When two PC's transmit onto a bus at the same time there is a likely chance that they will collide. When packets collide on a network bus there is no explosion or crashing sound. However the packets which have collided will be corrupted. The packets will not be destroyed in the strictest sense of the word but they will be corrupted beyond recognition. The electronic signals which represent the packet will continue to travel along the cable. It is this fact which enables the network to detect the collision. Although the exact mechanics of collision detection is beyond the scope of this course it is important to understand how a collision can occur and the consequences of the collision. The diagram below shows a typical collision.

PC A and PC B both place packets on the network.

Both packets travel down the bus towards one another. The arrows show the direction the packets are traveling in.

Both packets have met in the middle and caused a collision. The data is now corrupted and can no longer be used.

The corrupted packets then travel on down the bus. The collision will be detected and the packets resent after a random amount of time.