SGI Developer Toolbox 6.1/SGI Developer Toolbox 6.1 - Disc 4.iso/public/fax/src/doc/class1.txt

Text File | 1994-08-01 | 34KB | 661 lines

                   SUPRA TECHNICAL SUPPORT BULLETIN
               CLASS 1 FAX COMMANDS FOR SUPRA FAXMODEMS
                              6/19/92

Supra Corporation
7101 Supra Drive SW, Albany, OR  97321
General [phone] / Sales [phone] / Fax [phone]
Supra Tech Support  [phone]  8:00am - 5:00pm PST, M-F

Supra BBS........[phone]  24 Hours
CompuServe.......76004,565
BIX..............SupraCorp
America Online...SupraCorp2
GEnie............SupraTech
AppleLink........D2456
UseNet [e-mail]
            .....supra![e-mail]

SUPRA's DISCLAIMER:
   The following information has been taken from Rockwell's RC144AC
manual. It has not been taken from the CCITT Class 1 documentation,
which is copyrighted by the CCITT.  This information is provided for
educational purposes only.  To fully understand this information
requires a through knowledge of the T.4 fax image and the T.30 fax
session protocol standards.  Due to the nature of this information,
Supra's engineers and technical support can not and will not provide any
help or support on this information.  We STRONGLY urge anyone attempting
to develop fax software to get the required documentation from Global
Engineering or the TIA.

SHORT HISTORY OF CLASS 1 AND 2
  In 1988 the CCITT TR29.2 committee accepted the Class 1 standard for
communication between fax software and fax modems.  The committee also
voted on, but did not accept for various technical reasons, the Class 2
standard.  A year later, they had slightly revised the standard but
again did not accept it.  Software and hardware manufactures decided to
unofficially adopt this standard until the TR29.2 committee could
develop an acceptable standard.  Since so many companies have used the
unofficial standard, the TR29.2 committee has designated that when the
standard is officially adopted it will be known as Class 2.0.  Over the
last year or so, the TR29.2 committee has voted on several revisions to
the Class 2 standard.  Their last vote was early May '92.  A no vote for
technical reasons was entered.  The TR29.2 committee is now reviewing
the technical issues that were raised.  At this time, Supra has not
heard of a projected date for the next ballot.

WHAT IS THE DIFFERENCE BETWEEN CLASS 1 AND 2
  Class 1 fax software handles all of the T.4 fax image and T.30 session
protocol information and timing.  Thus, the ability to communicate
properly with various fax machines is more a function of the software
than the fax modem.  Class 2 fax software generates a T.4  fax page
image and sends it to the fax modem a page at a time.  The fax modem
then handles the T.30 session protocol information and timing.  This
relieves the computer's cpu from some work.  The ability to communicate
properly with various fax machines is more a function of the fax modem
than the software.  However, to further complicate matters, class 2 fax
software can issue Class 1 commands and take over some of the duties of
the Class 2 fax modem.

  When customers have a problem communicating correctly with a fax
machine/modem, it can be very difficult to determine which is at fault,
 the software or the hardware.  Supra has collected numerous Class 1 and
2 fax software for a variety of different computers.  When we receive a
report of a problem, we use these programs to determine if it is a
software or hardware problem.  If it is a hardware problem, we notify
Rockwell, otherwise we notify the software company.

BUG REPORTS
  Supra is dedicated to making the best product for the best price.  If
you feel that you have found a bug, please fax or send a letter to the
attention of:

   SUPRA V32/BIS FAX BUG

Please fully describe the 'bug' (specific steps to generate it, phone
numbers to call, make and model of fax/modem, rev of our ROM (from I3
command) ), why you believe that it is a bug, what specific section of
Class 2 applies to this bug and how you would like the bug to be fixed.
Please remember that there are issues that have not been addressed or
settled by the TR29.2 committee in the Class 2 specifications. (i.e. how
the DCD and DTR lines are handled while in fax mode.)


WHERE TO GET OFFICIAL FAX DOCUMENTATION

  Telecommunications Industry Association
  1722 Eye St. NW
  Suite 440
  Washington, DC  20006

You need to ask for:

    Class 1 documentation - EIA/TIA-578
    Class 2 documentation - Electronic Industries Association and
Telecommunications Industry Association TIA Project Number 2388,
Asynchronous Facsimile DCE Control Standard, Service Class 2, TR-29.2
Committee Letter Ballot

  Global Engineering Documents
  2805 McGaw Ave
  Irvin, CA  92713
  800-854-7179
  714-261-1455
  714-261-7892 (Fax)

You need to ask for:

    EIA/TIA-578 - Class 1 documentation
    EIA/TIA-592 - Class 2 documentation
    CCITT v7.3  - T.1 - T.90 standards, includes T.4 & T.30

(The cost for the above docs will run close to $200.  But Global will
also update you on any changes or additions to those standards you
purchase.)

Global Engineering will not have the Class 2 documentation until approx.
a month after the TR29.2 committee accepts it.  Most of those companies
which have developed Class 2 fax software either sit on the TR29.2
committee or know someone who does.  It may be possible to receive the
documentation from the TIA if you present a credible proposal.  Supra
has no knowledge of what this proposal should consist of or who you need
to talk to.


See also "CLASS 1 FAX COMMANDS FOR SUPRA FAXMODEMS" which is available
on Supra BBS.



6 FAX CLASS 1 OPERATION

6.1  FAX I/O PROCESSING

The fax I/O interface supports asynchronous serial and parallel
interfaces.  The interface rate is 19200 bps.  Start and stop elements
are removed from the transmit data and added to the receive data.  Both
transmit and receive data is buffered.  Flow control using XON/XOFF
(DC1/DC3) or RTS/CTS is provided.

Unique control character strings are identified, filtered, or reinserted
into the I/O data stream.  These control characters and their resultant
action are described below.

6.1.1 DTE TO MODEM TRANSMIT DATA STREAM

Characters Detected       Action taken

<DLE><data>               Delete <DLE><data> characters

<DLE><ETX>                Recognize as a string terminator, and take
                          appropriate action

<DLE><DLE>                Replace with single <DLE> character

6.1.2 MODEM TO DTE RECEIVE DATA STREAM

Characters Detected     Action taken

<DLE>                   Insert extra <DLE> ahead of <DLE>

The modem also identifies the end of a frame by inserting <DLE><ETX>
into the data stream after the FCS bytes.

6.1.3  FAX MODE SELECTION

Fax class 1 commands are identified in Table 6-1 and defined in Table 6-
2.  Fax modes and rates are determined by the AT+F commands as described
in Table 6-2.

6.1.4  FAX ORIGINATION

Origination of fax calls is made using the ATD command.  Upon completion
of the dial function, a calling tone at 1100 Hz, with a cadence of 0.5
seconds ON, and 3 seconds off is transmitted.  The modem automatically
enters mode +FRH=3 and sends the CONNECT message to the DTE when FSK
flags are detected from the remote.

6.1.5  FAX ANSWERING

Answering of fax calls is identical to answering of data calls with the
exception that the modem enters the fax handshaking mode instead of the
data handshaking mode after going off-hook.  If +FAE=0, the modem ,
after sending answer tone, automatically enters fax mode (+FTH=3), sends
the CONNECT message to the DTE, and starts sending FSK flags.  If
+FAE=1, the modem determines if the caller is a data modem or fax modem
and sends the DATA or FAX result code, respectively, to the DTE.

Table 6-1.  Fax Class 1 Commands

-----------------------------------------------------------
|   Command        Function                               |
|---------------------------------------------------------|
|   SERVICE CLASS ID                                      |
|---------------------------------------------------------|
|   +FCLASS=       Service Class                          |
|---------------------------------------------------------|
|   FAX CLASS 1 COMMANDS                                  |
|---------------------------------------------------------|
|   +FTS=n         Stop Transmission and Wait             |
|   +FRS=n         Receive Silence                        |
|   +FTM=n         Transmit Data                          |
|   +FRM=n         Receive Data                           |
|   +FTH=n         Transmit Data with HDLC Framing        |
|   +FRH=n         Receive Data with HDLC Framing         |
|---------------------------------------------------------|


6.1.6  FAX CONTROL TRANSMISSION

Fax control transmission is initiated by the AT+FTH=n command.  After
this command is issued, the modem generates the CONNECT message and
transmits carrier in the modulation scheme specified by the parameter n.
The modem then transmits HDLC flags for a minimum of 1 second.  The
modem continues to transmit the HDLC flags until it receives a character
from the DTE.

When characters are received from the DTE, the modem adds start and end
flags, performs zero-bit insertion, generates FCS, and deletes
<DLE><chr> character pairs before transmitting the characters to the
remote fax machine.  Each <DLE><DLE> sequence is transmitted as a single
<DLE>.  <DLE><ETX> is considered as the end of frame marker and is not
transmitted.  All data received from the DTE afar <DLE><ETX> is ignored
by the modem until the modem generates either the CONNECT, OK, or ERROR
result code.

If no more data is in the transmit buffer and the final bit was a 1 (bit
4 of the second byte received from the DTE), the modem generates the OK
result code and returns to the command mode.  If the final bit was a 0,
the modem generates the CONNECT message and waits for further data from
the DTE while transmitting HDLC flags.  If no more data is received
before 5 seconds elapse, the modem drops carrier, goes on-hook, and
generates the ERROR result code.

6.1.7  FAX CONTROL RECEPTION

Fax control reception is initiated using the AT+FRH=n command.  After
this command is issued, the modem looks for carrier in the modulation
scheme specified by the parameter n.  If no carrier is detected before
the period of time specified by register S7 expires, the modem generates
the NO CARRIER message and returns to command mode.  If carrier is
detected that is not the one specified by the parameter n, the modem
generates the +FCERROR message and returns to the command mode.  If the
specified carrier is detected, the modem generates the CONNECT message
and enters the HDLC receive mode.

In HDLC receive mode, the modem receives HDLC frames from the remote fax
machine, strips the flags, performs zero-bit deletion, performs error
checking, and handles <DLE><chr> character pairs before passing the data
to the DTE.  The modem prefixes each <DLE> character with another <DLE>
character before sending it to the DTE.  After the last byte in the
frame, the modem sends <DLE><ETX> to the DTE marking the end of the
frame.  The modem then generates either the OK message if errors were
detected (FCS is incorrect), and returns to command mode.

While in command mode, the modem continues to receive data in the
selected modulation scheme, and sends the data after sending the CONNECT
message to the DTE when the DTE reissues the +FRH command with the same
parameter.  If the DTE issues the +FRH command with a different
parameter, the modem clears all buffers and proceeds as described
previously.

If carrier is lost while in command mode and the DTE reissues the +FRH
command with the same parameter, and there is no data in the buffer, the
modem sends the ERROR result code to the DTE and returns to the command
mode.  If there is data in the buffer, the modem sends the next frame of
buffered data to the DTE, followed by <DLE><ETX>, and either the ERROR
result code if errors were detected or the OK result code if no errors
were detected.  The modem then returns to command mode.

The modem concludes an error is detected if the carrier is lost for any
period of time during or before the reception of a frame.  If carrier is
lost for a time period longer than the time specified by the register
S10, the modem finishes delivering the data in the receive buffer (if
any) to the DTE, sends <DLE><ETX>, generates the ERROR message, and
returns to command mode.  All subsequent data received from the remote
is discarded.

If the modem detects a frame abort sequence (seven consecutive ones with
no zero insertion) while it is waiting for a frame beginning flag (it
was receiving HDLC flags), it will wait for the HDLC flags again until
either carrier is lost, or the DTE aborts the process by sending an
abort character or by dropping DTR with &D2 in effect.  If the frame
abort sequence is detected while the modem is receiving a frame it
finishes delivering the data in the receive buffer (if any) to the DTE,
sends <DLE><ETX>, generates the ERROR message, and returns to command
mode.  The modem keeps looking for HDLC flags followed by more data from
the remote, with the selected modulation scheme.

If the modem detects a receive buffer overflow condition, it concludes
that there was a FCS error in that frame.  The modem will receive more
frames only if a starting flag is detected and there is room in the
receive buffer.  If a starting flag is detected and there is no room in
the buffer, the modem discards all data in that frame.

If the modem receives any character from the DTE after the +FRH command
(except flow control characters if software flow control is in effect),
or if the modem detects a high-to-low transition of the DTR signal while
&D1 is in effect, it sends <DLE><ETX> to the DTE, generates OK result
code, and returns to command mode.  The receive buffer is cleared and
all data received from the remote is discarded.  If the modem detects a
DTR drops while &D2 is in effect, it goes on-hook, sends <DLE><ETX> to
the DTE, generates OK result code, and returns to command mode.  If the
modem detects a DTR drop while &D3 is in effect, the modem performs a
warm reset.

6.1.8  FAX DATA TRANSMISSION

Fax Data transmission is initiated by the AT+FTM=n command.  After this command is issued, the modem generates the CONNECT message and transmits carrier in the modulation scheme specified by the parameter n.  The
modem then transmits constant 1 bits for a minimum of one second and
continues to transmit constant 1 bits until it receives a character from
the DTE.

When data is received from the DTE, the modem deletes start and stop
bits and deletes all <DLE><chr> character pairs before transmitting the
data to the remote.  Each <DLE><DLE> sequence is transmitted as a single
<DLE>.  <DLE><ETX> is considered as the end of stream marker, and is not
transmitted.  All data received from the DTE after the <DLE><ETX> is
ignored by the modem until the modem generates either the CONNECT, OK or
ERROR result code.

If no more data is in the transmit buffer, and the last transmitted
character was not an ASCII NULL, the modem generates the OK result code
and returns to the command  mode.  If the last character transmitted was
an ASCII NULL, the modem generates the CONNECT message to the DTE and
waits for further data from the DTE while transmitting NULLs to the
remote.  If more data is received before five seconds, elapse, the modem
continues to transmit the data as described in the previous paragraph.
If five seconds elapse and no data is received from the DTE, the modem
drops carrier, goes on-hook, and generates the ERROR result code.

6.1.9  FAX DATA RECEPTION

Fax data reception is initiated using the AT+FRM=n command.  After this
command is issued, the modem looks for carrier in the modulation scheme
specified by the parameter n. If no carrier is detected before the
period of time specified by register S7 expires, the modem generates the
NO CARRIER message and returns to command mode.  If carrier is detected
that is not the one specified by the parameter n, the modem generates
the +FCERROR message and returns to the command mode.  If the specified
carrier is detected, the modem generates the CONNECT message and enters
the data receive mode.

While in data receive mode, the modem receives data from the remote,
adds start and stop bits, and handles <DLE><chr> character pairs before
passing the data to the DTE.  The modem prefixes each <DLE> character
with another <DLE> character before sending it to the DTE.

If carrier is lost for a time period longer than the time specified by
the register S10, the modem finishes delivering the data in the receive
buffer (if any) to the DTE, sends <DLE><ETX>, generates the NO CARRIER
result code, and returns to the command mode.  All subsequent data
received from the remote is discarded.

If the modem detects a receive buffer overflow condition, it stops
receiving from the remote until there is room in the receive buffer.
The modem informs the DTE of the buffer overflow after it sends to the
DTE the last character that was stored in the buffer before the overflow
occurred.

If the modem receives any character from the DTE after the +FRM command
(except flow control characters if software flow control is in effect),
or if the modem detects a high-to-low transition of the DTR signal while
&D1 is in effect, it sends <DLE><ETX> to the DTE, generates the OK
result code, and returns to command mode.  The receive buffer is cleared
and all data received from the remote is discarded.  If loss of DTR is
detected while &D2 is in effect, the modem goes on-hook, sends
<DLE><ETX> followed by OK result code to the DTE, and returns to command
mode.  If the modem detects a DTR drop while &D3 is in effect, the modem
performs a warm reset.

6.2  EXAMPLES

Examples of calling (transmitting) and answering (receiving) one page
use fax class 1 commands are shown in Tables 6-3 and 6-4, respectively.

Table 6-2.  Fax Class 1 Command Definitions

Command         Description

+FCLASS=n     Select service class.  +FCLASS=n command set the active
                service class
                Parameters: 0-2
                  Default: 0
                Command options:
                  +FCLASS=0    Select Data Mode
                  +FCLASS=1    Select Facsimile class 1
                  +FCLASS=2    Select Facsimile class 2

+F<command>?  Report Active Configuration.  +F<command>? interrogates
              the modem to determine the active configuration.  Typical
              responses are:
                +FAE?     0 if autoanswer is disabled, 1 if auto answer
                          enabled.
                +FCLASS?  0 if in data mode; 1 if in fax class 1; 2 if
                          in fax class 2

+F<command>=?  Report Operating Capabilities.  +F<command>=? can be used
               to determine the operating capabilities of the modem.
               Typical responses are:
                 +FAE=?    0,1
                 +FCLASS=? 0,1,2
                 +FTM=?    3,24,48,72,96 (RC96AC)
                 +FRM=?    3,24,48,72,96 (RC96AC)
                 +FTM=?    3,24,48,72,73,74,96,97,98,121,122,145,146
                           (RC144AC)
                 +FRM=?    3,24,48,72,73,74,96,97,98,121,122,145,146
                           (RC144AC)

+FAEn          Data/Fax Auto Answer.  +FAEn allows the DTE to either
               restrict answering to class 1, or to automatically detect
               whether the calling station is a fax class 1 modem or
               data modem,, and answer accordingly.

               Parameters: 0,1
                   Default:0
               Command options:
                   n=0      Disable data/fax auto answer mode (default).
                            The modem answers as a fax modem only
                   n=1      Enable data/fax auto answer mode.  The modem
                            answers as a fax or data modem

+FTS=n         Stop Transmission and Wait.  +FTS=n causes the modem to
               terminate a transmission and wait for n 10 millisecond
               intervals before responding with the OK result code.  An
               ERROR response code results if this command is issued
               while the modem is on-hook.

+FRS=n         Receive Silence.  +FRS=n causes the modem to report back
               to the DTE with an OK result code after n millisecond
               intervals of silence have been detected on the line.
               This command is aborted if any character is received from
               the DTE.  The modem discards the aborting character and
               issues an OK result code.  An ERROR response code results
               if this command is issued while the mode is on-hook.

+FTM=n        Transmit Data.  +FTM=n causes the modem to transmit data
              using the modulation defined below.  An ERROR response
              code results if this command is issued while the modem is
              on-hook.

              Parameters:

              Command options:

                 +FTM=3     v.21 ch 2 300 bps
                 +FTM=24    v.27 ter 2400 bps
                 +FTM=48    v.27 ter 4800 bps
                 +FTM=72    v.29 7200 bps
                 +FTM=96    v.29 9600 bps
                 +FTM=73    v.17 7200 bps long
                 +FTM=74    v.17 7200 bps short
                 +FTM=96    v.29 9600 bps
                 +FTM=97    v.17 9600 bps long
                 +FTM=98    v.17 9600 bps short
                 +FTM=121   v.17 12000 bps long
                 +FTM=122   v.17 12000 bps short
                 +FTM=145   v.17 14400 bps long
                 +FTM=146   v.17 14400 bps short

+FRM=n       Receive Data.  +FRM=n causes the modem to enter the
             receiver mode using the modulation defined below.  An ERROR
             response code results if this command is issued while the
             modem is on-hook.

             Parameters:  See Command options

              Command options:

                 +FTM=3     v.21 ch 2 300 bps
                 +FTM=24    v.27 ter 2400 bps
                 +FTM=48    v.27 ter 4800 bps
                 +FTM=72    v.29 7200 bps
                 +FTM=96    v.29 9600 bps
                 +FTM=73    v.17 7200 bps long
                 +FTM=74    v.17 7200 bps short
                 +FTM=96    v.29 9600 bps
                 +FTM=97    v.17 9600 bps long
                 +FTM=98    v.17 9600 bps short
                 +FTM=121   v.17 12000 bps long
                 +FTM=122   v.17 12000 bps short
                 +FTM=145   v.17 14400 bps long
                 +FTM=146   v.17 14400 bps short

+FTH=n       Transmit data with HDLC Framing.  +FTH=n causes the modem
             to transmit data using HDLC protocol and the modulation
             defined below.  An ERROR response code results if this
             command is issued while the modem is on-hook.

             Parameters:  See Command options

              Command options:

                 +FTM=3     v.21 ch 2 300 bps
                 +FTM=24    v.27 ter 2400 bps
                 +FTM=48    v.27 ter 4800 bps
                 +FTM=72    v.29 7200 bps
                 +FTM=96    v.29 9600 bps
                 +FTM=73    v.17 7200 bps long
                 +FTM=74    v.17 7200 bps short
                 +FTM=96    v.29 9600 bps
                 +FTM=97    v.17 9600 bps long
                 +FTM=98    v.17 9600 bps short
                 +FTM=121   v.17 12000 bps long
                 +FTM=122   v.17 12000 bps short
                 +FTM=145   v.17 14400 bps long
                 +FTM=146   v.17 14400 bps short

+FRH=n     Receive data with HDLC Framing.  +FRH=n causes the modem to
           receive frames using HDLC protocol and the modulation defined
           below.  An ERROR response code results if this command is
           issued while the modem is on-hook.

           Parameters:  See Command options

              Command options:

                 +FTM=3     v.21 ch 2 300 bps
                 +FTM=24    v.27 ter 2400 bps
                 +FTM=48    v.27 ter 4800 bps
                 +FTM=72    v.29 7200 bps
                 +FTM=96    v.29 9600 bps
                 +FTM=73    v.17 7200 bps long
                 +FTM=74    v.17 7200 bps short
                 +FTM=96    v.29 9600 bps
                 +FTM=97    v.17 9600 bps long
                 +FTM=98    v.17 9600 bps short
                 +FTM=121   v.17 12000 bps long
                 +FTM=122   v.17 12000 bps short
                 +FTM=145   v.17 14400 bps long
                 +FTM=146   v.17 14400 bps short

Table 6-3  Fax Class 1 Calling Sequence (One Page)

|----------------------------------------------------------------------|
| DTE Commands | DCE Responses    | Remote Fax      |     Notes        |
|--------------|------------------|-----------------|------------------|
| AT+FCLASS=1  | OK               |                 | Set to Class 1   |
|----------------------------------------------------------------------|
|                         PHASE A                                      |
|----------------------------------------------------------------------|
| ATDTx        | dials            | answers         | +FRH=3 implied by|
|              |                  |                 | dialing          |
|              | CONNECT          | Send HDLC flags |                  |
|----------------------------------------------------------------------|
|                         PHASE B                                      |
|----------------------------------------------------------------------|
|              |                  | Send NSF frame  |                  |
|              | <NSF>,OK         |                 |                  |
| AT+FRH=3     | CONNECT          |                 |                  |
|              |                  | Send CSI frame  |                  |
|              | <CSI>,OK         |                 |                  |
| AT+FRH=3     | CONNECT          |                 |                  |
|              |                  | Send DIS frame  | Last frame bit=1 |
|              | <DIS>,OK         | drop carrier    |                  |
| AT+FTH=3     | Send HDLC flags  | receive flags   |                  |
|              | CONNECT          |                 |                  |
| <TSI>        | Send TSI frame   | Receive TSI     | Last frame bit=0 |
|              | CONNECT          |                 |                  |
| <DCS>        | Send DCS frame   | Recieve DCS     | Last frame bit=1 |
|              | detect last frame|                 |                  |
|              | bit              |                 |                  |
|              | <OK>,drop carrier|                 |                  |
| AT+FTS=8     | <OK>,wait 80ms   |                 |                  |
| AT+FTM=96    | send v.29        |                 |                  |
|              | CONNECT          |                 |                  |
| <TCF>        | Send TCF data    | Receive & check |                  |
| AT+FRH=3     | CONNECT          |                 |                  |
|              | Send CFR frame   |                 | Last frame bit=1 |
| <CFR>,OK     | drop carrier     |                 |                  |
|              | OK               |                 |                  |
|----------------------------------------------------------------------|
|                        PHASE C                                       |
|----------------------------------------------------------------------|
| AT+FTM=96    | send v.29        |                 |                  |
|              | CONNECT          |                 |                  |
| age data     | send page data   | receive data    |                  |
|              | OK               |                 |                  |
| AT+FTH=3     | send HDLC flags  | receive flags   |                  |
|              | CONNECT          |                 |                  |
|----------------------------------------------------------------------|
|                        PHASE D                                       |
|----------------------------------------------------------------------|
| <EOP>        | send EOP frame   | receive EOP     | Last frame bit=1 |
|              | OK,drop carrier  |                 |                  |
| AT+FRH=3     | CONNECT          |                 |                  |
|              |                  | send MCF frame  | Last frame bit=1 |
|              | <MCF>,OK         |                 |                  |
| AT+FTH=3     | send HDLC flags  | receive flags   |                  |
|              | CONNECT          |                 |                  |
| <DCN>        | send DCN frame   | receive DCN     | Last frame bit=1 |
|              | OK,drop carrier  |                 |                  |
|----------------------------------------------------------------------|
|                        PHASE E                                       |
|----------------------------------------------------------------------|
| ATH0         | OK,hang up       | hang up         |                  |
|----------------------------------------------------------------------|

Table 6-4  Fax Class 1 Answering Sequence (One Page)

|----------------------------------------------------------------------|
| DTE Commands | DCE Responses    | Remote Fax      |     Notes        |
|--------------|------------------|-----------------|------------------|
| AT+FCLASS=1  | OK               |                 |                  |
|----------------------------------------------------------------------|
|                        PHASE A                                       |
|----------------------------------------------------------------------|
|              |                  | Fax machine dial|                  |
|              | RING             |                 |                  |
| ATA          | modem answers    |                 |                  |
|              | send HDLC flags  | receive flags   | +FTH=3 implied by|
|              |                  |                 | answering        |
|              | CONNECT          |                 |                  |
|----------------------------------------------------------------------|
|                        PHASE B                                       |
|----------------------------------------------------------------------|
| <NSF>        | send NSF frame   | receive NSF     | last frame bit=0 |
|              | CONNECT          |                 |                  |
| <CSI>        | send CSI frame   | receive CSI     | last frame bit=0 |
|              | CONNECT          |                 |                  |
| <DSI>        | send DSI frame   | receive DSI     | last frame bit=1 |
|              | OK, drop carrier |                 |                  |
| AT+FRH=3     | CONNECT          |                 |                  |
|              |                  | send TSI frame  | last frame bit=0 |
|              | <TSI>,OK         |                 |                  |
| AT+FRH=3     | CONNECT          |                 |                  |
|              |                  | send DCS frame  | last frame bit=1 |
|              | <DCS>,OK         | drop carrier    |                  |
| AT+FRM=96    |                  |                 |                  |
|              |                  | send v.29       |                  |
|              | CONNECT          | send TCF frame  |                  |
|              | <TCF>            | drop carrier    |                  |
|              | NO CARRIER       |                 |                  |
| AT+FTH=3     | CONNECT          |                 |                  |
| <CFR>        | send CFR frame   | receive CFR     | last frame bit=1 |
|              | OK,drop carrier  |                 |                  |
|----------------------------------------------------------------------|
|                        PHASE C                                       |
|----------------------------------------------------------------------|
| AT+FRM=96    |                  |                 |                  |
|              |                  | send page data  |                  |
|              | <page data>      | drop carrier    |                  |
|              | NO CARRIER       |                 |                  |
|----------------------------------------------------------------------|
|                        PHASE D                                       |
|----------------------------------------------------------------------|
| AT+FRH=3     | CONNECT          |                 |                  |
|              |                  | send EOP frame  | last frame bit=1 |
|              | <EOP>,OK         |                 |                  |
| AT+FTH=3     | CONNECT          |                 |                  |
| <MCF>        | send MCF frame   | receive MCF     | last frame bit=1 |
|              | OK,drop carrier  |                 |                  |
| AT+FRH=3     | CONNECT          |                 |                  |
|              |                  | send DCN frame  | last frame bit=1 |
|              | <DCN>,OK         |                 |                  |
|----------------------------------------------------------------------|
|                        PHASE E                                       |
|----------------------------------------------------------------------|
| ATH0         | OK,hang up       | hang up         |                  |
|----------------------------------------------------------------------|