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

Supra Corporation
7101 Supra Drive SW, Albany, OR  97321
General (503) 967-2400 / Sales (503) 967-2410 / Fax (503) 967-2401
Supra Tech Support  (503) 967-2440  8:00am - 5:00pm PST, M-F

Supra BBS........(503) 967-2444  24 Hours
CompuServe.......76004,565
BIX..............SupraCorp
America Online...SupraCorp2
GEnie............SupraTech
AppleLink........D2456
UseNet EMail.....supratech%supra.uucp@cs.orst.edu
            .....supra!supratech@cs.orst.edu

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         |                  |
|----------------------------------------------------------------------|
