Introduction to SGSN

5/28/2018 Introduction to SGSN

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1 Tsoukalas Dimitrios COSMOTE Introduction to S G S N / Thursday 21 Mar, 2002

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-mail

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.


7/797 Tsoukalas Dimitrios COSMOTE Introduction to S G S N / Thursday 21 Mar, 2002

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).



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.



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.



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



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


Type 4+1four downlink channels and one uplink




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.



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



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)



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.



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



Overview of the GPRS network



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



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



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.



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



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



SGSN cabinet



HardwareConfiguration



DX 200 system architecture and SGSN block diagram



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.



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.



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:


2 active signalling and mobility management units (SMMU).

90.000 subscribers / 36 Mbps:



120.000 subscribers / 48 Mbps (maximum configuration): 16 active packet processing units (PAPU)


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




STATE STATE

----------------------------------------------------------------





STATE STATE

----------------------------------------------------------------



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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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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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.

Introduction to SGSN

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Transcript of Introduction to SGSN