[Iccrg] congestion control and visability to the user
swmike at swm.pp.se
Mon Mar 29 16:34:48 BST 2010
On Mon, 29 Mar 2010, michawe at ifi.uio.no wrote:
> My notion was that it's not, usually, because of standard TCP
> being "lame" (as Matt rightfully called it).
This is the first time in my 15+ year of networking that I've heard this
view of the world. I couldn't disagr ee more. Only time I wasn't able to
saturate my access link was when I was using Win95 or so, and it didn't s
upport window scaling and my internet connection was 100+ megabit/s and
the ftp server was 10ms away. I could n't disagree more with this view of
> However, in this world of CUBIC in Linux, a growing number
> of users with proper buffer sizing / window scaling, and,
> above all, users (or their (P2P) applications) opening as
> many connections as they need, I can imagine that what
> you say is true.
I don't kno wwhat part of the world where this hasn't been true for a
long++ time, but it's not in my neck of the woods.
> Well of course economical reasons are there. Bandwidth
> costs money. So, is all we're doing here with congestion
> control only about:
> 1) managing fairness within the user's local networks, and
> 2) making the network operate even if ISPs don't investe
> in enough core bandwidth, which apparently hardly ever
Again, ISPs only get away with congesting their cores if there isn't
enough competition in the market, and that's not a technical problem, it's
usually a political problem. Trying to handle this dysfunctional situation
by technical means is bound to fail. Why would someone invest in expensive
bw capacity/congestion/flow/fairness technology if said upgrade due to bw
constraints is already too expensive?I don't get it.
> XCP was really just an example. The point was that, given
> that we can get a benefit from explicit feedback for
> congestion control, it might be enough to do it on the
> first and last hop, where doing it might actually be feasible.
In my experience, the biggest congestion problem is in the upstream
direction from my CPE. Any normal user would have an ADSL modem or alike
there from some low-end manufacturer who won't invest a dollar more to do
anything more than FIFO because they're acting in an extremely tight
marketplace where every cent counts. There is already plenty of tech out
there to help in this siuation but they've chosen to do nothing.
Fair-queue is one which would hugely benefit all ADSL users (or anyone
with slow uplinks). This is not being done, and yet people are talking
about inveting eve nmore complicated mechanisms?
Mikael Abrahamsson email: swmike at swm.pp.se
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