1、ITU-T RECMN*I-530 (REV*L) 93 M LlBb253L 05830Z8 544 M NTERNATIONAL TELECOMMUNICATION UNION ITU-T TELECOMMUNICATION STAN DA RD IZAT I ON SECTOR OF IT 1.530 (03/93) INTEGRATED SERVICES DIGITAL NETWORK (ISDN) INTERNETWORK INTERFACES NETWORK INTERWORKING BETWEEN AN ISDN AND A PUBLIC SWITCHED TELEPHONE N
2、ETWORK (PSTN) ITU-T Recommendation 1.530 (Previously “CCIlT Recommendation“) ITU-T RECMNsI.530 (REV*1) 93 m 4862591 0583029 480 m FOREWORD The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of the International Telecom- munication Union. The ITU-T is responsible for studyi
3、ng technical, operating and tariff questions and issuing Recommendations on them 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 ITLJ-T Study Gro
4、ups which, in their turn, produce Recommendations on these topics. ITU-T Recommendation 1.530 was revised by the ITU-T Study Group Xwr (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
5、(ITU), the CCIIT ceased to exist as of 28 February 1993. In its place, the IT Telecommunication Standardization Sector (ITU-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 Similarly, in this reform process, the CCIR and the IFRB have been replaced by the Radiocommunication Sector.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 publicati
6、on of this Recommendation, no change has been made in the text to references containing the 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 structu
7、re. 2 telecommunication administration and a recognized operating agency. In this Recommendation, the expression “Administration” is used for conciseness to indicate both a O IT 1993 All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electroni
8、c or mechanical, including photocopying and microfh, without permission in writing fiom the IT. ITU-T RECMN*I.530 (REV*l) 73 D 48b259l 0583030 lT2 CONTENTS General . scope Abbreviations . Interworking configuration and network characteris tics 4.1 Interworking configurations . 4.2 Key ISDN and PSTN
9、characteristics and related interworking functions ISDN bearer services suitable for ISDN-PSTN interworking 5.1 ISDN bearer services suitable for ISDN to PSTN interworking (circuit) . 5.2 ISDN bearer services suitable for PSTN to ISDN interworking (circuit) . 5.3 ISDN bearer services suitable for IS
10、DN to PSTN interworking (packet) 5.4 ISDN bearer setvices suitable for PSTN to ISDN interworking (packet) Functional requirements for ISDN-PSTN interworking 7.1 Interworking between signalling systems . 7.2 Provision of interworking indications . 7.3 Generation of in-band tones and announcements . 7
11、.4 Handling of non-voice calls between ISDN and PSTN subscribers . 7.5 Control of speech processing and echo control devices . Handling of packet mode caUs between ISDNand PSTN subscribers Connection type suitable for ISDN-PSTN interworkhg . 7.6 A/m law encoding . Recommendation 1.530 (03/93) Page 1
12、 1 1 1 1 2 2 3 4 4 4 4 5 5 6 7 8 9 9 9 i ITU-T RECNN*I-530 (REV*I(L) 73 m 4862573 0583033 037 m Recommendation L530 NETWORK INTERWORKING BETWEEN AN ISDN AND A PUBLIC SWITCHED TELEPHONE NETWORK (PSTN) (Melbourne, 1988: ammended at Helsinki, 1993) 1 General In many countries, digitization of the exist
13、ing PSTN has been ongoing over a number of years through the implementation of digital switching and transmission facilities. Furthermore, common channel signalling systems (e.g. Signalling System No. 6, Signalling System No. 7) have been introduced or will soon be introduced in these networks. The
14、digitization of the user network access is one of the steps by which an IDN becomes an ISDN. However, it is foreseen that this wii be a long transition period for some networks. Thus, the purpose of this Recommendation is to identify the interworking functions and requirements to support interworkin
15、g between an ISDN and a PSTN. 2 Scope The purpose of this Recommendation is to describe the general arrangements for interworking between ISDN and PSTN. Both the provision of ISDN voice transmission and data transmission services are within the scope of this Recommendation. 3 Abbreviations For the p
16、urpose of this Recommendation, the following abbreviations are used: DTEData terminal equipment DTMF Dual-tone multiple frequency IDN Integrated digital network ISDN Integrated Services Digital Network ISUP ISDN user part LE Local exchange NT Network termination PABX Private Automatic Branch Exchang
17、e PSTN Public switched telephone network SS No. 7 Signalling System No. 7 TE Terminal equipment TA Terminal adaptor TUP Telephone user part. 4 Interworking configuration and network characteristics 4.1 Interworking configurations Recommendation 1.530 (03/93) 1 ITU-T RECNN*I.530 (REV* - at transit ex
18、change; - at international gateway offices. NOTE - The optimum location of each interworking function may be specific per interworking function and dependent on the usage of the service, network topology, etc. 5 ISDN bearer services suitable for ISDN-PSTN interworking This clause considers the subje
19、ct of ISDN services suitable for ISDN-PSTN interworking. The discussions dealing with the ISDN to/from PSTN direction are addressed in individual subclauses, as is the subject of circuit mode and packet mode. 2 Recommendation 1.530 (03/93) ITU-T RECMN*I.530 (REV*3) 93 m 4862593 0583033 901 m 5.1 ISD
20、N bearer services suitable for ISDN to PSTN interworking (circuit) I subscriber interface User network signalling User terminal equipment supported Interexchange signalhg Transmission facilities Information transfer mode Information transfer capability TABLE 1h.530 Key ISDN and PSTN characteristics
21、ISDN Digital Out-band (Rec. 1.441,1.45 1) Digital TE (ISDN NT, TE1 or TE2 + TA) SS No. 7 ISDN user part (ISW Digital Circuit/packet Speech, digital unrestricted, 3.1 kHz audio, multi-use, etc. PSTN Analogue Mainly in-band (e.g. DTMF) Analogue TE(e.g. dial pulse telephones, PABXs, modem- equipment DE
22、s) In-band (e.g. R1, R2 or; No. 4, No. 5) or out-band (e.g. SS No. 6, SS No. 7 Tup) Analogueldigital Circuit 3.1 kHz audio (voifvoice-band data) Interworking funcions a b, e C d, e a f f Interworking fnctbns a Analogue-todigital and digital-to-analogue conversion on transmission facilites. b Mapping
23、 between PSTN signals in the subscriber access and Recommendation 1.451 message for inra-exchange calls. c Support of communication between modemquipped PSTN DTES and ISDN terminals. d Conversion between the PSTN signalling system and Signalhg System No. 7 ISDN user part. e Mapping between signals i
24、n he ISDN subscriber (Recommendations 1.441,1.451) access and PSTN in-band interexchange signallling (e.g. Rl). f Further study required. Currently, there are four identified bearer services that could be used within de ISDN for ISDN to PSTN interworking. These are (refer to Recommendation 1.23 1) i
25、) U) circuit mode 64 kbits, 8 kHz structured bearer seMces, usable for speech information transfer (Note 1); circuit-mode 64 kbits, 8 kHz structured bearer services, usable for 3.1 kHz audio information transfer mote 2); iii) Circuit-mode 64 kbits unrestricted, 8 kHz structured bearer service (Note
26、3). iv) Circuit-mode 64 kbits, 8 kHz structured bearer service, usable for multi-use information transfer (Note 4). It is recognized that the communication characteristics obtained for each of these three bearer services on an ISDN to PSTN basis may not be de same as that obtained for ISDN to ISDN c
27、onfigurations. NOTE!3 1 This bearer service is used for the ISDN to PSTN-interworkuig for the purpose of speech information transfer. Recommendation 1.530 (03/93) 3 2 This bearer service is used for the ISDN to PSTN interworking for the purpose of 3.1 Wz audio information transfer. For PSTN to ISDN
28、interworking, this bearer service will be selected at the boundary of the PSTN to the ISDN for the purpose of speech information transfer and for 3.1 Wz audio information transfer. 3 This bearer service may be required for ISDN-PSTN interworking. Refer to Recommendation 1.231 for the 64 kbit/s inter
29、working service requirements. 4 When this bearer service is used for ISDN to PSTN interworking, special echo control procedures may be necessary (see 7.5). 5 ISDN-PSTN interworking means interworking both ways between ISDN and PSTN, while ISDN to PSTN refers to a call initiated in the ISDN and termi
30、nated in the PSTN, and PSTN to ISDN refers to a call initiated in the PSTN and terminated in ISDN. 5.2 ISDN bearer services suitable for PSTN to ISDN interworking (circuit) Currently, there is no internationally recognized method of service differentiation between voice and non-voice calls originati
31、ng in the PSTN. However, the “circuit-mode 64 kbit/s, 8 kT3z structured bearer service for 3.1 kHz audio information transfer” provides for the capability equivalent to PSTN. (see Recommendation 1.231.) Therefore, .PSTN calls may interwork to this service in ISDN. The call progress indicator within
32、ISUP will identify when interworking between ISDN and PSTN occurs. This indicator will enable the ISDN to select a connection that would support 3.1 kHz audio. A V-Series terminai connected to the ISDN via a terminal adaptor and using the 64 kbit/s unrestricted bearer service requires the use of an
33、IWF (including a modem) for calis from PSTN users. To effect the connection, a 64 kbit/s connection to the lWF would need to be used. 5.3 ISDN bearer services suitable for ISDN to PSTN interworking (packet) Currently, there are two identified bearer services that could be used witbin the ISDN, for I
34、SDN (packet mode Caus) to PSTN interworking: i) B-channek packet-mode, unrestricted digital information, service data unit integrity, X.25 link level, X.25 packet level bearer service; ii) D-channel: packet mode, unrestricted digital information, service data unit integrity, 1.441 link level, X.25 p
35、acket level bearer service. NOTE -Mechanisms are for interworking based on X.31 Case A and X.32 are covered in 8. 5.4 ISDN bearer services suitable for PSTN to ISDN interworking (packet) For further study. 6 Connection type suitable for ISDN-PSTN interworking This clause identifies the mapping of IS
36、DN bearer services and possible connection types for ISDN-PSTN interworking. Depending on the specifk ISDN bearer service being considered, more than one ISDN connection type may be applicable. However, in some cases the connection type may not be fully compatible with the requested bearer service,
37、thereby leading to downgrading of service. The ISDN bearer services and possible connection types that may be used are summarized in Table 2, under the four possible interworking cases. Refer to Recommendation 1.335 for more details regarding the mapping between ISDN bearer services and ISDN connect
38、ion types. 4 Recommendation 1.530 (03/93) ITU-T RECMN*I-530 (REV*1) 93 M 4862591 0583035 78L) M TABLE uI.530 64 kbits unrestricted Speech 3.1 kHz audio multi-use ISDN bearer services and connection types suitable for ISDN-PSTN interworking Y N R(1) Y R(1) N R(2) N Interworking PSTN to ISDN (circuit)
39、 ISDN to PSTN (packet) PSTN to ISDN (packet) I ISDN connection types I 64 kbits unrestricted Y N 3.1 IrHz audio R(1) N Virtual cail and permanent Y N virtual circuit Virtuai cail and permanent Y N virtual circuit unrestricted Speech ISDN bearer services categories ISDN to PSTN (circuit) Packet audio
40、 -qT N N N NIN Y Y: Yes Can be used (some interworking scenarios may require further study). N: NO Cannotbeused. R(1) R(2) NOTES 1 It is recognized that existing PSTN services must be supported by ISDN using currently defiied ISDN bearer services. 2 It is possible that the service obtained on each o
41、f the bearer services for ISDN to PSTN interworking may not be the same as that obtained for ISDN to ISDN configurations. 3 Refer to Recommendation 1.231 for the service requirements for 64 kbitls interworking. Various mechanisms for ISDN-PSTN interworking supporting V-Series terminals connected to
42、the ISDN using the 64 kbitls unrestricted bearer service are contained in Recommendation 1.515. Procedures require further study. 4 Other ISDN bearer services and connection types that may be applicable for ISDN-PSTN interworking are for further study. Can be used except when Alp-law conversion ando
43、r echo control may be required. Upon encounting interworking with the PSTN, appropriate echo control and Np-law conversion capabilities may need to be provided on the connection. 7 Functional requirements for ISDN-PSTN interworking 7.1 Interworking between signalling systems Interworking between sig
44、nalling systems, specifically for interexchange calls between the PSTN signalling system (which may be in-band) and Signalling System No. 7 (ISDN VP) on an ISDN, may be required. The interworking procedures are specified in Recommendation Q.699. For intra-exchange calk between the ISDN and PSTN subs
45、criber, interworking between 1.451 messages and signals in the PSTN subscriber access may also be required. Recommendation 1.530 (03/93) 5 7.2 Provision of interworking indications An interworking indication is required for the ISDN local exchange (LE) to know that ISDN-PSTN interworking has occurre
46、d. ISUP Q.761-Q.764 and 1.45UQ.931 protocols have the ability to identify this interworking situation to the ISDN LE and the ISDN terminal (caii progress indicator). The ISDN terminai would be informed in every case that ISDN-PSTN interworking has occurred. This information is required to satisfy as
47、 a minimum the requirement to: tell the terminai to connect the B-channel so that in-band tones and announcements can be received when ISDN-to-PSTN calls are originat tell data terminal equipment to anticipate in-band handshaking signals for ISDN-PSTN calls. - - - The following interworking scenario
48、s have been recognized: a) an ISDN-PSTN cail which uses a Signalling System No. 7 ISUP connection between the originating and terminating local exchanges; b) an ISDN-PSTN call which uses a non-Signalling System No. 7 ISUP connection (e.g. R1, Signalling System No. 7 TUP) between the originating and
49、terminating locai exchanges; c) an ISDN-PSTN call which involves a combination of Signalling System No. 7 ISUP and non-Signalling System No. 7 ISUP interexchange signalling connections between the originating and terminating local exchanges; d) an ISDN-PSTN call within the same local exchange (Le. no interexchange signalling). 7.2.1 Network indication of modification of communication characteristics The network will always provide an indication to the user of modification of communication characteristics. The modification of communication characteristics may be
