97 lines
3.4 KiB
HTML
97 lines
3.4 KiB
HTML
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">
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<HTML>
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<HEAD>
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<META NAME="GENERATOR" CONTENT="SGML-Tools 1.0.9">
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<TITLE>Sat (Satellite Technology) HOWTO: Appendix A - Notes</TITLE>
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<LINK HREF="Sat-HOWTO-9.html" REL=next>
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<LINK HREF="Sat-HOWTO-7.html" REL=previous>
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<LINK HREF="Sat-HOWTO.html#toc8" REL=contents>
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<A HREF="Sat-HOWTO-9.html">Next</A>
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<A HREF="Sat-HOWTO.html#toc8">Contents</A>
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<HR>
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<H2><A NAME="s8">8. Appendix A - Notes</A></H2>
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<H2><A NAME="ss8.1">8.1 Translation Dynamic IP -> MAC Address</A>
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</H2>
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<P>The translation used by some ISPs to calculate MAC address (which need
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to have your DVB card to receive their packets) is:
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<P>00 : 01 : IP[0] : IP[1] : IP[2] : IP[3]
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<P>where
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<P>IP[0].IP[1].IP[2].IP[3] is your
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dynamic IP address.
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<P>This feature is used, for example, by EON.
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<H2><A NAME="ss8.2">8.2 TCP Window</A>
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</H2>
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<P>Satellite connections are an interesting example of very high RTT (round
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trip time, access time): another example is the Mars - Earth communication
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or also the Moon - Earth one.
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<P>These connections have a very bad feature: very low interactively.
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<P>Typical network (or digital, generally) connections use the so called transmission
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"window", which represents the data buffer can be sent before waiting for an
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answer. In TCP/IP protocol stack this is the TCP Window.
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<P>
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<PRE>
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----------------------
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| - - - - - - - > can continue |-|-|-|---->
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| ----------------------
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| Buffer sendable before confirm
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| - - - - - - - <----------------------
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Confirmation Answering
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</PRE>
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<P>Now, if our communication has an high access time and if we had a little
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TCP Window we would lose very much time only waiting for the data confirmation
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(ACK), so the real bandwidth would decrease (for example if you have a 16KB
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TCP window, typical of Windows systems and a RTT of 400 ms, you cannot overcome
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16KB/0.4 = 40 KB/s)
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<P>Solution is to use a very high TCP Window (such as 256 KB or some MB).
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<P>Unfortunately, under many systems, is not so simple to have a great TCP
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Window, so, in latest years, it starts to appear new applications ("download
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accelerators" described in next section) that split in many pieces a file and
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download all them in the main time: this is just equivalent to download only
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one file with a single piece size, avoiding the RTT problem.
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<H2><A NAME="ss8.3">8.3 Download accelerator</A>
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</H2>
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<P>We report here some useful link to so called "download accelerator" which
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is an application that does 2 things:
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<P>
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<OL>
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<LI>resuming session management, it allows stopping downloading and restarting
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later (this can be done thanks to "resuming feature" introduced in Http and Ftp
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server, which allows you to specify at what byte number start to download).</LI>
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<LI>splitting, divide the file in many pieces and let them start in a multithreaded
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fashion.</LI>
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</OL>
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<P>As we saw in the previous section, a download accelerator allows us to
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increase satellite bandwidth.
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<H3>Under Linux</H3>
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<P>
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<UL>
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<LI>
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<A HREF="http://aria.rednoah.com/">Aria</A></LI>
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</UL>
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<H3>Under Windows</H3>
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<P>
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<UL>
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<LI>
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<A HREF="http://www.amazesoft.com">FlashGet</A></LI>
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<LI>
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<A HREF="http://www.getright.com">GetRight</A></LI>
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<LI>
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<A HREF="http://www.metaproducts.com">Mass Downloader</A></LI>
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</UL>
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<HR>
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<A HREF="Sat-HOWTO-7.html">Previous</A>
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<A HREF="Sat-HOWTO.html#toc8">Contents</A>
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