Re: [Bloat] Little's Law mea culpa, but not invalidating my main point

[Bob McMahon <bob.mcmahon@broadcom.com>]

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I believe end host's TCP stats are insufficient as seen per the "failed"
congested control mechanisms over the last decades. I think Jaffe pointed
this out in 1979 though he was using what's been deemed on this thread as
"spherical cow queueing theory."

"Flow control in store-and-forward computer networks is appropriate for
decentralized execution. A formal description of a class of "decentralized
flow control algorithms" is given. The feasibility of maximizing power with
such algorithms is investigated. On the assumption that communication links
behave like M/M/1 servers it is shown that no "decentralized flow control
algorithm" can maximize network power. Power has been suggested in the
literature as a network performance objective. It is also shown that no
objective based only on the users' throughputs and average delay is
decentralizable. Finally, a restricted class of algorithms cannot even
approximate power."

https://ieeexplore.ieee.org/document/1095152

Did Jaffe make a mistake?

Also, it's been observed that latency is non-parametric in it's
distributions and computing gaussians per the central limit theorem for OWD
feedback loops aren't effective. How does one design a control loop around
things that are non-parametric? It also begs the question, what are the
feed forward knobs that can actually help?

Bob

On Mon, Jul 12, 2021 at 12:07 PM Ben Greear <greearb@candelatech.com> wrote:

> Measuring one or a few links provides a bit of data, but seems like if
> someone is trying to understand
> a large and real network, then the OWD between point A and B needs to just
> be input into something much
> more grand.  Assuming real-time OWD data exists between 100 to 1000
> endpoint pairs, has anyone found a way
> to visualize this in a useful manner?
>
> Also, considering something better than ntp may not really scale to 1000+
> endpoints, maybe round-trip
> time is only viable way to get this type of data.  In that case, maybe
> clever logic could use things
> like trace-route to get some idea of how long it takes to get 'onto' the
> internet proper, and so estimate
> the last-mile latency.  My assumption is that the last-mile latency is
> where most of the pervasive
> assymetric network latencies would exist (or just ping 8.8.8.8 which is
> 20ms from everywhere due to
> $magic).
>
> Endpoints could also triangulate a bit if needed, using some anchor points
> in the network
> under test.
>
> Thanks,
> Ben
>
> On 7/12/21 11:21 AM, Bob McMahon wrote:
> > iperf 2 supports OWD and gives full histograms for TCP write to read,
> TCP connect times, latency of packets (with UDP), latency of "frames" with
> > simulated video traffic (TCP and UDP), xfer times of bursts with low
> duty cycle traffic, and TCP RTT (sampling based.) It also has support for
> sampling (per
> > interval reports) down to 100 usecs if configured with
> --enable-fastsampling, otherwise the fastest sampling is 5 ms. We've
> released all this as open source.
> >
> > OWD only works if the end realtime clocks are synchronized using a
> "machine level" protocol such as IEEE 1588 or PTP. Sadly, *most data
> centers don't provide
> > sufficient level of clock accuracy and the GPS pulse per second * to
> colo and vm customers.
> >
> > https://iperf2.sourceforge.io/iperf-manpage.html
> >
> > Bob
> >
> > On Mon, Jul 12, 2021 at 10:40 AM David P. Reed <dpreed@deepplum.com
> <mailto:dpreed@deepplum.com>> wrote:
> >
> >
> >     On Monday, July 12, 2021 9:46am, "Livingood, Jason" <
> Jason_Livingood@comcast.com <mailto:Jason_Livingood@comcast.com>> said:
> >
> >      > I think latency/delay is becoming seen to be as important
> certainly, if not a more direct proxy for end user QoE. This is all still
> evolving and I have
> >     to say is a super interesting & fun thing to work on. :-)
> >
> >     If I could manage to sell one idea to the management hierarchy of
> communications industry CEOs (operators, vendors, ...) it is this one:
> >
> >     "It's the end-to-end latency, stupid!"
> >
> >     And I mean, by end-to-end, latency to complete a task at a relevant
> layer of abstraction.
> >
> >     At the link level, it's packet send to packet receive completion.
> >
> >     But at the transport level including retransmission buffers, it's
> datagram (or message) origination until the acknowledgement arrives for
> that message being
> >     delivered after whatever number of retransmissions, freeing the
> retransmission buffer.
> >
> >     At the WWW level, it's mouse click to display update corresponding
> to completion of the request.
> >
> >     What should be noted is that lower level latencies don't directly
> predict the magnitude of higher-level latencies. But longer lower level
> latencies almost
> >     always amplfify higher level latencies. Often non-linearly.
> >
> >     Throughput is very, very weakly related to these latencies, in
> contrast.
> >
> >     The amplification process has to do with the presence of queueing.
> Queueing is ALWAYS bad for latency, and throughput only helps if it is in
> exactly the
> >     right place (the so-called input queue of the bottleneck process,
> which is often a link, but not always).
> >
> >     Can we get that slogan into Harvard Business Review? Can we get it
> taught in Managerial Accounting at HBS? (which does address
> logistics/supply chain queueing).
> >
> >
> >
> >
> >
> >
> >
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>
> --
> Ben Greear <greearb@candelatech.com>
> Candela Technologies Inc  http://www.candelatech.com
>
>

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