2.4 Determining Bandwidth Needs
2.4.3 Gathering traffic statistics
When determining bandwidth use in campus networks, many network administrators simply put as much bandwidth as possible in the uplinks from the access layer to the distribution layer and from the distribution layer to the core layer. In general, aggregate bandwidth of the access-layer devices should not exceed the bandwidth of the link they use to reach the distribution-layer switch. Further, the aggregate of all uplinks to the distribution switches should not exceed the bandwidth of the links to the core layer. These rules will help avoid a "bottleneck" situation where one link is overloading another link.

The following list outlines the traffic characteristics of the sample network. 

  • Eighty percent of the user traffic remains local to the floor. 
  • Twenty percent of the traffic must cross the core and reach the e-mail server. 
  • If all users simultaneously accessed the network, the switch would receive 24 ports x 4 Mbps, yielding an aggregate bandwidth of 96 Mbps. 

Table outlines these statistics.