On Wed, 20 Aug 2014, Jim Gettys wrote:
On Wed, Aug 20, 2014 at 3:12 AM, Eggert, Lars <l...@netapp.com> wrote:
On 2014-8-19, at 18:45, Dave Taht <dave.t...@gmail.com> wrote:
I figured y'all would be bemused by the wifi performance in the sigcomm
main conference room this morning...
http://snapon.lab.bufferbloat.net/~d/sigcomm_tuesday.png
There is a reason we budgeted a 1G uplink for SIGCOMM Helsinki and made
sure we had sufficient AP coverage...
And what kinds of AP's? All the 1G guarantees you is that your bottleneck
is in the wifi hop, and they can suffer as badly as anything else
(particularly consumer home routers).
The reason why 802.11 works ok at IETF and NANOG is that:
o) they use Cisco enterprise AP's, which are not badly over buffered. I
don't have data on which enterprise AP's are overbuffered.
o) they do a good job of placing the AP's, given a lot of experience
o) they turn on RED in the router, which, since there is a lot of
aggregated traffic, can actually help rather than hurt, and keep TCP
decently policed.
o) they play some interesting diffserv marking tricks to prioritize some
traffic, getting part of the effect the fq_codel gives you in its "new
flow" behavior by manual configuration. Fq_codel does much better without
having to mess around like this.
Would be nice if they (the folks who run the IETF network) wrote a BCP on
the topic; I urged them some IETF's ago, but if others asked, it would help.
If you try to use consumer home routers running factory firmware and hack
it yourself, you will likely lose no matter what you backhaul is (though
you might do ok using current CeroWrt/OpenWrt if you know what you are
doing.
here's a paper I did a couple years ago on the network we build for Scale '11
https://www.usenix.org/conference/lisa12/technical-sessions/presentation/lang_david_wireless
this year we had pretty much the same network layout with 2500 people (our most
crowded room holds ~450, but there are many rooms next to each other down the
hall)
we did do some DNS blacklisting to cut down a bit on the bandwidth requirements.
David Lang
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