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183 lines
5.0 KiB
HTML
183 lines
5.0 KiB
HTML
<!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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<!-- MUX.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>Multicasting</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 serviceMode;
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function set() {
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serviceMode = document.settings.serviceMode.value;
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simulator.setParameter("serviceMode", serviceMode);
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simulator.restart();
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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>Multicasting</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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MCAST (Multicasting) illustrates how data can be sent from a source to
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multiple destinations over a network. The following example shows a source,
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three destinations, and a further host that has no interest in the data.
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These are interconnected by routers A to F.
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</p>
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<center>
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<img src="multicast.gif" alt="Multicast Illustration"/>
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</center>
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<p>
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There are three strategies for sending data from the source to the
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destinations:
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</p>
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<dl>
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<dt><b>Broadcast</b>:</dt>
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<dt>
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<p>
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If the source does not know which networks the destinations are on, it
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must send a copy of the messages to each router that gives access to a
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possible destination. In this example, the source must send data to
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routers B, D, E and F. The result is inefficient in that 10 copies of
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the message must be sent.
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</p>
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</dt>
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<dt><b>Unicast</b>:</dt>
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<dt>
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<p>
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If the source knows which networks the destinations are on, it can send
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a copy of the messages only to the routers that gives access to these
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destinations. In this example, the source must send data to routers B, D
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and E. The result is more efficient than broadcast, but 8 copies of the
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message must still be sent.
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</p>
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</dt>
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<dt><b>Multicast</b>:</dt>
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<dt>
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<p>
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The source can instead rely on the routers to distribute messages,
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making copies only when necessary. In this example, the source sends
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just one message to router A, stating that it is for routers B, D and E.
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Router A looks at where the message is going, and delivers copies of the
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message to routers B and C (when it states that the message is for
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routers D and E). Router C then delivers copies of the message to
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routers D and E. The result is more efficient than unicast, with only 5
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copies of messages being sent. This is half the number for broadcast. On
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a much larger network, the transmission savings of multicast can be
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substantial.
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</p>
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</dt>
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</dl>
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<p>
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Each router stores the messages it receives and forwards them to their
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destination. The messages may be forwarded in any order since it depends on
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how busy the communications links are. When trying the simulation, you may
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find it easier to understand if you immediately forward router messages
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rather than let them build up. For this simulation, the communications
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channels are assumed to operate perfectly (no message corruption, loss or
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misordering).
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</p>
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<h2>Protocol Parameters</h2>
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<p>
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By default, multicasting uses the broadcast strategy. You can modify the way
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in which the protocol works by modifying the strategy. Click Change Settings
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after making this alteration. This will restart the whole simulation.
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</p>
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<form name="settings">
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<center>
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<table cellspacing="5">
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<tr>
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<td align="right">Multicasting Strategy:</td>
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<td>
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<select name="serviceMode">
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<option selected>Broadcast</option>
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<option>Unicast</option>
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<option>Multicast</option>
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</select>
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</td>
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</tr>
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<tr>
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<td align="center" colspan="2">
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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 the source and
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the six routers. Messages have the format
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<var>DT(Destinations,Mn)</var>. For broadcast and unicast, each
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message has one destination; for multicast, there can be multiple
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destinations. Messages are numbered <var>M0</var>, <var>M1</var>, etc.; no
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explicit data
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content is given.
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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="800" height="700"
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name="ProtocolSimulator">
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<param name="protocol" value="MCAST"/>
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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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