2.4 Determining Bandwidth Needs
2.4.4 Determining the access-layer requirements
As calculated in the previous section, the link between the access- and distribution-layer switches must be capable of carrying up to 96 Mbps of traffic. The decision for the type of link depends on the following factors: 
  • If the link is Fast Ethernet in full-duplex mode, the link is capable of carrying 100 Mbps of traffic in each direction. This type of link would indeed support a 96-Mbps load. 
  • If the link is standard Ethernet in full-duplex mode, the link is capable of carrying 10 Mbps of traffic. This capacity is one-tenth the offered load, and packets would be dropped after switch and port buffers are consumed. If this situation is unacceptable, then Fast Ethernet must be chosen. 
  • If virtual LANs (VLANs) are implemented in this network, then it is possible that the link may have to operate in "trunk" mode. If this were the case, then Fast Ethernet would be required.