1. STOP AND WAIT ARQ STOP WAIT AND

3. Aayush

5. Noiseless and Noisy Channels

6. Noisy Channel – Error free channels Noiseless Channel – Error creating channels PROTOCOLS FOR NOISY CHANNELS FOR NOISELESS CHANNELS SIMPLEST STOP AND WAIT ARQ STOP AND WAIT GO BACK N ARQ SELECTIVE REPEAT ARQ

7. STOP AND WAIT

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

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

12. Need for Sequence number

14. (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

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

16. 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 }

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

18. 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); } }

19. 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)

20. Advantages and disadvantages of Stop and Wait ARQ

21. 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

23. Only 1 frame is sent at a time.

26. 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.

27. THANK YOU