What is IAX?

IAX is a call control protocol for VoIP.

IAX was designed to replace the earlier call control protocols, H.323 and SIP.

IAX is much more bandwidth efficient than the competing VoIP call control protocols, enabling it to support more concurrent VoIP calls over the same amount of bandwidth.

IAX traffic uses UDP port 4569. The use of a single well-known port enables IAX to be compatible with NAT (Network Address Translation), which can be a serious difficulty for earlier VoIP call control protocols.

IAX supports authentication using RSA public keys with the SHA-1 message digest algorithm for digital signatures.

IAX was developed for the Asterisk PBX and originally stood for Inter-Asterisk eXchange. IAX is now supported by many other VoIP platforms.