With OPTIONS messages, Session Manager keeps track of the status of the SIP trunks and forwards calls, without any delay, onto entity links that are up or partially down. A partially down entity link indicates that one of the SIP entities is inaccessible and Session Manager must forward calls to other SIP entities that are accessible. By keeping track of the SIP entities that are inaccessible, Session Manager keeps call performance at an acceptable level and enables load balancing or fail-over configurations without the impact of delayed calls.

Sometimes, especially when interfacing with some third party entities, Session Manager receives nonstandard responses. In these situations, the Session Manager cannot determine whether the SIP entity is up or down. On the SIP Entities Details page, in the SIP Responses to an OPTIONS Request section, you can specify the list of specific SIP responses to OPTIONS messages for these SIP Entities so that Session Manager can track the SIP responses.

If you do not set this feature, calls can be delayed. When the Session Manager attempts to route a call over an inaccessible SIP entity, the Session Manager waits a specific time, indicated by “Timer B”, before trying for another SIP entity. If multiple SIP entities are involved, the sum of the wait times can cause substantial delays that might have an impact on service.