1、 INTERNATIONAL TELECOMMUNICATION UNION ITU-T V.250TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (07/2003) SERIES V: DATA COMMUNICATION OVER THE TELEPHONE NETWORK Control procedures Serial asynchronous automatic dialling and control ITU-T Recommendation V.250 ITU-T V-SERIES RECOMMENDATIONS DATA COM
2、MUNICATION 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 Simultaneous transmission of data and other signals V.60V.99 Interworking with other networks V.100V.199 Interfa
3、ce 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 Recommendations. ITU-T Rec. V.250 (07/2003) i ITU-T Recommendation V.250 Serial asynchronous automatic dialling and con
4、trol Summary This version of ITU-T Rec. V.250 integrates Amendment 1 (07/2001), Amendment 2 (03/2002) and Amendment 3 (07/2003) with the 05/1999 version of the Recommendation. This Recommendation defines commands and responses for use by a DTE to control a V-series DCE using serial data interchange
5、over an asynchronous interface. It contains four elements: codifies existing practice in common GSTN-DCE that use the ATtention (AT) command set; defines a format for orderly extension of the AT command set; provides a set for standardized extensions for common functions to identify the DCE, to cont
6、rol the DTE-DCE interface, and to control DCE-DCE protocols (signal conversion, error control and data compression); provides a mapping for these commands into V.25 bis frame format for use with DCEs employing synchronous serial interfaces. Source ITU-T Recommendation V.250 was approved on 14 July 2
7、003 by ITU-T Study Group 16 (2001-2004) under the ITU-T Recommendation A.8 procedure. Keywords AT Commands, data modems, data transmission, DCE control. ii ITU-T Rec. V.250 (07/2003) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of tel
8、ecommunications. The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. The World Telec
9、ommunication Standardization Assembly (WTSA), which meets every four years, establishes the topics for study by the ITU-T study groups which, in 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 ar
10、eas of information technology which fall within ITU-Ts purview, the necessary standards are prepared on a collaborative basis with ISO and IEC. NOTE In this Recommendation, the expression “Administration“ is used for conciseness to indicate both a telecommunication administration and a recognized op
11、erating agency. Compliance with this Recommendation is voluntary. However, the Recommendation may contain certain mandatory provisions (to ensure e.g., interoperability or applicability) and compliance with the Recommendation is achieved when all of these mandatory provisions are met. The words “sha
12、ll“ or some other obligatory language such as “must“ and the negative equivalents are used to express requirements. The use of such words does not suggest that compliance with the Recommendation is required of any party. INTELLECTUAL PROPERTY RIGHTS ITU draws attention to the possibility that the pr
13、actice or implementation of this Recommendation may involve 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 others outside of the Recommendation deve
14、lopment process. As of the date of approval of this Recommendation, ITU had not received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementors are cautioned that this may not represent the latest information and are there
15、fore strongly urged to consult the TSB patent database. ITU 2004 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU. ITU-T Rec. V.250 (07/2003) iii CONTENTS Page 1 Introduction and scope 1 2 References. 1 2.1 Norma
16、tive references 1 2.2 Informative references 2 3 Definitions and abbreviations. 3 3.1 Definitions 3 3.2 Abbreviations . 4 4 Physical layer 4 4.1 Circuits . 4 4.2 Character formatting. 5 4.3 Data rates 5 5 Syntax and procedures 5 5.1 Alphabet . 5 5.2 DTE commands lines . 6 5.3 Basic Syntax commands.
17、7 5.4 Extended Syntax commands. 8 5.5 Issuing commands 12 5.6 Executing commands 12 5.7 DCE responses 13 5.8 Manufacturer-specific characteristics. 16 6 Functions 17 6.1 Generic DCE control 18 6.2 DTE-DCE interface commands 25 6.3 Call control . 37 6.4 Modulation control commands. 48 6.5 Error contr
18、ol commands . 60 6.6 Data compression commands . 68 6.7 DCE testing 73 6.8 PCM DCE commands 85 6.9 V.59 Command (+TMO) 91 Appendix I Summary of basic and extended format commands 93 Appendix II DCE configuration, dialling, negotiation and reporting, example session. 95 Appendix III Encapsulation of
19、V.250 messages in V.25 bis DCE . 96 III.1 Scope 96 III.2 Encapsulation of V.250 messages 96 III.3 Applicable V.250 commands . 96 III.4 Applicable V.250 responses . 97 ITU-T Rec. V.250 (07/2003) 1 ITU-T Recommendation V.250 Serial asynchronous automatic dialling and control 1 Introduction and scope T
20、his Recommendation is applicable to the interconnection of Data Terminal Equipment (DTE) and Data Circuit-terminating Equipment (DCE) employing serial binary data operation via the ITU-T Recs V.100-series interchange circuits. This Recommendation contains four elements: codifies existing practice in
21、 common Asynchronous GSTN-DCE that use the ATtention (AT) command set. It identifies the protocol elements, procedures, and behaviours that were found to be held in common among a large portion of DCE manufacturers. It is intended, as much as possible, to preserve compatibility between DCEs and DTEs
22、. Most DCEs implement a number of extensions and behavioural differences beyond the descriptions in this Recommendation; such extensions and differences are explicitly permitted by this Recommendation (see 5.8); defines a format for extension of the AT command set in an orderly fashion. It reserves
23、the “+“ command prefix to be used by other standardized extensions, such as those found in ITU-T Recs T.31 and T.32 (Asynchronous Facsimile DCE Control); provides a set of standardized extensions, based on the extended “+“ command format. These commands identify the DCE, control the DTE-DCE interfac
24、e, and control DCE-DCE protocol behaviour (signal conversion, error control and data compression); provides a mapping of the commands defined in this Recommendation into V.25 bis frame format for use with DCEs employing synchronous serial interfaces. See Appendix III. The procedures described for au
25、tomatic calling equipment conforming to this Recommendation allow interworking with automatic answering equipment conforming to ITU-T Recs V.25 and V.25 bis. 2 References 2.1 Normative references The following ITU-T Recommendations and other references contain provisions which, through reference in
26、this text, constitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Recommendations and other references are subject to revision; users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent e
27、dition of the Recommendations and other references listed below. A list of the currently valid ITU-T Recommendations is regularly published. The reference to a document within this Recommendation does not give it, as a stand-alone document, the status of a Recommendation. ITU-T Recommendation Q.23 (
28、1988), Technical features of push-button telephone sets. ITU-T Recommendation T.50 (1992), International Reference Alphabet (IRA) (Formerly International Alphabet No. 5 or IA5) Information technology 7-bit coded character set for information interchange. ITU-T Recommendation V.4 (1988), General stru
29、cture of signals of International Alphabet No. 5 code for character oriented data transmission over public telephone networks. ITU-T Recommendation V.8 bis (2000), Procedures for the identification and selection of common modes of operation between data circuit-terminating equipments (DCEs) and 2 IT
30、U-T Rec. V.250 (07/2003) between data terminal equipments (DTEs) over the public switched telephone network and on leased point-to-point telephone-type circuits. ITU-T Recommendation V.24 (2000), List of definitions for interchange circuits between data terminal equipment (DTE) and data circuit-term
31、inating equipment (DCE). ITU-T Recommendation V.25 (1996), Automatic answering equipment and general procedures for automatic calling equipment on the general switched telephone network including procedures for disabling of echo control devices for both manually and automatically established calls.
32、Other relevant Recommendations are listed in the Supplement 1 to this Recommendation. 2.2 Informative references ITU-T Recommendation T.31 (1995), Asynchronous facsimile DCE control Service Class 1. ITU-T Recommendation T.32 (1995), Asynchronous facsimile DCE control Service Class 2. ITU-T Recommend
33、ation V.8 (2000), Procedures for starting sessions of data transmission over the public switched telephone network. ITU-T Recommendation V.14 (1993), Transmission of start-stop characters over synchronous bearer channels. ITU-T Recommendation V.18 (2000), Operational and interworking requirements fo
34、r DCEs operating in the text telephone mode. ITU-T Recommendation V.21 (1988), 300 bits per second duplex modem standardized for use in the general switched telephone network. ITU-T Recommendation V.22 (1988), 1200 bits per second duplex modem standardized for use in the general switched telephone n
35、etwork and on point-to-point 2-wire leased telephone-type circuits. ITU-T Recommendation V.22 bis (1988), 2400 bits per second duplex modem using the frequency division technique standardized for use on the general switched telephone network and on point-to-point 2-wire leased telephone-type circuit
36、s. ITU-T Recommendation V.23 (1988), 600/1200-baud modem standardized for use in the general switched telephone network. ITU-T Recommendation V.26 bis (1988), 2400/1200 bits per second modem standardized for use in the general switched telephone network. ITU-T Recommendation V.26 ter (1988), 2400 bi
37、ts per second duplex modem using the echo cancellation technique standardized for use on the general switched telephone network and on point-to-point 2-wire leased telephone-type circuits. ITU-T Recommendation V.27 ter (1988), 4800/2400 bits per second modem standardized for use in the general switc
38、hed telephone network. ITU-T Recommendation V.32 (1993), A family of 2-wire, duplex modems operating at data signalling rates of up to 9600 bit/s for use on the general switched telephone network and on leased telephone-type circuits. ITU-T Recommendation V.32 bis (1991), A duplex modem operating at
39、 data signalling rates of up to 14 400 bit/s for use on the general switched telephone network and on leased point-to-point 2-wire telephone-type circuits. ITU-T Rec. V.250 (07/2003) 3 ITU-T Recommendation V.34 (1998), A modem operating at data signalling rates of up to 33 600 bit/s for use on the g
40、eneral switched telephone network and on leased point-to-point 2-wire telephone-type circuits. ITU-T Recommendation V.42 (2002), Error-correcting procedures for DCEs using asynchronous-to-synchronous conversion. ITU-T Recommendation V.42 bis (1990), Data compression procedures for data circuit-termi
41、nating equipment (DCE) using error correction procedures. ITU-T Recommendation V.44 (2000), Data compression procedures. ITU-T Recommendation V.54 (1988), Loop test devices for modems. ITU-T Recommendation V.58 (1994), Management information model for V-Series DCEs. ITU-T Recommendation V.59 (2000),
42、 Managed objects for diagnostic information of public switched telephone network connected V-series modem DCEs. ITU-T Recommendation V.90 (1998), A digital modem and analogue modem pair for use on the Public Switched Telephone Network (PSTN) at data signalling rates of up to 56 000 bit/s downstream
43、and up to 33 600 bit/s upstream. ITU-T Recommendation V.91 (1999), A digital modem operating at data signalling rates of up to 64 000 bit/s for use on a 4-wire circuit switched connection and on leased point-to-point 4-wire digital circuits. ITU-T Recommendation V.92 (2000), Enhancements to Recommen
44、dation V.90. ITU-T Recommendation X.680 (2002)ISO/IEC 8824-1:2002, Information technology Abstract Syntax Notation One (ASN.1): Specification of basic notation. NOTE See Supplement 1 to this Recommendation for additional informative references. 3 Definitions and abbreviations 3.1 Definitions This Re
45、commendation defines the following terms: 3.1.1 command state: In Command State, the DCE is not communicating with a remote station, and the DCE is ready to accept commands. Data signals from the DTE on circuit 103 are treated as command lines and processed by the DCE, and DCE responses are sent to
46、the DTE on circuit 104. The DCE enters this state upon power-up, and when a call is disconnected. 3.1.2 online command state: In Online Command State, the DCE is communicating with a remote station, but treats signals from the DTE on circuit 103 as command lines and sends responses to the DTE on cir
47、cuit 104. Depending on the implementation, data received from the remote station during Online Command State may be either discarded or retained in the DCE until Online Data State is once again entered (by a command from the DTE). Data previously transmitted by the local DTE and buffered by the DCE
48、may be transmitted from the buffer to the remote DCE during Online Command State, or it may be discarded or transmission deferred until Online Data State is once again entered. Online Command State may be entered from Online Data state by a mechanism defined in 6.2.9 or by other manufacturer-defined
49、 means. 3.1.3 online data state: In Online Data State, the DCE is communicating with a remote station. Data signals from the DTE on circuit 103 are treated as data and transmitted to the remote station, and data received from the remote station are delivered to the DTE on circuit 104. Data and control signals are monitored by the DCE to detect events such as loss of the remote connection and DTE requests for disconnection or switching to Online Command State. Online Data State is entere
