Patent ID: 8364828

Claim:
A method of routing Session Initiation Protocol (SIP) messages within a SIP-based Call Session Server, the SIP messages being associated with a call session, the method comprising the steps of: receiving by the SIP Server, an incoming SIP message from an originating node; determining by the SIP Server, a session identifier (Routing Key) based upon at least one header field in the incoming SIP message, wherein the step of determining the Routing-Key includes: determining whether the incoming SIP message is a request message or a response message; when the incoming SIP message is a request message and a To-Tag is present, retrieving the Routing-Key utilizing the To-Tag of the incoming SIP message; when the incoming SIP message is a request message and the To-Tag is not present, generating the Routing-Key as a globally unique alphanumeric string in a manner that complies with stochastic properties of tags utilizing the Call-ID of the incoming SIP request message, the From-Tag of the incoming SIP request message, or both: and when the incoming SIP message is a response message, retrieving the Routing-Key utilizing the From-Tag of the incoming SIP message; utilizing the Routing-Key by the SIP Server, to identify a Back-to-Back User Agent (B2BUA) instance responsible for the call session; sending the incoming SIP message to the identified B2BUA instance; creating an outgoing SIP message by the B2BUA instance, wherein the B2BUA instance utilizes the Routing-Key to generate a header field in the outgoing SIP message; and sending by the SIP Server, the outgoing SIP message to a terminating node.