describing the selective repeat and go back n protocol.

1. Go Back – n & Selective RepeatProtocol

2. Go-Back-N protocol Concept Introduce a window of size n Can inject n packets on net before hearing an ACK Each packet is labeled with a sequence number.

3. ADVANTAGES OF GO-BACK N The 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 Protocol Go-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. FramesHandling 1 2 3 4 5 6 7 8 9 10 1 2 3 E 5 6 7 8 9 10 Sending window Receiving window contains the error in 4th frame.

7. in Go back n protocol…. Sending window 1 2 3 4 5 6 7 8 9 10 4 5 6 7 8 9 10 Receiving window 1 2 3 E 5 6 7 8 9 10 Frames are discarded. Retransmitting the discarded frames.

8. in Selective repeat protocol…. Sending window 1 2 3 4 5 6 7 8 9 10 4 Getting remaining frames from the buffer. Retransmitting frame. Receiving window 1 2 3 E 5 6 7 8 9 10 Output Buffer Error in 4th Frame 5 9 7 Reordering the frames. 8

9. COMPARISON CHART

10. THANK YOU !!!