SIP Session Agent Group Recursion
You can configure a SIP session agent group (SAG) to try all of its session agents rather than to the next-best local policy match if the first session agent in the SAG fails.
With this feature disabled, the Oracle® Enterprise Session Border Controller performs routing by using local policies, trunk group URIs, cached services routes, and local route tables. Local policies and trunk group URIs can use SAGs to find the most appropriate next-hop session agent based on the load balancing scheme you choose for that SAG: round robin, hunt, proportional distribution, least busy, and lowest sustained rate. When it locates a SAG and selects a specific session agent, the Oracle® Enterprise Session Border Controller tries only that single session agent. Instead of trying other members of the SAG, the Oracle® Enterprise Session Border Controller recurses to the local policy that is the next best match. This happens because the Oracle® Enterprise Session Border Controller typically chooses a SAG based on the fact that it has not breached its constraints, but the Oracle® Enterprise Session Border Controller only detects failed call attempts (due to unreachable next hops, unresolved ENUM queries, or SIP 4xx/5xx/6xx failure responses) after it has checked constraints. So the Oracle® Enterprise Session Border Controller only re-routes if there are additional matching local policies.
When you enable SIP SAG recursion, the Oracle® Enterprise Session Border Controller will try the additional session agents in the selected SAG if the previous session agent fails. You can also set specific response codes in the SAG configuration that terminate the recursion. This method of terminating recursion is similar to the Oracle® Enterprise Session Border Controller’s ability to stop recursion for SIP interfaces and session agents.
Session agents are selected according to the strategy you set for the SAG, and these affect the way that the Oracle® Enterprise Session Border Controller selects session agents when this feature enabled:
- Round robin and hunt—The Oracle® Enterprise Session Border Controller selects the first session agent according to the strategy, and it selects subsequent session agents based on the order they are entered into the configuration.
- Proportional distribution, least busy, and lowest sustained rate—The Oracle® Enterprise Session Border Controller selects session agents based on the list of session agents sorted by the criteria specified.
You can terminate recursion based on SIP response codes that you enter into the SAG configuration. You can configure a SAG with any SIP response code in the 3xx, 4xx, and 5xx groups. Since you can also set such a list in the session agent configuration, this list is additive to that one so that you can define additional codes for a session agent group with out having to repeat the ones set for a session agent.
