What Are The Responsibilities Of Data Link Layer?

Data Link layer is the 2nd layer of the OSI model. It is used for the reliable transfer of data across data link being used. Data Link Layer gets the raw data from physical layer try to make physical link reliable and provides the methods to activate and maintain the link. It gives guarantee to the higher layers that data send by this layer will be free of errors. It attempts to detect and recover the data that it gets from physical layer.

It uses two protocols as HDLC and LLC for providing its services. HDLC is known as high Level Data link Control. It is used on point to point data links. It can also be used on multi point data links. We can use it in a number of different ways because it is a general purpose data link control protocol. LLC is known as Logical Link Control. Its function is to provide reliable transfer of data across the data link between two communication bodies.

By using unacknowledged connectionless service user can initiate the transfer of data service with minimum protocol overheads. By using connection oriented services user can establish a logical connection, before sending the transfer of any data service.

Data link layer is responsible for the reliability of physical link. It makes sure that the data is delivered error free. On the sender side data link layer breaks down the data and packages it into frames by adding a header and a trailer and then makes sure that it is transmitted sequentially. On the destination device this layer is responsible for arranging the data and to bring the data back in the form it was delivered to data link layer in the source device. It is also responsible for handling acknowledgements.

It is further divided into two layers:
1. Media Access Control
2. Logical Link Control
Media Access Control Layer deals with the issue of accessing the shared communication medium as only one node can use the channel at one time in a network. It is important because if many devices try to send data at the same time then collision will take place. This will result in the loss of data.

Logical Link Control Layer is responsible for the establishment and maintenance of the data links between different network nodes. It also provides flow control and error detection. It provides two types of network services.
1. Connection Oriented Service
2. Connectionless Service

The Data Link Layer primary purpose is to get the packet ready for transmission on the wire. This primarily includes attaching the framing information and source and destination MAC info around the data packet. The next step down is the actual transmission on the medium.