Patent ID: 8179916

Claim:
A method, performed by a processor, comprising: receiving SIP protocol messages and H.323 protocol messages at an interworking function used to connect calls between networks using the different protocols; receiving, at the interworking function, a SIP protocol response message from a SIP protocol called endpoint after an H.323 protocol calling endpoint initiates a call, with the SIP protocol response message indicating that the SIP protocol called endpoint might send media including a ringback tone to be played at the H.323 protocol calling endpoint and where the SIP protocol causes a SIP protocol calling endpoint to start a timer when a SIP protocol response message is received so that ringback will be generated locally if no ringback media to be played is received at the SIP protocol calling endpoint before the timer expires; translating the SIP protocol response message to an H.323 protocol alerting message at the interworking function; sending the H.323 protocol alerting message and an H.323 protocol progress indicator from the interworking function to the H.323 protocol calling endpoint subsequent to receiving the SIP protocol response message at the interworking function, where the H.323 protocol calling endpoint generates a local ringback tone only if an H.323 protocol alerting message with no H.323 protocol progress indicator is received and where the H.323 protocol calling endpoint does not start a timer when an H.323 protocol alerting message and an H.323 protocol progress indicator are received; maintaining a timer at the interworking function; starting the timer maintained at the interworking function when the SIP protocol response message is received at the interworking function; and sending an H.323 protocol alerting message without an H.323 protocol progress indicator from the interworking function to the H.323 protocol calling endpoint to instruct the H.323 protocol calling endpoint to play a local ringback tone if the timer expires and no media is received from the SIP protocol called endpoint at the interworking function.