Overview

You establish SIP server redundancy by creating session agents, which are virtual representations of the SIP signaling entities. These agents are then collected into a session agent group, which is a logical collection of two or more session agents that behaves as a single aggregate entity.

Rather than direct signaling messages to a single session agent (IP), the signaling message is directed to a session agent group (SAG). The group will have a set distribution pattern: hunt, round robin, proportionally distributed, and so on. Signaling is spread amongst the agents using this chosen pattern.

You direct the signaling message by configuring a route policy, known as a local policy, which determines where SIP REQUESTS should be routed and/or forwarded. The values in the To and From headers in the SIP REQUEST are matched with the content of the local policy within the constraints set by the session agent’s previous hop value and SIP interface values such as the list of carriers.

To summarize, you need:

• two or more session agents
• a session group containg those session agents
• a local policy which directs traffic to the session agent group