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Chapter 5 – Call Control Commands
Multi-Tech Systems, Inc. Wireless GSM/GPRS AT Commands (Document Number S000293I) 21
Answer a Call A
Description: When the product receives a call, it sets the RingInd signal and sends the ASCII “RING” or “+CRING:
<type>” string to the application (+CRING if the cellular result code +CRC is enabled). Then it waits for
the application to accept the call with the ATA command.
Values: No parameters.
Syntax: ATA
Command Possible responses
RING
Note: Incoming call
ATA
Note: Answer to this incoming call
OK
Note: Call accepted
ATH
Note: Disconnect call
OK
Note: Call disconnected
Remote Disconnection
This message is used by the product to inform the application that an active call has been released by the remote user.
The product sends “NO CARRIER” to the application and sets the DCD signal.
In addition, for AOC, the product can release the call if credit has expired (release cause 68 with +CEER command).
Extended Error Report +CEER
Description: This command gives the cause of call release when the last call set up (originating or answering) failed.
Values: No parameters
Syntax: AT+CEER
Command Possible responses
ATD123456789;
Note: Outgoing voice call
NO CARRIER
Note: Call setup failure
AT+CEER
Note: Ask for reason of release
+CEER: Error <xxx>
OK
Note: <xxx>is the cause information element values
from GSM recommendation 04.08 or specific Call
accepted
Note: “NO CARRIER” indicates that the AT+CEER information is available for failure diagnosis.
DTMF Signals +VTD, +VTS
+VTD
Description: The product enables the user application to send DTMF tones over the GSM network. This command is
used to define tone duration (the default value is 70 ms ± 5 ms according to 3GPP 23.014).
Values: <n> tone duration.
This refers to an integer <n> that defines the length of tones emitted as a result of the +VTS
command. This does not affect the D command.
A value different than zero causes a tone of duration <n> *100 milliseconds.
A value of zero (default value) causes a tone duration of 70 ms ± 5 ms.
Note: The value is used modulo 256.