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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>17.3.2 Node structure</TITLE><META NAME="description" CONTENT="17.3.2 Node structure"><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="node213.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node213.html"><LINK REL="previous" HREF="node211.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node211.html"><LINK REL="up" HREF="node210.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node210.html"><LINK REL="next" HREF="node213.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node213.html"></HEAD><BODY ><!--Navigation Panel--><A NAME="tex2html4531" HREF="node213.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node213.html"><IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next" SRC="file:/usr/share/latex2html/icons/next.png"></A> <A NAME="tex2html4525" HREF="node210.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node210.html"><IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up" SRC="file:/usr/share/latex2html/icons/up.png"></A> <A NAME="tex2html4519" HREF="node211.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node211.html"><IMG WIDTH="63" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="previous" SRC="file:/usr/share/latex2html/icons/prev.png"></A> <A NAME="tex2html4527" 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="tex2html4529" 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="tex2html4532" HREF="node213.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node213.html">17.3.3 Detailed look at</A><B> Up:</B> <A NAME="tex2html4526" HREF="node210.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node210.html">17.3 Implementation</A><B> Previous:</B> <A NAME="tex2html4520" HREF="node211.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node211.html">17.3.1 Use of linked</A>   <B> <A NAME="tex2html4528" HREF="node1.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node1.html">Contents</A></B>   <B> <A NAME="tex2html4530" HREF="node590.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node590.html">Index</A></B> <BR><BR><!--End of Navigation Panel--><H2><A NAME="SECTION031432000000000000000">17.3.2 Node structure</A></H2><P><DIV ALIGN="CENTER"><A NAME="fig:sat-node"></A><A NAME="8048"></A><TABLE><CAPTION ALIGN="BOTTOM"><STRONG>Figure:</STRONG>Structure of class SatNode.</CAPTION><TR><TD><DIV ALIGN="CENTER">sat-node</DIV></TD></TR></TABLE></DIV><P>Figure <A HREF="node212.html#fig:sat-node" tppabs="http://www.isi.edu/nsnam/ns/doc/node212.html#fig:sat-node">17.5</A> is a schematic of the main components of a<TT>SatNode</TT>. The structure bears resemblance to the <TT>MobileNode</TT>in the wireless extensions, but there are several differences. Like all nodes, the SatNode has an ``entry'' point to a series of classifiers.The address classifier contains a slot table for forwarding packets to foreign nodes, but since OTcl routing is not used, all packets not destinedfor this node (and hence forwarded to the port classifier), are sent tothe default target, which points to a routing agent. Packets destinedon the node for port 255 are classified as routing packets and are alsoforwarded to the routing agent.<P>Each node contains one or more ``network stacks'' that include a generic<TT>SatLinkHead</TT> at the entry point of the link. The <TT>SatLinkHead</TT>is intended to serve as an API to get at other objects in the link structure,so it contains a number of pointers (although the API here has not beenfinalized). Packets leaving the network stack are sent to the node'sentry. An important feature is that each packet leaving a network stackhas its <TT>iface_</TT> field in the common packet header coded with theunique <TT>NetworkInterface</TT> index corresponding to the link. This valuecan be used to support distributed routing as described below.<P>The base class routing agent is <TT>class SatRouteAgent</TT>; it can be used in conjunction with centralized routing. SatRouteAgents containa forwarding table that resolves a packet's address to a particular LinkHead target- it is the job of the <TT>SatRouteObject</TT> to populate thistable correctly. The SatRouteAgent populates certain fields in the headerand then sends the packet down to the approprate link. To implementa distributed routing protocol, a new SatRouteAgent could be defined- thiswould learn about topology by noting the interface index marked in each packet as it came up the stack- a helper function in the node <TT>intf_to_target()</TT> allows it to resolve an index value toa particular LinkHead. <P>There are pointers to three additional objects in a SatNode. First,each SatNode contains a position object, discussed in the previous section.Second, each SatNode contains a <TT>LinkHandoffMgr</TT> that monitorsfor opportunities to hand links off and coordinates the handoffs. Satellitenodes and terminal nodes each have their specialized version of a LinkHandoffMgr.<P>Finally, a number of pointers to objects are contained in a SatNode. Wediscussed <TT>linklisthead_</TT> and <TT>nodehead_</TT> in the previous subsection. The <TT>uplink_</TT> and <TT>downlink_</TT> pointers areused for convenience under the assumption that, in most simulations,a satellite or a terminal has only one uplink and downlink channel.<P><HR><!--Navigation Panel--><A NAME="tex2html4531" HREF="node213.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node213.html"><IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next" SRC="file:/usr/share/latex2html/icons/next.png"></A> <A NAME="tex2html4525" HREF="node210.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node210.html"><IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up" SRC="file:/usr/share/latex2html/icons/up.png"></A> <A NAME="tex2html4519" HREF="node211.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node211.html"><IMG WIDTH="63" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="previous" SRC="file:/usr/share/latex2html/icons/prev.png"></A> <A NAME="tex2html4527" 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="tex2html4529" 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="tex2html4532" HREF="node213.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node213.html">17.3.3 Detailed look at</A><B> Up:</B> <A NAME="tex2html4526" HREF="node210.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node210.html">17.3 Implementation</A><B> Previous:</B> <A NAME="tex2html4520" HREF="node211.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node211.html">17.3.1 Use of linked</A>   <B> <A NAME="tex2html4528" HREF="node1.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node1.html">Contents</A></B>   <B> <A NAME="tex2html4530" 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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