Stop And Wait
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Stop And Wait

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Stop And Wait Stop And Wait Presentation Transcript

  • STOP AND WAIT ARQ
    STOP
    WAIT
    AND
  • Team members
    DNAA
    abc
    Nishita
    Ananya
    Archana
    Dhanusha
    Awesum4sum
    • Vinayak
    Lisha
    Anita
    Prabha
    Caroline
    View slide
  • Noiseless and Noisy Channels
  • STOP AND WAIT
  • Automatic Repeat reQuest
    • Is an error-control method for data transmission
    • uses acknowledgements and timeouts to achieve reliable data transmission over an unreliable service.
  • STOP AND WAIT ARQ
  • Frames
    Packet
    Error Free Packet
    Information Frame
    Transmitter
    Receiver
    Control Frame
    Timer is set after each frame transmission
  • Information Frame
    header
    Information Packet
    CRC
    Header
    CRC
    Acknowledgement Frame
  • 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
    }
  • Contd
    Waitforevent();
    if(event(arrivalnotification)
    {
    Receiveframe(ackno);
    If(ackno==Sn)
    {
    Stoptimer();
    Purge(Sn-1);
    Cansend=true;
    }
    }
    If(event(timeout))
    {
    Starttimer();
    Resendframe(Sn-1);
    }
    }
  • 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);
    }
    }
  • 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)
  • (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
  • Sequence Numbers
    Time-out
    Time
    A
    Frame
    0
    Frame
    2
    Frame
    0
    Frame
    1
    ACK
    ACK
    B
    (c) Premature Time-out
  • Advantages and disadvantages of Stop and Wait ARQ
  • 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
  • Disadvantages of Stop and Wait ARQ
    • Efficiency is very less.
    • Only 1 frame is sent at a time.
    • Timer should be set for each individual
    frame.
    • No pipelining.
    • Sender window size is 1 ( disadvantage
    over go back n ARQ).
    • Receiver window size is 1 ( disadvantage
    over selective repeat ARQ).
  • 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.
  • THANK YOU