[Babel-users] QoS for system critical packets on wireless

[Dave Taht]

On Fri, Jun 24, 2011 at 6:52 AM, Juliusz Chroboczek <jch at pps.jussieu.fr> wrote:
>>> Once you've fought the bloat, there's hopefully no further need to
>>> classify these packets.
>
>> As for classification, with asymmetric networks, the canonical example
>> of some level needed is moving interactive packets up in priority over
>> uploads.
>
> Unless your network is badly underprovisioned, some form of roughly
> fair share scheduling (say, SFQ) should be all you need.

That caveat is crucial. On the dark areas of these maps:

http://www.google.com/search?q=satellite+night&hl=en&client=ubuntu&hs=eu7&channel=fs&prmd=ivnsm&tbm=isch&tbo=u&source=univ&sa=X&ei=S5kETvjwBeWt0AGWip3oCw&ved=0CC8QsAQ&biw=955&bih=427

most of the dark areas will be underprovisioned for many years to come.

Every dense wireless network is underprovisioned. 3G, 4G, wifi, etc.

Lastly, bandwidth requests always expand to be in excess of what is
available. Once, we did youtube at 320x200. Then bittorrent... Now
it's netflix, and HQ video, and facetime, etc.

I have some hope that we've reached the end of the S-curve on normal
usages of bandwidth and that the technology and infrastructure can now
have some time to catch up. Classically under/over provisioning has
been cyclical.

>
>> Once you admit there is some need for classication,
>
> I certainly don't.  We should be simplifying our networks, not making
> them even more complex.  (Dave, I'm seriously worried you're heading in
> the wrong direction.)

Classifying traffic and looking at Ants has proved useful and in some
ways is a fallout from the background bufferbloat detector idea for
ntp of a few months back.

For example, I would never have spotted the syn flood limit a few days
back had I not been looking at mice and noticing a huge difference
between syn attempts and actual connections. Many other examples of
productive analysis exist of various forms of tcp streams vs the
bufferbloat background radiation, and doubtless, many other 'hacks'
exist that are harming the network more than help it.

At the moment I can filter against ant-like traffic and quickly
produce a scatter plot that at a glance shows the overall health of
the network.

As for the complexity, the network is already pretty complex as noted
earlier, and I would hope that being aware of the ants would lead
towards better diagnoses of the root causes of problems.

Raising the Ants to the same level of awareness academic analysis as
TCP mice and elephants have had would be a very good thing.

As for actually doing shaping, I have great hopes that once
bufferbloat is licked, and the fallout, and classic means of dealing
with great bandwidth disparities are more widely implemented, that
shaping techniques such as SFB and SFQ will work well again.

But that's all it is. Hope. I figure, at best, I'll have a network as
responsive and reliable as the networks I had in the mid 2000s.

>> I admit some fondness for diffserv...
>
> The first step is to admit you have a problem ;-)

Heh. Back in the early 80s I was one of the radical packet-heads, in
an all out war with the bell-heads. I've come to thinking that
although we won that battle, we lost the war. Nearly every voip
network uses separate provisioning, and I think that voice quality has
degraded significantly over the last decade.

I had a long cherished dream of one day being able to have a
'jam-o-phone' - a device that would let me play live music with the
housebound old buddy down the street, over the net, but even as
bandwidths have grown hugely, our ability to keep latencies and jitter
down to low levels has also degraded hugely.

>
> -- Juliusz
>



-- 
Dave Täht
SKYPE: davetaht
US Tel: 1-239-829-5608
http://the-edge.blogspot.com