Fax Operation
V.3600
9-5
AT Responses to the ATD Command
The function of this command is country-specific. The AT responses to
the ATD command are as follows:
NUMBER LIST FULL
Call failure; the delayed number list cannot store any more numbers.
DELAYED NUMBER WAIT xx MINUTES
Call failure; the number is on the delayed list and the call is delayed xx
minutes.
After dialing the specified number in fax mode, the modem generates
1100 Hz CNG tones in accordance with T.30 while trying to detect
either CED (answer back tone) or the HDLC preamble of the first T.30
frame. The CNG tones cease after detecting either of these two signals.
To allow proper interaction with manually answered fax stations,
detection of CED is not required. After detecting 1650 Hz (i.e., the
HDLC preamble of the first frame), the modem enters V.21 Channel 2
receive state with HDLC framing and returns a
CONNECT
result code.
This is because dialing in fax mode (
+FCLASS=1
) implies an initial
+FRH=3
command described in the “Fax Transmit and Receive Modes”
section on pa ge9-7.
Answer Command — A
The
A
command instructs the modem to answer the call. For fax
operation, set the modem for Service Class 1 operation before the
A
command is issued; use the
+FCLASS=1
command.
If the modem is in the on-line command state when an answer command
is issued (e.g., a connection is already established), the modem returns
an
ERROR
result code. Otherwise, it answers the call and generates a
2100 Hz CED (answer back) tone in accordance with T.30. The modem
then enters V.21 Channel 2 transmit state with HDLC framing and
returns a
CONNECT
result code. This is because answering a call in
fax mode (
+FCLASS=1
) implies an initial
+FTH=3
command
described in the “Fax Transmit and Receive Modes” section on
page 9-7. To allow proper interaction with a manually originated fax call
(in accordance with T.30), the modem does not require detection of
CNG before generating CED or entering HDLC transmit mode.
Summary of Contents for V.3600 Series
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