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)
15.
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
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
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.