PS GPRS Architecture

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GPRS Architecture: Interfacesand Protocols

Training Document

GPRS System Course

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GPRS Architecture: Iter!aces a" Protoco#s

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1 Introduction

GPRS provides mobile users access to value-added WAP services and differentexternal packet switched networks. These networks can be for example the!nternet or corporate intranets. The GS"-#SS provides the radio interface and

the GPRS core network handles mobilit$ and access to external packet

networks and services. This is shown in %i&ure '.

ore etwor

xternaac et

Networks

a uee

erv ces

7iure 1* GPRS access to acket switche" etworks

The GPRS network acts in parallel with the GS" network providin& packetswitched connections to the external networks. The re(uirements of a GPRS

network are the followin&)

The GPRS network must use as much of the existin& GS" infrastructure

with the smallest number of modifications to it.

Since a GPRS user ma$ be on more than one data session GPRS should

be able to support one or more packet-switched connections.

To support the bud&ets of various GPRS users it must be able to support

different *ualit$ of Service +*oS, subscriptions of the user.

The GPRS network architecture has to be compatible with future rd and

th &eneration mobile communication s$stems.

!t should be able to support both point-to-point and point-to-multipoint

data connections.

!t should provide secure access to external networks.

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A GPRS network must provide all of the functionalit$ of a GS" network for

packet switched networks and more. The GPRS is expected to perform the

functions of a traditional mobile communication network and a traditional

packet switched computer network. These functions are itemised below)

/apabilit$ to separate circuit switched and packet switched traffic from

mobile station +"S,

Radio resource mana&ement that is allocation of radio resources to

GPRS subscribers across the air interface

!nterfaces to !nternet intranets Public 0ata 1etworks +P01, and otherPublic 2and "obile 1etworks +P2"1,

Authenticate subscriber re(uests for packet switched resources

3ncr$pt data transmitted on the air interface for securit$ purposes

0ata compression for data transmitted over the air interface

!nteract with databases +42R562R, containin& subscriber informationsuch as !"S! securit$ data and subscription information

"obilit$ mana&ement as in GS"

2ocation mana&ement as in GS"

4andover as a GPRS subscriber moves within a covera&e area

Power control to minimise the transmitted power b$ the user

1etwork mana&ement that facilitates GPRS network mana&ement

Generation and collection of network performance statistics

Generation and collection of char&in& or billin& information

Si&nallin& links between the GPRS network elements

Routin& of packets to appropriate destination

Protocol conversion between networks that ma$ use different protocols

#ufferin& of data at GPRS nodes

Allocation of static or d$namic address for packets ori&inatin& from "S

Protection of the GPRS network from securit$ threats

/apabilit$ to monitor tar&et subscriber b$ law enforcement a&encies

Translation between lo&ical names and !P addresses usin& 0omain 1ame

S$stem +01S,

%acilitation of roamin& subscribers so that the$ can connect to home

networks

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0eliver$ of S"S messa&es throu&h the GPRS network

Redundanc$ mechanisms if one or more network elements were to fail

Translation between private and public addresses usin& 1AT and 1APT 0etection of fault$ or stolen GPRS handsets

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!et"or# elements

%i&ure 7 shows the architecture of a GPRS network. The GPRS s$stem brin&s

some new network elements to an existin& GS" network. These elements are)

Packet /ontrol 8nit +P/8,

Servin& GPRS Support 1ode +SGS1,) the "S/ of the GPRS network

Gatewa$ GPRS Support 1ode +GGS1,) &atewa$ to external networks

#order Gatewa$ +#G,) a &atewa$ to other P2"1

!ntra-P2"1 backbone) an !P based network inter-connectin& all the

GPRS elements

/har&in& Gatewa$ +/G,

2e&al !nterception Gatewa$ +2!G, 0omain 1ame S$stem +01S,

%irewalls) used wherever a connection to an external network is re(uired.

1ot all of the network elements are compulsor$ for ever$ GPRS network.

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$S S9

SGS!

GGS! Itraet

GGS! Iteret

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RouterSer-er

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SGSN E Ser-i GPRS Suort No"eGGSN E Gateway GPRS Suort No"eN;S E Network ;aae%et Syste%G E or"er Gateway9G E 9hari Gateway7 E 7irewa##IG E aw!u# Itercetio Gateway

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N;S

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OeratorSer-ices

AN

GGS!

7iure 2* GPRS architecture

.1 Pac#et Control 0nit PC02

The P/8 separates the circuit switched and packet switched traffic from the

user and sends them to the GS" and GPRS networks respectivel$. !t alsoperforms most of the radio resource mana&ement functions of the GPRS

network. The P/8 can be either located in the #TS #S/ or some other point

between the "S and the "S/. There will be at least one P/8 that serves a cell

in which GPRS services will be available. %rame Rela$ technolo&$ is bein&used at present to interconnect the P/8 to the GPRS core.

. Ser3ing GPRS Su''ort !ode SGS!2

The SGS1 is the most important element of the GPRS network. The SGS1 of

the GPRS network is e(uivalent to the "S/ of the GS" network. There mustat least one SGS1 in a GPRS network. There is a covera&e area associated with

a SGS1. As the network expands and the number of subscribers increases

there ma$ be more than one SGS1 in a network. The SGS1 has the followin&

functions)

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Protocol conversion +for example !P to %R,

/ipherin& of GPRS data between the "S and SGS1

0ata compression is used to minimise the si9e of transmitted data units

Authentication of GPRS users

"obilit$ mana&ement as the subscriber moves from one area to another

and possibl$ one SGS1 to another

Routin& of data to the relevant GGS1 when a connection to an external

network is re(uired

!nteraction with the 1SS +that is "S/562R 42R 3!R, via the SS:

network in order to retrieve subscription information

/ollection of char&in& data pertainin& to the use of GPRS users

Traffic statistics collections for network mana&ement purposes.

.% Gate"ay GPRS Su''ort !ode GGS!2

The GGS1 is the &atewa$ to external networks. 3ver$ connection to a fixedexternal data network has to &o throu&h a GGS1. The GGS1 acts as the anchor

point in a GPRS data connection even when the subscriber moves to another

SGS1 durin& roamin&. The GGS1 ma$ accept connection re(uest from SGS1

that is in another P2"1. 4ence the concept of covera&e area does not appl$ toGGS1. There are usuall$ two or more GGS1s in a network for redundanc$

purposes and the$ back up each other up in case of failure. The functions of aGGS1 are &iven below)

Routin& mobile-destined packets comin& from external networks to the

relevant SGS1

Routin& packets ori&inatin& from a mobile to the correct external

network

!nterfaces to external !P networks and deals with securit$ issues

/ollects char&in& data and traffic statistics

Allocates d$namic or static !P addresses to mobiles either b$ itself or

with the help of a 04/P or a RA0!8S server

!nvolved in the establishment of tunnels with the SGS1 and with other

external networks and 6P1.

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%rom the external network;s point of view the GGS1 is simpl$ a router to an !P

sub-network. This is shown below. When the GGS1 receives data addressed toa specific user in the mobile network it first checks if the address is active. !f it

is the GGS1 forwards the data to the SGS1 servin& the mobile. !f the addressis inactive the data is discarded. The GGS1 also routes mobile ori&inated

packets to the correct external network.

.ost1*222*33*

9ororate su&etwork131*44*1*000

GPRS su&etwork1*222*33*000

.ost131*44*1*3

Router

Router

AN

Iteret

7iure 3* GPRS etwork as see &y aother "ata etwork

.& Domain !ame Ser3ers

These devices convert !P names into !P addresses for example

server.nokia.com to '..'ect all packets that are not part of a GPRS subscriber-

initiated connection. The firewall can also include 1AT +1etwork Address

Translation, see theIntroduction to TCP/IPmodule.

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.6 ,order Gate"ay

The #order Gatewa$ +#G, is a router that can provide a direct GPRS tunnel

between different operators; GPRS networks. This is referred to as an inter-P2"1 data network. !t is more secure to transfer data between two operators;P2"1 networks throu&h a direct connection rather than via the public !nternet.

The #order Gatewa$ will commence operation once the GPRS roamin&

a&reements between various operators have been si&ned. !t will essentiall$

allow a roamin& subscriber to connect to compan$ intranet throu&h the 4omeGGS1 via the visitin& P2"1 network.

.) Charging Gate"ay

GPRS users have to be char&ed for the use of the network. !n a GS" network

char&in& is based on the destination duration and time of call. 4owever GPRSoffers connectionless service to users so it not possible to char&e subscribers

on the connection duration. /har&in& has to be based on the volume

destination *oS and other parameters of a connectionless data transfer. TheseGPRS char&in& data are &enerated b$ all the SGS1s and GGS1s in the

network. This data is referred to as /har&in& 0ata Records or /0Rs. ?ne data

session ma$ &enerate a number of /0Rs so these need to collected and

processed. The /har&in& Gatewa$ +/G, collects all of these records sortsthem processes it and passes it on to the #illin& S$stem. 4ere the GPRS

subscriber is billed for the data transaction. All /0Rs contain uni(ue

subscriber and connection identifiers to distin&uish it. A protocol called GTP;+pronounced GTP prime, is used for the transfer of data records between GS1sand the /har&in& Gatewa$.

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% GPRS interfaces

The GPRS s$stem introduces new interfaces to the GS" network. %i&ure illustrates the lo&ical architecture with the interfaces and reference points of thecombined GS"5GPRS network.

.R

Air 0m2

G(

GsGr Gf

Gn

GnIterDP;N

GPRS&ack&oe

G'

0tera#acketetwork

Gi

SGSN

IR

S9

;S9F6R

S;SDG;S9

Gd

GGSN

G

Signalling and data

Signalling

Ga

Ga

9G

7iure 4* GPRS iter!aces

/onnections from the GPRS s$stem to the 1SS part of the GS" network are

implemented throu&h the SS: network. The GPRS element interfacin& with the1SS is SGS1. The important interfaces to the 1SS are the SGS1-42R +Gr,

SGS1-3!R +Gf, and SGS1-"S/562R +Gs,. The other interfaces are

implemented throu&h the intra-P2"1 backbone network +Gn, the inter-P2"1

backbone network +Gp, or the external networks +Gi,.

The interfaces used b$ the GPRS s$stem are described below)

Umbetween an "S and the GPRS fixed network part. The 8m is the

access interface the "S uses to access the GPRS network. The radiointerface to the #TS is the same interface used b$ the existin& GS"

network with some GPRS specific chan&es.

Gbbetween a SGS1 and a #SS. The Gb interface carries the GPRS

traffic and si&nallin& between the GS" radio network +#SS, and the

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GPRS network. %rame Rela$ based network services is used for this

interface.

Gnbetween two GS1s within the same P2"1. The Gn provides a data

and si&nallin& interface in the !ntra-P2"1 backbone. The GPRSTunnellin& Protocol +GTP, is used in the Gn +and in the Gp, interface

over the !P based backbone network.

Gpbetween two GS1s in various P2"1s. The Gp interface provides thesame functionalit$ as the Gn interface but it also provides to&ether with

the #G and the %irewall all the functions needed for inter-P2"1

networkin& that is securit$ routin& etc.

Grbetween an SGS1 and the 42R. The Gr &ives the SGS1 access to

subscriber information in the 42R. The 42R can be located in a

different P2"1 than the SGS1 +"AP,.

Gabetween the GS1s and the /G inside the same P2"1. The Ga

provides a data and si&nallin& interface. This interface is used forsendin& the char&in& data records &enerated b$ GS1s to the /G. The

protocol used is GTP; an enhanced version of GTP.

Gsbetween a SGS1 and a "S/. The SGS1 can send location data to the

"S/ or receive pa&in& re(uests from the "S/ via this optional

interface. The Gs interface will &reatl$ improve the effectiveness of the

radio and network resources in the combined GS"5GPRS network. Thisinterface uses #SSAP@ protocol.

Gdbetween the S"S-G"S/ and an SGS1 and between S"S-!W"S/

and an SGS1. The Gd interface is available for more efficient use of the

S"S services +"AP,.

Gfbetween an SGS1 and the 3!R. The Gf &ives the SGS1 access to

GPRS user e(uipment information. The 3!R maintains three different

lists of mobile e(uipment) black listfor stolen mobilesgrey listformobiles under observation and white listfor other mobiles +"AP,.

Gcbetween the GGS1 and the 42R. The GGS1 ma$ re(uest the

location of an "S via this optionalinterface. The interface can be used ifthe GGS1 needs to forward packets to an "S that is not active.

There are two different reference pointsin the GPRS network. The Gi is

GPRS specific but the R is common with the circuit switched GS" network)

Gibetween a GGS1 and an external network. The GPRS network isconnected to an external data networks via this interface. The GPRS

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s$stem will support a variet$ of data networks. #ecause of that the Gi is

not a standard interface but merel$ a reference point.

Rbetween terminal e(uipment and mobile termination. This reference

point connects terminal e(uipment to mobile termination thus allowin&for example a laptop-P/ to transmit data over the GS"-phone. The

ph$sical R interface follows for example the !T8-T 6.756.7 or theP/"/!A P/-/ard standards.

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& Transfer of 'ac#ets (et"een GS!s

8ser data packets are sent over the GPRS backbone in ;containers;. When a

packet comin& from an external packet network arrives at the GGS1 it isinserted in a container and sent to the SGS1. The stream of containers inside

the GPRS backbone network is totall$ transparent to the user) To the user itseems like he5she is connected directl$ via a router +the GGS1, to external

networks. !n data communications this t$pe of virtual stream of containers is

called a tunnel. We sa$ that the GS1s are performin& tunnellin& of user

packets see %i&ure


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0ser 'ac#etTunnel ID:

I4SI5

T67 GTP PAC+7TIP 8TCP90DP2

/ho is the user

To "hich GS!

GS! IP;

address

7.g. a TCP9IP 'ac#etcarrying e;mail

7iure B* G$P cotaier

%rom the point of view of the user and the external network the GTP packetsthat contain the user packets could be transferred between the GS1s usin& an$

technolo&$ for example AT" C.7


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GGS1

GTP

IP IP

IP backbone data using private IP addresses

SGS1"S

IP

GTPTunnel

user data using 'public' IP addresses

7iure C* $ras!er o! ackets &etwee the GGSN a" the ;S

$S S9

SGS!

GGS!

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!ote

%or additional information on the GPRS transmission protocols see the

Appendix D GPRS transmission plane protocols.

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5 Roaming

4ere we will look at how GPRS functions when a subscriber is roamin& in

another network. #efore an$ roamin& can take place roamin& a&reements needto be si&ned between various operators. 2et us start with an example)

The diplomat boards a plane in Helsinki and departs for Singapore. After a

relaing !!"hour flight she arri#es the net morning in Singapore. At the

airport$ she immediately switches on her %P&S 'S.

SGS!SGS!

%&assyItraet

Siaore

GPRSack&oe

.O;Oerator

GPRS

G

G

*GPRS8NS

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ack&oe

D!SD!S

GGSN

GS;OPRA$OR, 7i#a"

6isite" Oerator, Siaore

8NS.O;

1

%

%i&ure E. Roamin& case steps ' 7 and

!. The diplomat chooses to use her home network access point$ because she

wants to securely access her e"mail.

7. The "S sends the P0P context activation re(uest to the SGS1. An

important piece of information is the access point name +AP1, which in

this case isembassy.fi.This is shown in %i&ure E. The Sin&apore

operatorFs SGS1 checks with the Gbase if an AP1 like the one "S

re(uested is permitted in the userFs subscription. !n this caseever$thin& is ?.

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. 1ow the Sin&apore SGS1 needs to send the context activation creation

re(uest to the GS"?P3RA?T?R.%! GGS1. The GGS1 is somewherein %inland and the Sin&apore SGS1 does not know the GGS1 !P address.

So it sends a (uer$ to the local 01S in the Sin&apore operatorFs networkaskin& the (uestion ;What is the !P address of embass$.fi.;H

SGSN

4%&assyItraet

Si(a)oreGPRS

3ack&oe

.O;4O)erator

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3G

3G

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D!S

.GPRS

D!S

IterDP2;NGPRS

3ack&oe

D!SD!S

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6isite" O)erator, Si(a)ore

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&

*

%i&ure '=. Roamin& case step and e


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A&&re-iatios

!ppendi" # GPR$ transmission plane protocols

%. &vervie' of protocols used in GPR$

A GPRS network introduces man$ new protocols desi&ned to conve$ user data

in a reliable and secure wa$. !nformation is passed between the existin& GS"

network and the GPRS network b$ emplo$in& protocols on two separate planes)

Transmission plane protocols are used for the transmission of user data

and control functions.

$ignalling plane protocols are used to conve$ si&nallin& informationthat controls and supports the transmission plane functions.

The transmission plane protocols conve$ user data in the form of !P data&ramsfrom the mobile station to external networks such as the !nternet or corporate

data networks.The si&nallin& plane contains man$ protocols that are alread$ emplo$ed in

existin& GS" network elements.

%.% GPR$ transmission plane protocols

%i&ure '. Transmission plane protocols

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%.( Transmission protocols in t)e Um interface

%.(.% P)ysical layer

The ph$sical la$er can be divided into the Radio *re+uency ,R*-la$er and the

P)ysical inkla$er.

The Radio *re+uency ,R*-is the normal GS" ph$sical radio la$er. Amon&

other thin&s the R% la$er specifies)

the carrier fre(uenc$ characteristics and GS" radio channel structures

the radio modulation scheme used for the data

the radio transmitter and receiver characteristics as well as performance

re(uirements.

The GS" R% ph$sical la$er is used for GPRS with the possibilit$ for future

modifications.

The P)ysical inkla$er supports multiple "Ss sharin& a sin&le ph$sical

channel and provides communication between the "Ss and the network.

1etwork controlled handovers are not used in the GPRS service. !nstead

routin& area updates and cell updates are used.

The Ph$sical 2ink la$er is responsible for)

%orward 3rror /orrection +%3/, codin& allowin& the detection andcorrection of transmitted code words and the indication of incorrectable

code words

the interleavin& of one R2/ Radio #lock over four bursts in consecutive

T0"A frames.

%.(.( /edium !ccess 0ontrol ,/!0-

The "edium Access /ontrol +"A/, protocol handles the channel allocationand the multiplexin& that is the use of ph$sical la$er functions. The R2/ and

the "A/ to&ether form the ?S! 2a$er 7 protocol for the 8m interface.

The GPRS "A/ function is responsible for)

Providin& efficient multiplexin& of data and control si&nallin& on both

the uplink and downlink. This process is controlled b$ the network. ?n

the downlink multiplexin& is controlled b$ a schedulin& mechanism. ?n

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A&&re-iatios

the uplink multiplexin& is controlled b$ medium allocation to individual

users +for example in response to a service re(uest,.

"obile ori&inated channel access contention resolution between channel

access attempts includin& collision detection and recover$.

"obile terminated channel access schedulin& of access attempts

includin& (ueuin& of packet accesses.

Priorit$ handlin&.

%.(.1 T)e Radio ink 0ontrol ,R0-

The Radio 2ink /ontrol +R2/, protocol offers a reliable radio link to the upper

la$ers. Two modes of operation of the R2/ la$er are defined for information

transfer) unacknowled&ed and acknowled&ed. The R2/ la$er can support both

modes simultaneousl$.

The R2/ function is responsible for)

Providin& transfer of 2o&ical 2ink /ontrol la$er P08s +22/-P08,

between the 22/ la$er and the "A/ function.

Se&mentation and reassembl$ of 22/-P08s into R2/ 0ata #locks. See

%i&ure 7.

#ackward 3rror /orrection +#3/, procedures enablin& the selective

retransmission of uncorrectable code words. This process is &enerall$

known as Automatic Re(uest for Retransmission +AR*,.

2ote

The #lock /heck Se(uence for error detection is provided b$ the Ph$sical 2inkla$er.

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I!or%atio 7ie#"7. 79S

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7ie#". 9SI!or%atio

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ayer

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. E #ock .ea"er

9S E #ock 9heck Se/uece (he S899. co"i is use", 9S correso"s to the 7ire co"e)

%i&ure 7. Se&mentation of 22/-P08s into R2/ data blocks

%.(.3 ogical ink 0ontrol ,0-

The 2o&ical 2ink /ontrol +22/, la$er offers a secure and reliable lo&ical linkbetween the "S and the SGS1 for upper la$er protocols and is independent of

the lower la$ers.

The 22/ conve$s si&nallin& S"S and Subnetwork 0ependent /onver&ence

Protocol +S10/P, packets. S10/P exists between the "S and the SGS1 and

provides a mappin& and compression function between the network la$er +!P or

C.7< packets, and the lower la$ers. !t also performs se&mentation reassembl$and multiplexin&.

Two modes of operation of the 22/ la$er are defined for information transfer)

unackno'ledged and ackno'ledged. The 22/ la$er can support both modessimultaneousl$.

!n ackno'ledged mode the receipt of 22/-P08s is confirmed. The 22/la$er retransmits 22/-P08s if confirmation has not been received within a

certain timeout period.

!n unackno'ledged mode there is no confirmation re(uired for 228-P08s.

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Si&nallin& and S"S is transferred in unacknowled&ed mode.

!n unacknowled&ed mode the 22/ la$er offers he followin& two options)

Transport of 4protected4information means that if errors occur within

the 22/ information field the frame will be discarded.

Transport of 4unprotected4information means that if errors occurwithin the 22/ information field the frame will not be discarded.

The 22/ la$er supports several different *oS dela$ classes with differenttransfer dela$ characteristics.

The Packet 0ontrol Unit ,P0U- in t)e $0is responsible for the followin&

GPRS "A/ and R2/ la$er functions)

22/ la$er P08 se&mentation into R2/ blocks for downlink

transmission. 22/ la$er P08 reassembl$ from R2/ blocks for uplink transmission.

P0/4 schedulin& functions for the uplink and downlink data transfers.

P0/4 uplink AR* functions includin& R2/ block ack5nak.

P0/4 downlink AR* function includin& bufferin& and retransmissionof R2/ blocks.

/hannel access control functions for example access re(uests and&rants.

Radio channel mana&ement functions for example power control

con&estion control broadcast control information etc.

The 0)annel 0oding Unit ,00U- in t)e T$provides the followin&

functions)

The channel codin& functions +/S-' and /S-7, includin& %3/ and

interleavin&.

Radio channel measurement functions includin& received (ualit$ level

received si&nal level and information related to timin& advance

measurements.

The network la$er protocols for si&nallin& S"S and user data are multiplexed

to the lower la$ers in the followin& wa$ +see %i&ure ,)

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2$!PIis the 1etwork la$er Service Access Point !dentifier which is

used to identif$ the P0P context at the S10/P level.

$!PIis the Service Access Point !dentifier which is used to identif$ thepoints where the 22/ provides a service to a hi&her la$er. SAP!s have

different priorities.

TIis the Temporar$ 2o&ical 2ink !dentit$ which unambi&uousl$

identifies the lo&ical link between the "S and SGS1. T22! is used foraddressin& at the 22/ la$er.

%i&ure . "ultiplexin& of network protocols

22/ provides the services necessar$ to maintain a ciphered data link between

an "S and an SGS1. The 22/ la$er does not support direct communication

between two "Ss.

The 22/ connection is maintained as the "S moves between cells served b$the same SGS1. When the "S moves to a cell bein& served b$ a different

SGS1 the existin& connection is released and a new lo&ical connection isestablished with the new SGS1.

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A&&re-iatios

22/ is independent of the underl$in& radio interface protocols. !n order to

allow 22/ to operate with a variet$ of different radio interface protocols and

to ensure optimum performance it ma$ be necessar$ to ad>ust for example the

maximum 22/ P08 len&th and the 22/ protocol timer values. Such

ad>ustments can be made throu&h ne&otiation between the "S and the SGS1.The maximum len&th of an 22/ P08 shall not be &reater than 'B== octets

minus the #SSGP protocol control information.

The 2o&ical 2ink /ontrol la$er supports)

Service primitives allowin& the transfer of S10/P Protocol 0ata 8nits

+S1-P08s, between the Subnetwork 0ependent /onver&ence la$er and

the 2o&ical 2ink /ontrol la$er

Procedures for transferrin& 22-P08s between the "S and SGS1

includin&)

Procedures for unacknowled&ed point-to-point deliver$ of

22-P08s between the "S and the SGS1

Procedures for acknowled&ed reliable point-to-point deliver$ of

22-P08s between the "S and SGS1

Procedures for point-to-multipoint deliver$ of 22-P08s from the

SGS1 to the "S

Procedures for detectin& and recoverin& from lost or corrupted 22-P08s

Procedures for flow control of 22-P08s between the "S and the SGS1

Procedures for cipherin& of 22-P08s. The procedures are applicable to

both unacknowled&ed and acknowled&ed 22-P08 deliver$.

The 2o&ical 2ink /ontrol la$er functions are or&anised so that cipherin&resides immediatel$ above the R2/5"A/ la$er in the "S and immediatel$

above the #SSGP la$er in the SGS1.

A lo&ical communication pipe is established between the GGS1 and the "S

throu&h a SGS1. The 22/ protocol link is established between the "S and the

SGS1 upon GPRS attach. The GPRS Tunnellin& Protocol +GTP, establishes a

tunnel between the SGS1 and the GGS1 at P0P context activation. !n the 22/header the 1SAP! +1etwork la$er Service Access Point !dentifier, identifies

which application inside the "S the packet belon&s to.

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%.(.5 $20P ,$ubnet'ork ependent 0onvergence Protocol-

1etwork la$er protocols are intended to be capable of operatin& over a wide

variet$ of subnetworks and data links. GPRS supports several network la$erprotocols providin& protocol transparenc$ for the users of the service.

To enable the introduction of new network la$er protocols to be transferredover GPRS without an$ chan&es to GPRS all functions related to the transfer

of 1etwork la$er Protocol 0ata 8nits +1-P08s, are carried out in a transparent

wa$ b$ the GPRS network. This is one of the re(uirements of S10/P.

Another re(uirement of the S10/P is to provide functions that help to improve

channel efficienc$. This is achieved b$ means of compression techni(ues.

The set of protocol entities above the S10/P consists of commonl$ used

network protocols. The$ all use the same S10/P entit$ which then performs

multiplexin& of data comin& from different sources to be transferred usin& the

service provided b$ the 22/ la$er. The 1etwork Service Access Point!dentifier +1SAP!, is an index to the P0P context of the P0P that is usin& the

services provided b$ the S10/P +see %i&ure ,. ?ne P0P ma$ have several

P0P contexts and 1SAP!s.

3ach active 1SAP! uses the services provided b$ the Service Access Point

!dentifier +SAP!, in the 22/ la$er. "ore than one 1SAP!s ma$ be associatedwith the same SAP!.

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A&&re-iatios

7iure 4* SN9P use" to %u#ti#e0 "i!!eret rotoco#s

1.% Transmission 'rotocols in the G( interface

The Gb interface allows man$ users to be multiplexed over the same ph$sical

link usin& %rame Rela$ +%R,. #andwidth is allocated to a user upon activit$

+when data is sent or received, and is reallocated immediatel$ thereafter. This

is in contrast to the A-interface where a sin&le user has the exclusive use of a

dedicated ph$sical resource throu&hout the lifetime of a call irrespective ofactivit$.

GPRS si&nallin& and user data are sent in the same transmission plane and

therefore no separate dedicated ph$sical resources are re(uired to be allocated

for si&nallin& purposes.

0ata rates over the %rame Rela$ Gb interface ma$ var$ for each user without

restriction from 9ero data to the maximum possible line rate +for example

'E kbit5s which is the maximum available bit rate of a 7 "bit5s +3', link,.

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1.%.1 Physical -ayer Protocol

Several ph$sical la$er confi&urations and protocols are possible at the Gb

interface and the ph$sical resources are allocated b$ ?peration I "aintenance+?I", procedures. 1ormall$ a G:=5:= 7"bit5s connection is provided.

1.%. !et"or# Ser3ices layer

The Gb interface 1etwork Services la$er is based on *rame Relay. %rame

Rela$ virtual circuits are established between the SGS1 and #SS. 22/ P08sfrom man$ users are statisticall$ multiplexed onto these virtual circuits. These

virtual circuits ma$ traverse a network of %rame Rela$ switchin& nodes or ma$

>ust be provided on a point to point link between the #S/ and the SGS1 +if the

#S/ and SGS1 are co-located,. %rame Rela$ is used for si&nallin& and data

transmission over the Gb interface.The followin& characteristics appl$ for the %rame Rela$ connection)

The maximum %rame Rela$ information field si9e is 'B== octets.

The %rame Rela$ address len&th is two octets.

%rame Rela$ Permanent 6irtual /ircuits +P6/, are used.

The %rame Rela$ la$er offers detection of errors but no recover$ from

errors.

?ne or more %rame Rela$ P6/s are used between an SGS1 and a #SS

to transport #SSGP P08s.

1.%.% ,ase Station System GPRS Protocol ,SSGP2

The ase $tation $ystem GPR$ Protocol ,$$GP-transfers control and

si&nallin& information and user data between a #SS and the SGS1 over the Gb

interface.

The primar$ function of #SSGP is to provide *ualit$ of Service +*oS, and

routin& information that is re(uired to transmit user data between a #SS and an

SGS1.

A secondar$ function is to enable two ph$sicall$ distinct nodes the SGS1 and

#SS to operate node mana&ement control functions.There is a one-to-one relationship between the #SSGP protocol in the SGS1

and in the #SS. !f one SGS1 handles multiple #SSs the SGS1 has to have one#SSGP protocol device for each #SS.

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A&&re-iatios

The main functions for the #SSGP protocol are to)

provide a connectionless link between the SGS1 and the #SS

transfer data in an unconfirmed wa$ between the SGS1 and the #SS

provide for bi-directional control of the data flow between the SGS1 and

the #SS

handle pa&in& re(uests from the SGS1 to the #SS

&ive support for deletin& old messa&es in the #SS for example when an

"S chan&es #SSs

support multiple la$er 7 links between the SGS1 and the #SS.

1.& Transmission 'rotocols in the Gn interface

The Gn interface forms the GPRS backbone network.

1.&.1 -ayer 1 and layer

The % and the ( protocols are vendor dependent ?S! la$er ' and 7 protocols

that carr$ the !P data&rams for the GPRS backbone network between the SGS1

and the GGS1.

1.&. Internet Protocol IP2

TheInternet Protocol ,IP- data&ram in the Gn interface is only used in t)eGPR$ backbone net'ork. The GPRS backbone +core, network and the GPRS

subscribers use different !P addresses. This makes the GPRS backbone !P

network invisible to the subscribers and vice versa. The GPRS backbone

network carries the subscriber !P or C.7< traffic in a secure GPRS tunnel.

All data from the mobile subscribers or external networks is tunnelled in the

GPRS backbone.

1.&.% TCP or 0DP

T0P or UPare used to carr$ the GPRS Tunnellin& Protocol +GTP, P08sacross the GPRS backbone network. T/P is used for user C.7< data and 80P is

used for user !P data and si&nallin& in the Gn interface.

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1.&.& GPRS Tunnelling Protocol GTP2

The GPR$ Tunnelling Protocol ,GTP-allows multi-protocol packets to be

tunnelled throu&h the GPRS backbone between GPRS Support 1odes +GS1s,.This is illustrated in %i&ure


41/48

A&&re-iatios

7iure * GPRS $ue##i Protoco# rici#e

1.&.&.1 Signalling 'lane

!n the si&nallin& plane the GTP specifies a tunnel control and mana&ement

protocol which allows the SGS1 to provide GPRS network access for an "S.The si&nallin& plane also handles path mana&ement and location mana&ement.

Si&nallin& is used to create modif$ and delete tunnels.

The GTP si&nallin& flow is lo&icall$ associated with but separate from the

GTP tunnels. %or each GS1-GS1 pair one or more paths exist and one or more

tunnels ma$ use each path.

1.&.&. Transmission 'lane

!n the transmission plane the tunnel created b$ the si&nallin& plane is used to

carr$ user data packets between network elements connected to the GPRSbackbone network such as the SGS1s and GGS1s. 1o other s$stems need to

be aware of GTP for example the "Ss are connected to a SGS1 without bein&

aware of GTP.

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:8P.ea"er:8P

.ea"er

G$P.ea"erG$P

.ea"er

user IP 8ata

GPRSack&oe IP

.ea"er

GPRSack&oe IP

.ea"er

:ser 8ata Pay#oa" ($DP8:)(user IP 8ata)

:ser 8ata Pay#oa" ($DP8:)(user IP 8ata)

G$P.ea"erG$P

.ea"er

:ser 8ata Pay#oa" ($DP8:)(user IP 8atara%)


:8P.ea"er:8P

.ea"er

G$P.ea"erG$P

.ea"er



:8P ayer

G$P ayer

ack&oeIP ayer

7iure C* $he G$P rotoco# hea"er &ei a""e" to user "ata

A GTP tunnel is defined b$ two associated P0P contexts in different GS1nodes and is identified b$ a Tunnel !0 +T!0,. A GTP tunnel is necessar$ for

forwardin& packets between an external packet data network and an "S. The

Tunnel !0 identifies the "" and P0P contexts +"" /ontext !0 and a

1SAP!,.

The 1SAP! +1etwork Service Access Point !dentifier, is a fixed value between

= and '< that identifies a certain P0P context. !t identifies a P0P contextbelon&in& to a specific "" context !0.

1.&.* The GTP header

The GTP header contains 'B octets and is used for all GTP messa&es.

The information contained in the GTP header includes the followin&)

The t$pe of GTP messa&e +si&nallin& messa&es J '-


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A&&re-iatios

An 22/ frame number that is used for the !nter SGS1 Routin& 8pdate

procedure to co-ordinate the data transmission on the link la$er between

the "S and the SGS1.

A T!0 +Tunnel !dentifier, that points out "" and P0P contexts.The content of the GTP header differs dependin& on whether the header is used

for si&nallin& messa&es or user data +T-P08s,.

1.&.6 Tunnel ID TID2 format

The Tunnel !dentifier +T!0, consists of the followin&)

"obile /ountr$ /ode +"//,

"obile 1etwork /ode +"1/,

"obile Subscriber !dentification 1umber +"S!1, 1etwork Service Access Point !dentifier +1SAP!,

These represent the "" and P0P contexts.

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References

1okia 0C7== SGS1 Product 0escription

1okia GPRS /har&in& Gatewa$ Product 0escription

1okia G17 e


45/48

A&&re-iatios

A((re3iations

Ao// Advice of /har&e - /har&in&

Ao/! Advice of /har&e - !nformation

AP Access Point

AT" As$nchronous Transfer "ode

Au/ Authentication /entre

#//4 #roadcast /ontrol /hannel

#G #order Gatewa$

#G!WP #arrin& of GPRS !nterworkin& Profile+s,

#GP #order Gatewa$ Protocol

#S/ #ase Station /ontroller

#SS #ase Station Subs$stem

#SSAP #SS Application Part

#SSGP #SS GPRS Protocol

#SS"AP #SS "ana&ement Application Process

#TS #ase Transceiver Station

#TS" #TS "ana&ement

// /all /ontrol

//#S /ustomer /are and #illin& S$stem

//!TT /omitK /onsultatif !nternational TKlK&raphi(ue et

TKlKphoni(ue

/0R /all 0etail Record

/%1Rc /all %orwardin& on "obile Subscriber 1ot Reachable

/%8 /all %orwardin& 8nconditional

/G /har&in& Gatewa$

/G5A0 /G5Alarm 0ispatcher

/G5AR/ /G5Accountin& Record /ollection

/G5AR" /G5Accountin& Record "odification

/G5%T" /G5%ile Transfer "ana&er

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/21S /onnectionless 1etwork Service

/" /ommunication "ana&ement

/?1S /onnection-?riented 1etwork Service/8G /losed 8ser Group

0A"PS 0i&ital Advanced "obile Phone Service

0# 0atabase

0/S 0i&ital /ellular S$stem

04/P 0$namic 4ost /onfi&uration Protocol

01S 0omain 1ame S$stem

0RC 0iscontinuous Reception

0TAP 0irect Transfer Application Process30G3 3nhanced 0ata Rates for GS" 3volution

3!R 3(uipment !dentit$ Re&ister

3TS! 3uropean Telecommunications Standards !nstitute

3TS! 3uropean Telecommunications Standards !nstitute

%0"A %re(uenc$ 0ivision "ultiple Access

%TA" %ile Transfer Access and "ana&ement

%T"!0 Se(uential number of method instance

%TP %ile Transfer ProtocolG-/0R Gatewa$ GPRS Support 1ode-/all 0etail Record

GGS1 Gatewa$ GPRS Support 1ode

G"S/ Gatewa$ "S/

GPRS General Packet Radio Service

GS" Global S$stem for "obile /ommunications

GS1 GPRS Support 1ode

GTP GPRS Tunnellin& Protocol

GTPL GPRS Tunnel Protocol +enhanced,42R 4ome 2ocation Re&ister

4P2"1 4ome Public 2and "obile 1etwork

4S/S0 4i&h Speed /ircuit Switched 0ata

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A&&re-iatios

4T"2 4$per Text "arkup 2an&ua&e

4TTP 4$per Text Transfer Protocol

!/"P !nternet /ontrol "essa&e Protocol

!GRP !nterior Gatewa$ Routin& Protocol

!"3! !nternational "obile 3(uipment !dentit$

!"G! !nternational "obile Group !dentit$

!"S! !nternational "obile Subscriber !dentit$

!3T% !nternet 3n&ineerin& Task %orce

!P !nternet Protocol

!Pv !nternet Protocol version

!PvB !nternet Protocol version B

!S01 !nte&rated Services 0i&ital 1etwork

!T8 !nternational Telecommunication 8nion

!T8-T Telecommunication standardisation sector of !T8

2A 2ocation Area

2A1 2ocal Area 1etwork

2AP0 2ink Access Protocol for the 0 channel

2AP0m 2ink Access Protocol for the 0m channel

22/ 2o&ical 2ink /ontrol

"A/ "edium Access /ontrol

"AP "obile Application Part

"-/0R "obilit$ "ana&ement-/all 0etail Record

"3 "obile 3(uipment

"!#-!! "ana&ement !nformation #ase !!

"" "obilit$ "ana&ement

"o8 "emorandum of 8nderstandin&

"S "obile Station

"S/ "obile +services, Switchin& /entre

"T "obile Termination

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"TP "essa&e Transfer Part

1%S 1etwork %ile S$stem

1"S 1etwork "ana&ement Subs$stem1SAP! 1etwork la$er Service Access Point !dentifier

1SS 1etwork and Switchin& Subs$stem

?"/ ?perations and "aintenance /entre

?S! ?pen S$stem !nterconnection

?SP% ?pen Shortest Path %irst

?SS ?peration Subs$stem

PA//4 Packet Associated /ontrol /hannel

PA0 Packet Assembl$50isassembl$

Documents

PS GPRS Architecture