VoIP Hacks

Chapter 4. Asterisk

Hacks 41–58: Introduction

The Linux domain of free software is a land flowing like milk and honey with telephony hacks—the hackers’ Promised Land, so to speak. Of course, many of these hacks translate to BSD, and even to Mac OS X, since they’re cast from a similar Unix mold.

In this chapter, I’ll cover Asterisk—the open source telephony server designed originally for Linux, but now available for Mac OS X and BSD. Asterisk is a workhorse, a flexible, open system that’s the telephony equivalent of Apache, the world’s most widespread web server.

Because of its modularity and flexibility, Asterisk is as much a platform as is Linux. It’s sort of become the cornerstone of Linux-based telephony, thanks to a vibrant developer community and a sound, open source foundation.

Getting Telephony Devices Connected to Asterisk

Besides implementing "pure VoIP”—voice calls over packet networks like the Internet or your Internet Protocol local area network (IP LAN)—Asterisk can also handle legacy telephone technologies, such as analog phones and phone lines, T1 lines, and various kinds of legacy signaling methods. A large and growing selection of PC expansion (PCI) cards are available that facilitate connecting analog phones and phone lines to an Asterisk server. So, if you want, you can build an Asterisk server that doesn’t use VoIP at all—just legacy technologies like analog phones. Or you can build a server that bridges those previous-generation devices with Voice over IP.

The Asterisk ...