gprs fundamentals r2

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TechnologyTraining

GPRS

Fundamentals

March 1, 2012

Agilent Confidential


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Agenda

Understanding GPRS Network Element Architecture and

Basic Functions

Understanding Generic System Sizing

Understanding the Network Element Interconnections

Understanding the Network Node Access Types

Understanding the Network Call Flow(s)

Description of Network Protocols and Functions within the

Network

March 1, 2012

Agilent Confidential2


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What is GPRS?

A new bearer service for GSM that greatly improves and simplifies

wireless access to packet data networks ,e.g. to the internet.

Benefits of GPRS as Data Service On GSM air interface, profit from idle capacity

Internet and Intranet Accessthrough Wireless Application Protocol (WAP)

and a WAP browsers used to browse the web browser from mobile

devices such as mobile phones.

Applications, such as email by mobile phone, Instant Messaging, Multi-

Media Service (MMS), Short Message Service (SMS), tracking of stock-

market prices, sports results, news headlines, music downloads.

Seamless Applications - TCP/IP

Higher Data Rates (GPRS provides data rates of 56-114 Kbit/s)

Fast Sessions - Call setup / clear down

On the GSM air interface, users share physical resources

Step towards UMTS

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What is EDGE/EGPRS and Evolved EDGE?

Enhanced Data rates for GSMEvolution (EDGE) - also known asEnhanced GPRS (EGPRS)

Improved data transmission rates thanGPRS through the use of sophisticatedmethods of coding and transmittingdata

EDGE delivers higher bit-rates perradio channel, resulting in a 3 xincrease in capacity and performanceversus GPRS connection (i.e. up to236.8 Kbit/s for 4 timeslots up to 473.6Kbit/s for 8 timeslots - maximum)

EDGE was deployed on GSM networksbeginning in 2003

EDGE is standardized by 3GPP as partof the GSM family and is considered apre-3G radio technology and is part ofITU's 3G definition.

Evolved EDGE

Evolved EDGE continues in Release 7of the 3GPP standard

Reduced latency

Greater than doubled performance

Peak bit-rates of up to 1Mbit/s andtypical bit-rates of 400kbit/s can beexpected.

No commercial deploymentsyet Expected in 2012.

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GPRS Cell Hierarchy

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New GPRS Network ElementsGGSN

Is the last port of call in the GPRS networkbefore a connection between an ISP or

corporate networks router occurs.

The GGSN is basically a gateway, routerand firewall.

It also confirms user details with RADIUSservers for security, which are usually

situated in the IP network and outside of theGPRS network.

Data/Packet Counting as GPRS is billed onper megabyte basis.

PDU Tunneling.

Screening.

Address Mapping, Routing Tables.

SGSNTakes care of some important tasks, including Routing,Handover and IP address assignment.

Its a logical connection to the GPRS device and it works out

which BSC to route your connection to.In regards to cell re-selection, the SGSN is to make sure theconnection is not interrupted as the MS moves from one cell toanother.

If the user moves into a segment (i.e. Routing Area) of thenetwork that is managed by a different SGSN it will perform ahandoff to the new SGSN.

This is done extremely quickly and generally the user willnot notice this has happened.

Any packets that are lost during this process areretransmitted.

The SGSN has a link to a GGSN in another PLMN network insupport of GPRS roaming subscribers.

Ciphering, compression, data packet counting.

GSM Circuit Switched Interactions.

Support for delivery of SMS messages over GPRS.

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GSM/GPRS - Core Architecture

C

SGSN GGSN

VLR

MSC GMSC

HLRMS

Abis

A

Gb

Gn

Gr

D

ISUP

Gi

ISUP

BSC

BTSGs

Gp

GGSN

Home Network if Roaming

Serving

Network

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GSM/GPRS Access Architecture

Two new node types; Serving GPRS Support Node (SGSN) and Gateway GPRS Support Node(GGSN). With new (IP based) Gn interface

Several SGSNs (10s to 100s, but less than MSCs) and a few to 10s GGSNs

Connection to Internet occurs over GPRS packet network Frame Relay or IP link used to connect SGSN to BSC (Gb interface)

Calls still occur over the GSM transit network

Subscriber is attached to GSM and/or GPRS network

but cant use both at the same time unless MS or network supports Dual Transfer Mode (DTM) orMS is a GPRS class A device

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GPRS Mobile Stations

Class A - data and voice

simultaneously

The original idea of Class A was to operate in theCS domain (voice) and PS domain (data) with

complete independence which did mean supporting

2 frequencies at the same time (not just 900 &

1800 but also 2 frequencies within the same band).

This would have made handsets hugely complex

so it never really happened.

With Dual Transfer Mode (DTM) (also known assimple or pseudo class A) both voice and data are

on the same frequency and coordination is done by

the network.

Class B - data and voice, data

suspended during voice

Class Cdata only

Four Coding Schemes defined

CS1 9.05 kbit / second per

timeslot CS2 13.40

CS3 15.60

CS4 21.40

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IdentitiesIMSI, P-TMSI, TLLI

IMSI(International Mobile Subscriber Identity) is up to 15 digit long number:-

The first 3 digits are the Mobile Country Code (MCC),

The next 2 or 3 digits are the Mobile Network Code (MNC) Either 2 digits (European standard) or 3 digits (North American standard).

The remaining digits are the Mobile Subscription Identification Number (MSIN) within the

carriers network's customer base.

The IMSI conforms to the ITU E.212 numbering standard.

P-TMSI(Packet-TMSI) Equivalent of the GSM TMSI, but assigned by the SGSNand used on the Gb links

TLLIDerived from the P-TMSI. Used when moving between SGSNs

Local TLLI derived from P-TMSI

Foreign TLLI as seen by SGSN, TLLI from previous SGSN

Random TLLI generated by mobile in absence of a valid P-TMSI

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APN

APNis a mechanism to determine how a MS communicates via the GPRS network to a

host site (i.e., how the GPRS carrier network passes IP traffic to the host networke.g. the

Internet).

APNs are general-purpose and are available to multiple MSs or can be customized forparticular customers to address unique requirements.

The APNs can be type of service dependant e.g. WAP, Mobile Web/Email or general in use.

Examples of APN are:

internet.mncXYZ.mccABC.gprs.

wap.voicestream.com (for WAP sessions)

payandgo.o2.co.uk (for Pay as You Go WAP sessions)

mobile.o2.co.uk (for mobile web / email)

general.t-mobile.uk (for all session types)

three.co.uk (for all session types)

APNs consists of two parts as shown in the figure to the right-----

Network Identifier: Defines the external network to which the GGSN is

connected. Optionally, it may also include the service requested by the

user. This part of the APN is mandatory.

Operator Identifier: Defines the specific operators packet domain network

in which the GGSN is located. This part of the APN is optional.

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Nodes - The SGSN

Similar to the GSM MSC. Handles the GPRS attached subscribers

Gr - to fetch and updatethe subscriber information

Gn - IP link to other GSNs(SGSNs or GGSNs)

Gs - to update VLR withMS location for Paging viathe SGSN - used whensubscriber receives a

Mobile Terminated GPRS call GbIP or Frame relay link to

communicate with BSC(note that this is ciphered)

GpName for Gn link to a GGSN in another network in support of GPRSroaming MS

The only delta between them is that Gp will have a Border Gateway (i.e. a firewall)between the SGSN and GGSN in the other GPRS PLMN operator.

Gdfor SGSN to send & receive SMS text messages from the SMScenter.

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Nodes - The GGSN

Routes IP packets to/fromthe SGSN, essentially a router

Gn - IP link used toconnect to SGSNs

This interface has ALLsubscriber information intactand (optionally) locationinformation (e.g. cell id)

Gi - IP link to the Packet Data Network e.g. Internet, Corporate VPNetci.e. is the raw IP connection

This interface has NO subscriber identification or location information (e.g.cell id)

In addition, the Gi interface also handles communication towards RADIUS

and DHCP servers for authentication and IP address allocation. Gc(optional link) allow GGSN to get subscriber information when

receive packet for unknown subscriber e.g. Network Requested Call

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GPRS Roaming

The IP backbone network wascreated to carry GTP-tunnels viathe Gp interface between the

GPRS Support Nodes (GSNs) indifferent GSM/GPRS Operators

The Gp interface allowed mobileend-users to make use of the GPRSservices of their home network whileroaming in a visited network.

GRX - GPRS Roaming eXchange: Is in fact an inter-PLMN IP backbone and is termed the GRX.

Instead of every GPRS PLMN having to connect to every roaming partnerdirectly, they connect to one or many GRX providers.

GRX provides for routing, interconnecting and some additional services,

such as DNS.

The GRX model is used to interconnect in excess of 300 networksand has proven highly successful

GRX

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Procedure - GPRS Attach

7d. Cancel Location Ack

7c. Cancel Location

7b. Update Location

7g. Update Location Ack

7e. Insert Subscriber Data

7f. Insert Subscriber Data Ack

6d. Insert Subscriber Data

6c. Cancel Location Ack

6b. Cancel Location

3. Identity Response

2. Identification Response

2. Identification Request

1. Attach Request

5. IMEI Check

3. Identity Request

4. Authentication

6a. Update Location

7a. Location Update Request

7h. Location Update Accept

6f. Update Location Ack

6e. Insert Subscriber Data Ack

MS BSS new SGSN old SGSN GGSN HLR EIR

old

MSC/VLR

new

MSC/VLR

9. Attach Complete

8. Attach Accept

10. TMSI Reallocation Complete

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Procedure - GPRS Detach

3. IMSI Detach Indication

2. Delete PDP Context Response

1. Detach Request2. Delete PDP Context Request

5. Detach Accept

MS BSS GGSNSGSN MSC/VLR

4. GPRS Detach Indication


1. Detach Request

2. Delete PDP Context Request

4. Detach Accept

MS BSS GGSNSGSN MSC/VLR


HLRMS BSS GGSNSGSN MSC/VLR

3. Delete PDP Context Request

1. Cancel Location


2. Detach Request

6. Cancel Location Ack


5. Detach Accept

MS Initiated

SGSN Initiated

HLR Initiated

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Procedure - Inter SGSN RA/LA Update

Old SGSN used to getPDP Context details(assuming MS has a

PDP Context)

PDP Contextinformation in GGSNmodified with the newSGSN

Update GPRS Locationto update the HLR, getthe subscriber detailsand clear old record

Note that packets maystill arrive at the oldSGSN and need to bebuffered then forwarded

12b. Cancel Location

12c. Cancel Location Ack

12d. Insert Subscriber Data

16. TMSI Reallocation Complete

12f. Update Location Ack

13. Location Update Accept

15. Routeing Area Update Complete

14. Routeing Area Update Accept

8. Cancel Location

8. Cancel Location Ack

6. Update PDP Context Response

6. Update PDP Context Request

7. Update Location

10. Update Location Ack

12a. Update Location

11. Location Update Request

2. SGSN Context Response3. Security Functions

2. SGSN Context Request

1. Routeing Area Update Request

9. Insert Subscriber Data

9. Insert Subscriber Data Ack

12e. Insert Subscriber Data Ack

MS BSS GGSNold SGSNnew SGSN HLR

new

MSC/VLR

old

MSC/VLR

5. Forward Packets

4. SGSN Context Acknowledge

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ProcedurePDP Context Activation

MS requests a PDP Context for the chosen APN

SGSN uses DNS to find the IP address of the GGSN for that APN and asks to create acontext

GGSN uses RADIUS to authenticate the user and DHCP to obtain an IP address

That IP address is passed back to the UT

MS

BSC

Activate PDP Ctxt (apn) DNS Query (apn.mnc.mcc.gprs)

Activate PDP Ctxt Acc (MS IP)

DNS Resp (GGSN IP)

SGSN DNS GGSN

Create PDP Context Request

Create PDP Context Resp (MS IP)

AAA DHCP

RADIUS Auth

DHCP Request

DHCP Resp (MS IP)

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ProcedureSecondary PDP Context

Used to create a second (or 3rdetc) PDP Context for the same APN

GGSN uses a Traffic Flow Template (TFT) to distinguish between packets

Allows the contexts to have different QoS parameters

Activate Secondary PDP Context sent with reference to the 1stPDP context

GGSN is the same as the first so no APN or DNS lookup required MS has already been authenticated so no RADIUS (though maybe for billing)

Same IP address used so no DHCP required

Main use is IMS services; one flow for signaling and another for the data

MS

BSC

Activate Secondary PDP (1st)

Activate 2ndPDP Acc

SGSN GGSN

Create PDP Context Request (1st)

Create PDP Context Resp

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PDN

Procedure - GPRS Data Flow

GTP-U T-PDU message used to encapsulate IP packets on the Gninterface

Separate protocol (SNDCP) used on the Gb interface

Gb Gn Gi

BSC SGSN GGSN

Attach

Activate PDP GTP-C Create PDP

GTP Delete PDPDeactivate PDP

Detach

IPPacketIP

Packet

IP

Packet

GTP-USNDCP

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Protocol Architecture

Transmission Plane

The protocols provide transmission of user data and its associated

signaling

Signaling Plane

Comprises protocols for the control and support of functions of the

transmission plane

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Um Gb Gn Gi

GMM / SM

LLC

RLC

MAC

GSM RF

MS

RLC

MAC

GSM RF

BSSGP

Network

Service

(FrameRelay)L1 bis

BSS

BSSGP

Network

Service

(FrameRelay)L1 bis

GMM / SM

LLC

IP

L2

(Ethernet)

L1

GTP

UDP / TCP

SGSN

IP

L2

(Ethernet)

L1

GTP

UDP

GGSN

GRPS Signaling Control Plane

Assuming Gb

uses Frame

Relay as

transport.

Assuming Gbuses IP as

transport.

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ProtocolsGTP and SNDCP

SNDCP (Sub networkDependent Convergence

Protocol) Data compression support

GPRS Tunnel Protocol(GTP) is the core networkprotocol in GPRS i.e. used

by GSNs GTP carries both signalingand the user data packets

On Gn the data is carriedwithin a GTP T-PDU

message On Gb they are carried

using SNDCP

IP Packet

GTP (T-PDU message)

UDP

IP

Lower layer protocols

GTP

UDP

IP


Gn Signaling Gn User Data

IP Packet

SNDCP

LLC

BSSGP


Gb User Data

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ProtocolsGTP Versions and TunnelingThree GTP versions:

GTP version 0 (GTPv0) - no longer supportedbeyond release 99.

GTP version 1 (GTPv1) - still supported today, by

2.5G & 3G RAN networks. GTP versions 2 (GTPv2)recently introduced for

support of 4G RAN networks (out of scope of thispresentation).

GPRS MS is connected to a SGSN withoutbeing aware of the protocol version being used.

GTPv1 introduces the concept of primary andsecondary contexts for an MS. A GTP tunnel is an encapsulation of the user

packets between the GGSN and the SGSN in

GTP/ UDP/IP only. GTPv1 is actually effectively two protocols: one for

control (called GTP-C and uses port 2123) and onefor user data tunneling (called GTP-U and usesport 2152).

A primary context is associated with an IP addressand indicates other parameters like the APN to beattached to the receiving GSN.

Secondary contexts created for this primary PDPcontext share the IP address and other parametersalready associated with the primary context.

This allows the MS to initiate another context with adifferent QoS requirement and also share the IPaddress already obtained for the primary context.

Primary and secondary contexts share the TunnelEndpoint ID (TEID) on the control plane and havedifferent TEID values in the data plane.

Since all primary and associated secondarycontexts share the IP address, Traffic FlowTemplates (TFT) are introduced to classify traffic inthe downlink direction towards the MS.

TFTs are exchanged during context creation.

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ProtocolsGTP TunnelingGTP control plane messages (GTP-C) are used toexchange the tunnel information and to create, updateor delete a tunnelare called tunnel managementsignaling messages:

Create PDP Context Request/Response, Update PDPContext Request/Response and Delete PDP ContextRequest/Response.

The GTP user data messages (GTP-U) are used toload the T-PDUs (Transport Protocol Data Unit)passing through the GTP tunnel.

The receiving end side of a GTP tunnel locally assignsthe TEID value the transmitting side has to use.

The GTP-U Tunnel identifies in each node with a

TEID, an IP address and a UDP port number. A GTP-U tunnel is necessary to enable forwarding packetsbetween GTP-U entities.

There is a mechanism for verifying connectivity fromone GSN to another GSN. This uses two messages.

echo request

echo response

As often as every 60 seconds, a GSN can send an

echo request to every other GSN with which it has anactive connection.

If the other end does not respond it can be treated asdown and the active connections to it will be deleted

The SGSN shall include either the MS provided APN,a subscribed APN or an SGSN selected APN in themessage; the Access Point Name may be used by theGGSN to differentiate accesses to different externalnetworks.

For contexts created by the Secondary PDP ContextActivation Procedure the SGSN shall include thelinked NSAPI. Linked NSAPI indicates the NSAPIassigned to any one of the already activated PDPcontexts for this PDP address or two IP addresses(one IPv4 and one IPv6 if PDP Type IPv4v6 issupported and used) and APN.

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ProtocolsBSSGP and GPRS MM/SM

BSSGP (BSS GPRS Protocol) used by the SGSN to control the BSS Uplink and Downlink Radio resources

LLC (Logical Link Control)

Ciphering

GPRS Mobile Management (MM) / Session Management (SM) used by the SGSN andUT for sessions (contexts) and mobility SM messages for Session Management i.e. PDP Contexts e.g. Activate PDP Context

MM messages for Mobility Management e.g. Routing Area Update

The BSS does not interpret the GMM/SM messages

GPRS MM GPRS SM

LLC

BSSGP

Low er layer protoco ls

SGSNUT BSC

BSSGP

GPRS MM and SM

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ProtocolsGPRS Abis

GPRS Abis, the protocol contains

various PCU frame types (see figurebelow right) that are vendor specificformat.

NOTE:This means each extractingsignaling and data from the GPRS Abisinterface requires support for multiple

equipment vendors proprietary protocols(e.g. Ericsson, Nokia Siemens Networks,Huawei, Alcatel Lucent).

NOET:In GPRS, the Abis signalingmessages and data packets are allcarried in the Abis (voice) TRAUtimeslots. This means, any attempt todecode GPRS Abis signaling + user datawould require a huge amount of CPUprocessing. As decoding every AbisTRAU message is a very largeprocessing taskthe volumes arecolossal.

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GPRS Re-SelectionIn GPRS (as in GSM), the mobile performs cell re-selectionincluding Routing Area update whencrossing RA boundary.

However, there are some differences compared with

GSM: In GPRS, the mobile performs cell re-selection when itis in idle mode AND during active sessions, i.e. packettransfer.

In GPRS, the cell reselection is either performed by themobile autonomously or optionally controlled by thenetworksee figure to right.

If the MS is in GPRS dedicated mode (i.e. activesession) then the changes from one cell to another is

performed according to the network-controlledhandover procedures detailed to the right.

The previous SGSN is requested to transmit theundelivered data to the new SGSN.

In GPRS, its possible (but not typically setup) for thenetwork to order the MS to send measurement reportsto the network and to suspend its normal cellreselection and accept decisions from the network

instead.

This means typically theres no GPRS RRmeasurement reports transferred across the GPRSAbis interface.

The degree to which the mobile station resigns itsradio network control is variable and is ordered indetail by the parameter: NETWORK_CONTROLORDER

NC0 (normal mobile station control) The mobile stationperforms autonomous cell reselection.

NC1 (mobile station control with measurement reports)The mobile station sends measurement reports to thenetwork according to additional information in themessage NC1. It continues its normal cell reselection.

NC2 (network control) The mobile station sendsmeasurement reports to the network according toadditional information in the message NC2. It does notperform cell reselection on its own, and can only make

a cell reselection according to a cell reselectioncommand received from the network.

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ProtocolsBSSAP+

Used on the Gs link

Current SGSN updated in VLR during Routing Area Update

Current MSC VLR updated in SGSN during Location Update

If MS needs paged by the MSC the request is sent over the Gs

This uses fewer radio resources as SGSN has a more precise MSlocation

The rest of procedure occurs as normal

BSSAP+

Connectionless SCCP

Low er layer proto cols

Gs

MSC

VLR

SGSN

Incoming Call

PS Paging

Paging Resp

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Protocols - LLC Details

Reliable link between SGSN and BSS

Sequence Control

Error detection

Retransmission

Flow Control

Complete LLC Frame can be ciphered

Provision of one or more logical link connections discriminatedbetween by means of a DLCI

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Protocol - BSSGP Details

Provision by an SGSN to a BSS of radio related information

used by the RLC/MAC function

Provision by a BSS to an SGSN of radio related informationderived from the RLC/MAC function

Provision of functionality to enable two physically distinct

nodes, an SGSN and a BSS, to operate node management

control functions GMM - Paging and radio status

NM - Flow Control and Resets

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Network Node Access Types Access Network

Gb over IP

The increased demand for packet switched traffic transmission cost

efficiency can be met by deploying IP in the transmission network. IP offers an alternative way to configure the sub network of the Gb

interface:

The sub network is IP-based and the physical layer is Ethernet

The introduction of IP makes it possible to build an efficient transport

network for the IP based multimedia services of the future.

Both the IPv6 and IPv4 protocol versions are supported.

IP transport can be used in parallel with FR under the same BSC.

Within one BCS, separate PCUs can use different transmission media in

the BSC. The capacity of the Gb interface remains the same, regardless of

whether IP or FR is used as the transport technology.

Agilent Confidential

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IuFlex & SGSN Pooling The requirements to have a BSC

(i.e. RAN node) controlled by asingle MSC server or SGSN leadto certain limitations.

Allowing the BSCs to connect to anumber of MSC servers orSGSNs increases the networksperformance in terms ofscalability, distributing the networkload amongst the serving entities,

and reducing the requiredsignaling as the user roams.

The solution shall enable thereduction of signaling within thecore network (e.g reduction of theHLR signaling traffic).

IuFlex capable nodes such as theBSC shall be able to select anyCN node such as the SGSN/MSCServer within a pool area.

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Review of Available System Information by Link

Meta-data

The Gn interface can

provide meta-data forsubscriber identity (IMSI)

Content: Data

Content is most readilyavailable on the Gn

interface, which allows

association with the

subscriber identify

GPRS Meta Data CDR Fields

DescriptionGnLink

Timestamp Reason Email, WAP, SMS, MMS, Web Service , Etc. IMSI End User Address Access Point Name (APN) Cell ID Routing Area Identifier (RAI) Source IP Address Destination IP Address SGSN Signaling Address (IP Address to use for Signaling to SGSN) SGSN User Data Address (IP Address to use for User Data to SGSN) GGSN Signaling Address (IP Address to use for Signaling to GGSN) GGSN User Data Address (IP Address to use for User Data to SGSN) GPRS Tunneling Protocol (GTP) Tunnel ID Cause Code SGSN Signaling & User Data TEIDs GGSN Signaling & User Data TEIDs Network SAPI (NSAPI)

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Summary / Q&A

Understanding GPRS Network Element Architecture and

Basic Functions

Understanding Generic System Sizing

Understanding the Network Element Interconnections

Understanding the Network Node Access Types

Understanding the Network Call Flow(s)

Description of Network Protocols and Functions within the

Network

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gprs fundamentals r2

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