Asterisk is an open-source free communication software building framework. It can modify a simple computer into a communication server. By using asterisk we can connect a telephone to make calls to each other, and we can connect two different telephony services like Voice Over Internet Protocol service(VoIP) we connect with Public Switched Telephony Network(PSTN). We are usually Known as Asterisk as its symbol "*".

Historical Background of Asterisk
Asterisk was originally designed for Linux in 1999 by Mark Spencer. It was initially developed in America but with the passage of time, it becomes popular throughout the world because it is open source and freely available. Now asterisk is supported by the different operating systems such as OpenBSD, Mac OS X, NetBSD, Solaris, and FreeBSD.Asterisk can be used for small medium and large size organizations. We can boot it as an external disk drive and a flash drive and you can also use a virtual machine or live CD.

Requirements To Run Asterisk
Lets we see some of the requirements to make Asterisk functional.
1. You can use a stand-alone dedicated server or computer for the high running performance of asterisk.

2. You can use a SIP phone with an asterisk for communication.

3. You can use a Local Area Network(LAN) with an asterisk for communication.

4. You can use VoIP and PSTN as a trunk with an asterisk for termination.

Features Of Asterisk
Asterisk software has many features let us see some of these features.

1. Asterisk Gateway Interface(AGI) is a very useful feature of asterisk. By using the AGI program we can integrate different programming languages through the standard stream system.

2. Asterisk provides the feature of customization. By using an asterisk server you can write different dial plans according to your needs.

3. Asterisk software supports the feature of conference calling.

4. Asterisk software also supports the voice mail calling feature.

5. Feature of automatic call distribution is supported by asterisk software.

6. Interactive Voice Response(IVR) is a very useful feature of asterisk.

7. Customization feature of asterisk enables us to make a call center application in an asterisk. By using asterisk we can create call center functionality like call queue, Integrated Voice Response, Autodialer, Call monitoring feature, Call Recording, and centralized monitoring.

8. Asterisk support different type of protocols like Media Gateway Control Protocol(MGCP), Session Initiation Protocol(SIP) and Voice Over Internet Protocol(VoIP), etc.