Voice over Internet Protocol (VoIP) refers to the ability of placing and receiving voice calls over the IP network. The call might or might not traverse the Public Switched Telephone Network (PSTN) network. The PSTN network is the traditional telephone network that everyone uses to call friends, family, and colleagues. VoIP is different from Remote Call Control (RCC). RCC is related to controlling the Private Branch eXchange (PBX) phone from a computer running Office Communicator, whereas in VoIP the audio traffic is carried over the IP network. VoIP has the potential of eliminating the need for a PBX network, which most large organizations must deploy and maintain in addition to their IP network. Managing these two independent networks, each with its own idiosyncrasies, requires administrators with various technical backgrounds and skills. Figure 10-1 illustrates the different types of voice networks.

Figure 10-1. PSTN vs. RCC vs. VoIP

VoIP technology promises to deliver on many improvements, such as infrastructure and network consolidation, lower management and toll costs, and better interoperability between systems from different vendors. The VoIP capabilities of Office Communications Server 2007 can replace PBX functionality in many cases and interoperate with existing PBXs in other cases.

Microsoft's VoIP offering, Office Communications Server 2007, provides an integrated user experience where voice communication is integrated into the same applications used by information workers to communicate electronically, such as Microsoft Office 2007, SharePoint 2007, and Exchange 2007. With Office Communications Server 2007, Voice becomes one of many communications modes—e-mail, instant messaging (IM), Web conferencing, file transfer, video—that are accessible from a single consistent user interface. This ease of use encourages user adoption of more advanced features such as call forwarding, call redirection, and multiparty calls, which most users with traditional PBX phones seldom use.

Another important advantage is portability. With Office Communicator 2007 installed on their laptops and an edge server deployed in their organizations' peripheral networks, users have access to their work numbers from anywhere in the world where Internet connectivity is available. This is a powerful proposition given a global economy where more and more workers telecommute. Office Communications Server 2007 makes it possible for information workers to free themselves from the constraints of the office or cubicle.