By Rob Helm [bio]
Posted: Oct. 15, 2007

The following an excerpt of a Research Report published by Directions on Microsoft, an independent research firm focused exclusively on Microsoft strategy & technology. More samples of our content, as well as a list of upcoming articles and reports are also available.

Communications Server 2007 is the center of Microsoft's solution for unified communications solutions. Shown here are the major Microsoft components in such a solution. Users employ the Communicator 2007 application on client PCs for instant messaging (IM), presence, and voice or video calls. The separate Live Meeting 2007 client supports Web conferences, which can incorporate voice and video as well as other media, such as text chat and application sharing.

Communications Server has several roles:

• Register and track the addresses of users and their PCs
• Log and control communications sessions (e.g., place and end voice calls)
• Publish user presence information
• Distribute audio, video, and other media for multiparty communications sessions (such as voice conference calls)
• Host Web conferences including shared conference content, such as PowerPoint presentations
• Enable connection by clients other than Communicator and Live Meeting, including Communicator-compatible phones for voice and presence, and Web browsers and mobile phones for IM and presence.

Communications Server authenticates users against Active Directory and imports user communication addresses (such as phone numbers) from the directory. Communicator and Communications Server can also record voice messages and notify users of waiting messages in the Unified Messaging component of Exchange Server 2007 SP1, which enables users to receive both e-mail and voice mail in a single inbox.

Communications Server uses the Session Initiation Protocol (SIP) and extensions to control communications sessions, the Real-Time Transport Protocol (RTP) or its secure variant SRTP to distribute audio and video media, proprietary codecs for voice compression, and Microsoft-specific protocols for Web conferencing and some other tasks.

The system shown here is simplified. Additional Communications Server components and third-party hardware components secure remote access over the Internet and allow integration with existing phone systems and the public phone network. Communications Server components can also be distributed across multiple server farms and typically require load balancing hardware for redundancy and performance.