Acknowledgement Aims - Universität Kassel - ComTec

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CT2 – SS05

GPRS (General Packet Radio Service)

Prof. Dr. Klaus DavidChair for Communication Technologies

(ComTec)

Vorlesung XX SS05 GPRS version 1.0.ppt

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Acknowledgement

• The Author would like to acknowledge valuable contributions from Mr. Ilker Demirel (Condat AG) and Mr. Ulrich Siebert (ComTec)

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Aims

• Understand the principle services, architecture and protocols of GPRS

• Have an overview of GPRS terminals and the QoS (Quality of Service) concept in GPRS

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Overview

• GPRS in a nutshell

• System Overview and protocols

• Air Interface

• Abbreviations• References

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Overview



• Air Interface


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GPRS in a nutshell

• Interworking with X.25 and the Internet• Packet oriented with a possible multiplexing of

up to 8 timeslots – capacity on demand –statistical multiplexing

• “always online”

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GPRS in a nutshell

• Point-to-Point and Point-to-Multipoint Multicast and Point- to - Multipoint Groupecast

• Different QoS values specified• Access time typically 0.5 to 1 s• Charging can be based on volume, QoS and not

just air-time

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GPRS in a nutshell

• Three types of handhelds:– Class A: Speech and GPRS Data - transfer are

possible at the same time– Class B: Speech or GPRS Data - transfer are possible.

Automatic switching between both possible, incoming call in any of the 2 possible

– Class C: only one of the two, manual switch, if in one mode (like GPRS) then unreachable on other mode (like GSM).

• SMS via GPRS possible

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QoS Reliability

Table: Reliability classes

Reliabilityclass

Lost SDUprobability

(a)

DuplicateSDU

probability

Out ofSequence

SDUprobability

Corrupt SDUprobability

(b)

Example of applicationcharacteristics.

1 10-9

10-9

10-9

10-9

Error sensitive, no error correctioncapability, limited error tolerance

capability.

2 10-4

10-5

10-5

10-6

Error sensitive, limited error correctioncapability, good error tolerance

capability.

3 10-2

10-5

10-5

10-2

Not error sensitive, error correctioncapability and/or very good error

tolerance capability.

SDU Service Data UnitSource 3G TS 22.060 V3.2.0 (1999-12), Service description, Stage 1

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QoS Delay

Table: Delay classes

Delay (maximum values)SDU size: 128 octets SDU size: 1024 octets

Delay ClassMeanTransferDelay (sec)

95 percentileDelay (sec)

MeanTransferDelay (sec)

95 percentileDelay (sec)

1. (Predictive) < 0.5 < 1.5 < 2 < 72. (Predictive) < 5 < 25 < 15 < 753. (Predictive) < 50 < 250 < 75 < 3754. (Best Effort) Unspecified

Source 3G TS 22.060 V3.2.0 (1999-12), Service description, Stage 1

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GPRS capable Mobiles – Nokia -

500 €500 €n/aPrice :

84g97x19x43HSCSD43,2kBit

111g129x19x47HSCSD,BT43,2kBit

n/an/aHSCSD

Weight:Size:Features:Data:

Nokia 8310Nokia 6310Nokia 6250Type :

Feb 2002

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GPRS capable Mobiles – Siemens -

360 €360 €Price :

99g109x20x46HSCSD,BT4 Slots :3RX/1TX

93g109x20x46

4Slots:3RX/1TX

Weight:Size:Features:Data:

Siemens ME45Siemens S45Type :

Feb 2002

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GPRS capable Mobiles - Ericsson -

220 €350 €600 €Price :

82g105x20x45

n/a

105g130x16x50HSCSD,BT

n/a

85g101x20x48HSCSD, BT, Color-Display, 500 contactsinl. Email, EMS

3RX/1TX

Weight:Size:Features:

Data :

R600R520mT68Type :

Feb 2002

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GPRS capable Mobiles – Motorola -

700 €350 €450 €Price :

109g87x24x452nd DisplayUKW Radio1TX/4RX

108g125x27x49USB Interface

1TX/4RX

79g84x21x44

1TX/4RX


Data :

v60Timeport 280v66Type :

Feb 2002

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GPRS capable PDAs

600 €900 €950 €Price :

155g98x28x608 MB

180g133x80x16Windows CEBluetooth64MB

303g132x26x82Pocket PC,65k Colours,32MB,


MotorolaAccompli 008

Compaq 3870Siemens SX45Type :

Feb 2002

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Costs for transmission

1MB/m.Incl.

1MB forWAP incl.

Add-Ons

0,49/day0,04/hour0,49/hour0,49/dayAdditionalcosts

----------19,95-----19,95p. month

-----Basiccosts

90.-490.-190.-690.-190.- 1

70.- ²690.-10MB

9.-49.-19.-69.-19.- 1

7.- ²69,001MB

0,090,490,190,690,191

0,07²0,6910kB

Viag-Interkom

E-PlusD2World L

D2By call

D1pro

D1eco

All prices in DM1 WAP ; ² other Data

Feb 2002

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Overview



• Air Interface


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Network Architecture

Source : Siemens

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Logical Architecture: packet domain core network

G f

U u

U m

D

G i

G n

IuG c

CE

G p

G s

S ignalling and D ata T ransfer InterfaceS ignalling Interface

M S C /V L R

T E M T U T R A N T EP D N

G rIu

H L R

O ther P L M N

S G S N

G G S N

G d

S M -S CS M S -G M S C

S M S -IW M SC

G G S N

E IRS G S N

G nC G F

G aG a

B illingS ystem

G bT E M T B S S

R

AR

Source 3G TS 23.060 V3.2.1 (2000-01), General Packet Radio Service (GPRS); Service description; Stage 2

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SGSN (Serving GPRS Support Node)

Interfaces• Gb Interface to PCU (packet control unit) and

BSC• Gs Interface for Mobility management• Gn Interface to the GGSN• Gd SMSC

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SGSN (Serving GPRS Support Node)

Functions• Routing in SGSN area and mobility management• Session Management• Paging• Charging/ Traffic Measurements• Cyphering (for non GPRS services in the BTS)

and Authentication

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Interface SGSN-MSC/VLR

• Allows• Combined Attach• Combined Location Updating• Paging• Periodic up-dates

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GGSN (Gateway GPRS Support Node)

• Gi Interface to external PDNs (Packet Data Networks). Typically IP Networks (IPv4 or IPv6) and X.25 Networks

• Major task Routing i.e. address translation (GSM IMSI and Internet Address) and encapsulation

• Screening/ Filter• Charging/ Traffic Measurements

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GPRS User Plane Protocols

Relay

NetworkService

GTP-U

Application

IP / X.25

SNDCP

LLC

RLC

MAC

GSM RF

SNDCP

LLC

BSSGP

L1bis

RLC

MAC

GSM RF

BSSGP

L1bis

Relay

L2

L1

IP

L2

L1

IP

GTP-U

IP / X.25

Um Gb Gn GiMS BSS SGSN GGSN

NetworkService

UDP /TCP

UDP /TCP

Figure : User Plane for GPRS

Source 3G TS 23.060 V3.2.1 (2000-01), General Packet Radio Service (GPRS);Service description; Stage 2

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• SNDCP (Subnetwork Dependent Convergence Protocol)– Multiplexing– Segmentation/ Reassembly– Compression/ Decompression

• LLC (Logical Link Control-Layer)– based on ARQ guarantees the SNDCP layer close to

zero errors (similar to the RLP (Radio Link Protocol))– In reality garantee difficult

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• RLC (Radio Link Control)– also based on ARQ, more effective due to smaller

packets than LLC

• Why 2 times ARQ on LLC and RLC layer:– SDNCP requires very little errors– allows to recover from errors caused by BSS change

• MAC (Medium Access Control)– based on Slotted Aloha

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• BSSGP (Basestation System GPRS Protocol)– Routing and QoS Information

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• GTP (GPRS Tunnel Protocol)– encapsulation of IP – Datagramms – for transmission

between SGSN – SGSN – GGSN– procedures in signalling as well as user plane– signalling being used for:

• establishing, modifying and deleting tunnels

• tunnel identifier (TID) = IMSI + Network Layer Service Access Point Identifier NSAPI identifies a PDP context uniquely

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MS can be in three situations

[Eberspächer]

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MS can be in three situations

• Idle mode:– MS listens to PBCCH and CCCH

– No PDCH allocated

– MS prepared to tranmsitt LLC/PDUs

• Standby– MS can move between BTSs of same RA without

sending up-date packets

– Paging required

– Answering to paging ⇒ ready

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GPRS Control Plane Protocols

BSSGPRelay

GMM/SM

LLC

RLC

MAC

GSM RF

GMM/SM

LLC

BSSGP

L1bis

Um GbMS BSS 2G-SGSN

NetworkService

RLC

MAC

GSM RF L1bis

NetworkService

Figure: Control Plane MS – 2G-SGSN


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GPRS Protocols Control Plane• The control plane consists of protocols for control and

support of the user plane functions:

• controlling the packet domain network access connections, such as attaching to and detaching from the packet domain network;

• controlling the attributes of an established network access connection, such as activation of a PDP address;

• controlling the routeing path of an established network connection in order to support user mobility; and

• controlling the assignment of network resources to meet changing user demands.


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GPRS Protocols Control Plane

• GMM/SM (GPRS Mobility Management and Session Management)– GPRS Attach/ Detach

– security functions

– routing area updates

– Activation/ Deactivation/ Modification of PDP (Packet Data Protocol) context

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Overview



• Air Interface


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GPRS Physical Layer

• allocation of time slot resources of up- and downlink can be asymmetric

• time slots allocated for GPRS (can be done dynamically) are called: PDCH (Packet Data Channel)

• MS gets told in downlink which timeslots to be used in up-link (information in USF Uplink State Flag)

• Four coding schemes, CS-1 to CS-4, are defined for the packet data traffic channels.

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GPRS Physical Layer

• All coding schemes are mandatory for MSs. Only CS-1 is mandatory for the network.

• The first step of the coding procedure is to add a Block Check Sequence (BCS) for error detection.

• For CS-1 - CS-3, the second step consists of pre-coding USF (except for CS-1), adding four tail bits and a half rate convolutional coding for error correction that is punctured to give the desired coding rate.

• For CS-4 there is no coding for error correction.

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GPRS Physical Layer

• CS-X type determined by Stealing Flag

• theoretically up to 171,2 kbit/s (minus signalling)

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Radio Block structure for CS-1 to CS-3

rate 1/2 convolutional coding

puncturing

456 bits

USF BCS

Radio Block

GSM 03.64 version 7.0.0 Release 1997

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Radio Block structure for CS-4

GSM 03.64 version 7.0.0 Release 1997

blockcode no coding

456 bits

USF BCS

Radio Block

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Coding parameters for the coding schemes

BCS Block Check SequenceUSF Uplink State FlagGSM 03.64 version 7.0.0 Release 1997

Scheme Code rate USF Pre-codedUSF

RadioBlock

excl. USFand BCS

BCS Tail Codedbits

Puncturedbits

Data ratekb/s

CS-1 1/2 3 3 181 40 4 456 0 9.05

CS-2 ≈2/3 3 6 268 16 4 588 132 13.4

CS-3 ≈3/4 3 6 312 16 4 676 220 15.6

CS-4 1 3 12 428 16 - 456 - 21.4

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Data Rates

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GPRS Logical Channels

[Eberspächer]

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GPRS Logical Channels

• PBCCH (Packet Broadcast Control Channel) additional to GPRS system info also the other GSM info available, thereby listening to BCCH not required

• 52 - Multiframe is typically used für PDCHs

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Overview



• Air Interface


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GPRS Abbreviations• BCS Block Check Sequence • BSSGP Basestation System GPRS Protocol• GGSN Gateway GPRS Support Node• GTP GPRS Tunnel Protocol• LLC Logical Link Control-Layer• MAC Medium Access Control• NSAPI Network Layer Service Access Point Identifier• PBCCH Packet Broadcast Control Channel • PCU Packet Control Unit• PDCH Packet Data Channel• PDN Packet Data Networks• PDP Packet Data Protocol• RLC Radio Link Control• SGSN Serving GPRS Support Node• SNDCP Subnetwork Dependent Convergence Protocol• TCAP Transaction Capabilities Application Part• TID tunnel identifier• USF Uplink State Flag

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Overview



• Air Interface


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References

• [David 2002] K. David und T. Benkner, "Digitale Mobilfunksysteme - Grundlagen und aktuelle Systeme", Teubner Verlag (Reihe Informationstechnik), 2. Auflage 2002 (erhältlich ab Juni 2002)

• [Eberspächer] J. Eberspächer, H.-J. Vögel, C. Bettstetter, „GSM Global System for Mobile Communication“, Teubner Verlag, 3. Auflage, 2000

• [Witt 2000] M. Witt (Hrsg.), „GPRS Start in die mobile Zukunft“, mitp 2000

• [G. Heine 2001] G. Heine und H. Sagkob, „GPRS –Gateway zu Mobilfunknetzen der 3. Generation“, Franzis‘2001

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References

• GSM 04.08 GMM, RR, GRR, SM• GSM 4.60 GRR• GSM 4.64 LLC• GSM 4.65 SNDC• GSM 5.02/ 5.08 layer 1, GRR• GSM 7.60, 9.60, 9.61 and RFC 1661/2 for PPP

Acknowledgement Aims - Universität Kassel - ComTec

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