02_tm2110eu01tm_0003_gprs

GPRS - General Packet Radio Services Siemens

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Contents

1 GPRS Objectives and Advantages 3

1.1 GPRS Objectives and Advantages 4

1.2 Standardization 6

2 Basic Principles 9

2.1 Management of Radio Resources/ Coding Schemes 10

2.2 GPRS Subscriber Profile 12

2.3 Quality of Service (QoS) Profiles 14

3 GPRS-Architecture 19

3.1 GPRS Architecture 20

3.2 GSM Phase 2+, Interfaces 22

3.3 New Network Elements for GPRS 24

4 Logical Functions 31

4.1 Logical Functions in the GPRS Network 32

4.2 Allocation of Logical Functions 38

GPRS - General Packet Radio Services

Siemens GPRS - General Packet Radio Services

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1 GPRS Objectives and Advantages

Objectives & Standardization

GPRSGeneral Packet Radio Services

Fig. 1


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1.1 GPRS Objectives and Advantages

The transmission of data is becoming increasingly important in the field of telecom-munication. In the fixed network, the transmission of extensive data files and E-mailand contacts to the Intra- and Internet is by far in excess of language transmission.The need for mobile data transport is increasing at a similarly impressive rate, yet thepresently available mobile communication systems, even GSM, still present a num-ber of shortcomings.

Disadvantages for the user in GSM Phase 1/2:

In GSM (phase 1/2), the data rate is limited to a peak value of 9.6 kbit/s

Links to the data networks need to be routed via PSTN/ISDN (Additional charging ofthe user for using a transit network)

The user is billed for the connection duration instead of being billed for his/her actualuse of the network (data volume)

The set-up of a connection takes more time (ca. 20s if a modem is used)

The length of SMS is limited (160 alphanumerical characters)

Disadvantages for the provider in GMS Phase 1/2:

Inefficient resource management & the number of users is limited.

HSCSD (High Speed Circuit Switched Data)

In principle, transmission rates of up to 115.2 kbit/s can be achieved with HSCSD.Combining 4 timeslots, the ISDN transmission rate can be matched. One problem ofHSCSD, however, is the circuit switched data transmission. Efficient resource man-agement is impossible. Additional costs arise for the user. For this reason HSCSD isessentially suited for applications involving high but constant transmission rates(videotelephony).

GPRS (GENERAL PACKET RADIO SERVICES)

GPRS is, on the one hand, intended to provide the possibility of transmitting largevolumes of data in a very short time. On the other hand it is meant to ensure effectivemanagement of available resources, which will increase the number of users and re-duce the costs arising for the individual user (volume-oriented fees).

Another positive consequence of the introduction of GPRS is its direct access to theIntra- and Internet and the possibility to use point-to-point and point-to-multipointservices side by side. An important aspect is that GSM networks are prepared for theintroduction of UMTS.


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GPRS Objectives& Advantages

data rate restricted to max. 9,6 kbi t/s

GSM-PDN connections via PSTN/ISDN

time dependent charging

long durance for setups (Modems)

SMS length restr icted (160 character)

unefficient resource management

restricted number of user

Strong demand for mobile data transmissionGSM Phase1/2: multiple restrictions

PSTN

Modem

ISDN

Service provider

access pointBSS

SSS

IP

Modem

SMSC

SMS

PDNs

Intranet

Internet

PSPDN

BS-udi

BS-

3.1 kHz

audio

HSCSD:high data rates !

But: circuit switched

resource unefficient

time dependent charging !!

GPRS: high data rates reducing costs (volume dependent charging) resource efficient Point-to-Multipoint services for PMR market no SMS restrictions direct IP/X.25 connection prerequisite for UMTS introduction future proof solution

Fig. 2 Limitations of the network architecture


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1.2 Standardization

The introduction of GPRS into the GSM Recommendations is carried out in twophases.

Phase 1 of GPRS introduction was completed by ETSI in the Annual Release 1997(03/98) and includes all central GPRS functions.

Phase 1 supports:

Point-to-point transfer of user data

TCP/IP and X.25 bearer services

GPRS identities

GPRS safety (a new ciphering algorithm specially designed for packet data)

Support of volume-oriented billing

In Phase 2, further extensions are planned for all requirements to be met by GPRS:

Support of point-to multipoint (PTM) services

Support of special point-to-point and point-to-multipoint services for applications suchas traffic telematics and GSM-R (PTM-Group Call: PTM-Multicast)

Support of further additional services

Support of additional interworking functions (e.g. ISDN)

Phase 2 will be completed in 1998 or 1999.

GPRS Phase 1 includes the introduction of a number of new recommendations;some of the existing recommendations have been modified to cover other GPRSfunctions, too.

The following recommendations are of central importance:

Rec. 02.60 General GPRS Overview

Rec. 03.60 GPRS System and architecture description

Rec. 03.64 Radio architecture description


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GPRS-Standardisation

ETSI

GPRS Standardisation in 2 Phases

Rec. 02.60

General GPRS Overview

Rec. 03.60

GPRS system &

architecture description

Rec. 03.64

Radio architecture descriptionVery important:

PtP Data transmission

TCP/IP & X.25 Bearer Services

GPRS Identities

GPRS Security (Ciphering)

SMS via GPRS

volume dependent charging

Phase 1:

(Rel.`97)

PtM data transmission

Broadcast & Group Call traffic telematic, GSM-R

further interworking

functionality

further services

Phase 2:(Rel.`98/99)

Fig. 3 Standardization of GPRS in phases


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2 Basic Principles

Basics


Fig. 4


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2.1 Management of Radio Resources/ CodingSchemes

In a GPRS-supported cell , one or several physical channels can be allocated toGPRS transmission. These physical channels (Packet Data Channels PDCHs) areshared by GPRS mobile stations and are taken from the common/shared pool of allavailable physical channels of the cell.

Distribution of the physical channels for various logical packet data channels is basedon blocks of 4 normal bursts each. Uplink (UL) and downlink (DL) for GPRS packetdata are assigned separately (consideration of asymmetrical traffic peaks). Allocationof circuit switched services and GPRS is achieved dynamically, depending on whatcapacities are required (capacity on demand). PDCHs need not be allocated per-manently; however, it is possible for the operator to permanently or temporarily re-serve a number of physical channels for GPRS traffic.

New GPRS coding schemes (CS) - CS1 - CS4 - have been defined for the transmis-sion of packet data traffic channel PDTCH (Rec. 03.64). Coding schemes can be as-signed as a function of the quality of the radio interface. Normally, groups of 4 burstblocks each are coded together.

CS-1 makes use of the same coding scheme as has been specified for SDCCH inGSM Rec. 05.03. It consists of a half rate convolutional code for forward error correc-tion FEC. CS-1 corresponds to a data rate of 9.05 kbit/s.

CS-4 has no redundancy in transmission (no FEC) and corresponds to a data rate of21.4 kbit/s.

CS-2 and CS-3 represent punctured versions of the same half rate convolutionalcode as CS-1.

CS-2 corresponds to a rate of 13.4 kbit/s, while CS-3 corresponds to a data rate of15.6 kbit/s.

In principle, 1 to 8 time slots TS of a TDMA frame can be combined dynamically for auser for the transmission of GPRS packet data. Theoretically it is thus possible toachieve peak performances of up to 171.2 kbit/s (8x21.4 kbit/s) with GPRS.


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9,05 kbit/s

13,4 kbit/s

15,6 kbit/s

21,4 kbit/s

CS-1

CS-2

CS-3

CS-4

Coding

Schemes

different

redundancy (FEC)

Um transmission quality

Radio Resource Management / Coding Schemes

CS & PS (GPRS):

capacity on demand

Physical channel of one cell

GPRS-MSs:

sharing physical channel

GPRS-MSs:

combining 1-8 TS

Up to

171,2 kbit/s(theoretically)

1 - 8

channel

GPRS-MSs:

asymmetric UL / DL

Fig. 5 Management of radio resources: coding schemes, FEC, and redundancy


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2.2 GPRS Subscriber Profile

The GPRS Subscriber Profile is the description of the services a subscriber is al-lowed to use. Essentially, it contains the description of the packet data protocol used.A subscriber may also use different packet data protocols (PDPs), or one PDP withdifferent addresses. The following parameters are available for each PDP:

The packet network address is necessary to identify the subscriber in the publicdata net. Either dynamically assigned (temporary) addresses or (in the future) staticaddresses are used in case of IP. The problem of the dynamic addresses will beovercome with the change from Ipv4 to IPv6. In GPRS is two layer 2 protocols areallowed, X.25 or IP.

The quality of service QoS: QoS describes various parameters. The subscriberprofile defines the highest values of the QoS parameters that can be used by thesubscriber.

The screening profile: This profile depends on the PDP used and on the capacity ofthe GPRS nodes. It serves to restrict acceptance during transmission/reception ofpacket data. For example, a subscriber can be restricted with respect to his possiblelocation, or with respect to certain specific applications.

The GGSN address: The GGSN address indicates which GGSN is used by the sub-scriber. In this way the point of access to external packet data networks PDN is de-fined. The internal routing of the data is done by IP protocol, the GSNs will have IPaddresses. A DNS function is needed to find the destination of the data packets (ad-

dress translating: e.g. www.gsn-xxx.com 129.64.39.123)


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GPRS Subscriber Profile

Subscription profile

used Packet Data Protocols PDP

possible: 1 Subscriber - different PDPs / 1 PDP with different addresses

PDPParameter

Packet

network addressstatic/dynamic

IP address

QoS

Quality of Servicehighest QoS-

parameter values inSubscriber Profile

Screening

Profilelimits receiving / emission

of data packets

GGSN addressAccess to external PDN

Fig. 6 Part of the GPRS subscriber profile are the PDPs and their parameters


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2.3 Quality of Service (QoS) Profiles

The different applications that will make use of packet-oriented data transmission viaGPRS require different qualities of transmission. GPRS can meet these different re-quirements because it can vary the quality of service (QoS) over a wide range of at-tributes. The quality of service profile (Rec. 02.60, 03.60) permits selection of the fol-lowing attributes:

Precedence class

Delay class

Reliability class

Peak throughput class

Mean throughput class.

By combining the variation possibilities of the individual attributes a large number ofQoS profiles can be achieved. Only a limited proportion of the possible QoS profilesneed PLMN-specific support.

Precedence Class

Three different classes have been defined to allow assessment of the importance ofthe data packets, in case of limited resources or overload:

1: High precedence

2: Normal precedence

3: Low precedence

Delay Class

GSM Rec.02.60 defines 4 delay classes (1 to 4). However, a PLMN only needs to re-alize part of these. The minimum requirement is the support of the so-called besteffort delay class (Class 4). Delay requirements (maximum delay) concern the delayof transported data through the entire GPRS network (the first two columns refer todata packets 128 bytes in length, while the last two columns apply to packets 1024bytes in length).

Delay Class mean transferdelay (sec)

95% delay(sec)

mean transferdelay (sec)

95% delay(sec)

1 < 0,5 < 1,5 < 2 < 7

2 < 5 < 25 < 15 < 75

3 < 50 < 250 < 75 < 375

4 (Best Effort) unspecified unspecified unspecified unspecified


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Quality of Service QoS - Profile

Different requirements for different applications multiple GPRS QoS profiles

precedence class

delay class

reliability class

Peak

throughputclass

mean throughput

class

PLMN must support onlylimited QoS service profile

Fig. 7 Quality of service parameters


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Reliability Class

Transmission reliability is defined with respect to the probability of data loss, data de-livery beyond/outside the sequence, twofold data delivery, and data falsification(probabilities 10-2 to 10-9):. 5 reliability classes (1 to 5) have been defined, 1 guaran-teeing the highest and 5 the lowest degree of reliability. Highest reliability (Class 1) isrequired for error-sensitive, non-real-time applications which have no possibility ofcompensating for data loss; lowest reliability (Class 5) is needed for real-time appli-cations which can get over data loss.

Peak Throughput Class

The peak throughput class defines the maximum data rate to be expected (inbytes/s). However, there is no guarantee that this data rate/throughput can beachieved over a certain period of time. This depends on the capacity of the MS andthe availability of radio resources. 9 throughput classes have been defined, rangingfrom Class 1 with 1000 bytes/s (8 kbit/s) to 256,000 bytes (2048 kbit/s). The maxi-mum data rate doubles from one class to the next.

Mean Throughput Class

The mean throughput class represents the mean data rate /throughput to be ex-pected for data transport via the GPRS network during an activated link. A total of 19classes have been defined. Class 1 is best effort and means that the data rate forthe MS is made available on the basis of demand and availability of resources.

Class 2 stands for 100 bytes/h (0.22 bit/s), class 3 for 200 bytes/h, class 4 for 500bytes/h and class 5 for 1000 bytes/h, etc. till Class 19 which stands for 50000000bytes/h (111 kbit/s).


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Quality of Service QoS - Profile

Precedence Class1: high priority

2: normal priority

3: low priority Delay Class mean transferdelay (sec)

95% delay(sec)

mean transferdelay (sec)

95% delay(sec)

1 < 0,5 < 1,5 < 2 < 72 < 5 < 25 < 15 < 75

3 < 50 < 250 < 75 < 3754 (Best Effort) unspecified unspecified unspecified unspecified

Delay Class

SDU size: 128 Byte 1024 Byte

minimum

requirements

Reliability Class1 - 5 (lowest):

data loss probability

out of sequence probability

dup licate probability

corrupt da ta probability

probabilities 10-9 - 10-2

peak throughput Class1 - 9: > 8 kbit /s - >2048 kbit/s

maximum data rate

no guarantee for this data rates

over a longer period o f time

mean throughput Classmedium, guaranteed da ta rate; Class 1 - 19 :

1: best effort

100 Byte/h (0,22 bi t/s) / 200 / 500 / 1000 / ... /

50 Mio. Byte /h (111 kbit/s)

Fig. 8 QoS is an assumption of several parameters which are defined in the recommendations


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3 GPRS-Architecture

Architecture


Fig. 9


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3.1 GPRS Architecture

For introducing GPRS, the logical GSM architecture is extended by two functionalunits:

The Serving GPRS Support Node SGSN is on the same hierarchic level as MSCand has functions comparable to those of a Visited MSC (VMSC).

The Gateway GPRS Support Node GGSN has functions comparable with those of aGateway MSC (GMSC) and offers interworking functions for establishing contactbetween the GSM/GPRS-PLMN and external packet data networks PDN

A GPRS Support Node GSN includes the central functions required to support theGPRS. One PLMN can contain one or more GSNs.

In addition to GSN, extensions of functions in other GSM functional units are neces-sary:

In the BSS a Packet Control Unit PCU ensures the reception/adaptation of packetdata from SGSN into BSS and vice versa.

GPRS subscriber data are added to the HLR. On the following pages of this scriptthis extension will be termed GPRS Register GR.


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Channel Codec Unit CCUin BTS

for channel coding

Mobile

DTE

SGSNServing GPRSSupport Node

PSTN

Internet

Intranet

X.25

GGSNGateway GPRSSupport Node

VMSC /

VLRGMSC

HLR

New network entities:

SGSN(access to BSS)

GGSN

(access to PDN)

GPRS - Architecture

ISDNPCU

BSS

GPRS subscription data

(GPRS Register GR)

Packet Control Unit PCUfor

protocol conversion &

radio resourcemanagement

Fig. 10 Outline of the GPRS architecture


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3.2 GSM Phase 2+, Interfaces

Integration of functions GGSN and SGSN (which are necessary for GPRS) into aGSM-PLMN makes it necessary to provide names for a series of new interfaces inaddition to interfaces A-G already defined in the GSM-PLMN:

Gb - between an SGSN and a BSS; Gb allows the exchange of signaling and userdata: Unlike the A-interface, in which a user is assigned a certain physical resourcefor the entire/full duration of a connection, on Gb a resource is only assigned in caseof activity (i. e. when data are being transmitted/received). A large number of sub-scribers use the same physical resources. The same holds for interfaces Gi, Gn andGp.

Gc - between a GGSN and an HLR

Gd - between an SMS-GMSC / SMS-IWMSC and an SGSN

Gf - between an SGSN and an EIR

Gi - between GPRS and an external packet data network PDN

Gn - between two GPRS support nodes GSN within the same PLMN

Gp - between two GSN located in different PLMNs. The Gp interface allows the sup-porting of GPRS services over an area of cooperating GPRS PLMNs.

Gr - between an SGSN and an HLR

Gs - between an SGSN and an MSC/VLR; serves to support an MS using bothGPRS and circuit switched services (e.g. update of location information).


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PSTN

X.25

GSM Phase 2+ Architecture:

Interfaces, Network Elements

ISDN

IP

IWF/TC: Interworking Function / Transcoder

IWF/

TC

A

Gb

Iu(PS)Gi

GMSC

GGSN

GSM Phase 2+

Core Network

MSC

SGSN

HLR/ACEIRCSE

Iu(CS)

A

Gn

TRAU

B

S

C

BTS

BTS

Abis

UE(USIM)

Uu

Um

MS(SIM)

E

E Gd

GSM BSS

Asub

GsGr Gc

UMTS

Terrestrial

Radio

Access

Network

Gf

VLR

SLR

SMS-GMSC

SMS-IWMSC

Fig. 11 Common GSM/GPRS/UMTS core network, coexistence of two radio access networks (GSM BSS/UTRAN)


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3.3 New Network Elements for GPRS

3.3.1 Serving GPRS Support Node (SGSN) Functions

SGSN realizes a large number of functions for performing GPRS services.

SGSN is on the same hierarchic level as an MSC and handles many functions com-parable to a Visited MSC (VMSC).

SGSN

is the node serving GPRS mobile stations in a region assigned to it;

traces the location of the respective GPRS MSs (Mobility Management functions);

is responsible for the paging of MS;

performs security functions and access control (authentication/cipher setting pro-cedures,...) Procedures are based on the same algorithm, ciphers and criteria asin the former GSM. Ciphering algorithms have been optimized for the transmissionof packet data;

has routing/traffic-management functions;

collects data connected with fees/charges;

realizes the interfaces to GGSN (Gn), PCU (Gb), other PLMNs (Gp), HLR (Gr),VLR (Gs), SMS-GMSC (Gd), EIR (Gf).

3.3.2 Gateway GPRS Support Node (GGSN) Functions

GGSN realizes functions comparable to those of a gateway MSC.

GGSN

is the node allowing contact/interworking between a GSM PLMN and a packetdata network PDN (realization Gi-interface);

contains the routing information for GPRS subscribers available in the PLMN.Routing information serves to contact the respective SGSN in the providing area ofwhich an MS is momentarily located;

has a screening function;

can inquire about location informations from the HLR via the optional Gc interface

transfers data/signaling to SGSN via Gn interface.


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GGSN

SGSN & GGSN

SGSN

Serving GPRS Support Node SGSN serves MSs in SGSN area

Mobility Management functions, e.g

Update Location, Attach, Paging,..

Security and access control:

Authentication, Cipher setting, IMEI Check...

New cipher algorithm

Routing / Traffic-Management

collecting charging data

realises Interfaces: Gn, Gb, Gd, Gp, Gr, Gs, Gf

controls subscribers in its service area (SLR)

Gateway GPRS Support Node SGSN Gi-,Gn-Interface: Interworking PLMN PDN

Routing Information for attached GPRS user

Screening / Filtering

collecting charging data

optional Gc interface

Fig. 12 Tasks of GGSN and SGSN


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3.3.3 Physical Realization SGSN/GGSN

SGSN and GGSN functions, respectively, can be located within the same physicalunit or at different locations in different physical units. SGSN and GGSN include theinternet protocol (IP) routing function and can be linked together/Interconnected withIP routers (IP-based GPRS backbone network for Gn). The same holds for the Gpinterface (SGSN and GGSN in different PLMNs); in addition there are safety func-tions for inter-PLMN communication.

HLR (GPRS Register GR)

HLR includes the GPRS subscriber information (GPRS Register GR) and routing in-formation. Access to HLR is possible from SGSN via Gr and from GGSN via Gc in-terface.


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SGSN & GGSN:physical location

External

IP Network

GGSN

SGSN

HLR (GR)

BSS PCU

GPRS-MS

MSC/VLR

BSS PCU

HLR: GPRS subscriber data

(GPRS Register GR) Routing information

Gb

Gb

Gi

GrGs

SGSN & GGSN

in samephysical entity

SGSN

GGSN

SGSN

GGSN

GGSN

BSS PCU

GPRS-MS

BSS PCU

External

X.25 Network

IP-based

Backbone

Network

Gn

Gp

Security functions

for Inte r-PLMN

communication

otherPLMN

SGSN & GGSN

in differentphysical entities /

location

External

IP Network

Fig. 13 Different physical locations of SGSN and GGSN


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3.3.4 Packet Control Unit PCU

In the BSS, the PCU serves

for the management of GPRS radio channels (Radio Channel Management func-tions), e.g. power control, congestion control, broadcast control information

for the temporal organization of the packet data transfer for uplink and downlink

it has channel access control functions, e.g. access request and grants

it serves for converting protocols from the Gb interface to the radio interface Um.

Three options for positioning the PCU are provided in Rec. 03.60:

Option A: In the BTS

Option B: in the BSC

Option C: In spatial connection with the SGSN

The different positions may be used due to the different solutions of the vendors andwith regard to the traffic which has to be handled by the PCU/BSS.

3.3.5 Channel Codec Unit CCU

The CCU contains the following functions:

Channel coding, including forward error correction FEC and interleaving

Radio channel measurements, including received quality and signal level, timing ad-vance measurements

3.3.6 GPRS Mobile Stations MS

A GPRS MS can work in three different operational modes. The operational modedepends on the service an MS is attached to (GPRS or GPRS and other GSM serv-ices) and on the mobile stations capacity of simultaneously handling GPRS andother GSM services.

Class A operational mode: The MS is attached to GPRS and other GMS servicesand the MS supports the simultaneous handling of GPRS and other GSM services.

Class B operational mode: The MS is attached to GPRS and other GMS services,but the MS cannot handle them simultaneously.

Class C operational mode: The MS is attached exclusively to GPRS services.

Note: Various GSM specifications use the terms GPRS Class-A MS, GPRS Class-BMS, GPRS Class-C MS.


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CCU

CCUPCU

BTS BSC site GSN site

CCU

CCU


CCU

CCU


PCU

PCU

A

B

C

optional:

PCU-locationPCU, CCU, GPRS - MS

Um Abis

Gb

GPRS-MS:(operational mode)

Class-A: MS attached to

GPRS & non-GPRS

simultaneous handling

Class-B: as A, not simultaneous

Class-C: GPRS only

MS

MS

MS

Packet Control Unit PCU Channel Access Control functions

Radio Channel Management functions

(Power Control, Congestion Contro l,...)

scheduling data transmission (UL/DL)

protocol conversion (Gb Um)

Gb

Channel Codec Unit CCU Channel Coding (FEC, Interleaving,..)

Radio Channel Measurement funcions

(received quality & signal level, TA,..)

Fig. 14 Positioning of the new network elements in the GSM BSS


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4 Logical Functions

Logical Functions


Fig. 15


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4.1 Logical Functions in the GPRS Network

The tasks required for the handling of processes in the GSM-/GPRS network arestructured into logical functions. These functions may contain a large number of indi-vidual functions. Logical functions are:

Network access control functions

Packet routing and transfer functions

Mobility management functions

Logical link management functions

Network management functions.

4.1.1 Network Access Control Functions

Network access means the way or manner in which a subscriber gains access to atelecommunication network to make use of the services this network provides. Anaccess protocol consists of a defined set of procedures which makes access to thenetwork possible. Network access can be obtained both from the MS and from thefixed network part of the GPRS network. Depending on the provider, the interface toexternal data networks can support various access protocols, e.g. IP or X.25. Thefollowing functions have been defined for access to the GPRS network:

Registration function: Registration stands for linking the identity of the mobile radiosubscriber to his packet data protocol (or protocols), the PLMN-internal addressesand the point of access of the user to external data Protocol (PDP) networks. Thislink can be static (HLR entry), or it can be effected on demand.

Authentication and authorization function: This function stands for the identifica-tion of the subscriber and for access legitimacy when a service is demanded. In addi-tion, the legitimacy of the use of this particular service is controlled. The authentica-tion function is carried out in conjunction with the mobility management functions.

Admission control function: Admission control is intended for determining the net-work resources required for performing the desired service (QoS). It also decideswhether these resources are available, and lastly it is used for reserving resources.Admission control is effected in conjunction with the radio resource managementfunctions to enable assessment of radio resources requirements in each individualcell.

Message screening function: A "screening" function is combined with the filtering ofunauthorized or undesirable information/messages. In the introduction stage ofGPRS a network-controlled screening function is supported. Subscription-controlledand user-controlled screening may be additionally provided at a later stage.

Packet terminal adaptation function: This function adapts data packets re-ceived/transmitted from/to the terminal equipment TE to a form suited for transportthrough the GPRS network.


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Charging data collection function: This function is used for collecting data requiredfor billing

Logical functionsin GPRS networks

Network Access

ControlFunctions

MobilityManagement

Functions

Radio ResourceManagement

Functions

Packet Routeing

& TransferFunctions

Logical LinkManagement

Functions

NetworkManagement

Functions

Fig. 16 Logical functions of the GPRS network


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4.1.2 Packet Routing and Transfer Functions

A route consists of an orderly list of nodes used for the transfer of messages withinand between the PLMNs. Each route consists of the node of origin, no node, one orseveral relay nodes, and the node of destination. Routing is the process of deter-mining and using the route for the transmission of a message within or betweenPLMNs.

Relay function: Transferring data received by a node from another node to the nextnode of the route.

*Routing function: Determining the transmission path for the next hop on the routetowards the GPRS support node (GSN) the message is intended for. Data transmis-sion between GSNs can be effected via external data networks possessing their ownrouting functions, e. g. X.25, Frame Relay or ATM networks.

Address translation and mapping function: Address translation means transformingone address into another, different address. It can be used to transform addresses ofexternal network protocols into internal network addresses (for routing purposes).Address mapping is used to copy a network address into another network address ofthe same type (e.g. for the routing and transmitting of messages from one networknode to the next).

Encapsulation function: Encapsulation means supplementing address- and controlinformation into one data unit for the routing of packets within or between PLMNs.The opposite process is called decapsulation. Encapsulation and decapsulation iseffected between the GSN of the GPRS-PLMN as well as between the SGSN andthe MS.

Tunneling Function: Tunneling means the transfer of encapsulated data units in thePLMN. A tunnel is a two-way point-to-point path, only the endpoints of which areidentified.

Compression function: for the optimal use of radio link capacity.

Ciphering function: preventing eavesdropping

Domain name server function: Decoding logical GSN names in GSN addresses. Thisfunction is a standard function of the internet.

4.1.3 Mobility Management Functions

Mobility management functions are used to enable tracing the actual location of amobile station in either the home-PLMN or a Visited-PLMN.


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Relay: forwarding data received from one

node to the next node in the route

Routeing: determining the route for transmission (next hop ) Address Translation / Mapping: conversion of one address to another

address of different type (extern intern / intern for next hop)

En- / Decapsulation: addition of address & control information to a

data unit for routeing & relaying of messages (GSN-GSN; SGSN MS) Tunneling: transfer of encapsulated data

Compressing: optimises radio path capacity

Ciphering: preserves user data confidentiality

Domain Name Server: resolves logical GSN names

to GSN addresses

Registration: associates users Mobile Id with users PDP(s) & address(es) within the PLMN & with users access point(s)

to external networks (static or dynamic association)

Authentication & Authorisation: check identity & demanded services

Admission Control: calculation of resources for demanded serviceavailability & reservation

Message Screening: filtering un-authorised messages

Packet Terminal Adaption: adapts data packets from / to TE

Charging Data Collection: collects data for charging

Network Access Control Functions

Packet Routeing & Transfer Functions

Fig. 17 Packet Routing and Transfer Functions in the GPRS network


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4.1.4 Logical Link Management Functions

Logical link management functions concern maintenance of a communication chan-nel between an MS and the PLMN via the radio interface Um. These functions in-clude the coordination of link state information between the MS and the PLMN andthe monitoring of data transfer activities via the logical link.

Logical link establishment function: Building up a logical link by during GPRS at-tach.

Logical link maintenance function: Monitoring of the state of the logical link andstate modification control.

Logical link release function: De-allocation of resources associated with the logicallink.

4.1.5 Radio Resource Management Functions

Radio resource management functions include allocation and maintenance of com-munication channels via the radio interface. The GSM radio resources must be di-vided /distributed between circuit switched services and GPRS.

Um management function: Managing available physical channels of cells and de-termining the share of radio resources allocated for use in the GPRS. This share mayvary from cell to cell.

Cell selection function: Allows the MS to select the optimal cell for a communicationpath. This includes measurement and evaluation of the signal quality of neighboringcells and detection and avoidance of overload in the eligible cells.

Um-tranx function: Offers capacity for packet data transfer via Um. The function in-cludes a. o. procedures for multiplexing packets via shared physical channels, forretaining packets in the MS, for error detection and correction, and for flow control.

Path management function: Management of packet data communication betweenBSS and serving GSN node. Establishing and canceling these paths can be effectedeither dynamically ( (amount of traffic data) or statically (maximum load to be ex-pected for each cell).

4.1.6 Network Management Functions

Network management functions provide mechanisms for the support of GPRS-related operation & maintenance functions.


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Maintenance of communication channel,

co-ordination Link state information & supervision of

data transfer activity over the logical link MS - SGSN

Logical Link Establishment Logical Link Maintenance Logical Link Release

Keep track of current MS-location

Mobility Management Functions

Allocation & maintenance of radio communication path

Um Management: manage resources GPRS / non GPRS

Cell Selection: select optimal cell (by MS)

Um-tranx: MAC via Um, user multiplexing, packet discrimination within MS, error detection & correction, flow control procedures

Path Management:

manages packet data communication

BSSSGSN

(dynamic data traffic or static)

Radio Resource

Management Functions

mechanism to support O&M functions related to GPRS

Network Management

Functions

Logical Link

Management Functions

Fig. 18 Mobility Management, Logical Link, Radio Resource and Network Management Functions


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4.2 Allocation of Logical Functions

The tasks described in the logical functions can be allocated to various functionalunits of the GSM-/GPRS network. The mobile station MS, the base station subsys-tem BSS (with the packet control unit PCU and channel codec unit CCU), the servingGPRS support node SGSN and the gateway GPRS support node GGSN participatein handling the following functions:


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Function MS BSS SGSN GGSN HLR

Network Access Control:

Registration X

Authentication & Authorization X X X

Admission Control X X X

Message Screening X

Packet Terminal Adaptation X

Charging Data Collection X X

Packet Routing & Transfer:

Relay X X X X

Routing X X X X

Address Translation & Map-ping

X X X

Encapsulation X X X

Tunneling X X

Compression X X

Ciphering X X X

Domain Name Server X

Mobility Management X X X X

Logical Link Management:

Logical Link Establishment X X

Logical Link Maintenance X X

Logical Link Release X X

Radio Resource Management:

Um Management X X

Cell Selection X X

Um-Tranx X X

Path Management X X


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GPRS - General Packet Radio ServicesGPRS Objectives and AdvantagesGPRS Objectives and AdvantagesStandardization

Basic PrinciplesManagement of Radio Resources/ Coding SchemesGPRS Subscriber ProfileQuality of Service (QoS) Profiles

GPRS-ArchitectureGPRS ArchitectureGSM Phase 2+, InterfacesNew Network Elements for GPRSServing GPRS Support Node (SGSN) FunctionsGateway GPRS Support Node (GGSN) FunctionsPhysical Realization SGSN/GGSNPacket Control Unit PCUChannel Codec Unit CCUGPRS Mobile Stations MS

Logical FunctionsLogical Functions in the GPRS NetworkNetwork Access Control FunctionsPacket Routing and Transfer FunctionsMobility Management FunctionsLogical Link Management FunctionsRadio Resource Management FunctionsNetwork Management Functions

Allocation of Logical Functions

Documents

02_tm2110eu01tm_0003_gprs