Office Communications Server Enterprise Edition consists of the following:

• Microsoft Office Communications Server 2007, Back-End Database server, which provides shared storage for all Enterprise Edition servers within the pool. This database runs on Microsoft SQL Server 2005 with Service Pack 1 (SP1) (32-bit or 64-bit) or SQL Server 2000 with SP4 or later, and it can be clustered in an active-passive configuration for higher availability. This back-end database must be configured as a separate, dedicated computer. Installing any Enterprise Edition servers on the same computer as the back-end database is not supported.
  
• Enterprise pools (one or more computers running Office Communications Server Enterprise Edition) that are connected to the Back-End Database server. To provide scalability and failover, client requests are distributed across the servers that run Enterprise Edition. If your pool consists of more than one server, a load balancer is required. If your pool consists of only one server, which is connected to a separate SQL database server, a load balancer is not required.
  

Office Communications Server Enterprise Edition consists of several server roles:

• Front End Server, which houses instant messaging, presence, telephony, conferencing servers, and all essential user services operations.
  
• Web Conferencing Server, which enables on-premise conferencing.
  
• Audio/Video Conferencing Server, which enables users to share audio and video streams.
  
• Web Components Server, which enables users 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.
    

In an expanded configuration, each of the server roles previously described (the Front End Server, the Web Components Server, the Web Conferencing Server, and the Audio/Video Conferencing Server) is installed on its own dedicated computer. The expanded configuration is best suited for organizations where high availability and maximum performance throughput are important. This configuration provides benefits with regard to scalability and high availability, but it creates additional complexity in the administration and deployment of the pool.

Enterprise Edition also supports deployment in a consolidated configuration; all server roles are installed together on each Enterprise Edition Server within a pool. This configuration simplifies deployment and administration. The consolidated configuration reduces the number of servers required while maintaining high availability, and so it should appeal to large and medium-sized organizations that require high availability combined with minimal deployment costs. These advantages, however, come at the price of reduced performance throughput per server.

For more information about these configurations, see the Microsoft Office Communications Server 2007 Planning Guide.