[Rpm] Outch! I found a problem with responsiveness

[Sebastian Moeller]

HI Christoph

On 11 October 2021 23:01:20 CEST, Christoph Paasch via Rpm <rpm at lists.bufferbloat.net> wrote:
Hello Simon,

On 10/05/21 - 23:43, Simon Leinen via Rpm wrote:
Hallo Christoph,

That's right. BB is a transient problem that is extremely short-lived.

Having tried for the past year to reliably demo the user-visible
impact of bufferbloat, I have learned two things:

1. When it happens, it is bad - really bad.
2. However, it is very difficult to trigger it "on-demand".

I seem to be able to trigger it quite reliably by using mobile data
while traveling on the train and doing normal remote work.  Here in
Switzerland I often see RTTs in excess of 10 seconds.  In France I have
seen more than two MINUTES.

wow! Were you able to trace it down? (like, on which device it happend)

Maybe I should start setting up systematic measurements.  For example,
if I just sent pings both from my laptop to a well-connected fixed host,
and vice-versa, while capturing all ICMP packets on both ends, I should
be able to learn about bufferbloat in both directions.

Having tried to debug some bufferbloat problems in a complex
enterprise-network, it is extremely hard to pinpoint where the bufferbloat
happens.

Especially on such kind of a train network, where there is possible either a
VPN or GRE-tunnel involved to get the data out on the Internet...

	[SM] Mmmh, to really localize points of congestion, I assume one needs continuous traceroutes (like mtr or pingplotter) from both directions and ideally one-way delay measurements. Tunnels where the congested node might be invisible add to the challenge. But getting information for the reverse path is really important especially for internet targets as path's are very likely to be asymmetrical with handover between different AS at wildly different locations in both directions.


If you have macOS Monterey, you could run the networkQuality tool to see how
much bufferbloat there is.

	[SM] Is that officially out or still in late beta/RC?

Cheers,
Christoph


It would be even better to have this in a mobile (web) app that could
record/send location data from the mobile node, to spot the regions
(presumably around tunnels and other connectivity-challenged areas)
where the problem tends to occur most often.  Alternatively, correlate
the probe timestamps with real-time location data provided by the
railway company.

Cheers,
--
Simon.
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