數(shù)字程控交換系統(tǒng)：第一部分 概述

1、數(shù)字程控交換系統(tǒng)Reference糜正琨,交換技術(shù), 清華大學(xué)出版社John G.van Bosse，Signaling in telecommunication networks，John Wiley&Sons，Inc.，1997 任劍秋, S12系統(tǒng)結(jié)構(gòu)(EC74),上海貝爾培訓(xùn)中心任劍秋, S12呼叫局?jǐn)?shù)據(jù)管理(EC74),上海貝爾培訓(xùn)中心Chapter 1: 概述Chapter 2：SCCP 和 TCAPChapter 3：S1240數(shù)字程控交換機(jī)Chapter 4：C&C08數(shù)字程控交換機(jī)Chapter 1概述交換的定義和交換機(jī)的發(fā)展S1240程控交換機(jī)簡(jiǎn)介程控交換機(jī)的主要技術(shù)指標(biāo)1

2、.1 交換Switching貝爾1876年發(fā)明電話點(diǎn)對(duì)點(diǎn)通信：線路利用率很低（n(n-1)/2）交換Switching貝爾電話公司1878年開(kāi)辦了第一個(gè)交換局（人工操作）“交換”（switching）：對(duì)信息的傳遞進(jìn)行開(kāi)關(guān)控制，從而將一條電話線轉(zhuǎn)接到另一條電話線，使它們連通起來(lái)。Categorizing switchingSPC: Stored program controlThe Switchboard in the Central Office（Manual）You picked up the transmitter (off-hook)a flap signals this at the

3、 switchboard in the central officethe operator answers you tell her: Give me the Undertakerand she establishes the connection - this was very comfortableStep by step crossbarA Stronger automatic exchange電信交換的基本技術(shù)：交換結(jié)點(diǎn)高度抽象的系統(tǒng)結(jié)構(gòu)接口接口互連控制信令數(shù)字交換網(wǎng)絡(luò)用戶(hù)線：UNI中繼線：NNI信令也通過(guò)接口傳送信令是控制的依據(jù)根據(jù)信令,控制不同的接口進(jìn)行互連Basic Signa

4、ls NowQuelle: Siegmund, Intelligente NetzeSignalling trafficUser trafficB-subA-subOff-hookNetworkDial toneDialingRingingRing toneAnswerAnswer Ind.ReleaseReleaseRelease IndCall Set-upRelease節(jié)點(diǎn)功能網(wǎng)絡(luò)層次1.2 S1240系統(tǒng)結(jié)構(gòu)硬件功能結(jié)構(gòu)話路系統(tǒng)數(shù)字程控系統(tǒng)硬件功能結(jié)構(gòu)數(shù)字交換網(wǎng)絡(luò)信令設(shè)備處理機(jī)存儲(chǔ)器I/O接口模擬終端數(shù)字終端 數(shù)字中繼線 模擬中繼線用戶(hù)集中級(jí) 用戶(hù)電路控制系統(tǒng) 用戶(hù)線(S1240模塊簡(jiǎn)

5、介模擬用戶(hù)模塊(ASM)：是模擬用戶(hù)和交換機(jī)的接口,它為模擬用戶(hù)提供用戶(hù)線終端電路。外設(shè)及裝載模塊（P&L）：負(fù)責(zé)交換機(jī)和外設(shè)間的通信以及系統(tǒng)中位處理器的下行裝載。一個(gè)交換機(jī)總是裝備兩個(gè)P&L模塊，工作在主備用狀態(tài)。時(shí)鐘和信號(hào)音模塊（ CTM）：產(chǎn)生8MHZ的系統(tǒng)時(shí)鐘，分步到所有控制單元，以確保系統(tǒng)的同步運(yùn)行，CTM還負(fù)責(zé)產(chǎn)生交換機(jī)控制用的信號(hào)音以及實(shí)時(shí)時(shí)間。數(shù)字中繼模塊（DTM）：提供2Mb/s的PCM鏈路高性能公共信道模塊（HCCM）：處理7號(hào)信令輔助控制單元模塊（ACM）：提供呼叫處理等程序和數(shù)據(jù)等。1.3 程控交換機(jī)的主要技術(shù)指標(biāo)控制部件的呼叫處理能力BHCA（Busy hours c

6、all attempts）交換機(jī)可以同時(shí)連接的話路數(shù)，即話務(wù)量Erl Chapter 2：SCCP 和 TCAP 復(fù)習(xí)：MTP1、MTP2、MTP3、TUP小結(jié)交換技術(shù)基礎(chǔ)中的信令SCCPTCAP2.1 Review of MTP123 and TUPSignaling:The ITU-T defines signaling as, The exchange of information (other than by speech) specifically concerned with the establishment, release and other control of calls

7、, and network management, in automatic telecommunications operation. Traditional network:Call: speech, signaling IP network:Session: media, controlSS7 StackThe message transfer part (MTP) was designed to transfer TUP/ ISUP messages between exchanges at the ends of a trunk(trunk-related).The signalin

8、g connection control part (SCCP), in combination with MTP provides the transfer of messages that are not related to individual trunks, for example, transaction messages. The combination of MTP and SCCP is known as the network service part (NSP) of SS7, and is the equivalent of layers1,2, and 3 of th

9、e OSI (open systems interconnection) protocols in data communication systems .NSPReview of MTP2/3Review of TUPExample2.2小結(jié)交換技術(shù)基礎(chǔ)中的信令板書(shū)2.3 Signaling Connection Control Part (SCCP) and Transaction Capabilities Application Part (TCAP)Introduction to TransactionIntroduction to SCCPThe SCCP Message Struc

10、tureGlobal Title (GT) routingConnection-oriented SCCPIntroduction to TCAP2.3.1 Introduction to Transactions Definitions:Remote Operation. This is an operation that is not trunk-related, and is executed by one signaling point (SP), at the request of another SP.Transaction. This is a dialogue consisti

11、ng of signaling messages between two SPs, for the execution of one or more remote operations . Transactions can involve two exchanges, an exchange and a network database, an exchange and a maintenance center, etc.Application Service Element (ASE). Each application that requires remote operations has

12、 an ASE, which handles the signaling aspects for that application. an ASE is uniquely identified by the point code (PC) of its signaling point, and its subsystem number (SSN).2.3.1 Introduction to TransactionsApplications:“on-line” transactionsIntelligent Network ServicesServices for Mobile Telecomm

13、unicationMinimal time, lessshort messages“off-line” transactionsCentralized Operation, Administration, and Maintenance (OAM)Bulk Data TransferLess time critical, morelonger messagesLocation Update(LAIp,TMSIp)(LAIp,TMSIp,LAIn)(LAIp,TMSIp)(IMSI)(IMSI)(IMSI)(MS Record)(LAIn,TMSIn)(LAIn,TMSIn)2.3.2 Intr

14、oduction to SCCPPosition of SCCP in signaling system No.7TCAP and ISUP are SCCP users. In turn, the ASEs at a signaling point are users of TCAP, and can be considered as “indirect” SCCP users.Message Transfer EnhancementsSCCP expands the addressing capability of SS7, allowing up to 127 subsystems at

15、 a signaling point.SCCP allows a calling subsystem to address a called subsystem by a global title (GT).SI (Service Indicator)Derivation of called addressA VLR initiates a transaction with the HLR of a mobile identified by IMSI. VLR derives the called address from IMSI.(D interface)A gateway MSC ini

16、tiates a transaction with the HLR of a mobile identified by MSISDN. GMSC derives the address from MSISDN. (C interface)VLR1 initiates a transaction with VLR2, which covers a particular location area (LAI). In this case, VLR1 derives the address of VLR2 from LAI. (G interface)A VLR initiates a transa

17、ction with its associated MSC. The interface between these two entities is internal (B interface), and addressing is not required.An HLR initiates a transaction with the VLR serving a MS. HLR uses the stored VLR address when it initiates its transaction. (D interface)2.3.2 Introduction to SCCPSCCP M

18、essage Transfer Services The SCCP provides two categories of service for data transfer: connection-oriented services and connectionless services. Within each service category, two classes of service are defined as follows:Class 0 Basic connectionless classClass 1 In-sequence delivery connectionless

19、classClass 2 Basic connection-oriented classClass 3 Flow control connection-oriented class2.3.2 Introduction to SCCPSCCP routing control (SCRC) Provides additional routing beyond that offered by MTP3, through the use of global titles.SCCP management (SCMG) it aims to maintain the message traffic of

20、the SCCP users congestion and failure conditions in the signaling network, signaling points, and subsystems.SCCP connection-oriented control (SCOC) Responsible for setting up and releasing a virtual connection between two SCCP users. SCOC can offer features including sequencing, flow control, and se

21、gmentation and can override congestion procedures by assigning data priority.SCCP connectionless control (SCLC) Responsible for transferring data between SCCP users without creating a virtual connection. The SCCP ArchitectureSCCP Connectionless Control (SCLC)These services are provided without setti

22、ng up a logical connection.SCCP Connection-Oriented Control (SCOC)Connection Establishment PhaseData Transfer PhaseConnection Release Phase2.3.2 The SCCP Message StructureAs with all other MTP users, SCCP messages are composed of three parts: a mandatory fixed part(MF);mandatory variable part(MV);an

23、 optional part(O). The SCCP Message Structure : Mandatory Fixed Part (MF)The mandatory fixed part consists of 1those parameters that must be present in the message and that are of a fixed length. Because the parameters are of a fixed length and are mandatory, no length indicator is required. because

24、 the parameter types and their order is known from the SCCP message type, no parameter names are required for stating the parameter types.The mandatory fixed part contains 2pointers to the mandatory variable part and 3the optional part of the message. The SCCP Message Structure : Mandatory Variable

25、Part (MV)The mandatory variable part consists of those parameters that must be present in the message and that are of a variable length. A pointer is used to indicate the start of each parameter. A length indicator precedes each parameter because the parameters are of a variable length. No parameter

26、 tags are required to state the parameter types because the parameter types and their order is explicitly defined by the SCCP message type. The SCCP Message Structure : Optional Part (O)The optional part consists of those parameters that are not always necessary. Each parameter is preceded by a para

27、meter name and a length indicator. The SCCP Message TypesMMessage ParametersEXAMPLE: Connection Request (CR)Connection-oriented protocol Class 2 or 3 uses a CR message during the connection establishment phase. It is sent by an originating SCCP user to a destination SCCP user to set up a signaling c

28、onnection (a virtual connection) between the two signaling points. The various parameters that compose the message dictate the connection requirements. After receiving the CR message, SCCP initiates the virtual connection setup, if possible.Message Parameter Called party Address(CDA)3GPP SSN ITU-T S

29、SNGT- format2.3.4 Global Title (GT) routingIn 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 tables in all exchanges, and would entail a large effort when an

30、 item in the tables has to be added or removed.A better arrangement is to let the exchanges use the received 800 number as a global title (GT) address, which is the “functional” address of an R800 at a database with information on the 800 number, and install the GT translation capability in the SCCP

31、s of the signal transfer points (STP) of the network. The SCCP at the originating exchange then routes the query message to a directly connected STP, whose SCCP translates GT into the PC + SSN address of the destination. From this point on, the message can be routed by MTP to its destination.A globa

32、l title is an address, such as dialed-digits, which does not explicitly contain information that would allow routing in the SS7 network.Transfer of Unitdata MessagesQuery messageResponse messageThe second messageFinal and Intermediate GT TranslationsExample in GSMa VLR in Country A originates a MAP

33、Update Location message. The message contains the DPC of a Country As International Switching 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 the HLR (an E.164 number). The ISC at Country A changes the DPC to be an I

34、SC of Country B. Again, this PC is already provisioned in its 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 into a PC+SSN; therefore, it performs the GTT. Thus, the message is routed to the HLR via the G

35、MSC using only the PC+SSN. GT translations are usually centralised at STPs to allow routing changes to be made easily.2.3.5 CONNECTION-ORIENTED SCCPConnection-oriented service is the preferred way for transactions that involve the transfer of large amounts of data.Transactions of this nature are not

36、 call-related and can be deferred, say for several minutes.Connection-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 ReferencesDuri

37、ng the exchange of the connection request and the connection confirm messages, the subsystems and SCCPs allocate reference numbers to identify the connection, and build records that store reference numbers, and address parameters that are associated with the connection.The records are consulted when

38、 sending-or receiving- a data form message, and are discarded at the end of the connection. Building the RecordsCID (Connection identifier) :A connection identifier uniquely identifies a connection at a signaling point.SLR (Source Local Reference , Par.11): This identifies the connection, as known b

39、y the SCCP. It is included in SCCP messages to and from the other SCCP.DLR (Destination Local Reference , Par.3): This identifies the connection,as known by the SCCP at the other end of the connection, and is included in SCCP messages.BBuilding the Records(1):We explore the build-up of the records.

40、: Subsystem P initiates the transaction. It establishes a connection record, and allocates the connection identification value (CID) = x. It then passes an N-connect request that includes the called and calling party addresses, and CID. The called party address may be a global title or a DPC + SSN a

41、ddress. The calling party address is always in the format PC + SSN (PC = a, SSN = p).Building the Records(2):On receipt of the request, SCCP-A establishes a connection record. It enters the received connection identifier (CID = x) in the record. The calling party address (PC = a, SSN = p) is entered

42、 as the “l(fā)ocal” party address. SCCP-A then allocates a source local reference value (SLR = v), and a signaling link selector value (SLS = m), and sends a connection request message that includes the called and calling party addresses (Par.1 and Par.3), and source local reference (Par. 11).Building t

43、he Records(3):On receipt of the message, SCCP-B establishes its record. It enters the received called party address (which may have undergone global title translation, and now is PC = b, SSN = q) as the “l(fā)ocal” party address. The received calling party address (PC = a, SSN = p), and source local ref

44、erence (SLR = v), are entered as the “remote” party address, and “destination” local reference (DLR). SCCP-B also allocates a connection identifier CID = y. It then passes an N-connect indication to subsystem Q (the “l(fā)ocal” party) that includes the connection identifier. Building the Records(4):Assu

45、ming that the subsystem accepts the connection request, it builds a connection record, and enters the received connection identifier (CID = y). It then passes an N-connect response to SCCP-B, including CID = y.Building the Records(5):SCCP-B accesses the record in which CID = y, and allocates a sourc

46、e local reference (SLR = w), and a signaling link selector (SLS = n). It then sends a connection confirm message, using the “remote” party address (PC = a, SSN =p) as called party address, the “l(fā)ocal” party address (PC = b, SSN = q) as calling party address (PC = b, SSN = q), the source local refere

47、nce (SLR = w), and the destination local reference (DLR = v).Building the Records(6):The SCCP message arrives at SCCP-A. It accesses the record whose source local reference matches the received DLR = v. It then enters the received calling party address as “remote” party address, and passes an N-conn

48、ect confirmation that includes CID = x, to the “l(fā)ocal” party identified by SSN = p. At this point all connection records are complete, and the transfer of subsystem data can start.Transfer of a data form12.4.1 Introduction to TCAPThe transaction capabilities application part (TCAP) of signaling syst

49、em No.7, in conjunction with the signaling control connection part (SCCP) and the message transfer part (MTP) l-3, enables application service elements(ASE) at two nodes (the TCAP term for signaling points) to conduct transactions.2.4.2 IntroductionA component is a communication between ASEs. It can

50、 contain a requested operation, or the results of the operation. A message (containing one or more components) is the unit of communication between two TCAPs.2.4.2 TCAP MessagesA TCAP message consists of a TCAP portion, which is processed by TCAP, and a components portion with one or more components

51、, which is passed transparently.A transaction is a set of related TCAP messages that are exchanged between network nodes. The transaction portion identifies the messages that belong to the same transaction using a Transaction Identifier (TRID).The messages component portion contains the actual instr

52、uctions, or operations, that are being sent to the remote application.TCAP Messagesa Begin message always starts a transaction, an End message normally ends the transaction. Transaction Identifier(1)A transaction identifier (TID) is a reference number that identifies a transaction to the involved AS

53、E, and to the TCAP of its node.Transaction Identifier(2)A TCAP has a pool of TIDs. When ASE-1 at node A initiates a transaction with ASE-2 at node B, TCAP-A seizes an available TID-say TID = p-from its pool, and allocates it to the transaction. TCAP-A also establishes a record that associates ASE-1

54、with local TID = p. It also passes TID = p to ASE-1.The begin message from TCAP-A includes an originating TID field (OTID) which has the value OTID = p, TCAP-B allocates TID = q to the new transaction at its node, and establishes a record that associates ASE-2,the local TID = q, and the remote TID = p. It also passes TID = q to ASE-2,along with the component(s) in the begin message.The transaction is now identified for ASE-1 and TCAP-A by TID = p, and for ASE-2 and TCAP-B by TID = q.Transaction Identifier(3)In case (a), ASE-2 requests TCAP-B to send an end message