The original IAX protocol is deprecated and has been superseded by a second version, commonly called IAX2.
IAX uses a single User Datagram Protocol (UDP) data stream and port number, by default 4569, between endpoints for both session signaling and media payloads.
When trunking, data from multiple sessions are merged into a single stream of packets between two endpoints, reducing the IP overhead.
Both versions of the IAX protocol were created by Mark Spencer and much of the development was carried out in the Asterisk open-source community.
The primary goals for IAX are to minimize bandwidth used in media transmissions, and to provide native network address translation (NAT) transparency.