99 lines
4.7 KiB
HTML
99 lines
4.7 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN">
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<!--Converted with LaTeX2HTML 96.1-c (Feb 29, 1996) by Nikos Drakos (nikos@cbl.leeds.ac.uk), CBLU, University of Leeds -->
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<HTML>
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<HEAD>
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<TITLE>Introduction to TCP/IP-Networks</TITLE>
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</HEAD>
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<BODY LANG="EN">
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<A HREF="node1.html"><IMG WIDTH=65 HEIGHT=24 ALIGN=BOTTOM ALT="contents" SRC="contents_motif.gif"></A> <BR>
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<B> Next:</B> <A HREF="node9.html">Ethernets</A>
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<B>Up:</B> <A HREF="node7.html">TCP/IP Networks</A>
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<B> Previous:</B> <A HREF="node7.html">TCP/IP Networks</A>
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<BR> <P>
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<H2><A NAME="SECTION003310000">Introduction to TCP/IP-Networks</A></H2>
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TCP/IP traces its origins to a research project funded by the United
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States DARPA (Defense Advanced Research Projects Agency) in 1969. This
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was an experimental network, the ARPANET, which was converted into an
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operational one in 1975, after it had proven to be a success.
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<p>
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In 1983, the new protocol suite TCP/IP was adopted as a standard, and
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all hosts on the network were required to use it. When ARPANET finally
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grew into the Internet (with ARPANET itself passing out of existence in
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1990), the use of TCP/IP had spread to networks beyond the Internet
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itself. Most notable are local area networks, but in the advent
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of fast digital telephone equipment, such as ISDN, it also has a
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promising future as a transport for dial-up networks.
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<P>
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<A NAME="331"></A>
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<A NAME="332"></A>
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<A NAME="333"></A>
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For something concrete to look at as we discuss TCP/IP throughout the
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following sections, we will consider Groucho Marx University (GMU),
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situated somewhere in Fredland, as an example. Most departments run
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their own local area networks, while some share one, and others run
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several of them. They are all interconnected, and are hooked to the
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Internet through a single high-speed link.
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<P>
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<A NAME="334"></A>
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Suppose your box is connected to a LAN of hosts at the
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Mathematics Department, and its name is erdos. To access a host at
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the Physics Department, say quark, you enter the following
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command:
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<pre>
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$ rlogin quark.physics
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Welcome to the Physics Department at GMU
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(ttyq2) login:
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</pre>
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At the prompt, you enter your login name, say andres, and
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your password. You are then given a shell on quark, to which
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you can type as if you were sitting at the system's console. After
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you exit the shell, you are returned to your own machine's prompt.
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You have just used one of the instantaneous, interactive applications
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that TCP/IP provides: remote login.
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<P>
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<A NAME="343"></A>
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While being logged into quark, you might also want to run an
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X11-based application, like a function plotting program, or a PostScript
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previewer. To tell this application that you want to have its windows
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displayed on your host's screen, you have to set the DISPLAY
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environment variable:
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<pre>
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$ export DISPLAY=erdos.maths:0.0
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</pre>
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If you now start your application, it will contact your X server
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instead of quark's, and display all its windows on your screen.
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Of course, this requires that you have X11 running on erdos.
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The point here is that TCP/IP allows quark and erdos
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to send X11 packets back and forth to give you the illusion that
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you're on a single system. The network is almost transparent here.
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<P>
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Another very important application in TCP/IP networks is NFS, which
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stands for <em>Network File System</em>. It is another form of making the
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network transparent, because it basically allows you to mount directory
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hierarchies from other hosts, so that they appear like local file
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systems. For example, all users' home directories can be on a central
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server machine, from which all other hosts on the LAN mount the
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directory. The effect of this is that users can log into any machine,
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and find themselves in the same home directory. Similarly, it is
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possible to install applications that require large amounts of disk
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space (such as TeX) on only one machine, and export these directories
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to other machines. We will come back to NFS in chapter-<A HREF="node140.html#nfs"><IMG ALIGN=BOTTOM ALT="gif" SRC="cross_ref_motif.gif"></A>.
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<P>
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Of course, these are only examples of what you can do over TCP/IP
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networks. The possibilities are almost limitless.
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<P>
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We will now have a closer look at the way TCP/IP works. You will need
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this to understand how and why you have to configure your machine. We
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will start by examining the hardware, and slowly work our way up.
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<P>
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<HR><A HREF="node1.html"><IMG WIDTH=65 HEIGHT=24 ALIGN=BOTTOM ALT="contents" SRC="contents_motif.gif"></A> <BR>
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<B> Next:</B> <A HREF="node9.html">Ethernets</A>
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<B>Up:</B> <A HREF="node7.html">TCP/IP Networks</A>
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<B> Previous:</B> <A HREF="node7.html">TCP/IP Networks</A>
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<P><ADDRESS>
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<I>Andrew Anderson <BR>
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Thu Mar 7 23:22:06 EST 1996</I>
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</ADDRESS>
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