1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 8 TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU05“,)#G0G0$!4!G0G0.%47/2+342!.3-)33)/. G0G03).!,).G0G0!.$G0G037)4#().$%4!),%$G0G0!22!.%-%.43G0G0(b) that it is essential to make it possible to allow interworking between DTEs connected to the different types
2、of PDNs;(c) that CCITT services, e.g. telematic services, can be carried by PSPDN or CSPDN or both, as defined inexisting Recommendations T.70 and X.300;(d) that Recommendation T.70 defines the network-independent basic transport service for telematic services;(e) that Recommendation X.300 defines g
3、eneral principles for interworking between public networks, andbetween public networks and other networks for the provision of data transmission services;(f) that Recommendation X.322 defines general arrangements for interworking between PSPDNs andCSPDNs for the provision of data transmission servic
4、es;(g) that Recommendation X.75 defines procedures for PSPDN/PSPDN interworking and thatRecommendation X.71 defines procedures for CSPDN/CSPDN interworking;(h) that Recommendation X.25 defines the user interface to PSPDNs, and that RecommendationsX.21/X.21 bis define the user interface to CSPDNs;una
5、nimously declares the viewthat detailed arrangements for interworking between CSPDNs and PSPDNs on the basis of RecommendationT.70 for telematic services shall be in accordance with the procedures specified in this Recommendation.CONTENTS0 Introduction1 Scope and field of application2 References3 De
6、finitions4 Abbreviations5 General aspects5.1 Circuit switched public data network5.2 Packet switched public data network6 Specification of interworking functions6.1 Connection establishment phase6.1.1 Connection establishment initiated on the CSPDN side6.1.2 Connection establishment initiated on the
7、 PSPDN side2 Fascicle VIII.3 - Rec. X.826.2 Connection release phase6.2.1 Connection release initiated on the CSPDN side6.2.2 Connection release initiated on the PSPDN side6.2.3 Connection release initiated by the IWF T.706.3 Data transfer phase6.3.1 Handling of user data6.3.2 Handling of qualifier
8、bit6.3.3 Handling of delivery confirmation bit6.3.4 Handling of more data bit6.3.5 Reset7 Restart request7.1 Restart request initiated by the PSPDN7.2 Restart request initiated by the IWF T.70Appendix I - Items in relationship to the OSI connection-mode network service0 IntroductionThis Recommendati
9、on is one of a set of Recommendations produced to facilitate considerations of interworkingbetween networks. It is based on Recommendation X.300, which defines the general principles for interworking betweenpublic networks, and between public networks and other networks for the provision of data tra
10、nsmission services.Recommendation X.300 indicates in particular how collections of physical equipment can be represented as“Subnetworks“ for consideration in interworking situations.This Recommendation describes the interworking arrangements between circuit switched public data networks(CSPDN) and p
11、acket switched public data networks (PSPDN) based on CCITT Recommendation T.70.1 Scope and field of applicationThe purpose of this Recommendation is to describe the detailed arrangements for the interworking betweenCSPDNs and PSPDNs based on Recommendation T.70. These arrangements are applicable onl
12、y to the interworkinginvolving telematic services, and not to the interworking involving communication capabilities described inRecommendation X.300.The mapping of protocol data units taken from different protocols is limited to the capabilities of each of theprotocols. The functions that are requir
13、ed to provide the full OSI connection-mode network service (CONS) and theirrelation to this Recommendation can be found in the Appendix I.2 ReferencesRecommendation T.70 Network-independent basic transport service for telematic services,Recommendation X.1 International user classes of service in pub
14、lic data networks and integrated services digitalnetworks (ISDNs),Recommendation X.2 International data transmission services and optional user facilities in public data networksand ISDNs,Recommendation X.21 Interface between data terminal equipment (DTE) and data circuit-terminating equipment(DCE)
15、for synchronous operation on public data networks,Recommendation X.21 bis Use on public data networks of data terminal equipment (DTE) which is designed forinterfacing to synchronous V-series modems,Recommendation X.25 Interface between data terminal equipment (DTE) and data circuit-terminating equi
16、pment(DCE) for terminals operating in the packet mode and connected to public data networksby dedicated circuit,Recommendation X.71 Decentralized terminal and transit control signalling system on international circuitsbetween synchronous data networks,Recommendation X.75 Packet switched signalling s
17、ystem between public networks providing data transmissionservices,Recommendation X.121 International numbering plan for public data networks,Recommendation X.300 General principles for interworking between public networks, and between public networksand other networks for the provision of data trans
18、mission services.Fascicle VIII.3 - Rec. X.82 33 DefinitionsNo specific definitions need to be taken into account.4 AbbreviationsCLI Calling Line IdentificationCONS Connection-mode Network ServiceCOT Class of TrafficCP Call ProgressCSPDN Circuit Switched Public Data NetworkCUG Closed User GroupDM Dis
19、connected ModeDNIC Data Network Identification CodeDTE Data Terminal EquipmentEOS End of SelectionIWF Interworking FunctionNS Network ServiceOSI Open Systems InterconnectionPDN Public Data NetworksPSPDN Packet Switched Public Data NetworkQOS Quality of ServiceSABM Set Asynchronous Balanced ModeTID T
20、erminal IdentifierTTC Transit Through ConnectTTD Transit Centres Through ConnectedUA Unnumbered AcknowledgmentUC User Class5 General aspectsThis Recommendation, in describing interworking arrangements between two subnetworks, adheres to thegeneral principles of Recommendation X.300. The environments
21、 of these two subnetworks are described in thefollowing sections.5.1 Circuit switched public data networkThe CSPDN provides switched data transmission services as defined in Recommendation X.1 and X.2 for theprovision of data transmission services. The transmission capability of the CSPDN may also b
22、e used for the provision oftelematic services defined in the T-series Recommendations.Note - For additional application rules for telematic services see 3.3 of CCITT Recommendation T.70.5.2 Packet switched public data networkThe PSPDN provides packet switched data transmission services as defined in
23、 Recommendation X.1 and X.2 forthe provision of data transmission services. The transmission capability of the PSPDN may also be used for the provisionof telematic services defined in the T-series Recommendations.Note - For additional application rules for telematic services see 3.1 of CCITT Recomme
24、ndation T.70.4 Fascicle VIII.3 - Rec. X.826 Specification of interworking functionsThis section describes the detailed mapping for the interworking between CSPDNs and PSPDNs based onRecommendation T.70.6.1 Connection establishment phase6.1.1 Connection establishment initiated on the CSPDN sideFigure
25、s 2/X.82 to 6/X.82 show the signalling when a terminal connected to the CSPDN initiates a call towards aterminal in the PSPDN. The order of events in time might be different for unrelated signals received from the circuit andpacket switched side, depending on the transmission delays and response tim
26、es in both subnetworks.While Figure 2/X.82 represents the successful connection establishment several possible unsuccessful callattempts are shown in figures 3/X.82 to 6/X.82.6.1.1.1 Selection signalsAny non allocated selection character shall result in the call being cleared with a call progress si
27、gnal.1) First class-of-traffic character (1st COT)Alternative routing allowed/not allowed is not transferred to the PSPDN.The implementation of transit/terminal indicator Bit 1 is as follows:If Bit 1 = 0 the DNIC is included in the selection signals;If Bit 1 = 1 the DNIC is not included in the selec
28、tion signals.2) First user class character (1st UC)1st UC is only used to indicate that 2nd UC follows.3) Second user class character (2nd UC)When the 2nd UC indicate TELETEX by “1001“ in the bits b1 to b4, this shall be mapped to “00000010“in the first octet of the call user data field of the call
29、request packet of Recommendation X.75. In case thereis no 2 UC or in cases of coding other than “1001“ the call attempt may either be rejected or continued.Note - This reflects the status of Recommendation T.70. However, the transparency of the call user datafield needs further consideration. Other
30、possible mapping requirements e.g. to the class of traffic facility ofRecommendation X.75 are for further study.Fascicle VIII.3 - Rec. X.82 54) Second class-of-traffic character (2nd COT)Bit b1 is used to indicate national/international traffic, and is not to be transferred in theRecommendation X.75
31、 signalling. The bits b2 and b3 indicate whether the called line identification of thecalled terminal is requested (b2) and/or the closed user group characters of the calling terminal arefollowing.5) Third class-of-traffic character (3rd COT)When receiving a 3rd COT the call attempt may either be re
32、jected or continued. The possible future use ofthe 3rd COT is for further study.6) Closed user group characters(CUG)The closed user group characters are transferred as CUG utility in Recommendation X.75. If the CUGsequence contains less than 4 characters, excluding DNIC, zeros are inserted in the X.
33、75 CUG utility. If aCUG DNIC is not included in the X.71 signalling, a dummy DNIC of “0000“ is inserted in the CUGutility.7) Network or service identification signalThe IWF T70 shall return a DNIC.8) Called DTE addressThe selection signals received from the CSPDN are transferred into the X.75 addres
34、s field. If the calledDTE address does not contain a DNIC, a DNIC shall be added by the IWF T.70.6.1.1.2 Transit through connect signal (TTC)The Calling line identification shall always be required (b2 = 1).6.1.1.3 Calling line identification signal (CLI)The calling line identification signals are u
35、sed in the calling DTE address field in the X.75 Call Request Packet.If the calling line ID does not contain a CNIC, a DNIC may be added by the IWF T.70.6.1.1.4 Call progress signal (CP)The call progress signal “terminal called“ is sent to inform the calling terminal that the call is being establish
36、ed.The IWF may repeat this CP in order to avoid that the call attempt is cleared by the calling DTE before the callattempt in the PSPDN is either connected or timed out and cleared.6.1.1.5 Call request packet1) Called and calling DTE addressThe called DTE address is obtained from the DNIC and the ca
37、lled terminal number in the X.71 selectionsignals. The end of selection character is not transferred.The calling DTE address is obtained from the X.71 calling line identification signals. If no DNIC isincluded, the DNIC of the calling network will be inserted.2) Network utilitiesThe throughput class
38、 indication shall be signalled and the value indicated shall be mapped to the bit rate onthe circuit switched side. A lower throughput class in the call connected packet may be accepted.The default value of 2 for window size, and 128 for packet size, shall apply for all calls and needstherefore not
39、be signalled. The use of other values is subject to bilateral agreement.3) User facilitiesNo user facilities shall be signalled.4) Call user dataSee 6.1.1.1, item 3).6.1.1.6 SABM commandThe calling terminal uses address (B) in commands and (A) in responses, the IWF T.70 uses address (A) incommands a
40、nd (B) in responses according to Recommendation T.70.After receiving the originating through connection signal the IWF T.70 shall wait for the link set up by the DTEconnected to the CSPDN. After a time-out condition the IWF T.70 may attempt to set up the link level itself.6 Fascicle VIII.3 - Rec. X.
41、82Fascicle VIII.3 - Rec. X.82 78 Fascicle VIII.3 - Rec. X.826.1.2 Connection establishment initiated on the PSPDN sideFigures 7/X.82 to 11/X.82 show the signalling when a terminal connected to the PSPDN initiates a call towards aterminal in the CSPDN. The order of events in time might be different f
42、or unrelated signals received from the circuit andpacket switched side, depending on the transmission delays and response times in both subnetworks.While Figure 7/X.82 represents the successful connection establishment several possible unsuccessful callattempts are shown in Figures 8/X.82 to 11/X.82
43、.6.1.2.1 Call request packetThe called DTE address always includes a DNIC which may be transferred to the CSPDN.The calling DTE address is stored and will be transferred later in the calling line identification signal, ifrequested by the called DTE.1) Network utilitiesThe transit network identificat
44、ion code shall not be transferred in the X.71 signalling, since DNICs cannotbe signalled in X.71 in the forward direction.The call identifier shall not be signalled in X.71.If the received throughput class indication is greater than the data signalling on the circuit switched side,the value of the d
45、ata signalling rate shall be returned. In all other cases the received value is returned.The default values of 2 for window size, and 128 for packet size, shall apply for all calls. The use of othervalues is subject to bilateral agreement.According to Recommendation T.70 terminals shall not use the
46、fast select facility. the receipt of fast selectindication shall result in sending a clear request packet.The closed user group and closed user group with outgoing access are mapped to the corresponding signalsin Recommendation X.71.The transit delay indication cannot be signalled in Recommendation
47、X.71.2) User facilitiesFor further study.Fascicle VIII.3 - Rec. X.82 93) Call user dataThe telematic protocol identifier as defined in Recommendation T.70 is mapped to the 2nd UC inRecommendation X.71 (all remaining information will get lost). When receiving other codes in the firstoctet of the call
48、 user data field of the call request packet of Recommendation X.75 the call attempt mayeither be rejected or continued.Note - This reflects the status of Recommendation T.70. However, the transparency of the call user datafield needs further consideration. Other possible mapping requirements e.g. to
49、 the class of traffic facility ofRecommendation X.75 are for further study.6.1.2.2 Selection signals1) First class-of-traffic character (1st COT)“Alternative routing allowed“ is signalled. The X.75 called DTE address may be passed unchanged to theCSPDN or the DNIC may be stripped.Note - The X.75 addresses of the called and calling DTE always include a DNIC.Bit 1 is set accordingly. Bit 1 = 0: DNIC included; Bit 1 = 1: DNIC not included. “UC follows“ isindicated.2) First user class character (1st UC)1st UC is only used to indicate that the second class-of-traffic (2nd COT) character
