                   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         |                  |

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



