Asterisk (PBX)

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Asterisk Logo.svg
Developer(s) Digium
Stable release

13.0.0 (24 October 2014; 3 months ago (2014-10-24)) [±]

11.13.1 (20 October 2014; 3 months ago (2014-10-20)) [±]
Preview release

13.0.0-beta3 (October 20, 2014; 3 months ago (2014-10-20)) [±]

11.13.0-rc1 (September 19, 2014; 4 months ago (2014-09-19)) [±]
Written in C
Operating system Cross-platform
Type Voice over Internet Protocol
License GNU General Public License / Proprietary

Asterisk is a software implementation of a telephone private branch exchange (PBX); it was created in 1999 by Mark Spencer of Digium.[1][2] Like any PBX, it allows attached telephones to make calls to one another, and to connect to other telephone services, such as the public switched telephone network (PSTN) and Voice over Internet Protocol (VoIP) services. Its name comes from the asterisk symbol, *.

Asterisk is released with a dual license model, using the GNU General Public License (GPL) as a free software license and a proprietary software license to permit licensees to distribute proprietary, unpublished system components.

Originally designed for Linux, Asterisk runs on a variety of operating systems, including NetBSD, OpenBSD, FreeBSD, Mac OS X, and Solaris. Asterisk is small enough to run in an embedded environment such as Customer-premises equipment-hardware running OpenWrt.[3] There are complete self-contained versions that can boot from a storage device such as a flash drive or external disk drive (preferably IDE/PATA, SATA or mSATA; a USB-connected device can be used, but is often not recommended).[4] A live CD or virtual machine can also be used.[5]


The Asterisk software includes many features available in 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 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 voice over IP 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, and can serve as a gateway between IP phones and the public switched telephone network (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 among Asterisk PBXes, 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 long-distance calls over the Internet (toll bypass).

Asterisk was one of the first open source PBX software packages.[6]

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.


While initially developed in the United States, Asterisk has become a popular VoIP PBX worldwide because it is freely available under open-source licensing, and has a modular, extensible design. The American English, French, Persian (Farsi) and Mexican Spanish female voices along with other prompts, such as Australian English, for the interactive voice response and voice mail features are frequently updated with submissions from developers in many languages and dialects. A few novelty prompts are offered, such as the themed message "zombie apocalypse" for Halloween.[7] Additionally, voice sets are offered for commercial sale in various languages, dialects, and genders.

The default set of English-language Asterisk prompts, included with the package, are recorded by professional telephone voice Allison Smith in Calgary, Alberta.[8]

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.

See also[edit]


  1. ^ Olejniczak, Stephen P.; Kirby, Brady (2007). Asterisk For Dummies. John Wiley & Sons. ISBN 9780470098547. 
  2. ^ Van Meggelen, Jim; Smith, Jared; Madsen, Leif (2007). Asterisk: The Future of Telephony. O'Reilly Media, Inc. ISBN 9780596510480. 
  3. ^ "Asterisk on OpenWrt". Retrieved 2011-10-09. 
  4. ^ AstLinux: Boot via USB Flash Storage. "For production AstLinux installations, it is recommended to use flash storage connected off IDE, SATA or mSATA controllers ... it takes longer for USB storage devices to be recognized ... AstLinux may fail ... followed by the USB drive mounting a few seconds later."
  5. ^ AstLinux Users Guide Chapter 1
  6. ^ "74 Open Source VoIP Apps & Resources". VoIP Now. 2007-04-16. Archived from the original on 25 December 2007. Retrieved 2007-12-22. 
  7. ^
  8. ^
  • Asterisk: The Definitive Guide, 4th ed., Russell Bryant, Leif Madsen, and Jim Van Meggelen, pub. O'Reilly, 2013, ISBN 978-1449332426

External links[edit]