Introduction
Data Link Layer is layer 2 in OSI model. It is responsible for communications between adjacent network
nodes. It handles the data moving in and out across the physical layer. It also provides a well-defined
service to the network layer. Data link layer is divided into two sub layers. The Media Access Control
(MAC) and Logical Link Control (LLC).
Data-Link layer ensures that an initial connection has been set up, divides output data into data frames,
and handles the acknowledgements from a receiver that the data arrived successfully. It also ensures that
incoming data has been received successfully by analyzing bit patterns at special places in the frames.
In the following sections data link layer's functions- Error control and Flow control has been discussed.
After that MAC layer is explained. Multiple access protocols are explained in the MAC layer section.
Types of errors:
These interferences can change the timing and shape of the signal. If the signal is carrying binary encoded
data, such changes can alter the meaning of the data. These errors can be divided into two types: Single-
bit error and Burst error.
Single-bit Error
The term single-bit error means that only one bit of given data unit (such as a byte, character, or data unit)
is changed from 1 to 0 or from 0 to 1 as shown in Fig
single bit error
Single bit errors are least likely type of errors in serial data transmission. To see why, imagine a sender
sends data at 10 Mbps. This means that each bit lasts only for 0.1 μs (micro-second). For a single bit error
to occur noise must have duration of only 0.1 μs (micro-second), which is very rare. However, a single-bit
error can happen if we are having a parallel data transmission. For example, if 16 wires are used to send
all 16 bits of a word at the same time and one of the wires is noisy, one bit is corrupted in each word.
Burst Error:
The term burst error means that two or more bits in the data unit have changed from 0 to 1 or vice-versa.
Note that burst error doesn’t necessary means that error occurs in consecutive bits. The length of the burst
error is measured from the first corrupted bit to the last corrupted bit. Some bits in between may not be
corrupted.
