There are three techniques for error controlling in data link layer

Stop-and-Wait-ARQ:

• In this method sender does not send the next frame until it does not receive acknowledgement for the last sent frames.
• It starts a timer once frame is send, if ack is not received within the timer,it retransmits the frame.
• If a negative acknowledgement is received, frame is resend.

Go-Back-N ARQ:

• It uses windowing mechanism to achieve error correction.
• In this more than one frames can be send at once without waiting acknowledgment.
• Number of frames send depends upon the window size of receiver.
• If the acknowledgment is not received for any frame, it retransmits all the frame after which it does not receive positive ACK(NACK) or for which it does not receive any ACK.
• Below it did not receive ACK for frame 2, it retransmits all the frame from 2 onward.

Selective Repeat ARQ:

• This is also based on windowing mechanism.
• In this more than one frames can be send at once without waiting acknowledgment.
• Number of frames send depends upon the window size of receiver.
• The basic difference between G0-Back-N ARQ and selective Repeat ARQ is that in selective repeat ARQ, not all the frames are transmitted after which it did not receive ACK, rather only the frame for which it did not receive ack or for which it received NACK is retransmitted.
• Only frame 2 is retransmitted, not all the frames from 2 onward unlike that of Go-Back-N ARQ.

Categories: Networking