GPRS Technical Introduction Version1.0

May 2003May 2003 GPRS GPRS IntroductionIntroduction 11

GPRS IntroductionGPRS Introduction


ContentContent

General architecture and protocol layersGeneral architecture and protocol layers GPRS logical channelsGPRS logical channels Main transactionsMain transactions Network Operation ModeNetwork Operation Mode Allocation/De-allocation of radio resourcesAllocation/De-allocation of radio resources Cell selection/re-selectionCell selection/re-selection UL Power controlUL Power control CS AdaptationCS Adaptation Radio Link SupervisionRadio Link Supervision Quality of ServiceQuality of Service


Service overviewService overviewData transfer with GSM circuit VS packet switchedData transfer with GSM circuit VS packet switched

InternetInternetGSMGSMnetworknetwork

Air interfaceAir interface Access nodeAccess node

GPRSGPRS

networknetworkInternetInternet

Air interfaceAir interfaceAA

BB

CC

AA

BB

CC


GPRS architecture (2)GPRS architecture (2)


Orange’s GPRS architecture (1)Orange’s GPRS architecture (1)

MMFFSS11

MMFFSS22

MMFFSS33

SSP1SSP1

SSP2SSP2

SSP3SSP3

SSP4SSP4

SSP5SSP5

BSCsBSCs

TCTC

TCTC


GPRS architecture (3)GPRS architecture (3)

The GPRS Core is composed of:The GPRS Core is composed of: Serving GPRS Support Node (SGSN)Serving GPRS Support Node (SGSN)

On the same hierarchic level as an MSC/VLROn the same hierarchic level as an MSC/VLR Authentication & Register FunctionAuthentication & Register Function Mobility ManagementMobility Management Service Access Point to GPRS Network for GPRS MSService Access Point to GPRS Network for GPRS MS Protocol Conversion (IP Protocol Conversion (IP SNDCP & LLC Protocol) SNDCP & LLC Protocol)

Gateway GPRS Support Node (GGSN)Gateway GPRS Support Node (GGSN) Basic routing and translation between PDNs and Internal Basic routing and translation between PDNs and Internal

GPRS ProtocolGPRS Protocol Provide connection to OMC-GProvide connection to OMC-G Generation and transfer of charging data.Generation and transfer of charging data.


Protocol layers (1)Protocol layers (1)Transmission planeTransmission plane


Protocol layers (2)Protocol layers (2)Transmission and reception data flowTransmission and reception data flow

SNDCPSNDCPLayerLayer

IPIPPacketsPackets

LLCLLCFrameFrame

RLC/MACRLC/MACBlocksBlocks

Physical Physical Layer Layer BurstBurst

FH: Frame HeaderFH: Frame HeaderFCS: Frame Check SequenceFCS: Frame Check Sequence

BH: Block HeaderBH: Block HeaderBSC: Block Check SequenceBSC: Block Check Sequence

Compression (optional)Compression (optional)

Information FieldInformation FieldFHFH FCSFCS Information FieldInformation FieldFHFH FCSFCS

SegmentationSegmentation

Max 1520Max 1520

BHBH BCSBCS BHBH BCSBCS BHBH BCSBCS

Primary BlockPrimary Block Following Following BlockBlock

Normal BurstNormal Burst Normal BurstNormal Burst Normal BurstNormal Burst Normal BurstNormal Burst


Protocol layers (3)Protocol layers (3)Signaling planeSignaling plane

MACMAC

GSM-RFGSM-RF

LLCLLC

RLCRLC

GMM/SMGMM/SM

MSMS

MACMAC

GSM-RFGSM-RF

UmUm

BSSBSS

RLCRLC

relayrelay

BSSGPBSSGP

NSNS

L1bisL1bis

NSNS

L1bisL1bis

BSSGPBSSGP

GbGb

LLCLLC

SGSNSGSN

GMM/SMGMM/SM GTPGTP

L2L2

L1L1

IPIP

UDPUDP

relayrelay

L2L2

L1L1

IPIP

UDPUDP

GTPGTP

GGSNGGSN

GnGn


GSM standard/Alcatel GPRS architectureGSM standard/Alcatel GPRS architecture

A Packet Control Unit (PCU) is defined by the GSM A Packet Control Unit (PCU) is defined by the GSM standard :standard : handles RLC/MAC functionshandles RLC/MAC functions may be either in the BTS, the BSC or the SGSNmay be either in the BTS, the BSC or the SGSN Alcatel choice :Alcatel choice :

PCU in a new network element called the MFS to handle PCU in a new network element called the MFS to handle RLC/MAC functionsRLC/MAC functions

BTS

BTSBSC

BSC

MFS

Gb

AterSGSN


GPRS Logical Channel (1)GPRS Logical Channel (1)

Downlink onlyDownlink only

Uplink onlyUplink only

PTCCH/UPTCCH/U

PTCCH/DPTCCH/D

PACCHPACCHPDTCHPDTCH

PRACHPRACH

PAGCHPAGCH

PNCHPNCH

PPCHPPCH

PBCCHPBCCH

Packet Common Packet Common Control Channel: Control Channel: PCCCHPCCCH

Packet Packet Dedicated Dedicated Control ChannelControl Channel

Packet Broadcast Packet Broadcast Control Channel: Control Channel: PBCCHPBCCH

Packet Packet Traffic Traffic

ChannelChannel

PDCHPDCH


Multiplexing of GPRS logical channelsMultiplexing of GPRS logical channels

Several TBF (Temporary Block Flow) can be transmitted on one PDCHSeveral TBF (Temporary Block Flow) can be transmitted on one PDCH A TBF is identified by a TFI (Temporary Flow Identity: 5 bits) and it can use A TBF is identified by a TFI (Temporary Flow Identity: 5 bits) and it can use

several PDCHs (depending on the multislot capability of the MS)several PDCHs (depending on the multislot capability of the MS)

PDCH 1PDCH 1

B0B0 B1B1 B2B2 B3B3 B4B4 B5B5 B6B6 B7B7 B8B8 B9B9 B10B10 B11B11

PDCH 2PDCH 2


PDCH 3PDCH 3


TBF with TFI = 3TBF with TFI = 3 TBF with TFI = 19TBF with TFI = 19 TBF with TFI = 22TBF with TFI = 22


Main transactions (1)Main transactions (1)UL TBF establishment on CCCHUL TBF establishment on CCCH

MSMS BTSBTS BSCBSC MFSMFS

TA calculationTA calculationRACHRACHChannel request + TAChannel request + TA

Channel requestChannel request

ResourceResourceallocationallocation

AGCHAGCHImmediate assignmentImmediate assignment

Immediate assignmentImmediate assignment

TFI, USF, TAI, TATFI, USF, TAI, TAThe MS switchsThe MS switchson the assignedon the assignedPDCHPDCH Packet UL assignment, pollingPacket UL assignment, polling

TFI, USF, TAITFI, USF, TAIPACCHPACCH

Packet UL assignmentPacket UL assignment

Packet control AckPacket control Ack

PACCHPACCH ResourceResourceactivationactivation

RLC data block (TLLI, TFI)RLC data block (TLLI, TFI)

PACCHPACCH

Packet UL Ack/NackPacket UL Ack/NackPDTCHPDTCH

TLLI, TFITLLI, TFI


Main transactions (2)Main transactions (2)UL TBF establishment during a DL TBFUL TBF establishment during a DL TBF


Main transactions (3)Main transactions (3)DL TBF establishment on CCCHDL TBF establishment on CCCH


Main transactions (4)Main transactions (4)DL TBF establishment during an UL TBFDL TBF establishment during an UL TBF


Main transactions (5)Main transactions (5)

Location Location managementmanagement Cell updateCell update RA updateRA update RA/LA update RA/LA update

(only in NMO I)(only in NMO I)


Main transactions (6)Main transactions (6)

MS mobility MS mobility management stagesmanagement stages

IN GPRS IN GSMIDLE TURN OFF

STANDBY IDLEREADY* DEDICATED

* * Does not mean the MS is using resource(s)Does not mean the MS is using resource(s)

MM RR

IDLE NO RADIO RESOURCE ALLOCATEDDEDICATED TCH CONNECTION

MM RR

IDLE PACKET IDLE MODE

STANDBY PACKET IDLE MODE

READY PACKET IDLE or PACKET TRANSFER MODE

In GSMIn GSM

In GPRSIn GPRS


Network Mode of OperationNetwork Mode of Operation

Mode CS paging channelPS paging channel Remarks

PPCH PPCH Gs interface

PCH PCH Gs interface

PACCH NA Gs interface

PCH PCH no Gs interface

PCH PCH no Gs interface

PCH PPCH no Gs interface

I

II

III


Allocation/De-allocation of radio resources (1)Allocation/De-allocation of radio resources (1)

AllocationAllocation Step 1Step 1 : The MFS determines the multislot configurations supported by : The MFS determines the multislot configurations supported by

the MS.the MS. Step 2Step 2 : The MFS analyses the constraints due to a possible : The MFS analyses the constraints due to a possible

concurrent TBF in the opposite direction : some TS may be unusable.concurrent TBF in the opposite direction : some TS may be unusable. Step 3Step 3 : The MFS selects an allocation scheme. : The MFS selects an allocation scheme. Step 4Step 4 : The MFS serves the request. : The MFS serves the request.

De-allocationDe-allocation GPRS low loadGPRS low load : The MFS de-allocates inactive PDCH as long as : The MFS de-allocates inactive PDCH as long as

more than MIN_PDCH_GROUP PDCH are allocated, or inactive PDCH more than MIN_PDCH_GROUP PDCH are allocated, or inactive PDCH are de-allocated after a delay. are de-allocated after a delay.

High load situationHigh load situation : The MFS marks allocated PDCH exceeding the : The MFS marks allocated PDCH exceeding the maximum allowed number of PDCH as unavailable for new TBF. When maximum allowed number of PDCH as unavailable for new TBF. When all the TBF carried by these PDCH are released, the MFS de-allocates all the TBF carried by these PDCH are released, the MFS de-allocates the PDCH without delay.the PDCH without delay.


Allocation/De-allocation of radio resources (2)Allocation/De-allocation of radio resources (2)


Cell selection and re-selectionCell selection and re-selection

Cell selection :Cell selection : Using the C1 criteria as in GSMUsing the C1 criteria as in GSM

Cell re-selection :Cell re-selection : Using the C1 and C2 criteria as in GSMUsing the C1 and C2 criteria as in GSM CELL_RESELECT_HYSTERESIS is used if :CELL_RESELECT_HYSTERESIS is used if :

the new cell belongs to a different routeing areathe new cell belongs to a different routeing area the MS is in the Ready state (in packet transfer mode)the MS is in the Ready state (in packet transfer mode)..

No dedicated GPRS neighbour cells list : using the same No dedicated GPRS neighbour cells list : using the same neighbour cells list as in GSM idle mode.neighbour cells list as in GSM idle mode.

Cannot prevent MS to re-select a cell with no GPRS enable.Cannot prevent MS to re-select a cell with no GPRS enable. If C2 parameters are used in order to give a higher priority to a If C2 parameters are used in order to give a higher priority to a

given layer (Micro cell layer) for circuit mode, the same priority given layer (Micro cell layer) for circuit mode, the same priority is applied for packet mode.is applied for packet mode.


UL Power ControlUL Power Control

Measurement : MS use DL level measurements to determine the Measurement : MS use DL level measurements to determine the powerpower In packet idle mode : BCCH of the serving cellIn packet idle mode : BCCH of the serving cell In packet transfer mode :BCCH of the serving cell or all the blocks of In packet transfer mode :BCCH of the serving cell or all the blocks of

one of the PDCH carrying the PACCH.one of the PDCH carrying the PACCH. Averaging :Averaging :

Use of a recursive filtering to obtain an average level.Use of a recursive filtering to obtain an average level.CCnn = a * SS = a * SSnn + (1-a) * C + (1-a) * Cn-1n-1

Average levels calculated in packet idle mode used in packet transfer Average levels calculated in packet idle mode used in packet transfer mode and vice versa.mode and vice versa.

MS PowerMS Power : : MS power for access on RACH : MS_TXPWR_MAX_CCHMS power for access on RACH : MS_TXPWR_MAX_CCH MS use the same power during a radio block (4 bursts)MS use the same power during a radio block (4 bursts) MS power = min(MS power = min(0 - 0 - ch - ch - * (C + 48), MS_TXPWR_MAX_CCH) * (C + 48), MS_TXPWR_MAX_CCH)


CS Adaptation (1)CS Adaptation (1)

Four coding schemes are defined :Four coding schemes are defined : CS1 (9.05 kbit/s data rate)CS1 (9.05 kbit/s data rate) CS2 (13.4 kbit/s data rate)CS2 (13.4 kbit/s data rate) CS3 (15.6 kbit/s data rate)CS3 (15.6 kbit/s data rate) CS4 (21.4 kbit/s data rate)CS4 (21.4 kbit/s data rate)

For AlcatelFor Alcatel CS1 is always used for signallingCS1 is always used for signalling CS1 and CS2 are used for trafficCS1 and CS2 are used for traffic CS3 and CS4 are not available in release B6.2.CS3 and CS4 are not available in release B6.2.


CS Adaptation (2)CS Adaptation (2)

AV_RXQUALAV_RXQUAL

AV_RXLEVAV_RXLEV

CS_QUAL_2_1CS_QUAL_2_1

CS_QUAL_1_2CS_QUAL_1_2

CS_LEVCS_LEV

CS 1 areaCS 1 area Hysteresis areaHysteresis area

CS 2 areaCS 2 area

AlgorithmAlgorithm CS1 -> CS2 :CS1 -> CS2 :

AV_RXQUAL < CS_QUAL_1_2 and AV_RXLEV > CS_LEVAV_RXQUAL < CS_QUAL_1_2 and AV_RXLEV > CS_LEV CS2 -> CS1 :CS2 -> CS1 :

AV_RXQUAL >= CS_QUAL_2_1 or AV_RXLEV <= CS_LEVAV_RXQUAL >= CS_QUAL_2_1 or AV_RXLEV <= CS_LEV


Radio Link SupervisionRadio Link Supervision

During an UL or DL packet transmission, the During an UL or DL packet transmission, the corresponding TBF can be released due to abnormal corresponding TBF can be released due to abnormal situations :situations : too high retransmission ratetoo high retransmission rate no acknowledgement or data receivedno acknowledgement or data received

The abnormal release is always followed by the re-The abnormal release is always followed by the re-establishment of the TBF in case of uplink transfer establishment of the TBF in case of uplink transfer (initiative of the MS).(initiative of the MS).

In case of downlink transfer, most of the SGSN do not In case of downlink transfer, most of the SGSN do not take the initiative to re-establish the TBF.take the initiative to re-establish the TBF.


Quality of Service (1)Quality of Service (1)



Different levels of QoS shall be distinguished :Different levels of QoS shall be distinguished : User QoS profile :User QoS profile :

end to end QoS granted to a user application.end to end QoS granted to a user application. GPRS QoS profile :GPRS QoS profile :

QoS granted in the GPRS network between the MS and the PDN.QoS granted in the GPRS network between the MS and the PDN. defined in term of Service precedence, Transfer delay, Mean and defined in term of Service precedence, Transfer delay, Mean and

peak throughputs and reliability.peak throughputs and reliability. Radio QoS profile :Radio QoS profile :

QoS granted on the radio interfaceQoS granted on the radio interface defined in term of Throughput, Service precedence, RLC reliability defined in term of Throughput, Service precedence, RLC reliability

mode, and Transfer delaymode, and Transfer delay OPTIM OPTIM parts of Um interface : LLC, RLC/MAC, GSM RF parts of Um interface : LLC, RLC/MAC, GSM RF Network Layers (SNDCP & IP/X25 & Application) are included if Network Layers (SNDCP & IP/X25 & Application) are included if

capable with IP/X25 & Applications knowledge.capable with IP/X25 & Applications knowledge.



ETSI R’97 principles :ETSI R’97 principles : GPRS QoS is negotiated GPRS QoS is negotiated

between the MS and the between the MS and the SGSN, at PDP context SGSN, at PDP context activation.activation.

The BSS is not involved in The BSS is not involved in QoS negotiation.QoS negotiation.

No absolute QoS can be No absolute QoS can be guaranteed by the BSS.guaranteed by the BSS.

SGSN and GGSN play the SGSN and GGSN play the main role in QoS main role in QoS managementmanagement

5 GPRS QoS attributes in the R’97 standard5 GPRS QoS attributes in the R’97 standard Precedence Class : relative importance of Precedence Class : relative importance of

service under congestion; 3 values are service under congestion; 3 values are defined.defined.

Delay Class : total delay measured between Delay Class : total delay measured between R or S point and Gi; 4 values are defined.R or S point and Gi; 4 values are defined.

Reliability Class : mainly linked to Ack/Not Reliability Class : mainly linked to Ack/Not Ack modes at RLC and LLC levels and within Ack modes at RLC and LLC levels and within the backbone network; 5 values are defined.the backbone network; 5 values are defined.

Peak Throughput Class : measured at Gi and Peak Throughput Class : measured at Gi and R reference points;R reference points;9 values, ranging from 8 kbit/s up to 2048 9 values, ranging from 8 kbit/s up to 2048 kbit/skbit/s

Mean Throughput Class : measured at the Gi Mean Throughput Class : measured at the Gi and R reference points; 19 values, ranging and R reference points; 19 values, ranging from Best Effort up to 111 kbit/sfrom Best Effort up to 111 kbit/s



QoS Follow upQoS Follow up GPRS QoS is not an isolated topic.GPRS QoS is not an isolated topic. It is necessary to use GSM counters in order to complete the It is necessary to use GSM counters in order to complete the

analyse of GPRS QoS and the impact of GPRS on GSM QoS.analyse of GPRS QoS and the impact of GPRS on GSM QoS. The BSS QoS does not allow to have a complete understanding The BSS QoS does not allow to have a complete understanding

of the end to end QoS seen by the user.of the end to end QoS seen by the user. Indeed, upper protocol layers (TCP for example) have a great Indeed, upper protocol layers (TCP for example) have a great

impact on the global QoS (out of Optimization scope).impact on the global QoS (out of Optimization scope). The GSS (SGSN & GGSN) also has a great impact on the The GSS (SGSN & GGSN) also has a great impact on the

global QoS.global QoS.

GPRS Technical Introduction Version1.0

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