1、 ITU-T RECMN*d.939 93 = 4862591 0590653 549 INTERNATIONAL TELECOMMUNICATION UNION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU Q.939 (03/93) DIGITAL SUBSCRIBER SIGNALLING SYSTEM No. 1 NETWORK LAYER DIGITAL SUBSCRIBER SIGNALLING SERVICE INDICATOR CODINGS FQR ISDN TELECOMMUNICATIONS SERVICES
2、SYSTEM NO. 1 (DSS 1) - TYPICAL DSS 1 !TU-T Recommendation Q.939 (Previously “CCITT Recommendation”) ITU-T RECMN*Q.939 93 m 486259L 0590652 485 FOREWORD The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of the International Telecom- munication Union. The ITU-T is responsib
3、le for studying 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 ITU
4、-T Study Groups which, in their turn, produce Recommendations on these topics. ITU-T Recommendation Q.939 was prepared by the ITU-T Study Group XI (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 Telecommunic
5、ation Union (ITU), the CCITT ceased to exist as of 28 February 1993. In its place, the ITU 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 Similarly, in this reform process, the CCIR and the IFRB have been replaced by the Radiocommunication Sector.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 de
6、lay publication of this Recommendation, no change has been made in the text to references containing 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 n
7、ew ITU structure. 2 telecommunication administration and a recognized operating agency. In this Recommendation, the expression ?Administration? is used for conciseness to indicate both a O ITU 1994 All rights reserved. No part of this publication may be reproduced or utilized in any form or by any m
8、eans, electronic or mechanical, including photocopying and microfilm, without permission in writing from the ITU. 311 CONTENTS Introduction Scope and objective List of telecommunications services and specific user applications covered by codings General principles applicable to all services Impact o
9、f interworking situations 5.1 5.2 Incoming calls from non-ISDNs . BC and LLC application guidelines Request and recognition of a circuit-mode bearer service 6.1.1 Circuit-mode 64 kbits 8 kHz structured bearer service category usable for speech information transfer 6.1.2 Circuit-mode 64 kbitfs unrest
10、ricted 8 kHz structured bearer service category . 6.1.3 Circuit-mode 64 kbitfs 8 kHz structured bearer service category usable for 3.1 kHz audio information transfer . 6.1.4 Circuit-mode 64 kbitfs 8 kHz structured multi-use bearer service category . 6.1.5 Circuit-mode multi-rate bearer service for a
11、n ISDN interface 6.2.1 Virtual call bearer services support of X.25 terminal equipment allowing access to the ISDN virtual circuit service (case B of Recommendation X.31) . 6.2.2 Frame mode bearer services 6.3.1 Telephony teleservice (3.1 kHz bandwidth) . 6.3.2 6.3.3 Telefax G4 service (using circui
12、t-mode bearer capability) . 6.3.4 ISDN syntax-based Videotex service . 6.3.5 ISDN Videotelephony teleservice . 6.3.6 Facsimile group 2/3 service Specific user applications of the circuit-mode 64 kbit/s unrestricted 8 kHz structured bearer service . 7.1.1 Support of terminal adaptors V.l 10 and X.30
13、7.1.2 Support of terminal adaptors V.120 7.1.3 Support of X.25 terminal equipment allowing access to PSPDN via AU (case A of Recommendation X.3 1) Specific user applications of the circuit-mode 64 kbitfs 8 kHz structured bearer service category usable for 3.1 kHz audio information transfer . 7.2.1 V
14、oice-band data via modem . Codings for calls originating in a PSTN Request and recognition of a basic telecommunications service in an ISDN environment . 6.1 6.2 Packet-mode bearer services categories 6.3 Request and recognition of a teleservice Teletex service (using circuit-mode bearer capability)
15、 . Codings applicable to specific user applications 7.1 7.2 9 Abbreviations . Page 1 1 2 3 4 4 4 4 5 5 6 9 10 10 10 10 12 14 14 16 20 24 28 28 30 30 30 38 42 46 46 49 49 Recommendation 4.939 (03/93) 1 Recommendation Q.939 DIGITAL SUBSCRIBER SIGNALLING SYSTEM NO. 1 (DSS 1) - TYPICAL DSS 1 SERVICE IND
16、ICATOR CODINGS FOR ISDN TELECOMMUNICATIONS SERVICES (Helsinki, 1993) 1 Introduction This Recommendation specifies the coding of the information elements Bearer capability (BC), High layer compatibility (HLC) and Low layer compatibility (LLC) to be used by terminals supporting the ISDN telecommunicat
17、ions services identified in the 1.200-Series Recommendations and operating in the demand mode. It is based on Recommen- dation 4.931 including its relevant Annexes (B and I) and on Recommendation 4.933. For each service it is specified which field values the calling user is requested to send and whi
18、ch field values the called user could expect to receive in a pure ISDN environment (see clauses 6 and 7). Interworking situations with the public switched telephone network (PSTN) are also covered where appropriate (see clause 8). A later version of this Recom- mendation may include interworking sce
19、narios with the CSPDN and the PSPDN. Unless otherwise stated, the use of the term terminal (TE) in this Recommendation refers to customers terminal apparatus which may be a TE1 (Terminai Equipment Type l), a TA (Terminal Adaptor) together with a TE2 (Terminal Equipment Type 2) or an NT2 (Network Ter
20、mination Type 2) as defined in Recommendation 1.41 1. The terms “terminal” and “user” are used interchangeably. The exact bit patterns correlated with the named field values can be found in the following subclauses of Recommendation 4.93 1 : - in 4.5.5 as for the Bearer capability information elemen
21、t; - in 4.5.17 as for the High layer compatibility information element; and - in 4.5.19 as for the Low layer compatibility information element. For the frame mode bearer services the exact bit patterns can be found in 4.5.YQ.933 (BC) and 4.5.2VQ.933 (LLC). Generally, the information elements BC, HLC
22、 and LLC serve the following purposes: At the calling side, the network shall check that the bearer service requested by the calling user in the Bearer capability information element matches with the bearer service provided to that user by the network (Annex B/Q.931). At the called side, the called
23、user performs network-to-user compatibility checking based on the content of the BC-information element, and user-to-user compatibility checking based on the content of the BC-, HLC- and LLC-information elements (see Annex BlQ.93 1). 2 Scope and objective This Recommendation provides supplementary i
24、nformation on the usage of the compatibility information elements for individual telecommunications services. It considers the telecommunications services as they are specified for public ISDNs. It does not specify additional codings of the compatibility information elements (BC, HLC and LLC) which
25、might be required to support the request and provision of telecommunications services by private networks. The list of services currently covered in this Recommendation is given in clause 3. The list may require to be enhanced when new services will be defined andor when the functionality of network
26、s and terminai equipment has progressed. Recommendation 4.939 (03/93) 1 ITU-T RECMM*Q.939 93 48b259L 0.590655 194 Since some bearer services can be used to support various user applications, additional information on such applications is specified - in 7.1 for the circuit-mode 64 kbitis unrestricted
27、 8 IrHz structured bearer service, and - in 7.2 for the circuit-mode 64 kbitis 8 lcHz structured 3.1 kHz audio bearer service. The specific objective of this Recommendation is to provide guidance on the correct usage of Q.931 codepoints to the different CCITT Study Groups dealing with services, ISDN
28、 terminals and terminal adaptors. The Recommendation shall help to assure interoperability of terminals supporting the same telecommunications service and shall enable terminals to operate on different public ISDNs. The typical codings specified in clause 6 should be supported by all users and netwo
29、rks supporting the corresponding telecommunications service. Other variants of these codings may be supported in addition, however, these variants might not provide for worldwide interoperability. The codings given in clause 7 are not exhaustive. They illustrate typical user applications involving b
30、it rate adaption schemes where CCITT standardized interfaces are used. 3 The following telecommunications services are covered in clause 6: List of telecommunications services and specific user applications covered by codings 1 ) Circuit-mode bearer services categories - Circuit-mode 64 kbitis 8 kHz
31、 structured bearer service category usable for speech information transfer (digital telephony) Circuit-mode 64 kbit/s unrestricted 8 kHz structured bearer service category Circuit-mode 64 kbit/s 8 kHz structured bearer service category usable for 3.1 kHz audio information transfer - - 2) Packet-mode
32、 bearer service categories - Virtual call bearer service (case B of Recommendation X.3 1) i) Access through the B-channel i) Access through the D-channel - Frame mode bearer services i) ii) Circuit-switched access to remote frame handler (case A of Recommendation Q.933) Frame relay virtual call bear
33、er service (case A and case B of Recommendation 4.933) 3) Teleservices - - Teletex service - Telefax group 4 service - ISDN syntax-based Videotex service - Facsimile group 213 service Telephony teleservice (3.1 kHz bandwidth) The following specific user applications of some bearer services are cover
34、ed in clause 7: a) Specific user applications of the circuit-mode 64 kbitis unrestricted 8 kHz structured bearer service: i) Support of terminai adaptors V.110 and X.30 - Synchronous mode of operation - Asynchronous mode of operation Support of terminal adaptors V. 120 2) 2 Recommendation Q.939 (03/
35、93) ITU-T RECRN*Q=939 93 4862591 0590656 020 Equipment connected to the R interface Analogue telephone 3) Support of X.25 terminal equipment allowing access to PSPDN via AU (case A of Recommen- dation X.31) - - Rate adaption using X.3 1 HDLC flag stuffing Rate adaption corresponding to Recommendatio
36、ns V. 1 10 and X.30. b) Specific user applications of the circuit-mode 64 kbit/s 8 kHz structured 3.1 kHz audio bearer service: BC-/HLC-LLC-codepoints used, at the S/T interface BC HLC LLC Speech Telephony - i) Voice-band data via modem Facsimile group 2/3 equipment Voice-band data equipment via mod
37、em 4 General principles applicable to all services 3.1 Wz audio Facsimile group 2/3 - 3.1 kHz audio - Modem type For all services the following principles apply: i) The LLC information element is transferred transparently through an ISDN between the calling entity and the addressed entity. However,
38、dependent on the charging principles applied, some networks may perform checks on the length of the LLC information elements. The HLC information element is transferred transparently through an ISDN between the calling entity and the addressed entity. However, some networks may check its content, e.
39、g. to associate a supplementary service to a teleservice. 2) 3) Where bearer services are specified, the HLC information element will normally not be present unless they are used to support high layer applications. The codings shown consider the general case. In special terminal arrangements the use
40、r may need to rely on address information only. In these cases the supplementary services DDI or MSN shall be used. 4) 5) A TE2 together with a TA are assumed to provide the same functionality as a TEl. Therefore, a TA connected to a coincident S and T reference point will not generate and send a pr
41、ogress indicator value #I when setting up a connection. Consequently, a TA, e.g. adapting a two-wire analogue PSTN user-network interface to the ISDN user-network interface will generate the BC and, if appropriate, the HLC and LLC information elements in accordance with the type of equipment it serv
42、es at the R reference point, viz. Conventions applied for the presentation of the codings: 1) Octets 1 and 2 of the compatibility information elements, indicating the information element identifier and length respectively, are omitted from the considerations and therefore not shown in the examples.
43、2) A dash instead of a field value indicates: a) b) Field values in brackets ( ) may or may not be included at the calling side and therefore not be present at the called side. at the calling side: This field is not included in the information element; at the called side: This field is not present.
44、3) Recommendation Q.939 (0-3) 3 ITU-T RECMN*Q-939 93 4862593 0590657 Tb7 = 5 Impact of interworking situations 5.1 Incoming calls from non-ISDNs In the case of interworking with non-ISDNs, HLC and LLC information elements may be absent, and this interworking is shown with the presence of the Progres
45、s indicator information element. When this occurs, the terminal should accept the incoming call according to Annex B/Q.931, i.e. it should regard the compatibility as successful if it is compatible with the included information, which as a minimum will be the Bearer capability information element. 5
46、.2 BC and LLC application guidelines In many cases, the same low layer information (e.g. the user rate and the rate adaption technique applied) can be coded in either the BC or the LLC information element. However, the provision of information in the one or the other information element has conseque
47、nces with respect to the selection or the denial of a network provided interworking function. The following guidelines exist for the application of Bearer capability (BC) and Low layer compatibility (LLC) information elements according to Annex YQ.93 1 : - Type I - Information used only at the desti
48、nation end to allow decision regarding terminal compatibility. This information, if required, shall be coded into octets (3a and) 5 to 7 of the LLC information element. - Type If - Information to permit the network to select the bearer service. This information shall be coded into: - Octets 3 and 4
49、of the BC information element for circuit-mode traffic. - Type III - Information used by the addressed user to determine terminal compatibility and used by the network to facilitate interworking with other ISDNs or other dedicated networks. This information is encoded into octet 5 (including octets 5a-5d if appropriate) of the BC information element. Octets 3 and 4,6 and 7 of the BC information element for packet-mode traffic. - These types of information can be used as follows: - Case I - If the originating user wishes to transfer information end-to-end to ensure end
