65 lines
3.2 KiB
HTML
65 lines
3.2 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>Protocol Overview</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="node182.html">Tuning the Transmission Protocol</A>
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<B>Up:</B> <A HREF="node180.html">UUCP Low-Level Protocols</A>
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<B> Previous:</B> <A HREF="node180.html">UUCP Low-Level Protocols</A>
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<BR> <P>
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<H2><A NAME="SECTION0014610000">Protocol Overview</A></H2>
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<P>
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<A NAME="6452"></A>
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<P>
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As UUCP is used over different types of connections, such as serial
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lines or TCP, or even X.25, specific low-level protocols are needed. In
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addition, several implementations of UUCP have introduced different
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protocols that do roughly the same thing.
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<P>
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Protocols can be divided into two categories: streaming and
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packet-oriented protocols. Protocols of the latter variety transfer a
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file as a whole, possibly computing a checksum over it. This is nearly
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free of any overhead, but requires a reliable connection, because any
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error will cause the whole file to be retransmitted. These protocols
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are commonly used over TCP connections, but are not suitable for use
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over telephone lines. Although modern modems do quite a good job at
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error correction, they are not perfect, nor is there any error
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detection between your computer and the modem.
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<P>
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On the other hand, packet protocols split up the file into several
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chunks of equal size. Each packet is sent and received separately, a
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checksum is computed, and an acknowledgement is returned to the sender.
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To make this more efficient, sliding-window protocols were invented,
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which allow for a limited number (a window) of outstanding
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acknoledgements at any time. This greatly reduces the amount of time
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uucico has to wait during a transmission. Still, the relatively
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large overhead compared to a streaming protocol make packet protocols
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inefficient for use over TCP.
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<P>
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The width of the data path also makes a difference. Sometimes, sending
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eight-bit characters over a serial connection is impossible, for
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instance if the connection goes through a stupid terminal server. In
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this case, characters with the eighth bit set have to be quoted on
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transmission. When you transmit eight-bit characters over a seven-bit
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connection, they have to be Under worst-case assumptions, this doubles
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the amount of data to be transmitted, although compression done by the
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hardware may compensate for this. Lines that can transmit arbitrary
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eight-bit characters are usually called eight-bit clean. This is the
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case for all TCP connections, as well as for most modem connections.
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<P>
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The following protocols are available with Taylor UUCP 1.04:
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<P>
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<P><P><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="node182.html">Tuning the Transmission Protocol</A>
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<B>Up:</B> <A HREF="node180.html">UUCP Low-Level Protocols</A>
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<B> Previous:</B> <A HREF="node180.html">UUCP Low-Level Protocols</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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</BODY>
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</HTML>
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