Introduction to the
Linux Support Services, Inc.
Presented first at Libre Software Meeting 2002
July 9, 2002
Introduction to Asterisk
Asterisk is a fully Open Source, hybrid TDM and packet voice PBX and IVR platform.
Asterisk is and has been Open Source under GNU GPL (with an exception permitted
for linking with the OpenH323 project, in order to provide H.323 support). Commercial
licensing is available from Linux Support Services, Inc. (http://www.linux-support.net) for
applications in which the GPL is inappropriate.
Unlike many modern "soft switches", Asterisk can use both traditional TDM
technology and packet voice (Voice over IP and Voice over Frame Relay) protocols. Calls
switched on TDM interfaces provide lag-less TDM call quality, while retaining
interoperability with VoIP packetized protocols.
Asterisk acts as a full featured PBX, supporting virtually all conventional call
features on station interfaces, such as Caller*ID, Call Waiting,Caller*ID on Call Waiting, Call
Forward/Busy, Call Forward/No Answer, Call Forward Variable, Stutter Dialtone, Three-way
Calling, Supervised Transfer, Unsupervised Transfer, ADSI enhancements, Voicemail,
Meet-me Conferencing, Least Cost Routing, VoIP gatewaying, Call Detail Records, etc. At
the same time, Asterisk provides full IVR capability, programmable at several layers, from a
low-level C interface, to high level AGI scripting (analogous to CGI) and extension logic
interfaces. Asterisk IVR applications run seamlessly from one interface to another, and need
not know anything about the physical interface, protocol, or codec of the call they are
working with, since Asterisk provides total abstraction for all those concepts.
Asterisk supports a variety of hardware interfaces for bringing in telephony channels
to a Linux box. In order of best supported to least supported:
Zaptel (Zapata Telephony) interface
The zaptel telephony infrastruct