A pool is a group of servers that provide the services offered by Office Communications Server 2007. The server roles available within a pool include:

• Front End Server
  
• Web Conferencing Server
  
• Audio/Video Conferencing Server
  
• Web Components Server
  

The Front End Server provide IM, presence, and conferencing services and are connected to a SQL Server database for storing user and conference information. An Enterprise Edition pool typically consists of two or more Front End Servers, which are fronted by a hardware load balancer and connected to a Back-End Database. You can also deploy a single Front End Server without a load balancer.

The Web Conferencing Server provides Web Conferencing services. It manages conference data collaboration, including native support for Microsoft Office PowerPoint presentations, Microsoft Office document sharing, white boarding, application sharing, polling, Q&A, compliance logging, annotations, meeting summaries, handouts, and various multimedia formats. The Web Conferencing Server uses PSOM (Persistent Shared Object Model), a Live Meeting protocol, for uploading slides to a meeting.

The Audio/Video Conferencing Server provides Audio/Video Conferencing services. It provides multiparty IP audio and video mixing and relaying, including Microsoft RoundTable, by using industry standard RTP (Real-time Transport Protocol) and RTCP (Real-time Transport Control Protocol).

The Web Components Server provides address book downloads and expansion of distribution lists. It enables user to do the following:

• Access meeting presentations and other content from Web conferences.
  
• Download Address Book Server files to provide Communicator with global address list information.
  
• Expand membership in distribution groups and other data that is used by the Web Conferencing Server.