[Tmrg] Round-table PFLDnet submission

[Lawrence D. Dunn]

Lachlan,
   SIlence from me just meant that I haven't had time to ponder it sufficiently.
   Since I trust you quite a bit, if "enough" other weigh in, and 
rough consensus is
   declared before I have a chance to think on it, I won't gripe. ;-)

Larry
--

At 11:49 PM -0800 12/2/07, Lachlan Andrew wrote:
>Greetings all,
>
>Does silence mean people are happy with my new proposal to measure
>load in terms of simultaneous sessions in a processor sharing M/G/1
>queue?
>
>We're aiming to have this settled within a week, so now would be a
>good time to comment on this or any other issues with the document
>(see attached .dvi).
>
>Also, I'd ask all authors to commit regularly to CVS so that we can
>all see the latest.
>
>Currently it looks like the RTT section is entirely empty.  Sally, do
>you mind if I cut-and-paste the discussion of RTTs from your section
>into that section?  Again, I'll take silence as permission :)  (We can
>always back it out of CVS.)
>
>Cheers,
>Lachlan
>
>On 28/11/2007, Lachlan Andrew <lachlan.andrew at gmail.com> wrote:
>>  Greetings Sally and everyone,
>>
>>  In the description of delay/throughput tradeoff, it talks about
>>  "moderate congestion" as 1-2% packet loss with NewReno.  Unless I'm
>>  mistaken, that says "windows should be about 1/sqrt(0.01)=10 packets"
>>  (to within a small factor).  I'd prefer not to quantify the load that
>>  way.  Consider some scenarios:
>>
>>  56kbit/s:  10 packets of 12000 bits  > 200ms.  That means that for 56k
>>  tests with inter-city RTTs (50ms), a moderate level of load would be
>>  *half* of one flow.
>>
>>  100Mbit/s bottleneck, 100ms path.  "Moderate" congestion would be when
>>  2000 flows each gets about 50kbit/s.  To me, that is very heavy load.
>>  Indeed, however large the bottleneck bandwidth is, "moderate"
>>  congestion would be when 100ms paths give 50kbit/s per user.
>>
>>
>>  I'd much prefer to specify the load in terms of the offered load as a
>>  fraction of bandwidth.
>>
>>  I propose an alternative:  The "load" is the average number of flows
>>  if the traffic was served by an  M/G/1 queue with an ideal
>>  processor-sharing service discipline.
>>
>>  My reasons are:
>>  1. This scales properly as capacity increases, and is correctly
>>  independent of RTT
>>
>>  2. A processor-sharing M/G/1 queue is a model of roughly what we're
>>  aiming for with a single bottleneck (equal instantaneous rates).
>>
>>  3. For loads like 10%, this simply corresponds to 10% of the bandwidth.
>>
>>  4.  It reflects that, even at extreme overload, we want to consider a
>>  system whose average number of flows doesn't increase with time.
>>  Otherwise, the results would be   very   sensitive to duration, and we
>>  agreed that we should try to design tests which are   not   sensitive
>>  to the parameters.
>>
>>  Thoughts?
>
>
>--
>Lachlan Andrew  Dept of Computer Science, Caltech
>1200 E California Blvd, Mail Code 256-80, Pasadena CA 91125, USA
>Ph: +1 (626) 395-8820    Fax: +1 (626) 568-3603
>http://netlab.caltech.edu/~lachlan
>
>Content-Type: application/x-dvi; name=pfldnet2008.dvi
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>
>Attachment converted: PB17.1.65GB:pfldnet2008.dvi (    /    ) (002431F0)
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