When data is sent across a network, errors can be introduced. Errors can come from many different sources. For example the cable might be damaged, interference from other electrical devices or the cable might be too long and the signal has got weak. Errors can be introduced to data on any network at anytime. They are hard to predict when an error will occur. As such there must be mechanisms in place to prevent incorrect data being received.

When data is sent from one computer to another it is sent in a series of binary digits known as a packet. A packet can become corrupted upon transfer from one computer to another.

In this case some data is being sent from one PC to another. The data being sent is –

Imagine if an error was introduced. This would mean that one or more of the above bits would change. As a bit can only be 1 or 0, this could mean that they would invert.