<div dir="ltr">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."<br><br>"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."<font color="#333333" face="sans-serif"><span style="font-size:15px"><br></span></font><br><a href="https://ieeexplore.ieee.org/document/1095152">https://ieeexplore.ieee.org/document/1095152</a><br><br>Did Jaffe make a mistake?<br><br>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?<br><br>Bob</div><br><div class="gmail_quote"><div dir="ltr" class="gmail_attr">On Mon, Jul 12, 2021 at 12:07 PM Ben Greear <<a href="mailto:greearb@candelatech.com">greearb@candelatech.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">Measuring one or a few links provides a bit of data, but seems like if someone is trying to understand<br>
a large and real network, then the OWD between point A and B needs to just be input into something much<br>
more grand. Assuming real-time OWD data exists between 100 to 1000 endpoint pairs, has anyone found a way<br>
to visualize this in a useful manner?<br>
<br>
Also, considering something better than ntp may not really scale to 1000+ endpoints, maybe round-trip<br>
time is only viable way to get this type of data. In that case, maybe clever logic could use things<br>
like trace-route to get some idea of how long it takes to get 'onto' the internet proper, and so estimate<br>
the last-mile latency. My assumption is that the last-mile latency is where most of the pervasive<br>
assymetric network latencies would exist (or just ping 8.8.8.8 which is 20ms from everywhere due to<br>
$magic).<br>
<br>
Endpoints could also triangulate a bit if needed, using some anchor points in the network<br>
under test.<br>
<br>
Thanks,<br>
Ben<br>
<br>
On 7/12/21 11:21 AM, Bob McMahon wrote:<br>
> 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 <br>
> 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 <br>
> 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.<br>
> <br>
> 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 <br>
> sufficient level of clock accuracy and the GPS pulse per second * to colo and vm customers.<br>
> <br>
> <a href="https://iperf2.sourceforge.io/iperf-manpage.html" rel="noreferrer" target="_blank">https://iperf2.sourceforge.io/iperf-manpage.html</a><br>
> <br>
> Bob<br>
> <br>
> On Mon, Jul 12, 2021 at 10:40 AM David P. Reed <<a href="mailto:dpreed@deepplum.com" target="_blank">dpreed@deepplum.com</a> <mailto:<a href="mailto:dpreed@deepplum.com" target="_blank">dpreed@deepplum.com</a>>> wrote:<br>
> <br>
> <br>
> On Monday, July 12, 2021 9:46am, "Livingood, Jason" <<a href="mailto:Jason_Livingood@comcast.com" target="_blank">Jason_Livingood@comcast.com</a> <mailto:<a href="mailto:Jason_Livingood@comcast.com" target="_blank">Jason_Livingood@comcast.com</a>>> said:<br>
> <br>
> > 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<br>
> to say is a super interesting & fun thing to work on. :-)<br>
> <br>
> If I could manage to sell one idea to the management hierarchy of communications industry CEOs (operators, vendors, ...) it is this one:<br>
> <br>
> "It's the end-to-end latency, stupid!"<br>
> <br>
> And I mean, by end-to-end, latency to complete a task at a relevant layer of abstraction.<br>
> <br>
> At the link level, it's packet send to packet receive completion.<br>
> <br>
> But at the transport level including retransmission buffers, it's datagram (or message) origination until the acknowledgement arrives for that message being<br>
> delivered after whatever number of retransmissions, freeing the retransmission buffer.<br>
> <br>
> At the WWW level, it's mouse click to display update corresponding to completion of the request.<br>
> <br>
> 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<br>
> always amplfify higher level latencies. Often non-linearly.<br>
> <br>
> Throughput is very, very weakly related to these latencies, in contrast.<br>
> <br>
> 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<br>
> right place (the so-called input queue of the bottleneck process, which is often a link, but not always).<br>
> <br>
> 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).<br>
> <br>
> <br>
> <br>
> <br>
> <br>
> <br>
> <br>
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<br>
-- <br>
Ben Greear <<a href="mailto:greearb@candelatech.com" target="_blank">greearb@candelatech.com</a>><br>
Candela Technologies Inc <a href="http://www.candelatech.com" rel="noreferrer" target="_blank">http://www.candelatech.com</a><br>
<br>
</blockquote></div>
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