Asterisk is a complete PBX in software. It runs on Linux and provides all of the features you would expect from a PBX and more. Asterisk does voice over IP in three protocols, and can interoperate with almost all standards-based telephony equipment using relatively inexpensive hardware.
Asterisk provides Voicemail services with Directory, Call Conferencing, Interactive Voice Response, Call Queuing. It has support for three-way calling, caller ID services, ADSI, SIP and H.323 (as both client and gateway). Check the Features section for a more complete list.
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 E1 interfaces for interconnection to PRI lines and channel banks. In addition, an analog FXO card is available, and more analog interfaces are in the works.
Also supported are the Internet Line Jack and Internet Phone Jack products from Quicknet.
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 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 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 primarily developed on GNU/Linux for x/86. It is known to compile and run on GNU/Linux for PPC. Other platforms and standards based UNIX-like operating systems should be reasonably easy to port for anyone with the time and requisite skill to do so. Asterisk is available in the testing and unstable Debian archives, maintained thanks to Mark Purcell.
Who Made This?
Asterisk was originally written by Mark Spencer of Digium dba Linux Support Services, Inc. Code has been contributed from Open Source coders around the world, and testing and bug-patches from the community have provided invaluable aid to the development of this software.
Where is Asterisk going?
Asterisk growing fast with new features added frequently to the CVS tree. Mark Spencer and numerous contributors from around the world contribute new code and patches on a daily basis. To stay up-to-date on the growing feature list of Asterisk, please visit Digium's website for more information on subscribing to the Asterisk mailing lists.
http://www.asteriskpbx.com/