR TCH(s). HSCSD parameters for channel allocation are

required total radio interface data rate (Non-transparent service) requested radio interface user rate (Transparent service) maximum number of sub-channels service (Transparent/Non-transparent) MS multislot capability allowed radio interface rates per channel.The BSC receives the parameters in either the ASSIGNMENT REQUEST or the HANDOVER REQUEST message. An exception is the MS multislot class, which is not a part of the ASSIGNMENT REQUEST message. In a call setup, the MS informs its mul-tislot class with the CLASSMARK CHANGE message before the assignment.

The BSC tries to allocate as many channels as needed to fulfil the required total data rate. The fastest appropriate data rate per channel is used. For example, when the required data rate for transparent (T) service is 14.4 kbit/s, one 14.4 kbit/s channel is chosen. If only 9.6 kbit/s channel coding is supported, two 9.6 kbit/s channels are allo-cated, resulting in 19.2 kbit/s total data rate. In T service, extra data bits are padded with

DN9813893 17


Functionality of HSCSD and 14.4 kbit/s Data Servicesin BSC


fill by TAF or IWF respectively in MS or MSC. If total data rate 9.6 or 19.2 kbit/s for T service is requested, 9.6 kbit/s channel coding is used.

Channels in an HSCSD connection must be allocated from the same transceiver (TRX). The MS multislot capability determines how far the allocated time slots can be from each other. The number of channels for HSCSD connection at the first allocation after request or during the connection by downgrade procedure can be controlled with parameterisa-tion. For more information, see HSCSD load control. In the downgrade procedure, part of the channels of the HSCSD connection are released for other use, while the HSCSD connection is maintained with a reduced total data rate.

HSCSD service at the call setup or during the connection can be improved with directed retry or upgrade pending procedures. In the upgrade procedure, new channels are acti-vated and added to a current HSCSD connection, thus increasing the total data rate.

For more information on directed retry, see Directed Retry in BSC.

For transparent HSCSD connections, a certain number of FR TCHs must be allocated to meet the requested total data rate. If there are not enough channels in a cell, directed retry (DR) procedure can be used in call setup. If the target cell in a handover cannot provide the requested total data rate, the DR attempt is terminated and the call is released.

A non-transparent HSCSD call can be started with fewer FR TCHs than required. At least one channel is allocated for the HSCSD connection if there are free resources available in a cell. The upgrade pending procedure is started if the required total radio interface data rate cannot be fulfilled at the initial channel allocation or if the number of channels is decreased during the connection. Pending is maintained until the required data rate is reached.

Channel allocation parameters may change during a non-transparent HSCSD call, for example, the user may change the required total data rate. The MSC indicates the change by sending an ASSIGNMENT REQUEST message to the BSC. If there is a con-tradiction between the new parameters and the used radio interface resources, a resource downgrade is needed.

In pre-emption, a higher priority connection can occupy channel(s) from lower priority connection(s). The pre-emption capability indicator for the pre-emptive connection and the pre-emption vulnerability indicator for the call to be handed over or released must allow the pre-emption. An HSCSD call with a lower priority level can also be the target of a pre-emption. The resource downgrade procedure can be used for non-transparent connections using more than one channel.

For more information on pre-emption, see Radio Resource Pre-emption and Queuing.

Channel configuration changeThe BSC changes the number of used time slots in a multislot configuration with resource upgrade and downgrade procedures. The mode modify procedure can be used to change the channel coding of used channels.

The BSC configures BTS resources. The configuration determines the time slots used in uplink, the time slots used in downlink and which mode they use. When new channels are allocated, the BSC sends a CHANNEL ACTIVATION message. The BSC sends a MODE MODIFY message when the channel coding of the current channel is changed or if transfer mode is changed between the uni-directional and bi-directional modes.

The CONFIGURATION CHANGE COMMAND message commands the MS to use a new channel configuration. If the command instructs the MS to use a configuration it

18 DN9813893




does not support, it sends a CONFIGURATION CHANGE REJECT message with the cause 'channel mode unacceptable'.

A CHANNEL MODE MODIFY or CONFIGURATION CHANGE COMMAND message is used when a new channel mode is used for currently allocated channels.

After acknowledgement from the MS, the BSC sends a HANDOVER PERFORMED message to the MSC containing the new channel configuration.

The A and Ater interfacesThere are circuit pools (CIP) to support HSCSD connections on the A interface. A circuit pool is a group of circuits supporting the same channel type. Supported pools can handle all the existing connection types (half rate (HR), full rate (FR), enhanced full rate (EFR), FR data, adaptive multi-rate (AMR)) with either HSCSD max. 2 * FR data (HS2) or HSCSD max. 4 * FR data (HS4) or 14.4/14.5 kbit/s channel coding. HSCSD pools are supported with or without 14.4/14.5 kbit/s. See also HSCSD and 14.4 kbit/s Data Services effects on A interface procedures.

In HS4, a whole Ater PCM time slot is reserved for one connection. The reserved FR TCHs are connected to consecutive Ater subchannels. An exception to this is down-grade which can lead to the non-consecutive switching of the subchannel. In the subse-quent upgrade, the lowest possible subchannel is switched (see the figure below). See also 3GPP TS 48.020: Rate adaption on the Base Station System - Mobile-services Switching Centre (BSS-MSC) interface.

Figure 4 Example of Ater switching

Transcoder PCMs can be defined in Ater PCM in any order. All time slots in the last con-nected transcoder PCM cannot be allocated on Ater in certain combinations, because this would lead to ineffective use of hardware.

3 TCH/F HSCSD connection

Radio i/f

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DN9813893 19




Figure 5 Transmission example

Abisinterface

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20 DN9813893




Figure 6 Ater TSL allocation example

TSL

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DN9813893 21





In TCSM, TSLs 2...31 can be through connected to transcoder PCM TSLs 1...31.TCSM allows the last transcoder PCM to be partial.

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22 DN9813893





Power control and handover algorithm in HSCSD and 14.4/14.5 kbit/s connections

Measurement reportingThe signal level and quality are reported by every bi-directional channel in an HSCSD multislot call. The MS copies the neighbouring cell's measurement reports to every bi-directional channel. Uni-directional channels cannot report their mea-surements because they do not have an uplink SACCH where the measurement reports are sent. The quality measurement reported on the main channel is the worst quality measured among the main and the uni-directional downlink channel(s) used. See 3GPP TS 45.008: Radio subsystem link control.

In TCSM, TSLs 2...31 can be through connected to transcoderPCM TSLs 1...31.TCSM allows the last transcoder PCM to be partial.

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DN9813893 23




Radio link timeoutOnly the main SACCH is used for determining the Base Station Subsystem (BSS) radio link failure.

Power controlPower control is made individually for every bi-directional channel. The MS neglects power control information on a unidirectional channel. The BTS is commanded to use the same power in uni-directional channels as in the main channel. Power control is not made during automatic link adaptation signalling.

Automatic link adaptation (ALA)New threshold parameters are needed to trigger the ALA. In ALA, channel coding is changed during the call according to the uplink and downlink signal quality and the MS and BTS powers. On the edge of a cell, for example, the channel coding can drop from 14.5 kbit/s to 12.0 kbit/s. Channel coding is changed for all the channels in a multislot configuration. In NT transfer mode, the dropping of channel coding can lead to an increase of user data rate when the number of retransmissions of data bursts decreases. The ALA is also used in increasing channel coding from 12.0 kbit/s to 14.5 kbit/s. The ALA procedure is used only in the NT service.The channel coding change in the BTS is made using a MODE MODIFY message. Radio resources may be adjusted to meet the required total radio interface rate, if possible by the maximum allowed number of channels. If new channels are allo-cated or old channels are released, respectively either the resource upgrade or the downgrade procedure is used. In a single slot data connection, a CHANNEL MODE MODIFY message is used to command the MS to use the new channel coding. In a multislot connection, a CONFIGURATION CHANGE COMMAND message is used.

HandoverAny bi-directional HSCSD channel can trigger a handover. ALA is prohibited during handover signalling. All existing handover reasons are supported. See RF Power Control and Handover Algorithm .

14.4/14.5 kbit/s connection power control and automatic link adaptationRX_QUAL reported by the MS and the BTS indicates the quality of the sent frame, not the performance of the user data. The threshold for power control represents the predicted border of the acceptable user data performance for the speech or 9.6/12.0 kbit/s data. This is not adequate for the 14.4/14.5 kbit/s user data because 14.4/14.5 kbit/s channel coding can tolerate less errors. To maintain the 14.4/14.5 kbit/s per-formance adequate, the RX_QUAL needs to be kept higher and therefore the power increase must be started at a higher quality for 14.4/14.5 kbit/s calls than for other calls.The threshold parameter pc lower thresholds qual144 Rx level (LQR), Px (LQP), Nx (LQN) has been defined for triggering downlink and uplink power increase for 14.4/14.5 kbit/s connection. Its value should be set to higher quality than the ordinary power increase lower thresholds. The parameter power limit ALA (ALIM) determines the MS and BTS power levels where the channel coding is changed between 14.5 kbit/s and 12 kbit/s in the NT service. The power level is identified as an attenuation from the maximum allowed power of the MS/BTS. BTS power control is taken into account only if it is enabled. ALA is possible when ALA enabled (AENA) parameter enables ALA in the cell the connection uses either 14.5 kbit/s or 12.0 kbit/s channel coding 14.5 kbit/s and 12.0 kbit/s channel codings are both allowed for the connection

24 DN9813893




the A interface circuit pool used supports 14.5 kbit/s channel coding.For the MS, the power limit for ALA is defined asMS_ALA_PWR_LIMIT = MsTxPwrMax - ALIMThe BTS power control range is defined by the following parameters, BS TX pwr max (PMAX1) and BS TX pwr min (PMIN). The BTS power limit for ALA is defined asBTS_ALA_PWR_LIMIT = PMAX - ALIMWhen pc lower thresholds qual144 Rx level (LQR), Px (LQP), Nx (LQN) triggers, if either the BTS or the MS power value is higher than the power limit, channel

coding is changed to 12.0 kbit/s. After that, RX_QUAL is not monitored to pc lower thresholds qual144 Rx level (LQR), Px (LQP), Nx (LQN).

if BTS and MS power values are below their ALA limit powers, the power of the triggered link is increased.

When pc upper thresholds qual dl Rx qual (UDR), Px (UDP), Nx (UDN) or pc upper thresholds qual ul Rx qual (UUR), Px (UUP), Nx (UUN) triggers, the triggered link power is decreased if channel coding is 12.0 kbit/s and both BTS and MS power values are both

below their ALA power limits, channel coding is changed to 14.5 kbit/s.The parameter min int between ALA (AMIN) defines an interval that must be between two consecutive ALA procedures. The interval is, however, neglected if the power has been increased to its maximum value. If ALA from 14.5 kbit/s to 12.0 kbit/s is not made due to timer parameter, the triggered link power is increased.The parameter ALA enabled (AENA) is used to switch automatic link adaption function on and off cell by cell.14.4/14.5 kbit/s connection power control and automatic link adaptation parameters can be handled by the Power Control Parameter Handling MML commands.

Handover signallingThe handover is simultaneous for all radio interface time slots. All handover types: internal intra-cell, internal inter-cell and external handover are supported.

A separate channel activation for all the HSCSD channels is carried out before the selected channel configuration is forwarded to the mobile station in either the ASSIGN-MENT COMMAND (intra-cell handover) or the HANDOVER COMMAND. At handover completion, the BSC signals the new HSCSD configuration to the MSC.Channel coding and the number of channels may change during handover unless changes after the first allocation are denied in the request. 14.4/14.5 kbit/s is used when it is supported by the BSS. In transparent service, the total data rate may not change during the call. In the non-transparent service, the number of channels and channel coding may change during handover depending on the traffic situation in the target BTSs.For more information, see Handover Signalling in BSC.

Start of ciphering in HSCSDThe main signalling link controls the encryption procedure in order to start the ciphering. The encryption information for an additional HSCSD channel is forwarded to the corre-sponding FR TCH during initial channel activation or later in the MODE MODIFY

DN9813893 25




message. The change of the ciphering modes for separate channels within the HSCSD connection may not be perfectly synchronised.

HSCSD load controlBTS object parameters are used for HSCSD load control.With the parameter HSCSD TCH capacity minimum (HTM), a certain proportion of the cell capacity is offered for HSCSD use. In a low traffic load situation, the HSCSD calls can have more traffic channels (TCHs) than indicated by the parameter. Also, minimum HSCSD capacity may not be reached due to single slot traffic congestion.

In a highly loaded cell, it is possible to restrict the allocation of multislot configurations by the parameter HSCSD cell load upper limit (HCU). When the traffic load increases over the parameter value, each new HSCSD call is started with only one channel. Exceptions to this rule are:

minimum HSCSD capacity of the cell is not completely in use service request type is transparent.Resource upgrades are not made under multislot limitation time. As long as the cell load is greater than HSCSD cell load upper limit (HCU) value and the minimum HSCSD capacity is in use, the HSCSD capacity is reduced by downgrading one of the HSCSD connections for every incoming call.

Channels for transparent HSCSD request are not reserved if it leads to a multislot limi-tation situation.

In a state in which multislot allocation and HSCSD resource upgrades are allowed, the following takes place, depending on the situation:

if either the HSCSD load is more than HSCSD TCH capacity minimum (HTM) or the total cell load is more than UpperLimitCellLoadHSCSD, it causes no change in state

if the HSCSD load is more than HSCSD TCH capacity minimum (HTM) and the total cell load is more than HSCSD cell load upper limit (HCU) HSCSD resource upgrades and multislot allocations are denied and one resource down-grade is made for one of the HSCSD connections for every new channel allocation

In a state in which multislot allocation and resource upgrades are denied and downgrade for every new channel allocation is done, the following happens depending on the situ-ation:

if the HSCSD load is less than HSCSD TCH capacity minimum (HTM) or the total cell load is less than HSCSD cell load upper limit (HCU), multislot allocation and resource upgrade are still denied but HSCSD resource downgrade for every new allocation is stopped.

if the total cell load is less than HSCSD cell load lower limit (HCL) multislot allocation and resource upgrades are allowed.

Resource upgrades are denied in the Intelligent Underlay-Overlay (IUO) regular fre-quency area. The parameter HSCSD regular cell load upper limit (HRCU) determines the number of occupied TCHs in the IUO cell regular frequency area where single slot allocation is started. When the regular area load is under the threshold, mul-tislot allocations are possible. When the threshold is exceeded, multislot allocations are denied and one resource downgrade is made for one of the HSCSD connections for every new channel allocation.

26 DN9813893




In super-reuse frequencies, the HSCSD load is controlled with the parameters HSCSD TCH capacity minimum (HTM), HSCSD cell load upper limit (HCU) and HSCSD cell load lower limit (HCL) as in normal cells. The number of TCHs defined by the parameters is counted from the whole cell resources.

The parameter HSCSD upgrade guard time (HUT) determines a guard time between two consecutive resource upgrades. However, if the data rate can be increased significantly, the resource upgrade procedure can be made before the end of the guard time. The parameter HSCSD upgrade gain (HUG) determines the needed gain of the increased number of used channels before upgrade during guard time can be made. For example, an upgrade from two to three channels gives a 50% gain in data rate and upgrade from one to two gives a 100% gain.

The number of time slots to be released in the downgrade is defined by the parameter HSCSD minimum exhaust (HME).The parameter HSCSD downgrade guard time (HDT) determines a guard time between two consecutive resource downgrades. When the downgrade guard timer expires and the cell is totally congested, the downgrade is carried out if there is a call in any of the queues.

The HSCSD load control parameters can be handled by the Base Transceiver Station Handling MML commands.

DN9813893 27


HSCSD and 14.4 kbit/s Data Services effects on inter-face procedures


4 HSCSD and 14.4 kbit/s Data Services effects on interface procedures

4.1 HSCSD and 14.4 kbit/s Data Services effects on A interface proceduresEarly classmark sending procedureThe MS multislot class indication bit and MS multislot class (5 bits) indicate the DX MSC (MSC) the MS multislot capability with the MS Classmark 3 information element in the Classmark Update message. The Early Classmark Sending procedure must be used to allow HSCSD connections.

Assignment and external handover proceduresThe messages ASSIGNMENT REQUEST and HANDOVER REQUEST contain the mandatory information element Channel Type which defines the requested resources.

Figure 9 Channel type information element

With the Field Speech/data indicator, the MSC defines whether a speech or a data call is requested. In the case of a data call, Channel Rate and Type defines whether a single slot data or multislot data call is requested. When multislot data is requested, the maximum number of traffic channels and the possibility to change either the number of traffic channels or the used radio interface rate per channel after the first channel allo-cation are indicated. With the field Data Rate/Transparency Indicator the MSC defines whether a transparent or non-transparent service and which data rate is requested and what radio interface rates per channel are allowed to be used.

Figure 10 Coding of data rate/transparency indicator field

The field Rate in Data Rate/Transparency indicator shows

the radio interface data rate in a single slot non-transparent request the data rate in a single slot transparent request the required total radio interface data rate in a non-transparent multislot request the requested radio interface user rate in a transparent multislot request.The extension field Allowed Radio Interface Rate is optional and it indicates

other possible data rates allowed in a single slot non-transparent request

8 7 6 5 4 3 2 1

Element Identifier octet 1

Length octet 2

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Speech coding algorithm / octet 5Data Rate + Transparency ind

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ext spare octet 5aallowedr i/f rate

28 DN9813893




the allowed radio interface data rate per channel in a multislot request.The allowed radio interface rate extension field is not used in single slot transparent requests. If the extension is not included in the multislot request, the radio interface rate of 12.0/9.6 kbit/s is used.

In the external handover, the MSC informs the BSC of the MS multislot capability in the MS multislot class indication bit and the MS multislot class (5 bits) in the MS Classmark 3 information element in the HANDOVER REQUEST message.

The BSC informs the MSC of the selected radio interface rate per channel and the number of allocated traffic channels in a Chosen Channel information element which is included in the messages ASSIGNMENT COMPLETE and HANDOVER REQUEST ACKNOWLEDGE. The information element must always be used with multislot calls and with single slot calls when the BSC has chosen the used radio interface rate.

Messages HANDOVER REQUIRED and HANDOVER REQUEST can include the optional information element Current Channel. It indicates the used radio interface rate per channel and the number of allocated channels.

Both resource request messages include the Circuit Identity Code (CIC) of the A inter-face circuit, which the BSC can use to find out the transcoding properties. When there are several circuit pools defined on the A interface, the resource request acknowledge messages include an information element Circuit Pool, which indicates the circuit pool number that has been allocated for the connection.

When the BSC rejects the resource request because the pool implied by the CIC does not support any of the data functionalities indicated in the Channel Type, the cause value Circuit Pool Mismatch is returned to the MSC in the messages ASSIGNMENT FAILURE or HANDOVER FAILURE.

In both of these two cases, the Circuit Pool List information element will be included in the failure message. The Circuit Pool List presents the pools in the order of preference that the BSC wishes the A interface circuit to be allocated. The circuit pools are switched as seldom as possible and only existing A interface pools are represented in the list.

If Reversed Hunting is active in the BSC, the A interface circuit is allocated by the BSC. The changing of the circuit in the case that the initially selected circuit is not suitable is also handled by the BSC and thus the MSC is not involved.

ETSI specifications (see 3GPP TS 48.008: MSC-BSS Interface, Layer 3 Specification) define 50 circuit pools supporting different sets of speech and data codings.

The transcoder and submultiplexer TCSM2 supports six circuit types:

A FR speech version 1

FR speech version 2

FR data (14.5, 12, 6 kbit/s)

B HR speech version 1

C HR speech version 1

FR speech version 1

FR speech version 2

FR data (14.5, 12, 6 kbit/s)

DN9813893 29




D HR speech version 1

FR speech version 1

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FR data (14.5, 12, 6 kbit/s)

HSCSD max 2 * FR data (14.5, 12, 6 kbit/s)

E HR speech version 1

FR speech version 1

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FR data (14.5, 12, 6 kbit/s)

HSCSD max 4 * FR data (14.5, 12, 6 kbit/s).

F HR speech version 3 (AMR)

FR speech version 3 (AMR)

The transcoder and submultiplexer TCSM3i/Combi supports three circuit types:

G FR speech version 1

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FR speech version 5 (AMR-WB)

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FR data (14.5, 12, 6, 3.5 kbit/s)

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FR data (14.5, 12, 6, 3.5 kbit/s)


The BSC supports the following A interface circuit pools (for more information on circuit pools, see 3GPP TS 48.008: MSC-BSS Interface, Layer 3 Specification):

1 FR speech version 1

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DN9813893 31






FR data (14.5, 12, 6, 3.6 kbit/s)

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FR speech version 2

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FR data (14.5, 12, 6, 3.6 kbit/s)

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FR data (14.5, 12, 6, 3.6 kbit/s)

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HR data (6, 3.6 kbit/s)


EDGE max 2 x FR data (29.0 kbit/s)

EDGE FR data (43.5 kbit/s)


BSC internal handover and configuration change proceduresAfter the BSC internal handover or configuration change procedure, the BSC informs the MSC of the new radio interface rate per channel and the number of allocated traffic channels. This is included in the Chosen Channel information element in a HANDOVER PERFORMED message.

4.2 HSCSD and 14.4 kbit/s Data Services effects on the Abis interface proceduresChannel activation procedureThe Channel Activation Procedure can be used for channel activations in the call setup or handover phases and for the Resource Upgrade Procedure during an HSCSD con-nection to add new full rate traffic channels to an HSCSD configuration. A separate channel activation is performed for each subchannel in the HSCSD configuration.

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For the main HSCSD channel, activation types for intra-cell and inter-cell channel change are used (activation for assignment, activation for synchronous handover or activation for asynchronous handover) depending on the reason why the main channel is activated. Additional HSCSD channels are activated as related to multislot configura-tion.

A Channel Mode defines the characteristics of the activated channel. A full rate TCH channel Bm is used in the field Channel Rate and Type for single slot full rate data call. The Channel Rate and Type for an HSCSD channel is either

full rate TCH channel bi-directional Bm multislot configuration or full rate TCH channel uni-directional downlink Bm, Multislot configuration.In Data Rate + Transparency indicator, there is a radio interface data rate 14.5 kbit/s for non-transparent full rate data channels and a data rate 14.4 kbit/s for transparent full rate data channels.

Mode modify procedureThe Mode Modify Procedure can be used during a data call to

change the radio interface data rate change the uni/bi-directionality of an HSCSD channel start ciphering in an additional HSCSD channel or change the channel to speech mode.Full rate speech channels can be changed into data mode with the Mode Modify Proce-dure.

The Channel mode determines the new characteristics of the channel. Encryption infor-mation is a new optional information element in the MODE MODIFY message and it is included in the message if the ciphering key is to be applied.

4.3 HSCSD and 14.4 kbit/s Data Services effects on Radio interface proceduresEarly classmark sending procedureThe MS multislot class indication bit and the MS multislot class (5 bits) are used by the MS to indicate to the MS multislot capability to the network. The fields are part of the Mobile Station Classmark 3 information element in the CLASSMARK CHANGE message. The Early Classmark Sending procedure must be used for allowing HSCSD connections.

Assignment and handover proceduresThe ASSIGNMENT COMMAND and HANDOVER COMMAND messages indicate the MS the initial call type and channel configuration. In the radio interface, there is a data channel mode for 14.5 kbit/s radio interface rate.

The HSCSD multislot configuration can be indicated to the MS either in the Channel Description 2 or Multislot allocation information element. The former is used instead of the Channel Description information element and it has exactly the same format. The use of the Channel description 2 IE is possible when

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the symmetry of all the additional HSCSD channels is equal, that is, all the additional HSCSD channels are uni-directional or all the additional HSCSD channels are bi-directional.

channels are allocated from the consecutive time slots the position of the HSCSD main channel is correct. If there is one additional HSCSD

channel, the main channel is in the greater time slot position. If there are two or more additional channels, the main channel is in the second greatest time slot number.

The Multislot allocation IE is used when it is impossible to use the Channel Description 2. The use of the multislot Allocation IE is indicated in the Channel Description IE field Channel Type and TDMA Offset. The Multislot Allocation IE defines a bit map of addi-tional channels of multislot configuration in uplink and downlink directions. If the uplink bit map is not included in the element, the time slots indicated by the downlink bit map are allocated in both downlink and uplink directions.

Configuration change proceduresThree messages are related to HSCSD in the Configuration Change Procedure:

The CONFIGURATION CHANGE COMMAND is sent on the main Dedicated Control Channel (DCCH) from the network to the MS to change the channel config-uration of a multislot configuration

The CONFIGURATION CHANGE ACKNOWLEDGE message is sent on the main DCCH from the MS to the network to indicate that the MS has changed to the ordered channel configuration successfully

The CONFIGURATION CHANGE REJECT message is sent on the main DCCH from the MS to the network to indicate that the MS has not managed to switch to the channel configuration ordered by the CONFIGURATION CHANGE COMMAND and is still using the previous configuration

Configuration Change Procedure can be used to

add new channels to the HSCSD configuration remove channels from the HSCSD configuration or change the radio interface rates for all the channels in the HSCSD configuration.Channel mode modify procedureA Channel Mode Modify Procedure is used when changing the channel mode between speech and data or when changing the radio interface data rate of the data channel. In the Nokia Siemens Networks BSC implementation, Channel Mode Modify is used only when changing the mode for a channel in a single slot connection or for an HSCSD main channel as the only channel in the HSCSD configuration. The change between speech and data is not made for channels in a multislot configuration. The changing of the radio interface data rate for channels in a multislot configuration is made with the Configura-tion change procedure.

DN9813893 35


Schemes in HSCSD and 14.4 kbit/s Data Services

Id:0900d80580590c8dConfidential

5 Schemes in HSCSD and 14.4 kbit/s Data ServicesThe following schemes are described below:

Assignment in HSCSD and 14.4 kbit/s Data Services HSCSD FACCH call setup Subsequent assignment in HSCSD and 14.4 kbit/s Data Services Configuration changes, basic schemes BSC internal handover External handover HSCSD and 14.4 kbit/s Data Service request checks Interoperability of HSCSD procedures Channel allocation Resource upgrade Resource downgrade Switching of HSCSD connection Power control

36 DN9813893




Assignment in HSCSD and 14.4 kbit/s Data Services

Figure 11 Mobile-originated call setup, basic scheme

MS BTS BSC MSC

**** NORMAL SIGNALLING ****

1 2

**** NORMAL SIGNALLING ****

3

4

5

10

11

12

13

14

16

17

**** CONVERSATION PHASE ****

**** RELEASE OF A CALL ****

18

19

20

Classmark_ChangeClassmark_Update

Setup

Call_Proceeding

Assignment_Request

Physical_Context_Request

Physical_Context_Confirm

Channel_Activation

Channel_Activation

Channel_Activation_ack

Channel_Activation_ack

Assignment_Command

SABM

Establish_Indication

UA

Assignment_Complete

Assignment_Complete

Clear_Command

Channel_Release

Clear_Complete

15

6

8

9

7

DN9813893 37




Figure 12 Mobile-originated call setup, basic scheme

Mobile-originated call setup, basic scheme:1. The MS sends its multislot capability information to the network

using the early classmark sending procedure. The CLASSMARK CHANGE message includes the Mobile Station Classmark 3 IE defining the MS multislot capabilities.

3. The MS and the MSC negotiate the characteristics of the HSCSD call.

5. The MSC requests data connection. The Channel Type IE specifies the characteristics for the connection (see HSCSD and 14.4 kbit/s Data Services effects on A interface procedures).The BSC checks the correctness of the request, the applicability of the A interface circuit pool and the BSS capability to serve the request as defined in HSCSD and 14.4 kbit/s data service request checks.The BSC allocates the channels (see Channel allocation) and determines the HSCSD main channel and the uni/bi-directionality of each allocated channel (HSCSD configuration), taking into account the MS multislot capability.

9. A separate channel activation is applied for each HSCSD channel. The CHANNEL ACTIVATION message includes IEs Channel mode and Activation Type, which determine the characteristics of the acti-vated channel (see HSCSD and 14.4 kbit/s Data Services effects on the Abis interface procedures).

12. The BSC sends the ASSIGNMENT COMMAND on the main HSCSD channel to the MS establishing the data call. Channel Description 2 IE and the Channel Mode IE determine a single slot 14.4/14.5 kbit/s data call. HSCSD multislot configuration is deter-mined by either the Channel Description 2 IE or Multislot Allocation IE as defined in HSCSD and 14.4 kbit/s Data Services effects on Radio interface procedures and the selected channel coding is indi-cated in Channel Mode IE.

14. The BSC switches separate Abis PCM TSLs to consecutive A inter-face PCM TSLs as defined in Switching of HSCSD connection.

MS BTS BSC MSC

21

22

23

24

27

28

DISC

UA

Release_Indication

RF_Channel_Release

RF_Channel_Release

RF_Channel_Release_Ack


Deactivate_SACCH

25

26

38 DN9813893




17. The BSC informs the MSC about the number of allocated channels and the chosen channel coding with the Chosen Channel IE (see HSCSD and 14.4 kbit/s Data Services effects on A interface proce-dures).The circuit pool of the A interface circuit implied by the CIC of the ASSIGNMENT REQUEST is sent to the MSC in the Circuit Pool IE if there exists more than one pool on the A interface.

19. CHANNEL RELEASE is sent only on the main HSCSD channel.21. DEACTIVATE SACCH is sent only on the main HSCSD channel.24. RELEASE INDICATION is sent only on the main HSCSD channel.26. Separate RF CHANNEL RELEASE messages are sent for each

HSCSD channel. Mobile-terminated call setup:

From the BSC viewpoint, the mobile-terminated HSCSD call setup case does not differ from the mobile-originated case. At the call setup the MS and the MSC nego-tiate the characteristics of the HSCSD call with messages SETUP and CALL CON-FIRMED. From the ASSIGMENT REQUEST onwards, the signalling is as in the mobile-originated case.

Abnormal cases in call setupIf the BSC finds the ASSIGNMENT REQUEST incorrect or the BSS is unable to serve the request as defined in HSCSD and 14.4 kbit/s data service request checks, the BSC sends an ASSIGNMENT FAILURE message to the MSC.If any of the CHANNEL ACTIVATION messages to the BTS fails, the whole HSCSD call setup is terminated. All successfully activated channels are released and the ASSIGNMENT FAILURE message is sent to the MSC.If the MS rejects the ASSIGNMENT COMMAND, all the channels are released from the BTS and the ASSIGNMENT FAILURE message is sent to the MSC.

HSCSD FACCH call setupAn HSCSD FACCH call setup is possible for non-transparent connections and transpar-ent connections needing only one channel. Otherwise the BSC rejects the ASSIGN-MENT REQUEST for the HSCSD FACCH call setup with the cause 'Invalid Message Contents'. Checkings in FACCH setup for HSCSD and 14.4 kbit/s connections are described in Checking the HSCSD and 14.4 kbit/s data service requests.

The HSCSD non-transparent connection established with the FACCH call setup is started with one channel. The BSC counts the number of channels needed and resource upgrade is possible after the assignment has been completed.

Subsequent assignment in HSCSD and 14.4 kbit/s Data ServicesSubsequent assignment for HSCSD data connections can be carried out when the user-defined maximum number of channels or required data rate is changed. However, sub-sequent assignment from high speed to multi-slot data is not supported. The BSC rejects such requests by sending an ASSIGNMENT FAILURE message to the MSC.

Checkings in the subsequent assignment are for HSCSD and 14.4/14.5 kbit/s connec-tions are described in HSCSD and 14.4 kbit/s data service request checks.

User-initiated service level upgrade or downgradeThe MSC sends an ASSIGNMENT REQUEST in which HSCSD parameters have been changed by the maximum number of channels or the air interface user rate. The BSC recounts the number of needed channels using the current channel coding. If there are more channels currently allocated than indicated by the new

DN9813893 39




maximum number of channels, the resource downgrade procedure is used to release the extra channels before sending the ASSIGNMENT COMPLETE message. If the new parameters allow the use of more channels than currently allo-cated, the ASSIGNMENT COMPLETE is sent first and the resource upgrade can be done later as a separate procedure.

Abnormal casesIf mode modification towards the BTS fails, the current mode is kept. The BSC sends an ASSIGNMENT FAILURE message to the MSC with a cause 'requested transcod-ing/rate adaption unavailable'.If mode modification towards the MS fails, the BSC sends an ASSIGNMENT FAILURE message to the MSC with the cause 'requested transcoding/rate adaption unavailable'.If resource downgrade fails in a user-initiated service level downgrade, the current configuration is maintained. The BSC sends an ASSIGNMENT FAILURE message to the MSC with a cause 'requested transcoding/rate adaption unavailable'.

Configuration changes, basic schemes

Resource downgradeThe BSC initiates the downgrade procedure (see Functionality of HSCSD and 14.4 kbit/s Data Services in BSC, HSCSD load control and Resource downgrade) and defines the new configuration for the HSCSD connection. Multiple channels may be released from the configuration during the same procedure. In this example, the HSCSD configuration is downgraded from 3+1 to 2+2 configuration. A mode modify procedure is needed when the uni/bi-directionality of a remaining channel is changed. The network has to use bi-directional channels whenever it is allowed by the MS multislot capability.

Figure 13 Resource downgrade from 3+1 to 2+2 HSCSD configuration, basic scheme

Resource downgrade from 3+1 to 2+2 HSCSD configuration, basic scheme1. A remaining uni-directional subchannel is changed to bi-directional.

**** HSCSD 3+1 connection ongoing ***

**** Resource downgrade decision ***

1

4

7

MS BTS BSC MSC

Mode_Modify

Mode_Modify_Ack

Configuration_Change_Command

Configuration_Change_Ack

Handover_Performed

RF_Channel_Release


2

3

5

6

40 DN9813893




3. The BSC informs the MS of the new HSCSD configuration in the Multislot Allocation IE.The BSC switches the new configuration to the A interface as described in Switching of HSCSD connection.

5. The MSC is informed of the new number of channels and the used channel coding in the Chosen Channel IE.

6. The downgraded channel is released. Resource upgrade

The BSC initiates the upgrade (see Functionality of HSCSD and 14.4 kbit/s Data Services in BSC, HSCSD load control and Resource Upgrade) and defines the new configuration for the HSCSD connection. Multiple channels may be added to the configuration during the same procedure. In this example HSCSD configuration is upgraded from 2+2 to 3+1 configuration. The mode modify procedure is needed when the uni/bi-directionality of a remaining channel is changed. Uni-directional channels are used to achieve higher total data rates with type 1 HSCSD MSS.

Figure 14 Resource upgrade from 2+2 to 3+1 HSCSD configuration, basic scheme

Resource upgrade from 2+2 to 3+1 HSCSD configuration, basic scheme1. The new upgraded uni-directional channel is activated.3. The previously allocated bi-directional channel is changed to a uni-

directional one.5. The Multislot Allocation IE indicates the new HSCSD configuration

to the MS.The BSC switches the new configuration to the A interface as described in Switching of HSCSD connection.

7. The new number of channels and the used channel coding are indi-cated to the MSC in the Chosen Channel IE.

Automatic Link Adaptation (ALA)The BSC initiates the ALA procedure by the signal quality, BTS power and MS power as defined in 14.4/14.5 kbit/s connection power control and automatic link adaptation. The new channel coding is forwarded to the BSC, which may add a

**** HSCSD 2+2 connection ongoing ***

**** Resource upgrade decision ***

1

6

MS BTS BSC MSC

2

5

7

3

4

Channel_Activation

Channel_Activation_Ack



Handover_Performed

Mode_Modify

Mode_Modify_Ack

DN9813893 41




resource upgrade or downgrade procedure to be carried out during the same signal-ling. The BSC defines the new configuration for the HSCSD connection. Channel coding is changed to all channels belonging to the HSCSD connection. In this example, the required air interface user rate is 29.0/36.0 kbit/s. The HSCSD connec-tion is started with 14.5 kbit/s channel coding using 2+2 configuration. Channel coding is changed to 12.0 kbit/s in ALA and the BSC changes the HSCSD configu-ration to 3+1.When the channel coding is changed for a single slot non-transparent (NT) connec-tion, a CHANNEL MODE MODIFY message is used instead of a CONFIGURATION CHANGE COMMAND message to command the MS.

Figure 15 Resource upgrade from 2+2 to 3+1 HSCSD configuration, basic scheme

Resource upgrade from 2+2 to 3+1 HSCSD configuration, basic scheme1. The new upgraded uni-directional channel is activated. 12.0 kbit/s

rate in channel mode is used.3. The previously allocated bi-directional channel is changed to uni-

directional using the rate of 12.0 kbit/s in channel mode.5. The rate of 12.0 kbit/s in channel mode is changed for the HSCSD

main channel too.7. The Multislot Allocation IE indicates the new HSCSD configuration

to the MS. The 12.0 kbit/s channel mode is used.The BSC switches the new configuration to the A interface as described in Switching of HSCSD connection.

9. The new number of channels and the used channel coding are indi-cated to the MSC in the Chosen Channel IE.

1

8

MS BTS BSC MSC

2

7

9

3

4

**** HSCSD 2+2 connection using ******* 14.5 channel coding ongoing ***

**** ALA decision to 12.0 kbit/s ******* RNDSEB decides to upgrade ***

5

6

Channel_Activation

Channel_Actication_Ack

Mode_Modify

Mode_Modify_Ack

Mode_Modify

Mode_Modify_Ack



Handover_Performed

42 DN9813893




Abnormal CasesIf channel activation or mode modification for any of the commanded subchannels or configuration change command to the MS is rejected, the old configuration is returned. New channels are released and mode modification is redone for the channels that were modified. In the case of timer expiry, the HSCSD call is cleared.If the MS sends a CONFIGURATION CHANGE REJECT message with a cause 'channel mode unacceptable', the BSC prevents further configuration changes for the connection and if the automatic link adaptation (ALA) was a part of the configu-ration change procedure, it prevents further ALA procedures for the connection.If the switching of the new configuration fails, the BSC sends a CLEAR REQUEST message to the MSC.

BSC internal handoverThere are no HSCSD-specific differences in BSC internal, intra-cell or inter-cell han-dovers. The following signalling example describes a BSC internal, inter-cell handover. The source cell non-transparent HSCSD configuration is 2+2 using 14.5 kbit/s channel coding. In the target cell 3+1 non-transparent HSCSD configuration is allocated using the 12.0 kbit/s channel coding.

DN9813893 43




Figure 16 BSC internal inter-cell handover, basic scheme

BSC i

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