Asterisk is a

software Software consists of computer programs that instruct the Execution (computing), execution of a computer. Software also includes design documents and specifications. The history of software is closely tied to the development of digital comput ...

implementation of a

private branch exchange A business telephone system is a telephone system typically used in business environments, encompassing the range of technology from the key telephone system (KTS) to the private branch exchange (PBX). A business telephone system differs from ...

(PBX). In conjunction with suitable

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

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

telephone call A telephone call, phone call, voice call, or simply a call, is the effective use of a connection over a telephone network between the calling party and the called party. Telephone calls are the form of human communication that was first enabl ...

s between

telecommunication Telecommunication, often used in its plural form or abbreviated as telecom, is the transmission of information over a distance using electronic means, typically through cables, radio waves, or other communication technologies. These means of ...

endpoints such as customary

telephone A telephone, colloquially referred to as a phone, is a telecommunications device that enables 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 ...

sets, destinations on the

public switched telephone network The public switched telephone network (PSTN) is the aggregate of the world's telephone networks that are operated by national, regional, or local telephony operators. It provides infrastructure and services for public telephony. The PSTN consists o ...

(PSTN) and devices or services on

voice over Internet Protocol Voice over Internet Protocol (VoIP), also known as IP telephony, is a set of technologies used primarily for voice communication sessions over Internet Protocol (IP) networks, such as the Internet. VoIP enables Voice call, voice calls to be tran ...

(VoIP) networks. Its name comes from the

asterisk The asterisk ( ), from Late Latin , from Ancient Greek , , "little star", is a Typography, typographical symbol. It is so called because it resembles a conventional image of a star (heraldry), heraldic star. Computer scientists and Mathematici ...

(*) 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, has been a division of

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

. Originally designed for

Linux Linux ( ) is a family of open source Unix-like operating systems based on the Linux kernel, an kernel (operating system), operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically package manager, pac ...

, Asterisk runs on a variety of

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

s, including

NetBSD NetBSD is a free and open-source Unix-like operating system based on the Berkeley Software Distribution (BSD). It was the first open-source BSD descendant officially released after 386BSD was fork (software development), forked. It continues to ...

OpenBSD OpenBSD is a security-focused operating system, security-focused, free software, Unix-like operating system based on the Berkeley Software Distribution (BSD). Theo de Raadt created OpenBSD in 1995 by fork (software development), forking NetBSD ...

FreeBSD FreeBSD is a free-software Unix-like operating system descended from the Berkeley Software Distribution (BSD). The first version was released in 1993 developed from 386BSD, one of the first fully functional and free Unix clones on affordable ...

macOS macOS, previously OS X and originally Mac OS X, is a Unix, Unix-based operating system developed and marketed by Apple Inc., Apple since 2001. It is the current operating system for Apple's Mac (computer), Mac computers. With ...

, and

Solaris Solaris is the Latin word for sun. It 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 ** ''Sol ...

, 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 kernel, Linux, primarily used on Embedded system, embedded devices to Router (computing), route network traffic. The main components ...

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 callers to leave a Voice recording, recorded message when the recipient has been unable (or unwilling) to answer the Telephone, phone. Calls may ...

conference call A conference call (sometimes called an audio teleconference or ATC) is a telephone call in which several people share a telephone line at the same time. The conference call may be designed to allow the called party to participate during the cal ...

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 telephony, IVR allows customers to interact with a ...

(phone menus), and

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

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

stdin In computer programming, standard streams are preconnected 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 preconnected 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

VOIP Voice over Internet Protocol (VoIP), also known as IP telephony, is a set of technologies used primarily for voice communication sessions over Internet Protocol (IP) networks, such as the Internet. VoIP enables voice calls to be transmitted as ...

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 telecommunication protocol for signaling and call control in hybrid voice over IP (VoIP) and traditional telecommunication systems. It implements the media gateway control protocol architecture f ...

(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 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 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 voice over IP tele ...

(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 clie ...

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. ...

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 (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...

, Asterisk has become a popular

VoIP Voice over Internet Protocol (VoIP), also known as IP telephony, is a set of technologies used primarily for voice communication sessions over Internet Protocol (IP) networks, such as the Internet. VoIP enables voice calls to be transmitted as ...

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 geography of Halloween, observed in many countries on 31 October, the eve of the Western Christianity, Western Christian f ...

. 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 m0n0wall was an embedded firewall (networking), firewall distribution of FreeBSD, one of the Berkeley Software Distribution, BSD operating system descendants. It provided a small image which could be put on flash memory, Compact Flash cards as w ...

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

software distribution Software distribution is the process of delivering software to the end user. Free software distribution tools GNU Autotools are widely used for which consist of source files written in C++ and the C programming language, but are not limited t ...

. *

FreePBX FreePBX is a web-based open-source graphical user interface (GUI) that manages Asterisk, a voice over IP (VoIP) and telephony server. FreePBX is licensed under the GNU General Public License version 3, with commercial modules available under the ...

, an open-source

graphical user interface A graphical user interface, or GUI, is a form of user interface that allows user (computing), users to human–computer interaction, interact with electronic devices through Graphics, graphical icon (computing), icons and visual indicators such ...

, 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 previously used Asterisk, HylaFAX, Openfire and Postfix to offer PBX, fax,

instant messaging Instant messaging (IM) technology is a type of synchronous computer-mediated communication involving the immediate ( real-time) transmission of messages between two or more parties over the Internet or another computer network. Originally involv ...

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. * Grandstream's UCM series of IP-PBX appliances uses Asterisk with a custom web interface. * E-MetroTel UCX is a system developed by former

Nortel Nortel Networks Corporation (Nortel), formerly Northern Telecom Limited, was a Canadian Multinational corporation, multinational telecommunications and data networking equipment manufacturer headquartered in Ottawa, Ontario. It was founded in ...

engineers, running on Asterisk, designed to work with Nortel's digital and IP phones, as well as to integrate with other Nortel equipment. It also works with other products from other vendors, including

NEC is a Japanese multinational information technology and electronics corporation, headquartered at the NEC Supertower in Minato, Tokyo, Japan. It provides IT and network solutions, including cloud computing, artificial intelligence (AI), Inte ...

, Mitel,

Avaya Avaya LLC(), formerly Avaya Inc., is an American multinational technology company headquartered in Morristown, New Jersey, that provides cloud communications and workstream collaboration services. The company's platform includes unified commun ...

, and

Cisco Cisco Systems, Inc. (using the trademark Cisco) is an American multinational digital communications technology conglomerate corporation headquartered in San Jose, California. Cisco develops, manufactures, and sells networking hardware, s ...

. 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 computer hardware or software component 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 o ...

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 collaboration with Broadcom Inc., Broadcom. To commercialize the product and support its growing demand, the ...

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