The Essential Guide to Asterisk

Updated: August 20, 2012

Created by Mark Spencer of Digium Inc. in 1999, Asterisk is an open-source PBX , telephony engine and telephony applications toolkit. The world's cheapest telephone system , Asterisk is free and runs on inexpensive Linux servers and other Unix options on a variety of hardware.

How Asterisk Works

From a technical standpoint, Asterisk supports TDM (time-division multiplexing) and VoIP, is written in C and uses the Unix standard POSIX (portable operating system interface) to communicate with the operating system. From a developer's vantage point, Asterisk is the culmination of code contributed from open-source developers around the world. Testing and patches from the community have also aided in the software's development. Where businesses are concerned, Asterisk empowers developers to create advanced communication solutions at little or no cost, while providing the functionality as high-end business telephone systems.

Experts estimate that Asterisk can save companies upward of 50 percent compared with proprietary voice systems . That's because this open-source software can run on off-the-shelf computers or servers, and doesn't require companies to lock into a long-term relationship with a vendor or fork over thousands of dollars for a tailored solution. Rather, any programmer skilled in Linux can customize a telephone system to the needs of a particular business. For those with limited expertise, Digium offers service teams to provide technical support throughout the entire process, as well as complete PBX solutions and specialty Asterisk add-in cards.

How Asterisk Helps

Asterisk can be used for a number of applications. These include:

• Switch: Asterisk can be configured as the core of an IP or hybrid PBX, switching calls, managing routes, enabling features and connecting callers with the outside world over IP, analogue and digital connections. This open-source software's architecture also supports VoIP in many protocols, and can interoperate with almost all standards-based telephony equipment.
• Gateway: Asterisk can be built as the heart of a media gateway, bridging a traditional PSTN (public switched telephone network) to IP telephony.
• Feature or media server: At only a fraction of the cost, Asterisk offers all the functionality of a traditional PBX. Special capabilities include IVR (interactive voice response), conference bridge, automated attendant, voice-mail system , unified messaging and Web-based telephony interface.
• Call-center system: With its unprecedented flexibility, Asterisk can serve as the foundation of a complete ACD (automatic call distributor) system with IP-agent capabilities, advanced skills-based routing and predictive dialing.
• Network: Asterisk acts as a powerful and low-cost platform for feature servers, hosted services clusters, voice-mail systems and prepaid calling solutions.

Asterisk Key Features

Asterisk offers high-end features once reserved for pricey proprietary PBXs. These features include:

• Call parking: Call parking lets users place a call on hold on an extension other than their own.
• Call queuing: This features allows your to queue calls.
• Call recording: Users can record conversations for monitoring purposes. This is ideal in a call-center setting.
• E911: Enhanced 911 is essential to support today's VoIP solutions.
• Predictive dialer: Predictive dialing optimizes the time that agents spend on the phone by predialing numbers when the system determines an agent will become available. This is an excellent feature for enhancing customer service.
• Overhead paging: Also known as an intercom, overhead paging allows a centrally located speaker to be dialed into for making announcements. This is especially useful in large workspaces such as a warehouse or retail store.
• Streaming media access: This feature allows streaming of media such as MP3s directly into the phone system.
• Supervised transfer: Rather than ambushing an unsuspecting employee, supervised transfer lets an operator transfer a call to another extension by first announcing that call to the transferred extension.
• Voice mail to email: Asterisk's native voice mail can send an email to the voice-mail recipient, and can optionally attach a .wav file of the complete message.

Beyond Asterisk

Fueled by Asterisk's popularity, an increasing number of vendors are introducing GUI add-ons for Asterisk. Fonality's trixbox Pro , for example, claims to help developers deploy Asterisk with embedded MySQL and a built-in CRM component in under an hour. The trixbox Pro core is essentially a stable, feature-rich version of Asterisk with modifications made to decrease internal structure lock contention, improve database handling and decrease crash scenarios. The solution includes over 50 unique configuration files modified from the original Asterisk codes, created in an effort to eliminate the bugs and crash cases reported to plague native Asterisk software.

Not all Asterisk installations are trouble-free, which is why companies can now receive assistance from an ever-expanding roster of Asterisk consultants . Seeking the help of a third party is especially critical if a company is looking to slowly upgrade its telephony system infrastructure over a period of time rather than replace its traditional PBX phone system in one fell swoop.