SIP vs IAX

IAX and SIP are two different protocols for use with VoIP.

The main advantage of IAX, compared to SIP, is its ability to operate behind a NAT-router. IAX uses only 1 UDP connection for both control- and data-traffic. It is also possible to combine more than one channel (conversation) over this connection. This means only 1 (UDP) port has to be forwarded in the NAT-router to the Trixbox. IAX(2) uses a single UDP port 4569, the obsolete IAX1 protocol used port 5036. SIP uses port 5060

Links

• More on IAX versus SIP
• IAX/IAX2 Detailed description of the IAX/IAX2 protocol.
• Internet draft on IAX2 Whitepaper on IAX2