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|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. 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 under 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(GPL) as a free software license and a proprietary software license to permit licensees to distribute proprietary, unpublished system components.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 also 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 like Customer-premises equipment-hardware running OpenWrt.
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 a wide range of Voice over IP protocols, including the Session Initiation Protocol (SIP), the Media Gateway Control Protocol (MGCP), and H.323. Asterisk can interoperate with most SIP telephones, acting both as registrar and as a gateway between IP phones and the PSTN. The Inter-Asterisk eXchange (IAX2) protocol, RFC 5456, native to Asterisk, provides efficient trunking of calls among Asterisk PBXes, in addition to distributed configuration logic, and call completion to VoIP service providers who support it. Some telephones support the IAX2 protocol directly (see Comparison of VoIP software for examples).
By supporting a mix of traditional and VoIP telephony services, Asterisk allows deployers to build new telephone systems, or gradually migrate existing systems to new technologies. Some sites are using Asterisk servers to replace proprietary PBXes; others to provide additional features (such as voice mail or voice response menus, or virtual call shops) or to reduce costs by carrying long-distance calls over the Internet (toll bypass).
Asterisk was one of the first open source PBX software packages.
In addition to VoIP protocols, Asterisk supports many traditional circuit-switching protocols such as ISDN and SS7. This requires appropriate hardware interface cards supporting such protocols, marketed by third-party vendors. Each protocol requires the installation of software modules. With these features, Asterisk provides a wide spectrum of communications options.
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 new prompts like Australian English  for the Interactive voice response and voice mail features of Asterisk are frequently updated with submissions from developers in many languages and dialects. Additionally, voice sets are offered for commercial sale in different languages, dialects and genders.
Asterisk is a core component in many PABX in a box 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 as open source. Open-source examples include FreePBX and Elastix.
Asterisk is also included in the LinuxMCE home entertainment/automation system.
- 2600hz IPBX
- Comparison of VoIP software
- FreeSWITCH IPBX
- GateKeeper H.323
- GNU SIP Witch
- List of SIP software
- SIP Express Router
- Sippy B2BUA
- Olejniczak, Stephen P.; Kirby, Brady (2007). Asterisk For Dummies. John Wiley & Sons. ISBN 9780470098547.
- Van Meggelen, Jim; Smith, Jared; Madsen, Leif (2007). Asterisk: The Future of Telephony. O'Reilly Media, Inc. ISBN 9780596510480.
- "Asterisk on OpenWrt". Retrieved 2011-10-09.
- "74 Open Source VoIP Apps & Resources". VoIP Now. 2007-04-16. Archived from the original on 25 December 2007. Retrieved 2007-12-22.
- "Index of /pub/telephony/sounds". Downloads.asterisk.org. 2013-04-29. Retrieved 2013-05-26.
- Official website
- Asterisk Wiki
- Asterisk Documentation Project (download the O'Reilly book for free)
- Forbes article about Mark Spencer and Asterisk
- #asterisk on freenode
- Interview with Mark Spencer on Leo Laporte's TWIT.TV FLOSS Weekly podcast
- Selector Free MeetMe GUI
- AppKonference High-performance Asterisk conferencing module, is a fork of ("MeetMe" alternative)