Data/FAX Answer Procedure (FAX Class 2)

Data/FAX Answer Procedure (FAX Class 2.0)

When +FCLASS=2.0, the +FAA parameter determines whether the modem answers in the FAX mode or determines the mode during handshake. The outcome is the same for answering in response to the A command and autoanswering.

+FCLASS     +FAA     Procedure                                               

                                                                             

                                                                             

0           0        Answer as data modem                                    

                                                                             

                                                                             

0           1        Answer as data modem                                    

                                                                             

                                                                             

2.0         0        Answer as FAX modem                                     

                                                                             

                                                                             

2.0         1        Automatic data/FAX answer

If +FAA=1 and +FCLASS=2.0, then the silent period after an answer modem goes off hook is 4 seconds instead of the usual 2 seconds. This allows time to detect a FAX calling tone before sending answer tone.

The DTE speed should be set high enough to handle a FAX Class 2.0 call if answered. If a FAX calling tone is detected, the modem sends the +FCO result code before sending any other result codes. If a calling data modem is detected, the modem changes +FCLASS value to 0 and sends the +FDM result code before any other result codes.

A new procedure for carrier handshake is defined here to allow an answering modem to determine if the calling modem is a FAX modem. When the value of the parameter +FAA is 0, the normal data handshake is used. When the value of the parameter is 1, the following procedure is used by an answering modem.

Step 1   If FAX calling tone is detected, then send the T.30 DIS signal, and    

         attempt to connect per T.30, as a Class 2.0 DCE. If successful, set     

         +FCLASS to 2.0 and issue appropriate connect result codes. If FAX       

         calling tone is not detected, then go to step 2.                        

                                                                                

                                                                                

Step 2   Send V.25 answer tone for 3.3 +/- 0.7 seconds, followed by 75 +/- 20 ms 

         of silence. If the V.32 signal AA is received and V.32 or V.32bis is    

         enabled, then send AC and connect per V.32bis. If AA is not detected, go 

         to step 3.                                                              

                                                                                

                                                                                

Step 3   Send USB1 (unscrambled binary ones at 1200 bits/s, per V.22) for 3000  

         +/- 50 ms. If AA is detected during this time and V.32 or V.32bis is    

         enabled, send AC and connect per V.32bis. If the V.22bis signals SB1 or 

         S1 are detected during this time, send SB1 or S1, respectively, and     

         connect per V.22bis. If a 1270 Hz tone (from a Bell 103 modem) is       

         detected, send 2225 Hz and connect per Bell 103. If the time (3000 ms)  

         expires and no response has been detected, go to step 4.                

                                                                                

                                                                                

Step 4   Stop sending USB1, send the T.30 DIS signal, and attempt to connect per 

         T.30, as a Class 2.0 DCE. If successful, set +FCLASS to 2.0 and issue   

         appropriate result codes. If not successful, hang up.

Note: Other modem types may be prompted after step 4, after a suitable timeout period. Step 4 shows where the FAX prompt should be inserted into the normal Hayes carrier handshake process. Subsequent steps, if any, should follow normal Hayes practice.

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