1、INTERNATIONAL TELECOMMUNICATION UNION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU SERIES V: DATA COMMUN TELEPHONE NETWORK CAT Interfaces and voiceband modems v.75 (08196) ON OVER THE DSVD terminal control procedures ITU-T Recommendation V.75 (Previously “CCITT Recommendation“) STDDITU-T RE
2、CMN V-75-ENGL 177b E 48b257L Ob24346 b5T FOREWORD The ITU-T (Telecommunication Standardization Sector) is a permanent organ of the International Telecommunication Union (ITU). The ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommen- dations on them with a
3、 view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Conference (WTSC), which meets every four years, establishes the topics for study by the ITU-T Study Groups which, in their turn, produce Recommendations on these topics. The approval of Recom
4、mendations by the Members of the ITU-T is covered by the procedure laid down in WTSC ResolutionNo. 1 (Helsinki, March 1-12, 1993). ITU-T Recommendation V.75 was prepared by ITU-T Study Group 14 (1993-1996) and was approved under the WTSC Resolution No. 1 procedure on the 16th of August 1996. NOTE 1.
5、 telecommunication administration and a recognized operating agency. In this Recommendation, the expression “Administration” is used for conciseness to indicate both a 2. follows: The status of annexes and appendices attached to the Series V Recommendations should be interpreted as - - an annex to a
6、 Recommendation forms an integral part of the Recommendation; an appendix to a Recommendation does not form part of the Recommendation and only provides some complementary explanation or information specific to that Recommendation. O ITU 1997 All rights reserved. No part of this publication may be r
7、eproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the ITU. Recommendation V.75 (08/96) i 1 2 3 4 5 6 7 8 9 10 11 CONTENTS Scope Normative references . Definitions Symbols and abbreviations . Overview
8、5.1 Model of the DSVD control entity . 5.2 Services provided to the DSVD SCF 5.3 Services provided to the data protocol and audio processing functions . 5.4 Services provided by the MF DSVD procedures 6.1 Channel establishment 6.2 Channel establishment refusal 6.3 Channel release . 6.4 Capability ex
9、change 6.5 Data transfer . Master-slave determination Encoding of multiplexer function user-data fields . 8.1 User-data encoding in L-ESTABLISH primitive . 8.2 User-data encoding in L-RELEASE primitive . 8.3 User-data encoding in L-SETPARM primitive Encoding of audio header . Break handling . 10.1 T
10、ransfer of break signal 10.2 Receipt ofbre ak Segmentationreassembly . 11.1 Header octet coding Annex A . H.245 version 1 syntax additions for V.75 control functions Appendix I . Data forwarding conditions 11 Recommendation V.75 (08/96) Page 1 1 2 2 2 3 3 3 3 5 5 6 6 7 8 9 9 9 9 11 12 13 13 13 15 15
11、 16 20 INTRODUCTION This Recommendation describes the DSVD control procedures for exchanging terminal capabilities, transmission of control information and establishingheleasing audio and data channels between two Digital Simultaneous Voice and Data (DSVD) terminals that comply with Recommendation V
12、.706. This Recommendation should be associated with Recommendation H.245 i. Recommendation H.245 defines a common encoding and syntax for multimedia terminals. The procedures described within this Recommendation use a subset of H.245 control messages carried within conventional HDLC fiames specified
13、 by Recommendation V.76 to provide DSVD terminal control. . Recommendation V.75 (08196) 111 STD*ITU-T RECMN V.75-ENGL L77b M i8b259L Ob24350 080 M STD-ITU-T RECMN V.75-ENGL 177b m 98b257L 0624351 TI7 W Recommendation V.75 DSVD TERMINAL CONTROL PROCEDURES (Geneva, 1996) 1 Scope DSVD terminals provide
14、 communication of real-time audio and data information using ITU-T V-Series modems over the GSTN. This Recommendation specifies control procedures to establish a point-to-point DSVD connection. The procedures described within this Recommendation can be incorporated, for example, by a Multipoint Cont
15、rol Unit (MCU), to support a multipoint DSVD terminal conference. The procedures described within this Recommendation specifj the manner in which DSVD terminals with different connection capability sets exchange media and data link capability information so that a common mode of communication can be
16、 established. Procedures are defined for exchange of capabilities at the beginning of a DSVD connection and while a DSVD connection is in progress. Establishing the physical connection (call control) is outside the scope of this Recommendation and is described elsewhere. DSVD terminals are made awar
17、e of a remote terminals support of DSVD capabilities prior to a DSVD session using the procedures described in Recommendation V.8 bis 2. DSVD specifies the use of two types of media streams - data and audio. Data and audio streams are multiplexed onto one physical connection using LAP-based multiple
18、xing as defined in Recommendation V.76 7. Optional procedures are described within this Recommendation to support the exchange of connection capabilities that are independent of a media stream. 2 Normative references The following Recommendations contain provisions which, through reference in this t
19、ext, constitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations are subject to revision; all users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommend
20、ations listed below. A list of the currently valid ITU-T Recommendations is regularly published. ITU-T Recommendation H.245 (1 996), Control protocol for multimedia communication. ITU-T Recommendation V.8 bis (1996), Procedures for the identfzcation and selection of common modes of operation between
21、 Data Circuit-Terminating Equipments CES) and between Data Terminal Equipments (DTEs) over the general switched telephone network and leasedpoint-to-point telephone-type circuits. CCITT Recommendation V.25 (1984), Automatic answering equipment and/or parallel automatic calling equipment on the gener
22、al switched telephone network including procedures for disabling of echo control devices for both manually and automatically established calls. ITU-T Recommendation V.34 (1994), A modem operating at data signalling rates of up to 28 800 bits for use on the general switched telephone network and on l
23、easedpoint-to-point 2-wire telephone-type circuits. ITU-T Recommendation V.42 (1 993), Error-correcting procedures for DCEs using asynchronous-to- synchronous conversion. ITU-T Recommendation V.70 (1996), Procedures for the simultaneous transmission of data and digitally encoded voice signals over t
24、he GS“, or over, 2-wire leased point-to-point telephone fype circuit. ITU-T Recommendation V.76 (1996), Generic multiplexer using V.42 LAPM-basedprocedures. Recommendation V.75 (08/96) 1 STD-ITU-T RECMN V-75-ENGL 177b II 4Bb257L Ob24352 953 3 Definitions For the purposes of this Recommendation, the
25、following definitions apply. 3.1 refer. 3.2 which they refer. in-band: In-band messages are those that are transported within the channel or logical channel to which they out-of-band: Out-of-band messages are those that are transported outside of the channel or logical channel to 4 Symbols and abbre
26、viations For the purposes of this Recommendation, the following abbreviations are used. CE CESAP DCE DLCI DSVD DTE DTMF ERM GSTN I frame LAPM MF MFSAP PDU SAP SCF UNERM XID f-ame Control Entity Control Entity Service Access Point Data Circuit-Terminating Equipment Data Link Connection Identifier Dig
27、ital Simultaneous Voice and Data Data Terminal Equipment Dual Tone Multiple Frequency Error Recovery Mode General Switched Telephone Network LAPM frame for error corrected 1 PORTNUMBER media parameters - ERRORRECOVERY FORWARD PARAMETERS REVERSE PARAMETERS - response - confirm (all of above CE-SETPAR
28、M parameters) - chamei parameters - media association parameter CHANNELNUMBER PORTNUMBER CE-RELEASE CE-SETPARM - request - indication - response - confirm - ack - nack parameters REASON CE-D ATA - request - indication (all of above CE-SETPARM parameters) - session termination - simultaneous capabili
29、ties MODES SIMULCAPS PNalTI. No. la.1 la.2 la.3 1 a.4 la.5 1 a.6 1 a.7 1 a.8 la.9 la.10 la.11 la.12 la.13 la.14 la.15 la.16 la.17 la.18 la.19 1 a.20 la21 la.22 1 a.23 4 Recommendation V.75 (08/96) STD-ITU-T RECMN V-75-ENGL L77b W 48b259L Ob24355 bb2 Service TABLE lbN.75 Services provided to the data
30、 protocol and audio processing functions Primitive Types Release a channel Exchange terminal capabilities - request I - indication ransfer data 1 CE-DATA L-RELEASE L-SETPARM Parameters - channel parameters CHANNELNUMBER - media-data DATA AUDIO HEADER INFO - parameters DTMF SILENCE BREAK BREAKLENGTH
31、BREAKOPTION TABLE 2N.75 Services provided by the MF Param. No. 1b.l lb.2 lb.3 lb.4 lb.5 lb.6 lb.7 lb.8 Service Primitive Parameters indication response confirm request i I ;data indication request user-data indication control parameter response COMMAND - confirm RESPONSE I L-DATA Transfer informatio
32、n (emor corrected) - user-data I - request I - indication - request 1 -user-data - indication Transfer information (non-emor P-UNIXATA corrected) 6 DSVD procedures Procedures for DSVD use H.245 messages for teminal capability exchange, channel establishment and release and out- of-band control. Synt
33、ax in Recommendation H.245 supports the mandatory and optional modes of operation for DSVD terminals. Type in bold indicates message types and fields defmed in Recommendation H.245. 6.1 Channel establishment 6.1.1 Purpose Establish a logical channel within the multiplex to communicate information an
34、d indicate the mode to communicate on the channel. This function is mandatory. NOTE -Data Link Connection Identifiers LCIs) are assigned by Recommendation V.76 and are numerically independent of the DSVD SCF channel numbers. However, the DLCI and the DSVD SCF channel numbers have a one-to-one relati
35、onship through the DSVD CE. Recommendation V.75 (08/96) 5 6.1.2 MF service primitives The procedure uses the L-ESTABLISH multiplexer service primitive. 6.13 DSVD SCF service primitives The procedure uses the CE-ESTABLISH DSVD control entity primitive. 6.1.4 Procedure On receipt of a CE-ESTABLISH req
36、uest, the DSVD control entity shall transmit a H.245 OpenLogicalChannel message as the user-data of an L-ESTABLISH request. On receipt of an L-ESTABLISH indication with the H.245 OpenLogicalChannel message as the user-data, the responding DSVD control entity shall issue a CE-ESTABLISH indication. On
37、 receipt of a CE-ESTABLISH response, the responding DSVD control entity shall transmit a H.245 OpenLogicalChannelAck as the user-data of an L-ESTABLISH response. If CE-RELEASE response is received by the responding DSVD control entity indicating that the channel cannot be accepted by the DSVD contro
38、l entity user then 6.2 applies. On receipt of an L-ESTABLISH confm with an OpenLogicalChannelAck as the user-data, the DSVD control entity shall consider the channel established and issue a CE-ESTABLISH confirm. NOTE - An L-ESTABLISH request primitive shall contain the DataType as either Audiocapabi
39、lity or DataApplicationCapability when opening a channel for a media stream. Within either of these capability substructures shall be contained the H.245 data or audio mode to be transmitted on the channel once established. AN L-ESTABLISH request primitive with the DataApplicationCapability set to D
40、SVDControl indicates the request to establish an out-of-band control channel. 6.2 Channel establishment refusal 6.2.1 Purpose Describes the DSVD control entity functions action when refusing establishment of a channel. This could be due to the inability to accept another channel or an invalid mode s
41、election. This function is mandatory. 6.2.2 MF service primitives The procedure uses the L-RELEASE multiplexer service primitive. 6.2.3 DSVD SCF service primitives The procedure uses the CE-RELEASE DSVD control entity primitive. 6.2.4 Procedure On receipt of a CE-RELEASE request the DSVD control ent
42、ity shall transmit a H.245 OpenLogicalChannelReject message as the user-data of an L-RELEASE request. On receipt of an L-RELEASE indication containing the OpenLogicalChannelReject message as the user-data, the DSVD control entity shall issue a CE-RELEASE indication with the H.245 cause parameters as
43、 the CE-RELEASE reason parameter. NOTE -Reception of a CE-RELEASE indication from a DSVD control entity is not an indication of an error condition, but rather an indication of unsupported channel parameters, and that the channel may subsequently be established using other channel parameter values. 6
44、.3 Channel release 6.3.1 Purpose To close an existing channel. This function is mandatory. 6 Recommendation V.75 (08/96) - STDOITU-T RECMN V-75-ENGL L77b 48b2571 Ob24357 435 W 6.3.2 MF service primitives The procedure uses the L-RELEASE multiplexer service primitive. 6.3.3 DSVD SCF service primitive
45、s The procedure uses the CE-RELEASE DSVD control function primitive. 6.3.4 Procedure On receipt of a CE-RELEASE request, the initiating DSVD control entity shall transmit a H.245 CloseLogicalChannel message as the user-data field of an L-RELEASE request. The local DSVD CE shall consider the channel
46、closed. On receipt of an L-RELEASE indication with a H.245 CloseLogicalChannel message as the user-data field, the responding DSVD control entity shall issue a CE-RELEASE indication and issue an L-RELEASE request primitive with a H.245 CloseLogicalChanneAck message as the user-data field. The remote
47、 DSVD CE shall consider the channel closed. On receipt of an L-RELEASE indication the DSVD control entity shall consider the channel closed. 6.4 Capability exchange 6.4.1 Purpose These procedures invoked by both terminals in a DSVD session communicate the complete set of transmit and receive capabil
48、ities of each terminal. Syntax defined in Recommendation H.245 allows each terminal to convey the ability to handle simultaneous audio and data channels. Those capabilities that are not understood by a DSVD terminal shall be ignored and no fault implied. Non-standard capabilities may be signalled us
49、ing the H.245 NonStandardParameter structure defined in Recommen- dation H.245. 6.4.2 MF service primitives The procedure uses the L-SETPARM multiplexer service primitive for in-band capability negotiation and the L-DATA multiplexer service primitive for out-of-band capability negotiation. 6.4.3 DSVD SCF service primitives The procedure uses the CE-SETPARM DSVD control entity primitive. 6.4.4 In-band and out-of-band procedures The DSVD control entity may exchange terminal capabilities in-band or out-of-band. In-band exchange procedures use the same DLC for capabilit
