NNSquad - Network Neutrality Squad
[ NNSquad ] Q on FCC speed tests
Before we get to the item forwarded below, I'll note that in a new
article regarding the FCC Broadband Plan ( http://bit.ly/cCTHuk ) in
the New York Times (which I plan to address in some detail hopefully
within the next day or two), can be found this text:
[ my emphasis *** ]
"In a move that could affect policy decisions years from now, the
F.C.C. will begin assessing the speeds and costs of consumer broadband
service. ***Until then, consumers can take matters into their own hands
with a new suite of online and mobile phone applications released by
the F.C.C. that will allow them to test the speed of their home
Internet and see if they're paying for data speeds as advertised.***"
Using those current manual "do it yourself" tests for the purpose of
"seeing if they're paying for data speeds as advertised" is probably
the worst possible way to use them, for the various reasons I
discussed in ( http://bit.ly/dApdft ) -- and likely to result in
significant numbers of upset and confused subscribers who incorrectly
assume that the speeds displayed on any particular run are accurate
representations of the maximum speeds related to "what they're
paying for."
--Lauren--
NNSquad Moderator
----- Forwarded message from David Farber <dave@farber.net> -----
Date: Fri, 12 Mar 2010 22:04:53 -0500
From: David Farber <dave@farber.net>
Subject: [IP] Q on FCC speed tests
Reply-To: dave@farber.net
To: ip <ip@v2.listbox.com>
Begin forwarded message:
From: Karl Auerbach <karl@cavebear.com>
Date: March 12, 2010 8:15:46 PM EST
To: dave@farber.net
Cc: ip <ip@v2.listbox.com>
Subject: Q on FCC speed tests
Reply-To: karl@cavebear.com
Some things that I did not understand about the FCC "broadband" test
are these. Maybe I didn't read deep enough?
What part of the net are they measuring? Is it the characteristic of
the first IPv4/IPv6 hop? Or source to the second IP router? Or
source to the third IP router? Hop N? Or are they going to some
canonical target?
Are they doing it the simple, dumb way or are they doing a detailed
hop-by-hop analysis over a period of time using techniques pioneered
by Van Jacobson in "pathchar" and refined in subsequent tools like
"pchar"? (From what I saw when I ran it it appeared that they were
doing it using the simple, dumb way.)
What MTU size? (Some access paths don't support full 1500 byte MTU,
which can be a performance disaster for users whose software assumes
1500 or does not do Path MTU discovery.) And what about access nets,
if any, that might support jumbograms?
What QoS settings?
What about path asymmetry or load-balancing across parallel paths?
Do they measure things that can really cause protocol stacks to have
hysterics, things like reordering?
And do they measure the degree of buffering in the path? Some gear,
particularly consumer gear, often contains a lot of buffering that can
affect measurements.
And thinking of buffering, do the tests evaluate the kind of discard
policies on the path? Is the discard application protocol or packet
size agnostic? Is it tail drop, head drop, random drop? Does the
drop policy try to apply policies such preferring to drop TCP packets
over UDP packets, and preferring those TCP packets not containing ACK,
SYN, or FIN flags?
How a path reacts to flow dynamics can be very important to a user's
perceptions. VoIP is a nice steady, metronomed sequence of smallish
packets while some forms of high-grade video consist of burst-trains
of closely spaced large packets with the bursts occurring several
times a second.
Path evaluation and comparison isn't something that can be done
without considering the use to which the path will be put. For
example, in my "Fast Path Characterization Protocol" idea -
http://www.cavebear.com/archive/fpcp/fpcp-sept-19-2000.html - I carry
a hypothetical IP header and description of the flow dynamics in the
path measurement.
--karl--
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----- End forwarded message -----