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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<!-- SWP5.html (C) K. J. Turner 18/12/14 -->
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<title>
Sliding Window Protocol (5-Column)
</title>
<link rev="made" href="http://www.cs.stir.ac.uk/~kjt/"/>
<script type="text/javascript" language="JavaScript">
<!--
var simulator;
var maxSeq;
var maxSeqOld = 7;
var winSize
var winSizeOld = 3;
function validInteger(name, value, min, max) {
if (!value.match("\\d+") || value < min || value > max) {
alert("Value for " + name + " must be in range " + min + " to " + max);
return false;
}
else
return true;
}
function set () {
maxSeq = document.settings.maxSeq.value;
winSize = document.settings.winSize.value;
if (validInteger("Maximum Sequence Number", maxSeq, 1, 31) &&
validInteger("Window Size", winSize, 1, 31)) {
maxSeq = parseInt(maxSeq);
winSize = parseInt(winSize);
if (winSize <= maxSeq) {
if (maxSeq != maxSeqOld || winSize != winSizeOld) {
maxSeqOld = maxSeq;
winSizeOld = winSize;
simulator.setParameter("maxSeq", maxSeq);
simulator.setParameter("winSize", winSize);
simulator.restart();
}
}
else
alert("Window Size must be 1 to the Maximum Sequence Number");
}
}
//-->
</script>
</head>
<body background="simulator.jpeg"
onload="simulator=document.ProtocolSimulator">
<div style="text-align: center">
<h1>
Sliding Window Protocol Simulator
<br/>
(5-Column)
</h1>
<img src="simulator.gif" alt="Simulator Logo"/>
</div>
<p>
SWP (Sliding Window Protocol) is a connection-less protocol in one
direction between a pair of users. It allows data to be sent in one
direction subject to a maximum number of unacknowledged messages. If SWP is
operated with a window size of 1, it is equivalent to the <a
href="ABP.html">Alternating Bit Protocol</a>. The simulation below includes
the users; the <a href="SWP3.html">three-column</a> version omits them.
</p>
<p>
The protocol has a maximum number of messages that can be sent without
acknowledgement. If this window becomes full, the protocol is blocked
until an acknowledgement is received for the earliest outstanding
message. At this point the transmitter is clear to send more messages.
</p>
<h2>Protocol Parameters</h2>
<p>
The following settings are adequate for a simple simulation. For a more
advanced exploration, choose different options and click <em>Change
Settings</em>. This may cause the simulation to restart.
</p>
<form name="settings">
<center>
<table cellpadding="5">
<tr>
<td align="right">Maximum Sequence Number (1 to 31):</td>
<td><input type="text" name="maxSeq" value="7" size="2"/></td>
</tr>
<tr>
<td align="right">Window Size (1 to Maximum Sequence Number):</td>
<td><input type="text" name="winSize" value="3" size="2"/></td>
</tr>
<tr>
<td align="center" colspan="2">
<input type="button" name="btnSet" value="Change Settings"
onclick="set()"/>
</td>
</tr>
</table>
</center>
</form>
<h2>Protocol Simulation</h2>
<p>
The protocol simulation shows a time-sequence diagram with users A and B,
protocol entities A and B that support them, and a communications medium
that carries messages. Users request data transmissions with
<em>DatReq(DATAn),</em> and receive data transmissions as
<em>DatInd(DATAn)</em>. Data messages are simply numbered <em>DATA0</em>,
<em>DATA1</em>, etc. without explicit content. The transmitting protocol
sends the protocol message <em>DT(n)</em> that gives only the sequence
number, not the data. Once sequence numbers reach a maximum number (like
7), they wrap back round to 0. An acknowledgement <em>AK(n)</em> means
that the <em>DT</em> message numbered <em>n</em> is the next one expected
(i.e. all messages up to but not including this number have been
received). Since sequence numbers wrap round, an acknowledgement with
sequence number 1 refers to messages 0, 1, 7, 6, etc. Note that if a
<em>DT</em> message is received again due to re-transmission, it is
acknowledged but discarded.
</p>
<center>
<applet code="simulator.ProtocolSimulator.class"
archive="ProtocolSimulator.jar" width="750" height="700"
name="ProtocolSimulator">
<param name="protocol" value="SWP5"/>
</applet>
</center>
<hr/>
<p>
<a href="index.html"><img src="uparrow.gif" alt="Up Arrow"/></a>
Up one level to <a href="index.html">Protocol Simulators</a>
</p>
</body>
</html>