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135 lines
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135 lines
5.2 KiB
Plaintext
#use wml::template Title="echoping details"
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<!-- $Id$ -->
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<H2>echo service</H2>
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<P>echoping, with its default setting, assumes the remote host accepts
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such connections. Experience show that most Internet routers or hosts
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do not. Some Unices are not shipped with this service enabled and,
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anyway, the administrator is always free to close it (I think they
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shouldn't). echoping has therefore less chance to succeed than ping or
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bing. (On a typical Unix box, "echo" service is configured in
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/etc/inetd.conf but see the <A
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HREF="http://www.cert.org/advisories/CA-1996-01.html">CERT
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advisory</A>.)
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<H2>What does it measure?</H2>
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<P>echoping simply shows the elapsed time, including the time to set up the TCP
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connection and to transfer the data (but excluding the time for the
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- possible - DNS call). Therefore, it is unsuitable to physical
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line raw throughput measures (unlike bing). On the other end, the action it
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performs are close from a HTTP request and it is meaningful to use it
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(carefully) to measure Web performances.
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<H3>More on Linux</H3>
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<P>On operating systems, like Linux, who have the TCP_INFO option (see
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<A HREF="http://linuxgazette.net/136/pfeiffer.html">a detailed
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presentation</A>), echoping can also display interesting TCP information.
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<H2>UDP and inetd</H2>
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<P>With UDP servers you can have surprises: the first test is quite often
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much slower since inetd has to launch the process. After that, the process
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stays a while so the next texts run faster.
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<H2>A nice example</H2>
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<P>There are many, many traps when measuring something on the Internet. Just one
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example: 'echoping -w 0 -n 4 a-sunOS-machine' and you'll see the first test
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succeed in a very short time (if you are close from the machine) and all of
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the others take a much longer time (one second). With '-w 1' (wait one second
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between tests, the default), everything works fine: it seems the sockets on
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SunOS need time to recover :-)
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<H2>To measure performances on the Internet you can also see</H2>
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<H3>Unix</H3>
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<UL>
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<LI><A HREF="http://www.internet2.edu/~shalunov/thrulay/">thrulay</A>,
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measures the capacity of a network by sending a bulk TCP stream over it
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<LI><A
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HREF="http://www.freenix.fr/freenix/logiciels/bing.html">bing</A>, a
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bandwidth measurement tool
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<LI>pathchar or <A
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HREF="http://www.employees.org/~bmah/Software/pchar/">pchar</A>, a bandwidth measurement tool
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<LI>ping, probably available with your system
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<LI>traceroute, idem (otherwise, see <A HREF="ftp://ftp.ee.lbl.gov/">LBL</A>)
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<LI><A HREF="ftp://ftp.arl.mil/pub/ttcp/">ttcp</A>, the best measurement tool but it needs some control over the
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two machines
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<LI><A HREF="ftp://ftp.scl.ameslab.gov/pub/netpipe/">Netpipe</A>, it needs some control over the two machines
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<LI><A HREF="http://www.psc.edu/~pscnoc/treno_info.html">treno</A> (evaluates available bandwidth for TCP)
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<LI>spray is a tool which I dont't know very well. It is available on some
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machines (Sun, OSF/1).
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<LI>I've also heard of but never tried:
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<UL>
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<LI><A
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HREF="http://www.netperf.org/netperf/NetperfPage.html">Netperf</A>, a suite of Bandwidth Measuring programs from gnn@netcom.com
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These are <A HREF="ftp://ftp.netcom.com/~ftp/gnn/bwmeas-0.3.tar.Z">several
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programs</A> that measure bandwidth and jitter over several kinds of
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IPC links, including TCP and UDP.
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</UL>
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</UL>
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<H3>MacOS</H3>
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<UL>
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<LI>TCP Watcher, a very nice "swiss-army knife" tool, to test ping, DNS, echo.
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It includes an echo server. Available on <A
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HREF="http://www.info-mac.org/">Info-Mac</A> in "comm/inet".
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</UL>
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<H3>MS-Windows</H3>
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(I have little knowledge of that environment and I tested nothing.)
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<UL>
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<LI><A
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HREF="http://www.ccs.org/winsock/xref-e.html#echo_clients">WSNUTIL</A>.
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Seems to be an echo client and server.
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<LI><A
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HREF="http://www.winsite.com/info/pc/win95/misc/echox32.zip/">echox32</A>,
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an echo server
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<LI><A
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HREF="http://www.winsite.com/info/pc/win3/winsock/cfing13b.zip/">cfinger</A>,
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an
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echo client and server
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</UL>
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<H3>Windows-NT</H3>
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echo and other services can (apparently) be provided within
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'Simple TCP/IP Services' which
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can be enabled through the Network Control Panel
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<H3>Web clients</H3>
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You can ping or traceroute on the Web. See <A
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HREF="http://www.traceroute.org/">traceroute.org</A>.
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<P>Use all of them with care, the result is not obvious to interpret.
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<P>If you are interested in Internet measurements, there is an <A
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HREF="http://www.ietf.org/">Internet Engineering Task Force</A>
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Working Group, <A
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HREF="http://www.ietf.org/html.charters/ippm-charter.html">IPPM (IP
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Performance Metrics)</A> which produces many fine RFC that are really
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good to read. I appreciate RFC 2330 and 3148.
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<P>And don't forget to read RFC 1470 ("Tools for Monitoring and Debugging
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TCP/IP Internets and Interconnected Devices"), specially its "Benchmark"
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section and the Richard Stevens' books (all of them), published by
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Addison-Wesley.
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<P>Last, but not least, since statistics is typically a very neglected
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area in computer networks, <A
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HREF="http://www.statsoft.com/textbook/stbasic.html">Basic
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Statistics</A> is a fery useful resource. For the reasons why echoping
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displays median as well as average, see <A
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HREF="http://shlang.com/writing/mean-delay-considered-harmful.html">Mean
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Delay Considered Harmful</A>.
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