A collision domain is a group of Ethernet or Fast Ethernet devices that are directly connected by repeaters or Hubs. Only one device may transmit at anyone time inside of this collision domain. When a device is transmitting all other devices in the collision domain listen. The method by which this is accomplished is a simple means to guarantee that only one device is talking at a time. The construction of a network also will include such products as switches and routers. Collision domains are separated by these devices. These types of products also allow the separate collision domains to communicate with each other while maximizing bandwidth utilization. When device A decides to begin "talking" and device B has not completed "talking", this will cause collisions and all data must be transmitted again.
To prevent collisions from traveling to every workstation in the entire network, a bridge or switch can be installed. These devices will not forward collisions, but will permit broadcasts to all users and multicasts to specific groups to pass through. In addition, a router may be used to block broadcasts and multicasts from other points in the network.
