Data Link Layer
The Data link layer is the second layer of the OSI Model. The data link layer provides the Physical transmission of the data and handles flow control, errors, network topology. The Data Link layer ensures that the message is delivering to the proper destination in the network using the hardware address. This layer translates the message from the network layer in to the bits for the physical layer to transmit.
The Data link layer receives the massage into the pieces called the frame and adds the header containing hardware destination and the source address.
The Data link layer is subdivided into two parts-
1. LLC-It establishes and maintains the link between communicating devices.
2. MAC-It is a bottom sublayer.It controls how devices share a media channel.
Some hardware devices that communicate to the data link layer and the physical layer are hubs, switches, repeater, cable, connector, transmitter and receiver.
Responsibilities of Data link layer-
1. The data link layer receives the bits from the network layer and divides into manageable data unit called the frame.
2. The data link layer adds a header to the frame to define the physical address of the sender and the receiver.
3. If the rate at which the data is received and the send are different then data link layer imposes a flow control to manage the flow of the data.
4. The data link layer detect and transmit the damaged and the lost frame, it also uses the mechanism to prevent duplication of the frame. Error control is achieved through a trailer to the end of the frame.
Error control means error detection and correction .If any frame lost and damaged in the transmission it inform the sender to retransmit it. And the flow control co-ordinates the amount of data that can be sent.
Switches and Bridges are the layer 2 device and the protocols used in the data link layer are-HDLC, Frame Relay, PPP, FDDI, ATM etc.
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