InterAsterisk

InterAsterisk, short for Inter-Asterisk eXchange, refers to a VoIP signaling framework associated with the Asterisk project. It is most commonly known through the InterAsterisk eXchange protocol family, better known as IAX. The development of IAX aimed to provide efficient trunking between Asterisk-based systems and to improve traversal of firewalls and NAT environments compared with other VoIP signaling options.

Two major iterations exist: IAX1 and IAX2. IAX1 was the original protocol designed to carry both signaling and media over a single connection, facilitating lightweight and firewall-friendly communication between Asterisk servers. IAX2 introduced enhancements to call control, authentication mechanisms, and overall robustness, while retaining the core feature of multiplexed channels over a single UDP connection.

A defining technical characteristic of InterAsterisk/IAX is the use of a single UDP port (default 4569) for both signaling and media, simplifying network configuration. The protocol employs a compact binary header and supports multiple simultaneous calls through channel multiplexing, which can yield efficiency advantages in certain network topologies. IAX also includes mechanisms for authentication and basic security, and it provides options intended to improve compatibility with NAT and firewall environments.

In practice, InterAsterisk has been used primarily to connect Asterisk PBX systems, link gateways, and establish trunking between servers. While SIP emerged as the dominant VoIP signaling protocol in many deployments, IAX remains supported in Asterisk and related projects for compatibility and its NAT-friendly characteristics, particularly in environments where minimizing port exposure is advantageous.

See also: Asterisk, SIP, NAT traversal, Real-time Transport Protocol.