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 consist ...

implementation of a

private branch exchange A business telephone system is a multiline telephone system typically used in business environments, encompassing systems ranging in technology from the key telephone system (KTS) to the private branch exchange (PBX). A business telephone syst ...

(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 ...

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 The public switched telephone network (PSTN) provides infrastructure and services for public telecommunication. The PSTN is the aggregate of the world's circuit-switched telephone networks that are operated by national, regional, or local telep ...

(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 The asterisk ( ), from Late Latin , from Ancient Greek , ''asteriskos'', "little star", is a typographical symbol. It is so called because it resembles a conventional image of a heraldic star. Computer scientists and mathematicians often voc ...

(*) symbol for a signal used in dual-tone multi-frequency (DTMF) dialing. Asterisk was created in 1999 by Mark Spencer of Digium, which since 2018 is a division of Sangoma Technologies Corporation. 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, whi ...

, Asterisk runs on a variety of

operating system An operating system (OS) is system software that manages computer hardware, software resources, and provides common daemon (computing), services for computer programs. Time-sharing operating systems scheduler (computing), schedule tasks for ef ...

s, including

NetBSD NetBSD is a free and open-source Unix operating system based on the Berkeley Software Distribution (BSD). It was the first open-source BSD descendant officially released after 386BSD was forked. It continues to be actively developed and is ava ...

OpenBSD OpenBSD is a security-focused, free and open-source, Unix-like operating system based on the Berkeley Software Distribution (BSD). Theo de Raadt created OpenBSD in 1995 by forking NetBSD 1.0. According to the website, the OpenBSD project e ...

FreeBSD FreeBSD is a free and open-source Unix-like operating system descended from the Berkeley Software Distribution (BSD), which was based on Research Unix. The first version of FreeBSD was released in 1993. In 2005, FreeBSD was the most popular ...

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 la ...

, and Solaris, 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, conference calling,

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. 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 and stdout) 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 The Session Initiation Protocol (SIP) is a signaling protocol used for initiating, maintaining, and terminating communication sessions that include voice, video and messaging applications. SIP is used in Internet telephony, in private IP telepho ...

(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 gate ...

(MGCP), and

H.323 H.323 is a recommendation from the ITU Telecommunication Standardization Sector (ITU-T) that defines the protocols to provide audio-visual communication sessions on any packet network. The H.323 standard addresses call signaling and control, mu ...

. 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 over ...

. 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 (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 Continental United States, primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., ...

, 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 observan ...

. 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, a fork of the m0n0wall project, uses Asterisk PBX software to realize all telephony functions. * AstLinux is a "Network Appliance for Communications" open-source software distribution. * FreePBX, an open-source graphical user interface, bundles Asterisk as the core of its FreePBX Distro *

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 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 Ela ...

previously used Asterisk,

HylaFAX HylaFAX is a fax server for Unix-like computer systems. It uses a client-server design and supports the sending and receiving of faxes as well as text pages, on any scale from low to very high volumes, if necessary making use of large numbers of ...

, Openfire 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 e ...

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.

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