stop and wait arq

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GROUP 14: INDIGO AMULYA GURURAJ 1MS07IS006 BHARGAVI C S 1MS07IS013 MEGHANA N 1MS07IS050 TANUSHREE A G 1MS07IS139

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CONTENTS

Introduction Stop And Wait ARQ Sender Algorithm. Receiver Algorithm Efficiency Advantages & Disadvantages Applications Demo

INTRODUCTION

Data Communication channels are divided into two major types :-

(a)Noisy Channels. (b)Noiseless Channels. Noiseless Channels :- An ideal case

channel put forth by Niquest. Noisy Channel :- Practical case

channels , put forth by Shannon.

Continued Noiseless Channels :- (1) Simplest(2) Stop and Wait Noisy Channels(1) Stop and wait ARQ(2) Go Back N ARQ(3)Selective Repeat ARQ

STOP AND WAIT ARQ

Design Implementation .

SENDER ALGORITHM

Sn =0cansend = true;While(true){ WaitForEvent(); If(event(RequesTtoSend) AND cansend) { Getdata(); MakeFrame(Sn); StoreFrame(Sn); SendFrame(Sn); StartTimer(); Sn =Sn+1; Cansend =false; }

SENDER ALGORITHM (CONT..)WaitForEvent(); if( event ( Arrival notification)) { ReceiveFrame(ackno); If(not corrupted AND ackno == Sn) { Stop Timer(); PurgeFrame(Sn-1) cansend =true; } }If(event(Timeout)){

StartTimer(); ResendFrame(Sn-1);}}

RECEIVER SIDE ALGORITHM

Rn =0;While(true){

WaitForEvent(); If(event(ArrivalNotification)) { ReceiveFrame(); If( corrupted ( Frame)); Sleep(); If ( seqNo ==Rn) { Extract data(); Deliver data(); Rn =Rn+1; } SendFrame(Rn); }}

EFFICIENCY

Performance Analysis of Stop and Wait ARQ

Parameters: TRANSF: Frame transmission time at sender side TRANSA: ACK transmission time at receiver

side PROP: propagation delay PROC: Frame processing time p: Probability of frame error at sender side q: Probability of frame error at receiver side TIMEOUT: Sender time out

Calculations

Case 1 : Efficiency in transmitting an error free packet

Time taken to transmit an error free packet is:

Ts = TRANSF + TRANSA + 2(PROC+PROP)

In this case efficiency is:

E = TRANSF/Ts

This occurs with the probability (1-p)*(1-q)

Case 2: Efficiency in transmitting an error packetThe delivery of an error packet takes place with the probability: r = p + (1-p)*qThe average packet delay in ARQ scheme is D = TS + TIMEOUT(p/(1-p))In this case efficiency is: E = TRANSF/D

ADVANTAGES

Simple to implement. Frames numbering is modulo-2 i.e,

only 1 bit is required. Can be used for noisy channels. Has both error and flow control

mechanism. Has timer implementation.

DISADVANTAGES

When propagation delay is long, it is extremely inefficient.

Only one 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 Communications protocol (Bisync): character-oriented protocol

XModem: modem file transfer protocol

Trivial File Transfer Protocol : simple protocol for file transfer over UDP

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