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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>12. Packet Headers and Formats</TITLE><META NAME="description" CONTENT="12. Packet Headers and Formats"><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="node137.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node137.html"><LINK REL="previous" HREF="node121.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node121.html"><LINK REL="up" HREF="node29.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node29.html"><LINK REL="next" HREF="node128.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node128.html"></HEAD><BODY ><!--Navigation Panel--><A NAME="tex2html3237" HREF="node128.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node128.html"><IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next" SRC="file:/usr/share/latex2html/icons/next.png"></A> <A NAME="tex2html3231" HREF="node29.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node29.html"><IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up" SRC="file:/usr/share/latex2html/icons/up.png"></A> <A NAME="tex2html3225" HREF="node126.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node126.html"><IMG WIDTH="63" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="previous" SRC="file:/usr/share/latex2html/icons/prev.png"></A> <A NAME="tex2html3233" 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="tex2html3235" 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="tex2html3238" HREF="node128.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node128.html">12.1 A Protocol-Specific Packet</A><B> Up:</B> <A NAME="tex2html3232" HREF="node29.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node29.html">2 Simulator Basics</A><B> Previous:</B> <A NAME="tex2html3226" HREF="node126.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node126.html">11.3 Commands at a</A>   <B> <A NAME="tex2html3234" HREF="node1.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node1.html">Contents</A></B>   <B> <A NAME="tex2html3236" 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="SECTION03900000000000000000"></A><A NAME="chap:pformat"></A><BR>12. Packet Headers and Formats</H1><P>The procedures and functions described in this chapter can be found intcl/lib/ns-lib.tcl,tcl/lib/ns-packet.tcl, and packet.{cc, h}.<P>Objects in the Packet../ns-2/packets.h are the fundamental unit ofexchange between objects in the simulation.The class <TT>Packet</TT>provides enough information to link a packet on to a list(, in a <TT>PacketQueue</TT> or on a free list of packets),refer to a buffer containing packet headersthat are defined on a per-protocol basis,and to refer to a buffer of packet data.New protocols may define their own packet headers or may extendexisting headers with additional fields.<P>New packet headers are introduced into the simulatorby defining a C++ structure with the needed fields,defining a static class to provide OTcl linkage,and then modifying some of the simulator initialization codeto assign a byte offset in each packet where the new headeris to be located relative to others.<P>When the simulator is initialized through OTcl,a user may choose to enableonly a subset of the compiled-in packet formats, resulting ina modest savings of memory during the execution of the simulation.Presently, most configured-in packet formats are enabled.The management of which packet formats are currently enabledin a simulation is handled by a special packet header managerobject described below.This object supports an OTcl method used to specifywhich packet headers will be used in a simulation.If an object in the simulator makes use of a field in a headerwhich has not been enabled, a run-time fatal program abort occurs.<P><BR><HR><!--Table of Child-Links--><A NAME="CHILD_LINKS"><STRONG>Subsections</STRONG></A><UL><LI><A NAME="tex2html3239" HREF="node128.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node128.html">12.1 A Protocol-Specific Packet Header</A><UL><LI><A NAME="tex2html3240" HREF="node129.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node129.html">12.1.1 Adding a New Packet Header Type</A><LI><A NAME="tex2html3241" HREF="node130.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node130.html">12.1.2 Selectively Including Packet Headers in Your Simulation</A></UL><BR><LI><A NAME="tex2html3242" HREF="node131.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node131.html">12.2 Packet Classes</A><UL><LI><A NAME="tex2html3243" HREF="node132.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node132.html">12.2.1 The Packet Class</A><LI><A NAME="tex2html3244" HREF="node133.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node133.html">12.2.2 p_info Class</A><LI><A NAME="tex2html3245" HREF="node134.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node134.html">12.2.3 The hdr_cmn Class</A><LI><A NAME="tex2html3246" HREF="node135.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node135.html">12.2.4 The PacketHeaderManager Class</A></UL><BR><LI><A NAME="tex2html3247" HREF="node136.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node136.html">12.3 Commands at a glance</A></UL><!--End of Table of Child-Links--><HR><!--Navigation Panel--><A NAME="tex2html3237" HREF="node128.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node128.html"><IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next" SRC="file:/usr/share/latex2html/icons/next.png"></A> <A NAME="tex2html3231" HREF="node29.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node29.html"><IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up" SRC="file:/usr/share/latex2html/icons/up.png"></A> <A NAME="tex2html3225" HREF="node126.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node126.html"><IMG WIDTH="63" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="previous" SRC="file:/usr/share/latex2html/icons/prev.png"></A> <A NAME="tex2html3233" 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="tex2html3235" 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="tex2html3238" HREF="node128.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node128.html">12.1 A Protocol-Specific Packet</A><B> Up:</B> <A NAME="tex2html3232" HREF="node29.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node29.html">2 Simulator Basics</A><B> Previous:</B> <A NAME="tex2html3226" HREF="node126.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node126.html">11.3 Commands at a</A>   <B> <A NAME="tex2html3234" HREF="node1.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node1.html">Contents</A></B>   <B> <A NAME="tex2html3236" 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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