On Mon, 2 Feb 2015, [email protected] wrote:
On Sunday, February 1, 2015 11:21pm, "Avery Pennarun" <[email protected]>
said:
On Sun, Feb 1, 2015 at 9:43 AM, <[email protected]> wrote:
> Just to clarify, managing queueing in a single access point WiFi network is
> only a small part of the problem of fixing the rapidly degrading performance
> of WiFi based systems.
Can you explain what you mean by "rapidly degrading?" The performance
in odd situations is certainly not inspirational, but I haven't
noticed it getting worse over time.
I was being specific about the words "WiFi-based systems", and not WiFi
itself. An obvious example is GoGo, whose degradation is probably not
specifically in the WiFi portion, but in the bidirectional bufferbloat I can
measure whenever I fly (frequently!). But I also visit many enterprise sites
for my day job, and hotels. I do a few measurements when I can - almost
always encountering bufferbloat (severe) on the path to the public Internet
(whether wireless or not), but worse, encountering severe bad behavior on the
WiFi hop, remedied by using a wired connection. And then there are hotels, and
trains.
What's worse is that typical "sales office" connections in my past employers
are often quite poor.
Too many people deploy a couple apple Airports and think the problem is solved
(my current employer did the same thing). Part of the problem is that people
then think that this is the best that can be done with consumer equipment, and
that the only think they can do after that is to go spend $50K+ to buy an
"Enterprise" solution, that is then so complex to deploy that they may sit for
9+ months between when they arrive and when they are deployed (two employers of
mine have fallen into this trap). The idea that you can actually get good
service without spending a ton of money just isn't something that is out there.
All the 'networking vendors' out there push the proprietary "Enterprise"
solutions.
At SCaLE, we had one of these vendors come in one year and deploy their $10K/AP
"Enterprise" solutions, and it failed miserably (and they didn't have any info
or explination as to why).
Some of the best conference wifi I have seen (and here I will exclude the ones
I've setup to be fair :-) have been setup with consumer grade equipment.
I drool over the capabilities of some of the commercial equipment, but the
expertise in setting it up is far more important than the equipment used.
Now the causes of degradation are apparently multifaceted. Places that seem
to be fine fall off a cliff, because they used to be overprovisioned relative
to traffic load, but now are not. Of course capacity sharing should slow
everyone, but the cliff adds insult to injury.
The cliff is a real problem. It's not obvious to people how the various features
of WiFi interact to create the cliff, and it's not something that is easy to
duplicate for lab/performance/installation testing.
I have observed that deploying a lot of wifi stations that operate in basic
802.11b mode really does affect the folks with better gear in the same channel
a lot. A small packet occupies a disproportionate amount of channel time if
transmitted at 1 Mb/sec - and my theory (this is hard to measure informally,
so I could be wrong) is that "cheap" devices compete equally for packet time,
but consume much more than their share. My sense is that channel time should
be allocated fairly by the most basic MAC access decision - LBT and backoff,
not opportunities to transmit. This would eliminate the pokey puppy problem.
There are pragmatic ways to achieve this without changing the basic MAC access
decision, which is the firmest-of-ware.
It's even worse than you think, those long (time) packets sent at the slow rates
are far more likely to have other things interefere with them (something that
can't hear the transmission, but who's transmission will prevent the receiver
from hearing it) and so they are going to get retransmitted more frequently than
faster bitrate packets.
Anyway, degradation of WiFi services at a particular location over time is the
norm I observe.
well, to be fair, any service that's not updated as usage grows degrades over
time (including things in meatspace like bus service or freeway lanes).
Some of the worst hotel network service I have seen is at higher-end hotels that
implemented network service early and outsourced the job. Some of them are now
updating/replacing that service and getting much better. But between updates,
the service is always going to degrade under increased use.
David Lang
_______________________________________________
Cerowrt-devel mailing list
[email protected]
https://lists.bufferbloat.net/listinfo/cerowrt-devel
