Microsoft Communications 2010 Planning Tool uses the following metric to estimate user traffic at each site and the number of media ports that are required to support that traffic. The number of media ports in turn determine the number of Mediation Servers and gateways that will be required. The media gateways that most organizations consider deploying range in size from 2 to as many as 960 ports. (There are even larger gateways, but these are used mainly by telephone service providers.)

• For Light traffic (one PSTN call per hour) figure 15 users per port
  
  
• For Medium traffic (2 PSTN calls per hour) figure 10 users per port
  
  
• For Heavy traffic (3 or more PSTN calls per hour) figure 5 users per port
  
  

For example, an organization with 10,000 users and medium traffic would require 1000 ports. The number of gateways required would equal the total number of ports required as determined by the total capacity of the gateways.

Enabling media to bypass the Mediation Server reduces the number of ports required. The planning tool takes this into account when making its recommendations. For more information, see Media Bypass.