Patent ID: 8102839

Claim:
A method comprising: forming a session initiation protocol (SIP) INVITE at a first user equipment (UE-A) to establish a SIP dialog associated with originating a call in the CIS domain with a second user equipment (UE-B), the SIP INVITE message including a session description protocol (PSTN) payload comprising: a) a connection data field indicating public switched telephony network (PSTN) connection parameters; b) a media type indicating an audio stream; and c) an indication that the circuit-switched (CS) domain will be used for delay-sensitive class flow; sending the SIP INVITE message via an Internet Protocol Multimedia Subsystem (IMS); receiving a SIP response comprising a CS bearer media descriptor that includes a phone number associated with the UE-B; and sending, in response to receiving the SIP response, a circuit-switched call setup message to establish the call via the circuit switched domain, wherein the call setup message comprises the phone number associated with the UE-B.