1、CCITT RECMN*I-SOZ 93 E 4862593 0580805 522 INTERNATIONAL TELECOMMUN CATION UN ION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU INTEGRATED SERVICES DIGITAL NETWORK (ISDN) INTERNETWORK INTERFACES 1.501 (03/93) SERVICE INTERWORKING ITU-T Recommendation 1.501 (Previously “CCIlT Recommendation”)
2、 CCITT RECflN*I.5!JL 93 II 48b259L O580806 469 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 wi
3、th 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. ITU-T Recommendat
4、ion 1.501 was prepared 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 Intemational Telecommunication Union (ITU), the CCITT ceased to exist as of 28 February 1993. In its place, the Telecommun
5、ication Standardization Sector (IT-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 Similarly, in this reform process, the CCIR and the IFRB have been replaced by the Radiocommunication Sector.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 t
6、he acronyms “CCIT, 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 Recomme
7、ndation, 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 fro
8、m the ITU. CCITT RECMN*I.SOL 93 4Bb259L 0580807 3T5 m CONTENTS Page 1 General 2 Definitions . 3 Terminal functionality for service interworking . 3.1 ISDN speech terminals 3.2 ISDN 3.1 kHz audio terminals 3.3 ISDN terminals that use the bearer capability selection option . 4 Interworking requirement
9、s supporting service interworking . 4.1 4.2 4.3 Interworking of speech and 3.1 kHz audio services . Interworking options for Multi-use bearer service . Interworking of group 4 and group 3 facsimile terminals 5 Appendix I . A/p law conversion and supplementary Services 1.1 7 kHz audio terminals . 1.2
10、 Data/facsimile terminals . Network interworking reguirements supporting the bearer capability selection . 1 1 3 3 3 3 5 5 5 5 6 6 6 8 Recommendation 1.501 (03/93) i CCITT RECMNxI-50L 93 W Li862591 0580808 231 W Recommendation 1.501 SERVICE INTERWORKING (Helsinki, 1993) 1 General In the provision of
11、 services in an ISDN, there wili exist situations where a service will require interworking with one or more other services. The intent of this Recommendation is to develop the general principles of service interworking and identifj the key interworking requirements needed to support service interwo
12、rking in ISDNs, between ISDNs, and between ISDNs and other networks. Specific ISDN service descriptions, as viewed from a user perspective, are provided in the 1.200-Series Recommendations. Network interworking is provided in the 1.500-Series Recommendations. 2 Definitions teleservice interworking:
13、Refers to the functions and requirements supporting the communication of terminals belonging to different ISDN teleservices (e.g. ISDN teletex to ISDN telefax). Such interworking will involve the use of communication-dependent interworking functions as defined in Recommendation 1.5 10. Teleservice i
14、nterworking can be supported by interworking functions provided by the network, by a service provider, and/or by terminals. bearer service interworking: Refers to the funnctions and requirements supporting the communication of terminals operating over different ISDN bearer services within an ISDN. I
15、SDN internal interworking: Refers to the functions and requirements for interworking between different connection elements within an ISDN, for example to support the communication of terminals belonging to one and the same teleservice but supported by different low layer Capabilities. network interw
16、orking: Refers to the functions and requirements supporting the interworking of networks with different low layer capabilities in order to support the interworking of services across the network boundary, for example, to support 3.1 kHz audio transfer. Teleservices interworking and bearer services i
17、nterworking may also include the support of supplementary services as appropriate. These types of interworking are not mutually exclusive. In certain scenarios, more than one type of interworking may take place; for example, both teleservice interworking and network interworking may occur in the cas
18、e of ISDN facsimile group 4 to PSTN facsimile group 3 interworking. It is also-noted that the functionality to support beater services interworking and ISDN internal interworking may be the same in most ISDNs (see Tables 1 and 2). Recommendation 1.501 (03/93) 1 CCITT RECMN*I*5OL 93 W 4Bb259L 0580809
19、 178 Network interworking; additionally, service provider or terminal provided MTFs may or may not be required depending on service category Communication between terminals belonging to Same 1. Different ISDN teleservices Different 2. An ISDN teleservice and a teleservice offered by a dedicated netw
20、ork (e.g ISDN facsimiie group 4 to facsimile group 3 offered by a PSTN) 3. One and the same ISDN teleservice but supported by different ISDN bearer capabilities (e.g ISDN teletex circuit mode to ISDN teletex packet mode) TABLE lD.501 Interworking aspeects of teleservices -I- - Technical consequences
21、 for interworking Service provider or terminal provided high layer IWFs Service provider or terminal provided high layer IWFs and ISDN internal interworking ISDN internal interworking Characten-zation of interworking Teleservice interworking (Note) Teleservice interworking and network interworking I
22、SDN internal interworking IWF Interworking function NOTE - Teleservice interworking may include the support of supplementary services as appropriate. TABLE uI.501 Interworking aspects of bearer services Characterization of in terworking Technical consequences for interworking Communication between t
23、erminals belonging to 1. Different ISDN bearer services (e.g. circuit mode data on a 64 kbitls unrestricted bearer to packet mode data on a virtual circuit bem) 2. An ISDN bearer service and a network service offered by a dedicated network (e.g. PSPDN) ISDN internal interworking Network interworking
24、; additionally network or terminal provided IWFs may or may not be required depending on service category (see FigurelL.515) Bearer service interworking (Notes 1,3) Bearerhetwork service interworking (Note 2) NOTES 1 internal interworking 2 Assumes network interworking. 3 Clarification may be requir
25、ed on the commonalities andor differences between bearer service interworking and ISDN Bearer service interworking may include the support of supplementary services as appropriate. 2 Recommendation IS01 (03/93) CCITT RECMN*I=SOL 93 8 4Bb259L OSBOBLO 99T 8 3 Terminal functionality for service interwo
26、rking 3.1 ISDN speech terminals An ISDN speech terminal should: a) b) c) be capable of responding to an incoming call offering for bearer capability (BC)l) equal to speech; generate an outgoing call request with bearer capability set to speech; be capable of responding to an incoming call offering f
27、or bearer capability equal to 3.1 kHz audio when such call offering is accompanied by a call progress indicator that interworking with the PSTN has been encountered. 3.2 ISDN 3.1 kHz audio terminais An ISDN terminal that uses the 3.1 kHz Audio bearer service should: a) b) c) be capable of responding
28、 to an incoming call offering for bearer capability equal to 3.1 kHz audio; generate an outgoing call request with bearer capability set to 3.1 kHz audio; be capable of responding to an incoming call offering for bearer capability equal to 3.1 kHz audio when such call offering is accompanied by a ca
29、ll progress indicator that interworking with the PSTN has been encountered. 3.3 3.3.1 ISDN terminal characteristics ISDN terminals that intend to use the bearer capabiiity selection option2) of the Multi-Use bearer service (e.g. appropriately implemented 7 kHz audio terminals, videophones, group 4/g
30、roup 3 facsimile machines, etc.) should have the capabilities to: Generate an outgoing call request with the following combinations of bearer capabilities: speech followed by UDI-TA3), or 3.1 kHz audio followed by UDI-TA. The spec-I-TA combination indicates to the network that interworking with the
31、PSTN and ISDN speech terminals is allowed. If the CONNECT message from the destination contains a UDITA BC, then the terminal shall operate in a mode using a 64 kbit/s unrestricted connection. If the CONNECT message received from the destination contains a speech BC, or no BC, then the terminai shal
32、l operate in the G.7 1 1 mode. The 3.1 kHz AudioKJDI-TA combination indicates that interworking with the PSTN and ISDN 3.1 kHz audio terminals is allowed. If the CONNECT message from the destination contains a UDI-TA BC, then the terminal shall operate in a mode using a 64 kbit/s unrestricted connec
33、tion. If the CONNECT message received from the destination contains a 3.1 kHz audio BC, or no BC, then the terminal shail operate in the G.711 mode. As an example, this BC combination would be used by group 4/group 3 facsimile machines that wish to avail themselves of the automatic fallback mechanis
34、m. ISDN terminals that use the bearer capability selection option a) 1 BC refers to the bearer capability information element defined in Recommendation 4.931 2, The bearer capability selection option allows a caliing terminal Lo encode two bearer capabilities in a setup message, such that the altern
35、ative bearer capability is automatically invoked in case the preferred bearer capability is unavailable or if interworking (eg. to the PSTN) is encountered (Recommendation 4.931.). The term fallback is used hereafter Lo refer to the automatic invocation of the alternative bearer capability. NOTE - I
36、f a single bearer capability is encoded in the call request, this indicates that fallback is neither desired nor allowed. 3, UDI-TA: Unrestricted digital information, with tones and announcements (Recommendation 4.931 ). Recommendation 1.501 (03/93) 3 CCITT RECMN*I-50L 93 m 48b2591 0580811 82b m Bea
37、rer capability 1 b) Respond to an incoming call request containing the SpeecMJDI-TA or 3.1 kHz Audio/UDI-TA BC combination by including the UDI-TA BC in the CONNECT message when answering the call (if the terminai is available) and operate in a mode using the 64 kbitls unrestricted connection. If th
38、e terminals UDI-TA capability is unavailable for some reason, then the terminal may respond to the alternative bearer capability and include it in the CONNECT message. In addition, terminals that intend to use the Multi-use bearer service for inter-regional communication4) should have the capability
39、 to transmit and receive both A-law and p-law encoded PCM signals according to Recommendation G.711 (selected through prior knowledge or in-band detection) for speech or 3.1 kHz audio information transfer. 3.3.2 Customer Access Signalling To invoke this service, a SETUP message is sent which has 2 B
40、Cs in ascending order of desirability if fallback is allowed, but only the desired BC is used for no fallback. This is summarised in the Table 3. Bearer capability 2 TABLE 3B.501 SETUP message for service invocation 7 kHz Data/facsimile With fallback Octet 3 octet 5 octet 3 Octet 5 Speech (Note 1) R
41、ec. G.711 UDI-TA .221/.242/.230 (Note 3) (Note 4) 3,l Wz Rec. G.711 UDI-TA e.g. V.1101 Audio (Note 1) (Note 3) (Note 2) No fallback 7 wz Datdfacsimile UDI-TA .221/.242/.230 (Note 3) (Note 4) (Note 3) (Note 2) UDI-TA e.g. V.1101 NOTES 1 The difference between the speech and 3.1 kHz audio bearers is t
42、hat the former may be subject to coding algorithms which will not support the transmission of voiceband data; also, echo control devices on speech bearers may not be capable of being disabled. The 3.1 kHz audio bearer is specifically intended for voiceband data, but still requires echo control. 2 Oc
43、tet 5 may be absent. 3 The codepoint label UD- TA signifies that the “bearer capability” requested by the user and the “connection type” provided by the network include the same attributes as those requested or provided for 64 kbitls unrestricted digital. The difference is that tones and announcemen
44、ts (encoded to Recommendation G.711) are provided for the Multi-use bearer service a-nd are not provided for 64 kbitls unrestricted digital service. Although both 7 Wz and dakfacsimile could work (in thecase of no fallback) with the use of 64 kbitls unrestricted digital infomation (UDI) BC, use of t
45、he UDI-TA BC would provide the benefit to users of tones and announcements. Tones and announcements are not incompatible with most modems and facsimile machines, and are in fact desirable for most users. 4 The codepoint G.72YG.725 (Rec. 4.931 Blue Book) has been relabeled “H.221/H.242/H.230. This ne
46、w label is more appropriate, since the Multi-Use bearer is suitable for videotelephony, which has similar requirements to 7 kHz. 4, Inter-regional communication refers Lo calls between G.711 A-law and p-law coding regions. 4 Recommendation 1.501 (03/93) CCITT RECHNtI-501 93 I 48b2591 0580812 7b2 4 I
47、nterworking requirements supporting service interworking 4.1 ISDNs will recognize and accept service requests for both speech and 3.1 IrHz audio bearer capabilities. The ISDN will handle and route the service request according to the bearer capability indicated in the call setup message. However, if
48、 an ISDN (say TSDN A) decides to support only one of these bearer services, no interworking functions need to be provided by other ISDNs for calls to/from ISDN A because other ISDNs support both speech and 3.1 kHz audio services. For calls originating from a PSTN, or which have encountered interwork
49、ing with the PSTN, the interworking functions at the ISDNPSTN interworking point will identify call requests to an ISDN as 3.1 ICHZ audio calls and accompany such call request with a call progress indicator. ISDN speech or 3.1 kHz audio calls will be allowed to interwork to the PSTN. See Recommendation 1.530 for further information. Interworking of speech and 3.1 kHz audio services 4.2 The Multi-use bearer service provides the option for an ISDN to support interworking with the PSTN and with ISDN speech and 3.1 kHz audio terminals. Terminals that intend to use the Mult
