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<html><!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN"><!--Converted with jLaTeX2HTML 2002 (1.62) JA patch-1.4patched version by: Kenshi Muto, Debian Project.LaTeX2HTML 2002 (1.62),original version by: Nikos Drakos, CBLU, University of Leeds* revised and updated by: Marcus Hennecke, Ross Moore, Herb Swan* with significant contributions from: Jens Lippmann, Marek Rouchal, Martin Wilck and others --><HTML><HEAD><TITLE>14.2 Components of a LAN</TITLE><META NAME="description" CONTENT="14.2 Components of a LAN"><META NAME="keywords" CONTENT="everything"><META NAME="resource-type" CONTENT="document"><META NAME="distribution" CONTENT="global"><META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=iso-8859-1"><META NAME="Generator" CONTENT="jLaTeX2HTML v2002 JA patch-1.4"><META HTTP-EQUIV="Content-Style-Type" CONTENT="text/css"><LINK REL="STYLESHEET" HREF="everything.css" tppabs="http://www.isi.edu/nsnam/ns/doc/everything.css"><LINK REL="next" HREF="node145.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node145.html"><LINK REL="previous" HREF="node143.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node143.html"><LINK REL="up" HREF="node142.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node142.html"><LINK REL="next" HREF="node145.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node145.html"></HEAD><BODY ><!--Navigation Panel--><A NAME="tex2html3505" HREF="node145.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node145.html"><IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next" SRC="file:/usr/share/latex2html/icons/next.png"></A> <A NAME="tex2html3499" HREF="node142.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node142.html"><IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up" SRC="file:/usr/share/latex2html/icons/up.png"></A> <A NAME="tex2html3493" HREF="node143.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node143.html"><IMG WIDTH="63" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="previous" SRC="file:/usr/share/latex2html/icons/prev.png"></A> <A NAME="tex2html3501" HREF="node1.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node1.html"><IMG WIDTH="65" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="contents" SRC="file:/usr/share/latex2html/icons/contents.png"></A> <A NAME="tex2html3503" HREF="node590.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node590.html"><IMG WIDTH="43" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="index" SRC="file:/usr/share/latex2html/icons/index.png"></A> <BR><B> Next:</B> <A NAME="tex2html3506" HREF="node145.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node145.html">14.3 Channel Class</A><B> Up:</B> <A NAME="tex2html3500" HREF="node142.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node142.html">14. Local Area Networks</A><B> Previous:</B> <A NAME="tex2html3494" HREF="node143.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node143.html">14.1 Tcl configuration</A>   <B> <A NAME="tex2html3502" HREF="node1.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node1.html">Contents</A></B>   <B> <A NAME="tex2html3504" HREF="node590.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node590.html">Index</A></B> <BR><BR><!--End of Navigation Panel--><H1><A NAME="SECTION031120000000000000000"></A><A NAME="sec:lan_components"></A><BR>14.2 Components of a LAN</H1><P>LanLink captures the functionality of the three lowest layers in thenetwork stack:<P><OL><LI>Link Layer (LL)</LI><LI>Medium Access Control (MAC) Layer</LI><LI>Physical (PHY) Layer</LI></OL><P><DIV ALIGN="CENTER"><A NAME="fig:lan-connectivity"></A><A NAME="5853"></A><TABLE><CAPTION ALIGN="BOTTOM"><STRONG>Figure 14.1:</STRONG>Connectivity within a LAN</CAPTION><TR><TD><DIV ALIGN="CENTER">lan1</DIV></TD></TR></TABLE></DIV><P>Figure <A HREF="node144.html#fig:lan-connectivity" tppabs="http://www.isi.edu/nsnam/ns/doc/node144.html#fig:lan-connectivity">14.1</A> illustrates the extended networkstack that makes simulations of local area network possible in . Apacket sent down the stack flowsthrough the link layer (<TT>Queue</TT> and <TT>LL</TT>), the MAC layer(<TT>Mac</TT>), and the physical layer (<TT>Channel</TT> to<TT>Classifier/Mac</TT>). The packet then makes its way up the stack throughthe <TT>Mac</TT>, and the <TT>LL</TT>.<P>At the bottom of the stack, the physical layer is composed of twosimulation objects: the <TT>Channel</TT> and <TT>Classifier/Mac</TT>. The<TT>Channel</TT> object simulates the shared medium and supports the mediumaccess mechanisms of the MAC objects on the sending side of thetransmission. On the receiving side, the <TT>Classifier/Mac</TT> isresponsible for delivering and optionally replicating packets to thereceiving MAC objects.<P>Depending on the type of physical layer, the MAC layer must contain acertain set of functionalities such as: carrier sense, collisiondetection, collision avoidance, etc. Since these functionalities affectboth the sending and receiving sides, they are implemented in a single<TT>Mac</TT> object. For sending, the <TT>Mac</TT> object must follow a certainmedium access protocol before transmitting the packet on the channel.For receiving, the MAC layer is responsible for delivering the packet tothe link layer.<P>Above the MAC layer, the link layer can potentially have manyfunctionalities such as queuing and link-level retransmission. Theneed of having a wide variety of link-level schemes leads to thedivision of functionality into two components: <TT>Queue</TT> and<TT>LL</TT> (link-layer). The <TT>Queue</TT> object, simulating theinterface queue, belongs to the same <TT>Queue</TT> class that isdescribed in Chapter <A HREF="node64.html#chap:qmgmt" tppabs="http://www.isi.edu/nsnam/ns/doc/node64.html#chap:qmgmt">7</A>. The <TT>LL</TT> object implementsa particular data link protocol, such as ARQ. By combining both thesending and receiving functionalities into one module, the <TT>LL</TT>object can also support other mechanisms such as piggybacking.<P><HR><!--Navigation Panel--><A NAME="tex2html3505" HREF="node145.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node145.html"><IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next" SRC="file:/usr/share/latex2html/icons/next.png"></A> <A NAME="tex2html3499" HREF="node142.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node142.html"><IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up" SRC="file:/usr/share/latex2html/icons/up.png"></A> <A NAME="tex2html3493" HREF="node143.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node143.html"><IMG WIDTH="63" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="previous" SRC="file:/usr/share/latex2html/icons/prev.png"></A> <A NAME="tex2html3501" HREF="node1.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node1.html"><IMG WIDTH="65" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="contents" SRC="file:/usr/share/latex2html/icons/contents.png"></A> <A NAME="tex2html3503" HREF="node590.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node590.html"><IMG WIDTH="43" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="index" SRC="file:/usr/share/latex2html/icons/index.png"></A> <BR><B> Next:</B> <A NAME="tex2html3506" HREF="node145.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node145.html">14.3 Channel Class</A><B> Up:</B> <A NAME="tex2html3500" HREF="node142.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node142.html">14. Local Area Networks</A><B> Previous:</B> <A NAME="tex2html3494" HREF="node143.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node143.html">14.1 Tcl configuration</A>   <B> <A NAME="tex2html3502" HREF="node1.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node1.html">Contents</A></B>   <B> <A NAME="tex2html3504" HREF="node590.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node590.html">Index</A></B> <!--End of Navigation Panel--><ADDRESS>2003-09-23</ADDRESS></BODY></HTML>⌨️ 快捷键说明
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