Re: [Serusers] B2BUA and NAT.

Hi Amos! You can always put a B2BUA in the media path, not just for NAT traversal. Other applications like billing or privacy service are also common. Downsides are media quality, scalability and representing a single point of failure. B2BUA means a system standing in the signalling AND the media path. So a proxy in the normal SIP message path could "catch" the session, i.e. terminating the incoming call ("picking up the receiver") and build up new outgoing call to the target. Then it relays the voice from one call the other. It can change codec and other information as well on the way. In this respect SER isn't a B2BUA and will never be. SER itself just can handle and mangle SIP messages very good but can have only influence on the media *routing* with e.g. nathelper/rtpproxy or mediaproxy. It doesn't terminate SIP transactions or media sessions. If you're looking for a real B2BUA you might want to trake a look at Asterisk. RTP relay seems to be a cure-all regarding NAT problems - desipte the disadvantages. The only clients not working with RTP relay where those who didn't support symmetric SIP and symmetric RTP (i.e. sending and receiving data on the same port). Another set of clients not working are more than two STUN clients behind the same NAT and the NAT not supporting hairpin of media. In this situation SER assumes both UAs to have public adresses (i.e. not being behind a NAT) and to be able to communicate with each other, which isn't the case with the lack of hairpin of media. Signalling would work but you wonÄt hear voice. Alex Mack