The cold-war between Microsoft and Cisco for the much coveted "unified communications" market has escalated to all out war, with Microsoft Chairman Bill Gates predicting "the death of the PBX."

Before we delve deeper I have to come clean. My day job is as senior network engineer for a Cisco VoIP partner. I have a vested interest in seeing the Cisco side of things dominate. But long ago I realized there is no use digging your head in the sand when something new comes along. Hence the hours I should have devoted to studying for my CCIE Voice lab exam have instead been spent attempting (mostly successfully) to understand, use and integrate the Microsoft IP telephony and VoIP solutions to the best possible advantage.

Depending on who you talk to, unified communications is described as telephone and video collaboration, or as a converged network for voice and data, or used as an all-encompassing term to describe all forms of call and multimedia/cross-media message-management functions. For now, I'll use it to refer to any IP telephony solution that can co-exist with data.

Unless you have been living in a cave, you have to have noticed the buzz surrounding unified communications. In fact Gartner identifies it as one of the "Top 10 Strategic Technologies for 2008". It is a competitive space currently filled by traditional PBX vendors (such as Avaya, Nortel, Alcatel, etc.) and some would say dominated by Cisco who long ago realized that IP telephony is more than just a way to help sell more POE switches.

Microsoft entered the market with much gusto with the release of Office Communication Server 2007 in October but, truth be told, the company has been dabbling in this space long before.

That Microsoft has experience with VoIP should come as no surprise. After all, the fundamentals of VoIP and IP telephony are simple: signaling protocols (such as the open standards SIP, H.323 and MGCP and the Cisco-proprietary SCCP) create and tear down calls between two like-protocol end-points, while the actual voice is encoded inside a codec (such as G.711, G.729) and is then transported over an RTP stream (RTP being a simple extension to UDP).

Microsoft has employed aspects of the technology in a range of offerings. Microsoft's Xbox Live service, for example, uses voice to allow players to scream insults at enemy players or give orders to teammates while playing the hottest new Xbox title (such as Call of Duty 4). Microsoft Net Meeting, a rudimentary IP softphone, has been around for a long time, and before Office Communication Server there was Microsoft Live Communication Server 2005, a presence server that enabled Live Communication clients to see the status of other employees (for example, on the phone, in a meeting, etc.). Even the enterprise-staple, Microsoft Exchange 2007, has been getting in on the action, supporting "unified messaging" which, translated, basically means electronic, voice and fax "mail" all being accessible via a single interface.

Many of Microsoft's proposed IP telephony/VoIP products have only just come to market, so it is worth re-hashing the pieces that make up the Microsoft solution and where they coexist with (or replace, depending on which side of the fence you sit) traditional PBX technologies.

The oft-hyped Office Communication Server is essentially the PBX destroyer. Equipped out of the box with "presence" (something you need to buy as a separate server from Cisco) and integrated with existing address books and corporate directories, OCS acts as the PBX of old. End users install an OCS client that allows them to see the presence of other users, instant message them and call them, if desired.

If your corporation has been sold on the benefits of collaboration (multiple people being able to edit the same document/spreadsheet/presentation at the same time) you will need to fork out for Microsoft Office Live Meeting, which integrates seamlessly with OCS.

Your voicemail needs can then be taken care of with your existing Exchange 2007 server by simply configuring (and paying to enable) unified messaging.

In this battle Microsoft fights on the land, in the sea and in the air. To get the equivalent functionality in Ciscoland you would need four separate products (Cisco Call Manager, Presence, Unity and Meeting Place, respectively). When you factor in that you probably already have an Exchange server, it seems that your Microsoft VoIP defense budget leaves you room for other pressing domestic issues (virtualization perhaps?).