Configuring Supplementary Services; Call Hold And Retrieve - AudioCodes Mediant 800 User Manual

CHAPTER 28 Configuring Supplementary Services
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Configuring Supplementary Services

This section describes the Gateway application's SIP supplementary services that can enhance
your telephone service.
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Call Hold and Retrieve

For analog interfaces: Initiating call hold and retrieve:
■ Active calls can be put on-hold by pressing the phone's hook-flash button.
■ The party that initiates the hold is called the holding party; the other party is called the held
party.
■ After a successful Hold, the holding party hears a dial tone (HELD_TONE defined in the
device's Call Progress Tones file).
■ Call retrieve can be performed only by the holding party while the call is held and active.
■ The holding party performs the retrieve by pressing the telephone's hook-flash button.
■ After a successful retrieve, the voice is connected again.
■ 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 HoldFormat parameter.
For digital interfaces: Call hold and retrieve:
■ The party that initiates the hold is called the holding party; the other party is called the held
party.
■ After a successful Hold, the holding party hears a dial tone (HELD_TONE defined in the
device's Call Progress Tones file).
■ After a successful retrieve, the voice is connected again.
■ The hold and retrieve functionalities are implemented by re-INVITE messages. The IP address
0.0.0.0 as the connection IP address or the string 'a=inactive' in the received re-INVITE SDP
cause the device to enter Hold state and to play the held tone (configured in the device) to the
PBX/PSTN. If the string 'a=sendonly' is received in the SDP message, the device stops
sending RTP packets, but continues to listen to the incoming RTP packets. Usually, the
remote party plays, in this scenario, Music on Hold (MOH) and the device forwards the MOH to
the held party.
For analog interfaces: Receiving Hold/Retrieve:
■ When an active call receives a re-INVITE message with IP address 0.0.0.0 or 'inactive' string
in SDP, the devicestops sending RTP and plays a local held tone.
■ 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
music on-hold (or any other hold tone) is played (over IP) by the remote party.
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 HeldTimeout parameter.
The device also supports "double call hold" for FXS interfaces where the called party, which has
been placed on-hold by the calling party, can then place the calling party on hold as well and make a
call to another destination. The flowchart below provides an example of this type of call hold:
All call participants must support the specific supplementary service that is used.
When working with certain application servers (such as BroadSoft's BroadWorks)
in client server mode (the application server controls all supplementary services
and keypad features by itself), the device's supplementary services must be
disabled.
Mediant 800 Gateway & E-SBC | User's Manual
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