Asterisk: The Definitive Guide, 5th Edition

Chapter 7. Outside Connectivity

You cannot always control what goes on outside. But you can always control what goes on inside.

Wayne Dyer

In the previous chapters, we have covered a lot of important information that is essential to a working Asterisk system. However, we have yet to discuss something that is vital to any useful PBX: namely, connecting it to the outside world. In this chapter we will discuss outside connectivity.

The groundbreaking architecture of Asterisk was significant due in large part to the fact that it treats all channel types as equal. This is in contrast to a traditional PBX, where trunks (which connect to the outside world) and extensions (which connect to users and resources) are logically separated. The fact that the Asterisk dialplan treats all channels in a similar manner means that in an Asterisk system you can accomplish very easily things that are much more difficult (or impossible) to achieve on a traditional PBX.

This flexibility does come with a price, however. Since the system does not inherently know the difference between an internal resource (such as a telephone set) and an external resource (such as a telco circuit), it is up to you to ensure that your dialplan handles each type of resource appropriately.

The Basics of Trunking

The purpose of trunking is to provide a shared connection between two entities. Trees have trunks, and everything that passes between the roots and the leaves happens through the trunk. Railroads use the term “trunk” to ...