NAL Research Corporation (TN2012-02-V1.0)
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This command is not abortable, and finishes without waiting for a response from the network.
The interaction of this command with other commands based on other GSM supplementary
services is described in the GSM standard.
The following parameter values are currently supported:
<n>:
“0”
Releases all held calls or sets User Determined User Busy (UDUB) for a waiting call
“1”
Releases all active calls (if any exist) and accepts the other (held or waiting) call
“1X”
Releases a specific active call X
“2”
Places all active calls (if any exist) on hold and accepts the other (held or waiting)
call
“2X”
Places all active calls on hold except call X with which communication shall be
supported
“3”
Adds a held call to the conversation
“4”
Not supported (Connects the two calls and disconnects the subscriber from both
calls (ECT))
“4*dirno”
Not supported (Redirect an incoming or a waiting call to the specified
directory number)
“5”
Not supported ($(CCBS)$: Activates the Completion of Calls to Busy Subscriber
Request)
Test Command:
+CHLD=?
Test command returns the <n> values supported by the phone. The response is in the form:
+CHLD:(list of supported <n>s)
Note:
“AT+CHLD=0” can be used to set UDUB when there is an incoming call, whether or not
there is a current call active (or held), in order to support GSM 02.30 [5] subclauses 4.4.2.3
and 4.5.5.2.
A.8.121 +XCSI – Extended Call State Information
This proprietary unsolicited announcement was added to allow the DTE to keep track of call
state during Call Hold and Multiparty operations using AT+CHLD.
Exec Command:
none
Unsolicited Announcement:
+XCSI=<overall call_state>,<active call_state>,<held_call state>,<active index>,<held
index>
where:
<overall call_state>:
0
Idle (dialling possible)
1
One single-party call active
2
One multiparty call active
3
Incoming call arriving (otherwise idle)
4
One single-party call active, plus waiting call