is IAX Termination?
IAX is the Inter-Asterisk™
eXchange protocol used by Asterisk™ ,
an open source PBX server from Digium. It is used to
enable VoIP connections between Asterisk™ servers,
and between servers and clients that also use the IAX
protocol. IAX now most commonly refers to IAX2,
the second version of the IAX protocol. The original
IAX protocol has been deprecated almost universally
in favor of IAX2. IAX2 is very robust and full-featured
yet simple as far as protocols go. It is agnostic to
codecs and number of streams, meaning that it can be
used as a transport for virtually any type of data.
IAX2 uses a single UDP data stream (usually on port
4569) to communicate between endpoints, both for signaling
and data. The voice traffic is transmitted in-band,
making IAX2 easier to firewall and more likely to work
behind NAT. (This is in contrast
to SIP, which uses an out-of-band RTP stream to deliver
IAX2 supports trunking, wherein a single link carries
data and signaling for multiple channels. When trunking,
data from multiple calls are merged into a single set
of packets, meaning that one IP datagram can deliver
information for more than one call, reducing the effective
IP overhead without creating additional latency. This
is a big advantage for VoIP users, where IP headers
are large percentage of the bandwidth usage.
The IAX2 Protocol or Inter-Asterisk™ Exchange
Protocol was created by Mark Spencer for Asterisk™
for VoIP signaling. The protocol sets up internal sessions
and these sessions can use whichever codec they want
for voice transmission. The Inter-Asterisk™ Exchange
protocol essentially provides control and transmission
of streaming media over IP (Internet Protocol) networks.
IAX is extremely flexible and can be used with any type
of streaming media including video however it is mainly
designed for control of IP voice calls. IAX’s
design was based on many common control and transmission
standards today including Session Initiation Protocol
(SIP, which is the most common), Media Gateway Control
Protocol (MGCP) and Real-time Transfer Protocol (RTP).
The Primary goals for IAX was to minimize bandwidth
used in media transmissions with particular attention
drawn to control and individual voice calls and to provide
native support for NAT (Network Address Translation)
transparency. The basic structure of IAX is that it
multiplexes signaling and multiple media streams over
a single UDP (user datagram protocol) stream between
two computers. IAX is a binary protocol and is designed
and organized in a manner to reduce overhead especially
in regards to voice streams.
Asterisk™ is a complete PBX in software. It
runs on Linux, BSD and
MacOSX and provides all of the
features you would expect from a PBX and more. Asterisk™
does voice over IP in many protocols, and can interoperate
with almost all standards-based telephony equipment
using relatively inexpensive hardware.
Asterisk™ provides Voicemail services with Directory,
IVR (Interactive Voice Response) and
Call Queuing. It has support for three-way calling,
Caller ID services,
H.323 (as both client and
gateway). Check the Features section for a more complete
Asterisk™ needs no additional hardware for Voice
over IP. For interconnection with digital and analog
telephony equipment, Asterisk™ supports a number
of hardware devices, most notably all of the hardware
manufactured by Asterisk™ 's sponsors, Digium™.
Digium has single and quad span T1 and
for interconnection to PRI (Primary Rate Interface)
lines and channel banks as
well as a single port FXO (Foreign Exchange Office) card
and a one to four-port modular FXS
(Foreign Exchange Station) and FXO card.
Asterisk™ supports a wide range of TDM protocols
for the handling and transmission of voice over traditional
telephony interfaces. Asterisk™ supports US and
European standard signalling types used in standard
business phone systems, allowing it to bridge between
next generation voice-data integrated networks and existing
infrastructure. Asterisk™ not only supports traditional
phone equipment, it enhances them with additional capabilities.
Using the Inter-Asterisk™ eXchange (IAX™)
Voice over IP protocol, Asterisk™ merges voice
and data traffic seamlessly across disparate networks.
While using Packet Voice, it is possible to send data
such as URL information and images in-line with voice
traffic, allowing advanced integration of information.
Asterisk™ provides a central switching core,
with four APIs (Application Programming Interfaces) for modular loading of telephony applications,
hardware interfaces, file format handling, and codecs.
It allows for transparent switching between all supported
interfaces, allowing it to tie together a diverse mixture
of telephony systems into a single switching network.
Asterisk™ is a Trademarked Property of Digium™.