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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>17.2.2 Satellite links</TITLE><META NAME="description" CONTENT="17.2.2 Satellite links"><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="node202.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node202.html"><LINK REL="previous" HREF="node200.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node200.html"><LINK REL="up" HREF="node199.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node199.html"><LINK REL="next" HREF="node202.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node202.html"></HEAD><BODY ><!--Navigation Panel--><A NAME="tex2html4376" HREF="node202.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node202.html"><IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next" SRC="file:/usr/share/latex2html/icons/next.png"></A> <A NAME="tex2html4370" HREF="node199.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node199.html"><IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up" SRC="file:/usr/share/latex2html/icons/up.png"></A> <A NAME="tex2html4364" HREF="node200.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node200.html"><IMG WIDTH="63" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="previous" SRC="file:/usr/share/latex2html/icons/prev.png"></A> <A NAME="tex2html4372" 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="tex2html4374" 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="tex2html4377" HREF="node202.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node202.html">17.2.3 Handoffs</A><B> Up:</B> <A NAME="tex2html4371" HREF="node199.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node199.html">17.2 Using the satellite</A><B> Previous:</B> <A NAME="tex2html4365" HREF="node200.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node200.html">17.2.1 Nodes and node</A>   <B> <A NAME="tex2html4373" HREF="node1.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node1.html">Contents</A></B>   <B> <A NAME="tex2html4375" 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="SECTION031422000000000000000"></A><A NAME="sec:satellite_usage_links"></A><BR>17.2.2 Satellite links</H2><P><DIV ALIGN="CENTER"><A NAME="fig:sat-stack-basic"></A><A NAME="7770"></A><TABLE><CAPTION ALIGN="BOTTOM"><STRONG>Figure 17.3:</STRONG>Main components of a satellite network interface</CAPTION><TR><TD><DIV ALIGN="CENTER">sat-stack-basic</DIV></TD></TR></TABLE></DIV><P>Satellite links resemble wireless links, which are described in Chapter<A HREF="node171.html#chap:mobility" tppabs="http://www.isi.edu/nsnam/ns/doc/node171.html#chap:mobility">16</A>. Each satellitenode has one or more satellite network interface stacks, to whichchannels are connected to the physical layer object in the stack. Figure<A HREF="node201.html#fig:sat-stack-basic" tppabs="http://www.isi.edu/nsnam/ns/doc/node201.html#fig:sat-stack-basic">17.3</A> illustrates the major components. Satellitelinks differ from wireless links in two major respects: i) thetransmit and receive interfaces must be connected to different channels,and ii) there is no ARP implementation. Currently, the <EM>Radio Propagation Model</EM> is a placeholder for users to add more detailederror models if so desired; the current code does not use a propagationmodel.<P>Network interfaces can be added with the following instproc of<TT>Class Node/SatNode</TT>:<PRE>$node add-interface $type $ll $qtype $qlim $mac $mac_bw $phy</PRE>The <TT>add-interface</TT> instproc returns an index value that can be usedto access the network interface stack later in the simulation. By convention,the first interface created on a node is attached to the uplink and downlinkchannels of a satellite or terminal. Thefollowing parameters must be provided:<P><UL><LI><B>type</B>: The following link types can be indicated: <TT>geo</TT> or <TT>polar</TT> for links from a terminal to a geo or polar satellite, respectively, <TT>gsl</TT> and <TT>gsl-repeater</TT> for links from a satelliteto a terminal, and <TT>intraplane</TT>, <TT>interplane</TT>, and <TT>crossseam</TT>ISLs. The type field is used internally in the simulator to identify thedifferent types of links, but structurally they are all very similar.</LI><LI><B>ll</B>: The link layer type (<TT>class LL/Sat</TT> is currentlythe only one defined). </LI><LI><B>qtype</B>: The queue type (e.g., <TT>class Queue/DropTail</TT>).Any queue type may be used- however, if additional parameters beyond thelength of the queue are needed, then this instproc may need to be modifiedto include more arguments.</LI><LI><B>qlim</B>: The length of the interface queue, in packets.</LI><LI><B>mac</B>: The MAC type. Currently, two types are defined:<TT>class Mac/Sat</TT>- a basic MAC for links with only one receiver (i.e.,it does not do collision detection), and<TT>Class Mac/Sat/UnslottedAloha</TT>- an implementation of unslotted Aloha.</LI><LI><B>mac_bw</B>: The bandwidth of the link is set by this parameter, which controls the transmission time how fast the MAC sends. Thepacket size used to calculate the transmission time is the sum of thevalues <TT>size()</TT> in the common packet header and <TT>LINK_HDRSIZE</TT>,which is the size of any link layer headers. The default value for<TT>LINK_HDRSIZE</TT> is 16 bytes (settable in <TT>satlink.h</TT>).The transmission time is encoded in the packet header for use at thereceive MAC (to simulate waiting for a whole packet to arrive). </LI><LI><B>phy</B>: The physical layer- currently two Phys (<TT>Class Phy/Sat</TT> and <TT>Class Phy/Repeater</TT>) are defined. The class <TT>Phy/Sat</TT> just pass the information up and down the stack-as in the wireless code described in Chapter <A HREF="node171.html#chap:mobility" tppabs="http://www.isi.edu/nsnam/ns/doc/node171.html#chap:mobility">16</A>, a radio propagation model could be attached at this point. The class<TT>Phy/Repeater</TT> pipes any packets received on a receive interfacestraight through to a transmit interface.</LI></UL><P>An ISL can be added between two nodes using the following instproc:<PRE>$ns add-isl $ltype $node1 $node2 $bw $qtype $qlim</PRE>This creates two channels (of type <TT>Channel/Sat</TT>), and appropriatenetwork interfaces on both nodes, and attaches the channels to the network interfaces. The bandwidth of the link isset to <TT>bw</TT>. The linktype (<TT>ltype</TT>)must be specified as either <TT>intraplane</TT>, <TT>interplane</TT>, or <TT>crossseam</TT>.<P>A GSL involves adding network interfaces and a channel on board thesatellite (this is typically done using the wrapper methods describedin the next paragraph), and then defining the correct interfaces onthe terrestrial node and attaching them to the satellite link, as follows:<PRE>$node add-gsl $type $ll $qtype $qlim $mac $bw_up $phy \bs [$node_satellite set downlink_] [$node_satellite set uplink_]</PRE>Here, the <TT>type</TT> must be either <TT>geo</TT> or <TT>polar</TT>, and we make useof the <TT>downlink_</TT> and <TT>uplink_</TT> instvars of the satellite;therefore, the satellite's uplink and downlink must be created beforethis instproc is called.<P>By default, the node generator for satellite nodes (described inSection <A HREF="node46.html#sec:node:nodeconfig" tppabs="http://www.isi.edu/nsnam/ns/doc/node46.html#sec:node:nodeconfig">5.3</A>) will create nodes of a given type, give them an uplink anddownlink interface, and create and attach an (initial) uplink and downlinkchannel, based on the interface options specified.<P><HR><!--Navigation Panel--><A NAME="tex2html4376" HREF="node202.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node202.html"><IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next" SRC="file:/usr/share/latex2html/icons/next.png"></A> <A NAME="tex2html4370" HREF="node199.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node199.html"><IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up" SRC="file:/usr/share/latex2html/icons/up.png"></A> <A NAME="tex2html4364" HREF="node200.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node200.html"><IMG WIDTH="63" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="previous" SRC="file:/usr/share/latex2html/icons/prev.png"></A> <A NAME="tex2html4372" 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="tex2html4374" 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="tex2html4377" HREF="node202.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node202.html">17.2.3 Handoffs</A><B> Up:</B> <A NAME="tex2html4371" HREF="node199.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node199.html">17.2 Using the satellite</A><B> Previous:</B> <A NAME="tex2html4365" HREF="node200.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node200.html">17.2.1 Nodes and node</A>   <B> <A NAME="tex2html4373" HREF="node1.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node1.html">Contents</A></B>   <B> <A NAME="tex2html4375" 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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