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Encyclopedia > Asterisk PBX

Asterisk is a free software / open-source software implementation of a telephone private branch exchange (PBX). Like any PBX, it allows a number of attached telephones to make calls to one another, and to connect to other telephone services including the PSTN. "Its name comes from the asterisk symbol, *, which in Unix (including Linux) and DOS environments represents a wildcard, matching any sequence of characters in a filename." Image File history File links Asterisk_logo. ... This article is about free software as defined by the sociopolitical free software movement; for information on software distributed without charge, see freeware. ... Open source software refers to computer software available with its source code and under an open source license. ... A Private Branch eXchange (also called PBX, Private Business eXchange or PABX for Private Automatic Branch eXchange) is a telephone exchange that is owned by a private business, as opposed to one owned by a common carrier or by a telephone company. ... Look up Telephone in Wiktionary, the free dictionary. ... The public switched telephone network (PSTN) is the concatenation of the worlds public circuit-switched telephone networks, in much the same way that the Internet is the concatenation of the worlds public IP-based packet-switched networks. ... This article or section does not cite its references or sources. ... Unix or UNIX is a computer operating system originally developed in the 1960s and 1970s by a group of AT&T employees at Bell Labs including Ken Thompson, Dennis Ritchie, and Douglas McIlroy. ... Linux (also known as GNU/Linux) is a Unix-like computer operating system. ... ‹ The template below has been proposed for deletion. ...

Asterisk is released under a dual license scheme, the free software license being the GNU General Public License (GPL), the other being a commercial license as to allow closed/patented code, such as the G.729 codec to work with the system (although the G729 codec may work with the free or commercial versions). Mark Spencer of Digium originally created Asterisk and remains its primary maintainer however following Open Source development methods there are dozens of other programmers who have contributed features and functionality and have reported bugs. Originally designed for the Linux operating system, Asterisk now also runs on OpenBSD, FreeBSD, Mac OS X, Sun Solaris, and Microsoft Windows, although as the "native" platform, Linux is the best-supported of these. This page meets Wikipedias criteria for speedy deletion. ... Generally speaking, free software license is a phrase used by the free software movement to mean any software license that meets the free software definition of the Free Software Foundation (FSF). ... The GNU logo The GNU General Public License (GNU GPL or simply GPL) is a widely used free software license, originally written by Richard Stallman for the GNU project. ... G.729 From Wikipedia, the free encyclopedia You have new messages (changes). ... Mark Spencer (born April 8, 1977) is a computer engineer and is the original author of the GTK+-based instant messaging client Gaim and the L2TP daemon l2tpd. ... This article is about Digium, Inc. ... Linux (also known as GNU/Linux) is a Unix-like computer operating system. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... OpenBSD is a freely available Unix-like computer operating system descended from Berkeley Software Distribution (BSD), a Unix derivative developed at the University of California, Berkeley. ... FreeBSD is a Unix-like free operating system descended from AT&T UNIX via the Berkeley Software Distribution (BSD) branch through the 386BSD and 4. ... Mac OS X (official IPA pronunciation: ) is a line of proprietary, graphical operating systems developed, marketed, and sold by Apple Computer, the latest of which is pre-loaded on all currently shipping Macintosh computers. ... Solaris is a computer operating system developed by Sun Microsystems. ... Microsoft Windows is a family of operating systems by Microsoft. ...

The basic Asterisk software includes many features previously only available in expensive proprietary PBX systems -- voice mail, conference calling, interactive voice response (phone menus), and automatic call distribution. Users can create new functionality by writing dial plan scripts in Asterisk's own language, by adding custom modules written in C, or by writing Asterisk Gateway Interface scripts in Perl or other languages. Voicemail (or voice mail; abbreviated v-mail or vmail) is a specific application of an interactive voice response system. ... A conference call is a telephone call where the calling party wants to have more than one called party listen in to the audio portion of the call. ... In telephony, interactive voice response, or IVR, is a computerized system that allows a person, typically a telephone caller, to select an option from a voice menu and otherwise interface with a computer system. ... ACD, see ACD (disambiguation) In telephony, an Automatic Call Distributor (ACD) is a device that distributes incoming calls to a specific group of terminals that agents use. ... Wikibooks has a book on the topic of C Programming The C programming language (often, just C) is a general-purpose, procedural, imperative computer programming language developed in the early 1970s by Dennis Ritchie for use on the Unix operating system. ... Perl, also Practical Extraction and Report Language (a backronym, see below) is a dynamic procedural programming language designed by Larry Wall and first released in 1987. ...

To attach ordinary telephones to a Linux server running Asterisk, or to connect to PSTN trunk lines, the server must be fitted with special hardware. (An ordinary modem will not suffice.) Digium and a number of other firms sell PCI cards to attach telephones, telephone lines, T1 and E1 lines, and other analog and digital phone services to a server. The PCI cards that Digium sells as X100 or X101 are a particular Intel or Motorola WinModem with a resistor removed to change the PCI Device ID; this prevents the same WinModem that Digium modifies from being used unless a change is made to the driver so that the PCI Device ID is recognised (or by removing the resistors). A modem (from modulate and demodulate) is a device that modulates an analogue carrier signal to encode digital information, and also demodulates such a carrier signal to decode the transmitted information. ... This article is about Digium, Inc. ... 64-bit PCI expansion slots inside a Power Macintosh G4 The Peripheral Component Interconnect, or PCI Standard (in practice almost always shortened to PCI) specifies a computer bus for attaching peripheral devices to a computer motherboard. ... Two Network Interface Units, one with a single card, the other with two In telecommunications, T-carrier is the generic designator for any of several digitally multiplexed telecommunications carrier systems originally developed by Bell Labs and used in North America and Japan. ... To meet Wikipedias quality standards, this article or section may require cleanup. ...

Perhaps of more interest to many deployers today, Asterisk also supports a wide range of Voice over IP protocols, including SIP and H.323. Asterisk can interoperate with most SIP telephones, acting both as registrar and as a gateway between IP phones and the PSTN. Asterisk developers have also designed a new protocol, IAX, for efficient trunking of calls among Asterisk PBXes. A typical VoIP Solution A typical analog telephone adapter for connecting an ordinary phone to a VoIP network Voice over Internet Protocol, also called VoIP, IP Telephony, Internet telephony, Broadband telephony, Broadband Phone and Voice over Broadband is the routing of voice conversations over the Internet or through any other... The Session Initiation Protocol (SIP) is an application-layer control (signaling) protocol for creating, modifying, and terminating sessions with one or more participants. ... H.323 is an umbrella recommendation from the ITU-T, that defines the protocols to provide audio-visual communication sessions on any packet network. ... The public switched telephone network (PSTN) is the concatenation of the worlds public circuit-switched telephone networks, in much the same way that the Internet is the concatenation of the worlds public IP-based packet-switched networks. ... IAX is the Inter-Asterisk eXchange protocol used by Asterisk, an open source PBX server from Digium. ... // In computer networking, trunking describes using multiple network cables or ports in parallel to increase the link speed beyond the limits of any one single cable or port. ...

By supporting a mix of traditional and VoIP telephony services, Asterisk allows deployers to build new telephone systems efficiently, or gradually migrate existing systems to new technologies. Some sites are using Asterisk servers to replace aging proprietary PBXes; others to provide additional features (such as voice mail or phone menus) or to cut costs by carrying long-distance calls over the Internet (toll bypass).

VoIP telephone companies have begun to support Asterisk; many now offer IAX2 or SIP trunking direct to an Asterisk box as an alternative to providing the customer with an ATA. ITSP is an Internet Telephony Service Provider, selling telephone-like service based on VOIP technology. ... An Analog Telephony Adapter, or ATA, is a device used to connect one or more standard analog telephones to a Voice over IP based network. ...

As of October 18, 2006, the current release version of Asterisk is 1.2.13 October 18 is the 291st day of the year (292nd in leap years). ... 2006 (MMVI) is a common year starting on Sunday of the Gregorian calendar. ...



Asterisk, on its own, is not a complete system. The administrator must create a Dial Plan to make Asterisk respond to users. If Asterisk is to be used as a PBX, a dial plan has to be created specifically for this purpose. Defining the dial plan A dial plan establishes the expected number and pattern of digits for a telephone number. ...

Asterisk is controlled by editing a series of configuration files. One of these, extensions.conf, is where the administrator defines what actions Asterisk will take when calls are answered. A native language is used to define contexts, extensions and actions. Programming can also be done using the AGI interface which allows programs written in languages such as Perl, PHP and C. These programs issue Asterisk function-calls to handle the primitive functions.

There are several GUI interfaces for Asterisk, one of the most popular being FreePBX. These interfaces allow administrators to view, edit, and change most aspects of Asterisk via a web interface.


Unlike most next generation telephony applications and architectures, Asterisk is built using a monolithic model and does not break out individual parts of the application. An alternative application architecture would be disaggregated, where each architectural component could exist independently and therefore be scalable or easily accelerated with best of breed components. As an example, the media server portion of the Asterisk application is not implemented as a Voice Over IP media server and cannot be easily replaced with a hardware-based alternative. The Asterisk architecture therefore has inherent scalability problems in terms of raw performance and functional completeness. Due to the dual licensing nature of the Asterisk code and the feeling among some developers that changes required to the software were not incorporated in a timely manner, the Asterisk source base was forked in 2005 and established as OpenPBX. In software engineering, a project fork or branch happens when a developer (or a group of them) takes a copy of source code from one software package and starts to independently develop a new package. ... To meet Wikipedias quality standards, this article or section may require cleanup. ...

Asterisk's timing mechanism (both timestamps and wake-ups) is strongly biased toward systems which contain at least one of Digium's PCI boards. Users with other needs, including pure VoIP setups, are likely to experience timing problems. The problem can be somewhat reduced by loading a kernel module which emulates the timing functionality normally provided by Digium's PCI boards. As with the other Digium drivers, this driver has not been submitted for inclusion in the standard Linux kernel and thus presents the usual awkwardness associated with non-standard drivers. To meet Wikipedias quality standards, this article or section may require cleanup. ...


Various distributions of Asterisk exist, usually pre-packaged with an operating system. Some are fully Open Source and others commercial. Each distribution has its own set of features and packaged applications.

See also

Free software Portal

Image File history File links Portal. ... GNU Bayonne is a free telecommunications application server written primarily by David Sugar for the GNU project. ... trixbox (formerly known as Asterisk@Home) is a CentOS-based Linux distribution licensed under the GPL that combines Asterisk, a web GUI and other software. ... There are very few or no other articles that link to this one. ... sipX – The SIP PBX for Linux is an open source software implementation of a Session Initiation Protocol (SIP) based communications server. ...

Official website

  • Asterisk home page

  Results from FactBites:
Enterprise open source VoIP with Asterisk (1551 words)
Asterisk not only serves as an IP call signaling server (sometimes referred to as an IP PBX), but it also serves as a tradition TDM/analog PBX and seamlessly bridges the gap between the two worlds.
PBX is a very generic term that usually indicates some kind of central box that controls all the telephones.
Asterisk's parent company Digium makes PCI T1 and E1 adapters which are natively supported in Asterisk.
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