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GPRS

—General Packet Radio Service

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Outline

Introduction

GPRS Applications

GPRS normal service procedures

GPRS Architecture

GPRS protocol layering

GPRS data link layer and coding schemes

GPRS packet transfer

Limitations of GPRS

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IntroductionThe General Packet Radio System (GPRS) is a new service that provides actual packet radio access for mobile Global System for Mobile Communications (GSM) and time-division multiple access (TDMA) users.The main benefits of GPRS are that it reserves radio resources only when there is data to send and it reduces reliance on traditional circuit-switched network elements.Theoretical up to 171.2 kbps transmission speed are achievable using all eight timeslots at the same time.No dial-up connection is necessary, GPRS facilitates instant connections whereby information can be sent or received immediately as the need arises.GPRS facilitates several new applications that have not previously been available over GSM networks due to the limitations in speed and message length.GPRS fully enables Mobile Internet functionality by allowing interworking between the existing Internet and the new GPRS network.

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GPRS applicationsCommunications Use the mobile communications network purely as a pipe to access messages or information. — E-mail; fax; unified messaging; intranet/Internet accessValue-added services (VAS) Refer strictly to content provided by network operators to increase the value of their service to their subscribers. — E-commerce; banking; financial trading; Retail; ticket purchasing; Location-based applications Provide the ability to link push or pull information services with a user's location. — Navigation; traffic conditions; airline/rail schedules; location finder Vertical applications Apply to systems utilizing mobile architectures to support the carrying out of specific tasks within the value chain of a company. — Freight delivery; fleet management; sales-force automation Advertising

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GPRS normal service procedure (continue)Provision — GPRS services: Point To Point (PTP) and Point To Multipoint (PTM). — Quality of Service (QoS): 1) priority; 2) reliability; 3) delay; 4) user data throughput; 5) scheduled repeated transmission. WithdrawalGPRS-Attach and GPRS-Detach — Attach: MS indicates its presence to the PLMN (public mobile network) for the purpose of using the GPRS services. — Detach: MS indicates to the PLMN that the MS will no longer be using the GPRS services Registration By registering the service parameters, the subscriber optimizes the the its present, dynamic service profile within the limitations of the static subscription profile.Erasure The subscriber erases previously registered service parameter values from the service profile.

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GPRS normal service procedureInterrogation The subscriber interrogates the status/value of registered service parameters as defined in the current service profile. Activation The subscriber activates each of the registered interworking profiles independently within the limitations of the subscription profile. De-activation The subscriber de-activates the previously activated interworking profiles independently within the limitations of the subscription profile.Invocation and operation The GPRS service is invoked upon transmission or reception of GPRS data by subscribers.PIN and Password Management — Correct subscriber identification has been confirmed by entry of the current GSM PIN when GPRS-Attach operates. — GPRS services is offered to a subscriber with the subscription option of using a password to control the services.

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GPRS reference architectureGPRS can be thought of as an overlay network onto a GSM network.

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GPRS elementsNew terminals (mobiles): — Required to handle the enhanced air interface and packetize traffic. — A GPRS terminal can be one of three classes: A, B, or C.BSC/BTS: — BSC is required to provide a physical and logical data interface out of the base station subsystem (BSS) for packet data traffic. GPRS Network: — Gateway GPRS Service Node (GGSN) performs mobility management functions such as mobile subscriber attach/detach and location management. — Serving GPRS Service Node (SGSN) are interfaces to external IP networks such as the public Internet, other mobile service providers' GPRS services, or enterprise intranets.GPRS Mobility Management: Mobility management builds on the mechanisms used in GSM networks. — Home location register (HLR) — Visitor location register (VLR)

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GPRS protocol layeringTransmission plane protocol layering

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The transmission plane covers the protocols for user information transmission and associated control procedures.

Between SGSN and GGSN — GPRS tunnel protocol (GTP)

Between the SGSN and MS — Sub-network Dependent Convergence Protocol (SNDCP) — BSS GPRS protocol (BSSGP)

Between MS and BSS — Physical Link sublayer (PLL) — Physical RF sublayer (RFL) — Radio Link Control (RLC) — Medium Access Control (RLC/MAC)

GPRS protocol layeringTransmission plane protocol layering

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GPRS protocol layeringSignaling plane protocol layering

GPRS-specific mobility management protocol (GMM) is required within MS and SGSN to support the mobility functionality.

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Logical link control (LLC) — Provides a logical link between the MS and SGSN. — LLC layer protocol functionality is based on link access procedure-D (LAPD).

Radio link control/medium access control (RLC/MAC) — Provides services for information transfer over the physical layer of the GPRS radio interface. — RLC layer is responsible for the transmission of data block across the air interface and the backward error correction (BEC) procedures. — MAC layer is derived from a slotted ALOHA protocol, which performs contention resolution between channel access attempts.

GPRS data link layer

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GPRS packet transformation data flowPH User data Network layer

SNDCP layerPacket (N-PDU)

Segment Segment…

FH Info FSC

Segment Segment…

BH Info BCS Tail

Convolutional encoding

Burst Burst Burst Burst

LLC frame

RLC/MAC block

Normal burst

SNDCP layerLLC layer

LLC layerRLC/MAC layer

RLC/MAC layerPhysical layer

PH: Packet header FCS: Frame check sequence

FH: Frame header BCS: Block check sequence

BH: Block header Payloa

d456 bits

Add BCS

Add precoded

USF

Add tail bit

Coding Puncture

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GPRS RLC/MAC block structure

U S FU serDat a

T PCRLC

headerRLC dat a BCS

Payload

M A C headerRLC dat a

blockBlockcheck

sequence

U S FCont r ol T PC RLC/ M A C signaling inf or mat ion BCS

Payload

M A C headerRLC/ M A C cont r ol

b lockBlockcheck

sequence

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GPRS coding schemes

Maximal data rate = 8*21.4 = 171.2Kbps per user

SchemeCode rate

Payload BCSPre-coded

USFTailbits

Codedbits

Punct.bits

Data rate(kb/s)

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

SC-2 2/3 268 16 6 4 588 132 13.4

SC-3 3/4 312 16 6 4 676 220 15.6

SC-4 1 428 16 12 0 456 0 21.4

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GPRS logical channels-PDCHPacket Broadcast Control Channel (PBCCH)

Packet Broadcast Control Channel (PBCCH) — Broadcast

Packet Common Control Channel (PCCCH)Packet Random Access Channel (PRACH) — Random access

Packet Paging Channel (PPCH) — Paging

Packet Access Grant Channel (PAGCH) — Access grant

Packet Notification Channel (PNCH) — Multicast

Packet Traffic Channel (PTCH)Packet Data Transfer Channel (PDTCH) — Data

Packet Associated Control Channel (PACCH) — Associated control

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Mobile-Originated packet transferNetworkMS

Packet channel request

Random access

Tim

e

Packet immediate assignment

Packet resource assignment

Packet resource request

Transmission

RLC/MAC data

Acknowledgement

Acknowledgement

Retransmission of data in error

PRACH/RACH

PAGCH/AGCH

PACCH

PACCH

PDTCH

PACCH

PACCH

PDTCH

RLC/MAC block USFPATCH

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Mobile-Terminated packet transferNetworkMS Packet paging request

Random access

Tim

e

Packet channel request

Packet resource assignment

Packet paging response

Transmission

Frame transmission

Acknowledgement

Acknowledgement

Retransmission of blocks in error

PPCH/PCH

PAGCH/AGCH

PACCH

PDTCH

PACCH

PACCH

PDTCH

Packet immediate assignment

PRACH/RACH

PAGCH/AGCH

RLC/MAC block USFPDTCH

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Throughput VS. Input load in GPRS

Slotted ALOHA curve

GPRS cur ve

In p u t lo a d

Th

rou

ghp

ut

The throughput of the GPRS system performs as a slotted ALOHA system when the system is stable. When the system is overloaded, the throughput saturates at a maximum value.

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Limitation of GPRSLimited cell capacity for all users There are only limited radio resources that can be deployed for both voice and GPRS calls.Speeds much lower in reality It is unlikely that a network operator will allow all timeslots to be used by a single GPRS user. Support of GPRS mobile terminate by terminals is no ensured There has been no confirmation from any handset vendors that mobile terminated GPRS calls.Transit delays GPRS packets are sent in all different directions to reach the same destination. the result is that potential transit delays can occur. No store and forward There is no storage mechanism incorporated into the GPRS standard, apart from the incorporation of interconnection links between SMS and GPRS.