The 80-20 Rule

• Good Network Design: The 80-20 Rule

In a properly designed small to medium-sized network environment, 80 percent of the traffic on a given network segment is local (destined for a target in the same workgroup), and not more than 20 percent of the network traffic should need to move across a backbone (the spine that connects various segments or “subnetworks”). Backbone congestion can indicate that traffic patterns are not meeting the 80-20 rule. In this case, rather than adding switches or upgrading hubs, it may be easier to improve network performance by doing one of the following:
• Moving resources (applications, software programs, and files from one server to another, for example) to contain traffic locally within a workgroup
• Moving users (logically, if not physically) so that the workgroups more closely reflect the actual traffic patterns
• Adding servers so that users can access them locally without having to cross the backbone
http://surenthinknetworks.blogspot.com.tr/2013/02/good-network-design-80-20-rule.html