| Asterisk | |
|---|---|
 | |
| Developer | Sangoma Technologies Corporation |
| Stable release(s)[±] | |
| 21.3.1 (17 May 2024; 18 months ago (2024-05-17)[1]) 20.5.0 LTS (18 October 2023; 2 years ago (2023-10-18)[2]) | |
| Preview release(s)[±] | |
| Repository | |
| Written in | C |
| Type | Voice over Internet Protocol |
| License | GPLv2 with additional licenses available from Digium[5] |
| Website | www |
Asterisk is asoftware implementation of aprivate branch exchange (PBX). In conjunction with suitabletelephony hardware interfaces and network applications, Asterisk is used to establish and controltelephone calls betweentelecommunication endpoints such as customarytelephone sets, destinations on thepublic switched telephone network (PSTN) and devices or services onvoice over Internet Protocol (VoIP) networks. Its name comes from theasterisk (*) symbol for a signal used indual-tone multi-frequency (DTMF) dialing.
Asterisk was created in 1999 byMark Spencer ofDigium, which, since 2018, has been a division ofSangoma Technologies Corporation.[6][7] Originally designed forLinux,[8] Asterisk runs on a variety ofoperating systems, includingNetBSD,OpenBSD,FreeBSD,macOS, andSolaris, and can be installed in embedded systems based onOpenWrt.[9][10]
The Asterisk software includes many features available in commercial and proprietary PBX systems:voice mail,conference calling,interactive voice response (phone menus), andautomatic call distribution. Users can create new functionality by writing dial plan scripts in several of Asterisk's ownextensions languages by adding custom loadable modules written in PHP orC or by implementingAsterisk Gateway Interface (AGI) programs using any programming language capable of communicating via the standard streams system (stdin andstdout) or by network TCP sockets.
Asterisk supports several standardVOIP protocols, including theSession Initiation Protocol (SIP), theMedia Gateway Control Protocol (MGCP), andH.323. Asterisk supports most SIP telephones, acting both as registrar andback-to-back user agent. It can serve as a gateway between IP phones and the PSTN via T- or E-carrier interfaces or analog FXO cards if the DAHDI (Digium Asterisk Hardware Device Interface) library is installed. TheInter-Asterisk eXchange (IAX) protocol, RFC 5456, native to Asterisk, provides efficienttrunking 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 virtualcall 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 asISDN andSS7. This requires appropriate hardware interface cards, marketed by third-party vendors. Each protocol requires the installation of software modules. In Asterisk release 14 theOpus audio codec is supported.
While initially developed in theUnited States, Asterisk has become a popularVoIP 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.[11] A few novelty prompts are offered, such as jokes[12] and a themed "zombie apocalypse" message forHalloween.[13] 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.[14]
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.
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[20] 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, additionalcodecs and new features.[21] Some third-party add-ons are free;[22] a few even support embedded platforms such as theRaspberry Pi.[23]
FreePBX, the juggernaut of the Asterisk community. This interface (which is at the heart of many of the most popular Asterisk distributions, such as AsteriskNOW, Elastix, the FreePBX Distro, and PBX in a Flash), is unarguably a very large part of why Asterisk has been as successful as it has. With the FreePBX interface, you can configure and manage many aspects of an Asterisk system without touching a single configuration file. While we purists may like everyone to work only with the config files, we recognize that for many, learning Linux and editing these files by hand is simply not going to happen. For those folks, there is FreePBX, and it has our respect for the important contributions it has made to the success of Asterisk.
Based on Asterisk* version 16 open source telephony operating system
