Asterisk (PBX)

From Wikipedia, the free encyclopedia
Developer(s)Sangoma Technologies Corporation
Stable release(s) [±]
21.2.0 (18 March 2024; 44 days ago (2024-03-18)[1])

20.5.0 LTS (18 October 2023; 6 months ago (2023-10-18)[2])
19.8.1 (7 July 2023; 9 months ago (2023-07-07)[3])

18.20.0 LTS (18 October 2023; 6 months ago (2023-10-18)[4])
Preview release(s) [±]
Written inC
TypeVoice over Internet Protocol
LicenseGPLv2 with additional licenses available from Digium[5] Edit this on Wikidata

Asterisk is a software implementation of a private branch exchange (PBX). In conjunction with suitable telephony hardware interfaces and network applications, Asterisk is used to establish and control telephone calls between telecommunication endpoints such as customary telephone sets, destinations on the public switched telephone network (PSTN) and devices or services on voice over Internet Protocol (VoIP) networks. Its name comes from the asterisk (*) 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.[6][7] Originally designed for Linux,[8] Asterisk runs on a variety of operating systems, including NetBSD, OpenBSD, FreeBSD, macOS, and Solaris, and can be installed in embedded systems based on OpenWrt.[9][10]


The Asterisk software includes many features available in commercial and 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 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 and stdout) or by network TCP sockets.

Asterisk supports several standard VOIP protocols, including the Session Initiation Protocol (SIP), the Media Gateway Control Protocol (MGCP), and H.323. Asterisk supports most SIP telephones, acting both as registrar and back-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. The Inter-Asterisk eXchange (IAX) protocol, RFC 5456, native to Asterisk, provides efficient trunking 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 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.


While initially developed in the United States, Asterisk has become a popular VoIP 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 for Halloween.[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]

Derived products[edit]

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.[15]
  • FreePBX, an open-source graphical user interface, bundles Asterisk as the core of its FreePBX Distro[16]
  • LinuxMCE 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 and email functions, respectively, before switching to 3CX.
  • Issabel is an open-source Unified Communications 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.[17]

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[18] 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 codecs and new features.[19] Some third-party add-ons are free;[20] a few even support embedded platforms such as the Raspberry Pi.[21]

See also[edit]


  1. ^ "ChangeLog-21-current". Retrieved 15 April 2024.
  2. ^ "ChangeLog-20-current". Retrieved 27 Oct 2023.
  3. ^ "ChangeLog-19-current". Retrieved 27 Oct 2023.
  4. ^ "ChangeLog-18-current". Retrieved 27 Oct 2023.
  5. ^ "Asterisk LICENSE". GitHub. Retrieved 2020-02-13.
  6. ^ Olejniczak, Stephen P.; Kirby, Brady (2007). Asterisk For Dummies. John Wiley & Sons. ISBN 9780470098547.
  7. ^ Van Meggelen, Jim; Smith, Jared; Madsen, Leif (2007). Asterisk: The Future of Telephony. O'Reilly Media, Inc. ISBN 9780596510480.
  8. ^ The README for version 0.1.0 states: "Currently, the Asterisk Open Source PBX is only known to run on the Linux OS, although it may be portable to other UNIX-like operating systems as well." See here Archived 2017-02-12 at the Wayback Machine
  9. ^ "Asterisk on OpenWrt". 6 June 2018. Retrieved 2018-06-10.
  10. ^ AstLinux: Boot via USB Flash Storage[permanent dead link]
  11. ^ download page of sound files for Asterisk
  12. ^ ץ "You are not the next caller in line" Archived 2016-03-04 at the Wayback Machine, parody on-hold message where a pre-recorded Allison Smith sheepishly confesses (at 0:00:45) that the caller is actually *not* next in queue and would be lucky to get a response at 11:30pm from the cleaning lady after other workers had left for the day.
  13. ^ "Zombie-Proof Your Phone System". Archived from the original on 2016-03-05. Retrieved 2016-01-04.
  14. ^ "Asterisk Voice Recordings". The IVR Voice. Archived from the original on 2015-01-18. Retrieved 2015-01-17.
  15. ^
  16. ^ Madsen, Leif; Jim Van Meggelen; Russell Bryant (2013). Asterisk: The Definitive Guide, 4th Edition (4th ed.). O'Reilly Media. p. 800. ISBN 978-1-4493-3242-6. 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.
  17. ^ "astTECS - THE IP-PBX PEOPLE". VoIP-Info. 12 July 2008.
  18. ^ "Allison On Demand".
  19. ^ "Asterisk Software Add-Ons". Digium. 2015-12-29. Archived from the original on 2015-03-16. Retrieved 2016-01-04.
  20. ^ Riddell, Matt (2009-08-08). "35 Great free Asterisk applications". Archived from the original on 2015-04-26. Retrieved 2016-01-04.
  21. ^ "The 5-Minute PBX: Incredible PBX 11 and Incredible Fax Get a Facelift". Nerd Vittles. 2013-06-18. Retrieved 2016-01-04.

External links[edit]