ITU-T X 80-1988 INTERWORKING OF INTEREXCHANGE SIGNALLING SYSTEMS FOR CIRCUIT SWITCHED DATA SERVICES《适用于CCITT应用的开放系统互连(OSI)安全结构》.pdf

1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 8 TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU05“,)#G0G0$!4!G0G0.%47/2+342!.3-)33)/. G0G03).!,).G0G0!.$G0G037)4#().).4%27/2+).G0G0/ amended at Malaga-Torremolinos, 1984)The CCITT,considering(a) that Recommendations X.60 and X.71 define two different sign

2、alling systems which are intended for useon international circuits between synchronous data networks;(b) that Recommendation X.70 defines a signalling system which is intended for use on international circuitsbetween anisochronous data networks;(c) that Administrations and RPOAs have expressed inter

3、est in implementing Recommendations X.60, X.70or X.71 as national signalling systems between national data switching exchanges;(d) that Recommendations X.60, X.70 and X.71 have been defined to include the necessary signals to allowinterworking between any combination of these signalling systems;(e)

4、that there is a need to define the specific interworking requirements between these signalling systems;unanimously declaresthat interworking between any combination of signalling systems conforming to Recommendations X.60, X.70and X.71 should be as defined in this Recommendation.1 General1.1 Princip

5、lesThis Recommendation provides a set of interworking specifications for CCITT circuit-switched data signallingsystems. Interworking is defined as the controlled transfer of signalling information across an interface between differentsignalling systems where the significance of the transferred infor

6、mation is identical, or where significance is translated ina defined manner, and includes the performance of the appropriate interworking procedures in association with thetransfer. These interworking procedures will be performed by an interworking function at a boundary between the twointerworking

7、signalling systems.Interworking commences at call set-up when a link is established between two circuits using different signallingsystems and continues throughout the call until release of the connection occurs. Interworking ceases with the release ofthe connection, whether the release is initiated

8、 by the reception of a clear condition from either of the signalling systemsinvolved or by the interworking function itself in response to some abnormal condition.1.2 PresentationThe specifications are basically represented by flow charts consistent with the CCITT Specifications andDescriptions Lang

9、uage (SDL), described in Recommendations Z.101 to Z.103; and are used to describe the logicalrequirements of the interworking function. In addition, two tables are included to show the signalling sequences requiredfor a typical interworking situation. Narrative description has been reduced to a mini

10、mum.SDL provides a method of presentation which is both comprehensive and independent of implementation,ensuring that all interworking conditions can be covered in a systematic manner. The logic of each signalling system iscovered in the relevant signalling Recommendations X.60, X.70 or X.71.2 Fasci

11、cle VIII.3 - Rec. X.802 Interworking procedures between Recommendations X.60 and X.71The present 2 details the specific requirements for interworking between an X.60 and an X.71 signallingsystem.Table 1/X.80 illustrates the relationship between the signals on the X.60 side of the interworking functi

12、on and thecorresponding signals on the X.71 side. It illustrates the simple case of a basic call which originates in an “X.60network“ and terminates in an “X.71 network“, and which does not invoke any additional facilities, and it assumes thatthe call is successful. The call clear-down is initiated

13、by the customer in the X.60 network.There are, however, several combinations of facilities which could be required on a particular call whichcomplicate the interworking procedures, in particular the instant of connect through. In Table 1/X.80 the reception of theCall Connected (CC) signal from the R

14、ecommendation X.71 signalling system defines the conclusion of the call set-upsequence at the interworking point and hence the instant of connect through. If the call involves additional facilities thereception of the Transit Through Connect (TTC) signal from the Recommendation X.71 signalling syste

15、m initiates theadditional protocols necessary to setting up the call successfully. Table 2/X.80 illustrates an example involving theseadditional protocols for a call requiring both calling and called line identities and including a positive call progressindication.Appendix I to this Recommendation i

16、llustrates further examples of interworking situations which can occur forthe X.60 to X.71 case. The appendix illustrates examples of interworking situations where two “X.71 networks“ transitan “X.60 network“ or two “X.60 networks“ transit an “X.71 network“.2.1 Interworking from Recommendation X.60

17、to X.71Figure 1/X.80 shows the transit exchange interworking functions required to enable an X.60 to X.71 call to beconnected.In response to the selection information sent to the X.71 network, one of two signals may be received: CC orTTC as described above.Fascicle VIII.3 - Rec. X.8034Fascicle VIII.

18、3 - Rec. X.80Fascicle VIII.3 - Rec. X.80 56 Fascicle VIII.3 - Rec. X.80The consequent Call Accepted Message(s) (CAM) which are transmitted on the X.60 side of the interworkingunit function can contain:a) The call accepted signal when a CC signal was received on the X.71 side. Note that this type of

19、CAM(designated CAM 1) can also contain the called line identity and/or a positive call progress signal for callswhich have initiated the additional protocols and are now ready to connect through. See c) below.b) The transit through connect signal when a TTC signal was received on the X.71 side. The

20、TTC signal may ormay not request the calling line identity. The consequent call accepted message (designated CAM 2) cantherefore contain:i) a request for the calling line identity if it was requested and it is not available;ii) no request if the calling line identity is already available as part of

21、the originating address message;iii) no request if the calling line identity was not requested.In i) a calling line identity message is received from the X.60 side in response to the CAM 2. Then thecalling line identity can be transmitted on the X.71 side.In ii) the calling line identity can be tran

22、smitted on the X.71 side.In iii) a Transit centres Through-Connected (TTD) signal is transmitted on the X.71 side.c) A positive call progress signal and/or the called line identity when they were received on the X.71 sidepreceding the call connected (CC) signal. This information can be included in t

23、he CAM 1 sent on the X.60side to complete the through-connection.2.2 Interworking from Recommendation X.71 to X.60Figure 2/X.80 shows the transit exchange interworking functions required to enable an X.71 to X.60 call to beconnected.The signals that can be transmitted on the X.71 side of the interwo

24、rking unit function in response to a CAM 1 orCAM 2 message are as follows:a) The call connected (CC) signal either directly or after the transmission of called and/or calling lineidentification and/or a positive call progress signal.b) If the CAM 1 or CAM 2 contains a request for calling line identi

25、ty, a TTC signal is transmitted with a requestfor calling line identification on the X.71 side. In response, the calling line identity is received from the X.71side and a calling line identity message transmitted on the X.60 side.Note - If the calling line identity is sent as a result of a CAM 2 req

26、uest, a subsequent CAM 1, which maycontain the called line identity, must be sent on the X.60 side in order to complete the call set-up.c) Where calling line identity is not required by a CAM 2, a TTC signal is sent on the X.71 side. A TTD signalwill be received in response and this may be received

27、before or after a CAM 1, which may contain the calledline identity, has been received from the X.60 side in order to complete the call.d) In b) and c) a positive call progress signal and/or the called line identity can be sent on the X.71 side beforethe CC signal.e) Where a CAM 1 is received without

28、 a request for calling line identity but including the called line identity ora positive call progress signal, a TTC signal is sent on the X.71 side. When a TTD signal has been receivedin response, the called line identity and/or the positive call progress signal may be sent before the CC signal.2.3

29、 Call clear-downA call clear-down signal can originate in either the X.60 or X.71 network. The interworking function musttherefore be capable of detecting clear signals and messages, which can occur at any time during the call set-up or dataphase of a call, and take the appropriate action as detaile

30、d below:a) A clear request signal received from the X.71 networkThis will initiate disconnection of the call at the interworking function, the transmission of a clearconfirmation signal to the X.71 network and a clear message to the X.60 network. At this point interworkingceases and each network cle

31、ars down according to the normal X.60 or X.71 procedures.Fascicle VIII.3 - Rec. X.80 7b) A clear message received from the X.60 networkThis will initiate disconnection of the call at the interworking function, the transmission of a clear message tothe X.60 network and a clear request signal to the X

32、71 network. At this point interworking ceases and eachnetwork clears down according to the normal X.60 or X.71 procedures.Note - The interworking function may optionally detect the internetwork data circuit clear request signalinitiated by the user in the X.60 network. This will cause the disconnec

33、tion of the call at the interworkingfunction and initiate the same procedures as described above.2.4 Call failure conditions during call set-upSupervision of time-outs during call set-up takes place as stated in the signalling Recommendations X.71and X.60 respectively.The expiry of such a supervisor

34、y-timer will lead to normal clearing as shown in Figures 1/X.80 and 2/X.80.3 Interworking procedures between Recommendations X.70 and X.71Since the proposals for Recommendations X.70 and X.71 are closely related, interworking between an X.70 andan X.71 network should be straightforward; however the

35、interworking procedures required are for further study.4 Interworking procedures between Recommendations X.60 and X.70The required interworking procedures should be similar to the Recommendation X.60/71 case; however they arefor further study.8 Fascicle VIII.3 - Rec. X.80Fascicle VIII.3 - Rec. X.80

36、9APPENDIX I(to Recommendation X.80)Interworking cases, Recommendations X.60/X.71The following sequence charts illustrate examples of complex transit interworking situations.Key to sequence chartsO - Originating networkT - Transit networkD - Destination networkX - Data path through-connectRecommendat

37、ion X.60AM - Address messageAM (CLI) - Address message with calling line identity (CLI)AM (CDIR) - Address message with request for called line identity (CDI)AM (CLI + CDIR) - Address message with CLI and request for CDICAM 1 - Call accepted message contains call accepted signal; can contain CDI, CL

38、I requestand/or positive call progress signalCAM 2 - Call accepted message; TTC signal can contain CLI requestCLIM - Calling line identity messageRecommendation X.71CS - Calling signalSS - Selection signals; can include request for called line identityC.CONF - Call confirmation signalCC - Call conne

39、cted signalTTC - Transit through-connect signal can include request for Calling Line IdentityTTD - Transit centres through-connected signalCLI - Calling line identityCDI - Called line identityCP+ - Positive call progress signal10 Fascicle VIII.3 - Rec. X.801.1 Interworking, Recommendations X.60/X.71

40、/X.60a) Called line identity and/or positive call progress signal required, calling line identity not requiredb) Both called and calling line identity required and/or positive call progress signalFascicle VIII.3 - Rec. X.80 111.2 Interworking, Recommendations X.71/X.60/X.71a) Called line identity and/or positive call progress signal, calling identity not requiredb) Calling line identity and called line identity and/or positive call progress signal required