What is asterisk and what can it do?

Asterisk is a complete PBX in software. It runs on Linux and provides all of the features you would expect from a PBX and more. Asterisk does voice over IP in many protocols, and can interoperate with almost all standards-based telephony equipment using relatively inexpensive hardware. It is completely open source software.

Asterisk provides Voicemail services with Directory, Call Conferencing, Interactive Voice Response and Call Queuing. It has support for three-way calling, caller ID services, ADSI, SIP and H.323 (as both client and gateway) plus many more too numerous to list here. It also supports most codecs although you will have to pay a license fee to digium who wrote the asterisk system if you want to use the higher compressed G.729 codec.

Asterisk needs no additional hardware for Voice over IP. For interconnection with digital and analog telephony equipment, Asterisk supports a number of hardware devices.

Asterisk can be used in a wide variety of setups, and is attractive because of its price. Yes Asterisk itself is free, being open source, but it uses hardware that is less expensive then buying a whole package from, say, Cisco. Of course there are all the features Asterisk provides as well and if the feature isn't there, you can implement it yourself or hire someone to implement it for you.

It is now possible to build a pure software-based PBX. The VoIP carrier provides the interconnection to the public telephone network, external telephone numbers, and so on. With a Linux server, off-the-shelf LAN/WAN hardware, a broadband connection, and SIP-compatible telephone handsets, one can now build a fully functional telephone system, complete with high-end features.

The importance of this shift is that telephony is no longer the province of exotic and overpriced hardware. It is just another service that runs on standard-issue server hardware. Of course, specialized knowledge is required to configure and manage these systems. However, now that Asterisk is being deployed more and more into production environments and more people are becoming aware of it, so more people will have the skills to configure asterisk.

For thoses people out there not wanting to get too involved into configuring asterisk there is a version called Asterisk@home which is a bootable CD that will install everything you need to get your asterisk PBX up and going including RedHat Linux.

There are many resources available on the internet to help you configure asterisk. A list of Asterisk resources can be found here.