The Upper Tier architecture for Hosted Office Communications Server 2007 adds pools with more servers and a director pool to allow for more than one pool. The following structure shows a system that can handle up to 250,000 users. An additional director server would be required to further expand the number of pools.

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

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

The following figure shows the architecture for an Upper Tier deployment.

Figure: Architecture for Upper Tier deployment