InterAsteriskIAX

InterAsterisk eXchange Protocol, commonly abbreviated IAX, is a communications protocol developed for the Asterisk open‑source PBX system. It was designed to provide a more efficient and secure alternative to the traditional Session Initiation Protocol (SIP) for VoIP applications. IAX combines both media and signaling in a single port, commonly TCP port 4569, which reduces firewall complications and simplifies network configuration.

The protocol supports a wide range of voice and fax codecs, including G.723.1, G.729, and Opus, and can handle both traditional voice calls and various multimedia services such as video and instant messaging. IAX frames are structured in a lightweight format, which reduces overhead compared to SIP. It includes features for dynamic port allocation, and it allows for the use of external codecs via plugin modules.

Security in IAX is achieved through optional X.509 certificate authentication and support for MD5-based authentication for call sessions. In addition, IAX can be configured to use TUN/TAP virtual network interfaces for secure routing of media streams. The protocol has been extended to provide connections to other PBX platforms via the IAX2 extension, allowing interoperability among different implementations.

In practice, IAX is deployed in a mix of corporate environments, small office/home office (SOHO) setups, and in some public call termination services. While not as widely adopted as SIP, it remains popular among Asterisk users who prioritize simplicity and firewall friendliness. Documentation and community support are maintained by the Asterisk Project on the official website and through open source contribution platforms.