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© M. Baldi: see page 2

GPRSGeneral Packet Radio Service

Mario BaldiPolitecnico di Torino

(Technical University of Torino)mario.baldi[at]polito.it

staff.polito.it/mario.baldi

© M. Baldi: see page 2GPRS - 2

Copyright NoticeThis set of transparencies, hereinafter referred to as slides, is protected by copyright laws and provisions of International Treaties. The title and copyright regarding the slides (including, but not limited to, each and every image, photography, animation, video, audio, music and text) are property of the authors specified on page 1.The slides may be reproduced and used freely by research institutes, schools and Universities for non-profit, institutional purposes. In such cases, no authorization is requested.Any total or partial use or reproduction (including, but not limited to, reproduction on magnetic media, computer networks, and printed reproduction) is forbidden, unless explicitly authorized by the authors by means of written license.Information included in these slides is deemed as accurate at the date of publication. Such information is supplied for merely educational purposes and may not be used in designing systems, products, networks, etc. In any case, these slides are subject to changes without any previous notice. The authors do not assume any responsibility for the contents of these slides (including, but not limited to, accuracy, completeness, enforceability, updated-ness of information hereinafter provided). In any case, accordance with information hereinafter included must not be declared.In any case, this copyright notice must never be removed and must be reported even in partial uses.

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GeneralitiesBased on the existing GSM infrastructurePacket switching functionality

Better data transfer ratesStatistical multiplexing

Traffic based billing

Migration Path to 3G Networks

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Service TypesPoint-to-Point

Internet access by userPoint-to-Multipoint

Delivery of information (e.g. news) to multiple locations or interactive conference applications

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Circuit Switched Data (CSD)Before GPRSA channel is allocated to user for duration of connectionInefficient use of resourcesTime-based billingDeterministic quality of service

Resources allocated to communicationSuitable to real-time applications

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In GPRSResources are allocated to user only for the time it takes to send each packetA channel may be shared by many usersUser pays by the packetIdeal for “data” traffic

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ComparisonCSD

Lower bit rates14.4kbit/s

Reserved bandwidthFixed access timeTime-based billing

GPRSHigher bit rates

up to 170kbit/sShared bandwidthVariable access timesTraffic based billing

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GSM Network Architecture

BSC

BSCMSC

MS

MS

MS BTS

BTS

BTS

GMSC

PSTNISDN

EIRAUC

HLRVLR

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AcronymsMS: Mobile Station BSC: Base Station ControlerBTS: Base Transciever Station MSC: Mobile Switching ControlerGMSC: Gateway Mobile Switching ControlerPSTN: Public Switched Telephone Network

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AcronymsVLR: Visited Location RegisterEIR: Equipment Identity RegisterAUC: Authentication center HLR: Home Location RegisterPLMN: Public Land Mobile Network

E.g., GSM networkPDN: Packet Data Network

E.g., IP network, Internet, intranet

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GPRS Architecture

BSC

SGSN

MS

BTS

BTS

Other GPRS

PLMN

GGSN

PDN

Gb

GdGp

Gn

Gf

Gs

Gc

GGSN

EIRHLR

MSC/VLR

D

SMS-GMSCSMS-INMSC

Gi

Gr

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GPRS ArchitectureNew components

SGSN: Serving GPRS Support NodeGGSN: Gateway GPRS Support Node

Components needing upgradeHLRMSC/VLRMobile Station

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SGSNDelivers data packets from and to mobile stationsPacket Routing and Transfer from MS to GGSNMobility ManagementLogical Link ManagementAuthenticationBilling and maintaining user profiles

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GGSNInterfaces GPRS backbone network with external packet data networks (PDNs)

E.g., IP networks, InternetTranslation between PDP (packet data protocol) addresses and GSM addressesAuthentication and billingMany-to- many relations among SGSNsand GGSNs

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IP IP

Layer 2

Layer 1GPRS bearer

Gi

GGSN Protocol Architecture

Routingfunction

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Integrated Architecture Overview

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GPRS BackboneBased on the Internet Protocol (IP)Tunnels of data and signaling messages between GPRS support nodes (GSNs)

Intra-PLMN backbone networkInter-PLMN backbone network

Intra-PLMN backbone networks are connected by Border Gateways and an inter-PLMN backbone network

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GPRS Backbone Overview

PLMN1 PLMN2

MS

BTS

BSC

SGSNGn

Gn

Gn

SGSN

GGSNGi

BorderGateway

Gp

Border Gateway

GGSN

Router LANHost

SGSN

BSCBTS

Inter-PLMNGPRS

Backbone

Inter-PLMNGPRS

Backbone

Intra-PLMNGPRS

Backbone

Intra-PLMNGPRS

Backbone

Intra-PLMNGPRS

Backbone

Intra-PLMNGPRS

Backbone

Packet Data Network(PDN)

Eg.Internet,Intranet

Packet Data Network(PDN)

Eg.Internet,Intranet

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GTPGPRS Tunneling ProtocolTunnels user data and signaling on the GPRS backboneEncapsulates PDP (Packet Data Protocol) packets

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Protocol ArchitechtureTransmission Plane: GTPSignalling Plane

GTP tunnel control management protocolTunnel creation, modification, and deletion

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Registration of a Mobile NodeA mobile station must register itself with

GPRS network.GPRS attachGPRS detach

GPRS detach can be initiated by the MS or the network.

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Session ManagementSuccessfully attached MS gets one or more Packet Data Protocol (PDP) address.

Unique only for a particular session.PDP address consists of

PDP typePDP address assigned to MSRequested quality of serviceAddress of the corresponding GGSN

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PDP Address AssignmentStatic

Assigned by network operatorDynamic

Assigned by Corresponding GGSN.

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Packet Routing

PLMN1

MS

BTS

BSC

SGSN

SGSN

GGSNRouter LAN

Host

Intra-PLMNGPRS

Backbone

Intra-PLMNGPRS

Backbone

Packet Data Network(PDN)

Eg.Internet,Intranet

Packet Data Network(PDN)

Eg.Internet,Intranet

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Packet TransferA laptop connects with a GPRS-capable handsetThe handset communicates with GSM BSBS sends the GPRS packets to SGSNSGSN encapsulates packets Handset location information is updated in GSM components (e.g., HLR)SGSN sends encapsulated packets to GGSNGGSN decapsulates and sends to PDNs

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Packet Routing

PLMN1 PLMN2

MS

BTS

BSC

SGSNGn

Gn

Gn

SGSN

GGSNGi

BorderGateway

Gp

Border Gateway

GGSN

Router LANHost

SGSN

BSCBTS

Inter-PLMNGPRS

Backbone

Inter-PLMNGPRS

Backbone

Intra-PLMNGPRS

Backbone

Intra-PLMNGPRS

Backbone

Intra-PLMNGPRS

Backbone

Intra-PLMNGPRS

Backbone

Packet Data Network(PDN)

Eg.Internet,Intranet

Packet Data Network(PDN)

Eg.Internet,Intranet

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RoutingMS roaming in PLMN1 sends IP packet to host (e.g. Web server)Host sends reply packet to MS home PLMN2

PLMN2’s GGSN queries HLR and finds that MS is in PLMN1Packet is encapsulated and sent to SGSN in PLMN1

Packet travels over inter-PLMN backbone not through PDNNo encapsulation-decapsulation needed on GPRS backbones

SGSN decapsulates packet and delivers to MS

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Radio Interface ProtocolsUser plane and Control PlaneLayer 1

Physical (PHY)Combination of TDMA and FDMA

TDMA: Time Division Multiple AccessFDMA: Frequency Division Multiple Access

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Radio Interface Protocols: Layer 2Data LinkMedia Access Control (MAC)Radio Link Control (RLC) Packet Data Convergence Protocol (PDCP)

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Radio Interface Protocols: Layer 3Radio Resource Control (RRC)

Iu mode Radio Resource (RR)

A/Gb mode

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Physical LayerChannel separation: 200 kHzPower output control

Find minimum acceptable levelSynchronization with base stationHandoverQuality monitoring

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Release 5 Protocol ArchitecturePhysical ChannelsLogical, Control and Traffic ChannelsMedia Access Control and Radio Link ControlRadio Resource Control and Radio Resource

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Physical ChannelsDefined by timeslot (0-7) and radio frequency channelShared Basic Physical Sub Channel

Shared among several users (up to 8)Uplink Stage Flag (USF) controls multiple access

Dedicated Basic Physical Sub ChannelOne user

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Physical ChannelsPacket Data Channel (PDCH)

Dedicated to packet data traffic from logical channels

ControlUser data

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TDMA Frame Slots and Bursts

1

123

2

1

124

. . .

. . .

935 MHz935.2 MHz

960 MHz959.8 MHz

200 KHz

1

123

2

124

. . .

. . .

890 MHz890.2 MHz

915 MHz914.8 MHz

200 KHz

1 2 3 4 5 6 7 8

Data Burst = 156.25 bit periods

11 2 3 4 5 6 7 8

TDMA Frame

TDMA Frame

Uplink

Downlink

Time Slot

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Multi Slot OperationGPRS allows a mobile to transmit data in up to 8 PDCHs

Eight-slot operation3-bit USF at beginning of each radio block in downlink points to next uplink radio blockComparison with single-slot GSM

Higher delay at higher loadLow blocking rateImproved Throughput

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GPRS Air Inteface

0 1 2 43 5 6 7 0 1 2 3 40 1 2 43 5 6 7 0 1 2 3 4

0 1 2 43 5 6 7 0 1 2 3 40 1 2 43 5 6 7 0 1 2 3 4

Uplink

Downlink

Voice User1

Voice User2

GPRS User1

GPRS User2

GPRS User3

F1

F2

F3

F4

F1

F2

F3

F4

Time Slot Number

CarrierFrequency

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Media Access Control (MAC)Connection orientedConnections are called Temporary Block Flows (TBF)

Logical unidirectional connection between two MAC entitiesAllocated resources on PDCH(s)One PDCH can accomodate multiple TBFsTemporary Flow Identity (TFI) is unique among concurrent TBFs in the same directionGlobal_TFI to each station

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MS Initiated TBF EstablishmentOne Phase Access, orTwo Phase Access

MS BSS

PACKET UPLINK ASSIGNMENT PAGCH

PACKET CHANNEL REQUEST PRACH

PACKET RESOURCE REQUEST PACCH

PACKET UPLINK ASSIGNMENT PACCH

TBF Est. By MS: Two Phase Access

MS BSS

PACKET CHANNEL REQUEST PRACH

TBF Est. By MS: One Phase Access

PACKET UPLINK ASSIGNMENT PAGCH

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Network Initiated TBF Establishm.

MS BSSPACKET PAGING REQUEST PPCH

PACKET CHANNEL REQUEST PRACH

PACKET PAGING RESPONSE PACCH

PACKET DOWNLINK ASSIGNMENT PACCH or PAGCH

TBF Est. By Network

PACKET IMMEDIATE ASSIGNMENT PAGCH

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Channel Access & Resource AllocationSlotted Aloha

Used in PRACH (packet random access)MSs send packets in uplink direction at the beginning of a slotCollision: Back off -> timer (arbitrary) -> re-transmit

Time Division Multiple Access (TDMA)Predefined slots allocated by BSSContention-free channel accessAll logical channels except PRACH

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Quality of Service (QoS) SupportService Level Agreements to specify End-to-end QoSIP multimedia applications must be able to

Define their requirementsNegotiate their capabilitiesIdentify and select available media components

GPRS signaling supports various traffic typesConstant/variable bit rateConnection oriented/connection lessEtc.

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QoS Profile for GPRS BearersDescribes QoS requirements4 parameters:

Service precedence3 classes

Reliability3 classes

Delay4 classes

ThroughputMaximum and mean bit rates

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QoS Profile for GPRS BearersQoS profile is included in Packet Data Protocol (PDP) contextNegotiation managed through PDP procedures

ActivationModification Deactivation

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Packet Classification and SchedulingTBF tagged with TFITFI different for each TBFPacket scheduling algorithms are not defined by the standard

Defined and implemented by GPRS network designers and carriers

GPRS supports per-flow quantitative QoS with proper packet classification and scheduling algorithms (?)

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ReferencesJ. Cai, D. J. Goodman, “General Packet Radio Service in GSM”, IEEE Communications Magazine, Oct 1997C. Bettstetter, H.-J. Vögel, J. Eberspächer, "GSM Phase 2+ General Packet Radio Service GPRS: Architecture, Protocols, and Air Interface," IEEE Communications Survey, Vol. 2, No. 3, 1999 , http://www.comsoc.org/pubs/surveys/3q99issue/bettstetter.html“Wireless Internet Access based on GPRS”, IEEE Personal Comm. April 2000.

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ReferencesWikipedia: General Packet Radio Service, http://en.wikipedia.org/wiki/General_Packet_Radio_ServiceB. Ghribi and L. Logrippo, “Understanding GPRS: The GSM Packet Radio Service”, Computer Networks, vol. 34, pp. 763–779, 2000Herman Rao Yi-Bing Lin, I. Chlamtac, “General Packet Radio Service (GPRS): Architecture, Interfaces, and Deployment”, Journal of Wireless Communiations and Mobile Computing, vol. 1, n. 1, 2001.