The Middle Tier architecture for Hosted Office Communications Server 2007 uses an expanded Enterprise deployment for the pool server roles. This enables the environment to support up to 50,000 users with the ability to add more servers. The addition of more servers can then be made to increase the capacity of a particular component such as Web conferencing or IM easily.

The Middle Tier architecture includes both dedicated servers and servers running more than one role:

• Two servers running as a SQL cluster for back-end database
  
• One SQL server for CDR archiving
  
• Four servers running Front End server role
  
• Two servers running Web Conferencing server role
  
• Two servers running A/V Conferencing server role
  
• Two servers running Web Components server role
  
• Four servers running Access Edge server role
  
• Two servers running Web Conferencing Edge server role
  
• Two servers running A/V Edge server role
  
• Two servers running reverse proxy
  
• Two servers running communicator Web Access server role
  

The following figure shows the architecture for a Middle Tier deployment.

Figure: Architecture for Middle Tier deployment