On Fri, 9 Oct 2015, David Lang wrote:
On Fri, 9 Oct 2015, Joe Touch wrote:
On 10/9/2015 5:22 PM, David Lang wrote:
You don't want to acknowlege it, but TCP is broken in the face of
excessive buffering.
Arguably, buffering was broken and failed to provide the feedback to TCP
(see next paragraph)
TCPM isn't fixing that, grassroots efforts are
developing the fixes and AQM is formalizing the results.
TCPM fixed it in 2001 by providing the flags for ECN, which was enabled
by default in Windows since 2012. ALTQ support for ECN has been around
for nearly that long.
What's changed? Not the TCP reaction (except in extreme cases such as
for datacenters) but the router algs. And getting the router algs into
routers - esp. home devices.
if ECN solved the problem, then bufferbloat would have been a non-issue. A
large percentage of the home routers are running OpenWRT or similar with ECN
enabled. That didn't solve the problem.
when the investigation into bufferbloat started, we were assuming that the fix
was just to reduce the size of the buffers and/or make sure that ECN was
enabled. Experimentation showed that there was no buffer size that both enabled
full utilization of the links and avoided excessive delays. Switching buffers
from X packets to X bytes helped a lot, but not enough.
Part of what's changed is the usage patterns, but a lot of it is just that
things that worked when a fast network was 10Mb don't always scale across
several orders of magnatude.
David Lang
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