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From: CASNER@VENERA.ISI.EDU (Stephen Casner)
Newsgroups: comp.protocols.tcp-ip
Subject: Re: ICMP in ISO
Message-ID: <545647655.0.CASNER@VENERA.ISI.EDU>
Date: Fri, 17-Apr-87 02:47:35 EST
Article-I.D.: VENERA.545647655.0.CASNER
Posted: Fri Apr 17 02:47:35 1987
Date-Received: Sun, 19-Apr-87 10:45:16 EST
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We have used ICMP echoes frequently in testing the Wideband Satellite Net
and paths through the gateways that attach to it.  Aside from simply probing
for connectivity, using ICMP echoes allowed us to measure packet loss and
misordering characteristics that would be harder to discern by examination
of the behaviour of a transport protocol.  It is easy for an ICMP echo
tester to send packets at a regular rate and observe the delay distribution
of the echo replies.  The transmission rate of a transport protocol will
likely be affected by network anomolies, clouding the measurement.  We had
observed unexpected behavior in the NETBLT protocol we were testing; with
ICMP echoes we were able to get a better understanding of the performance
of the network to serve as a basis for further NETBLT tests.

One drawback of testing with ICMP echoes is that the path must be a round
trip.  Network performance may be different under unidirectional load.
ICMP-like datagrams are useful for testing between a separate transmitter
and receiver as well, but transmission time is then only relative rather
than absolute unless synchronized clocks are available (oh so nice to have!).

							-- Steve Casner
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