[e2e] [aqm] What is a good burst? -- AQM evaluation guidelines

[Detlef Bosau]

Am 15.12.2013 22:42, schrieb Fred Baker (fred):
> The second is clearly a burst, according to the definition, and I would argue that it is naturally
occurring. I imagine you have heard Van and/or Kathy talk about "good
queue" vs "bad queue". "Good queue" keeps enough traffic in it to fully
utilize its egress. "Bad queue" also does so, but does so in a manner
that also materially increases measured latency. This difference is what
is behind my comment on the objective of a congestion management
algorithm (such as TCP's but not limited to it) that its objective is to
keep the amount of data outstanding large enough to maximize its
transmission rate through the network, but not so large as to materially
increase measured latency or probability of loss. I would argue that
this concept of "Good Queue" is directly relevant to the concept of an
acceptable burst size. In the first transmission in a session, the
sender has no information about what it will experience, so it behoves
it to behave in a manner that is unlikely to create a significant amount
of "bad queue" - conservatively. But it by definition has no numbers by
which to quantify that. Hence, we make recommendations about the initial
window size. After that, I would argue that it should continue to behave
in a manner that doesn't led to "bad queue", but is free to operate in
any manner that seeks to keep the amount of data outstanding large
enough to maximize its transmission rate through the network, but not so
large as to materially increase measured latency or probability of loss.
At the point that it sends data in a manner that creates a sustained
queue, it has exceeded what would be considered a useful burst size.

Isn't this a perfect argument for doing congestion control locally and
not on the end nodes? An end node has absolutely no idea of good queues
and bad queues, in addition window halving as congestion response
neither sees this difference and empties good queues in the same way as
bad ones.

It may have sound extremely hard, when I called the end to end principle
a "fallacy" some days ago, but what you write here, supports exactly that.

-- 
------------------------------------------------------------------
Detlef Bosau
Galileistraße 30  
70565 Stuttgart                            Tel.:   +49 711 5208031
                                           mobile: +49 172 6819937
                                           skype:     detlef.bosau
                                           ICQ:          566129673
detlef.bosau at web.de                     http://www.detlef-bosau.de