GSM移动通信知识简介.ppt

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1、,GSM system overview,GSM移动通信知识简介Zheng Xinjian,GSM system overview,电话通信系统简介 简单而言，电话通信系统完成的主要功能包括：为电话呼叫的主、被叫双方临时建立一条传送话音的通路（比如基于物理中继线PCM的物理电路的连接通路，或者基于TCP/IP网的连接通路）。对通话双方的呼叫计费过程。呼叫计费主要由主、被叫的电话交换机（比如GSM系统的MSC交换机）根据呼叫事件完成；而传送话音通路的建立、维持，以及呼叫结束后通路的释放等过程，都需要参与到呼叫中的所有交换机依靠一种叫做信令的协议系统来完成，这种信令系统是一系列的约定（protoc

2、ol,协议)，通过这些约定使得电话交换机间能彼此识别对方的相关请求并做出应答，这些请求和应答构成了电话交换机间的“对话”，而通过这些“对话”就能完成上述的一系列有关电话通路的动作。至少同一个运营商的所有电话交换机都能识别并遵守这些约定（协议）。不同运营商可能使用不同的信令系统(比如，不同运营商有各自的MTP3层的SP码），它们间的通信可以通过信令关口局来完成，信令关口局对这些不同的信令（约定）进行转换。,GSM system overview,时分多路复用系统为了提高信道利用率，使多个信号沿同一信道传输而互相不干扰，称多路复用。目前采用较多的是频分多路复用和时分多路复用。时分多 路复用用于数字

3、通信，例如PCM通信。各路信号分别抽样、编码、再经时分复用分配器合路后送入信道；为保证正常通信，时分复用通信中利用了包括位同步(时钟同步)和帧同步的同步技术，这是数字通信的又一个重要特 点。位同步(时钟同步)用于保证接收端正确接收和判决发送端送来的每一个码元。帧同步是为了保证收、发各对应的话路在时间上保持一致，这样接收端就能正确接收发送端送来的每一个话路信号，当然这必须是在位同步(时钟同步)的前提下实现。,GSM system overview,时分复用的帧结构 时分多路复用的方式是用时隙来分割的，每一路信号分配一个时隙，帧同步码和信令码也各分配一个路时隙。PCM30/32(又称基群或一次群)

4、系统的意思是整个系 统共分为32个路时隙，其中30个时隙分别 用来传送30路话音信号，一个时隙用来传送帧同步码，另一个时隙用来传送信令码。PCM30/32路系统采用复帧的概念，其中一个复帧包含16帧，编号为F0帧、F1帧F15帧，一复帧的时间为2毫秒。每一帧(每帧的时间为125微秒)又包含有32个路时隙，其编号 为TS0、TS1、TS2TS31，每个路时隙的时间为3.9微秒。每一路时隙包含 有8个位，每个位时隙的时间为0.488微秒。偶帧TS0时隙传送帧同步码，其码型为0011011。奇帧TS0时隙码型为1A1SSSSS，其中A1是对端告警码，A1=0时表示帧同步，A1=1时表示帧失步；S为备

5、用比特，可用来传送业务码；为国际备用比特或传送循环冗余校 验码(CRC码)，它可用于监视误码。F0帧TS16时隙前4位码为复帧同步码，其码型为 0000；后四位码型为 1A211，A2为复帧失步对告码。F1F15帧的TS16时隙用来传送30个话路的信令码。帧频率应为8000帧/秒，帧周期为125微秒，所以PCM30/32路系统 的总数码率是：8000(帧/秒)32(路时隙/帧)8(bit/路时隙)=2048kbit/s=2.048Mbit/s NOTE:一个复幀才是真正意义上的完整的“幀”，16个幀组成复幀才是一个完整的功能体。：个注,GSM system overview,GSM系统组成简要

6、分析 假设移动用户A发起电话呼叫，被叫B也是移动用户。很明显：最终A所在的交换机需要建立到B用户所在交换机的电话通路 但是，因为GSM手机是可以移动（漫游）的，主叫A的交换机在A开始呼叫时并不知道B在哪儿，所以：系统需要有一种机制记录移动用户所在的位置（漫游在哪个交换机控制区）同时，还需要提供一种机制能让主叫交换机找到B所登记的交换机，以供建立电话呼叫连接 移动手机是通过无线系统接入交换机的，所以：GSM系统与PSTN（固定电话系统）比较，需要加入无线接入系统部分。由以上的几个需要，可以引入GSM系统的构成，以及GSM系统内的呼叫建立过程。,GSM system overview,The th

7、ree Subsystems of GSM,GSM system overview,NSS Elements,GSM system overview,BSS Elements,GSM system overview,NOKIA系统结构：MSCi&MSS architectureMGW architecture,GSM system overview,信令系统应用举例（Simplified steps in a call set up）：所有交换机间的互操作都需要协议的支持，下面以一个PSTN用户呼叫GSM用户为例来对信令系统的应用做一简要的介绍。,GSM system overview,信令系

8、统简介随着通信技术的发展，信令系统也在不断发展完善。在PSTN(public switched telephone network，即固定电话网络)系统中，所有的信令都跟呼叫有关，即跟呼叫通路的建立、维持、释放等有关。但在GSM系统中，除了呼叫通路相关的信令需求外，还有一系列的事件和通路建立的操作无关：比如手机在网络中的登记（Register）、漫游等并没有话音的传送，也就不需要传送话音通路的建立，但要完成这些事件却仍然需要在多个设备间传送相关消息（message)，这些消息的传送也要信令的支持。原来电话网络中使用的信令系统是CCS7七号信令系统，它和ISO组织（国际标准化组织）提出的OSI系

9、统的对应关系如下：,Only the lowest level in the protocol stack has the actual connection to the physical medium between the network nodes,and all data transfer must at least go through the lowest three levels.,GSM system overview,信令系统简介,GSM system overview,信令类型：呼叫相关信令 VS.呼叫无关信令exchange of information in orde

10、r to establish,maintain or release one specific call.A call attempt must be started or a call must be ongoing.消息的交换是为了建立，保持，释放一个 exchange of information that modifies the conditions under which multiple future calls take place.It happens without any call going on.电路相关信令 VS.电路无关信令.exchange of informa

11、tion that refers explicitly to the circuit through which a call is transmitted by identifying this circuit with an identification code(CIC).exchange of information that does not refer to a circuit but to other properties such as an identification of the subscriber,an identification number of a mobil

12、e station or other identifiers.,GSM system overview,Example of circuit-related and non-circuit-related signalling,Circuit-related Signaling flow,Basic call setup,Table 32/Q.763,GSM system overview,CCS7 protocols in various network elements,GSM system overview,3 different kinds of signal units,GSM sy

13、stem overview,Structure of messages from MTP users,GSM system overview,The Structure of the Network Management messages(SI=0000),GSM system overview,Structure of the standard routing label:Layer 3 of the MTP,GSM system overview,The SIO structure,GSM system overview,The SIO structure,GSM system overv

14、iew,User Parts,GSM system overview,Telephone User part,TUP message structure,GSM system overview,ISDN User part,ISUP message structure,GSM system overview,Example of a ISUP call establishment,GSM system overview,Application Parts,All GSM specific application parts need the SCCP services.This means t

15、hat:the SCCP should be able to perform routing functions for signalling messages which are sent from its users(SCCP subsystems)only MTP services can not fulfil the application part requirement.,GSM system overview,SCCP message structure,GSM system overview,TCAP message structure,GSM system overview,

16、基于无连结网络的TCAP的结构,事务处理子层完成对本端成份子层用户和远端事务处理子层用户之间通信过程的管理，是对对话的启动、保持和终结进行管理，包括对话过程异常情况的检测和处理。成份是事务处理子层负责传送对话消息的基本单元，成份子层完成对话中成份的处理，及对话的控制处理。,GSM system overview,TCAP message transfer,GSM system overview,MAP as TCAP user,Transaction Capability Application Part(TCAP),Mobile ApplicationPart(TCAP-User),MAPA

17、pplication Entity(AE),MAPApplication ServiceElement(ASE),MAPApplication ServiceElement(ASE),GSM system overview,Basic structure of MAP messages1/3,Order of transmission,Ptr toCLD,SCCP-UDT message,Routinglabel,Msg code,Ptr toCLG,Ptr touser data,CLDparameter,CLGparameter,Userdata,Length,Transparentdat

18、a,MsgTypeTag,Transactionportion,Componentportion,Lengthfield,BEGIN message(TCAP),GSM system overview,Basic structure of MAP messages2/3,MsgTypeTag,Transactionportion,Componentportion,Lengthfield,BEGIN message(TCAP),ComponentType Tag,Lengthfield,Lengthfield,Componentportion Tag,Invoke Component,Invok

19、e ID,Operation,Parameters,Order of transmission,GSM system overview,Basic structure of MAP messages3/3,ComponentType Tag,Lengthfield,Invoke ID,Operation,Parameters,Order of transmission,IMSIMSC numberMSC signalling address signalsLMS ID,Update Location,GSM system overview,Example:Location registrati

20、on operationUpdateLocation:=OPERATION-Timer mARGUMENTupdateLocationArgUpdateLocationArgRESULTupdateLocationResUpdateLocationResERRORS SystemFailure,DataMissing,-DataMissing must not be used in version 1UnexpectedDataValue,UnknownSubscriber,RoamingNotAllowed,GSM system overview,DATA Type:UpdateLocati

21、onArg:=SEQUENCE imsiIMSI,locationInfoLocationInfo,vlr-NumberISDN-AddressString,lmsi10 LMSIOPTIONAL,.IMSI:=TBCD-STRING(SIZE(3.8)-digits of MCC,MNC,MSIN are concatenated in this order.,GSM system overview,Error and error code:SystemFailure:=ERRORPARAMETERnetworkResourceNetworkResource-optionalsystemFa

22、ilure SystemFailure:=localValue 34,GSM system overview,BSSAP subparts(DTAP and BSSMAP),GSM system overview,Speech Transcoding and Processing The information transferred through the Air interface uses quite a wide frequency spectrum:the higher bit rate used,the wider spectrum it will take.If the spec

23、trum is wide,it decreases Air interface capacity.Inside the BSS,one traffic channel is 16 kbit/s including 3 kbit/s extra space for synchronisation purposes.These 3 kbit/s is also used by the BTS for TC controlling purposes.,GSM system overview,MAP interfaces between the network elements,MSC Server

24、in Rel 4 based network,RNC,GSM,BSC,WCDMA,MGW,ExternalIP networks,IP/ATMBackbone,MGW,PSTN/ISDN,Other PLMN,HLR,GGSN,A,A,Iu-CS,H.248,H.248,BICC CS-2,SIP-T,IN/SCE,APSE,MSS Interfaces&ProtocolsRel.4 Network,Iu-CS,MSCServer,AAL2ATM,TDM,H.248IP,MSCServer,Mc,MGW,Nc,AAL2/AAL5ATM,Nb,Mc,SigtranIP,BICC,SIPATM/I

25、P,无线接入接口(Iu,A):RANAP and BSSAPMSS之间接口(Nc):BICC and SIPATM AAL2承载用户数据,AAL5承载信令.SIGTRAN在IP网上传输SS7.MSS和MGW之间：H.248/MEGACOISUP,TUP 用于 TDM trunk 呼叫控制.,MAP,CAP,MGW,RTPIP,RANAPAAL5/ATM,SS7,SigtranIP,ATDM,BSSAP,H.248IP,R4 system,Protocols over IP,ATM network,MSC Server,MGW_A,MGW_B,RNC,MTP3,ISUP,M3UA,ISUP,SC

26、TP,IP,M3UA,SCCPb,SCTP,IP,RANAP,MTP3b,SCCPb,SAAL,ATM,RANAP,TranscodingG.711AMR,TDM,G.711,Nb_up,AMR,AAL2,ATM,SDH,H.248,SCTP/TCP,IP,M3UA,SCCP,SCTP,IP,TCAP,MAP,HLR,NodeB,BSC,BTS,MTP3,SCCP,BSSAP,M3UA,SCCP,SCTP,IP,BSSAP,IP network,MGW_A,MGW_B,RNC,MTP3,ISUP,M3UA,ISUP,SCTP,IP,M3UA,SCCPb,SCTP,IP,RANAP,MTP3b,

27、SCCPb,SAAL,ATM,RANAP,TDM,G.711,H.248,SCTP/TCP,IP,NodeB,MSC Server,SIP-T,UDP,IP,GSM codec/G.711,RTP,UDP,IP,ATM/PoS,HLR,MSC Server/Gateway ControlServer,GSM system overview,SCCP subsystems of MAP in the DX 200 architecture,GSM system overview,信令路由 从信令网全局而言，每一个网元都是一个信令点，每一个信令点都有用于全网唯一识别的ID。MTP层的ID是SPC地

28、址（Signaling Point Code，信令点编码）SCCP层的ID是GT地址（Global Title)这两个ID都可以用于信令网内寻路，但用于不同的情况。SCCP层必须有MTP的支持，SCCP地址在实际应用时通过GT分析得到MTP地址（下一网元的MTP层地址），即从哪一个相邻网元进入GSM网。,GSM system overview,MTP levels,GSM system overview,Functions of MTP level 2 and level 3,GSM system overview,Signalling message handling,GSM system

29、overview,Signalling routing methods(by MTP and SCCP),GSM system overview,Signalling routing(MTP and SCCP),SCTP启动流程,EndpointA,EndpointB,Create TCB,Create TCB,Client,SCTP as client,TX,RX,Association,IP,Server,SCTP as server,TX,RX,Association,Associate,Functionality of SCTP,User data1,User data2,Common

30、Header,Chunk Header,User data1,Chunk Header,User data2,IP Header,User data2,CommonHeader,Chunk Header,User data1,Chunk Header,IP,SCTP,ULP,Chunk Bundling,the SCTP packet as delivered to the lower layer consists of a common header followed by one or more chunksEach chunk may contain either user data o

31、r SCTP control informationSCTP user(ULP)has the option to request bundling of more than one user messages into a single SCTP packetThe chunk bundling function of SCTP is responsible for assembly of the complete SCTP packet and its disassembly at the receiving end,Bundling&Fragmentation,Big User Mess

32、age,Datagrams,BUNDLING,FRAGMENTATION,Small User Messages,One Datagram,SCTP Datagram Format,Common Header,Chunk#1,Chunk#3,Chunk#2,SCTP Datagram,Adler-32 Checksum,Verfication Tag,Chunk Value,Source port number,Destination port number,Common Header,Chunk ID,Chunk flags,Chunk Length,Chunk,SCTP-datagram

33、in IPv4-packet,SCTP,SCTP 数据包（PACKET),SCTP 数据包（PACKET),Chunk type,Chunk type field used to distinguish data chunks and different types of control chunks Examples of chunk types:0-Payload Data(DATA)1-Initiation(INIT)2-Initiation Acknowledgement(INIT ACK)3-Selective Acknowledgement(SACK)4-Heartbeat Req

34、uest(HEARTBEAT)5-Heartbeat Acknowledgement(HEARTBEAT ACK)6-Abort(ABORT)7-Shutdown(SHUTDOWN)8-Shutdown Acknowledgement(SHUTDOWN ACK)9-Operation Error(ERROR)10-State Cookie(COOKIE ECHO)11-Cookie Acknowledgement(COOKIE ACK)12-Reserved for Explicit Congestion Notification Echo(ECNE)13-Reserved for Conge

35、stion Window Reduced(CWR)14-Shutdown Complete(SHUTDOWN COMPLETE)15 to 62-reserved by IETF,SCTP DATA chunk format,Byte,Example of SCTP data chunk,Stream Control Transmission Protocol,Src Port:2945(2945),Dst Port:8010(8010)Source port:2945 Destination port:8010 Verification tag:0 x23a75d2e Checksum:0

36、x2436b406(correct CRC32C)DATA chunk(ordered,complete segment,TSN:3182377136,SID:0,SSN:54884,PPID:7,payload length:64 bytes)Chunk type:DATA(0)0.=Bit:Stop processing of the packet.0.=Bit:Do not report Chunk flags:0 x03.1=E-Bit:Last segment.1.=B-Bit:First segment.0.=U-Bit:Ordered deliviery Chunk length

37、:80 TSN:3182377136 Stream Identifier:0 x0000(o or 1)Stream sequence number:54884(单向计算,0-65535）Payload protocol identifier:H.248/MEGACO(7),INIT CHUNK,Byte,INIT ACK CHUNK,return,H.248/MEGACO in general,Master-slave protocolThe MGC(Media Gateway Controller)is the master and the MG(Media Gateway)the sla

38、veMG registers with the MGC and the association is setupa one-to-one protocol,MG is controlled by one MGCcan be ASN.1 binary codes or ASCII coded,MGC must support both,MG choosesSpecified in IETF(Megaco)and ITU-T(H.248)In 3GPP mandated between MSS and MGW for Rel.4In Rel.5 it is used between MGCF an

39、d MGW,and CSCF and MRFConnection model based on termination and contexts,Ta,Tb,terminations,MGW,context C,User data,User data,Protocol stack,Basic concepts,TERMINATIONa termination is an object that sources and sinks media streams.A termination may represent a physical end point as for example a tim

40、eslot on a PCM line.It may also represent a representation of a flow as for example a RTP stream in a single media terminationit also is used to represent AAL2 connections and other ATM PVCs and SVCsTermination是MGW的逻辑实体，它发起和/或接受媒体和/或控制流。Termination可用特性描述，如媒体流、modem和承载能力等特性，这些特性可以组成了一系列描述符。CONTEXTA c

41、ontext represents a collection of terminations.A context represents a call or session of a single or multiple media type.关联表明一些Termination间的关系。For example a context containing a TDM audio termination and a RTP audio termination would describe an audio SCN to IP call.EventsMGC may ask a MG to be noti

42、fied about certain events(e.g.off-hook,DTMF tone detection)occurring on a termination,H.248 Resource handling Overview Terminology,TerminationTermination is a logical entity on a MG that sources and/or sinks media and/or control streams.ContextContext is an association between Terminations.TopologyT

43、opology descriptor is used to specify flow directions between terminations in a Context.Stream Bi-directional media or control flow received/sent by a media gateway as part of a call or conference NULL ContextExisting Terminations that are not associated to any other Termination.ROOT terminationRefe

44、rring to the entire gateway instead of specific termination within it.,Context,Topology,Terminations,Ta,Tb,Stream,H.248 Resource handling Overview Terminology,cont,H.248 MessageH.248 message is a collection of Transactions.TransactionTransaction is a collection of Actions(transactionId).ActionAction

45、 is a collection of ActionRequests or ActionReplies for Context(contextId).CommandCommands provide a complete control of the properties of Terminations(terminationId).ServiceChange,AuditValue,AuditCapability,Add,Modify,Subtract,Move,NotifyDescriptorsThe parameters to a Command are termed Descriptors

46、.A Descriptor consists of a name and a list of items.For example Media,Local,Remote,Event and StatisticsPackageVariations in Terminations are accommodated in the protocol by allowing Terminations to have optional Properties,Events,Signals and Statistics implemented by MGWs.,H.248 Resource handling O

47、verviewH.248 message,Command1(terminationId1),Command2(terminationId2),Command3(terminationId3),Action1(contextId1),Transaction2(transactionId2),Command4(terminationId4),Command5(terminationId5),Action2(contextId2),Action3(contextId3),Command6(terminationId6),TCP/SCTP Header,IP Header,H.248 Message,

48、Transactions,Actions and Commands,Example of a H.248 message,Mc-interface Defined Commands,H.248 uses a series of commands to manipulate terminations,contexts,events,and signals.Add command adds a termination to a context and may be used to create a new context.增加termination的同时也create了一个新的关联.Subtrac

49、t command removes a termination from a context and may result in the context being released Move command moves a termination from one context to another Modify changes the state of the termination,e.g.applies tones or changes the through connection.修改temination的特性,事件和信号.Audit(value&capability)return

50、 information about the terminations,contexts,and general MG state and capabilities ServiceChange is used by the MG and MGC to inform about status changes.E.g.Terminations being taken out of use,restarts etc.Notify command,with which the MGW informs the MSS that one of the events the MSS was interest