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1、数字程控交换系统数字程控交换系统Referencen n糜正琨,交换技术, 清华大学出版社n nJohn G.van Bosse，Signaling in telecommunication networks，John Wiley&Sons，Inc.，1997 n n任剑秋, S12系统结构(EC74),上海贝尔培训中心n n任剑秋, S12呼叫局数据管理(EC74),上海贝尔培训中心n nChapter 1: Chapter 1: 概述概述n nChapter 2Chapter 2：SCCP SCCP 和和 TCAPTCAPn nChapter 3Chapter 3：S1240S1240数字
2、程控交换机数字程控交换机n nChapter 4Chapter 4：C&C08C&C08数字程控交换机数字程控交换机Chapter 1概述n n交换的定义和交换机的发展n nS1240程控交换机简介n n程控交换机的主要技术指标1.1 交换Switchingn n贝尔贝尔贝尔贝尔18761876年发明电话年发明电话年发明电话年发明电话 点对点通信：线路利用率很低（点对点通信：线路利用率很低（n(n-n(n-1)/21)/2）交换Switchingn n贝尔电话公司贝尔电话公司18781878年开年开办了第一个交换局（人办了第一个交换局（人工操作）工操作） “ “交换交换” ”（switchin
3、gswitching）：对）：对信息的传递进行开关控信息的传递进行开关控制，从而将一条电话线制，从而将一条电话线转接到另一条电话线，转接到另一条电话线，使它们连通起来。使它们连通起来。Categorizing switchingSPC: Stored program controlThe Switchboard in the Central Office（Manual）You picked up the You picked up the transmitter (off-hook)transmitter (off-hook)a flap signals this at a flap sign
4、als this at the switchboard in the the switchboard in the central officecentral officethe operator answers the operator answers you tell her: Give me you tell her: Give me the Undertakerthe Undertakerand she establishes and she establishes the connection - this the connection - this was very comfort
5、ablewas very comfortableStep by step crossbarA Stronger automatic exchange电信交换的基本技术：n n交换结点交换结点交换结点交换结点高度抽象的系统结构高度抽象的系统结构接口接口互连控制信令数字交换网络用户线：UNI中继线：NNI信令也通过接口传送信令是控制的依据根据信令根据信令, ,控制不同的接口进行互连控制不同的接口进行互连Basic Signals NowQuelle: Siegmund, Intelligente NetzeSignalling trafficUser trafficB-subA-subOff-ho
6、okNetworkDial toneDialingRingingRing toneAnswerAnswer Ind.ReleaseReleaseRelease IndCall Set-upRelease节点功能节点功能网络层次网络层次1.2 S1240系统结构硬件功能结构话路系统话路系统数字程控系统硬件功能结构数字交换网络信令设备处理机存储器I/O接口模拟终端数字终端 数字中继线 模拟中继线用户集中级 用户电路控制系统控制系统 用户线(S1240模块简介n n模拟用户模块模拟用户模块(ASM)(ASM)：是模拟用户和交换机的接口：是模拟用户和交换机的接口, ,它为它为模拟用户提供用户线终端电路
7、。模拟用户提供用户线终端电路。n n外设及装载模块（外设及装载模块（P&LP&L）：负责交换机和外设间的通信以）：负责交换机和外设间的通信以及系统中位处理器的下行装载。一个交换机总是装备两个及系统中位处理器的下行装载。一个交换机总是装备两个P&LP&L模块，工作在主备用状态。模块，工作在主备用状态。n n时钟和信号音模块（时钟和信号音模块（ CTMCTM）：产生）：产生8MHZ8MHZ的系统时钟，的系统时钟，分步到所有控制单元，以确保系统的同步运行，分步到所有控制单元，以确保系统的同步运行，CTMCTM还负还负责产生交换机控制用的信号音以及实时时间。责产生交换机控制用的信号音以及实时时间。n
8、n数字中继模块（数字中继模块（DTMDTM）：提供）：提供2Mb/s2Mb/s的的PCMPCM链路链路n n高性能公共信道模块（高性能公共信道模块（HCCMHCCM）：处理）：处理7 7号信令号信令n n辅助控制单元模块（辅助控制单元模块（ACMACM）：提供呼叫处理等程序和数据）：提供呼叫处理等程序和数据等。等。1.3 程控交换机的主要技术指标n n控制部件的呼叫处理能力BHCABHCA（Busy hours call attemptsBusy hours call attempts）n n交换机可以同时连接的话路数，即话务量Erl Erl Chapter 2：SCCP 和 TCAP n n
9、复习：MTP1、MTP2、MTP3、TUPn n小结交换技术基础中的信令n nSCCPn nTCAP2.1 Review of MTP123 and TUPn nSignaling:Signaling:The ITU-T defines signaling as, The ITU-T defines signaling as, The The exchange of information (other than exchange of information (other than by speech) specifically concerned by speech) specifical
10、ly concerned with the establishment, release and with the establishment, release and other control of calls, and network other control of calls, and network management, in automatic management, in automatic telecommunications operation.telecommunications operation. n nTraditional network:Traditional
11、 network: Call: speech, signaling Call: speech, signaling n nIP network:IP network: Session: media, controlSession: media, controlSS7 Stackn nThe message transfer part The message transfer part ( (MTPMTP) was designed to ) was designed to transfer TUP/ ISUP messages transfer TUP/ ISUP messages betwe
12、en exchanges at the ends between exchanges at the ends of a trunk(of a trunk(trunk-relatedtrunk-related).).n nThe signaling connection The signaling connection control part (control part (SCCPSCCP), in ), in combination with MTP provides combination with MTP provides the transfer of messages that th
13、e transfer of messages that are are not related to individual not related to individual trunkstrunks, for example, , for example, transaction messagestransaction messages. .n n The combination of MTP and The combination of MTP and SCCP is known as the network SCCP is known as the network service par
14、t (service part (NSPNSP) of SS7, and ) of SS7, and is the equivalent of layers1,2, is the equivalent of layers1,2, and 3 of the OSI (open and 3 of the OSI (open systems interconnection) systems interconnection) protocols in data protocols in data communication systems .communication systems .NSPRevi
15、ew of MTP2/3Review of MTP2/3Review of TUPExample2.2小结交换技术基础中的信令n n板书2.3 Signaling Connection Control Part (SCCP) and Transaction Capabilities Application Part (TCAP)n nIntroduction to Transactionn nIntroduction to SCCPn nThe SCCP Message Structuren nGlobal Title (GT) routingn nConnection-oriented SC
16、CPn nIntroduction to TCAP2.3.1 Introduction to Transactions Definitions:n nRemote OperationRemote Operation. . This is an operation that is This is an operation that is not not trunk-relatedtrunk-related, and is executed by one signaling point , and is executed by one signaling point (SP), at the re
17、quest of another SP.(SP), at the request of another SP.n nTransactionTransaction. . This is a dialogue consisting of signaling This is a dialogue consisting of signaling messages between two SPs, for the execution of one or messages between two SPs, for the execution of one or more more remote opera
18、tionsremote operations . . Transactions can involve two exchanges, an exchange Transactions can involve two exchanges, an exchange and a network database, an exchange and a and a network database, an exchange and a maintenance center, etc.maintenance center, etc.n nApplication Service Element (ASE).
19、Application Service Element (ASE). Each application Each application that requires remote operations has an ASE, which that requires remote operations has an ASE, which handles the signaling aspects for that applicationhandles the signaling aspects for that application. . an ASE is uniquely identifi
20、ed by the point code an ASE is uniquely identified by the point code (PC) of its signaling point, and its subsystem (PC) of its signaling point, and its subsystem number (SSN)number (SSN). .2.3.1 Introduction to TransactionsApplications:“ “on-lineon-line” ” transactions transactionsn nIntelligent Ne
21、twork ServicesIntelligent Network Servicesn nServices for Mobile TelecommunicationServices for Mobile TelecommunicationMinimal time, lessshort messagesMinimal time, lessshort messages“ “off-lineoff-line” ” transactions transactionsn nCentralized Operation, Administration, and Centralized Operation,
22、Administration, and Maintenance (OAM)Maintenance (OAM)n nBulk Data TransferBulk Data TransferLess time critical, morelonger messagesLess time critical, morelonger messagesLocation Update(LAIp,TMSIp)(LAIp,TMSIp)(LAIp,TMSIp,LAIn)(LAIp,TMSIp,LAIn)(LAIp,TMSIp)(LAIp,TMSIp)(IMSI)(IMSI)(IMSI)(IMSI)(IMSI)(I
23、MSI)(MS (MS Record)Record)(LAIn,TMSIn(LAIn,TMSIn) )(LAIn,TMSIn)(LAIn,TMSIn)2.3.2 Introduction to SCCPn nPosition of SCCP in signaling system No.7Position of SCCP in signaling system No.7qqTCAP and ISUP are SCCP users. In TCAP and ISUP are SCCP users. In turn, the ASEs at a signaling point turn, the
24、ASEs at a signaling point are users of TCAP, and can be are users of TCAP, and can be considered as considered as “ “indirectindirect” ” SCCP users. SCCP users.n nMessage Transfer EnhancementsMessage Transfer EnhancementsqqSCCP expands the addressing SCCP expands the addressing capability of SS7, al
25、lowing up to capability of SS7, allowing up to 127 subsystems at a signaling 127 subsystems at a signaling point.point.qqSCCP allows a calling subsystem to SCCP allows a calling subsystem to address a called subsystem by a address a called subsystem by a global title (GT)global title (GT). .SI (Serv
26、ice Indicator)Derivation of called addressn nA VLR initiates a transaction with the HLR of a A VLR initiates a transaction with the HLR of a mobile identified by IMSI. VLR derives the called mobile identified by IMSI. VLR derives the called address from address from IMSIIMSI.(.(D interfaceD interfac
27、e) )n nA gateway MSC initiates a transaction with the A gateway MSC initiates a transaction with the HLR of a mobile identified by MSISDN. GMSC HLR of a mobile identified by MSISDN. GMSC derives the address from derives the address from MSISDNMSISDN. (. (C interfaceC interface) )n nVLRVLR1 1 initiat
28、es a transaction with VLR initiates a transaction with VLR2 2, which , which covers a particular location area (LAI). In this covers a particular location area (LAI). In this case, VLRcase, VLR1 1 derives the address of VLR derives the address of VLR2 2 from from LAILAI. . ( (G interfaceG interface)
29、 )n nA VLR initiates a transaction with its associated A VLR initiates a transaction with its associated MSC. The interface between these two entities is MSC. The interface between these two entities is internal (internal (B interfaceB interface), and addressing is not ), and addressing is not requi
30、red.required.n nAn HLR initiates a transaction with the VLR An HLR initiates a transaction with the VLR serving a MS. HLR uses serving a MS. HLR uses the stored VLR addressthe stored VLR address when it initiates its transaction. (when it initiates its transaction. (D interfaceD interface) )2.3.2 In
31、troduction to SCCPn nSCCP Message Transfer ServicesSCCP Message Transfer Services The SCCP provides two categories of service The SCCP provides two categories of service for data transfer: for data transfer: connection-oriented connection-oriented servicesservices and and connectionless servicesconn
32、ectionless services. . Within each service category, two classes of Within each service category, two classes of service are defined as follows:service are defined as follows:qqClass 0Class 0 Basic connectionless class Basic connectionless classqqClass 1Class 1 In-sequence delivery In-sequence deliv
33、ery connectionless classconnectionless classqqClass 2Class 2 Basic connection-oriented class Basic connection-oriented classqqClass 3Class 3 Flow control connection- Flow control connection-oriented classoriented class2.3.2 Introduction to SCCPn nSCCP routing control SCCP routing control (SCRC)(SCRC
34、) Provides additional Provides additional routing beyond that offered by routing beyond that offered by MTP3, through the use of global MTP3, through the use of global titles.titles.n nSCCP management (SCMG)SCCP management (SCMG) it aims to maintain the message it aims to maintain the message traffi
35、c of the SCCP users traffic of the SCCP users congestion and failure congestion and failure conditions in the signaling conditions in the signaling network, signaling points, and network, signaling points, and subsystems.subsystems.n nSCCP connection-oriented SCCP connection-oriented control (SCOC)c
36、ontrol (SCOC) Responsible Responsible for setting up and releasing a for setting up and releasing a virtual connection between two virtual connection between two SCCP users. SCOC can offer SCCP users. SCOC can offer features including sequencing, features including sequencing, flow control, and segm
37、entation flow control, and segmentation and can override congestion and can override congestion procedures by assigning data procedures by assigning data priority.priority.n nSCCP connectionless control SCCP connectionless control (SCLC)(SCLC) Responsible for Responsible for transferring data betwee
38、n SCCP transferring data between SCCP users without creating a virtual users without creating a virtual connection. connection. The SCCP ArchitectureSCCP Connectionless Control (SCLC)n nThese services are provided without These services are provided without setting up a logical connection.setting up
39、 a logical connection.SCCP Connection-Oriented Control (SCOC)SCCP Connection-Oriented Control (SCOC)n nConnection Connection Establishment Establishment PhasePhasen nData Transfer Data Transfer PhasePhasen nConnection Release Connection Release PhasePhase2.3.2 The SCCP Message Structuren nAs with al
40、l other As with all other MTP usersMTP users, , SCCP SCCP messages are messages are composed of three composed of three parts: parts: a mandatory fixed a mandatory fixed partpart(MF)(MF); ; mandatory variable mandatory variable partpart(MV)(MV); ; an optional partan optional part(O)(O). . The SCCP M
41、essage Structure : Mandatory Fixed Part (MF)n nThe The mandatory fixed partmandatory fixed part consists of consists of 1 1those those parameters that must be parameters that must be present in the message and present in the message and that are of a fixed lengththat are of a fixed length. . Because
42、 the parameters are of Because the parameters are of a fixed length and are a fixed length and are mandatory, mandatory, no length no length indicator is required. indicator is required. because the parameter types because the parameter types and their order is known from and their order is known fr
43、om the the SCCP message typeSCCP message type, , no no parameter names are parameter names are required required for stating the for stating the parameter types.parameter types.n nThe mandatory fixed part The mandatory fixed part contains contains 2 2pointers to the pointers to the mandatory variabl
44、e part and mandatory variable part and 3 3the optional part of the the optional part of the messagemessage. . The SCCP Message Structure : Mandatory Variable Part (MV)n nThe mandatory variable part The mandatory variable part consists of consists of those parameters those parameters that must be pre
45、sent in the that must be present in the message and that are of a message and that are of a variable length.variable length. A pointerA pointer is used to indicate is used to indicate the start of each parameter. the start of each parameter. A A length indicatorlength indicator precedes precedes eac
46、h parameter because the each parameter because the parameters are of a variable parameters are of a variable length. length. No parameter tagsNo parameter tags are are required to state the parameter required to state the parameter types because the parameter types because the parameter types and th
47、eir order is types and their order is explicitly defined by explicitly defined by the SCCP the SCCP message typemessage type. . The SCCP Message Structure : Optional Part (O)n nThe optional part The optional part consists consists of of those parameters that those parameters that are not always nece
48、ssary.are not always necessary. Each parameter is Each parameter is preceded by a parameter preceded by a parameter name and a length name and a length indicatorindicator. . The SCCP Message TypesThe SCCP Message TypesMMessage ParametersMessage ParametersEXAMPLE: Connection Request (CR)n nConnection
49、-oriented protocol Class 2 or Connection-oriented protocol Class 2 or 3 uses a CR message during the 3 uses a CR message during the connection establishment phase. It is connection establishment phase. It is sent by an originating SCCP user to a sent by an originating SCCP user to a destination SCCP
50、 user to set up a destination SCCP user to set up a signaling connection (a virtual signaling connection (a virtual connection) between the two signaling connection) between the two signaling points. The various parameters that points. The various parameters that compose the message dictate the comp
51、ose the message dictate the connection requirements. After connection requirements. After receiving the CR message, SCCP receiving the CR message, SCCP initiates the virtual connection setup, if initiates the virtual connection setup, if possible.possible.Message Parameter Message Parameter Called p
52、arty Address(CDA)Called party Address(CDA)3GPP SSN ITU-T SSNGT- format2.3.4 Global Title (GT) routingnIn principle,exchange A could translate the received 800 number into a PC+ SSN called party address of an R800 in the appropriate database. However, this would require “800 number” translation table
53、s in all exchanges, and would entail a large effort when an item in the tables has to be added or removed.n nA better arrangement is to let the exchanges use A better arrangement is to let the exchanges use the received 800 number as a global title (the received 800 number as a global title (GTGT) )
54、 address, which is the address, which is the “ “functionalfunctional” ” address of an address of an R800 at a database with information on the 800 R800 at a database with information on the 800 number, and install the number, and install the GT translationGT translation capability capability in the
55、SCCPs of the signal transfer points (STP) of in the SCCPs of the signal transfer points (STP) of the network. The SCCP at the originating the network. The SCCP at the originating exchange then routes the query message to a exchange then routes the query message to a directly connected STP, whose SCC
56、P translates directly connected STP, whose SCCP translates GT into the PC + SSN address of the destination. GT into the PC + SSN address of the destination. From this point on, the message can be routed From this point on, the message can be routed by MTP to its destination.by MTP to its destination
57、.n nA global title is an address, such as A global title is an address, such as dialed-digits, which does not dialed-digits, which does not explicitly contain information that explicitly contain information that would allow routing in the SS7 would allow routing in the SS7 work.Transfer of Unitdata
58、MessagesnQuery messagenResponse messagenThe second messageFinal and Intermediate GT TranslationsExample in GSMn na VLR in Country A originates a MAP Update Location message. The a VLR in Country A originates a MAP Update Location message. The message contains the DPC of a Country As International Sw
59、itching message contains the DPC of a Country As International Switching Centre (ISC). The MSC/VLR contains the PC of the ISC that is Centre (ISC). The MSC/VLR contains the PC of the ISC that is provisioned in its routing tables. The message also contains the GT of provisioned in its routing tables.
60、 The message also contains the GT of the HLR (an E.164 number). The ISC at Country A changes the DPC to the HLR (an E.164 number). The ISC at Country A changes the DPC to be an ISC of Country B. Again, this PC is already provisioned in its be an ISC of Country B. Again, this PC is already provisione
61、d in its routing tables, and again, the GT of the HLR is present in the message. routing tables, and again, the GT of the HLR is present in the message. The ISC in Country B happens to have the data fill to translate the GT The ISC in Country B happens to have the data fill to translate the GT into
62、a PC+SSN; therefore, it performs the GTT. Thus, the message is into a PC+SSN; therefore, it performs the GTT. Thus, the message is routed to the HLR via the GMSC using only the PC+SSN. GT translations routed to the HLR via the GMSC using only the PC+SSN. GT translations are usually centralised at ST
63、Ps to allow routing changes to be made are usually centralised at STPs to allow routing changes to be made easily.easily.2.3.5 CONNECTION-ORIENTED SCCPn nConnection-oriented service is the preferred way for transactions that involve the transfer of large amounts of data.n nTransactions of this natur
64、e are not call-related and can be deferred, say for several minutes.n nConnection-oriented service gives the called subsystem an opportunity-at the time it receives a connection request- to determine whether it can handle the transaction at this time.Connection-oriented Class 2 ServiceRecords and Re
65、ferencesn nDuring the exchange of the connection During the exchange of the connection request and the connection confirm request and the connection confirm messages, the subsystems and SCCPs messages, the subsystems and SCCPs allocate reference numbers to identify allocate reference numbers to iden
66、tify the connection, and build records that the connection, and build records that store reference numbers,store reference numbers, and address and address parameters that are associated with the parameters that are associated with the connection.connection.n nThe records are consulted when sending-
67、The records are consulted when sending-or receiving- a data form message, and or receiving- a data form message, and are discarded at the end of the connection. are discarded at the end of the connection. Building the Recordsn nCID CID (Connection identifier) :A connection identifier uniquely identi
68、fies a (Connection identifier) :A connection identifier uniquely identifies a connection at a signaling point.connection at a signaling point.n nSLR SLR (Source Local Reference , Par.11): This identifies the connection, as (Source Local Reference , Par.11): This identifies the connection, as known b
69、y the SCCP. It is included in SCCP messages to and from the other known by the SCCP. It is included in SCCP messages to and from the other SCCP.SCCP.n nDLRDLR (Destination Local Reference , Par.3): This identifies the connection,as (Destination Local Reference , Par.3): This identifies the connectio
70、n,as known by the SCCP at the other end of the connection, and is included in known by the SCCP at the other end of the connection, and is included in SCCP messages.SCCP messages.BBuilding the Records(1):We explore the build-up We explore the build-up of the records. of the records. : Subsystem P in
71、itiates : Subsystem P initiates the transaction. It the transaction. It establishes a establishes a connection record,connection record, and allocates the and allocates the connection connection identification value identification value (CID) = x. It then (CID) = x. It then passes passes an N-connec
72、t an N-connect requestrequest that includes that includes the called and calling the called and calling party addresses, and party addresses, and CID. The called party CID. The called party address may be a address may be a global title or a DPC + global title or a DPC + SSN address. The SSN address
73、. The calling party address calling party address is always in the format is always in the format PC + SSN (PC = a, PC + SSN (PC = a, SSN = p).SSN = p).Building the Records(2):On receipt of the request, On receipt of the request, SCCP-A establishes a SCCP-A establishes a connection record.connection
74、 record. It It enters the received enters the received connection identifier connection identifier (CID = x) in the record. (CID = x) in the record. The calling party The calling party address (PC = a, SSN = address (PC = a, SSN = p) is entered as the p) is entered as the “ “locallocal” ” party addr
75、ess. party address. SCCP-A then allocates a SCCP-A then allocates a source local reference source local reference value (SLR = v), and a value (SLR = v), and a signaling link selector signaling link selector value (SLS = m), and value (SLS = m), and sends sends a connection a connection request mess
76、agerequest message that that includes the called and includes the called and calling party addresses calling party addresses (Par.1 and Par.3), and (Par.1 and Par.3), and source local reference source local reference (Par. 11).(Par. 11).Building the Records(3):On receipt of the message, On receipt o
77、f the message, SCCP-B establishes its SCCP-B establishes its record.record. It enters the It enters the received called party received called party address (which may address (which may have undergone global have undergone global title translation, and title translation, and now is PC = b, SSN = q)
78、now is PC = b, SSN = q) as the as the “ “locallocal” ” party party address. The received address. The received calling party address (PC calling party address (PC = a, SSN = p), and = a, SSN = p), and source local reference source local reference (SLR = v), are entered (SLR = v), are entered as the
79、as the “ “remoteremote” ” party party address, and address, and “ “destinationdestination” ” local reference (DLR). local reference (DLR). SCCP-B also allocates a SCCP-B also allocates a connection identifier CID connection identifier CID = y. It then passes = y. It then passes an an N-connect indic
80、ationN-connect indication to to subsystem Q (the subsystem Q (the “ “locallocal” ” party) that includes the party) that includes the connection identifier.connection identifier. Building the Records(4):Assuming that the Assuming that the subsystem accepts subsystem accepts the connection the connect
81、ion request, it builds a request, it builds a connection record,connection record, and enters the and enters the received connection received connection identifier (CID = y). identifier (CID = y). It then passes It then passes an N-an N-connect responseconnect response to to SCCP-B, including SCCP-B
82、, including CID = y.CID = y.Building the Records(5):SCCP-B SCCP-B accesses the accesses the record in which CID = yrecord in which CID = y, , and allocates a source and allocates a source local reference (SLR = local reference (SLR = w), and a signaling link w), and a signaling link selector (SLS =
83、n). It selector (SLS = n). It then sends then sends a connection a connection confirm messageconfirm message, using , using the the “ “remoteremote” ” party party address (PC = a, SSN address (PC = a, SSN =p) as called party =p) as called party address, the address, the “ “locallocal” ” party party
84、address (PC = b, SSN = address (PC = b, SSN = q) as calling party q) as calling party address (PC = b, SSN = address (PC = b, SSN = q), the source local q), the source local reference (SLR = w), reference (SLR = w), and the destination local and the destination local reference (DLR = v).reference (D
85、LR = v).Building the Records(6):The SCCP message arrives The SCCP message arrives at SCCP-A. It at SCCP-A. It accesses accesses the record whose source the record whose source local reference matches local reference matches the received DLR = vthe received DLR = v. It . It then enters the received t
86、hen enters the received calling party address as calling party address as “ “remoteremote” ” party address, party address, and passes and passes an N-an N-connect confirmationconnect confirmation that includes CID = x, to that includes CID = x, to the the “ “locallocal” ” party party identified by S
87、SN = p. identified by SSN = p. At this point all At this point all connection records are connection records are complete, and the complete, and the transfer of subsystem transfer of subsystem data can start.data can start.Transfer of a data form12.4.1 Introduction to TCAPn nThe transaction The tran
88、saction capabilities application capabilities application part (TCAP)part (TCAP) of of signaling system No.7, signaling system No.7, in conjunction with in conjunction with the signaling control the signaling control connection part connection part (SCCP) and the (SCCP) and the message transfer part
89、 message transfer part (MTP) l-3, enables (MTP) l-3, enables application service application service elements(ASE) at two elements(ASE) at two nodes (the TCAP term nodes (the TCAP term for signaling points) to for signaling points) to conduct transactions.conduct transactions.2.4.2 Introductionn nA
90、A componentcomponentcomponentcomponent is a is a communication communication between ASEs. It between ASEs. It can contain a can contain a requested requested operation, or the operation, or the results of the results of the operation. operation. n nA A messagemessagemessagemessage (containing one o
91、r (containing one or more components) more components) is the unit of is the unit of communication communication between two between two TCAPs.TCAPs.2.4.2 TCAP MessagesqqA TCAP message consists of A TCAP message consists of a TCAP portiona TCAP portion, which is , which is processed by TCAP, and pro
92、cessed by TCAP, and a components portiona components portion with with one or more components, which is passed one or more components, which is passed transparently.transparently.qqA transaction is a set of related TCAP messages that A transaction is a set of related TCAP messages that are exchanged
93、 between network nodes. The are exchanged between network nodes. The transaction portion identifies the messages that transaction portion identifies the messages that belong to the same transaction using a Transaction belong to the same transaction using a Transaction Identifier (TRID).Identifier (T
94、RID).qqThe messages component portion contains the actual The messages component portion contains the actual instructions, or operations, that are being sent to instructions, or operations, that are being sent to the remote application.the remote application.TCAP Messagesqa Begin message always star
95、ts a transaction, qan End message normally ends the transaction. Transaction Identifier(1)n nA A transaction identifier (TID)transaction identifier (TID) is a reference is a reference number that identifies a transaction to the involved number that identifies a transaction to the involved ASE, and t
96、o the TCAP of its node.ASE, and to the TCAP of its node.Transaction Identifier(2)n nA TCAP has a pool of TIDs. When ASE-1 at node A A TCAP has a pool of TIDs. When ASE-1 at node A initiates a transaction with ASE-2 at node B, TCAP-A initiates a transaction with ASE-2 at node B, TCAP-A seizes an avai
97、lable TID-say TID = p-from its pool, and seizes an available TID-say TID = p-from its pool, and allocates it to the transaction. TCAP-A also establishes a allocates it to the transaction. TCAP-A also establishes a record that associates ASE-1 with local TID = p. It also record that associates ASE-1
98、with local TID = p. It also passes TID = p to ASE-1.passes TID = p to ASE-1.n nThe begin message from TCAP-A includes an originating The begin message from TCAP-A includes an originating TID field (OTID) which has the value OTID = p, TCAP-B TID field (OTID) which has the value OTID = p, TCAP-B alloc
99、ates TID = q to the new transaction at its node, and allocates TID = q to the new transaction at its node, and establishes a record that associates ASE-2,the local TID establishes a record that associates ASE-2,the local TID = q, and the remote TID = p. It also passes TID = q to = q, and the remote
100、TID = p. It also passes TID = q to ASE-2,along with the component(s) in the begin ASE-2,along with the component(s) in the begin message.message.n nThe transaction is now identified for ASE-1 and The transaction is now identified for ASE-1 and TCAP-A by TID = p, and for ASE-2 and TCAP-B by TCAP-A by
101、 TID = p, and for ASE-2 and TCAP-B by TID = q.TID = q.Transaction Identifier(3)n nIn case (a), ASE-2 requests TCAP-B to send an end message, In case (a), ASE-2 requests TCAP-B to send an end message, which terminates the transaction. TCAP-B then returns TID = q to which terminates the transaction. T
102、CAP-B then returns TID = q to its TID pool. Its end message includes DTID = p. This identifies its TID pool. Its end message includes DTID = p. This identifies the transaction for TCAP-A,which then passes the component(s) in the transaction for TCAP-A,which then passes the component(s) in the messag
103、e to ASE-1 (the ASE that is currently associated with the message to ASE-1 (the ASE that is currently associated with TID = p). Since the transaction has ended, TCAP-B then erases its TID = p). Since the transaction has ended, TCAP-B then erases its record for the transaction, and returns TID =p to
104、its TID pool.record for the transaction, and returns TID =p to its TID pool.n nIn case (b), ASE-2 continues the transaction. The continue In case (b), ASE-2 continues the transaction. The continue message from TCAP-B includes OTID = q and DTID = p. TCAP-A message from TCAP-B includes OTID = q and DT
105、ID = p. TCAP-A then adds remote TID= q to the record that associates ASE-1 with then adds remote TID= q to the record that associates ASE-1 with local TID = p. In this example,ASE-1 also continues the local TID = p. In this example,ASE-1 also continues the transaction, and the continue message from
106、TCAP-A includes transaction, and the continue message from TCAP-A includes OTID = p and a destination transaction identifier DTID = q.The OTID = p and a destination transaction identifier DTID = q.The procedures for the end message of TCAP-B are as described procedures for the end message of TCAP-B
107、are as described above.above.2.4.3 ComponentsInvoke: specifies the requested operation. A Begin message always includes one (or more) invokes. Continue and End messages sometimes include invokes.Return Result, Last (RR-L): is a final response to an invoke.It contains the information obtained in a su
108、ccessful operation.Return Result, Not Last (RR-NL): is a non-final response to an invoke, and contains a part of the information generated by the operation.Return Error: This component is a final response to an invoke, and indicatesthat the requested operation was executed, and has failed.Reject: is
109、 a final response to a received component. It indicates that the component cannot be processed, because its syntax is not correct.Component Identifiersn nA transaction can involve A transaction can involve several invoke several invoke components. components. n nAn invoke is identified by An invoke
110、is identified by an an invoke-ID (IID)invoke-ID (IID). . n nEach ASE has a pool of Each ASE has a pool of IIDs, and allocates an IID IIDs, and allocates an IID when it originates an when it originates an invoke.invoke.n nIID identifies a particular IID identifies a particular operation in the operation in the transaction to both ASEs.transaction to both ASEs.小结:n nNO7七层协议栈的理解n n与电路相关/与电路无关n nSCCP的四种业务n nSCCP中的GT寻址
