[e2e] Once again buffer bloat and CC. Re: A Cute Story. Or: How to talk completely at cross purposes. Re: [ih] When was Go Back N adopted by TCP

Detlef Bosau detlef.bosau at web.de
Wed Aug 20 11:44:52 PDT 2014

Am 20.08.2014 um 19:13 schrieb Kathleen Nichols:
> If by "Coddle" you mean "codel", then you need to read about it more
> carefully.

Sorry, I refer to codel.
> Excessive delay is NOT defined as "a packet resides in the local router
> queue for more than 100 ms". 

At least that's what you wrote in your own paper.

> As for the value of the constant, you may
> wish to read the
> most recent I-D or watch the video of Van's talk on this at the IETF.

Could you help me with a link?

The problem however is a bit deeper. The main cause of buffer bloat (and
I expect contradiction here) the basic misconception of CC.

The purpose of sliding window in TCP is to fully utilize the links.
(This is by itself a misconception and mixes up master and slave in a
>From the OSI model, TCP is the master, the net is the slave. Hence, it
is up to the network to convey data as efficient as possible, it is not
up to TCP to utilize any links.)

However, actually TCP does not probe for link utilization but pumps data
into the buffers until the amount of data causes buffer overflow.
So the first thing is the purpose of sliding window, the second
(completely different) issue is what's actually achieved by VJCC probing.

(The more I think about it, probing is a really bad idea. And
particularly, probing for the wrong parameters is an even worse idea.)
> Perhaps improving CC will obviate the need for AQM. 
AQM and Codel and VJCC are - sorry for the harsh words - different names
for the same kludge.

Instead of doing proper ressource assignment, we force networks into
congestion. That is, and I thought about this statement a VERY long
time, highly questionable.

Detlef Bosau
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