1、INTERNATIONAL TELECOMMUNICATION UNION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU INTEGRATED SERVICES DIGITAL NETWORK (ISDN) INTERNETWORK INTERFACES 1.520 (03/93) GENERAL ARRANGEMENTS FOR NETWORK INTERWORKING BETWEEN ISDNs ITU-T Recommendation 1.520 (Previously “CCIlT Recornmendation”) ITU
2、-T RECMN*I.520 (REV*%) 93 I 4862571 0582801 7bl I FOREWORD The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of the International Telecom- munication Union. The ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them
3、 with a view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Conference (WTSC), which meets every four years, established the topics for study by the ITU-T Study Groups which, in their turn, produce Recommendations on these topics. IT-T Recommend
4、ation 1.520 was revisd by the -T Study Group XVIII (1988-1993) and was approved by the WTSC (Helsinki, March 1-12,1993). NOTES 1 As a consequence of a reform process within the International Telecommunication Union (), the CCIT ceased to exist as of 28 February 1993. In its place, the ITU Telecommun
5、ication Standardization Sector (rnr-T) was created as of 1 March 1993. Similarly, in this reform process, the CCIR and the IFRB have been replaced by the Radiocommunication Sector. In order not to delay publication of this Recommendation, no change has been made in the text to references containing
6、the acronyms “CCITT., CCIR or IFRB” or their associated entities such as Plenary Assembly, Secretariat, etc. Future editions of this Recommendation will contain the proper terminology related to the new ITU structure. 2 telecommunication administration and a recognized operating agency. In this Reco
7、mmendation, the expression “Administration” is used for conciseness to indicate both a O ITU 1993 All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing
8、from the ITU. (REVrJ) w . w CONTENTS 1 Introdution . 2 scope . 3 4 Required information and information handling Description of ISDN-ISDN interworking configurations 4.1 ISDN-ISDN interface where circuit mode bearer services are provided by both ISDNs 4.2 ISDN-ISDN InterFace where both ISDNs provide
9、 X.31 case B based packet mode bearer services 4.3 ISDN-ISDN interface where a circuit mode bearer service is provided by one ISDN to access either a PSPDN. or a PH and an X.31 case B packet mode bearer service provided by another ISDN ISDN-ISDN interworking via a transit network . ISDN-ISDN interfa
10、ce where an X.31 case B based packet mode bearer service is provided on ISDN-ISDN interface for circuit mode to additional packet mode service 5 Interworking functions . Generation of in-band tones and announcements for speech and 3.1 kHz audio bearer services . Cd negotiation between ISDNs 4.4 4.5
11、4.6 4.7 5.1 5.2 5.3 5.4 ISDN-ISDN interface for additional packet mode bearer services one ISDN and an additional packet mode bearer service is requested on mother ISDN . Echo control processing and speech processing . Compatibility checking between end users of different ISDNs . Functional interwor
12、king requirements for data transmission services . 6 7 References . Appendix I . ISDN connections involving restricted 64 kbids transfer capability 1.1 General . 1.2 Interworking with ISDNs providing restricted 64 kbids 1.3 Considerations for terminal designed to operate with restricted 64 kbids tra
13、nsfer capability Recommendation 1.528 (03/93) Page 1 1 1 4 4 4 5 5 5 6 6 7 7 7 7 9 9 10 10 10 10 12 i ITU-T RECflN*I-SZO (REV*l) 93 m 4862591 0582803 534 m Recommendation 1.520 GENERAL ARRANGEMENTS FOR NETWORK INTERWORKING BETWEEN ISDNs (Melbourne, 1988; amended at Helsinki, 1993) 1 Introdution The
14、number of ISDNs existing in the world is increasing and more than one ISDN may exist even within a single country. Therefore, ISDN-ISDN network interfaces should be standardized to facilitate the interworking between ISDNs and to extend connectivity world-wide. 2 Scope The purposes of this Recommend
15、ation are 1) 2) to identify the general arrangements for ISDN-ISDN interworking, and to define the functions and other requirements for the ISDN-ISDN interface. Recommendation 1.324 defines the reference point between two interconnected ISDNs to be the reference point. This Recommendation identifies
16、 other Recommendations which should be applied to the Nx reference point and clarifies the functions and requirements for interworking at the Nx reference point. 3 Required information and information handling Figure 1 iiustrates the general configuration for interworking between two ISDNs. The info
17、rmation given in Tables 1, 2 and 3, when required, has to be carried by Signalling System No. 7 (SS No. 7) ISUP and X.75, and is handled at the IWF in one of the following ways: i) information is terminated at the IWF and is not transferred to other ISDNs; ii) information is interpreted at the IWF a
18、nd is transferred to other ISDNs; iii) information is transferred through the IWF transparently; iv) information is newly generated at the IWF. Tables 1, 2 and 3 also show the classification of information into the above four categories services, circuit mode supplementary services and packet mode b
19、earer services, respectively. circuit mode bearer Additional information required specifically for OAM (Operational, Administrative and Maintenance) functions is for further study. FIGW 1L.520 General configuration for interworking between two ISDNs Recommendation 1.520 (03/93) 1 Category i ii iii (
20、Note 8) iv TABLE 1A.520 Information required for IWF between JSDNs for circuit mode bearer services Required information First transit network subsequent to IWF Called party number (Note 1) Calling partys category (Note 2) Bearer capability Call indicators (Note 3) Use of satellite (Note 4) Calling
21、party number Subaddress Calling partys category Terminai compatibility (Note 5) User-to-user signalling Cause Charge Cause for interworking Charging information (Note 6) Change of services (Note 7) Rec. 4.931 information element Transit network selection Called party number/Key pad (Unnecessary) Bea
22、rer capability (Unnecessary) (Unnecessary) Calling party number Subaddress (Unnecessary) Low layer compatibility High layer compatibility User-to-user information element Cause (Unnecessary) Cause (Unnecessary) (Should be defined) Rec. Q.763 parameter name Transit network selection Called party numb
23、er/Subsequent number Calling partys category Transmission medium requirements User service information Forward call indicators Backward call indicators Nature of connection indicators Calling party number Access transport Calling partys category Access transport User-to-user information Cause indica
24、tor Charge information Cause indicator Charge information (Should be defined) NOTES 1 For charging use. 2 3 For discrimination of priority calordinary call. These indicators are used to identify: a) international incoming call, b) available end-to-end signalling system, c) charged calhoncharged call
25、. 4 When a satellite circuit is employed for an interworking call at the interworking point, this information is processed at the IWF. If a satellite circuit is not employed for a call, this information is transferred through the IWF transparently. 5 There may be cases where the terminal compatibili
26、ty information is processed (see 5.4). 6 This information is used only when access charging is necessary. 7 Ail ISDNs do not necessarily provide identical services (or connection types). When a change of services occurs at the lWF, the network should send the indication for change of services and ma
27、y solicit acceptance of change of services to a calling user in certain cases (see 5.3.1). 8 The information in this categoq is transferred through the IWF transparently. 2 Recommendation 1.520 (03193) ITU-T RECMN*I-520 (REVbL) 93 4862573 0582805 307 = category Requiredinfornation Rec. 4.931 informa
28、tion element Rec. 4.763 information element iii Network specific facility Key pad facility Feaue activation Feature indication Supplementary senice request ii Progressindicator Suspendmesume indicator (Should be defined) Progress indicator Access transport Notification indicator SuspendResume indica
29、tor Progress indicator TABLE 3D.520 Information required for IWF between ISDNs for packet mode bearer services (in-band signalling) category i ii iii iv Required information Transit network idenfification Packet type Logical channel number Called party number Throughput class Window size Packet size
30、 Call identer Transit delay selection User-to-user information Calling party number Terminai compatibility Subaddress Cause Cause for interworking Charging Rec. X.25 information ROA selection Packet type identifier Logical channel number Called DTE address Throughput class negotiation Flow control p
31、arameter negotiation Flow control parameter negotiation (unnecessary) Transit delay indicatiodselection Fast select identifier Calling DTE address (Call user data) Calling address extension Called address extension Diagnestic code (Should be defined) Charging information Rec. X.75 information I Tran
32、sit network identification I I Packet type identifier Logical channel number Called DTE address Throughput class indication Window size indication Packet size indication Call identifier Transit delay indication Fast select indication Calling DTE adress (Should be defined) Called address extension Ca
33、lling address extension Diagnestic code (Should be defined) (Should be defined) NOTE - The relationship between X.25 facilities and ISDN supplementary services is for furthet study. Recommendation 1.520 (03/93) 3 ITU-T RECMN*I-520 (REV*1) 93 4862591 0582806 243 4 4.1 Description of ISDN-ISDN interwo
34、rking configurations ISDN-ISDN interface where circuit mode bearer services are provided by both ISDNs See Figure 2. Nx 1 ISDN, ss No. 7 Ti 3O1610-93/w2 cc circuit switched FIGURE! 2I.520 ISDN, interworking WithISDN, I 4.1.1 Bearer services Individual bearer service categories are defined in the 1.2
35、30-Series Recommendations. Layer 1 interworking specifications are recommended in Recommendation 1.511. Layers 2 and 3 in the U-plane are passed transparently. 4.1.2 Supplementary services 4.1.2.1 Other than user-to-user signaihg For supplementary services other than user-to-user signalling, call co
36、ntrol information is transferred via Signalling System No. 7 across the N, reference point. The interface for user information transfer is not different from that of basic bearer services. 4.1.2.2 User-to-user signalling services There are two methods of transferring user-to-user signalling. One is
37、transfer of user-to-user signalling within Q.931 call control messages which have been mapped into Signalling System No. 7 messages and then are conveyed via the Signalling System No. 7 network. The other is transfer of user-to-user signalling within stand alone USER INFO messages (which have been m
38、apped into Signalling System No. 7 messages and then are conveyed via the Signalling System No. 7 network), or optionally may be transferred via packet handlers (PHs) in some ISDNs. In the case where user-to-user signalling is transferred between packet handlers (PHs) in both ISDNs, the X.75 protoco
39、l may be applied to the internetwork interface to transfer user-to-user signalling. In the case where user-to-user signalling is transferred via Signalling System No. 7 networks in both ISDNs or at least in one ISDN, the Signalling System No. 7 protocol should be applied to the internetwork interfac
40、e for user-to-user signalling. 4.1.3 Signalling System No. 7 for the control of circuit mode services at the Nx reference point For the control of circuit mode services in the long term, Signalling System No. 7 with ISUP will be used at the Nx reference point. 4.2 ISDN-ISDN Interface where both ISDN
41、s provide X.31 case B based packet mode bearer services See Figure 3. 4 Recommendation 1.520 (03/93) The X.75 protocol is used to transfer X.3 1 based packet mode services at the Nx reference point. Layers 1, 2, and 3 for this interface are specified in Recommandation X.75. Yi 1 x75 X31 case 6 X31 c
42、aseB Ti1620-93/w3 ps packetswitched FIG= 3fi.520 ISDNps interworking with ISDNS 4.3 ISDN-ISDN interface where a circuit mode bearer service is provided by one ISDN to access either a PSPDN, or a PH and an X.31 case B packet mode bearer service provided by another ISDN With this type of interworking,
43、 two different configurations are considered, I and II. In configuration I, inworking between the two ISDNs utilizes X.75 interexchange signalling. See Figure 4. In configuration II, a circuit switched access to the PH in the ISDNe) is provided, and the interworking between the two ISDNs utilizes a
44、Signalling System No. 7 protocol This interworking arrangement applies for data transmission services. General arrangements are covered in 6.3K.320. There are two possibilities: i) X.31 case A interworking with X.31 case B. Case A refers to the situation where a transparent circuit switched access t
45、o PSPDN is provided by ISDN. Case B refers to the situation where a packet mode bearer service is provided by an ISDN PH. ii) ISDN circuit switched access to an ISDN PH (this case may exist if the originating ISDN does not have PH functionality). Several aspects of interworking for data transmission
46、 services as well as their appiication to other transmission services are for farther study. 4.4 ISDN-ISDN interworking via a transit network ISDN-ISDN interworking via a transit network (see Figure 5) may be a useful configuration in the short term for extending specific ISDN services on an end-to-
47、end basis. Special transmission, switching and signaling capabilities may have to be deployed in the transit network to ensure that the specific ISDN service is available end-to-end. The detailed interworking functions and interfaces for this configuration are for further study. 4.5 ISDN-ISDN interf
48、ace for additional packet mode bearer services For packet mode services that are currently under study, out-band call control signalling is used. The same out-band caU control is used for circuit mode services. Two alternatives can be considered for this out-band cd control: enhancement of Signallin
49、g System No. 7 and enhancement of the D-channel protocol. The choice between the two alternatives is for further study. Recommendation 1.520 (03/93) 5 ITU-T RECMN*I=520 (REV* II II II + II FIGURE I.lA.520 Interworking with ISDNs providing restricted 64 kbis ISDN 1 may have some arrangements having only restricted 64 kbit/s transfer capability. ISDN 2 is unrestricted. In both cases, at the reference points S or T, the 1.412 user-network interfaces are provided. However, where restricted 64 kbit/s arrangements are involved, only information streams not havi
