1、INTERNATIONAL TELECOMMUNICATION UNION ITU-T TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU SERIES V: DATA COMMUNICATION OVER THE TELEPHONE NETWORK Interfaces and voiceband modems V.61 (08/96) A simultaneous voice plus data modem, operating at a voice plus data signalling rate of 4800 bills, with op
2、tional automatic switching to data-only signalling rates of up to 14 400 bills, for use on the general switched telephone network and on leased point-to-point 2-wire telephone type circuits ITU-T Recommendation V.61 (Previously “CCITT Recommendation”) - ITU-T V-SERIES RECOMMENDATIONS DATA COMMUNICAT
3、ION OVER THE TELEPHONE NETWORK I 1 - General II Il 3 - Wideband modems 4 - Errorcontrol 5 - Transmission quality and maintenance 6 - Interworking with other networks For firrther details, please refer to ITU-T List of Recommendations. FOREWORD The ITU-T (Telecommunication Standardization Sector) is
4、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 view to standardizing telecommunications on a worldwide basis. The World Telecommunication Standardizatio
5、n Conference (WTSC), which meets every four years, establishes the topics for study by the IT-T Study Groups which, in their turn, produce Recommendations on these topics. The approval of Recommendations by the Members of the ITU-T is covered by the procedure laid down in WTSC Resolution No. 1 (Hels
6、inki, March 1-12, 1993). ITU-T Recommendation V.61 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. telecommunication administration and a recognized operating agency. In this Recommendation, the expressio
7、n “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 Recommendation forms an integral part of the Recommendation; an appendix to a Recommendation does not for
8、m 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 reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and mi
9、crofilm, without permission in writing fiom the ITU. Recommendation V.61 (08/96) 1 6 9 10 11 12 11 CONTENTS Introduction References Definitions Abbreviations . Line signals 5.1 Carrier frequency and modulation rate . 5.2 Transmitted spectrum . 5.3 Audio frames 5.5 Audio plus data coding . 5.7 Multip
10、lexingldemultiplexing of data and control segments Interfaces 6.1 DTE interface 6.2 Audio interface . Scrambler and descrambler 7.1 Scrambler/descrambler allocation . 5.4 Data-only coding 5.6 Control segment encoding Operating procedures . 8.1 Call establishment. capabilities exchange. and mode sele
11、ction procedures . 8.2 V.25 automatic answering sequence . 8.3 Symbol rate determination signal . 8.4 Channel holding signal . 8.5 Round trip delay estimating signals 8.6 Receiver conditioning signal 8.7 Rate signal Start-up procedure 9.1 Call mode modem . 9.2 Answer mode modem . Retrain procedure .
12、 10.1 Call mode modem . 10.2 Answer mode modem . 10.3 Operation of circuits 107 and 109 during retrain procedure . Rate renegotiating procedure . 1 1.1 Initiating procedure . 1 1.2 Responding procedure Testing facilities . Recommendation V.61 (08/96) Page 1 2 2 3 3 3 4 4 5 8 15 16 16 16 18 18 19 20
13、20 20 20 20 20 20 23 24 25 27 28 29 29 29 29 29 31 31 STD*ITU-T RECMN V*bL-ENGL 177b Li8b259L Ob28233 78T Recommendation V.61 A SIMULTANEOUS VOICE PLUS DATA MODEM, OPERATING AT A VOICE PLUS DATA SIGNALLING RATE OF 4800 bit/s, WITH OPTIONAL OF UP TO 14400 bit/s, FOR USE ON THE GENERAL SWITCHED AUTOMA
14、TIC SWITCHING TO DATA-ONLY SIGNALLING RATES TELEPHONE NETWORK AND ON LEASED POINT-TO-POINT 2-WIRE TELEPHONE TYPE CIRCUITS (Geneva, 1996) 1 Introduction This modem is intended for use on connections on General Switched Telephone Networks (GSTNs) and on point-to- point 2-wire leased telephone type cir
15、cuits. The principal Characteristics of the modem are as follows: Framed Quadrature Audiornata Modulation (Framed QADM) transmission with simultaneous transmission of duplex audio information and a synchronous audio plus data signalling rate of 4800 bids; optional automatic switching between the dat
16、a-only signalling rate and the audio plus data signalling rate to increase the data signalling rate to up to 14 400 bids during periods of audio silence; optional user controlled switching between the data-only signalling rate and the data plus audio signalling rate; independence of data plus audio
17、and data-only modes in each direction of transmission; call establishment procedures from both the audio interface and the data interface; call establishment procedures from the data interface before or after voice connection establishment; separation of audio and data channels during audio plus dat
18、a transmission via quadrature audiodata modulation; Quadrature Amplitude Modulation (QAM) transmission with the following synchronous data-only signalling rates implemented in the modem: - 14400 bids, - 12 O00 bids, - 9600 bids, - 7200bit/s, - 4800bids; duplex mode of operation on GSTN and point-to-
19、point 2-wire leased circuits; channel separation of both data and audio by echo cancellation techniques; quadrature amplitude modulation for each channel with synchronous line transmission at either 3000 symbolss or 2800 symbolss; exchange of symbol rate determination signals during start-up to esta
20、blish the symbol rate; m) exchange of rate sequences during start-up to establish the data signalling rates; n) a procedure to change the data signalling rates without retraining; o) a duplex auxiliary control channel with a conditional signalling rate up to 342 bits. NOTE - The transmit and receive
21、 data-only signalling rates in each modem shall be the same. The instantaneous transmit and receive data signalling rates may not be the same due to data-only transmission due to audio silence or user control in either direction. Recommendation V.61 (08/96) 1 STD-ITU-T RECMN VObL-ENGL L77b H 48b259L
22、 Ob28234 bLb H 2 References The following 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 other references are subject t
23、o revision; all users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent editions of the Recommendations and other references listed below. A list of currently valid IT-T Recommendations is regularly published. IS0 21 10:1989, Information techn
24、ology -Data communication - 25-pole DTE-DCE interface connector and contact number assignments. CCITT Recommendation V.2 (1980), Power levels for data transmission over telephone lines. ITU-T Recommendation V.8 bis (1996), Procedures for the identification and selection of common modes of operation
25、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. IT-T Recommendation V. 1 O (1993), Electrical characteristics for unbalanced double-current interchange ci
26、rcuits operating at data signalling rates nominally up to 100 kbith. IT-T Recommendation V. 1 1 (1 993), Electrical characteristics for balanced double-current interchange circuits operating at data signalling rates up to 10 Mbitls. IT-T Recommendation V.14 (1993), Transmission of start-stop charact
27、ers over synchronous bearer channels. IT-T Recommendation V.24 (1993), List of definitions for interchange circuits between Data Terminal Equipment (DTE) and Data Circuit- terminating Equipment (DCE). CCITT Recommendation V.25 (1 984), Automatic answering equipment and/or parallel automatic calling
28、equipment on the general switched telephone network including procedures for disabling of echo control devices for both manually and automatically established calls. IT-T Recommendation V.28 (1 993), Electrical characteristics for unbalanced double-current interchange circuits. CCITT Recommendation
29、V.32 bis (1991), A duplex modem operating at data signalling rates of up to 14 40Obish for use on the general switched telephone network and on leased point-to-point 2-wire telephone-type circuits. ITU-T Recommendation V.42 (1 993), Error correcting procedures for DCEs using asynchronous-to- synchro
30、nous conversion. CCITT Recommendation V.54 (1988), Loop test devices for modems. 3 Definitions For the purposes of the Recommendation, the following definitions apply: 3.1 answer mode modem: The modem which initiates the start-up procedure with the V.25 answer sequence. Note that, when this sequence
31、 follows completion of V.8 bis procedures, either modem may be designated as answer mode modem, regardless of which modem physically answers a call. 3.2 audio plus data operation: Operation in which audio information is being transmitted in addition to data bits, using QADM modulation. 3.3 auxiliary
32、 channel: A variable bit rate data channel (up to 342 bids) which, along with the user data and additional control data, is multiplexed into the bit stream transmitted by the modem. Data conveyed in the auxiliary channel is independent from the user data and is conveyed as part of the control data.
33、2 Recommendation V.61 (08/96) STD-ITU-T RECMN V-bL-ENGL L99b 48b257L Ob28235 552 3.4 call mode modem: The modem which is conditioned to detect the V.25 answer sequence as initiation of the start-up procedure. Note that, when this sequence follows completion of V.8 bis procedures, either modem may be
34、 designated as call mode modem-, regardless of which modem physically places a call. 3.5 operation. The control data is independent from the user data. control data: Data which is transmitted during the control segment of each frame and used to control modem 3.6 data-only operation: Operation in whi
35、ch only data bits are being transmitted, using QAM modulation. 3.7 frame: A period 70 symbols in length, comprising a user data segment and a control segment. 3.8 pre-emphasis: A linear equalization method in which the transmitted audio signal is filtered to compensate for the spectral characteristi
36、cs of the signal. he-emphasis may be fixed, in which case the filtering compensates for the expected long-term average of the spectrum, or adaptive, in which case the filtering compensates for the short-term spectral content of the audio signal. The pre-emphasis filtering applied to the audio signal
37、 in the transmitter is reversed by a complementary de-emphasis filter in the receiver. 3.9 during the start-up, retrain, and rate negotiation procedures. synchronizing signal elements: Signal elements A, B, C, and D in the signal space diagrams, which are used 3.10 data. user data: Data which is pro
38、vided by the user for transmission. The user data is independent from the control 3.11 variable data rate operation: Operation in which either QADM or QAM modulation may be used in any given frame. Determination of which type of modulation to use in each frame is based on audio silence detection in
39、the transmitter, and communicated to the remote receiver via control data. 4 Abbreviations For the purposes of this Recommendation, the following abbreviations are used: CCITT International Telegraph and Telephone Consultative Committee GPA Generating Polynomial - Answer modem GPC Generating Polynom
40、ial - Call modem GSTN General Switched Telephone Network IS0 international Organization for Standardization ITU-T QADM Quadrature Audiornata Modulation QAM Quadrature Amplitude Modulation International Telecommunications Union - Telecommunication Standardization Sector 5 Line signais 5.1 Carrier fre
41、quency and modulation rate Two modulation rates are provided. The first is 3000 symbols/s f 0.01%. The second is 2800 symbolds f 0.01%. When the modulation rate is 3000 symbolds, the carrier frequency is to be 1800 i 1 Hz. When the modulation rate is 2800 symbols/s, the carrier frequency is to be 16
42、80 1 Hz. In both cases, the receiver must be able to operate with a maximum received frequency offset of up to I 7 Hz. Recommendation V.61 (08196) 3 STDeITU-T RECMN V-bL-ENGL L77b 48b2571 0b2823b 477 5.2 Transmitted spectrum The transmitted power level must conform to Recommendation V.2. With contin
43、uous binary ones applied to the data input of the multiplexer and a long-term stationary audio signal applied to the audio input of the transmitter, the transmitted energy density at the band edges shall be attenuated 4.5 f 2.5 dB with respect to the maximum in-band energy density. When the modulati
44、on rate is 3000 symbols/s, the band edges shall be measured at 300 Hz and 3300 Hz. When the modulation rate is 2800 symbols/s, the band edges shall be measured at 280 Hz and 3080 Hz. 5.3 Audio frames 5.3.1 Frame structure A fiame structure is used to transmit both user data and control information i
45、n the data signal elements. Each frame is 70 symbols in length and comprises two main segments. The first segment contains user data. The second segment contains control information including audio parameters. Both segments may contain audio information. Symbols within a fiame shall be identified as
46、 symbol 1 through symbol 70. When the modulation rate is 3000 symbols/s, user data is transmitted in symbols 1 through 56 and control information is transmitted in symbols 57 through 70. When the modulation rate is 2800 symbols/s, user data is transmitted in symbols 1 through 60 and control informat
47、ion is transmitted in symbols 61 through 70. There are two types of frames. In audio plus data frames, audio information is combined with user or control data and transmitted in the QADM constellation described in 5.5.1.1. In data-only frames, user or control data is transmitted at the data-only rat
48、e negotiated during the most recent start-up, retrain, or rate negotiation procedure, using the QAM constellation defined for that rate in 5.4. 5.3.2 Optional variable data rate operation The modem optionally may employ variable data rate operation, increasing the transmitted data signalling rate fr
49、om the data plus audio signalling rate to the data-only signalling rate during frames in which silence is detected in the input audio signal. If variable data rate operation is employed, the modem shall determine during each frame whether there is sufficient information in the audio signal to transmit data plus audio in the succeeding frame. The modem shall then transmit information regarding the state of the succeeding frame during the control segment of the current frame (see 5.6). The modem shall condition itself to transmit signal elements using the selected (data-only or data p
