Patent ID: 8335221

Claim:
A method for listening to a signal tone from a called party by a calling party during network interworking applicable to an Internet Protocol Multimedia Subsystem (IMS) network which employs Session Initiation Protocol (SIP) as call control signaling, wherein the IMS network is connected to a circuit domain network via a Media Gateway Control Unit and accesses a user terminal via a network access node, the method comprising: instructing, by the Media Gateway Control Unit, a media gateway (MGW) to open a media stream channel when the media gateway control unit receives an Address Complete message or Call Progress message from the circuit domain network, sending, by the Media Gateway Control Unit, a ringing response message to the calling party of the IMS network if the received Address Complete message or Call Progress message carries an indicator indicating the called party is free; and sending, by the Media Gateway Control Unit, a call failure indicator of a failed call but successful media stream setup to the calling party of the IMS network if the received Address Complete message or Call Progress message does not carry the indicator indicating the called party is free; and receiving, by the calling party of the IMS network, a ring-back tone indicating successful call through the media stream channel if the calling party receives the ringing response message, or a signal tone or voice announcement indicating failed call through the media stream channel if the calling party receives the call failure indicator of the failed call but successful media stream setup; wherein the calling party is a user in the IMS network, while the called party is a user in a circuit domain network.