
	    Page 1			   Document TR30.4.1/89-01001R4
							 January   1989

		      ELECTRONIC INDUSTRIES ASSOCIATION
			 AD HOC SUBCOMMITTEE TR30.4.1

	    Project:  PN-2188, Asynchronous Facsimile DCE Control
		      Standard

	    Source:   Data Race, Inc

	    Subject:  DTE-DCE Interface Description for Facsimile
	    Operations with Minimum DCE Facilities ("Class 1")

	    1.	 Introduction

		 At the September 15, 1988 meeting of the TR30.2.3
	    committee, Les Staples of Data Race was requested to produce
	    a working paper for the "Class 1" DTE-DCE interface for
	    Facsimile Operation embodying the features and facilities
	    agreed upon by the committee.  At the November meeting in
	    Las Vegas, the first draft of that paper was submitted.
	    Many useful suggestions and comments were made at that
	    meeting.  A second draft was presented at the January 1989
	    committee meeting.	The committee has been renamed TR30.4.1.
	    A large number of good suggestions were incorporated,
	    resulting in this, the third draft of that paper.

		 Several changes to the original paper have been made to
	    facilitate a simple 3-wire electrical interface,  to
	    eliminate the need for the DTE to be able to detect and
	    handle the BREAK signal, and to eliminate the requirement
	    for the DTE to be able to force the DCE to Command Mode.

	    The attendees at the January, 1989 meeting were in general
	    agreement on the workability of this paper in this form.
	    The major changes made at the January 1989 meeting were:

		 . requirement for the DCE to support XON/XOFF

		 . removal of NULL padding ability during FAX transmit

		 . add of DCE capability to detect the Final bit in
		   the C-Field of an HDLC frame it is transmitting and
		   to use the Final-bit detection to cause a return to
		   Command Mode.

		 . add of OK response code each time the DCE returns
		   to Command Mode for consistancy.

		 . add of CONNECT response code each time the DCE exits
		   Command Mode while On-Line for consistancy


	    Page 2				    TR30.4.1/89-01001R4

	    2.	 Description of Interface

		 The interface described is an extension of the
	    asynchronous modem control "AT" command set currently under
	    study by the TR30.4 committee and uses the format proposed
	    by the TR30.4 committee.  Every effort has been made to keep
	    this level of interface as simple as possible with minimum
	    requirements for processing placed on the DCE.  The ability
	    to efficiently operate with the current T.4 Recommendation
	    as well as with a future error-protected facsimile
	    transmission protocol, such as that specified in the Revised
	    Recommendation T.4, AP IX-24-E, was also a consideration.

	    An object of this paper is to allow a single port rate
	    setting throughout the facsimile operation.  Port rate
	    setting methodologies are left to PN-2120.

	    Bi-directional flow control is specified in all modes to
	    prevent loss of data.  The DCE must be capable of using in-
	    band (XON-XOFF) and, optionally, electrical lead signaling
	    (RTS-CTS).	Methodologies for specifying to the DCE the flow
	    control method to be used are left to PN-2120.


	    Page 3				    TR30.4.1/89-01001R4

	    2.1  Electrical Interface - Data and Control Signals

		 The described interface assumes a serial asynchronous
	    connection between the DTE and the DCE consisting of, as a
	    minimum, Circuit BA (Transmitted Data), Circuit BB (Received
	    Data), and Circuit AB (Signal Ground).  Circuit CA (Request
	    To Send) may optionally be used by the DTE to flow-control
	    the DCE, and Circuit CB (Clear To Send) may optionally be
	    used by the DCE to flow-control the DTE.  Circuit CD (Data
	    Terminal Ready) may optionally be used by the DTE to control
	    the Off-Hook and Command Mode states of the DCE.  The
	    specific use of these leads are left to PN-2120.

	    2.2  Firmware Interface - Commands and Registers

	    2.2.1     Modulation Control Register

		 The described interface uses a single register to
	    determine the desired modulation type.  This register may be
	    set and examined by the normal ATSr commands.  Register 65
	    has been chosen for this description, but another currently-
	    unused register may be used in its place.  Values in the
	    register select:

		      Value	     Modulation
		       3	V.29 - 7200 BPS
		       4	V.29 - 9600 BPS
		       5	V.27 - 2400 BPS
		       6	V.27 - 4800 BPS
		      10	V.21 -	  300 BPS
		      11	TONE - 2100 Hz (CED)
		      12	TONE - 1100 Hz (CNG - EOM)
		      13	V.33Bis 12000 BPS*
		      14	V.33Bis 14400 BPS*
		      15	V.xx	19200 BPS
		      21   Reserved for DTMF tone detect

	    *These speeds are not required but the values are reserved
	    for future implementations.


	    2.2.2     Dialing and Answering

	    2.2.2.1   Dialing

	    The normal ATD<dial string> is used to dial a facsimile
	    call.  If the DCE is set for CED Tone mode, normal DCE call
	    progress detection and reporting will be used.  When the DCE
	    detects the configured tone, it will send the CONNECT
	    response code to the DTE, followed by the OK response code
	    indicating that the DCE is in Command Mode.


	    Page 4				    TR30.4.1/89-01001R4

	    2.2.2.2   Answering

	    The normal ATA command or Automatic Answering is used to
	    cause the DCE to come off-hook in answer mode.  In facsimile
	    operation, when Register 65 is one of the defined the
	    defined facsimile modes, the CONNECT result code will be
	    immediately sent to the DTE and the DCE will enter Command
	    Mode.  The DTE would normally immediately order the DCE to
	    transmit the 2100 Hz CED tone.

	    2.3.2     Facsimile Transmission and Reception

		 Facsimile transmission and reception is controlled by
	    four commands which are specific to facsimile operation.
	    Since the data set over the interface is asynchronous,
	    containing start and stop bits, it is necessary to set the
	    DTE-DCE interface to a higher data rate than the line
	    modulation rate.  Since the maximum line modulation rate
	    specified in Recommendation T.4 is 9600 BPS, it is
	    convenient to set the DTE-DCE interface rate to 19,200 BPS.
	    The DCE performs buffering and flow-control as described in
	    the remainder of this document.  An object is to allow the
	    entire facsimile operation to be accomplished at a single
	    port rate.	Methodologies for port rate setting are left to
	    PN-2120.


	    Page 5				    TR30.4.1/89-01001R4

	    2.3.2.1 Facsimile Transmit

		 The command AT+FT is used to cause the DCE to transmit
	    using the modulation selected by the content of the
	    Modulation Control Register.  The DCE should be Off-Hook
	    when this command is issued by the DTE.  The DCE will return
	    the CONNECT response code and immediately send the proper
	    training sequence in the selected mode (if any) followed by
	    data.

		 The DCE buffers data in this mode.  The configured
	    flow-control method will be used by the DTE as necessary to
	    pause the DTE.

		 When the DCE's transmit buffer becomes empty, the DCE
	    will stop transmitting, lower transmit carrier, and return
	    to command mode, returning the OK result code.  The DTE may
	    force the DCE to command mode by making Circuit CD (Data
	    Terminal Ready) false, if so configured.  When the DCE
	    returns to command mode, it will lower its transmit carrier.

		 If the mode chosen is TONE, the DCE will immediately
	    begin to send the configured tone when the command is
	    issued.  If the DTE sends any subsequent data to the DCE,
	    DCE will return to command mode.  If the data from the DTE
	    which aborts the receive process is a valid command, the
	    command will be executed correctly.


	    Page 6				    TR30.4.1/89-01001R4


	    2.3.2.2 Facsimile Receive

		 The command AT+FR causes the DCE to enter receive mode.
	    The DCE receives in the modulation mode specified in the
	    Modulation Control Register.  The DCE will wait up to the
	    time set in Register 7 for carrier to be detected.	If the
	    signal fails to be detected within that time, the modem
	    returns to Command Mode and sends the NO CARRIER response
	    code.

		 If the selected mode is detected (Receive Line Signal
	    Detect in the proper mode), the DCE will send the CONNECT
	    result code to the DTE.

		 If a signal is detected, but it is not the selected
	    mode, the DCE will send a CERROR (Connect Error) result code
	    to the DTE.  This result code may optionally contain a
	    numeric code indicating the type of signal that the DCE has
	    determined that it is detecting.

		 If the modulation selected is TONE, the CONNECT result
	    code will be returned when the selected tone is detected for
	    the period of time set in Register 9 , the Carrier Detect
	    Response Time register, (0.1 second increments, default 0.6
	    seconds).  The DCE will then return to command mode.

		 In data modes, the DCE will return to Command Mode upon
	    loss of carrier for the period of time set in Register 10,
	    sending the normal NO CARRIER result code.

		 The DCE will obey the configured flow control from the
	    DTE.

		 If the DTE sends any data to the DCE other than XON or
	    XOFF while the DCE is in a Receive mode,  the DCE will
	    return to command mode.  If the data from the DTE which
	    aborts the receive process is a valid command, the command
	    will be executed correctly.

		 The DTE may force the DCE to command mode by making
	    Circuit CD (Data Terminal Ready) false, if so configured.


	    Page 7				    TR30.4.1/89-01001R4

	    2.3.2.3 HDLC Transmit

		 The command AT+FTH causes the DCE to transmit frames in
	    HDLC protocol using the modulation mode chosen in the
	    Modulation Control Register.  If, when the command is
	    executed, the mode set in the Modulation Control Register is
	    not a valid synchronous mode, the response code ERROR will
	    be returned by the DCE and the DCE will return to command
	    mode.
		 The DCE will return the CONNECT result code and
	    transmit training followed by flags until the first byte of
	    data is sent by the DTE.  When the buffer becomes empty the
	    DCE will append the Frame Check Sequence and a closing Flag
	    to the frame and return to Command Mode, sending the result
	    code CONNECT to the DTE.  The DCE will continue to send
	    flags until one of the following actions is taken by the
	    DTE.

		 . The DTE sends additional data.  This action causes
		   the DCE to send another frame.

		 . The DTE forces the DCE to Command Mode via Circuit CD
		   (Data Terminal Ready) or the Escape Sequence.

		 . The period of time in Register 10, the Carrier Detect
		   Response Time, elapses from the time when the DCE
		   reported the CONNECT result code without the DTE
		   sending additional data to the DCE.

		   The DCE detects the FINAL bit in the C-field of the
		   frame.

		 When the DCE stops transmitting and returns to Command
	    Mode and sends the the DTE the OK result code or the NO
	    CARRIER result code in the case of S10 expiration.

		 The DCE performs HDLC zero insertion and Frame Check
	    Sequence generation while in this mode.

		 The DCE buffers data in HDLC transmit mode.   The DCE
	    will use the configured method of flow-control to pause the
	    DTE as necessary.
	    


	    Page 8				    TR30.4.1/89-01001R4

	    2.3.2.4  HDLC Receive

		 The command AT+FRH causes the DCE to receive frames in
	    HDLC protocol using the modulation mode selected in the
	    Modulation Control Register.  If, when the command is
	    executed, the mode set in the Modulation Control Register is
	    not a valid synchronous mode, the response code ERROR will
	    be returned by the DCE and the DCE will return to command
	    mode.

	    If the selected mode is detected (Receive Line Signal Detect
	    in the proper mode), the DCE will send the CONNECT result
	    code to the DTE.

		 If a signal is detected, but it is not the selected
	    mode, the DCE will send a CERROR (Connect Error) result code
	    to the DTE.  This result code may optionally contain a
	    numeric code indicating the type of signal that the DCE has
	    determined that it is detecting.

		 The DCE strips Flags and receives and buffers frames.
	    The received data, starting with the first non-Flag byte and
	    continuing through the last FCS byte will be transferred to
	    the DTE.  The DCE performs HDLC zero-deletion and error
	    checking.  When the last byte of FCS has been sent to the
	    DTE, the DCE may optionally inform the DTE of End-Of-Frame
	    by generating a BREAK signal.  After the FCS bytes,
	    following the optional BREAK, the DCE will inform the DTE of
	    the status of the frame reception by returning a result code
	    of OK, if the frame was received correctly, or ERROR, if the
	    frame was received in error.

		 The DCE will obey the configured form of flow control
	    from the DTE.

		 After sending the Result Code indicating the frame
	    reception is complete, the DCE continues to receive and
	    buffer data in the selected mode.  If the DTE issues another
	    HDLC Receive command, the buffered data will be sent to the
	    DCE and HDLC reception will proceed.  If any other command
	    is issued by the DTE, the DCE will stop the receive process.
	    Any buffered data will be discarded and the command will be
	    obeyed.

		 The DCE will return to Command Mode upon loss of
	    carrier for the period of time set in Register 9, sending
	    the normal NO CARRIER result code.


	    Page 9				    TR30.4.1/89-01001R4

		 In this mode, the DTE may force the DCE to command mode
	    with the Escape Sequence or by making Circuit CD (Data
	    Terminal Ready) false, if so configured.


	    2.4  Optional Features

	    2.4.1  Data Buffering

	    In order to allow a computer, such as a multi-user one,
	    which may not always be able to quickly respond to avoid
	    having under-run conditions when transmitting a facsimile,
	    significant buffering in the DCE may be desirable.	The
	    ability to buffer up to 3 seconds of data for transmission
	    (less than 4 kilobytes of buffer) may be provided as an
	    option.

	    2.4.2  DTMF Detection

	    A desirable feature of a multi-function DCE which is capable
	    of facsimile and various forms of data communications would
	    be to be able to detect Dual Tone Multi-Frequency digits to
	    tell a program what service the caller desires.

	    In this operation, the calling DCE would respond to a
	    secondary dialtone emitted by the answering DCE and send one
	    or more digits.  These digits would result in unsolicited
	    result codes to the DTE.


	    Page 11				    TR30.4.1/89-01001R4


	    2.4.2.1  Suggested DTMF implementation.

	    Examples:

		 Dial string at caller:  ATDT<number>@x (where x is a
	    digit).

		 Command sequence to answering DCE:

		 Upon Detection of RING:  ATH1+FT (The H1 causes the DTE
	    to come Off-Hook.  The @ in the dial string causes the DCE
	    to wait for silence before continuing.  The +FT with the
	    proper tone setting in register 65 causes the DCE to send a
	    short tone.  The DTE then goes into DTMF detect mode.

		 If the DCE detects a DTMF digit it sends the DTE an
	    unsolicited response code consisting of an ! (exclamation)
	    followed by the digit received.  The DCE is in a form of
	    Command Mode.  Any command sent to the DCE will cause it to
	    exit the DTMF detection mode and be obeyed.

		 Many of the currently available facsimile data-pumps
	    cannot quickly detect a DTMF digit without additional
	    hardware.  They are, however, capable of detecting the
	    column tones, allowing at least the digits 1, 2, and 3 to be
	    detected.

	    A better syntax may be determined by the TR30.4 group which
	    will satisfy this function.

