Welcome back to the Transparent Telephony series. If you're a new reader, you may want to start at the beginning: Part 1 - An Introduction.

In the previous installment, we walked through installing Asterisk. In this article, we'll be picking up where we left off and configuring Asterisk to make and receive phone calls using VoIP!

Specifically, we'll:

Welcome back to the Transparent Telephony series. If you're new, you may want to check out part 1 here: Transparent Telephony - Part 1 - An Introduction.

This series is designed for technical people, programmers, and just general enthusiasts who want to learn: how telephony works, how to setup your own phone server (PBX), how to write telephony applications, and how to reduce your phone expenses. There are tons of neat things you can do with telephony knowledge, so keep reading!

This article will walk you through installing Asterisk on your CentOS or Ubuntu server. If you are going to install on a virtual machine to follow along, I recommend using VirtualBox, as everything should work out of the box. Certain virtual machine programs like Xen have kernel issues which makes installing Asterisk difficult. Also, never ever use Asterisk in production on a virtual machine! You'll have timing issues (this will be explained later in the series).

Introduction

The Asterisk Gateway Interface, commonly referred to as AGI, is a language-independent API for processing calls. It allows programmers to write simple programs to manipulate and route calls on Asterisk servers in a simple, easy manner.

This article provides a technical introduction to the AGI, explaining how it works, how it can be used, where you can find API documentation, and even provides some basic code samples which demonstrate how to use the AGI. The intended audience is programmers, telephony enthusiasts, or IT people who want to learn more about adding functionality to their Asterisk PBX systems. This is not a full programming reference, and will not explain how to write AGI programs, it will merely teach you what the AGI provides and how to use it high-level.

Intro

Denial of Service attacks are nothing new to people in the IT and computer security world. DoS attacks are a very simplistic form of attack which aim to flood the target (whether it be a computer, mobile device, or phone line) with traffic so that it cannot process legitimate traffic. While being simple simple to perform, DoS attacks are often difficult to defend against without significant downtime.

Today I'm going to show you how to perform a DoS attack on a phone line. This process is simple, quick to perform, and very illegal. Before we get started, I'd just like to remind you that this article is for educational purposes only! All the code I'm putting into this article is python, and should work on any system with python 2.4+.

So you've probably heard the word telephony thrown around from time to time. Maybe you were hanging out in a certain IRC channel, wanted to root your cell phone, or maybe, just maybe, you were actually interested in doing something cool with your computers and phones.

This article is the first of a series. I'm going to try my best to explain what telephony is, how it works, and how to write cool programs that integrate voice and data. Telephony is a huge market, and used everywhere (think cell phones). We are living in a time when telephony is casual, common, and popular. While being so huge, it often astounds me to think of how few programmers and tech people ever get around to learning about it, or playing with it. There are very few telephony programmers, and even less proper documentation. My hopes are that these articles will give you a solid foundation in telephony and inspire you to play around with it on your own, and do cool things.

Now that we've got the basics out of the way, let's get down to business...