Asterisk is a

software Software is a set of computer programs and associated documentation and data. This is in contrast to hardware, from which the system is built and which actually performs the work. At the lowest programming level, executable code consists ...

implementation of a private branch exchange (PBX). In conjunction with suitable

telephony Telephony ( ) is the field of technology involving the development, application, and deployment of telecommunication services for the purpose of electronic transmission of voice, fax, or data, between distant parties. The history of telephony is i ...

hardware interfaces and network applications, Asterisk is used to establish and control

telephone call A telephone call is a connection over a telephone network between the called party and the calling party. First telephone call The first telephone call was made on March 10, 1876, by Alexander Graham Bell. Bell demonstrated his ability to "ta ...

s between

telecommunication Telecommunication is the transmission of information by various types of technologies over wire, radio, optical, or other electromagnetic systems. It has its origin in the desire of humans for communication over a distance greater than that fe ...

endpoints, such as customary

telephone A telephone is a telecommunications device that permits two or more users to conduct a conversation when they are too far apart to be easily heard directly. A telephone converts sound, typically and most efficiently the human voice, into e ...

sets, destinations on the public switched telephone network (PSTN), and devices or services on

voice over Internet Protocol Voice over Internet Protocol (VoIP), also called IP telephony, is a method and group of technologies for the delivery of voice communications and multimedia sessions over Internet Protocol (IP) networks, such as the Internet. The terms Internet t ...

(VoIP) networks. Its name comes from the asterisk (*) symbol for a signal used in

dual-tone multi-frequency Dual-tone multi-frequency signaling (DTMF) is a telecommunication signaling system using the voice-frequency band over telephone lines between telephone equipment and other communications devices and switching centers. DTMF was first developed ...

(DTMF) dialing. Asterisk was created in 1999 by Mark Spencer of

Digium Digium, Inc. is a communications technology company based in Huntsville, Alabama, and since 2018, a subsidiary of Sangoma Technologies Corporation. The company makes VoIP business phone systems, IP phones, and hardware products. It was founded ...

, which since 2018 is a division of

Sangoma Technologies Corporation Sangoma Technologies Corporation (Sangoma) provides Communications as a Service (“CaaS”) products globally for businesses. It was founded in 1984. It is publicly traded on the Toronto Stock Exchange. Acquisitions Sangoma acquired FreePBX ...

. Originally designed for

Linux Linux ( or ) is a family of open-source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically packaged as a Linux distribution, which ...

, Asterisk runs on a variety of

operating system An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs. Time-sharing operating systems schedule tasks for efficient use of the system and may also in ...

s, including NetBSD, OpenBSD, FreeBSD,

macOS macOS (; previously OS X and originally Mac OS X) is a Unix operating system developed and marketed by Apple Inc. since 2001. It is the primary operating system for Apple's Mac computers. Within the market of desktop and lapt ...

, and

Solaris Solaris may refer to: Arts and entertainment Literature, television and film * ''Solaris'' (novel), a 1961 science fiction novel by Stanisław Lem ** ''Solaris'' (1968 film), directed by Boris Nirenburg ** ''Solaris'' (1972 film), directed by ...

, and can be installed in embedded systems based on

OpenWrt OpenWrt (from ''open wireless router'') is an open-source project for embedded operating systems based on Linux, primarily used on embedded devices to route network traffic. The main components are Linux, util-linux, musl, and BusyBox. All ...

Features

The Asterisk software includes many features available in commercial and proprietary PBX systems:

voice mail A voicemail system (also known as voice message or voice bank) is a computer-based system that allows users and subscribers to exchange personal voice messages; to select and deliver voice information; and to process transactions relating to ind ...

conference call A conference call is a telephone call in which someone talks to several people at the same time. The conference call may be designed to allow the called party to participate during the call or set up so that the called party merely listens into ...

ing,

interactive voice response Interactive voice response (IVR) is a technology that allows telephone users to interact with a computer-operated telephone system through the use of voice and DTMF tones input with a keypad. In telecommunications, IVR allows customers to interac ...

(phone menus), and

automatic call distribution An automated call distribution system, commonly known as automatic call distributor (ACD), is a telephony device that answers and distributes incoming calls to a specific group of terminals or agents within an organization. ACDs direct calls based ...

. Users can create new functionality by writing dial plan scripts in several of Asterisk's own ''extensions'' languages, by adding custom loadable modules written in PHP or C, or by implementing ''

Asterisk Gateway Interface Asterisk Gateway Interface (AGI) is a software interface and communications protocol for application level control of selected features of the Asterisk PBX. AGI allows an external, user-written program, launched from the Asterisk dial plan via pi ...

'' (AGI) programs using any programming language capable of communicating via the standard streams system (

stdin In computer programming, standard streams are interconnected input and output communication channels between a computer program and its environment when it begins execution. The three input/output (I/O) connections are called standard input (stdin ...

and

stdout In computer programming, standard streams are interconnected input and output communication channels between a computer program and its environment when it begins execution. The three input/output (I/O) connections are called standard input (stdin ...

) or by network TCP sockets. Asterisk supports several standard

voice over IP Voice over Internet Protocol (VoIP), also called IP telephony, is a method and group of technologies for the delivery of voice communications and multimedia sessions over Internet Protocol (IP) networks, such as the Internet. The terms Internet t ...

protocols, including the Session Initiation Protocol (SIP), the

Media Gateway Control Protocol The Media Gateway Control Protocol (MGCP) is a signaling and call control communication protocol used in voice over IP (VoIP) telecommunication systems. It implements the media gateway control protocol architecture for controlling media gatew ...

(MGCP), and H.323. Asterisk supports most SIP telephones, acting both as registrar and

back-to-back user agent A back-to-back user agent (B2BUA) is a logical network element in Session Initiation Protocol (SIP) applications., ''SIP: Session Initiation Protocol'', IETF, The Internet Society (2002) SIP is a signaling protocol for managing multimedia Voice ove ...

. It can serve as a gateway between IP phones and the PSTN via T- or E-carrier interfaces or analog FXO cards. The

Inter-Asterisk eXchange Inter-Asterisk eXchange (IAX) is a communications protocol native to the Asterisk private branch exchange (PBX) software, and is supported by a few other softswitches, PBX systems, and softphones. It is used for transporting VoIP telephony session ...

(IAX) protocol, RFC 5456, native to Asterisk, provides efficient

trunking In telecommunications, trunking is a technology for providing network access to multiple clients simultaneously by sharing a set of circuits, carriers, channels, or frequencies, instead of providing individual circuits or channels for each cli ...

of calls between Asterisk PBX systems, in addition to distributing some configuration logic. Many VoIP service providers support it for call completion into the PSTN, often because they themselves have deployed Asterisk or offer it as a hosted application. Some telephones also support the IAX protocol. By supporting a variety of traditional and VoIP telephony services, Asterisk allows deployers to build telephone systems, or migrate existing systems to new technologies. Some sites are using Asterisk to replace proprietary PBXes, others provide additional features, such as voice mail or voice response menus, or virtual call shops, or to reduce cost by carrying both local and long-distance calls over the Internet. In addition to VoIP protocols, Asterisk supports traditional circuit-switching protocols such as

ISDN Integrated Services Digital Network (ISDN) is a set of communication standards for simultaneous digital transmission of voice, video, data, and other network services over the digitalised circuits of the public switched telephone network. Work ...

and SS7. This requires appropriate hardware interface cards, marketed by third-party vendors. Each protocol requires the installation of software modules. In Asterisk release 14 the Opus audio codec is supported.

Internationalization

While initially developed in the

United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...

, Asterisk has become a popular

VoIP Voice over Internet Protocol (VoIP), also called IP telephony, is a method and group of technologies for the delivery of voice communications and multimedia sessions over Internet Protocol (IP) networks, such as the Internet. The terms Internet t ...

PBX worldwide. It allows having multiple sets of voice prompts identified by language (and even multiple sets of prompts for each language) as well as support for time formats in different languages. Several sets of prompts for the interactive voice response and voice mail features are included with Asterisk: American, British, and Australian English, Canadian French, Japanese, Russian, Mexican Spanish and Swedish. A few novelty prompts are offered, such as jokes and a themed "zombie apocalypse" message for

Halloween Halloween or Hallowe'en (less commonly known as Allhalloween, All Hallows' Eve, or All Saints' Eve) is a celebration observed in many countries on 31 October, the eve of the Western Christian feast of All Saints' Day. It begins the observanc ...

. Additionally, voice sets are offered for commercial sale in various languages, dialects, and genders. The default set of English-language Asterisk prompts are recorded by professional telephone voice Allison Smith.

Derived products

Asterisk is a core component in many commercial products and open-source projects. Some of the commercial products are hardware and software bundles, for which the manufacturer supports and releases the software with an open-source distribution model. *

AskoziaPBX AskoziaPBX is a closed source telephone system (or " PBX") firmware. It is a fork of the m0n0wall project and uses the Asterisk private branch exchange (PBX) software to realize all telephony functions. Prior to version 2.1, AskoziaPBX was rele ...

, a fork of the

m0n0wall m0n0wall was an embedded firewall distribution of FreeBSD, one of the BSD operating system descendants. It provides a small image which can be put on Compact Flash cards as well as on CD-ROMs and hard disks. It runs on a number of embedded pla ...

project, uses Asterisk PBX software to realize all telephony functions. * AstLinux is a "Network Appliance for Communications" open-source software distribution. *

FreePBX FreePBX is a web-based open-source graphical user interface (GUI) that manages Asterisk, a voice over IP and telephony server. FreePBX is licensed under the GNU General Public License version 3. It is a component of the FreePBX Distro, which is ...

, an open-source graphical user interface, bundles Asterisk as the core of its

FreePBX Distro The FreePBX Distro is a freeware unified communications software system that consists of a graphical user interface (GUI) for configuring, controlling, and managing Asterisk PBX software. The FreePBX Distro includes packages that offer VoIP, PBX, F ...

LinuxMCE LinuxMCE (Linux Media Center Edition) is a free and open source software platform with a 10-foot user interface designed to allow a computer to act as a home theater PC (HTPC) for the living-room TV, personal video recorder, and home automation ...

bundles Asterisk to provide telephony; there is also an embedded version of Asterisk for OpenWrt routers. * PBX in a Flash/Incredible PBX and

trixbox trixbox (formerly Asterisk@Home) was a software PBX based on Asterisk. trixbox was initially released under the name Asterisk@Home. In October 2006 it was renamed to trixbox after Digium requested that its developers cease the use of the word ...

are software PBXes based on Asterisk. *

Elastix Elastix is an unified communications server software that brings together IP PBX, email, IM, faxing and collaboration functionality. It has a Web interface and includes capabilities such as a call center software with predictive dialing. The El ...

previously used Asterisk, HylaFAX,

Openfire Openfire (previously known as Wildfire, and Jive Messenger) is an instant messaging (IM) and groupchat server for the Extensible Messaging and Presence Protocol (XMPP). It is written in Java and licensed under the Apache License 2.0. History The ...

and Postfix to offer PBX, fax, instant messaging and email functions, respectively, before switching to 3CX. * Issabel is an open-source

Unified Communications Unified communications (UC) is a business and marketing concept describing the integration of enterprise communication services such as instant messaging (chat), presence information, voice (including IP telephony), mobility features (including ...

software which uses Asterisk for telephony functions. It was forked from the open-source versions of Elastix when 3CX acquired it. * *astTECS uses Asterisk in its VoIP and mobile gateways. Various add-on products, often commercial, are available that extend Asterisk features and capabilities. The standard voice prompts included with the system are free. A business can purchase matching voice announcements of its company name, IVR menu options and employee or department names (as a library of live recordings of common names or a set of fully customised prompts recorded by the same professional voice talent) at additional cost for seamless integration into the system. Other add-ons provide fax support, text-to-speech, additional

codec A codec is a device or computer program that encodes or decodes a data stream or signal. ''Codec'' is a portmanteau of coder/decoder. In electronic communications, an endec is a device that acts as both an encoder and a decoder on a signal or ...

s and new features. Some third-party add-ons are free; a few even support embedded platforms such as the

Raspberry Pi Raspberry Pi () is a series of small single-board computers (SBCs) developed in the United Kingdom by the Raspberry Pi Foundation in association with Broadcom. The Raspberry Pi project originally leaned towards the promotion of teaching basic ...

References

External links

* {{Official website Free VoIP software Free business software Free software programmed in C Free communication software Telephone exchange equipment Videotelephony Lua (programming language)-scriptable software 1999 software

Features

Internationalization

Derived products

See also

References

External links