1、INTERNATIONAL TELECOMMUNICATION UNIONITU-T V.8TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU(11/2000)SERIES V: DATA COMMUNICATION OVER THETELEPHONE NETWORKGeneralProcedures for starting sessions of datatransmission over the public switchedtelephone networkITU-T Recommendation V.8(Formerly CCITT Recom
2、mendation)ITU-T V-SERIES RECOMMENDATIONSDATA COMMUNICATION OVER THE TELEPHONE NETWORKGeneral V.1V.9Interfaces and voiceband modems V.10V.34Wideband modems V.35V.39Error control V.40V.49Transmission quality and maintenance V.50V.59Simultaneous transmission of data and other signals V.60V.99Interworki
3、ng with other networks V.100V.199Interface layer specifications for data communication V.200V.249Control procedures V.250V.299Modems on digital circuits V.300V.399For further details, please refer to the list of ITU-T Recommendations.ITU-T V.8 (11/2000) iITU-T Recommendation V.8Procedures for starti
4、ng sessions of data transmissionover the public switched telephone networkSummaryThis Recommendation defines signals to be exchanged between DCEs over the PSTN when asession of data transmission needs to be established, but before signals are exchanged which arespecific to a particular Recommendatio
5、n. It provides means to automatically determine the bestavailable operational mode between two DCEs connected via the PSTN, provides a timely indicationto Circuit Multiplication Equipments on the V-series modulation to be employed in a new session ofdata transmission, provides a means to enable a PS
6、TN call to be passed on automatically to anappropriate DCE, and provides signals for interacting with PSTN echo-control equipment.This Recommendation was revised in 1998 and 1999 to define additional call function types, defineprocedures for the exchange of non-standard facilities information and ad
7、d support for PCMmodulation modes.This Recommendation was revised in 2000 to provide support for V.92 features, correct errors in the1999 version, clarify the use of the prot0 octet, and add clause 10 to address compatibility withfuture revisions of this Recommendation.SourceITU-T Recommendation V.8
8、 was revised by ITU-T Study Group 16 (2001-2004) and approvedunder the WTSA Resolution 1 procedure on 17 November 2000.ii ITU-T V.8 (11/2000)FOREWORDThe International Telecommunication Union (ITU) is the United Nations specialized agency in the field oftelecommunications. The ITU Telecommunication S
9、tandardization Sector (ITU-T) is a permanent organ ofITU. ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendationson them with a view to standardizing telecommunications on a worldwide basis.The World Telecommunication Standardization Assembly (WTSA), w
10、hich meets every four years,establishes the topics for study by the ITU-T study groups which, in turn, produce Recommendations on thesetopics.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
11、-Ts purview, the necessary standards areprepared on a collaborative basis with ISO and IEC.NOTEIn this Recommendation, the expression “Administration“ is used for conciseness to indicate both atelecommunication administration and a recognized operating agency.INTELLECTUAL PROPERTY RIGHTSITU draws at
12、tention to the possibility that the practice or implementation of this Recommendation mayinvolve the use of a claimed Intellectual Property Right. ITU takes no position concerning the evidence,validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or other
13、soutside of the Recommendation development process.As of the date of approval of this Recommendation, ITU had received notice of intellectual property,protected by patents, which may be required to implement this Recommendation. However, implementors arecautioned that this may not represent the late
14、st information and are therefore strongly urged to consult theTSB patent database. ITU 2001All 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 from ITU
15、.ITU-T V.8 (11/2000) iiiCONTENTSPage1 Scope 12 References 13 Definitions 34 Overview of the Recommendation. 34.1 Call indication 34.2 Call menu/Joint menu exchange. 35 Coding format. 45.1 Category octets . 45.2 Extension octets 46 Code tables . 46.1 Call functions 56.2 Modulation modes 66.3 PCM Mode
16、m availability . 76.4 Protocols. 76.5 PSTN access . 86.6 Non-standard facilities 87 Descriptions of signals . 97.1 Function indicator signal CI . 97.2 Modified answer tone ANSam . 97.3 The Call Menu signal CM 97.4 The Joint Menu signal JM 108 Data session start-up procedure 118.1 Start-up procedure
17、in the call DCE 118.1.1 Call signal transmission 118.1.2 Call menu transmission . 128.2 Start-up procedure in the answer DCE. 128.2.1 ANS transmission 128.2.2 ANSam transmission. 128.2.3 JM transmission. 129 DTE-DCE interchange circuits. 1310 Compatibility 13ITU-T V.8 (11/2000) 1ITU-T Recommendation
18、 V.8Procedures for starting sessions of data transmissionover the public switched telephone network1ScopeThis Recommendation defines signals to be exchanged between DCEs over the PSTN when asession of data transmission needs to be established, but before signals are exchanged which arespecific to a
19、particular modem Recommendation.This Recommendation provides the following features: A means to determine automatically, prior to initiation of modem handshake, the bestavailable operational mode between two DCEs connected via the PSTN. Many DCEs canprovide operation according to a number of differe
20、nt V-series modem Recommendations. A timely indication to Circuit Multiplication Equipments (CMEs) on the V-seriesmodulation to be employed in any new session of data transmission. CMEs in the PSTN willincreasingly need to deploy demodulation/remodulation in order to maintain and improvedata signall
21、ing rates. A means to enable a PSTN call to be passed on automatically to an appropriate DCE, withthe minimum potential for adversely affecting existing DCEs. Signals for interacting with PSTN echo-control equipment, as provided for in ITU-T V.25.Implementors should note that this Recommendation is
22、designed to be extensible, and care must betaken to ensure compatibility with future revisions of this Recommendation. See clauses 6 and 10.2 ReferencesThe following ITU-T Recommendations and other references contain provisions which, throughreference in this text, constitute provisions of this Reco
23、mmendation. At the time of publication, theeditions indicated were valid. All Recommendations and other references are subject to revision; allusers of this Recommendation are therefore encouraged to investigate the possibility of applying themost recent edition of the Recommendations and other refe
24、rences listed below. A list of the currentlyvalid ITU-T Recommendations is regularly published. ITU-T H.324 (1998), Terminal for low bit-rate multimedia communication. ITU-T T.30 (1999), Procedures for document facsimile transmission in the general switchedtelephone network. ITU-T T.35 (2000), Proce
25、dure for the allocation of ITU-T defined codes for non-standardfacilities. ITU-T T.66 (1999), Facsimile code points for use with Recommendations V.8 and V.8 bis. ITU-T T.101 (1994), International interworking for videotex services. ITU-T V.2 (1988), Power levels for data transmission over telephone
26、lines. ITU-T V.17 (1991), A 2-wire modem for facsimile applications with rates up to 14 400 bit/s. ITU-T V.18 (1998), Operational and interworking requirements for DCEs operating in thetext telephone mode. ITU-T V.21 (1988), 300 bits per second duplex modem standardized for use in the generalswitche
27、d telephone network.2 ITU-T V.8 (11/2000) ITU-T V.22 (1988), 1200 bits per second duplex modem standardized for use in the generalswitched telephone network and on point-to-point 2-wire leased telephone-type circuits. ITU-T V.22 bis (1988), 2400 bits per second duplex modem using the frequency divis
28、iontechnique standardized for use on the general switched telephone network and on point-to-point 2-wire leased telephone-type circuits. ITU-T V.23 (1988), 600/1200-baud modem standardized for use in the general switchedtelephone network. ITU-T V.25 (1996), Automatic answering equipment and general
29、procedures for automaticcalling equipment on the general switched telephone network including procedures fordisabling of echo control devices for both manually and automatically established calls. ITU-T V.26 bis (1988), 2400/1200 bits per second modem standardized for use in thegeneral switched tele
30、phone network. ITU-T V.26 ter (1988), 2400 bits per second duplex modem using the echo cancellationtechnique standardized for use on the general switched telephone network and on point-to-point 2-wire leased telephone-type circuits. ITU-T V.27 ter (1984), 4800/2400 bits per second modem standardized
31、 for use in thegeneral switched telephone network. ITU-T V.291(1988), 9600 bits per second modem standardized for use on point-to-point 4-wire leased telephone-type circuits. ITU-T V.32 (1993), A family of 2-wire, duplex modems operating at data signalling rates ofup to 9600 bit/s for use on the gen
32、eral switched telephone network and on leased telephone-type circuits. ITU-T V.32 bis (1991), A duplex modem operating at data signalling rates of up to 14 400bit/s for use on the general switched telephone network and on leased point-to-point 2-wiretelephone-type circuits. ITU-T V.34 (1998), A mode
33、m operating at data signalling rates of up to 33 600 bit/s for useon the general switched telephone network and on leased point-to-point 2-wire telephone-type circuits. ITU-T V.42 (1996), Error-correcting procedures for DCEs using asynchronous-to-synchronous conversion. ITU-T V.90 (1998), A digital
34、modem and analogue modem pair for use on the PublicSwitched Telephone Network (PSTN) at data signalling rates of up to 56 000 bit/sdownstream and up to 33 600 bit/s upstream. ITU-T V.91 (1999), A digital modem operating at data signalling rates of up to 64 000 bit/sfor use in a 4-wire circuit switch
35、ed connection and on leased point-to-point 4-wire digitalcircuits. ITU-T V.92 (2000), Enhancements to Recommendation V.90._1With PSTN usage defined in a T-series Recommendation.ITU-T V.8 (11/2000) 33 DefinitionsThis Recommendation defines the following terms:3.1 call indicator signal (CI): A signal
36、transmitted from the call DCE to indicate the generalcommunication function. CI is transmitted with an ON/OFF cadence defined in 7.1. The ON periodsconsist of a repetitive sequence of bits at 300 bit/s, modulating V.21(L), the low-band channeldefined in ITU-T V.21.3.2 signal CNG: The call tone defin
37、ed in ITU-T T.30.3.3 signal CT: Any call tone allowed for in ITU-T V.25.3.4 call menu signal (CM): A signal (see 7.3) transmitted from the call DCE primarily toindicate modulation modes available in the call DCE. CM consists of a repetitive sequence of bits at300 bit/s, modulating V.21(L), the low-b
38、and channel defined in ITU-T V.21.3.5 CM terminator (CJ): A signal which acknowledges the detection of a JM signal andindicates the end of a CM signal. CJ consists of three consecutive octets of all ZEROs with start andstop bits, modulating V.21(L) at 300 bit/s.3.6 joint menu signal (JM): A signal (
39、see 7.4) transmitted from the answer DCE primarily toindicate modulation modes available jointly in the call and answer DCEs. JM consists of a repetitivesequence of bits at 300 bit/s, modulating V.21(H), the high-band channel defined in ITU-T V.21.3.7 ANS: Answer tone as defined in ITU-T V.25.3.8 AN
40、Sam: A sinewave signal at 2100 Hz, amplitude-modulated, as defined in 7.2.3.9 sigC: A signal transmitted by a call DCE specific to a V-series modem Recommendation.3.10 sigA: A signal transmitted by an answer DCE specific to a V-series modemRecommendation.3.11 PCM Modem: A class of modems as specifie
41、d in the ITU-T V.9x series ofRecommendations.4 Overview of the Recommendation4.1 Call indicationThe V.8 alternative to call tone (CT), signal CI, carries information to permit the selection of callfunctions, e.g. facsimile or data. The subsequent CM/JM exchange also provides for this function aswell
42、 as other functions outlined in this Recommendation.4.2 Call menu/Joint menu exchangeThe exchange of call menu and joint menu signals, CM and JM, enables DCEs to choose, for aforthcoming data session on the PSTN, the best V-series modulation mode from those available inboth the call and answer DCEs.
43、The CM/JM exchange also provides for protocol selection, PSTN access indication, and non-standard facilities.JM signals also provide information in a form suitable for PSTN Circuit Multiplication Equipment(CME) prior to the onset of modem training.4 ITU-T V.8 (11/2000)5 Coding formatSignals CI, CM a
44、nd JM use a common coding format. Each of these signals consists of a repeatedsequence of bits. A sequence consists of 10 ONEs followed by 10 bits for synchronization and theninformation-bearing octets, each octet being preceded by a start-bit (ZERO), and followed by a stop-bit (ONE).To avoid confus
45、ion of signal JM with T.30 signals which also use V.21(H) modulation, a codingconstraint is maintained which ensures that HDLC flags (01111110) cannot appear in the bit stream.Each octet lies within one “information category“. The coding format allows information categoriesto be expanded for special
46、 applications, while keeping signals brief for the majority of applications.The first information category in a sequence shall be the call function. No particular ordering isrequired for subsequent information categories. All information within one category shall be carriedin one octet or, when nece
47、ssary, in an ordered sequence of octets.5.1 Category octetsCategory octets are those which occur first in any new information category, and include a 4-bit codeidentifying the information category. The format is shown below with bits listed from left to right inorder of transmission:start-bit (0) b0
48、 b1 b2 b3 0 b5 b6 b7 stop-bit (1)Bits b0-b3 make up the category tag with b0 the least significant bit, b4 is set to ZERO to preventflag simulation, and bits b5-b7 are “option bits“ relevant to the information category.5.2 Extension octetsWhen 3 option bits are inadequate for a particular category,
49、any number of extension octets mayfollow directly after a category octet. The format for an extension octet is shown below:start-bit (0)b0b1b2010b6b7stop-bit (1)Bits b0-b2, b6 and b7 provide five additional option bits in the current category. Bit b4 is set to ONEin order to distinguish an extension octet from a category octet, and bits b3 and b5 are set to ZEROto prevent flag simulation.6 Code tablesInformation categories and extension octets beyond those specified in the tables below are allreserved for future definition by the ITU-T
