Data Link Control is the service provided by the Data Link Layer to offer reliable data transfer over the physical channel. It takes the physical layer’s bits and finds an error.
This creates an error-free communications path among network nodes over the physical medium, frames messages for communication, tests the integrity of received messages, manages access to and uses the medium, ensures the proper sequence of transmitted data.
It contains sequencing frames and transmitting control frames for acceptance. A noisy channel can avoid scanning of bits, falling bits from a frame, introducing specific bits in the frame, frames final sinking, etc.
The objective of error control is to support that the data received by the receiver is exactly the data shared by the sender. As the communication channel is highly unreliable, the receiver must be able to deal with the received data, if it contains an error. The term error control is defined as the process of identification or correction of an error that occurred in the transmitted data.
Error detection and error recovery are an elemental part of reliable service, and hence they are essential to implement error control structure on an end-to-end basis. It is used to control errors from misplaced or matching segments. The transport layer enables definite segment sequence numbers to the message’s multiple packets, generating virtual circuits, enabling only one virtual circuit per session.
Following are the types of errors −
These errors appear when only a single bit in a data packet is changed from 1 to 0 or 0 to 1. These errors are most feasible to appear in the parallel transmission of data.
Suppose a block of information is sent over the network
00011101 ----------------→ 00001101 Block Sent Block received
When this block is received, the fourth bit beginning from MSB is changed from1 to 0. Therefore a single-bit error has appeared
Burst error appears when 2 or more bits in the data packet have changed from 1 to 0 or 0 to 1. These errors are most feasible to appear in serial data transmission. For example, consider the following block of data when sent across the network.
00110011 ----------------→ 11000011 Block Sent Block received
Therefore in this block, beginning from MSB, 4 bits have changed from 1 to 0 and 0 to 1. Hence the length of burst error is 4 because 4 bits have been changed.