This document discusses Selective Repeat ARQ, a method of automatic repeat request for error control in data transmission. It defines key terms like send window, receive window, and sliding window. It explains that in Selective Repeat ARQ, only the frame that needs to be retransmitted is sent again, allowing out-of-order frames. This leads to higher efficiency than other ARQ methods like Go-Back-N where multiple frames need to be retransmitted. Charts comparing the efficiencies of different ARQ methods under varying frame loss probabilities are also presented.

1. fr 1 fr 2 fr 0 fr 3 fr 4 fr 5 fr 2 fr 8 fr 7 fr 11 fr 6 fr 9 fr 10 fr 12 Time A B ACK2 NAK2 ACK7 ACK8 ACK9 ACK10 ACK11 ACK12 ACK2 ACK2 ACK1 ACK2 SELECTIVE REPEAT ARQ

2. -BY GROUP16: QUADMASTERS Hari Prasad Deepak Pavan S Prakash GROUP2: OLDBRIDGE Anil Manjunath Ganeshan Himanshu GROUP1: CHARISMA Nagchandrika Sridevi Madhura Ramya GROUP8: VINTAGE BOYS PavanRao Harsh Amar Tabrez GROUP: CHARMUSAFIR Ankan Pavan Kumar Chandan Chandresh

3. Basics What is ARQ? What is Selective Repeat ARQ? introduction

5. In Selective Repeat ARQ, the size of the sender and the receiver window must be at most one half of 2^m. Terminology: Sf – Send window, first outstanding frame Sn – Send Window, next frame to send Sw – Maximum size of sliding window (2^(m-1)) Rn – Receive window, next frame expected Concept of sliding window

6. Send window for selective repeat arq Send window, first outstanding frame Sf Sn Send window, next frame to send Frames sent but not acknowledged Frames that can be sent Frames already acknowledged Frames that cannot be sent Ssize = 2^(m-1)

7. Receive window for selective repeat arq Receive window, Next frame expected. Rn Frames that can be received and stored for later delivery. Colored boxes, already received. Frames that cannot be received. Frames already received Rsize = 2^(m-1)

9. Only the required frame can be retransmitted.

10. Out of order frames can be accepted.Advantages

12. Service Specific Connection Oriented Protocolapplications

13. Efficiency of slelective repeat arq Assume Pf frame loss probability, then number of transmissions required to deliver a frame is: tf / (1-Pf)

14. Comparison of ARQ Efficiencies Assume na and noare negligible relative to nf, and L = 2(tprop+tproc)R/nf=(Ws-1), then Selective-Repeat: Go-Back-N: For Pf≈0, SR & GBN same Stop-and-Wait: For Pf->1, GBN & SW same

15. Arq efficiencies 10-9 10-8 10-7 10-6 10-5 10-4 10-3 10-2 10-1 p Delay-Bandwidth product = 10, 100

16. Comparison chart

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