http://www.rfc-editor.org/rfc/rfc5456.txt
RFC 5456: IAX: Inter-Asterisk eXchange Version 2, M. Spencer, B. Capouch, E. Guy, F. Miller, K. Shumard2010-02-01T23:00:00-00:00IAX is an "all in one" protocol for handling multimedia in IP networks. It combines both control and media services in the same protocol. In addition, IAX uses a single UDP data stream on a static port greatly simplifying Network Address Translation (NAT) gateway traversal, eliminating the need for other protocols to work around NAT, and simplifying network and firewall management. IAX employs a compact encoding that decreases bandwidth usage and is well suited for Internet telephony service. In addition, its open nature permits new payload type additions needed to support additional services. This document is not an Internet Standards Track specification; it is published for informational purposes.