As an alternate to SIP, the Asterisk team developed a new Inter-Asterisk eXchange (IAX) communication protocol. It is used for transporting VoIP telephony sessions between servers and terminal devices.
The original IAX protocol was not widely popular, and hence the development team came with second version of IAX commonly known as IAX2. It uses a single UDP data stream on a static port and can be used for any type of streaming media including video, but is mainly designed for IP voice calls. IAX2 also known as RFC 5456.
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.
Many software have added its support to their systems now, and this number is rapidly growing.