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TAU-4M.IP Subscriber gateway
4.3
Call Algorithm Involving Forwarding Server
This section describes a connection initiation scenario between two gateways involving forwarding server.
In this case, caller gateway (Subscriber A) establishes connection unassisted, and the forwarding server only
translates callee permanent address into its current address. Subscriber obtains forwarding server address from
the network administrator.
Algorithm description:
1.
Subscriber A rings up Subscriber B. Forwarding server receives the command for processing.
2.
Forwarding server receives the command for processing.
3.
Forwarding server requests the information on the Subscriber B current address from the location
server. Received information (the callee current address and the list of callee registered addresses)
is sent to Subscriber A in '302 moved temporarily' message.
4.
Subscriber A gateway confirms the reception of reply from the forwarding server.
5.
Subscriber A rings up Subscriber B directly.
6.
Subscriber B gateway receives the command for processing.
7.
Subscriber B is free. Subscriber B is free. In this moment, 'ringing' tone is sent to the Subscriber B
phone, and 'ringback' tone to Subscriber A phone.
8.
Subscriber B answers the call.
9.
Subscriber A gateway confirms session establishment.
10.
Subscriber A clears back, 'busy' audio tone is sent to the Subscriber B.
11.
Subscriber B gateway confirms received clearback command.
