Did you know that it’s possible to build an entire telephony system centered around computers? One which is free of licensing costs too? Asterisk is a free software application written to do just that, and much more. Why? For the uninitiated, here’s why…

Wherever you go, your free software PBX follows!

The telephony industry has been facing a real crisis since the last decade. While the computer industry has undergone a host of transformations since its inception a couple of decades ago, the century old telephony industry has had problems coping with new ideas and advances. The reason for this is the lack of innovative thinking among makers of proprietary technologies that constitute the chaotic mess that we call the telephone system. These systems suffer from all the drawbacks that inherently bug all closed, proprietary systems. The problems surface as these systems progress deeper into their life cycle. The problems caused are typical of closed proprietary systems. From interoperability and scalability problems to problems caused due to lack of foresight during designing, these problems usually warrant expensive remedies. The technology used in these proprietary systems is usually closed and usually remains unpublished. Add to it the expensive licensing fees for this “sophisticated” proprietary technology and it becomes a no-no for users such as home users and small business users who also want a sophisticated, flexible telephony solution but cannot afford the expensive price tags. The success of revolutions like GNU/Linux is attributed to combined efforts of the likes of Linus Torvalds and a pool of geniuses, academicians, hobbyists, and geeks worldwide. Nobody in the telephony industry wanted to build an open, clean, scalable and seamlessly inter-operable platform for telephony like the internet. Fortunately for us, someone from computer science did! Meet Mark Spencer and his brainchild, aptly christened “Asterisk”. Asterisk is the “” character that appears on a standard touch-tone telephone pad. This “” character represents a wild card character in the world of computer systems, meaning that it can represent anything from a single character to multiple characters. And this is precisely what Mark Spencer intended Asterisk to represent in the world of telephony—anything and everything. Asterisk not only encompasses what we can presently do with telephony but also whatever we may think of doing with it in future. It is a revolution in the making and is all set to transform telephony.

Get your facts right…

So what exactly is Asterisk? Asterisk is a telephony platform that exists entirely in software. It is distributed under the GNU GPL (General Public License). This makes it possible for everybody to build and deploy their own customized professional telephony solution, from large corporations in search of a reliable ITSP platform to individuals who want to have their own PBX system.

Asterisk was created by Mark Spencer, the founder of Digium (formerly Linux Support Services).

Digium, a company founded by Mark Spencer is actively backing Asterisk. In fact, the purpose of creating Digium was largely for providing support services for the free software PBX. Today, Digium designs and supplies hardware for interfacing Asterisk with a host of networks including PSTN and ISDN PRI.

In compliance with free software tradition, community support for Asterisk is available through a host of portals including Digium’s support portal and a number of other websites like voipinfo.org which are powered by hordes of Asterisk enthusiasts and professionals. Community support is also available through FreeNode IRC channel where Asterisk developers and serious Asterisk geeks meet. Commercial support for Asterisk is available through Diguim and many other commercial establishments, some of whom are dedicated only to Asterisk installation and application development like Asterisk@Office.

How is Asterisk better than traditional telephony systems?

Asterisk is built as a vast flexible software platform composed of a bunch of programs that can perform whatever functions you program them to do instead of a bunch of wires and circuits which perform fixed functions in their range of operation. This is the reason why Asterisk achieves a degree of flexibility which traditional telephony platforms cannot do, no matter how ambitiously designed they are. Due to its being a software program, Asterisk’s extensibility is almost infinite, limited only by the goals of its developers.

What can be done using Asterisk?

The possibilities with Asterisk are unlimited. It can be used to build almost anything from a small home PBX to an ITSP (Internet Telephony Service Provider). With features that include voice mail, teleconferencing and call parking, Asterisk easily rivals the features of most modern PBX systems. Asterisk supports inter communications using protocols like the popular SIP or the newer IAX (Inter-Asterisk Exchange), H.323, MGCP, Skinny/SCCP and UNISTIM. To connect your PBX to the traditional PSTN (your telephone system) you can choose from a variety of options like traditional telephone lines, ISDN BRI lines, ISDN PRI lines and VoIP trunks from VoIP providers. Asterisk supports many popular codecs such as GSM, Ilibc, Speex, MP3, G.711, G.726, G. 723 and G729 for compression. Small businesses can set up Asterisk to have all features of a modern PBX at a fraction of the cost. Big corporations and businesses can build a PBX which can seamlessly connect their offices around the globe irrespective of their geographic locations.

What features of interest does Asterisk have for developers?

Asterisk is a developer’s dream come true. It has in-built database AstDB, a Berkeley DB Version 1 database. You can also have Asterisk connect to traditional relational databases using AGI, a standard interface with which external programs can control Asterisk dialplan. AGI can be written using many programming languages, though the language of choice is Perl due to its prowess in text processing. Using Asterisk in conjunction with AGI, you can integrate Asterisk into almost any computer application you like. Such is the power of Asterisk.

Selecting hardware and OS for Asterisk

Asterisk runs on Linux (preferably kernel 2.6 and above) with mostly any garden variety Intel X86 based CPU (I tested it with an old Intel Pentium II CPU running at 333 MHz with 128 MB of RAM and it seemed to work). But a powerful CPU like a Pentium 4 (preferably the multithreaded HT version or Dual Core) is recommended. The reason for this is that Asterisk may have to perform transcoding on incompatibly encoded streams (say GSM and MP3) in order to interlink them. This guzzles down a lot of CPU juice. Furthermore, the reason that Intel based CPUs are preferred is that not only do these CPUs have higher clock speeds (GigaHertz) but they have deeper pipelines. Such CPUs excel in operations such as encoding and decoding which have hardly any branching instructions that might require flushing of the CPU pipeline and hence make full use of the higher CPU speed.

Asterisk has been known to work with Windows and MacOS X but with severely crippled functionality. We won’t discuss other platforms here.

Installing Asterisk

Note that you require root privileges to install and run Asterisk. To install Asterisk, you have to have some distribution of Linux installed on your machine. So far, Asterisk is known to work with Debian, Fedora, Gentoo, Mandrake, Red Hat, Red Hat Enterprise Clones, CentOS, Pie Box, Tao Linux, Whitebox, Slackware, SUSE and Yellow Dog. So here are simplified the Asterisk installation steps… Make a directory for asterisk and related sources, change into it using the cd command and proceed.

 
# mkdir /usr/src/asterisk-src 
# cd /usr/src/asterisk-src