Version 5.8 423 September 2009
SIP User's Manual 9. IP Telephony Capabilities
9.15.1 Call Hold and Retrieve
Initiating Call Hold and Retrieve:
The party that initiates the hold is called the
Active calls can be put on-hold by pressing the phone's hook-flash button.
holding party; the other party is called the
held
After a successful Hold, the holding party hears a Dial tone (HELD_TONE defined in
the device's Call Progress Tones file).
party.
Call retrieve can be performed only by the holding party while the call is held and
active.
After a successful retrieve, the voice is connected again.
The holding party performs the retrieve by pressing the telephone's hook-flash button.
Receiving Hold / Retrieve:
Hold is performed by sending a Re-INVITE message with IP address 0.0.0.0 or
a=sendonly in the SDP according to the parameter HoldFormat.
When an active call receives a Re-INVITE message with either the IP address 0.0.0.0
or the ‘inactive’ string in SDP, the device
stops sending RTP and plays a local Held
tone.
You can also configure the device to keep a call on-hold for a user-defined time after which
the call is disconnected, using the ini file parameter HeldTimeout (refer to ''Configuring
Supplementary Services'' on page
When an active call receives a Re-INVITE message with the ‘sendonly’ string in SDP,
the device stops sending RTP and listens to the remote party. In this mode, it is
expected that on-hold music (or any other hold tone) is played (over IP) by the remote
party.
114).
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