Asterisk Handbook Project Version 1(1).pdf

The *Asterisk Handbook

An Operator's Guide to Configuring the

Asterisk Private Branch Exchange Server

Mack Allison and Mark Spencer

Purpose of this Document -

The purpose of this document is to detail the steps to configuring an Asterisk Private

Branch Exchange Server. Basic telephony concepts are reviewed, and the design and layout of

an Asterisk installation is discussed. This document should help the reader plan and design

an installation for an enterprise installation, from the planning stages to configuring the

system.

Installation of the Asterisk software is covered in another document released

separately. Both documents are made available free of charge at www.linux-support.net.

Getting Support -

Community Support: Asterisk has a number of sources for support. As an open source

project, Asterisk has a community support network primarily via mailing lists and the Internet

relay chat system. Asterisk.org is a central place for open source and developer information.

A FAQ is available, as well as updates on the most recent developments in Asterisk. You can

questions about how to make things work, and share ideas and configuration tips. To sign up

for the Asterisk mailing list, send an e-mail message to asterisk-request@marko.net , with the

word 'subscribe' in the body of the message. You will receive a response e-mail verifying your

request and detailing how to make use of the mailing list.

Asterisk users (including the maintainer and project staff) can also be found on the

#asterisk channel on irc.openprojects.net . On IRC, you can chat with other users in real time

from anywhere in the world, and get advice and help from knowledgeable users of all

experience levels. For new IRC users, more information about IRC is available from

www.irc.net .

Commercial Support: Commercial support for Asterisk is available from Linux Support

Services, Inc. Linux Support Services is the primary sponsor of the Asterisk project, and

maintains copyright to the source code. LSS was founded by the primary author of the

Asterisk software, and offers a line of compatible hardware, commercial support for Asterisk,

and custom development and deployment services. Special license terms are also available for

the Asterisk software. For more information about products and services offered by Linux

Support Services, go to www.linux-support.net , or send an e-mail to sales@linux -support.net.

Documentation: Documentation on the Asterisk PBX is distributed in the Downloads

section at www.linux-support.net.

Installation of Asterisk -

Asterisk is distributed in source code form for maximum flexibility. Debian

GNU/Linux 3.x users can fetch packages from the Debian archives. Other distributions may

also offer Asterisk in binary format for their distributions. The best way to install Asterisk is

from source code, available from Linux Support Services as Linux standard tar.gz archives.

For detailed information on installing Asterisk, fetch the document 'Installing Asterisk' from

the downloads section at www.linux-support.net

Asterisk and Zaptel Telephony Interfaces -

Asterisk is commonly used with the Zaptel compatible interfaces sold by Linux Support

Services. In order to use Asterisk with Zaptel compatible telephony devices, the zaptel drivers

and Zapata libraries must be installed on the system prior to installing Asterisk. For

information on installing these software packages, go to the downloads section at www.linux-

support.net, and fetch the software and installation manuals.

Using the documentation and source code available at www.linux-support.net,

installation of Asterisk is quite straightforward and should take only a few minutes of

interactive time. Compile time varies based on the host system performance, but it's less than

10 minutes on a Pentium 450 or G4/400.

Currently, only the PowerPC and x86 architectures have been tested, and the PowerPC

has only been tested using the Motorola G4 processors used in higher end Apple hardware.

Athlon optimized kernels are not currently supported. If you have an AMD Athlon

family processor (K7, Athlon, Duron, Thunderbird, or XP) it is recommended that you use a

kernel compiled for i686 with MMX optimizations on.

An Introduction to Telephony (Linux Style)

This section is intended primarily for person's who have very limited telephony

background, though most Asterisk users will benefit from reading this. In this section, we'll

go over some common telephony concepts, the basic functions of a PBX from a technical

standpoint, and how all this fits together on the Linux platform with the Asterisk server.

Asterisk is what we call a 'Hybrid VoIP/TDM Private Branch Exchange Server.' What

this means is that Asterisk supports both traditional analog and digital telephony equipment

(commonly referred to as TDM) and the new arena of Voice over IP, in which voice traffic is

carried over modern data networks just as other data, in IP packets. For this reason Voice

over IP is often referred to as Packet Voice. Both technologies have their strengths and

weaknesses, and for the foreseeable future, they will live side by side. Asterisk is designed to

facilitate inter-operation between VoIP and TDM as seamlessly as possible.

TDM Equipment - The backbone of traditional telephony.

TDM equipment is the stuff telephony is made of today. Most of this equipment is

analog, and uses a variety of signaling types and technologies to do the job. An extensive

knowledge of TDM systems is not necessary to run an Asterisk server. There are a few terms

to understand when using Asterisk in conjunction with channel banks and analog handsets, or

using Asterisk to terminate and route a T1 line for voice traffic.

Phone equipment is normally signaled using Foreign Exchange signaling. There are

two sides to this signal, the Office side and the Station side, commonly referred to as FXO and

FXS. This is (slightly) analogous to client and server. A simple example of FXO and FXS

exists in (almost) everyone's home. The wall jack you plug the phone into is an FXS device. It

provides FXS signaling to the FXO device you connect to it, most commonly a

simple handset. The handset, an FXO device, provides FXO signaling to the FXS device on

the other end.

This may be confusing at first. FXO devices provide FXO signaling, and are signaled

with FXS signaling. FXS devices provide FXS signaling and are signaled with FXO signaling.

What this means in practice is that FXO devices are signaled with FXS, and vice versa. This

will be essential to keep in mind when setting up Zaptel TDM interface devices for use with

Asterisk.

Many users will choose to use a T1 interface device and a channel bank to handle both

incoming and outgoing calls. A T1 line carries 24 channels. A channel bank is a device that

breaks a T1 line into its separate channels and provides a means to connect these separated

channels to telephone handsets or incoming telephone lines. The channel bank may have any

mixture of FXO and FXS channels available depending on its model and configuration. The

FXO

Channels on the channel bank can be connected to standard incoming analog lines, in place of

a telephone handset. The FXO channels will typically be connected to desk phones for users

in the office.

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