STOP AND WAIT ARQ

STOP

AND

WAIT

Team members

DNAA

• Nishita• Ananya• Archana• Dhanusha Awesum4sum

• Lisha• Anita• Prabha• Caroline

Krazzy4

• Royston• Aayush• Himanshu• Vinayak

Noiseless and

Noisy Channels

PROTOCOLSPROTOCOLS

FOR NOISELESS CHANNELS FOR NOISY

CHANNELS

SIMPLEST

STOP AND WAIT

STOP AND WAIT ARQ

GO BACK N ARQ

SELECTIVE REPEAT ARQ

Noisy Channel – Error free channelsNoiseless Channel – Error creating 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

FramesPacket Error Free Packet

Transmitter Receiver

Information Frame

Control Frame

Timer is set after each frame transmission

Information Frame

Acknowledgement Frame

header Information Packet CRC

Header CRC

Need for Sequence

number

Need for Sequence Numbers(a) Frame 1 lost

A

B

Frame 0

Frame 1

ACK

Frame 1

ACK

TimeTime-out

Frame 2

(b) ACK lost

A

B

Frame 0

Frame 1

ACK

Frame 1

ACK

TimeTime-out

Frame 2

ACK

Sequence Numbers(c) Premature Time-out

A

B

Frame 0

Frame 0

ACK

Frame1

ACK

Time

Time-out

Frame 2

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

}

ContdWaitforevent();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);

}}

(0,0) (0,1)

(1,0) (1,1)

Global State:(Slast, Rnext)

Error-free frame 0arrives at receiver

ACK forframe 0arrives attransmitter

ACK forframe 1arrives attransmitter Error-free frame 1

arrives at receiver

Transmitter A Receiver B

SlastRnext

0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1

Timer

Rnext

Slast

1-Bit Sequence Numbering Suffices

Advantages and disadvantages

of Stop and Wait ARQ

Advantages of Stop and Wait ARQ over simple Stop and Wait protocol

1. It can be used for noisy channels2. It has both error and flow control

mechanism3. It has a timer implementation

• 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).

Disadvantages of Stop and Wait 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