Similar to Microsoft® Office Business Applications, "Unified Communications" (UC) describes not a single product, but rather an entire architectural concept. Unlike Microsoft Office Business Applications (OBA), UC goes beyond interconnected software to include hardware devices, with the intent of uniting voice and computer by integrating legacy PBX systems with new communications servers. UC is big, and powerful, with many components and endpoints which present many opportunities for developers. This overview will describe the basic structure and core software, and then delve into the various APIs available to developers for taking advantage of key UC features.

What Is Unified Communications?
In a nutshell, Unified Communications bridges the phone and the computer and brings activities related to both into a single, software-based architecture. This opens up a realm of opportunities for developers to build communications-driven applications on top of this software platform.

Microsoft's approach to Unified Communications can be classified into four general workloads:

Voice Over IP
While VoIP solutions have existed for several years, Microsoft is working with third-party partners to connect its software solution—Microsoft Office Communications Server—with the next generation of hardware and services to make greater use of the potential of digital audio formats and IP telephony.

Conferencing
With its Microsoft Office Communicator and Windows® Live Meeting products, Microsoft offers new video conferencing facilities with high quality desktop and mobile solutions. With Office Communications Server 2007 (OCS 2007), users can host and participate in Web conferences that include rich media presentations, live Webcam, VoIP, roundtable video, recordings, and file transfer "handouts."

Unified Messaging
A key piece of the UC concept, Unified Messaging (UM) integrates multiple communication streams, such as email, voice mail, and fax, consolidating them into a single inbox that can then be retrieved using multiple endpoints, such as laptop, mobile device, or Web browser. Though UM has been around awhile, its role within UC, particularly in combination with VoIP and presence information, makes it a much more powerful productivity tool.

Presence
Management of presence, i.e. your availability and whereabouts, would have to be the hallmark of Unified Communications. Examples and demonstrations of using presence abound on MSDN, but basic functionality will look familiar to anyone who uses the status toggle on their IM client. As implemented in Office Communicator, though, "presence" includes not only availability but also degrees of availability depending on who is trying to contact you. And with its inclusion in the overall UC architecture, presence information integrates smoothly with your various communication endpoints. (See "What Is Presence" for more information.)

Software and Hardware Components of Unified Communications
Looking at UC as a whole, several different products come into play, both on the server and the client side. The two biggies are Exchange 2007, which you're no doubt quite familiar with already, and Office Communications Server 2007, a new product based on Live Communications Server which sits at the heart of all this. The table below lists the software that helps make up the Unified Communications architecture, along with the workload they play a role in.

Software	VoIP	Conf	UM	Presence
Office Communications Server 2007	X	X		X
Office Communicator 2007	X	X	X	X
Office Communicator Mobile 2007				X
Office Communicator Web Access 2007	X
Office Live Meeting 2007		X
Exchange 2007			X
Office Outlook® 2007			X	X
Office Outlook® Web Access			X
Hardware
IP-PBX Gateway for legacy phone systems	X		X
VoIP Phones	X	X	X