INTERNATIONAL TELECOMMUNICATION UNION
`
`TELECOMMUNICATION
`STANDARDIZATION SECTOR
`OF ITU
`
`V.250
`
`(05/99)
`
`SERIES V: DATA COMMUNICATION OVER THE
`TELEPHONE NETWORK
`Control procedures
`
`Serial asynchronous automatic dialling and
`control
`
`ITU-T Recommendation V.250
`(Previously CCITT Recommendation)
`
`Unified v Uniloc
`IPR2018-00199
`Unified 1024
`
`

`

`ITU-T V-SERIES RECOMMENDATIONS
`DATA COMMUNICATION OVER THE TELEPHONE NETWORK
`
`General
`Interfaces and voiceband modems
`Wideband modems
`Error control
`Transmission quality and maintenance
`Simultaneous transmission of data and other signals
`Interworking with other networks
`Interface layer specifications for data communication
`Control procedures
`Modems on digital circuits
`
`For further details, please refer to ITU-T List of Recommendations.
`
`V.1–V.9
`V.10–V.34
`V.35–V.39
`V.40–V.49
`V.50–V.59
`V.60–V.99
`V.100–V.199
`V.200–V.249
`V.250–V.299
`V.300–V.399
`
`

`

`ITU-T RECOMMENDATION V.250
`
`SERIAL ASYNCHRONOUS AUTOMATIC DIALLING AND CONTROL
`
`Summary
`
`This Recommendation defines commands and responses for use by a DTE to control a V-series DCE
`using serial data interchange 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 of standardized extensions for common functions to identify the DCE, to
`control 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
`Former ITU-T Recommendation V.25 ter (07/97) body was renumbered as Recommendation V.250
`on 6 February 1998 without further modification. Annex A to V.25 ter was renumbered as V.251.
`ITU-T Recommendation V.250 was revised by ITU-T Study Group 16 (1997-2000) and was
`approved under the WTSC Resolution No. 1 procedure on 27 May 1999.
`
`Keywords
`AT Commands, Data Modems, Data Transmission, DCE control.
`
`
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`Recommendation V.250 (05/99)
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`FOREWORD
`ITU (International Telecommunication Union) is the United Nations Specialized Agency in the field of
`telecommunications. The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of
`the ITU. The 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 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 Recommendations by the Members of the ITU-T is covered by the procedure laid down in
`WTSC Resolution No. 1.
`In some areas of information technology which fall within ITU-T’s purview, the necessary standards are
`prepared on a collaborative basis with ISO and IEC.
`
`NOTE
`In this Recommendation the term recognized operating agency (ROA) includes any individual, company,
`corporation or governmental organization that operates a public correspondence service. The terms
`Administration, ROA and public correspondence are defined in the Constitution of the ITU (Geneva, 1992).
`
`INTELLECTUAL PROPERTY RIGHTS=
`The ITU draws attention to the possibility that the practice or implementation of this Recommendation may
`involve the use of a claimed Intellectual Property Right. The 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 development process.
`As of the date of approval of this Recommendation, the 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 therefore strongly urged to consult the
`TSB patent database.
`
` ITU 2000
`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 microfilm, without permission in writing from the ITU.
`
`ii
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`=
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`

`CONTENTS
`
`1
`2
`2.1
`2.2
`3
`4
`4.1
`4.2
`4.3
`5
`5.1
`5.2
`
`5.3
`
`5.4
`
`5.5
`5.6
`
`5.7
`
`Introduction and scope................................................................................................
`References...................................................................................................................
`Normative references..................................................................................................
`Informative references ................................................................................................
`Definitions and abbreviations .....................................................................................
`Physical layer ..............................................................................................................
`Circuits........................................................................................................................
`Character formatting ...................................................................................................
`Data rates ....................................................................................................................
`Syntax and procedures ................................................................................................
`Alphabet......................................................................................................................
`DTE commands lines..................................................................................................
`5.2.1 Command line general format .......................................................................
`5.2.2 Command line editing ...................................................................................
`5.2.3 Command line echo.......................................................................................
`5.2.4 Repeating a command line.............................................................................
`5.2.5 Types of DTE commands ..............................................................................
`5.2.6 DTE command syntax ...................................................................................
`Basic syntax commands..............................................................................................
`5.3.1 Basic syntax command format.......................................................................
`5.3.2 S-parameters ..................................................................................................
`Extended syntax commands........................................................................................
`5.4.1 Command naming rules.................................................................................
`5.4.2 Values ............................................................................................................
`5.4.3 Action commands..........................................................................................
`5.4.4 Parameter commands.....................................................................................
`5.4.5 Additional syntax rules..................................................................................
`Issuing commands.......................................................................................................
`Executing commands..................................................................................................
`5.6.1 Aborting commands ......................................................................................
`5.6.2 Handling of invalid numbers and S-parameter values...................................
`DCE responses............................................................................................................
`5.7.1 Responses ......................................................................................................
`5.7.2 Extended syntax result codes.........................................................................
`5.7.3
`Information text formats for test commands .................................................
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`5.8
`
`6
`6.1
`
`6.2
`
`6.3
`
`Manufacturer-specific characteristics .........................................................................
`5.8.1 Extensions......................................................................................................
`5.8.2 Behavioural differences.................................................................................
`Functions.....................................................................................................................
`Generic DCE control...................................................................................................
`6.1.1 Reset to default configuration........................................................................
`6.1.2 Set to factory-defined configuration..............................................................
`6.1.3 Request identification information ................................................................
`6.1.4 Request manufacturer identification (++++GMI) ................................................
`6.1.5 Request model identification (++++GMM) .........................................................
`6.1.6 Request revision identification (++++GMR) .......................................................
`6.1.7 Request product serial number identification (++++GSN) ..................................
`6.1.8 Request global object identification (++++GOI) .................................................
`6.1.9 Request complete capabilities list (++++GCAP).................................................
`6.1.10 Country of installation, (++++GCI) .....................................................................
`DTE-DCE interface commands ..................................................................................
`6.2.1 Command line termination character.............................................................
`6.2.2 Response formatting character ......................................................................
`6.2.3 Command line editing character....................................................................
`6.2.4 Command echo..............................................................................................
`6.2.5 Result code suppression.................................................................................
`6.2.6 DCE response format.....................................................................................
`6.2.7 Result code selection and call progress monitoring control ..........................
`6.2.8 Circuit 109 (Received line signal detector) behaviour ..................................
`6.2.9 Circuit 108 (Data terminal ready) behaviour.................................................
`6.2.10 Fixed DTE rate (++++IPR) ..................................................................................
`6.2.11 DTE-DCE character framing (++++ICF).............................................................
`6.2.12 DTE-DCE local flow control (++++IFC).............................................................
`6.2.13 DTE-DCE local rate reporting (++++ILRR)........................................................
`6.2.14 ++++ICLOK Select Sync Transmit Clock Source ...............................................
`6.2.15 ++++ILSD Select Long Space Disconnect Option...............................................
`6.2.16 ++++IDSR Select Data Set Ready Option ...........................................................
`6.2.17 ++++IRTS Select Synchronous Mode RTS Option.............................................
`Call control .................................................................................................................
`6.3.1 Dial ................................................................................................................
`6.3.2 Select tone dialling (command).....................................................................
`6.3.3 Select pulse dialling (command) ...................................................................
`6.3.4
`Incoming call indication ................................................................................
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`6.4
`
`6.5
`
`6.3.5 Answer...........................................................................................................
`6.3.6 Hook control..................................................................................................
`6.3.7 Return to online data state .............................................................................
`6.3.8 Automatic answer..........................................................................................
`6.3.9 Pause before blind dialling ............................................................................
`6.3.10 Connection completion timeout.....................................................................
`6.3.11 Comma dial modifier time.............................................................................
`6.3.12 Automatic disconnect delay...........................................................................
`6.3.13 Monitor speaker loudness..............................................................................
`6.3.14 Monitor speaker mode...................................................................................
`6.3.15 ++++ASTO store telephone number....................................................................
`Modulation control commands ...................................................................................
`6.4.1 Modulation selection (++++MS)..........................................................................
`6.4.2 Modulation automode control (++++MA) ...........................................................
`6.4.3 Modulation reporting control (++++MR) ............................................................
`6.4.4 V.18 Selection (++++MV18S).............................................................................
`6.4.5 V.18 Reporting control (++++MV18R)...............................................................
`6.4.6 V.18 Answering message editing (++++MV18AM)............................................
`6.4.7 Order of probes (++++MV18P) ...........................................................................
`6.4.8 Seamless rate change enable (++++MSC) ...........................................................
`Error control commands .............................................................................................
`6.5.1 Error control selection (++++ES).........................................................................
`6.5.2 Break handling in error control operation (++++EB)...........................................
`6.5.3 Selective repeat (++++ESR).................................................................................
`32-bit frame check sequence (++++EFCS)..........................................................
`6.5.4
`6.5.5 Error control reporting (++++ER)........................................................................
`6.5.6 Call termination buffer management (++++ETBM)............................................
`++++EWIND Window Size.................................................................................
`6.5.7
`++++EFRAM Frame Length................................................................................
`6.5.8
`Data compression commands .....................................................................................
`6.6.1 Data compression (++++DS) ...............................................................................
`6.6.2 Data compression reporting (++++DR) ...............................................................
`DCE testing.................................................................................................................
`6.7.1 List of Test Commands and Parameters ........................................................
`6.7.2 Test Commands and Parameters....................................................................
`Appendix I – Summary of basic and extended format commands...........................................
`Appendix II – DCE configuration, dialling, negotiation and reporting, example session .......
`
`6.6
`
`6.7
`
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`Appendix III – Encapsulation of V.250 messages in V.25 bis DCE........................................
`III.1
`Scope...........................................................................................................................
`III.2
`Encapsulation of V.250 messages...............................................................................
`III.3 Applicable V.250 commands......................................................................................
`III.4 Applicable V.250 responses........................................................................................
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`Recommendation V.250
`
`SERIAL ASYNCHRONOUS AUTOMATIC DIALLING AND CONTROL
`(revised in 1999)
`
`–
`
`Introduction and scope
`1
`This Recommendation is applicable to the interconnection of Data Terminal Equipment (DTE) and
`Data Circuit-terminating Equipment (DCE) employing serial binary data operation via the
`V.100-series interchange circuits.
`This Recommendation contains four elements:
`–
`codifies existing practice in 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. 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 the
`"+" command prefix to be used by other standardized extensions, such as those found in
`Recommendations T.31 and T.32 (Asynchronous Facsimile DCE Control, Study Group 8);
`provides a set of standardized extensions, based on the extended "+" command format.
`These commands identify the DCE, control the DTE-DCE interface, 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 automatic calling equipment conforming to this Recommendation
`allow interworking with automatic answering equipment conforming to Recommendations V.25 and
`V.25 bis.
`
`–
`
`–
`
`2
`
`References
`
`Normative references
`2.1
`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 other references are subject to revision; all
`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.
`–
`CCITT Recommendation Q.23 (1988), Technical features of push-button telephone sets.
`–
`CCITT 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.
`CCITT Recommendation V.4 (1988), General structure of signals of international alphabet
`No. 5 code for character oriented data transmission over public telephone networks.
`
`–
`
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`–
`
`ITU-T Recommendation V.8 bis (1998), Procedures for the identification and selection of
`common modes of operation between Data Circuit-terminating Equipments (DCEs) and
`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 (1996), List of definitions for interchange circuits between
`Data Terminal Equipment (DTE) and Data Circuit-terminating 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.
`Other relevant Recommendations are listed in the Supplement 1 to Recommendation V.250.
`
`–
`
`–
`
`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 Recommendation V.8 (1998), 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 (1998), Operational and interworking requirements for DCEs
`operating in the text telephone mode.
`CCITT Recommendation V.21 (1988), 300 bits per second duplex modem standardized for
`use in the general switched telephone network.
`CCITT Recommendation V.22 (1988), 1200 bits per second duplex modem standardized for
`use in the general switched telephone network and on point-to-point 2-wire leased
`telephone-type circuits.
`CCITT 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 circuits.
`CCITT Recommendation V.23 (1988), 600/1200-baud modem standardized for use in the
`general switched telephone network.
`CCITT Recommendation V.26 bis (1988), 2400/1200 bits per second modem standardized
`for use in the general switched telephone network.
`CCITT Recommendation V.26 ter (1988), 2400 bits 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.
`CCITT Recommendation V.27 ter (1988), 4800/2400 bits per second modem standardized
`for use in the general switched 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.
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`–
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`–
`
`–
`
`CCITT Recommendation V.32 bis (1991), A duplex modem operating at 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 Recommendation V.34 (1998), A modem operating at data signalling rates of up to
`33 600 bit/s for use on the general switched telephone network and on leased point-to-point
`2-wire telephone-type circuits.
`ITU-T Recommendation V.42 (1996), Error-correcting procedures for DCEs using
`asynchronous-to-synchronous conversion.
`CCITT Recommendation V.42 bis (1990), Data compression procedures for Data Circuit-
`terminating Equipment (DCE) using error correcting procedures.
`CCITT Recommendation V.54 (1988), Loop test devices for modems.
`ITU-T Recommendation V.58 (1994), Management Information model for V-Series DCEs.
`CCITT Recommendation X.208 (1988), Specification of Abstract Syntax Notation One
`(ASN.1).
`CCITT Recommendation X.209 (1988), Specification of basic encoding rules for Abstract
`Syntax Notation One (ASN.1).
`NOTE – See Supplement 1 to Recommendation V.250 for additional informative references.
`
`–
`
`–
`–
`–
`
`–
`
`Definitions and abbreviations
`3
`This Recommendation defines the following terms:
`3.1
`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 the DTE on circuit 104.
`The DCE enters this state upon power-up, and when a call is disconnected.
`3.2
`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 circuit 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 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 means.
`3.3
`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 entered by
`successful completion of a command to originate or answer a call, by automatically answering a call,
`or by a DTE command to return to Online Data state from Online Command state.
`3.4
`direct mode: Mode of OnLine Data State whereby the V.24 circuits 103 (transmit data) and
`104 (received data) transfer data at the same rate or rates in use on the DCE-to-DCE communication
`channels. The DCE does not buffer data in either direction, nor does it implement flow control. For
`DCE modulation methods that transfer data synchronously, this mode implies the use of V.14
`synchronous/asynchronous protocol within the DCE.
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`buffered mode: Mode of OnLine Data State whereby the V.24 circuits 103 (transmit data)
`3.5
`and 104 (received data) transfer data at data rates independent of the rates in use on the DCE-to-DCE
`communication channels. The DCE buffers the data rate differences as required. Neither error
`control nor data compression is used. For DCE modulation methods that transfer data synchronously,
`this mode implies the use of V.14 synchronous/asynchronous protocol within the DCE. For DCE
`modulation methods that transfer data asynchronously, asynchronous start-stop framing is used on
`the DCE-to-DCE communications channels.
`leadin: Commands defined using the extended syntax defined in 5.2.3 begin with a "+"
`3.6
`character. The second character is reserved for a particular function or application. That two-
`character sequence, "+<char>" is the Leadin.
`3.7
`[...]: Square brackets are used to indicate that the enclosed items are optional. The square
`brackets themselves do not appear in the command line.
`<<<<...>>>>: Angle brackets are used to enclose the names of other syntactical elements. When
`3.8
`those elements appear in an actual command line, the actual element is used and the angle brackets
`are omitted.
`All other characters, including "?", "=", parentheses, etc., shall appear in commands as written.
`CCITT International Telephone and Telegraph Consultative Committee
`IRA
`International Reference Alphabet (Recommendation T.50)
`ITU-T International Telecommunication Union – Telecommunication Standardization Sector
`
`Physical layer
`4
`The circuits listed in 4.1 are intercepted and controlled by the DCE. The DCE is designed so that it
`will function properly if only these circuits are connected or implemented. V.24 circuit designators
`are listed in this subclause.
`
`Circuits
`4.1
`Signal Ground (Circuit 102) – Connection of this circuit is required for proper recognition of signals
`on other circuits.
`Transmitted Data (Circuit 103) – While in command state or online command state, data signals are
`processed by the DCE and not transmitted to the remote station.
`Received Data ( Circuit 104) – While in command state or online command state, data received from
`the remote station may be ignored (see clause 3, definition of Online Command State), and the DCE
`generates responses on this circuit.
`Data Terminal Ready (Circuit 108/2) – The DCE monitors the effect of changes in the state of this
`circuit on the operation of the underlying DCE and operates accordingly. For example, if the DCE
`responds to an on-to-off transition on this circuit by disconnecting a call, the DCE will act
`accordingly by returning from online data state to command state.
`Received Line Signal Detector (Circuit 109) – The DCE may intercept this signal so that the
`issuance of result codes can be properly coordinated with transitions on this signal.
`Calling Indicator (Circuit 125) – The DCE may intercept this signal so that it can detect network
`alerting signals and automatically answer, if so conditioned by the appropriate command (S0,
`see 6.3.8).
`
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`

`Character formatting
`4.2
`During command state and online command state, data transmitted between the DTE and DCE shall
`conform to the requirements for start-stop data transmission specified in Recommendation V.4 and
`ISO 1177. Parity may be even, odd, mark, space or not used. Each character shall have at least one
`complete stop element. The DCE should accept commands using any combination of parity and stop
`elements supported during online data state. These shall include, as a minimum, the following
`combinations, as defined in Annex B/V.42, each of which consists of ten total bits (including the
`start element):
`–
`7 data bits, even parity, 1 stop element;
`–
`7 data bits, odd parity, 1 stop element;
`–
`7 data bits, space parity, 1 stop element;
`–
`7 data bits, mark parity, 1 stop element (7 data bits, no parity bit, 2 stop elements);
`–
`8 data bits, no parity, 1 stop element.
`During online data state, the DCE shall be transparent to changes in data format; the use of a
`particular format during command state should not restrict the use of other formats that are supported
`during online data state. However, DCE responses issued to indicate transition from online data state
`back to command state are issued using the same format and parity as the last command line issued
`by the DTE (see 5.7), and the DTE must therefore be prepared to recognize these responses even
`though the character format may have been changed.
`See 6.2.11 for a command to explicitly select the DTE-DCE character format.
`
`Data rates
`4.3
`The DCE shall be able to accept commands at either 1200 bit/s or 9600 bit/s. It is desirable that the
`DCE be able to accept commands and automatically detect the rate being used by the DTE at all
`rates supported by the DCE on the DTE-DCE interface. The DCE may provide a strap, switch, or
`other facility to define the rate at which the DTE is operating; however, while the rate is so selected,
`the DCE shall continue to be capable of accepting commands at either 1200 bit/s or 9600 bit/s.
`See 6.2.10 for a command to explicitly select the DTE-DCE rate.
`When operating in the online command state, th