ELTEX TAU-36.IP - 8 Connection Establishment Algorithms; Algorithm of a Successful Call Via SIP Protocol

________________________________________________________________________________
_________________________________________________________________________________
Universal Network Terminal TAU-72.IP/TAU-36.IP 233
8 CONNECTION ESTABLISHMENT ALGORITHMS
8.1 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.
Fig. 15—SIP call algorithm
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.