InterAsterisk eXchange

InterAsterisk eXchange ( IAX ) is a protocol that is used by the open source PBX Asterisk. It serves both the connection between individual Asterisk servers as well as for communication to terminals with which thereby Voice-over- IP calls are possible. Currently find the version 2 ( IAX2 ) use.

Other standards for IP telephony are the widely used SIP and H.323.

IAX/IAX2, in contrast to some of the other VoIP protocols advantages of IP telephony, since the protocol used is less complicated. In detail: For the signaling process and for the transmission of the audio stream only one port is needed (port 4569 ). The IAX protocol usually has no NAT or firewall issues that occur when using the SIP or H.323: Clients who register on the server, the connection can be kept open. If the server is behind a firewall, the port can not be forwarded.

Due to the small overhead of the IAX/IAX2-Protokolls - compared to SIP or H.323 - in combination with a narrowband codec, such as GSM, iLBC or G.729, even VoIP connections via an analog modem is possible ( with a data rate of 38 kbit / s in both directions).

The objectives of IAX

The following properties were the main objectives of the development of IAX:

  • The bandwidth used for multimedia transmission should be as small as possible
  • Special attention was devoted to the control of transmission and a single voice connection
  • A NAT support should already be installed

IAX can therefore be transmitted over a single UDP connection control signals and more calls and video messages between two computers or terminals. IAX is a binary protocol, with which the bandwidth is very well used. In a few places, it has Mark Spencer, creator of the Protocol, decided to consume slightly more total bandwidth, but to be more efficient in individual talks.

IAX clients

Hardware

  • Digium IAXy
  • Virbiage 3010 (also known as the Freshtel 3010 and the Tesco IPA 1000 sold)
  • ALLNET VoIP phone with SIP and IAX2 ALL7960
  • Critical Links edgeBOX telephone system, radius server and router with SIP and IAX edgeBOX
  • Snom VoIP Phone

Software

  • DiAx ( freeware for Windows)
  • Firefly (for Windows)
  • Iaxcomm (Open Source, Linux, Mac OS X and Windows)
  • IAXPhone ( crippleware, for Windows)
  • Zoiper 2.0 Free Idefisk earlier (for Linux, Mac OS X and Windows)
  • Kiax (Open Source, Linux and Windows)
  • LoudHush ( crippleware, for Mac OS X)
  • PURtel ( fixed at PURtel, Windows)
  • YakaPhone (Open Source for Windows)
  • Yate, Yate -gtk2 (Open Source)
  • ZiaxPhone ( freeware, for Sharp Zaurus )
Session Initiation Protocol Mark Spencer (computer engineer)
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