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Asterisk comes in many flavors. Below are the most popular versions currently available.

What is Asterisk?

Asterisk is an open source software implementation of a telephone private branch exchange (PBX). Like any PBX, it allows a number of attached telephones to make calls to one another, and to connect to other telephone services including the PSTN. "Its name comes from the asterisk symbol, *, which in UNIX (including Linux) and DOS environments represents a wildcard, matching any filename."

Mark Spencer of Digium originally created Asterisk and remains its primary maintainer; dozens of other programmers have contributed features and functionality. Originally designed for the Linux operating system, Asterisk now also runs on OpenBSD, FreeBSD, Mac OS X, Sun Solaris, and Microsoft Windows, although as the "native" platform, Linux is the best-supported of these.

The basic Asterisk software includes many features previously only available in expensive 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 Asterisk's own language, by adding custom modules written in C, or by writing Asterisk Gateway Interface scripts in Perl or other languages.

To attach ordinary telephones to a Linux server running Asterisk, or to connect to PSTN trunk lines, the server must be fitted with special hardware. (An ordinary modem will not suffice.) Digium and a number of other firms sell PCI cards to attach telephones, telephone lines, T1 and E1 lines, and other analog and digital phone services to a server.

Perhaps of more interest to many deployers today, Asterisk also supports a wide range of Voice over IP protocols, including SIP and H.323. Asterisk can interoperate with most SIP telephones, acting both as registrar and as a gateway between IP phones and the PSTN. Asterisk developers have also designed a new protocol, IAX, for efficient trunking of calls among Asterisk PBXes.

By supporting a mix of traditional and VoIP telephony services, Asterisk allows deployers to build new telephone systems efficiently, or gradually migrate existing systems to new technologies. Some sites are using Asterisk servers to replace aging proprietary PBXes; others to provide additional features (such as voice mail or phone menus) or to cut costs by carrying long-distance calls over the Internet (toll bypass).

What is Asterisk@Home?

Asterisk@Home was created to make installing Asterisk easy. Experimenting with Asterisk should be fun and not take hours, days or asterisk experts to set up. Don't let the name Asterisk@Home fool you either. Asterisk@Home contains the full version of asterisk and other pre-configured software that makes this self installing/configuring CD a fully functional PBX upon installation.

Asterisk@Home is not crippled in any way. In fact, it's just the opposite. It's not only full-blown Asterisk but it's also AMP (Asterisk Management Panel, think of it as PHPmyAdmin for Asterisk) plus functioning music on hold (just try to get it working on a vanilla Linux box!) plus voice support for any speech application you can dream up plus a Flash Operator Panel plus ring groups plus calling queues plus conferencing plus DID routing plus SQL-compliant Call Detail Reporting plus SugarCRM contact management with integrated dialing plus SpanDSP fax support plus Microsoft Outlook TAPI integration with a Microsoft TAPI gateway (that works!) plus Apache, PHP, SSH, SFTP, SendMail, Web Mail, and MySQL integration plus Cisco XML support (to load your contact management info into your Cisco IP phones) plus xPL for Home Automation plus H.323 NetMeeting support plus turnkey support for SIP, IAX2, auto-configuring ZAP channels, and ENUM.

Are there folks that want to master calling plans, extension syntax, contexts, Linux, Apache, SendMail, MySQL, PHPmyAdmin, WebMin, Web Mail, Asterisk and all its add-on's plus Linux dependency hell? Absolutely. But Asterisk@Home doesn't preclude your using anything you learn. It just gives you an incredible, leveraged head start. Asterisk@Home is a deceptive moniker. It's not stripped-down, crippled, or condensed in any way. Quite the contrary, it's Asterisk on Steroids , plain and simple.

What is Asterisk Business Edition?

Digium™ the leader in open source telephony, offers Asterisk Business Edition, a professional-grade version of its acclaimed open source PBX for the Linux operating system. Asterisk Business Edition provides tested reliability of critical functions and features, tailored for small- and medium-sized business applications. An Asterisk technical manual and quick-start documentation supplements the package, making Asterisk even easier to install, configure, and use.

Asterisk Business Edition is backed by Digium's professional support team with a full one year limited warranty. This provides enterprise environments with a PBX and telephony platform suitable for critical business applications.

Digium's comprehensive test program ensures Asterisk Business Edition's reliability, performance, and interoperability with key hardware, software, and protocols. Digium hardware cards are tested for full compatibility with Asterisk Business Edition, as are several select models of servers, VoIP, and TDM devices. All major software features in Asterisk Business Edition are thoroughly tested for functionality and reliability. Test bed systems are also subjected to extreme stress conditions using Empirix™ test equipment to simulate hundreds of thousands of calls in various real-world combinations and configurations.

As a result, customers can rely on their combination of proven Asterisk software and Digium hardware to work together to provide a feature-rich PBX or VoIP system.