When connecting or forwarding calls between remote subscribers over different SIP lines, the SIP proxy in the LANCOM VoIP Router attempts to connect the two callers by means of a REFER or a Re-INVITE. The two external subscribers are not always able to reach one another directly and so the connection may fail. This is because the SIP providers do not make the necessary adaptations, e.g. translation of the target IP addresses. To improve performance in these situations, the SIP proxy in the LANCOM VoIP Routers has been additionally equipped with a media proxy.
The media proxy helps to establish connections and forward calls between subscribers who are reachable over different types of telephone line (e.g. SIP PBX line and SIP provider line). The media streams, generally RTP connections, remain unchanged. The media proxy changes the ports and IP addresses in the data packets and it adapts special media end points to the corresponding target networks (ARF networks, interface and IP address).