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1、Motorola Confidential Proprietary!MOTOROLA and the Stylized M Logo are registered in the US Patent&Trademark Office.All other product or service names are the property of their respective owners.Motorola,Inc.2002.中国移动中国移动GPRS无线优化课题交流会无线优化课题交流会Solution CenterGTSS ChinaMotorola22 十月 2022Motorola Confi
2、dential Proprietary!Page 2q1.GPRS业务模型分析业务模型分析22 十月 2022Motorola Confidential Proprietary!Page 3Motorola USTM View of User ServicesMotorola USTM View of User ServicesUSTM considers service activity from the GPRS/UMTS users point of view:(USTM stands for Unified Simple Traffic Models)User ApplicationT
3、elecommunications NetworkUser ApplicationApplication Level Service ActivityAt this level the application service behaviour is relatively network implementation independent.However,as the traffic is transported over the network,traffic behaviour within the network will depend on the network implement
4、ation and configuration22 十月 2022Motorola Confidential Proprietary!Page 4Example:Example:Application Protocols Interaction Application Protocols InteractionAs the application interacts with different protocols in the network implementation,application traffic becomes packets.ApplicationApplicationUM
5、TS NetworkUTRANCore NetworkInternetTCP/IPPacket ActivityApplication-level ActivityPacket behaviour may be different in different protocol layers,and parts of the network,i.e:UTRANUMTS Core NetworkExternal Packet Data NetworkTCP&IP packetsRLC SDURadio frames22 十月 2022Motorola Confidential Proprietary
6、!Page 5Layered Traffic Modelling ApproachLayered Traffic Modelling ApproachThe traffic characteristics of a service can be very complex.It is often described by a layered service workload modelservice workload model data application model in USTM.The following is a view of the FTP service:SessionBur
7、st(File)Packetttt22 十月 2022Motorola Confidential Proprietary!Page 6Definition of A SessionDefinition of A SessionvA service session is a logical entity.vIndependent of transmission direction.vIt is basically described as the period where a user is actively using the service.vDuring an active service
8、 session,the network must maintain connectivity between the users in that session.ServiceDefinition of SessionTelephony:Telephone call durationWWW:Web browsing session(difficult to determine finish)FTP:Period downloading from single serverEmail(download):From connecting to email server to disconnect
9、ionSessions are described by:Session Duration(D)Session Inter-arrival time(I)DIt22 十月 2022Motorola Confidential Proprietary!Page 7Definition of A BurstDefinition of A BurstServiceExample of BurstTelephony:Active talk spurtWWW:HTTP objects in a WWW page downloadFTP:Transfer of a file between server c
10、lientEmail(download):A file containing single email with MIME encoded attachmentsSMS:One text messageBursts described by:Burst Size/Duration()Inter-burst time(T)TtvThe Burst represents a block of real traffic that the application sends/receives.vThe Burst is the activity that the bearer channels in
11、the network see.vFor many services,a burst equates to the transfer of a file or message.vThe burst is uni-directional(uplink and downlink bursts are different).Note:Burst duration may be driven by data size/link speed/load22 十月 2022Motorola Confidential Proprietary!Page 8More Examples of Burst More
12、Examples of Burst Telephony:Speech burstsUplinkDownlinkWWW:File burstsUplinkDownlinkPage DownloadsSMS MO:Message BurstUplinkSpeech samples encoded into speech frames.Whilst originator is talking,speech frame activity generates the speech burst.Complex WWW pages may contain multiple objects located o
13、n different servers.Downloading an object is an HTTP request/response transaction.Unidirectional transmission of the SMS packet.22 十月 2022Motorola Confidential Proprietary!Page 9A complete View Example:A complete View Example:WWW Traffic ModelWWW Traffic ModelSAWWW Application Summary:SessionObjects
14、tDItBurststULDLBurstPacketTD-Session durationI-Session inter-arrival time-Burst durationT-Inter-burst timeS-Packet sizeA-Packet inter-arrival time22 十月 2022Motorola Confidential Proprietary!Page 10PDP ContextsPDP ContextsA PDP context is a logical pipe that provides the transfer of user data across
15、the UMTS network.UMTSExternalNetworkApplicationPDP ContextApplicationFrom either end,the PDP context will look like an IP termination(IP address/port)that offers a given level of IP QoS(e.g.acts as a DiffServ code point).Note:The PDP context does not really see the user application,but only sees the
16、 IP QoS requirements.UMTSUserLANPDPExt.IPTETETETEUMTS looks like an IP routerReal Network=MS ModemGGSNUEUERemote Host22 十月 2022Motorola Confidential Proprietary!Page 11PDP Contexts vs.Sessions in USTMPDP Contexts vs.Sessions in USTMvA service session needs a connection across the IP networks to oper
17、ate.vThus a service session needs a PDP context over UMTS for its duration.vHowever,a PDP context may exist before and after a particular service session.vMore than one service session can use a single PDP context.vDifferent services sessions may share a single PDP context.vPDP contexts may change s
18、tates(active,standby).This is transparent to the service.Service A sessionsService B sessionsPDP Contextst22 十月 2022Motorola Confidential Proprietary!Page 12Data Collection pointsRANCorePDNGbMDTTPCtcpdump/windumpTcptrace/EtherrealNetsenseGiGb ConsultantRadComGb Link AnalysisEnd-to-End AnalysisPerfor
19、mance Benchmarkingtcpdump/windumpTcptrace/EtherrealNetsenseEnd-to-End AnalysisEnd User(Data and RF Stats)K1205Gb SnoopGDSScriptsBOTGi Link AnalysistcpdumpWindumpTcptraceEtherrealNetsenseTCP AnalyzerTEMS22 十月 2022Motorola Confidential Proprietary!Page 13用户数据流与协议栈用户数据流与协议栈用户数据用户数据(IP包包)从终端出发跨过从终端出发跨过G
20、PRS承载到达因特网承载到达因特网,途中进行了大量的协议封装和解封装途中进行了大量的协议封装和解封装,传输完成后传输完成后,在在GGSN还原成原来的用户数据还原成原来的用户数据(IP包包),从从GGSN经经Gi接口进入因特网接口进入因特网,我们选择我们选择Gi接口作为用户数据流的侦听接口作为用户数据流的侦听和分析点和分析点.BSS/PCUSGSN因特网因特网GGSNPPPIPTCP/UDPHTTP etc.L2L1IPTCP/UDPHTTP etc.L2L122 十月 2022Motorola Confidential Proprietary!Page 14Gi接口用户数据的封装接口用户数据的
21、封装WAP数据从数据从GGSN出发封装到出发封装到GRE隧道协议中去隧道协议中去WAP网关网关,WAP网关作为代理访问服务站点网关作为代理访问服务站点WWW服务服务,电子邮件服务以及其它因特网服务经过电子邮件服务以及其它因特网服务经过TCP/UDP封装后封装后,直接进入因特网去服务站点直接进入因特网去服务站点因特网因特网GGSNWap GWGRETCP/UDPwww serverOther AppsMail serviceIPTCP/UDP/GREHTTP/WAP/POP3&SMTP/etc.L2L1NetworkTransportApplicationData LinkPhysical22
22、十月 2022Motorola Confidential Proprietary!Page 15协议栈与分析内容协议栈与分析内容ApplicationPresentationSessionTransportNetworkData LinkPhysicalApplicationPresentationSessionTransportNetworkData LinkPhysical封装后的应用层报文和实际传输的数据,如FTP DataApplicationApplication应用层报文(控制消息等),如FTP Control在应用层只能看到“应用消息”,它被封装到传输层和网络层与数据一起被传输,
23、在应用层的话务量分析没有意义.应用层做会话分析,传输层做连接分析和话务分析.传输协议分析应用协议分析应用会话分析传输连接分析传输流量分析网络流量分析22 十月 2022Motorola Confidential Proprietary!Page 16分析内容分析内容分析内容22 十月 2022Motorola Confidential Proprietary!Page 17qCase Study in 2003 from a European Network22 十月 2022Motorola Confidential Proprietary!Page 18Detailed Analysis
24、GeneralTotal FiguresTotal FiguresAll Sessions+10kByte SessionsTotal Traffic:440MByte330MByteDL/UL Ratio:4,7532,55Sessions:647786936TCP Sessions:80%100%Session Duration(Avg):10s(85%)1min 50secTraffic per TCP Session(Avg):7,1kB47kBTraffic per UDP Session(Avg):1,1kBN/AAverage Segment Size(DL/UL):320/N/
25、A Bytes780/330 Bytes+10kByte SessionsAll sessions with more than 10kByte traffic in downlink are counted.Source:TCPDump/TCPTrace22 十月 2022Motorola Confidential Proprietary!Page 19Detailed Analysis GeneralApplication Usage(in term of sessions)Source:TCPDump/TCPTraceAll Sessions1%650 Sessions+10kB Ses
26、sions(in DL)1%70 Sessions22 十月 2022Motorola Confidential Proprietary!Page 20Detailed Analysis GeneralApplication Usage(in term of bytes)Source:TCPDump/TCPTraceAll Sessions1%650 Sessions+10kB Sessions(in DL)1%70 Sessions22 十月 2022Motorola Confidential Proprietary!Page 21Detailed Analysis GeneralTrans
27、port Protocol UsageMajor TrafficTCPHTTPEmailSource:TCPDump/TCPTraceUDPWAPDNSBytesSessionsAll Sessions22 十月 2022Motorola Confidential Proprietary!Page 22Detailed Analysis GeneralPacket Size(UL and DL)Source:TCPDump/NetSenseAll Sessions22 十月 2022Motorola Confidential Proprietary!Page 23Detailed Analys
28、is TCP ParameterSegment SizeRequestedAppliedWindow SizeInitial,Avg/StdDev/Min/MaxAppliedSelective ACK UsageOut of Order PacketsSource:TCPDump/TCPTrace22 十月 2022Motorola Confidential Proprietary!Page 24Detailed Analysis TCP Parameter Selective Acknowledge/Out of Order(on Gi)Source:TCPDump/TCPTraceSel
29、ective AcknowledgeAll Sessions+10kByte Sessions(DL)DL:24%0,04%Used in X%of the TCP SessionsUL:24%2%Used in X%of the TCP SessionsOut of Order PacketsDL:0,16%2,93%TCP Sessions with OoO PacketsUL:0,07%0,22%TCP Sessions with OoO Packets22 十月 2022Motorola Confidential Proprietary!Page 25Conclusion&Recomm
30、endationsqSystem OptimisationqHW/SW DimensioningqFeature Priorization22 十月 2022Motorola Confidential Proprietary!Page 26Conclusion&RecommendationsSystem OptimisationqShort Sessions-GeneralHTTP1.1 is usedCauses Low ThroughputLow SACK usage for large transfers3%out of order packet for large transfers
31、on Gi!Recommendation:TCP Stack Tuning ProxySelective ACK,RetransmissionsTCP Client Window Size Tuning(via Driver Installation?)Important for CS3-4Further Analysis on Why so many short(HTTP)sessions?“22 十月 2022Motorola Confidential Proprietary!Page 27Conclusion&Recommendations Hardware/Software Dimen
32、sioningqSegment Size+60%of packets are+500BytesRecommendation:Maximum LLC length optimisation(Max.Improvement 1%)qHardware DimensioningTraffic Distribution,Busy Hour 2pm with 1/3 above minimum22 十月 2022Motorola Confidential Proprietary!Page 28Conclusion&Recommendations Feature PriorizationqSession D
33、urationSessions are mainly very shortRecommendation:Overlapping TBF and Rapid Interleaving are very importantqSession IntervalTypically below 5seconds.Shows benefit of Super-CoattailRecommendation:SCT Parameters are set well22 十月 2022Motorola Confidential Proprietary!Page 29Conclusion&Recommendation
34、s Feature PriorizationqApplication Usage97%of the traffic is TCPUDP traffic is WAP(is connection oriented)and DNSRecommendation:LLC Acknowledgement not necessary22 十月 2022Motorola Confidential Proprietary!Page 30q案例：案例：引入新应用引入新应用(Push to Talk)22 十月 2022Motorola Confidential Proprietary!Page 31Case S
35、tudy Five-Introduction of new application&understanding its impactqCustom Telemetry application was modelled and simulated by GSMSq8 GPRS Timeslots were considered per cellq250,500&750 users in a cell were simulated250 Users500 Users750 Users22 十月 2022Motorola Confidential Proprietary!Page 32New Cha
36、llenges with PTT over GPRSqPTT is the first always-on application to be deployed over GPRS NetworkPDP context is always on and TBF is setup during conversations could be a capacity constraintqRequirements on GPRS NetworkMinimal latency Optimal bandwidth to support PTT trafficCell Reselection&Routing
37、 Area Update delays should be minimalUplink/downlink TBF release duration should be optimal,to enable PTT conversation to use the same TBF and avoid setting up a new TBF,for every push22 十月 2022Motorola Confidential Proprietary!Page 33Optimise SGSN Ready Timer ValueqIn STANDBY no data reception is p
38、ossible.To get back to READY state,the mobile needs to be paged,thus increasing the set-up time,for the first push.Benefit:By increasing the Ready Timer on the SGSN,the mobiles stay longer in READY state.Drawback:Increased ready timer increases the number GMM signaling messages and causes higher bat
39、tery consumption.STANDBYIDLEREADYGPRS attachGPRSdetachREADY timer expiry or forced to STANDBYPDUtrans-mission22 十月 2022Motorola Confidential Proprietary!Page 34Optimised use of PBCCH/PCCH featurePBCCH/PCCCH provides more signalling capabilities for both GSM voice and GPRS service by moving all GPRS
40、signalling on to the PBCCH/PCCCH.It reduces internal signalling traffic over the GSL and RSL since there are fewer requests,assignments or paging messages over GSL and RSL.This is due to GPRS signalling traffic shall be carried over the TRAU GDS 22 十月 2022Motorola Confidential Proprietary!Page 35Opt
41、imised use of PBCCH/PCCH featureBenefits for PTTqIncreased signalling capacity to support PTT type applicationqSeparated signalling for GPRS(PTT)and GSMqFaster pagingqShorter TBF set-up times in heavily loaded networks(cells)compared to the situation without the PBCCH/CCCH feature.DrawbacksqBy reser
42、ving a timeslot for a PBCCH/PCCCH,capacity will be lost for GPRS,though it should be noted that a PBCCH/PCCCH timeslot may still be used for user data(only PPCH&PAGCH i.e.downlink,no uplink).If a cell is RAC boundary,the resource on the cell will be used for location area updates and so leave less r
43、esource for user data.qNot all existing GPRS MSs support PBCCH and these MSs wont be able to attach when PBCCH is present in the cell22 十月 2022Motorola Confidential Proprietary!Page 36Optimising DRX timerqThe gprs_drx_timer_max parameter controls how long the mobile station stays in non-DRX mode,whe
44、n it has left the packet transfer mode and enters the packet idle mode.The maximum value of this parameter is 3 seconds.qBenefit for PTTDecreasing set-up times for consecutive“pushes”,when done within 3 seconds(or whatever duration is set)after last data transmission/reception.qDrawbackOptimizing th
45、e non-DRX timer is important to increase MS battery lifetime22 十月 2022Motorola Confidential Proprietary!Page 37One Phase accessqOne Phase access is recommended for GPRS Network to reduce TBF set-up times,this works well for lightly loaded network.qFor a congested network,this may result into RSL con
46、gestion.To avoid using the RSL to notify the PCU of an access,the BTS forces the mobile to perform a two-phase access,with the mobile sending a PRR on the reserved block.Since this reserved block is on a PDCH,this signalling is carried out on GPRS TRAU and not the RSL,thereby reducing RSL load.(This
47、 requires that uplink blocks are reserved for only PACKET RESOURCE REQUESTS)By reserving blocks for PRRs and forcing two phase packet access RSL congestion is reduced,but the trade off is that two phase packet access results in a much slower TBF establishment time than both one phase and enhanced on
48、e phase.22 十月 2022Motorola Confidential Proprietary!Page 38PTT Performance Enhancement22 十月 2022Motorola Confidential Proprietary!Page 39qGPRS网络无线优化原则及案例分析网络无线优化原则及案例分析22 十月 2022Motorola Confidential Proprietary!Page 40GPRS 网络结构22 十月 2022Motorola Confidential Proprietary!Page 41GPRS优化所涉及的网络单元22 十月 2
49、022Motorola Confidential Proprietary!Page 42AirIPCircuit载干比载干比载干比载干比吞吐量吞吐量吞吐量吞吐量误码率误码率误码率误码率延迟延迟延迟延迟传输速率传输速率传输速率传输速率Network CMCC主要统计主要统计重传率重传率重传率重传率CSCS比率比率比率比率无线参数无线参数无线参数无线参数时钟时钟时钟时钟 终端应终端应用测试用测试路测路测数据数据GPRS优化所涉及的改善指标22 十月 2022Motorola Confidential Proprietary!Page 43GPRS 的优化方式SnifferSnifferHP3790
50、7HP37907接口测试接口测试接口测试接口测试MDTTMDTT手段手段工具工具路测路测路测路测CTPCTPSwordFishSwordFishgNPMgNPMTcpdumpTcpdump/Tcptrace/Tcptrace终端用终端用终端用终端用户测试户测试户测试户测试性能测试性能测试性能测试性能测试IPIP包监测包监测包监测包监测数据库审计数据库审计数据库审计数据库审计应用层应用层传输层传输层MSPCUBTSBSCCorporateVPNWAPGatewayRadiusDHCPDNSFRBillingLIANSGSNGGSNISSIOSIOS22 十月 2022Motorola Confi