A Service Profile is a group of Initial Filter Criteria, each with an attached priority. Each user can have such a Service Profile attached and this is downloaded from the HSS to the S-CSCF on initial registration, profile changes or when there is a message towards a user that has a Service Profile containing at least an Initial Filter Criteria applicable for the terminating towards unregistered user case.

The Initial Filter Criteria will be evaluated for each initial request in the priority order. On a match, the request is forwarded to the respective Application Server. If the Application Server responds with a final response, that response is relayed back and the matching session is terminated. If the Application Server responds with a modified request (proxy mode), the matching session is resumed. When the matching session ends the message will be forwarded further.