Session Agents Session Groups and Local Policy

When you configure session routing for SIP and H.323, you can use session agents, session agent groups and local policies to define routing. (Using session agents and session agent groups is not required.)

• session agent: defines a signaling endpoint. It is a next hop signaling entity that can be configured to apply traffic shaping attributes.
• session agent group (SAG): contains individual session agents. Members of a SAG are logically equivalent (although they might vary in their individual constraints) and can be used interchangeably.

  You apply an allocation strategy to the SAG to allocate traffic across the group members. Session agent groups also assist in load balancing among session agents.

• local policy: indicates where session request messages, such as SIP INVITES, are routed and/or forwarded. You use a local policy to set a preference for selecting one route over another.

Another element of routing is the realm. Realms are used when an SBC communicates with multiple network elements over a shared intermediate connection. Defining realms allows sessions to go through a connection point between the two networks.

When you configure a realm, you give it an identifier, which stores the name of the realm associated with a sip-interface. The realm identifier value is also needed when you configure session agents and local policies. You can associate a realm with a session agent to identify the realm for sessions coming from or going to the session agent. You also need the realm identifier when you configure local policy to identify the egress realm (realm of the next hop).