____________________________________________________________________________________
____________________________________________________________________________________
114
TAU-4M.IP Subscriber gateway
4
CONNECTION ESTABLISHMENT ALGORITHMS
4.1
Algorithm of a Successful Call via SIP Protocol
SIP is a session initiation protocol, that performs basic call management tasks such as starting and
finishing session.
SIP defines 3 basic connection initiation scenarios: between users, involving proxy server, involving
forwarding server. Basic connection initiation algorithms are described in IETF RFC 3665. This section describes
an example of a connection initiation scenario via SIP between two gateways that know each other IP addresses
in advance.
Algorithm description:
1.
Subscriber A rings up Subscriber B.
2.
Subscriber B gateway receives the command for processing.
3.
Subscriber B is free. In this moment, 'ringing' tone is sent to the Subscriber B phone, and
'ringback' tone to Subscriber A phone.
4.
Subscriber B answers the call.
5.
Subscriber A gateway confirms session establishment.
6.
Subscriber A clears back, 'busy' audio tone is sent to the Subscriber B.
7.
Subscriber B gateway confirms received clearback command.
