@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ @ @ @ FAX CLASS 1 CALL SELECTION SPECIFICATION @ @ @ @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ U.S. Robotics, Inc. 8100 North McCormick Boulevard Skokie, IL 60076-2999 INTRODUCTION ------------ The following defines the DCE Control mechanism for U. S. Robotics Data & Facsimile modems that provide automatic received Call Discrimination and Selection. This definition assumes that the DTE initiates in a fax state and turns control over to a Data mode program when a data call is detected by the DCE. DETECTING A FAX CALL -------------------- The DTE software starts by placing the modem in Fax mode by issuing an AT+FCLASS=1, and then turning on Call Selection with AT+FAA=1. The modem answers an incoming call using an ATS0 or an ATA from the DTE, and then goes off hook and looks for 100ms of 1100Hz of calling tone. This 1100Hz detector runs for 3.2 seconds. If a calling tone is detected, the modem sends the "FAX" message to the DTE, and then sends 2100Hz for 3 seconds, followed by V.21 channel 2 flags. A CONNECT response is sent to the DTE at the start of the flag data. The DTE software then negotiates in Fax mode. If a calling tone is not detected during the 3.2 second period, the normal Data mode answer tones are sent. If a connection is established in Data mode, the modem sends the "DATA" message to the DTE, and goes into on-line command mode. The DTE sends an initialization string, followed by an ATO. The ATO command instructs the modem to go back on-line and issue the CONNECT [rate] message. When the data pump determines that a Data mode connection cannot be established, the modem falls back to Fax mode. A 2100 Hz tone is sent, followed by V.21 channel 2 flags and a CONNECT message. INVOCATION OF MODE ------------------ NOTE: This command is only valid while in Fax mode (+FCLASS=1). Command: +FAA=[mode] Options: AT+FAA =0 Disable Call Selection =1 Enable Call Selection =? Returns possible +FAA values [0,1] Command: AT+FAA? returns the current value of +FAA= [0 or 1]. NOTE: The +FAA parameter is set to zero when the AT+FCLASS=0 command is issued. CONNECT RESPONSES ----------------- Verbal response: FAX Numeric response: 64 The FAX connect response is returned after a call has been answered under Call Selection (+FAA=1) and detected as a fax call. After the FAX response is returned, the DCE sends a 2100 Hz fax answer tone for 3 seconds. Verbal response: CONNECT Numeric response: 1 The CONNECT response is returned after the DCE begins transmitting HDLC flags in the V.21 HDLC transmit state. This indicates to the DTE that the DCE is ready to receive HDLC T.30 frame data. The CONNECT response follows the FAX connect message after a fax call is detected. If data is not received from the DTE in response to this CONNECT message, the modem will return to the on-hook state. Any character from the DTE in response to the CONNECT message will cause the DCE to remain in the off-hook state. We recommend that the S19 inactivity timer be used to prevent the modem from remaining in the off- hook state if the fax/data software does not properly distinguish the FAX response. Verbal response: DATA Numeric response: 63 The DATA connect response is returned after a call has been answered under Call Selection (+FAA=1) and is detected as a data call. The DATA message is sent when the DCE successfully establishes a data connection, and switches to the command state. The ATO command is then used by the DTE to return the DCE to the on-line state. Response: CONNECT [rate] The CONNECT [rate] response is returned after the DTE issues the ATO command to return the DCE to the on-line state. This is in response to a DATA connect message (see DATA response). The [rate] value is the rate at which the modem connects in answer mode.