[e2e] 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 Jun 4 01:44:56 PDT 2014

Am 04.06.2014 02:01, schrieb Andrew Mcgregor:
> Bufferbloat definitely does impair performance, by slowing down
> feedback it increases the variance of the system workload, which
> inevitably causes either packet drops because there is a finite buffer
> limit in reach, or by causing such large delays that retransmission
> timers fire for packets that are still in flight.  In either case, the
> system is doing excess work.

I absolutely agree with that. And I did not say anything else.

It is, however, interesting, that probing schemes as, e.g., VJCC simply
don't consider buffer bloat. On the contrary, they produce it because a
path is "pumped up" with workload as long as no packets are discarded.

We try to alleviate the problem e.g. by ECN, where switches indicate
that their buffers grow extremely large, or intentionally discarding
packets, e.g. CODDLE, in order to have the senders slow down.

However, the basic algorithm in VJCC is chasing congestion - and lead
the flow in a nearly congested state again and again.

While Jains approaches attempt to achieve am optimum performance.

NB: I mentioned a performance metrics throughput / sojourn time, AFAIK
this is neither mentioned in the Bible nor in the Quran or the Talmud
and the Nobel Price is still pending.

I can well imagine that users only assess one of these two parameters,
e.g. in a FTP transfer, I'm only interested in a high throughput.
In an interactive ssh session, I'm primarily interested in a little
sojourn time.

Detlef Bosau
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