On Wed, 20 Aug 2014, Jim Gettys wrote:
On Wed, Aug 20, 2014 at 3:12 AM, Eggert, Lars <[email protected]> wrote:
On 2014-8-19, at 18:45, Dave Taht <[email protected]> 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.
I also remember a problem that was solved by turning down the transmit
power of the APs, as they were causing problems due to too much
interference between them. Sometimes the solutions aren't all intuitive,
and +1 on the experience of running these kinds of networks being
important.
--
Mikael Abrahamsson email: [email protected]
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