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Introduction to [ S G S N ]
Internal Presentation for the NSS Group,
Prepared by D. Tsoukalas
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What is GPRS? 1/3
GPRS enables the access to standard data networks
(internet, intranet, etc.) via GSM using IP-packet-
based communication (Packet switching). GPRS
uses the existing GSM radio network(BSS), withenhancements, but requires a new core network to
carry the packet based data traffic and to offer
access to external data networks. The traditional
circuit network still remains and offers primarily voice
services and, in addition, circuit switched data
services (HSCSD)
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What is GPRS? 2/3
SGSN is one of the essential elements required to
implement the GPRS in a GSM network. Along with
the Gateway GPRS Support Node (GGSN). SGSN is
needed for new services based on packed switchedconnections. GPRS brings fast data access
combined with the benefit of being continuously
connected always on
Circuit switched connections continue to be routed
via MSC, While packet switched connections will be
made via SGSN.
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What is GPRS? 3/3 General Packet Radio Service (GPRS) Enhancement to the existing digital GSM voice-based network
Is a mobile telephony network system that will allow faster data
transfer speed, theoretically up to 172 kb/s for a single user, (but
many simultaneous users will decrease the speed).
Conveys data across the mobile network using IP-based packet
switching
Always on - more efficient utilisation of network resources
This new technology makes it possible for users to make
telephone calls and transmit data at the same time.
Higher data rates (up to 40kb/s initially) than existing GSM
circuit switched technology (9.6kb/s)
Stepping stone to high bandwidth third-generation mobile
networks (3G-UMTS)
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GPRS Key Points
GPRS uses a packet-based technique which willenhance GSM data services significantly, especially
for bursty Internet / Intranet traffic.
Using a packet data service, subscribers are always
connected and always on-line so services will beeasy and quick to access.
The evolution path towards 3G is taken in different
steps: GSM, HSCSD, GPRS, EDGE, UMTS.
Some applications examples: web-browsing
e-banking
e-commerce
lottery
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Main features of GPRSBefore introduction of GPRS, the radio capacity was used forcalls and data transmission within the GSM network in a rather
inefficient way.
For data transmission the entire channel was occupied and was
thus insufficiently used.
With the GPRS technology, the channel is used more efficiently
owing to the possibility of more than one user sharing the same
channel. GPRS telephones uses several channels for data
transfer thus facilitating greater transfer speeds.
The GPRS infrastructure and mobile phones support a datatransmission speed of up to 13.4Kbits per channel.
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Overview of GPRS
The existing GSM networks are based on circuit switching
(CS)techniques. However, for present-day services, based on
Internet Protocol (IP) applications like e-mail and web browsing,
GSM circuit switching is inefficient for data transmission.
GSMs Release 97 has introduced the General Packet Radio
Services (GPRS) which maintains the GSM Base Station
Subsystem (BSS) access technologies but provides packet
switched (PS)data services to the mobile station (MS).
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Circuit Switched (CS)
Connections
Standard GSM uses Circuit Switched (CS)connections. Each
time a connection is required between two points, a link
between the two points, is established and the network
resources are reserved and dedicated for the use of that single
call (a subscriber) for the entire duration of the call.
Circuit switched connections have relatively low delay in the
network and have traditionally been used in fixed and mobilenetworks for speech and data.
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Packet Switched Connections (PS)
Data networks, such as the Internet, Frame Relay and X.25 etc.
use Packet Switched connections. With packet switching, the
data is divided up to into packets,each packet having an
identifier or address which is used by routers in the network to
pass the packet to its intended destination where they are re-assembled.GPRS brings packet switching techniques to GSM
networks.
Bandwidth in a packet switched network in not reserved
continuously as is the case with circuit switching. Instead,
network bandwidth is allocated when required and released
when not needed.
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GPRS MS Classes
Class B Monitors control
channels for GPRS and
other GSM services
simultaneously, but canonly operate one set of
services at one time.
simultaneous
attach
activation
monitor
no simultaneous traffic
Class A Operates GPRS and
other GSM services
simultaneously.
simultaneous attach
activation
monitor
invocation
traffic of GSM and GPRS
Class C Exclusively operates
GPRSservices
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GPRS MS
Owing to the fact that more than one channel is used
for downlink, the GPRS mobile phones make
possible greater data transmission speeds. There are
several types of phones with regard to the number ofchannels they use for data transmission...
Type 2+1two downlink channels and one uplink
data transmission channel
Type 3+1three downlink channels and one uplink
data transmission channel
Type 4+1four downlink channels and one uplink
data transmission channel
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MS Data Transmission Speeds
The supported data transmission speed
per channel is 13.4Kbits. Depending on
the type of phone, the following datatransmission speeds are theoretically
possible... Type 2+1: Receive 26.8Kbits and send 13.4Kbits.
Type 3+1: Receive 40.2Kbits and send 13.4Kbits.
Type 4+1: Receive 53.6Kbits and send 13.4Kbits.
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Mobility and Session
Management Mobility Management handles the subscriber when he is requesting
access to the GPRS network or when he wants to stop using the GPRS
network. Mobility Management transfers the necessary information
from another SGSN when the subscriber moves from one routing area
to another.
GPRS ATTACH / DETACH
LOCATION UPDATES
Session Management handles the establishment and release of
connections to the IP network outside the GPRS network. When thesubscriber changes a routing area, Session Management handles the
re-establishment of these connections in the new SGSN.
PDP CONTEXT ACTIVATION / DEACTIVATION
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Mobility Management StatesThe tracking of the location of an MS depends on the mobility management state.GPRS has three mobility management states.
The three MM states are: IDLE, READY, STANDBY
Each state describes a certain level of functionality and information allocated.
The change between the states happens upon activity or when a timer expires.
IDLE (not GPRS attached, e.g.
MS is switched off)
(no valid MM context)
MS:
not reachable
PLMN selection
cell selection
READY (active phase)
SGSN:
RAand CI
MS:
receive/transmit PDPs
PLMN selection
cell selection
(de-)activation of PDP
contexts
STANDBY (ended act. Phase)
logical link between
MS and SGSN
SGSN:
RA
PtP paging
MS:
cell selection
RA Update
(de-)activation of PDP
contextsGPRS Attach READYtimer expired
or force to STANDBY
STANDBYtimer expired
GPRS Detach PDU transmission (traffic)
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Mobility Management When the subscriber wants to start using the GPRS service, the MS performs a GPRS
attach procedure. Similarly when the GPRS service is not used anymore, the MS sends an
indication of a GPRS detach to the network.
The MS can be in either idle, standby or ready state. State transitions are caused bysubscriber activity (e.g. attach), timer expiry and initiation of data transfer. The timer values
are controlled by the network and signalled to the MS during the GPRS attach, because the
MS and the SGSN must have same timer values in use.
When the ready timer expires, the MS moves to the standby state. Similarly, when the MS
reachable timer expires, the MS moves to the idle state. Timer values can be changed with
the SGSN Parameter Handling. It is also possible to prevent usage of timers totally so that
they never expire. When the MS is in idle state, the network has no knowledge about its location and the
SGSN does not maintain a MM context for the MS. A GPRS attach takes the MS from the
idle state to the ready state.
During the standby state, the SGSN tracks the location of the subscribers with the accuracy
of a routing area (RA). The MS initiates an RA update (RAU) when it moves to a new routing
area. The MS gets the routing area identifiers (RAI) from the BSS. The Nokia SGSN
supports combined GPRS/IMSI attach and detach, as well as combined routing area andlocation area updates.
Paging procedure is used to obtain the-cell specific location of the MS. When the MS enters
the ready state, that is, starts signalling or transmitting data, the subscriber location is
tracked in the accuracy of a cell. Cell update takes place with any uplink packet.
Both the MS and the SGSN may initiate a GPRS detach. The network initiates a GPRS
detach due to a command from the HLR or an SGSN failure. During a GPRS detach, GMM
control initiates deactivation of all active PDP contexts for the MS.
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GPRS Architecture
Serving GPRS Support Node (SGSN)
function comparable to VMSC)*
Gateway GPRS Support Node (GGSN)
function comparable to GMSC*
*VMSC Visited MSC/VLR
*GMSC Gateway MSC/VLR
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Overview of the GPRS network
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GPRS InterfacesETSI Standards define several interfaces for the GPRS
network. SGSN has to support interfaces Gb, Gn, Gp, Gd,
Gr and Gf. In addition, Gs is specified as optional in
standards. The Ga interface is needed to carry charging
information (not shown).
Gbinterface transfers user data to and from the BSS (FR).
Gn interface supports user data transmission between
SGSN and the backbone (GGSN) (GTP).
Gpis exactly the same as Gn.
Gd interface between SGSN and the gateway MSC
supports SMS delivery via GPRS.
Gr interface for mobility management functions.
Subscription information is retrieved from the HLR via Gr
(MAP).
Gf interface is similar to the Gr but it is used for terminal
authentication instead (IMEI check) (MAP).
Gs interface links the mobility management of the SGSN
to the equivalent mobility management of the MSC/VLR.Gs enables a combined GPRS and IMSI attach. In
addition, Gs makes possible to page terminals for circuit
switched service via GPRS (BSSAP+).
Gainterface connects the SGSN to the charging gateway
and carries the CDRs generated by the SGSN to the CG
to be further delivered to the operator's billing system.
GiGGSN to external data networks
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SGSN and GGSN
Serving GPRS Support
Node (SGSN)The SGSN is the core GPRS unit, equivalent
to the MSC in a standard GSM network. It
handles e.g. call routing, mobilitymanagement and charging functions, and
acts as the gateway between the GPRS
network and the BSS. Converts protocols used in the IP
backbone (GGSN etc.) to protocols used
in the BSS and the MS
Takes care of authentication and MobilityManagement (Location Update, paging
etc.)
Routes data to the relevant GGSN when
connection to an external network is
required
Collects charging data and traffic
statistics
Gateway GPRS Support
Node (GGSN)The GGSN acts as a Domain Name System,
Border Gateway and a Firewall, including
Network Access Translation (NAT). Eachof the functions can also be disabled or
run in a separate device when required.
Acts as an interface between GPRS
network and external data network. (From
the external point of view, the GGSN is
simply a router to a sub-network)
Collects charging data and trafficstatistics
can allocate IP-addresses for users
routes packets coming from external
networks towards SGSN and vice versa
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Core Network Subsystem-CNS
MSC/VLRThe MSC/VLR is not involved in GPRS
data transfer, but supports signalling
for class A,B mobiles as well as
SMS delivery.
To allow support for terminals that are
attached to both GSM and GPRS
services (A and B type) Nokia has
implemented the Gs interface
between the MSC/VLR and the
SGSN (supporting paging andcombined procedures for class Aand B mobiles).
HLR & EIRAs for circuit switched services,
subscriber information for GPRS is
stored in HLR. The HLR supports
procedures such as GPRS
attach/detach and authentication.
Nokia has implemented interfaces
between the HLR and the SGSN
(Gr) and EIR and SGSN (Gr).
The interface implementation is MAP
ver.3
For SMS support, one new parameter
per subscriber has been added in
the HLR to indicate whether MT
SMS should be delivered via the
MSC or the SGSN.
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Serving GPRS Support Node
(SGSN) functions:The SGSN is placed on the same hierarchical level as the VMSC. A VMSC/VLR holds
information for authentication and authorisation, the present location of the subscriber etc.
Many VMSC functions have also to be taken care by the SGSN:
The supply area of a SGSN is composed of location areas / routing areas. Using the Mobility
Management Functions, the SGSN keeps track of the GPRS MS, as long as the GPRS
mobile selects cells under administration of the SGSN. If there is a MTC, paging will activated by the SGSN (Gs).
The SGSN is responsible for access control, which comprises authentication and
authorisation procedures.
If there has been a connection established between the GPRS MS and the GPRS network,
the SGSN is responsible to keep up a logical connection even if there is no data
transmission (no physical connection). By doing so GPRS can both react on bursty
transmission and dynamically allocate radio resources to circuit and packet switchedapplications.
It realises the interface to the BSS (Gb), to the GGSNs and SGSNs (Gn), and to other
GPRS PLMNs (Gp). Hereby both signalling and user data can be transmitted. The
interfaces Gr, Gs, and Gf to the MSC/VLR, HLR, and EIR are used sorely for signalling
information.
A hit t
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Functional units of the Nokia
SGSNThe most important functional units of the Nokia
SGSN are:
Packet Processing Unit (PAPU)
Signalling and Mobility Management Unit
(SMMU)
Marker and Charging Unit (MCHU)
Operation and Maintenance Unit (OMU)
The high-speed Message Bus (MB)
interconnecting computer units
Group Switch (GSW) for semipermanent
connections within the system
Exchange Terminals (ET) for transmissionand signalling connections
Clock and Synchronisation Units (CLS)
Architecture
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SGSN cabinet
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HardwareConfiguration
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DX 200 system architecture and SGSN block diagram
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Redundancy principlesIn the Nokia SGSN design, great attention is paid to reliability. The following redundancy methods are
applied:
Either 2Nredundancy principle with one active unit and a hot standby unit (all duplicated units), or
N+1redundancy principle with one unit, active or in reserve, in addition to what is required by dimensioning.
All parts of the system have an appropriate type of redundancy:
SMMUandPAPU
SMMU and PAPU have N+1 redundancy, that is, one extra SMMU/PAPU unit which is only used if
one of the active units fails.
MCHU, OMU, MB, GSWand CLS
The units are all hot standby (2N) redundant. In addition, MCHU and OMU have mirrored pairs of
disks.
ET The units are not critical, because failure of a single unit does not prevent the service. Each interface
must always be supported by at least two ETs backing up each other. Thus, the ET units are not
redundant as such, within the system itself.
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Signalling and mobility
management unit (SMMU) SMMU's main purpose is to support subscriber mobility management
functionality. For that it uses several SS7-based interfaces: Gr, Gd, Gs
and Gf that connect the SGSN to various NSS network elements.
SMMU supports the MTP, SCCP, TCAP, BSSAP+ and MAP protocols
that are used on those interfaces. The protocol stack for Gr, Gd and Gfis the same, whereas the stack for Gs differs slightly from that.
For handling mobility management, SMMU has a database for visiting
GPRS subscribers. The database can store up to 30.000 subscribers
simultaneously. Subscribed PDP contexts are also stored in a database
in SMMU. The database supports 150.000 subscriptions. Thus each
subscriber may have on average 5 subscribed PDP contexts. A
subscriber can have up to 50 PDP context subscriptions. Up to 2500
APNs can be configured in each SMMU to be used by PDP contexts.
The SGSN supports up to 10.000 APNs.
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Packet processing unit (PAPU)The main purpose of PAPU is to process the user data to/from the BSS and relay it from/to the
GPRS backbone network. For that, PAPU maintains the active PDP contexts for up to 7500
subscribers, i.e. at maximum 15.000 PDP contexts. In order to carry the user data between
the BSS (Gb) and the Backbone (Gn), PAPU needs to support a large set of protocols,
including:
Frame Relay (FR)
Network Service (NS)
Base Station Subsystem GPRS Protocol (BSSGP) Logical Link Control (LLC)
Subnetwork Dependent Convergence Protocol (SNDCP)
GPRS Tunnelling Protocol (GTP)
User Datagram Protocol (UDP)
Internet Protocol (IP)
Ethernet
GPRS mobility management and session management use the services provided by the LLC layer.
In a sense, they make up a protocol layer of their own. In addition to GMM and SM, also SMS
functionality uses the LLC layer to carry short messages to and from the subscriber.
GMM and SM entities are used by PAPU to handle location and session management control tasks
towards the MS and other GSNs. One PAPU unit handles up to 3 Mbps of user data traffic,
downlink and uplink combined.
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Marker and charging unit
(MCHU) The main purpose of MCHU is to produce accurate charging
information and send it to the charging gateway. In addition,
MCHU collects and stores statistical data about the whole
system. The unit also works as a subscriber database distributorfor SMMU units and performs PTMSI allocation.
The marker functionality maintains the semipermanent
connections through the group switch. These connections are
used internally to connect signalling terminals and frame relay
bearer channels to external PCM time slots.
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Operation and maintenance
unit (OMU)
OMU is the interface between the Nokia SGSN and a higher-
level network management system and/or the local operator.
The OMU is also used for system maintenance: both hw and swconfiguration is performed via OMU. In addition, the unit handles
system supervision, diagnostics, recovery and alarm functions.
The OMU can produce local alarm printouts or send the fault
indications to the NMS. In the event of a fault, the OMU
automatically activates appropriate recovery and diagnosticsprocedures.
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Message bus (MB)
A duplicated high-speed bus is used for
signalling and data interchange between the
system's computer units. User data is nottransferred via message bus.
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Group switch (GSW)
GSW is needed for semipermanent connections that
are used internally to connect SS7 signalling
terminals in SMMUs, and frame relay bearer
channels from PAPUs, via ETs to external PCM timeslots. Switching in traditional sense is not performed.
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Exchange terminal (ET)
All 2 Mbps PCM interfaces for the Gb, Gd, Gs, Gr
and Gf are connected via ETs (ET2E). Each ET2E
plug-in-unit supports two bi-directional PCM circuits.
The ETs adapt the external PCM circuits to the GSWand synchronise the system clock. Synchronisation is
included in the bit frame. Each ET2E is connected to
the GSW and the CLS unit via permanent wired
connections.
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Clock and synchronisation unit
(CLS)
CLS distributes timing reference signals to the
functional units of the system. It can operateplesiochronously or synchronously (hierarchical) with
the timing references it has received from the digital
PCM trunks.
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SGSN-Peripheral devices
The peripheral O&M devices for the Nokia
SGSN are:
disk units
printers
visual display units
DAT tape units
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GPRS interfaces
The GPRS communicates on one hand with other network elements in the GSM system and on
the other hand with equipment in the Packet Data Network using the following standard
interfaces:
Interface Destination Interface type
Gb BSS Signalling/ data transfer
Gs MSC/VLR Signalling CCS#7
Gd SMS-GMSC, SMS-IWMSC Signalling/ data transfer
Gr HLR (from SGSN) Signalling CCS#7
Gc HLR (from GGSN) Signalling/ data transfer CCS#7
Gf EIR Signalling CCS#7
Gi Packet data network Signalling/ data transfer Gn Packet data network Signalling/ data transfer
Gp SGSN in other PLMN Signalling/ data transfer
GPRS i t f
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GPRS interfaces
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GPRS interfaces
Gb interface
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Gb interface (SGSN-BSC)
The logical Gb interface covers both the interface between the SGSN and the BSC (BSS) and
the interface between the SGSN and the MS. In addition, the interface contains both
transmission and signalling planes. In other words, there are no dedicated physical
resources for signalling purposes, but signalling and data are kept apart by using logical
identifiers.
On the transmission plane, the Gbprotocol stack comprises the following entities:
Layer 1physical media: one or more PCM E1circuits with G.703 interface. Compliant with/6/.
Network Service layer, transports BSSGP PDUs. NS is based on the frame relay
connection between BSS and SGSN. Including either direct point-to-point frame relay
connections or an intermediate frame relay network. Protocol-wise, network service layer
can be further divided to frame relay and network service control layers. NS layer is
compliant with /7/.
BSS GPRSprotocol (BSSGP)is compliant with /8/.
The transmission plane of the Gb interface
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The transmissionplane of the Gb interface
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The signalling plane of the Gb
interface
The necessary signalling
is carried using the same
protocols as are being
used to carry the user
data.
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Frame relay
Frame relay offers Bearer Channels (BC) to
its users. For redundant transmission, there
are at least two bearer channels per PCU(NSEI). The Bearer Channel Identifier (BCI) is
unique in both ends. A bearer channel can
consist of 1...31 64 kbps time slots.
COSMOTE Implementation of (Gb)
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COSMOTE Implementation of (Gb)
interface
MSCKOL01(ET-497,737)&NYM01(ET-531,683,725) have Physical connection to SGSN
BSC
BSC
PCU1/NSEI_1
PCU3/ NSEI_3
PCU2/ NSEI_2
TCSM_1
TCSM_2
VMSC GMSC
MSCKOL01/MSCNYM01Through
connected
Through connected
(semipermanent)
TSEM0
SGSN
1 arrow = 1 Bearer Channel = 1 Tsl = 64kbp/s1 BC=1 NSEI
Through connected
(semipermanent)
TSEM0
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Network Service control layer
On both sides of the Gb interface there is a logical entity called network service entity
(NSE). NSEs are identified with Network Service Entity Identifiers (NSEIs). NSEI must be
identical and unique at both sides, because there is a direct relationship between the two
NSEs.
Each Packet Control Unit (PCU) in the BSC supports one NSE. Since up to 64 PCUs can be
served by one PAPU, PAPU also supports several NSEs.
NSEs at the BSS and the SGSN are connected with one or more network service virtualconnections (NS-VC). NS-VCs also have their own identifiers, Network Service Virtual
Connection Identifiers (NS-VCI). The number of the NS-VCs in the SGSN is equal to the
number of the DLCs. In other words, each NS-VC in the network service control layer maps
one-to-one onto the DLCs of the frame relay layer.
Because one bearer channel supports several DLCs, it can also be shared by several NS-
VCs. Load sharing can be applied so that the traffic of one cell can be routed via several,
evenly loaded NS-VCs. The NS-VC capacity can be controlled with the CommittedInformation Rate (CIR) parameter in steps of 16 kbps. In this way, flow control is also
performed although it is not supported by the frame relay layer. In contrast to the DLCI, the
NS-VCI must always be identical at both sides. The NS-VCI is also unique in the whole
SGSN.
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Network Service Virtual
Connection (NS-VC) NS-VCs are end-to-end virtual connections between the BSS and SGSN. The
physical link in the Gb interface is the Frame Relay Bearer channel. NS-VC is
the Frame Relay permanent virtual connection (PVC) and corresponds to the
Frame Relay DLCI (Data Link Connection Identifier) together with the Bearer
channel identifier. Each NS-VC is identified by means of a NS-VCI (Network
Service Virtual Connection Identifier).
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Network Service Virtual
Connection Group (NSE) NSE identifies a group of NS-VCs in the SGSN.
The NSEI is used by the SGSN to determine the NS-VC that provides service to
a BSSGP Virtual connection (BVC).
One NSE is configured between two peer NSs (BSS & SGSN). At each side ofthe Gb interface, there is a one-to-one correspondence between a group of NS-
VCs and a NSEI.
The NSEI has an end-to-end significance across the Gb interface at NS level,
but only local significance at the BSSGP level.
Each PAPU can contain 64 NSEs and within one NSE a maximum of four NS-
VCs are supported.
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BSSGP layer
BSSGP supports the BSSGP virtual connections (BVCs) so that each cell always has one
BVC over the Gb interface.
The BVC has its own identifier, BSSGP Virtual Connection Identifier (BVCI). The BVCI has
an end-to-end significance. In this way, both the BSC and the SGSN can identify cells with
the BVCI.
The BVCI is unique only within an NSE. BVCI=0 is reserved for signalling purposes.
One NS-VC supports several BVCs.
Within one NSE, the NS-VCs are shared by all BVCs.
BSSGP supports both cell-specific (BVC) and MS-specific flow control. The figure Gb
interface between the SGSN and the BSS gives an example on how the Gb interface can be
configured and how the SGSN sees the bearer channels, DLCIs, NS-VCs, NSEIs and cell
mappings over the Gb interface.
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BSSGP Virtual Connection
(BVC) BVCs are communication paths between peer NS user entities on the BSSGP level. Each
BVC is supported by one NSE and it is used to transport Network Service Service Data
Units (NS SDUs) between peer NS users.
Each BVC is identified by means of a BVCI which has end-to-end significance across the
Gb interface. Each BVC is unique between two peer NSs.
BSSGP supports the BSSGP virtual connections (BVC) so that each cell always has one
BVC over the Gb interface. The BVC identifier, BVCI, is only unique within an NSE. The two
types of BVCs are a signalling BVC and a PTP BVC.
Before the system creates any BVCs, the location area (LA) served by the SGSN must be
configured. See Gb Interface Handling /2/. Also the mobile country code (MCC) and mobile
network code (MNC) must be set in advance. See GSM Network and MSC/HLR Specific
Number Handling (WV) /3/.
Gb interface between the SGSN and the BSS
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Gb interface between the SGSN and the BSS
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Cell object
On the SGSN level acell means a BVC. Each GPRS capable cell in the BSS has a BVC
instance in the SGSN.
When the NS layer has been created, it is possible to create cells for the BSSGP layer. In
the SGSN the user cannot create cells or routing areas. The system creates them
automatically.
When the user enables GPRS capability in a cell in the BSS, the system resets a BVC for
the Gb interface. In the SGSN the BSSGP layer notices an unknown BVC on the Gbinterface. The system then creates a new BVC to the BSSGP layer.
The BVC is related to an NSE and it is unique within an NSE. Cell parameters are BVCI,
LAC, RAC and CI. LAC, RAC and CI identify the cell uniquely in the SGSN.
If the automatic cell creation function in the SGSN notices that a cell cannot be created
because a cell with the same BVCI already exists under the NSE or the NSE is unknown or
it is configured to another PAPU, the system sets alarm RADIO NETWORK
CONFIGURATION MISMATCH (2994). If the automatic cell creation function in the SGSN notices that an association between a
location area (LA) and Visitor Location Register (VLR) is missing, the system sets alarm
LOCATION AREA MSC/VLR ASSOCIATION IS MISSING (2996).
Routing area object
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Routing area object Mobility management in the GPRS network is handled in a similar way to the existing GSM system. One or
more cells form a routing area (RA), which is a subset of one location area (LA). The routing area is unique
within a location area. One routing area is served by one SGSN. One routing area is served by one PAPU
of the SGSN. Routing areas are configured in the BSS, and the SGSN receives the RAC information from
the BVC during automatic cell creation.
RAC: Routing Area Code
RAI: Routing Area Identity
RAI: MCC+MNC+LAC+RAC
1RAC
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Gb interface Capacity One PAPUunit supports up to 64 packet control units (PCU)in the BSS.
PCM E1/T1 layer (L1bis) The available 120 PCM circuits can be freely allocated between Gb and SS7 based
interfaces.
Frame relay (network service layer)
Each PAPU unit supports a maximum of 64 frame relay bearer channels, 64 kbps each.
Thus the SGSN can support a maximum of 16*64=1024 bearer channels. The bit rate of one
bearer channel is N*64kbps, where N is 1...31 (ETSI) and 1...24 (ANSI).
Network Service control layer
The maximum number of supported network service entities (NSE) per PAPU is 64, and
therefore 16*64=1024 per SGSN.
Each NSE can have a maximum of 4 network service virtual connections (NS-VC)
configured. This means that at maximum 256 NS-VCs are supported per PAPU, and
therefore 16*256=4096 per SGSN.
The minimum supported committed information rate (CIR) per NS-VC is 16 kbps. One FR
bearer channel can thus have a maximum of 124 NS-VCs configured that is, (64
kbps/16kbps)*31 (ETSI) and (64 kbps/16 kbps) *24 (ANSI).
BSS GPRS protocol (BSSGP) layer
The maximum number of supported BVCs (that is, cells) per PAPU is 3000. The Nokia
SGSN supports up to 24.000 cells. One PAPU supports up to 1000 routing areas. Thus the
SGSN can support up to 16.000 routing areas. One routing area is always served by one
PAPU only. The SGSN supports up to 2000 location areas. Location areas can freely cross
PAPU/SGSN boundaries.
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GPRS interfaces
Gn,Gp,Ga,Gr,Gf,Gs,NMS interfaces
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Gn interface The Gn interface exists between an SGSN and another SGSN or GGSN in the same PLMN.
The Gn interface is an open interface. The functionality in the Gp interface (between GSNsin different PLMNs) is similar to that of the Gn interface. The figure below illustrates the
protocol stack in the Gn interface.
The Gn protocol stack consists of GPRS Tunnelling Protocol (GTP), User Datagram
Protocol (UDP) and Internet Protocol (IP). The SGSN receives data packets from the MS
and sends data packets to the GGSN and vice versa. In inter-SGSN routing area updates,
data is transferred (re-routed) from the previous SGSN to the new SGSN. In addition to data
transfer, the SGSN has a signalling connection to GSNs. All these network elements areconnected to the operator's IP backbone.
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Gp interface (SGSN-BG)
From the SGSN's point of view, the Gp interface is exactly the same as
the Gn interface. The Gp is used in roaming when the home network
GGSN has to be used in order to access the desired data network. The
connection to the border gateway (BG) is created via the GPRS
backbone in the same way as to GSN elements. The Gp protocol stackand the related functionality are the same as with the Gn.
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Ga interface (SGSN-CG)
The charging records (CDR) are sent from the SGSN to the charging
gateway (CG) via the GPRS backbone. Alternatively, the SGSN may
be connected to a billing system directly - without effects to the
interface itself. The protocols used are the same as with the Gn and Gp
with the exception that the GTP supports charging-specific additions,thus the name extended GTP or GTP'. GTP' is supported according to
/13/
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Gr interface (SGSN-HLR)
The Gr interface is a standard SS7 MAP interface and connects theSGSN to the HLRs. The main purpose of the Gr is to provide the SGSN
with an access to the GPRS subscription information in the HLR. Also,
Gr supports mobility management, that is, the new SGSN is signalled
to HLR during inter-SGSN routing area update.
The protocol stack of the Gr interface consists of MAP, TCAP, SCCP,
and MTP. The interface is used for signalling purposes only.
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SS7 MAP signalling on the Gr interfaceMessage Transfer Part (MTP) complies with /14/
Signalling Connection Control Part (SCCP) complies with /15/ Transaction Capabilities Application Part (TCAP) complies with /16/
Mobile Application Part (MAP) complies with /9/
The Gr interface requires the MAP version 3, that is, the MAP protocol with
GPRS additions. The following operations are supported:
UpdateGPRSLocation
InsertSubscriberData
DeleteSubscriberData
PurgeMS
CancelLocation
ReadyForSM
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Gf interface (SGSN-EIR)
The Gf interface connects SGSNs to the EIR in order to support terminal
authentication. No GPRS-specific signalling information needs to be
supported. The supported operations are:
Send Authentication Info
Reset
Check IMEI
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Gd interface (SGSN-GMSC)
The Gd interface connects the SGSN to the Gateway MSC in order to
support SMS delivery via GPRS. As with Gf, no GPRS-specific
signalling information needs to be supported. Thus MAP version 1 or 2
is enough for SMS delivery over the Gd interface.
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Gs interface (SGSN-
MSC/VLR) The Gs interface links the SGSN's visiting subscriber database to the VLR in an
MSC. This enables support for circuit switched services, for instance, paging for
CS subscribers via SGSN.
In contrast to other SS7 interfaces, the Gs interface is not based on MAP. Gs
uses BSSAP+ protocol that has been specified for this purpose only. The other
difference is that BSSAP+ uses the services of the SCCP directly.
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SS7 BSSAP+ signalling between the SGSN and the VLR
on the Gs interface
The Gs complies with /10/ (giving requirements to SCCP and MTP) and /11/(BSSAP+ specification).
The supported operations are:
CS paging
IMSI attach for a GPRS attached MS
Combined RA/LA update
GPRS attach for an IMSI attached MS
Non-GPRS alert
MS information enquiry
IMSI detach
GPRS detach
MM information Reset (MSC/VLR SGSN).
NMS interface (SGSN-NMS)
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NMS interface (SGSN-NMS)
The Nokia SGSN provides the following types of interfacesfor the NMS. Depending on operator needs, one of
these may be used:
LAN/Ethernet (standard, integrated in MCHU unit)
digital X.25 (via AS7 signalling interface, using PCM
TSL)
analog X.25 (including V.24, V.35, V.36 or X.21 link)
The SGSN/BB-NMS interface is an open interface. The
SGSN-NMS interface is based on the CMISE and
FTAM (Q3) of the OSI model.
The main SGSN operations supported by the NMS are:
alarm monitoring and upload
remote MML session
Gb interface configuration management measurement management and upload of the
measurement results
real time management
operational security (for example, user ID and password
management, security reporting)
limited SNMP support, for example, IP-related statistics
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Configurations and capacity
The standard SGSN configuration steps are:
30.000 subscribers / 12 Mbps (minimum configuration):
4 active packet processing units (PAPU)
1 active signalling and mobility management unit (SMMU).
60.000 subscribers / 24 Mbps:
8 active packet processing units (PAPU)
2 active signalling and mobility management units (SMMU).
90.000 subscribers / 36 Mbps:
12 active packet processing units (PAPU)
3 active signalling and mobility management units (SMMU).
120.000 subscribers / 48 Mbps (maximum configuration): 16 active packet processing units (PAPU)
4 active signalling and mobility management units (SMMU).
Extensions can be implemented into SGSN online. Extensions do not
require a software update.
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Connectivity
SGSN supports the following physical interfaces to be used in various
logical GPRS interfaces:
a maximum of 16+1 100-BaseTX Ethernet connections towards GPRS
backbone (Gn and Gp)
a maximum of 1+1 100-BaseTX Ethernet connections towards charginggateway (Ga)
a maximum of 1024 64 kbps frame relay links towards the BSC (Gb)
a maximum of 120 E1 PCM circuits (Gb and all SS7-based interfaces)
a maximum of 96 SS7 signalling links, 24 in each SMMU (Gr, Gd, Gf
and Gs interfaces)
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Subscriber and session capacity
The maximum GPRS attached subscriber capacity for the Nokia SGSN
is 120.000, each subscriber having up to 2 simultaneously active PDP
contexts. Subscriber capacity is modularly added with steps of 30.000
subscribers by adding new functional units. Each SMMU supports
30.000 and each PAPU 7500 subscribers with their PDP contexts.
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Packet processing capacity
The packet processing capacity depends on various factors, such as
packet length, whether data compression is used or not, and whether
acknowledged or unacknowledged LLC mode is used. Thus the actual
SGSN data rate may vary depending on the factors mentioned above.
Each PAPU offers packet processing capacity of 3 Mbps, both downlinkand uplink combined. With the maximum system configuration of 16
active PAPU units, the Nokia SGSN capacity, with ciphered
connections and without use of compression, is 48 Mbps.
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SMS capacity
In addition to user data transfer, the Nokia SGSN supports the delivery
of 300.000 short messages during busy hour.
Data buffering capacity Packet-based communication in a mobile environment requires
effective buffering mechanisms. The Nokia SGSN offers extensive
buffering capability for the following purposes:
Gn interface (GTP payload): 240 MB buffer for GTP payload (IP
packets), 15 MB in each PAPU. Not used in acknowledged LLC mode.
Gb interface (LLC frames): 240 MB buffer for BSS flow control, 15 MB
in each PAPU.
LLC windows: Max 10 kB window per MS per direction (negotiated
between the MS and the SGSN). Not used in unacknowledged LLC
mode.
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Output NSCI-NSEI FWO:BCSU=0&&8;
DX 200 KOLETI1 2002-03-18 02:06:00
NETWORK SERVICE VIRTUAL CONNECTION PARAMETERS:
NSEI-00008 BCSU-02 PCU-09
NS-VCI NAME AD OP DLCI OP CIR BEARER CHANNEL
STATE STATE
----------------------------------------------------------------
00006 KOL10_0_6 U WO-EX 016 AV-EX 0032 0000 KOL1_0
00009 KOL10_0_9 U WO-EX 017 AV-EX 0032 0000 KOL1_0
NSEI-00010 BCSU-03 PCU-09
NS-VCI NAME AD OP DLCI OP CIR BEARER CHANNEL
STATE STATE
----------------------------------------------------------------
00008 KOL12_2_8 U WO-EX 016 AV-EX 0016 0002 KOL1_2
00011 KOL12_2_11 U WO-EX 017 AV-EX 0048 0002 KOL1_2
NSEI-00009 BCSU-08 PCU-09
NS-VCI NAME AD OP DLCI OP CIR BEARER CHANNEL
STATE STATE
----------------------------------------------------------------
00007 KOL11_1_7 U WO-EX 016 AV-EX 0016 0001 KOL1_1
00010 KOL11_1_10 U WO-EX 017 AV-EX 0048 0001 KOL1_1
COMMAND EXECUTED
< ZFUI;
LOADING PROGRAM VERSION 4.10-0
DX 200 KOLETI1 2002-03-18 02:17:40
INTERROGATING FRAME RELAY BEARER CHANNEL DATA
BEARER BEARER BEARER CHANNEL EXT TIME
ID NAME RATE (KBIT/S) PCM SLOTS UNIT TERM FUNCT
------ ---------- -------------- ---- ------ ------ ---- -----
0 KOL1_0 64 32 27 BCSU-2 9 0
1 KOL1_1 64 32 26 BCSU-8 9 02 KOL1_2 64 34 29 BCSU-3 9 0
COMMAND EXECUTED
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OUTPUT BTS PARAMETERS
(GPRS) EQO:BTS=1:GPRS; DX 200 KOLETI1 2002-03-18 02:23:03
BCF-001 BTS-001 AMPELOKIA
-------------------------------------
BTS ADMINISTRATIVE STATE ... UNLOCKED
BTS OPERATIONAL STATE ...... WO
BTS BACKGROUND DATA STATE .. NOT DEFINED
GPRS ENABLED.............................(GENA)... Y
NETWORK SERVICE ENTITY IDENTIFIER.....(NSEI)... 8
BSSGP VIRTUAL CONNECTION IDENTIFIER...(BVCI)... 10001
ROUTING AREA IDENTIFICATION..............(RAI)
MOBILE COUNTRY CODE...................(MCC).... 202
MOBILE NETWORK CODE...................(MNC).... 01
LOCATION AREA CODE....................(LAC).... 00001
ROUTING AREA CODE........................(RAC).... 3
DEDICATED GPRS CAPACITY..................(CDED)... 1 %
DEFAULT GPRS CAPACITY....................(CDEF)... 15 %
PREFER BCCH FREQUENCY GPRS...............(BFG).... N
COMMAND EXECUTED
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Output Gb interface CGR in BSC
(CGR of Bearer Channels) RCI:GSW:NCGR=GB;
CRCT CIC ORD CTRL HUNT STATE DCS
32-26 - 1 - - WO-EX -
34-29 - 2 - - WO-EX -
32-27 - 3 - - WO-EX -
COMMAND EXECUTED
OUTPUT TRANSCODER PCM
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INFOR. ZWGO; ET_PCM 32 TC_PCM TYPE ET_PCM_TSLS NR64 = 6
TCSM-32 1 FR 1 && 8
2 FR 9 && 16
3 FR 17 && 24
4 FR 25 && 25
THROUGH CONNECTIONS
32 - 26 1 - 30
32 - 27 1 - 29
32 - 28 1 - 31
32 - 29 1 - 16
32 - 30 2 - 16
32 - 31 3 - 16
ET_PCM 34 TC_PCM TYPE ET_PCM_TSLS NR64 = 3
TCSM-34 1 FR 1 && 8
2 FR 9 && 16
3 FR 17 && 24
4 HS4&D144 25 && 28
THROUGH CONNECTIONS
34 - 29 1 - 31
34 - 30 2 - 16
34 - 31 1 - 16
DISPLAY GPRS DATA
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DISPLAY GPRS DATA
in HLR MNO:IMSI=202010200837339;
DX 200 HLRI_60023 2002-03-18 02:54:59
GPRS DATA PARAMETERS
IMSI .................... 202010200837339
SGSN ADDRESS ............ 30971290000
MT-SMS VIA SGSN ......... N
NETWORK ACCESS .......... BOTH
PDP CONTEXT ID .......... 1
PDP TYPE ................ IPv4
PDP ADDRESS .............
VPLMN ALLOWED ........... N
PRECEDENCE CLASS ........ 2
DELAY CLASS ............. 4
RELIABILITY CLASS ....... 3
PEAK THROUGHPUT CLASS ... 9
MEAN THROUGHPUT CLASS ... 18
APN ..................... WAP
PDP CONTEXT ID .......... 2
PDP TYPE ................ IPv4
PDP ADDRESS .............
VPLMN ALLOWED ........... N
PRECEDENCE CLASS ........ 2
DELAY CLASS ............. 4
RELIABILITY CLASS ....... 3
PEAK THROUGHPUT CLASS ... 9
MEAN THROUGHPUT CLASS ... 18
APN ..................... internet
COMMAND EXECUTED
OUTPUT SGSN PARAMETERS ZEJH;
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SGSN PARAMETERS:
IMEI CHECK MODE........ ..........................(ICHM) ON
AUTHENTICATION MODE...............................(AUM) ON
PTMSI SIGNATURE MODE..............................(PSMO) ON
CIPHERING MODE IN USE.............................(CIPINUSE) ON
CIPHERING MODE AFTER SYSTEM RESET.................(CIP) ON
READY STATE TIMER.................................(RDY) 000-44 mm-s
MS REACHABLE TIMER................................(MSRT) 090-00 mm-s
PERIODIC RA UPDATE TIMER..........................(PRAU) 054-00 mm-s
VLR PERIODIC CLEANING START TIME..................(CTIM) 02:00 hh:mm
DETACHED SUBSCRIBER STORAGE TIME..................(STT) 001-00 ddd-hh
UTILISATION RATE DEPENDENT CLEANING...............(UDC) 80 %
UTILISATION RATE ZERO LIMIT.......................(UDL) 100 %
FORCED TO STANDBY ................................(FTS) N
N3 REQUESTS.......................................(N3) 5 T3 RESPONSE.......................................(T3) 3 s
TECHO.............................................(TECHO) 120 s
T3 TUNNEL.........................................(T3T) 20 s
GGSN NETWORK IDENTIFIER...........................(GNI)
internet
GGSN OPERATOR POINT NAME..........................(GOI)
mnc001.mcc202.gprs
GS MODE............................................(GM) OFF
LLC RETRANSMISSION TIMER, SGSN PROPOSED VALUE......(LLCTIM) 10.0 s
LLC RETRANSMISSION COUNT, SGSN PROPOSED VALUE......(LLCCO) 3 RE-TRANSMISSION....................................(RET) 2
CS PAGING SENDING TIME TO UNKNOWN MS AFTER RESET...(CPM) 20
COMMAND EXECUTED
RA PAGING REPETITION..............................(RPR) 3.0 s
RA PAGING AREA....................................(RPA) 3SGSN PAGING AREA..................................(SPA) 0
NS BLOCK TIMER....................................(NBT) 3 s
NS RESET TIMER....................................(NRT) 30 s
NS TEST TIMER.....................................(NTT) 60 s
NS ALIVE TIMER....................................(NAT) 30 s
NS BLOCK RETRIES..................................(NBR) 3
NS UNBLOCK RETRIES................................(NUR) 3
NS ALIVE RETRIES..................................(NAR) 10
NS RESET RETRIES..................................(NRR) 255
BVC RESET TIMER...................................(BRT) 3 s
BVC RESET RETRIES.................................(BRR) 3
DATA COMPRESSION..................................(COMP) ON
HEADER COMPRESSION................................(VJHC) ON
V42BIS USERS......................................(V42) 20 %
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END
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AlarmsThis section lists the alarms related to Data Network Administration.
Gb interface
-2994 RADIO NETWORK CONFIGURATION MISMATCH
-2995 ROUTING AREA CONFIGURATION ERROR IN BSS
-2996 LOCATION AREA MSC/VLR ASSOCIATION IS MISSING
-3019 NETWORK SERVICE ENTITY UNAVAILABLE
-3020 NETWORK SERVICE VIRTUAL CONNECTION UNAVAILABLE
-3021 NETWORK SERVICE VIRTUAL CONNECTION UNBLOCK PROCEDURE FAILED
-3022 NETWORK SERVICE VIRTUAL CONNECTION BLOCK PROCEDURE FAILED
-3023 NETWORK SERVICE VIRTUAL CONNECTION RESET PROCEDURE FAILED
-3024 NETWORK SERVICE ENTITY CONFIGURATION MISMATCH
-3025 NETWORK SERVICE VIRTUAL CONNECTION TEST PROCEDURE FAILED
-3026 NETWORK SERVICE VIRTUAL CONNECTION PROTOCOL ERROR
- 3028 NETWORK SERVICE VIRTUAL CONNECTION IDENTIFIER UNKNOWN -3031 BSSGP VIRTUAL CONNECTION RESET PROCEDURE FAILED
-3032 BSSGP VIRTUAL CONNECTION PROTOCOL ERROR
Gn interface
There are no alarms related directly to the Gn interface.
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NETWORK SERVICE VIRTUAL CONNECTION
TEST PROCEDURE FAILED (3025)
When the NS-VC test procedure has failed, alarm NETWORK SERVICE VIRTUAL
CONNECTION TEST PROCEDURE FAILED (3025) is set for the NS-VC, the SGSN changes the
state of the NS-VC to BL-SY, informs the BSS and reorganises BSSGP traffic to use other unblocked
NS-VCs of the NSE, if there any any available. Alarm NETWORK SERVICE VIRTUAL
CONNECTION TEST PROCEDURE FAILED(3025) is cancelled when the next successful test
procedure is executed for the NS-VC.
The alive test of a Network Service Virtual Connection has failed as many consecutive times as defined
with the NS-Alive-Retries parameter. The system marks the virtual connection blocked in theoriginating side and initiates a reset procedure. The system cannot use the connection for General
Packet Radio Service, that is, the data transfer capacity has decreased.
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NETWORK SERVICE VIRTUAL CONNECTION
UNAVAILABLE (3020)
When the SGSN has detected the unavailability of a bearer channel,
the states of all the related NS-VCs are set to BL-SY, the BSS is
informed, BSSGP traffic is reorganised to use other unblocked NS-VCs
of the NSE, if there are any available and alarm NETWORK SERVICE
VIRTUAL CONNECTION UNAVAILABLE (3020) is set for the NS-VC.If the NS-VC is already user-blocked when the unavailability of the
bearer channel is detected, the NS-VC state is not changed, no alarm
is set and the BSS is not informed.
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NETWORK SERVICE VIRTUAL CONNECTION
BLOCK PROCEDURE FAILED (3022)
If the SGSN does not receive acknowledgement NS-BLOCK-ACK PDU
from the BSS within the time period defined with parameter NS block
timer, the sending of NS-BLOCK PDU is repeated as many times as is
defined with parameter NS block retries. If no acknowledgement is
received from the BSS within defined retry attempts, the procedure isstopped and alarm NETWORK SERVICE VIRTUAL CONNECTION
BLOCK PROCEDURE FAILED (3022) is set for the NS-VC. The alarm
is cancelled when the NS-VC state has changed successfully.