IAX2 is the VoIP protocol used by the open source PBX solution, Asterisk. It has many strengths over other protocols like SIP, Skinny or H.323.

The basic idea behind the development of the IAX protocol is its simplicity. Namely, IAX has the ability to act transparently with Network Address Translation (NAT) firewalls without the need of complicated supplicant protocols such as a STUN server. Other advantages include a friently in-band voice transport mechanism. Compared to SIP, which could use up to 10,000 different ports, IAX only uses one port for all its communication.