|  | 5.5 |

Collisions and Collision Domains in Shared Layer Environments

| 5.5.2 | Collisions and collision domains

A situation that can occur, when two bits propagate at the same time on the same network, is a collision. A small, slow network could work out a system that allowed only two computers to send messages, each agreeing to take turns. That would mean that they could both send messages, but there would be only one bit on the system. The problem is that many computers are connected to large networks, each one wanting to communicate billions of bits every second. It's also important to remember that the "bits" are actually packets containing many bits.

Serious problems can occur as a result of too much traffic on a network. If there is only one cable that interconnects all of the devices on a network, the possibility of conflicts with more than one user sending data at the same time is very high. The same is true if segments of a network are only connected by non-filtering devices, such as repeaters. Ethernet allows only one data packet to access the cable at any one time. If more than one node attempts to transmit at the same time, a collision occurs, and the data from each device suffers damage .

The area within the network, where the data packets originated and collided, is called a collision domain, and includes all shared media environments. One wire may be connected to another wire through patch cables, transceivers, patch panels, repeaters, and even hubs. All of these Layer 1 interconnections are part of the collision domain.