User guide

VoIP appliances will allow you to set a “jitter buffer.” A jitter buffer is a shared data area where voice

packets can be collected, stored, and sent to the voice processor in evenly spaced intervals. The jitter

buffer, which is located at the receiving end of the voice connection, intentionally delays the arriving

packets so that the end user experiences a clear connection with little sound distortion.

The two kinds of jitter buffers are called static and dynamic. A static jitter buffer

is hardware-based and is configured by the manufacturer. A dynamic jitter

buffer is software-based and can be configured by the user.

A common value for a dynamic jitter buffer is 100 ms. You can improve the quality of the conversation

(good noise) by increasing the buffer but with the drawback of increasing the overall delay.Hands on –

Building your PBX

5. Hands on – Building your PBX

5.1 What do I need?

The first thing that you are going to need is a personal computer. Any computer manufactured after

year 2000 should be powerful enough to run

Asterisk

and get you started. The computer should run

any flavour of the Linux operating system.

The cheapest and easiest option to start learning is to use “softphones.” The first exercise should be to

learn how to place a phone call between two computers using your own PBX. The simplest testbed to

get you started is two computers with sound cards on which to install two VoIP software clients, and a

third computer to install

Asterisk

In the case that you want to use VoIP hardware clients (such as VoIP phones or ATAs), or to interface

with the PSTN, you are going to need some of the hardware described in Section 3.5.

If you plan to build a portable PBX that runs with low power, have a look at mini-ITX boards. The EPIA

M10000 board (known as Nehemiah) has two PCI slots where you can plug a Digium TDM400P Card.

25. If you are a newcomer to Linux consider downloading or order a CD of Ubuntu. http://www.ubuntu.com

26. A good supplier of VoIP hardware with special discounts for non-profit projects is http://www.avanzada7.com

27. A “portable PBX” will allow you to showcase the technology with the amazing advantage of being able to carry your own

Telephone Exchange as hand luggage.

Page 19 TRICALCAR | www.wilac.net/tricalcar – Version: February 2008