1. STOP AND WAIT ARQ STOP WAIT AND

3. Aayush

5. Noiseless and Noisy Channels

6. STOP AND WAIT

9. Frames Packet Error Free Packet Information Frame Transmitter Receiver Control Frame Timer is set after each frame transmission

10. Information Frame header Information Packet CRC Header CRC Acknowledgement Frame

11. Sender-site algorithm for stop and wait ARQ Sn=0; Cansend=true; While(true) { Waitforevent() If(event(requesttosend)AND cansend) { Getdata(); Makeframe(Sn); Storeframe(Sn) Sendframe(Sn); Starttimer() Cansend=false }

12. Contd Waitforevent(); if(event(arrivalnotification) { Receiveframe(ackno); If(ackno==Sn) { Stoptimer(); Purge(Sn-1); Cansend=true; } } If(event(timeout)) { Starttimer(); Resendframe(Sn-1); } }

13. Receiver-site algorithm for Stop and Wait ARQ Rn = 0; While (true) { WaitForEvent ( ); If (Event (ArrivalNotification) ) { ReceiveFrame ( ); If (corrupted (frame) ); sleep ( ); { ExtractData ( ); DelieverData ( ); Rn = Rn + 1; } SendFrame (Rn); } }

14. 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 Rnext Slast Timer Slast Receiver B Transmitter A Rnext 1-Bit Sequence Numbering Suffices Global State: (Slast, Rnext) Error-free frame 0 arrives at receiver (0,0) (0,1) ACK for frame 0 arrives at transmitter ACK for frame 1 arrives at transmitter Error-free frame 1 arrives at receiver (1,0) (1,1)

16. (a) Frame 1 lost Time-out Time A Frame 1 Frame 1 Frame 2 Frame 0 ACK ACK B (b) ACK lost Time-out Time A Frame 0 Frame 1 Frame 1 Frame 2 ACK ACK ACK B Need for Sequence Numbers

17. Sequence Numbers Time-out Time A Frame 0 Frame 2 Frame 0 Frame 1 ACK ACK B (c) Premature Time-out

18. Advantages and disadvantages of Stop and Wait ARQ

19. Advantages of Stop and Wait ARQ over simple Stop and Wait protocol It can be used for noisy channels It has both error and flow control mechanism It has a timer implementation

21. Only 1 frame is sent at a time.

24. Applications IBM Binary Synchronous Communication Protocol (Bisync): Character-oriented data link control. Xmodem: Modem file transfer protocol. Trivial file transfer protocol (RFC 1350): simple protocol for file transfer over UDP.

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