Appendix B – Detailed Examples
Multi-Tech Systems, Inc. AT Commands for Wireless Modems with IP Connectivity (S000333D)
58
Automatic Call-Back to Incoming Calls
This example covers the following: When an incoming call is received, the modem validates the associated CLI (Calling
Line Identity), ignores (doesn’t answer) the call and then automatically dials a pre-defined phone number.
Description:
When receiving an incoming call it is possible for the attached equipment to either accept the call, let
the modem answer the call automatically, or to not answer the call and then let the modem
automatically call a pre-defined number using the ‘call-back mechanism’.
This application note addresses the ‘automatic call-back’ mechanism implemented in the modem.
Configuration:
Configuration
•
RINGCOUNT and ANSWERMODE must be configured in accordance with the ATS0
configuration for not interacting.
•
The CALLSCREENNUM parameter configuration with a decimal phone number needs the caller
line identity service from the operator and the AT+CLIP=1 command sent to the software.
AT#RINGCOUNT
Automatic
call-back activation
When this parameter is set to 2 or 3, the modem will not answer an incoming call, but instead
automatically :
•
Calls back either of the DIALN1 or DIALN2 numbers (depending on the DIALSELECT
parameter setting) or attempts a GPRS connection (depending on the GPRSMODE parameter
setting) if ANSWERMODE is set to 2 by internally issuing an AT#CONNECTIONSTART
command-- if the associated CLI (Calling Line Identity) matches the CALLSCREENNUM
parameter.
•
Calls back the caller number (CALLSCREENNUM number) if ANSWERMODE is set to 3 by
internally issuing an AT#CONNECTIONSTART command-- if the associated CLI (Calling Line
Identity) matches the CALLSCREENNUM parameter.
AT#ANSWERMODE =
2
Æ
call back the ISP or attempt GPRS connection.
AT#ANSWERMODE =
3
Æ
call back the caller (dependant on the CALLSCREENNUM number
parameter setting).
Caller ID validation When the GSM line subscription includes the caller ID service, it is possible to direct the modem to
validate the CLI (Calling Line Identity) of the incoming call before executing the ‘call back’
mechanism. Please take care of its format, communicated by the network. The default value = 0
deactivate the mechanism.
If no check is necessary the CALLSCREENNUM parameter must be set to ‘*’.
AT#CALLSCREENNUM
Timer before call-
back
When the ‘+CRING’ signals have ceased on the GSM line, it is possible to configure the time (in
seconds) that the modem will wait before going off hook and dialing the DIALN1 or DIALN2 phone
number, or attempt to make a GPRS connection.
AT#CALLBACKTIMER
Operation:
Validation of CLI
before call back
When receiving an incoming call, the modem ignores the call but still validates the associated CLI
(Calling Line Identity) against the CALLSCREENNUM parameter.
If the associated CLI (Calling Line Identity) and CALLSCREENNUM don’t match, no further
operations take place.
If the associated CLI (Calling Line Identity) matches the CALLSCREENNUM parameter, the
modem waits for the last RING signal and then for the CALLBACKTIMER period before going off
hook and initiating the call back mechanism, by internally issuing the AT#CONNECTIONSTART
command.
The process is then similar to the standard AT#CONNECTIONSTART process, using
GPRSMODE.
Other AT Parameters:
AT#PPPMODE, GPRSMODE
Other AT# Commands:
AT#CONNECTIONSTART
