Introduction to Networking

Error Detection at the Data Link Layer

When data is transmitted from one device to another device, then the data may change during transmission.  If the sending data is not identical to the receiving data, then it is the error state.

For reliable communication, errors must be detected and then corrected.

Note: Error Deduction and correction are implemented either at data link layer (layer 2) or transport layer (layer 3) of OSI Model.

Types of Errors

Errors can be classified into two categories

1. Single-Bit Error

If only one bit of transmitted data unit is changed i.e. from 1 to 0 or from 0 to 1 then it is a single bit error. The following figure shows the one-bit change,

2. Burst Error

If two or more bits are changed (i.e., from 0 to 1 or from 1 to 0), then it is a Burst Error. The Burst Error is calculated from the first corrupted bit to the last corrupted bit.

How to Detect the Errors?

Error deduction means to decide whether the received data is correct or not without having a copy of original data.

To detect or correct errors we need to send some extra bits along with original message (data). These extra bits are called redundant bits. To detect errors, we use Generator and Checker.

Generator: The generator is used at the sender end to generate redundancy bits. These redundancy bits are appended with sending data.

Checker: Checker is used at receiver end, it verify the data and redundancy bits. If sending information is unchanged, then data is accepted; otherwise, it is rejected.

Block diagram of error deduction is given below

Error Detecting Techniques

The most popular Error Detecting Techniques are

  • Single parity check
  • Two-dimensional parity check
  • Checksum
  • Cyclic redundancy check

In the next lectures, we will explain all types of error-detecting techniques