The SIP routing system consults the internal SIP registration In-memory database to determine whether the SIP call originated from a remote worker.

If SIP registration database lookup is successful, the SIP routing system uses the Subscriber Flow previously matched during the SIP registration process for taking routing decisions. The SIP routing system performs Policy Invocation and Route Resolution using the Subscriber Flow found.

If SIP registration database lookup fails, the SIP routing system refuses the call by generating a SIP error response as the request did not match either a Server or Subscriber Flow. An Incidence/Syslog is raised for administrative reasons.