[Cerowrt-devel] [Bloat] Little's Law mea culpa, but not invalidating my main point
David P. Reed
dpreed at deepplum.com
Mon Jul 12 13:40:30 EDT 2021
On Monday, July 12, 2021 9:46am, "Livingood, Jason" <Jason_Livingood at 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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