___________________________________________________________________________________
___________________________________________________________________________________
138 RG-5400 Subscriber router
5
CONNECTION ESTABLISHMENT ALGORITHM
5.1
Algorithm of a Successful Call via SIP
SIP (Session Initiation Protocol) 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.
