[Bloat] [EXTERNAL] Re: Terminology for Laypeople

Bob McMahon bob.mcmahon at broadcom.com
Mon May 17 20:47:49 EDT 2021


iperf 2 <https://sourceforge.net/projects/iperf2/> supports one way delay
and histograms for UDP packets, TCP writes to reads, and frames. The trick
is to synchronize the clocks using something like PTPd2 or PTP4l to a
reference, e.g. the GPS atomic clock. One can build a stratum 1 time server
with a raspberry pi 4 and a GPS receiver that gives pulse per second. The
output supports histograms and mean/min/max/stdev. \The network power
metric uses avg throughput over one way delay.

For  internal use we have more granularity than end/end and everything is
mapped to the GPS time domain which allows for per message delay
analysis as well as system analysis as a function of time.

We're finding that one way delay is becoming a key performance metric for
our WiFi customers and peak throughput less so.

Bob

On Mon, May 17, 2021 at 2:27 PM Matt Mathis <mattmathis at google.com> wrote:

> I just got a cool idea: I wonder if it is original....?
>
> Write or adapt a spec based on "A One-way Active Measurement Protocol"
> (OWAMP - RFC4656), as an application layer LAG metric.   Suitably framed
> OWAMP messages could be injected as close as possible to the socket write
> in the sending applications, and decoded as close as possible to the
> receiving application's read, independent of all other protocol details.
>
> This could expose lag, latency and jitter in a standardized way, that can
> be reported by the applications and replicated by measurement diagnostics
> that can be compared apples-to-apples.  The default data collection should
> probably be histograms of one way delays.
>
> This would expose problematic delays in all parts of the stack, including
> excess socket buffers, etc.
>
> This could be adapted to any application protocol that has an appropriate
> framing layer, including ndt7.
>
> Thanks,
> --MM--
> The best way to predict the future is to create it.  - Alan Kay
>
> We must not tolerate intolerance;
>        however our response must be carefully measured:
>             too strong would be hypocritical and risks spiraling out of
> control;
>             too weak risks being mistaken for tacit approval.
>
>
> On Mon, May 17, 2021 at 4:14 AM Jonathan Morton <chromatix99 at gmail.com>
> wrote:
>
>> On 13 May, 2021, at 12:10 am, Michael Richardson <mcr at sandelman.ca>
>> wrote:
>>
>> But, I'm looking for terminology that I can use with my mother-in-law.
>>
>>
>> Here's a slide I used a while ago, which seems to be relevant here:
>>
>>
>> The important thing about the term "quick" in this context is that
>> throughput capacity can contribute to it in some circumstances, but is
>> mostly irrelevant in others.  For small requests, throughput is irrelevant
>> and quickness is a direct result of low latency.
>>
>> For a grandmother-friendly analogy, consider what you'd do if you wanted
>> milk for your breakfast cereal, but found the fridge was empty.  The ideal
>> solution to this problem would be to walk down the road to the village shop
>> and buy a bottle of milk, then walk back home.  That might take about ten
>> minutes - reasonably "quick".  It might take twice that long if you have to
>> wait for someone who wants to scratch off a dozen lottery tickets right at
>> the counter while paying by cheque; it's politer for such people to step
>> out of the way.
>>
>> My village doesn't have a shop, so that's not an option.  But I've seen
>> dairy tankers going along the main road, so I could consider flagging one
>> of them down.  Most of them ignore the lunatic trying to do that, and the
>> one that does (five hours later) decides to offload a thousand gallons of
>> milk instead of the pint I actually wanted, to make it worth his while.
>> That made rather a mess of my kitchen and was quite expensive.  Dairy
>> tankers are set up for "fast" transport of milk - high throughput, not
>> optimised for latency.
>>
>> The non-lunatic alternative would be to get on my bicycle and go to the
>> supermarket in town.  That takes about two hours, there and back.  It takes
>> me basically the same amount of time to fetch that one bottle of milk as it
>> would to conduct a full shopping trip, and I can't reduce that time at all
>> without upgrading to something faster than a bicycle, or moving house to
>> somewhere closer to town.  That's latency for you.
>>
>>  - Jonathan Morton
>> _______________________________________________
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>> Bloat at lists.bufferbloat.net
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>>
>

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