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Universal Network Terminal TAU-32M.IP 261
10.
SIP server translates Subscriber A call request directed at Subscriber B.
11.
Subscriber B gateway receives the command for processing.
12.
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.
13.
Subscriber B answers the call.
14.
Subscriber A gateway confirms session establishment.
15.
Subscriber A clears back, 'busy' audio tone is sent to the Subscriber B.
16.
Subscriber B gateway confirms received clearback command.
8.3
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.
Fig. 23—Call algorithm involving forwarding server
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.