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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>31.4.0.0.5 Functions for Managing the Retransmission Timer</TITLE><META NAME="description" CONTENT="31.4.0.0.5 Functions for Managing the Retransmission Timer"><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="previous" HREF="node396.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node396.html"><LINK REL="up" HREF="node392.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node392.html"><LINK REL="next" HREF="node398.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node398.html"></HEAD><BODY ><!--Navigation Panel--><A NAME="tex2html7479" HREF="node398.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node398.html"><IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next" SRC="file:/usr/share/latex2html/icons/next.png"></A> <A NAME="tex2html7473" HREF="node392.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node392.html"><IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up" SRC="file:/usr/share/latex2html/icons/up.png"></A> <A NAME="tex2html7469" HREF="node396.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node396.html"><IMG WIDTH="63" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="previous" SRC="file:/usr/share/latex2html/icons/prev.png"></A> <A NAME="tex2html7475" 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="tex2html7477" 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="tex2html7480" HREF="node398.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node398.html">31.5 Tracing TCP Dynamics</A><B> Up:</B> <A NAME="tex2html7474" HREF="node392.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node392.html">31.4 Architecture and Internals</A><B> Previous:</B> <A NAME="tex2html7470" HREF="node396.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node396.html">31.4.0.0.4 Functions for Processing</A>   <B> <A NAME="tex2html7476" HREF="node1.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node1.html">Contents</A></B>   <B> <A NAME="tex2html7478" HREF="node590.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node590.html">Index</A></B> <BR><BR><!--End of Navigation Panel--><H4><A NAME="SECTION06240050000000000000">31.4.0.0.5 Functions for Managing the Retransmission Timer</A></H4><P>These functions serve two purposes: estimating the round-trip timeand setting the actual retransmission timer.<B>rtt_init</B> - this function initializes <TT>srtt_</TT> and <TT>rtt_</TT>to zero, sets <TT>rttvar_</TT> to , and sets the backoffmultiplier to one.<P><B>rtt_timeout</B> - this function gives the timeout value in seconds thatshould be used to schedule the next retransmission timer.It computes this based on the current estimates of the mean and deviationof the round-trip time. In addition, it implements Karn'sexponential timer backoff for multiple consecutive retransmission timeouts.<P><B>rtt_update</B> - this function takes as argument the measured RTTand averages it in to the running mean and deviation estimatorsaccording to the description above.Note that <TT>t_srtt_</TT> and <TT>t_rttvar</TT> are bothstored in fixed-point (integers).They have 3 and 2 bits, respectively, to the right of the binarypoint.<P><B>reset_rtx_timer</B> - This function is invoked during fast retransmitor during a timeout.It sets a retransmission timerby calling <TT>set_rtx_timer</TT> and if invoked by a timeout also calls<TT>rtt_backoff</TT>.<P><B>rtt_backoff</B> - this function backs off the retransmission timer(by doubling it).<P><B>newtimer</B> - this function called only when a new ACK arrives.If the sender's left window edge is beyond the ACK, then<TT>set_rtx_timer</TT> is called, otherwise if a retransmission timeris pending it is cancelled.<P><HR><!--Navigation Panel--><A NAME="tex2html7479" HREF="node398.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node398.html"><IMG WIDTH="37" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="next" SRC="file:/usr/share/latex2html/icons/next.png"></A> <A NAME="tex2html7473" HREF="node392.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node392.html"><IMG WIDTH="26" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="up" SRC="file:/usr/share/latex2html/icons/up.png"></A> <A NAME="tex2html7469" HREF="node396.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node396.html"><IMG WIDTH="63" HEIGHT="24" ALIGN="BOTTOM" BORDER="0" ALT="previous" SRC="file:/usr/share/latex2html/icons/prev.png"></A> <A NAME="tex2html7475" 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="tex2html7477" 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="tex2html7480" HREF="node398.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node398.html">31.5 Tracing TCP Dynamics</A><B> Up:</B> <A NAME="tex2html7474" HREF="node392.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node392.html">31.4 Architecture and Internals</A><B> Previous:</B> <A NAME="tex2html7470" HREF="node396.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node396.html">31.4.0.0.4 Functions for Processing</A>   <B> <A NAME="tex2html7476" HREF="node1.html" tppabs="http://www.isi.edu/nsnam/ns/doc/node1.html">Contents</A></B>   <B> <A NAME="tex2html7478" 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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