US Patent 7778243 Method for DTMF transfer by RTP

A method for DTMF transmission between different address systems in a communication system containing a first network (NW) 20A including an SIP terminal 41A connected to an SIP server 30A, a second network (NW) 20B including an SIP terminal 41B connected to an SIP server 30B, and an SIP converter 10 connecting the first and the second NWs. When the SIP converter 10 detects coded DTMF information from one of the NWs while a session is established between the SIP terminal 41A and the SIP terminal 41B, the SIP converter 10 determines whether the other of the NWs supports the coded DTMF information. If the other of the NWs does not support the coded DTMF information, the SIP converter 10 stores voice-data DTMF corresponding to the coded DTMF information into a payload of RTP and transfers the information to the SIP terminal of the other network.