Methods to route a bearer via circuit switching to an internet protocol multimedia system node using session initiation protocol contact header

摘要

A method of call routing is provided. The method comprises receiving 204 a session initiation protocol (SIP) INVITE message that contains a uniform resource identifier (URI) of a called party and that identifies that a bearer for a call to the called party is to be set-up at least in part over the circuit switching domain. The method also comprises determining 208 a digit string associated with the URI. The method also comprises sending 212 a SIP informational response message having a contact header that contains information based on the digit string.