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16. SUPPLEMENTARY SERVICES
249
LZT 123 7361 R1B
16.13 AT+CHLD Call Hold and Multiparty
This command allows control of the following call related services:
• a call can be temporarily disconnected from the ME but the
connection is retained by the network;
• multiparty conversation (conference calls);
• the served subscriber who has two calls (one held and the other
either active or alerting) can connect the other parties and release the
served subscriber's own connection.
Calls can be put on hold, recovered, released, added to conversation,
and transferred similarly as defined in 3GPP TS 22.030.
This is based on the GSM/UMTS supplementary services HOLD (Call
Hold; refer 3GPP TS 22.083 clause 2), MPTY (MultiParty; refer 3GPP
TS 22.084) and ECT (Explicit Call Transfer; refer 3GPP TS 22.091).
The interaction of this command with other commands based on other
GSM/UMTS supplementary services is described in the GSM/UMTS
standards.
Note! Call Hold and MultiParty are only applicable to teleservice 11.
It is recommended (although optional) that test command returns a list
of operations which are supported. The call number required by some
operations is denoted by “x” (e.g. +CHLD: (0,0x,1,1x,2,2x,3)).
Description Command Possible Responses
Request call related
supplementary services
AT+CHLD=<n> • +CME ERROR <err>
•OK
• ERROR
Show if the command is
supported
AT+CHLD=? • +CHLD: (list of
supported <n>s)
• +CME ERROR <err>
•OK
• ERROR
<n> Description
... Integer type; equals to numbers entered before SEND button in GSM
02.30 subclause 4.5.5.1
0 Releases all held calls or sets User Determined User Busy (UDUB) for
a waiting call
0X Releases a specific call X from a held multiparty call
1 Releases all active calls (if any exist) and accepts the other (held or
waiting) call
1X Releases a specific active call X