Before defining asterisk, it will be helpful to understand the telephone system. In residential homes, there is typically one phone number that reaches the household and when it does, it rings the phone(s) in the residence. In the business enterprise, a phone system needs a swtichboard to be in place to route phone calls throughout the business. When calling into a business phone system, an operator or automated attendant will direct the phone call to the intended destination.

The original phone system, known as POTS (Plain old telephone system) carried analog voice data across telephone lines. The telephone network is referred to as the Public switched telephone network (PSTN). Over the years new telephony technologies emerged and the current trend for businesses is to use Voice over Internet Protocol (VOIP) to handle their phone systems. Rather than relying on the PSTN, calls using VOIP send phone data across the Internet.

Asterisk was originally created to be a Private Branch Exchange (PBX) system connecting the business phone systems to the POTS. Today, Asterisk is known for being an IP PBX system, also called a Unified Communications system, which basically means that it acts as a central switching system for phone calls using the Internet. Asterisk centrally handles the traffic between a business’s phones and also acts as a gatekeeper to the public phone network.

Asterisk is open source, meaning the code that was written to create the application is freely available. It is written in the C Programming language and can be installed on Linux or the Macintosh operating system.

With Asterisk, a company can connect the software to a phone number, provide extensions to their employees, setup voicemail systems, play music while on hold, provide interactive voice menus to customers, setup conference calling, and program the system to handle phone calls with an unlimited number of options. In addition to the typical phone services, Asterisk can be configured to handle many newer technologies such as SMS, email, instant messaging, and video conferencing.