1、 International Telecommunication Union ITU-T V.140TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (01/2005) SERIES V: DATA COMMUNICATION OVER THE TELEPHONE NETWORK Interworking with other networks Procedures for establishing communication between two multiprotocol audiovisual terminals using digital
2、 channels at a multiple of 64 or 56 kbit/s ITU-T Recommendation V.140 ITU-T V-SERIES RECOMMENDATIONS DATA COMMUNICATION OVER THE TELEPHONE NETWORK General V.1V.9 Interfaces and voiceband modems V.10V.34 Wideband modems V.35V.39 Error control V.40V.49 Transmission quality and maintenance V.50V.59 Sim
3、ultaneous transmission of data and other signals V.60V.99 Interworking with other networks V.100V.199 Interface layer specifications for data communication V.200V.249 Control procedures V.250V.299 Modems on digital circuits V.300V.399 For further details, please refer to the list of ITU-T Recommenda
4、tions. ITU-T Rec. V.140 (01/2005) i ITU-T Recommendation V.140 Procedures for establishing communication between two multiprotocol audiovisual terminals using digital channels at a multiple of 64 or 56 kbit/s Summary This Recommendation describes a standardized method for automatic mode negotiation,
5、 detection of bit alignment, and confirmation of subchannel connectivity for multimedia terminals on digital networks. This new protocol provides backward compatibility with existing standards and creates an extensible mechanism to negotiate future protocols. The two primary benefits from implementi
6、ng this Recommendation are: 1) improved reliability in completing calls and successfully establishing multimedia communications, since peculiar network characteristics (such as “restricted“ networks) that interfere with call establishment and protocol negotiations are automatically handled by V.140
7、procedures; and 2) for terminals that support multiple communication modes, an automatic means of selecting modes. Principal features of this Recommendation include the ability to find bit alignment, detect remote network type, and perform in-band testing of channel characteristics; a flexible and e
8、xtensible capability exchange and mode selection facility is also built-in. V.140 procedures apply to every channel of a multi-channel call and begin following establishment of the end-to-end digital connection, and before any multimedia or other communication protocols are initiated. The procedures
9、 are divided into three phases: Phase 1 Send/search for V.140 signature (note that V.8/V.8 bis, voice, and H.221 FAS, or any subset of these may be simultaneously transmitted). If such signature is detected, proceed to: Phase 2 Characterize the digital connection (64 vs 56 kbit/s, detect octet/septe
10、t alignment), and diagnose any odd characteristics of the network, (i.e., it could be restricted, that is, it transfers only 7 of 8 bits to the far-end). Once this is complete, Phase 3 Exchange mode capabilities (similar to V.8 bis) and select desired operation mode. Modes can include voice communic
11、ations, multimedia communications, and channel aggregation protocols, but capabilities are kept simple, given that the purpose of this Recommendation is only to select a particular protocol, not to determine all of the parameters related to that protocol (which can typically be determined using the
12、protocol itself). The Phase 1 procedures have been designed to allow simultaneously signalling of other protocols, such as H.320, to minimize the amount of time lost in beginning communications if a terminal that implements V.140 finds itself communicating with a terminal that does not. Following Ph
13、ase 3, a terminal can immediately begin procedures associated with the selected operation mode. This revised version incorporates corrections to errors noted between the original approval in February 1998 until November 2004. In particular, the bit order illustrated in Figure 11 has been corrected t
14、o match the body text, and in Annex A incomplete ASN.1 syntax has been restored and references to multilink operation according to Annex F/H.324 have been added. Source ITU-T Recommendation V.140 was approved on 8 January 2005 by ITU-T Study Group 16 (2005-2008) under the ITU-T Recommendation A.8 pr
15、ocedure. ii ITU-T Rec. V.140 (01/2005) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunications. The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technic
16、al, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardization Assembly (WTSA), which meets every four years, establishes the topics for study by the ITU-T study groups which, in
17、 turn, produce Recommendations on these topics. The approval of ITU-T Recommendations is covered by the procedure laid down in WTSA Resolution 1. In some areas of information technology which fall within ITU-Ts purview, the necessary standards are prepared on a collaborative basis with ISO and IEC.
18、NOTE In this Recommendation, the expression “Administration“ is used for conciseness to indicate both a telecommunication administration and a recognized operating agency. Compliance with this Recommendation is voluntary. However, the Recommendation may contain certain mandatory provisions (to ensur
19、e e.g. interoperability or applicability) and compliance with the Recommendation is achieved when all of these mandatory provisions are met. The words “shall“ or some other obligatory language such as “must“ and the negative equivalents are used to express requirements. The use of such words does no
20、t suggest that compliance with the Recommendation is required of any party. INTELLECTUAL PROPERTY RIGHTS ITU draws attention to the possibility that the practice or implementation of this Recommendation may involve the use of a claimed Intellectual Property Right. ITU takes no position concerning th
21、e evidence, validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or others outside of the Recommendation development process. As of the date of approval of this Recommendation, ITU had not received notice of intellectual property, protected by patents, w
22、hich may be required to implement this Recommendation. However, implementors are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database. ITU 2005 All rights reserved. No part of this publication may be reproduced, by any means
23、 whatsoever, without the prior written permission of ITU. ITU-T Rec. V.140 (01/2005) iii CONTENTS Page 1 Introduction and scope 1 2 References. 1 3 Definitions 2 4 Abbreviations 3 5 Conventions 3 6 Overview 4 6.1 Phase 1 V.140 signature transmission and acquisition 4 6.2 Phase 2 Channel characteriza
24、tion 4 6.3 Phase 3 Capability exchange and mode selection . 5 6.4 Using V.140 to switch among multimedia operation modes . 5 6.5 Interoperability with terminals that do not support V.140 . 5 6.6 Interworking with PSDSNs 6 7 Network types. 6 8 Signals 7 8.1 Data stream model 7 8.2 Phase 1 V.140 signa
25、ture block and compatible protocol field 8 8.3 Phase 2 Alignment probing . 12 8.4 Phase 3 signals 15 8.5 Phase 3 HDLC framing 17 9 Procedures 19 9.1 Channel establishment 19 9.2 Phase 1 Signature transmission and acquisition 20 9.3 Phase 2 Determination of network characteristics and bit alignment .
26、 22 9.4 Phase 3 Role arbitration, capability exchange, and mode selection 26 9.5 Entering selected mode. 28 10 Resuming V.140 from a selected mode 28 Annex A ASN.1 definition of Phase 3 PDU values 29 ITU-T Rec. V.140 (01/2005) 1 ITU-T Recommendation V.140 Procedures for establishing communication be
27、tween two multiprotocol audiovisual terminals using digital channels at a multiple of 64 or 56 kbit/s 1 Introduction and scope This Recommendation defines automatic mode negotiation and selection for multiprotocol audiovisual terminals connected to digital networks such as the ISDN. The procedures i
28、n this Recommendation are intended to avoid interference with those of pre-existing Recommendations. The procedures in this Recommendation automatically determine network connectivity and bit alignment between terminals. Also, they enable prompt and accurate negotiation of a common mode of operation
29、 when one or both terminals support multiple protocols for audiovisual communication. For example, a terminal might support H.320, H.324 over voiceband modem, and H.323 over ISDN; in this case, the procedures in this Recommendation would be used to negotiate a common protocol, e.g., H.323. Once a mo
30、de is selected, further negotiations as recommended for that mode may use information derived from V.140 negotiations, if applicable. V.140 procedures can also be used to provide an optional initial voice telephony mode before proceeding to multimedia telephony, and to switch from one multimedia tel
31、ephony mode to another, or back into voice telephony mode. The means by which digital channels are established between terminals are outside the scope of this Recommendation (see ITU-T Rec. H.200/AV.420). Information regarding the nature of the endpoint terminals available from D-channel signalling
32、may be useful in further accelerating V.140 negotiations; use of such information is for further study. The procedures of this Recommendation concern only the flow of signals along the fixed digital paths used for the transport of audiovisual content during the call, at integer multiples of 64 kbit/
33、s (or 56 kbit/s in certain networks). 2 References The following ITU-T Recommendations and other references contain provisions which, through reference in this text, constitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and o
34、ther references are subject to revision; users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendations and other references listed below. A list of the currently valid ITU-T Recommendations is regularly published. The
35、reference to a document within this Recommendation does not give it, as a stand-alone document, the status of a Recommendation. ITU-T Recommendation G.711 (1988), Pulse code modulation (PCM) of voice frequencies. ITU-T Recommendation H.221 (2004), Frame structure for a 64 to 1920 kbit/s channel in a
36、udiovisual teleservices. ITU-T Recommendation H.242 (2004), System for establishing communication between audiovisual terminals using digital channels up to 2 Mbit/s. ITU-T Recommendation H.320 (2004), Narrow-band visual telephone systems and terminal equipment. ITU-T Recommendation H.324 (2002), Te
37、rminal for low bit-rate multimedia communication. 2 ITU-T Rec. V.140 (01/2005) ITU-T Recommendation V.8 (2000), Procedures for starting sessions of data transmission over the public switched telephone network. ITU-T Recommendation V.8 bis (2000), Procedures for the identification and selection of co
38、mmon modes of operation between data circuit-terminating equipments (DCEs) and between data terminal equipments (DTEs) over the general switched telephone network and on leased point-to-point telephone-type circuits. ITU-T Recommendation X.680 (2002) | ISO/IEC 8824-1:2002, Information technology Abs
39、tract Syntax Notation One (ASN.1): Specification of basic notation. ITU-T Recommendation X.691 (2002) | ISO/IEC 8825-2:2002, Information technology ASN.1 encoding rules: Specification of Packed Encoding Rules (PER). ISO/IEC 3309:1993, Information technology Telecommunications and information exchang
40、e between systems High-level data link control (HDLC) procedures Frame structure. ISO/IEC 13871:1995, Information technology Telecommunications and information exchange between systems Private telecommunications networks Digital channel aggregation. 3 Definitions This Recommendation defines the foll
41、owing terms: 3.1 56C interface: A 56 kbit/s network interface which transfers all bits to the far-end. 3.2 64C interface: A 64 kbit/s network interface which transfers all bits to the network. 3.3 64R interface: A 64 kbit/s network interface which transfers 7 of each 8 bits to the far-end, for a net
42、 throughput of 56 kbit/s. 3.4 acquire: To detect a signal a sufficient number of times to meet the specified acquisition criteria. 3.5 aligned channel: A channel for which network byte timing is available to the terminal. Ordinarily, an aligned channel is needed to transport unframed G.711 voice tel
43、ephony. Network interfaces which do not pass network byte timing, such as V.35 interfaces, cause the terminal to operate as if connected to a non-aligned channel. 3.6 byte: A septet for networks with either a 56C or 64R interface. Also, an octet for networks with a 64C interface. 3.7 detect: To rece
44、ive a given signal a single time. 3.8 octet: A group of 8 bits. For Phases 1 and 2, if on an aligned channel, each new octet begins at the time specified by network timing. 3.9 protocol data unit (PDU): An HDLC frame carrying a Phase 3 message. 3.10 public switched data service network (PSDSN): A 56
45、 kbit/s public switched data service network, for example the “Switched-56“ network in the United States as specified by TIA/EIA-596. Such a network may be sensitive to emulation of escape codes by data entering the network via a 64C interface. 3.11 restricted channel: A channel carried on a network
46、 whose B-channels are effectively restricted to 56 kbit/s, or whose channels at H0or higher are restricted by ones-density considerations. This can be because the terminal is on a 56C interface or a 64R interface or because of the nature of the network. ITU-T Rec. V.140 (01/2005) 3 3.12 round-trip:
47、Given two terminals, A and B, connected via an ISDN, a round-trip is the transmission via the ISDN of a message from terminal A to terminal B and then from terminal B to terminal A; it is generally assumed that the time required to process and otherwise manipulate the message is negligible compared
48、to the time required for transmission and propagation. 3.13 reflected signature pattern (RSP): A bit pattern transmitted during Phase 2 that is computed from the bit pattern in a particular subchannel as received from a remote terminal. RSP is transmitted in the same subchannel in which it is receiv
49、ed to signal the alignment of subchannels received at the terminal. 3.14 septet: A group of 7 bits. If on an aligned channel, each new septet begins at the time specified by network timing. 3.15 signature pattern (SP): A bit pattern transmitted within an individual subchannel to signal the presence of V.140 support and to permit determination of subchannel alignment and continuity. 3.16 subchannel: The bits in a particular bit position of a sequence of bytes. Bits within a byte are numbered 1, 2, 3, 4, in order
