1、Page 1 Recommendation T/CS 49-08 (Vienna 1982) SYSTEM L1 MULTIFREQUENCY CODE CALL CONTROL SIGNALLING PROCEDURES Recommendation proposed by Working Group T/WG 11 “Switching and Signalling” (CS) Text of the Recommendation adopted by the “Telecomminiications” Commission: “The European Conference of Pos
2、tal and Telecommunications Administrations, considering - that Recommendation T/CS 49-07 i provides for multifrequency code (MFC) signalling functions between private automatic branch exchanges (PABXs), which are suitable for the fast set-up of calls and the provision of supplementary services, - th
3、at supplementary services already available to extension users within a single PABX need to be extended to extension users on others PABXs within a private network, recommends to the members, that the signalling procedures specified below are used when MFC interregister signalling is applied between
4、 private branch exchanges in different countries.” 1. 1.1. 1.1.1. 1.1.2. 1.1.3. O 1.1.4. 1.1.5. 1.2. 1.2.1. 1.2.2. GENERAL Outline On international inter-PABX lines, System L1 MFC interregister signalling, as specified in Recommenda- tion T/CS 49-07 i, is used in conjunction with L1 line signalling,
5、 as specified in Recommendation System L1 MFC provides, in principle, the inter-PABX signalling capability to enable a wide range from set-up of simple calls to a variety of supplementary services to be made available to extension users and operators. The range of supplementary services provided by
6、a PABX is optional, and depends upon customer requirements and PABX capability. In any given private network, PABXs of differing capability will be encountered, and the procedures specified for System L1 MFC in this Recommendation take this into account. During the initial set-up of the call, an int
7、erchange of terminal status information takes place between originating and terminating PABXs. This enables certain subsequent supplementary service demands, from either the interconnected terminals or a third party, to be processed locally without recourse to inter-PABX signalling. Where a suppleme
8、ntary service demand requires inter-PABX signalling, the request is handled by the responding PABX on an accept or reject basis, depending upon the availability of the service at that PABX. PABXs that do not provide any supplementary services, but require System L1 MFC signalling capability for fast
9、 call set-up and private network compatibility reasons, can utilise a subset of System L1 MFC signalling procedures referred to as basic. The basic subset provides, as a minimum, the necessary repertoire of signals to establish an extension-to-extension call, with an optional procedure to provide lo
10、cally applied supervisory tones and limited class-of-service information. T/CS 49-01 2. Signals Iriterregister signals The System L1 MFC interregister signals, as well as the 2280 Hz signal for the initiation of the MFC signalling, are specified in Recommendation TJCS 49-07 i. This includes their al
11、location to the multifre- quency codes and the abbreviations used. Line signals Table 1 (T/CS 49-08) shows the System L1 line signals which are used in conjunction with System L1 MFC interregister signalling. The meanings of these signals comply with Recommendation T/CS 41-01 3. The requirements for
12、 the transmission of these signals are given in Recommendation T/CS 49-01 2. Edition of September 15, 1986 TICS 49-08 E Page 2 2. 2.1. 2.2. 2.2.1. 2.2.2. 2.2.3. 2.2.4. 2.2.5. 2.2.6. 2.2.7. 2.2.8. 2.2.9. 2.2.10. Seizing Answer Clear-forward Clear-back Cleared Forward-service-request-recall Fonvard-li
13、nk-recall Backward-service-reques t-recall Backward-link-recall Table 1 (T/CS 49-08). Line signals used for System L1 MFC. SIGNALLING PROCEDURES General This section gives the signalling procedures in three parts: - outline of call control procedures; - description of the signalling procedures for s
14、election, subset compatibility check and dialogue phases; Note: This part requires further study. See contribution T/CS (82) 109 4, - signal flows in arrow chart form and SDL sequence charts according to CCITT Recommendation Z. 101 Note: The SDL diagrams are included in this Recommendation to assist
15、 in the understanding of the technical text, and must only be used in association with the text. Outline of call control procedures Establishment of a call by means of System L1 MFC can be considered in three main phases: the selection phase, the subset compatibility check phase, and the dialogue ph
16、ase. The selection phase, which includes access to an enhanced routing subset), is standard in all System LI MFC applications. It enables establishment of an ordinary call. The dialogue phase is carried out by one of the following signalling procedures subsets: - Basic: - Enhanced: - Manufacturer: s
17、ubsets enabling specific manufacturers procedures to be used (see Paragraph 2.5.3.). Where part of a multi-link call is routed via a non-MFC private circuit, no dialogue phase will take place. The particular subset used will depend upon the capabilities of the interconnected PABXs, and is determined
18、 by the subset compatibility check, which is carried out after the selection phase and before possibly entering the dialogue phase. When the dialogue phase has been entered, both PABXs exchange information regarding the originating and destination parties in either basic or enhanced working. The sig
19、nalling procedures structure in Figure 1 (T/CS 49-08) shows the relationship between the subsets. In basic working, the dialogue phase interchange is limited to one signal in each direction. In enhanced working, the interchange involves at least two signals in each direction and, if a supplementary
20、service is involved, may extend to many more, except for states such as parked where only one signal interchange need take place. The signal exchange for a supplementary service is a function of the service concerned. The procedures based on supplementary services harmonised by CEPT are specified in
21、 Annexes to this Recommendation. Proce- dures required for other categories of supplementary services, e.g. defined for national use or marketed by PABX providers, are not covered in this Recommendation. However, provisions are made in System L1 MFC to gain access to such procedures (see Paragraph 2
22、.5.2.3.). In basic working, the service-request-recall and link-recall signals are not used. 5, 2.102 6 and 2.104 7. provides a minimum interworking capability to enable simple call set-up; provides capability for call set-up plus access to supplementary service procedures; “Under study. Edition of
23、September 15, 1986 CEPT T/CS*Yq-O*E 2 m 2326434 0005004 T m A-1 1 Line seizure System L1 WC select i on A-7 L Enhanced r Manufacturer Subset compatibility check R TICS 49-08 E Page 3 I Supplementary service request 7 RR I I Non-harmonised supp l emen t ary - Harmonlsed supplementary serv I ces Conve
24、rsation or clear-down I Legerzd: R = revert. RR = register-recall. A = group A backward signal. Figure 1 (T/CS 49-08). System L1 signalling procedures structure. Edition of September 15, 1986 CEPT T/CS*49-O8*E 82 232b4L4 0005005 L 9 TICS 49-08 E Page 4 2.2.11. PABXs with transit functions must be ca
25、pable of repeating a service-request-recall signal to the next link. If a transit switch is not capable of using a link-recall signal, it will take no action on its recognition. Signalling procedures for the selection phase The selection phase covers all signalling necessary to establish a connectio
26、n between the originating and destination PABXs, including the forwarding of the required extension number to the destination PABX. The selection phase is entered, following the application of the seizing signal by the originating PABX. On recognition of the seizing signal, the responding PABX prepa
27、res to receive MFC signals and applies the proceed-to-send signal. As a multi-link call is progressively set-up across a network (see Recommendation T/CS 49-07 i), each transit switch applies a seizing signal to the subsequent link, and each responding PABX applies the proceed-to-send signal. To fac
28、ilitate network management, backward MFC signals are used during the selection phase to i) 2.3. request address signals (routing digits and extension number) one after the other from the originating PABX, as required by the transit switch or terminating PABX; when all address digits have been sent,
29、the originating PABX responds if it receives a further send-next-digit signal by sending the no-further- digit signal (1-15); ii) inform the originating PABX of the progress of the call, e.g. how many transit switches have been encountered; iii) inform the originating PABX of alternative routing tha
30、t has occurred at a transit switch; iv) inform the originating PABX that access to the public switched telephone network (PSTN) is about to occur; v) request entry into the optional enhanced routing subset) in order to influence the routing of the call, e.g. special quality circuits for data. Figure
31、 2 (T/CS 49-08) shows the selection phase in arrow chart form. Figure 3 (T/CS 49-08) shows the entry into the enhanced routing subset in arrow chart form. Signalling procedures for subset compatibility check On completion of selection, it is necessary for the originating and destination PABXs to det
32、ermine whether MFC signalling is going to continue, and if so, which procedure subset is to be used for the remainder of the call handling. If no further MFC signalling is possible (e.g. a non-MFC route or a PSTN has been encountered by a transit switch), an address-complete, no-MFC, set-up-speech-p
33、ath signal will be sent (A-6). Where further MFC signalling is possible, the subset compatibility check is initiated by the destination PABX, which applies one of the following signals (see Figure 1 (T/CS 49-08): i) Address-complete, enhanced, change-over-to-reception-of-group-B signals (A-1 1); ii)
34、 Address-complete, request-subset-identity (A-7); iii) Address-complete, basic, change-over-to-reception-of-group-B signals (A-3). The originating PABX responds by either: (a) implicitly accepting the proposed subset (enhanced or basic) by sending forward information as shown in Section 2.5.; or (b)
35、 implicitly agreeing to attempt entry into a manufacturer subset by sending forward its subset identity digit(s) for subset compatibility checking (the range required and the allocation of subset identity digits is under study); or (c) rejecting the proposed subset by sending either the enhanced-req
36、uest-not-accepted or the manufacturer- request-not-accepted signal. The originating PABX cannot reject a request to enter basic. On receipt of either a request-not-accepted signal or an incompatible manufacturer subset identity, the destination PABX will offer another subset. This interaction will c
37、ontinue until a common subset is found (usually enhanced or basic). Figure 4 (T/CS 49-08) shows the subset compatibility check in arrow chart form. 2.4. 2.5. Signalling procedures for the dialogue phase On completion of the subset compatibility check, both PABXs enter one of the following procedures
38、 subsets. “Under study. Edition of September 15, 1986 S-eize (line signal) , L 1 I CEPT T/CS*47-O*E 2 = 2326434 0005006 3 W I - -. TICS 49-08 E Page 5 O O O O 1 Proceed to send (line signal) i-N (routing digit) / A-1 (send next signal) +- I-N (routing digit) - Continue as shown in fig. 2 Continue as
39、 shown in fin. 2 e- A-10 (enhanced routing-information ready) e. + I-N (next digit) Continue as shown in fig. 2 1-13 (C/O to enhanced routing) - .- 2 - - -_ - - - - - - - - - - - - - -. -0 3LI I ANNEX I I-_- -1 , A-7 (C/O to user subsvstem) Enter user subsvstem 1-12 (user request not accepted) A-I 1
40、 (address complete-erihance C/O to group I I/B working) ubsystem v 11-12 (enhanced system request not accepted) A-3 (address complete-basic- C/O to group I I/B working 111-9 (limited list of call class info) INo I e- -1. . IV-14 (request not accepted-further V MFC signalling possible) / ; To / -/ .
41、fig. * /I a 0-14 (reject acknowledged) (C/O to group I I i/C working) IV-15 (request backward service category) andior service identity digit(S) IV-I4 (request not accepted- further MFC possible) 0-14 (rejection acknowledged) (C/O to group I I I/C working) Process backward supplementary service I _I
42、 IV-I4 (request not accepted- further MFC signalling possible) D-14 (rejection acknowledged) (C/O to group II l/C working) IV-I3 (OK further MFC signalling possible) D-13 (acceptance acknowledged) (C/O to group I I I/C working) Figure 7 (T/CS 49-08). Backward supplementary service request. 7 VT c L
43、P g TICS 49-08 E Page 13 PABX(0) PABX(T) fig. 6 o I A / / / SUPP supp / I svce svce Q D-15 (send next signal) I I I I IV-15 (end of digits) D-13 (OK-C/O to group IIIK working) fig. 6 Figure 8 (T/CS 49-08). Calling line identity request (CLI). Edition of September 15, 1986 CEPT T/CS*49-08* 2 W 232b41
44、4 0005015 4 W T/CS 49-08 E Page 14 2.5.2.8. Sequential processing of supplementary service requests During a call it is possible, although improbable, that more than one service demand will need to be processed at a given time. Examples of this are listed below. i) Clash of supplementary services: a
45、n incoming call has diversion-override capability and the called party has diversion activated. ii) Second attempt: a supplementary service or calling line identification is required, following an unsuc- cessful attempt to change-over to manufacturer. iii) Enhancement of a supplementary service: fol
46、lowing a supplementary service request, the PABX wants to change-over to manicfacturer for a specific enhancement. To enable a number of supplementary service requests to be processed sequentially, the following signals are included in groups IV and D: OK/acceptance-acknowledged, change-over-to-grou
47、ps-III-and-C D-13 Request-not-accepted/rejection-acknowledged, change-over-to-groups-III-and-C D- 14 OK, further-MFC-signalling-possible IV-13 Request-not-accepted, further-MFC-signalling-possible IV-14 These signals, which may be used either on completion of a supplementary service or on rejection
48、of a service request, return the signalling to groups III and C allocations, thus enabling the PABXs to either request a further service or conclude MFC signalling. On each return to groups III and C signalling, the originating PABX has priority. When the originating PABX has no further requests to
49、make, it sends a no-further- supplementary-service-request signal (111-1 5), The responding PABX, on receipt of this signal, either sends a supplementary service request or concludes MFC signalling by sending a conclude-MFC-signalling signal c-l. When the subset compatibility check has identified a common manufacturer subset, call handling continues in accordance with the appropriate specifications. However, once manufacturer subset procedures have been entere
