The Cyclic Redundancy Check

Taken from lecture notes by Otfried Schwarzkopf, Williams College.

  1. A significant role of the Data Link layer is to convert the potentially unreliable physical link between two machines into an apparently very reliable link.

  2. This is done by including redundant information in each transmitted frame. Depending on the nature of the link and the data one can either: Most current networks take the former approach.

  3. One widely used parity bit based error detection scheme is the cyclic redundancy check or CRC.

  4. How about an example:

  5. I hope this is all strange enough that you feel compelled to ask "Why bother?". If so, the answer comes in two parts:

  6. Let's start by seeing how the mathematics underlying the CRC can be used to investigate its ability to detect errors.