[e2e] What's wrong with this picture?

Loki Jorgenson ljorgenson at apparentnetworks.com
Tue Sep 8 09:29:08 PDT 2009

Satellite link?  Probably geostationary from the looks of it (around
600ms RTT) - possibly more than one bounce in certain cases.  The
buffers on satellite link modems can be quite large to boot.  Little to
no loss is not surprising given their retransmit capabilities.
Apparently part of a fail-over if it returned to terrestrial values in
the morning.

That accounts for anything up to about 2 seconds.  The really high 5-10
second RTTs still seem pretty extreme even for satellites....

Loki Jorgenson
Apparent Networks
t   604 433 2333 ext 105
m   604 250-4642

-----Original Message-----

Message: 1
Date: Sun, 06 Sep 2009 21:00:16 -0400
From: "David P. Reed" <dpreed at reed.com>
Subject: [e2e] What's wrong with this picture?
To: end2end-interest list <end2end-interest at postel.org>
Message-ID: <4AA45B20.6030705 at reed.com>
Content-Type: text/plain; charset="iso-8859-1"

For those who have some idea of how TCP does congestion control, I ask 
"what's wrong with this picture?"  And perhaps those who know someone 
responsible at the Internet Access Provider involved, perhaps we could 
organize some consulting help...

(Hint: the problem relates to a question, "why are there no lost IP 
datagrams?", and a second hint is that the ping time this morning was 
about 193 milliseconds.)

$ ping lcs.mit.edu
PING lcs.mit.edu ( 56(84) bytes of data.
64 bytes from zermatt.csail.mit.edu ( icmp_seq=1 ttl=44 
time=6330 ms
64 bytes from zermatt.csail.mit.edu ( icmp_seq=2 ttl=44 
time=6005 ms

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