235 lines
6.6 KiB
HTML
235 lines
6.6 KiB
HTML
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
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"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<!-- SWP3.html (C) K. J. Turner 18/12/14 -->
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<html xmlns="http://www.w3.org/1999/xhtml">
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<head>
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<title>Sliding Window Protocol (3-Column)</title>
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<link rev="made" href="http://www.cs.stir.ac.uk/~kjt/"/>
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<script type="text/javascript" language="JavaScript">
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<!--
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var simulator;
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var mediumType;
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var mediumTypeOld;
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var maxSeq;
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var maxSeqOld = 7;
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var winSize
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var winSizeOld = 3;
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function validInteger(name, value, min, max) {
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if (!value.match("\\d+") || value < min || value > max) {
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alert("Value for " + name + " must be in range " + min + " to " + max);
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return false;
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}
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else
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return true;
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}
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function set() {
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mediumType =
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document.settings.medium[0].checked
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? 2
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: document.settings.medium[1].checked
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? 1
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: 0;
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if (mediumType != mediumTypeOld) {
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mediumTypeOld = mediumType;
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simulator.setParameter("mediumType", mediumType);
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simulator.restart();
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}
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maxSeq = document.settings.maxSeq.value;
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winSize = document.settings.winSize.value;
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if (validInteger("Maximum Sequence Number", maxSeq, 1, 31) &&
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validInteger("Window Size", winSize, 1, 31)) {
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maxSeq = parseInt(maxSeq);
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winSize = parseInt(winSize);
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if (winSize <= maxSeq) {
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if (maxSeq != maxSeqOld || winSize != winSizeOld) {
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maxSeqOld = maxSeq;
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winSizeOld = winSize;
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simulator.setParameter("maxSeq", maxSeq);
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simulator.setParameter("winSize", winSize);
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simulator.restart();
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}
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}
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else
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alert("Window Size must be 1 to the Maximum Sequence Number");
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}
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}
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//-->
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</script>
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</head>
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<body background="simulator.jpeg"
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onload="simulator=document.ProtocolSimulator; set();">
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<div style="text-align: center">
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<h1>
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Sliding Window Protocol Simulator
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<br/>
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(3-Column)
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</h1>
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<img src="simulator.gif" alt="Simulator Logo"/>
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</div>
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<h2>Protocol Description</h2>
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<p>
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SWP (Sliding Window Protocol) a connection-less protocol. It allows data
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to be sent in one direction between a pair of protocol entities, subject to
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a maximum number of unacknowledged messages. If SWP is operated with a
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window size of 1, it is equivalent to the <a href="ABP.html">Alternating Bit
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Protocol</a>. The simulation below does not include the users; see the <a
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href="SWP5.html">five-column</a> version for this.
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</p>
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<p>
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The protocol has a maximum number of messages that can be sent without
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acknowledgement. If this window becomes full, the protocol is blocked
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until an acknowledgement is received for the earliest outstanding
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message. At this point the transmitter is clear to send more messages.
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</p>
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<h2>Protocol Parameters</h2>
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<p>
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The following settings are adequate for a simple simulation. For a more
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advanced exploration, choose different options and click <em>Change
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Settings</em>. This may cause the simulation to restart.
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</p>
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<p>
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Optionally set the level of control that the simulator user needs over
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the medium:
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</p>
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<dl>
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<dt><b>Automatic</b>:</dt>
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<dd>
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Messages are delivered immediately without loss. This is suitable for
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initial experimentation, but limits what can be explored. For example,
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message are never lost and never have to be timed out and resent.
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</dd>
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<dt><b>Delivery</b>:</dt>
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<dd>
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Alternatively, message delivery may be controlled - though messages
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will still never be lost. Choose this option to allow messages to be
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delivered in different orders and to be resent.
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</dd>
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<dt><b>Delivery/Loss</b>:</dt>
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<dd>
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Finally, delivery and loss of messages may be completely controlled.
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This is the most comprehensive option, but also the most complex one to
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manage.
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</dd>
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</dl>
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<p>
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Optionally set the maximum sequence number used by the protocol: this is
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one less than the modulus. Sequence numbers wrap round to zero when they
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pass the maximum. Optionally set the maximum window size permitted: this
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must not exceed the maximum sequence number. Changing either of these
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parameters will restart the simulation.
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</p>
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<form name="settings">
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<center>
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<table cellpadding="5">
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<tr>
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<td align="right">Medium Control:</td>
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<td>
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<input type="radio" name="medium" value="2"
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checked="checked"/>Automatic
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</td>
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<td>
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<input type="radio" name="medium" value="1"/>Delivery
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</td>
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<td>
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<input type="radio" name="medium" value="0"/>Delivery/Loss
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</td>
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</tr>
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<tr>
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<td align="right">Maximum Sequence Number (1 to 31):</td>
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<td colspan="3">
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<input type="text" name="maxSeq" value="7" size="2"/>
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</td>
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</tr>
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<tr>
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<td align="right">Window Size (1 to Maximum Sequence Number):</td>
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<td colspan="3">
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<input type="text" name="winSize" value="3" size="2"/>
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</td>
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</tr>
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<tr>
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<td align="center" colspan="4">
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<input type="button" name="btnSet" value="Change Settings"
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onclick="set()"/>
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</td>
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</tr>
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</table>
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</center>
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</form>
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<h2>Protocol Simulation</h2>
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<p>
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The protocol simulation shows a time-sequence diagram with transmitting
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and receiving protocol entities, and a communications medium that carries
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messages. The transmitter simply sends messages numbered <em>DT(0)</em>,
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<em>DT(1)</em>, etc. Once sequence numbers reach a maximum number (like
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7), they wrap back round to 0. The content of messages is not explicitly
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identified. An acknowledgement <em>AK(n)</em> means that the <em>DT</em>
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message numbered <em>n</em> is the next one expected (i.e. all messages
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up to but not including this number have been received). Since sequence
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numbers wrap round, an acknowledgement with sequence number 1 refers to
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messages 0, 1, 7, 6, etc. Note that if a <em>DT</em> message is received
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again due to re-transmission, it is acknowledged but discarded.
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</p>
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<center>
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<applet code="simulator.ProtocolSimulator.class"
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archive="ProtocolSimulator.jar" width="600" height="700"
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name="ProtocolSimulator">
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<param name="protocol" value="SWP3"/>
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</applet>
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</center>
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<hr/>
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<p>
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<a href="index.html"><img src="uparrow.gif" alt="Up Arrow"/></a>
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Up one level to <a href="index.html">Protocol Simulators</a>
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</p>
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</body>
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</html>
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