Accessing Exchange 2007 Unified Messaging: Introduction

This how-to guide takes you through the steps required to access Exchange 2007 Unified Messaging features, such as Outlook Voice Access, using the open source tools Asterisk/Trixbox and sipX.

I’ve worked in several IT departments over the years, and thankfully, I have never been required to provide support for a company’s telephony systems. It has been an arrangement that has served me well over time. As an IT Pro, I have never seen the need to know or care about how telephony systems worked. As long as I could configure the odd ADSL modem, as far as I was concerned, I didn’t need to know any more. In most organisations, PBX support is usually outsourced to an external company. Sometimes the IT department manages this relationship, but in my experience, wherever possible, the IT department tries to stay as far away from the phone system as possible.

Recently, I’ve come to the realisation that my telephony-ignorance is unavoidably going to have to go. The rapid expansion of VoIP technologies is seeing more and more businesses replace their aging legacy PBXs with IP based PBXs and handsets. Telephony systems will be integrated into our physical networks, run on our servers, and even integrate with our desktop PCs. There’s just no escaping it.

The IP-PBX does provide an array of benefits over traditional systems. It provides integration with existing infrastructure, lower overheads and allows for a high level of customisation. By making use of standards based technologies, businesses have a lot more options available to them for managing their internal and external business communications. The Unified Messaging features integrated into Microsoft Exchange Server 2007 highlight the industry trend of moving to IP-PBXs. A company can integrate their IP-PBX with Microsoft Exchange, and truly unify their business communications in a single place, which is accessible through all the well-known interface of Microsoft Outlook.

This means that it is time for IT Pros, especially those that work with Microsoft Exchange, to start getting familiar with the technologies associated with VoIP. Traditional telephony will eventually be replaced in the workplace, and I’m afraid the IT department will not be able to weasel its way out of it this time. :)

Fortunately, we can get experience working with VoIP and Exchange UM without an existing IP-PBX or Exchange 2007 infrastructure, and we can do so at little or no cost. Leveraging the power of virtualisation, we can setup a working system on a single PC. These instructions will detail how to set up a system that will allow you to make use of Exchange UM and familiarise yourself with the VoIP protocols, giving you a valuable heads-up for when VoIP makes its way into your workplace. This guide will take you though the steps required to connect to your Exchange Server via a SIP based phone, or through a standard PSTN telephone connection.

We will use two open source products, Asterisk and sipX, to access Exchange UM. Exchange utilises SIP (Session Initiation Protocol) over TCP to provide access to its Unified Messaging features. The IP-PBX software we will use is called Asterisk, and it uses SIP over UDP for communications. We will use a third product, sipX which handles both SIP/TCP and SIP/UDP and acts as a gateway between the two systems.

Next: Part 1 - Requirements

Part 2 - Implementation Plan

Part 3 - Configuring the Exchange Server

Part 4 - Configuring the sipX Server

Part 5 - Configuring the SIP Client

Part 6 - Configuring the Trixbox/Asterisk Server