The Data Link Layer of OSI Model

The data link layer (Layer 2) converts the raw transmission facility provided by the physical layer to a reliable and error-free link.

The main functions of the data link layer are as follows −

• It breaks up the stream of bits into data frames having sizes from a few hundred to a few thousand bytes.
• It ensures distribution of the frames to the different systems. For this, it adds a header to the frame containing the address of the sender and the receiver.
• In case of reliable connection, this layer ensures that the receiver sends an acknowledgement frame. In absence of acknowledgement frames, frame retransmission is done. It also has mechanisms to identify duplicate frames.
• The data link layer ensures flow control of transmission so that a fast sender does not drown a slow receiver.
• In the case of broadcast networks, this layer also controls access to the shared channel.