Go-Back-N and Selective Repeat are two data transmission protocols. Go-Back-N allows the sender to transmit multiple packets before receiving ACKs, but retransmits all packets after the lost packet when an error occurs. Selective Repeat retransmits only the packet with errors, avoiding unnecessary retransmissions. It uses buffers to store packets for potential retransmission, handling errors more efficiently than Go-Back-N when delays or data rates are high.

1. Go Back – n & Selective RepeatProtocol

2. Go-Back-N protocolConceptIntroduce a window of size nCan inject n packets on net before hearing an ACKEach packet is labeled with a sequence number.

3. ADVANTAGES OF GO-BACK NThe sender can send many frames at a time. Timer can be set for a group of frames. One ACK can acknowledge more than one frames. Efficiency is more.

4. DISADVANTAGES Buffer requirement.Transmitter needs to store the last N packets.Scheme is inefficient when delay is large and data transmission rate is high. Unnecessary Retransmission of many error-free packets.

5. Selective Repeat ProtocolGo-Back-N inefficient because multiple frames are resent when errors or losses occur.SR protocol retransmits only an individual frame containing the error.Buffer is provided in this case.

6. FramesHandling12345678910123E5678910Sending windowReceiving window contains the error in 4th frame.

7. in Go back n protocol….Sending window1234567891045678910Receiving window123E5678910Frames are discarded.Retransmitting the discarded frames.

8. in Selective repeat protocol….Sending window123456789104Getting remaining frames from the buffer.Retransmitting frame.Receiving window123E5678910Output BufferError in 4th Frame597Reordering the frames.8

9. COMPARISON CHART

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