To cut down on the amount of broadcast traffic you can create Virtual LANs (or VLANs for short) which operate as separate broadcast domains. This means that members of a VLAN can only talk directly to other members of the VLAN as shown in the Figure above.
In the example shown above, up to 80 users can perform simultaneous 100 Mbps transfers or 8 power users can transfer at 1 Gbps to 2 servers which are quad linked with 4 x 1 Gbps connections.
The Gigabit Ethernet trunk between the two switches would become a bottleneck if one type of traffic was allowed to dominate the link. This could reduce the quality of the voice or video traffic. By assigning priority classes for each type of traffic, the switches are able to ensure that:
- VoIP traffic is always given the highest priority and is transmitted before anything else
- Video traffic is given priority but is also rate limited to ensure that the video streams do not swamp the receiver and are delivered at the rate required
- Normal fi le transfer is given a lower priority and is processed on a best effort basis
- Broadcast traffic is given the lowest priority and may be dropped if the available bandwidth is not enough