120 VoIP Subscriber Gateways
Access to this service is established via subscriber port settings menu 'FXS' by selecting
'Attended calltransfer', 'Unattended calltransfer', or 'Local Calltransfer' in 'Flash transfer' field and
selecting 'Call waiting' checkbox.
Service usage:
If you receive a new call while being in a call state, you may do the following:
- R 0 — reject a new call;
- R 1 — answer the waiting call;
- R 2 — switch to a new call;
- R – short clearback (flash).
4.3 Three-way conference call
Three-way conference is a service, that enables simultaneous phone communication for 3
subscribers. For entering conference mode, see Section Call transfer.
Subscriber that started the conference seems to be its initiator; two other subscribers are the
participants.
Two modes are available: local and remote; in the first mode, the conference is established
locally by the initiator subscriber; in the second, the conference is established using a remote server,
the so-called conference server.
4.3.1 Local conference
In the conference mode, short clearback 'flash' pressed by the initiator is ignored. Signalling
protocol messages, received from the participants and intended to put the initiator side into hold
mode, force this participant to leave the conference. At that, the initiator and the second participant
will switch into the ordinary two-party call mode.
The conference terminates, when initiator leaves; in this case, both participants will receive
clearback message. If one of the participants leaves the conference, the initiator and the second
participant will switch into a standard two-party call. Short flash clearback is processed as described in
Sections 4.1 and 4.2.
Figure below shows an algorithm of '3-way conference' service performed locally by the initiator
via SIP protocol.
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