In previous article Framing we had seen than, sender transmits packets in the form of frame to the receiver. But there is a travel of frame between sender to the receiver. So there is chances of error to occur in this travel.
Now in this article we will see how error is control in data link layer.
With positive and negative acknowledgement about a frame.
- If the sender receives a positive acknowledgement about a frame, the frame has received safely.
- A negative acknowledgement means that something has gone wrong and the frame must be transmitted again.
What if frame not received by receiver?
- Here timer concept is used.
- When the sender transmits a frame, it also starts a timer.
- Before expiry of this timer acknowledgement from receiver must reach to the sender.
- In absent of acknowledgement sender will again transmit the frame.
What is acknowledgement sent by receiver not reached to sender?
- In this case may possible sender sent multiple frames.
- To prevent from receiving same frames by receiver sender assign a sequence number to the frame.
- By seeing sequence number receiver identifies that its duplicate frame.