A WebRTC system, device and method enabling a P2P communication when both ends of a communication are WebRTC enabled devices. The system and devices also enable a WebRTC client to SIP device communication. A SIP interworking function is configured to receive a SDP1 from an originating WebRTC and obtain local media information from a media interworking function. The first SIP interworking function is configured to create a SDP2 based on the SDP1 and the local media information, create a SIP message comprising a message-body field including the SDP2 and an SIP extension header field including the SDP1, and send the SIP message to an IMS or SIP server.