Data link layer of the OSI model : definition

Data link layer:

Data link layer is the second layer of the OSI model. It handles data transfer between network and physical layers. Data unit at the data link layer is called as frame. Data link layer receives data from network layer. It adds header and trailer to the data and passes data to the physical layer. At the receiver said, data link layer receives data from the physical layer. It detaches header and trailer from the data and passes data to the network layer.

Responsibilities of the data link layer are:

☼Framing – the physical layer delivers raw bits from the source to destination. During transmission, the value of the bits can change. It is also possible that the number of bits received by the receiver may be different from the number of bits sent by the sender. To resolve this problem, the data link layer organizes the bits into manageable data units called as frames.

☼Physical addressing – Data links layer adds header to the frame which contains the physical address of the sends and/or receiver. Headers are assigned when the frames are to be distributed to various systems within the network.

☼Error control – Another function of the data link layer is error control. Error control detects and corrects errors. During transmission, if a frame is lost or corrupted, the data link layer retransmits that frames. It also prevents duplication of frames. Error control is accomplished using trailer at the end of the frame.