Explain data link layer in details.

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 Solution :-

Ans Data link layer: Data link layer is the second layer of the OSI model. It accepts the data from the Network layer, attaches header & trailer and send it to the physical layer. At receives side it accepts the data from the physical layer snip of header & footer & gives back to network layer the way it has taken. 

Working:

  • It is responsible for transmitting group of bits between the adjacent nodes. 
  • The group of bits is called as frame. 
  • The data link in a network model layer transforms the physical layer, a raw transmission facility, to a reliable link. 
  • It makes the physical layer appear error-free to the upper layer (network layer). 
  • Figure shows the relationship of the data link layer to the network and physical layers of network model.
  • The data link layer in a network model is responsible for moving frames from one node to the next.

Other responsibilities of the data link layer in a network model include the following:

1. Framing:
The data link layer in a network model divides the stream of bits received from 
the network layer into manageable data units called frames.
2. Physical addressing:
If frames are to be distributed to different systems on the network model, the data link layer in network model adds a header to the frame to define the sender and/or receiver of the frame. If the frame is intended for a system outside the sender's network, the receiver address is the address of the device that connects the network to the next one.
3. Flow control:
If the rate at which the data are absorbed by the receiver is less than the rate at which data are produced in the sender, the data link layer in network model imposes a flow control mechanism to avoid overwhelming the receiver.
4. Error control:
The data link in network model layer adds reliability to the physical layer by adding mechanisms to detect and retransmit damaged or lost frames. It also uses a mechanism to recognize duplicate frames. Error control is normally achieved through a trailer added to the end of the frame.
5. Access Control:
When two or more devices are connected to the same link, data link layer protocols in network model are necessary to determine which device has control 
over the link at any given time.

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