

How to make wifi work at tech conferences - cramforce
http://www.nonblocking.io/2011/05/how-to-make-wifi-work-at-tech.html

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willidiots
Overall a good article, although the claim that "WiFi has 11 channels and can
give you 220Mbit in the air" is just wrong. You'll never deploy on all 11
channels without causing massive adjacent channel interference. 802.11 likes
25 MHz per AP, and the 2.4GHz channels are only 5 MHz apart. Deploying on
anything other than 1, 6 or 11 will cause more problems than it will solve.

Additionally, dismissing the 5 GHz channels by claiming "those have lots of
issues with many devices" is a facile argument. Deploying 5GHz channels (of
which there are many more than 2.4GHz) is an excellent strategy in many cases
- it enables you to offload 5GHz-capable clients (laptops, tables) from the
2.4GHz radios, freeing them up for 2.4GHz-only systems (smartphones, old
laptops).

Anybody looking to deploy WiFi at a large conference needs to read Aruba
Networks' High-Density Validated Design Guide, regardless of the hardware
vendor you choose:

[http://www.arubanetworks.com/pdf/technology/DG_HighDensity_V...](http://www.arubanetworks.com/pdf/technology/DG_HighDensity_VRD.pdf)

Appendix B and C contain some excellent information on planning and theory.

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cramforce
I might have been a little harsh on the 5GHz. There is currently a pretty
widespread active problem (might depend on AP hardware/software) with some
Apple hardware that is pretty much impossible to debug on a large scale, so
that the only option we found was to disable it.

~~~
ewams
Don't dismiss a technology because of one hardware vendor's poor
implementation.

~~~
cramforce
You're right I changed the language. Actually we did use 5Ghz for the purpose
you described extensively in previous years.

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merubin75
I don't know about this conference, since I wasn't there. But speaking as
someone who has helped organize conferences attended by a few thousand people,
there are two points I would like to respectfully make:

1\. Sometimes, the conference is about PEOPLE and the content of the sessions.
I confess that at more than a few of the events I helped organize, it was no
accident that the WiFi was wonky or non-existent. Yes, some people bitched and
moaned, but the overall effect was that that attendees and speakers felt
engaged with each other because everyone put their laptops away and actually
paid attention to one another. In conversations and after-event surveys, the
#1 bit of positive feedback was, "Hurray for having an event where the WiFi
was turned off."

Yes, we all know that a lot of people attend events and use Social Media to
bring in a larger audience from those who could not attend (I do), but all too
often, I see people sitting there with laptops open to work e-mail. They're
not there to add anything to the discussion, and really, what's the point of
even being there?

Of course, a good conference organizer has already worked to insure that the
speakers are well-prepared, moderators are trained and will actually do their
job, and the content is valuable (not a sales pitch). It pains me to no end
when I attend an event that waste my time by not having those three items
checked off.

2\. "Now you booked a venue and they say that they can handle the WIFI for
you. Chances are, they are lying."

Respectfully, there's no conspiracy here. If your event is taking place at a
hotel or conference center, then more times than not, WiFi is an expensive
add-on (all things are expensive add-ons in the hospitality industry, but
that's a subject for a much longer post). You have no control over it, and in
fact, if you try to rig up a few routers and roll your own hotspot, you're
often in violation of your facility's contract which means fines or
blacklisting from future events.

Just my two cents from my own experience. Yours may differ, so we may
disagree, but no flames, please.

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gonzo
"Deploying on anything other than 1, 6 or 11 will cause more problems than it
will solve,"

This is a fundamental mistake. You are correct that the transmit mask of WiFi
allows for 3 'non-overlapping' channels in the 2.4GHz band, but the receivers
won't allow simultaneous operation on these three channels since the advent of
802.11g (and 802.11n made the situation worse.)

The receivers don't have enough adjacent channel rejection (ACR) to deal with
a strong (i.e. closer or high-EIRP) signal on an ajacent channel.

At 6Mbps, the IEEE standard requires 16 dB of adjacent channel rejection. The
amount of ACR required by the standard is lower as the modulation rate
increases. At 18Mbps the IEEE standard requires 11dB of ACR. At 54Mbps, the
ACR required by the standard is -1dB. While some chipsets perform above these
requirements one has to assume that the clients perform at the minimum, since
there is no way to control what client will wander into the room next.

Nobody wants to believe it, but the way to make 2.4GHz WiFi work for large
conferences is to run all the APs on the same channel (in any given 'band')

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siculars
I think the most interesting bit here is "At JSConf we introduced social
traffic which links all traffic to Twitter identities."[0][1] That is
pretty... epic.

Hey @BandwidthHog stop hogging all the intertubes. You making puppies cry!

[0]<http://social-traffic.streamie.org/preso/static/#slide17>

[1]<https://github.com/cramforce/social-traffic>

~~~
endgame
Clever? Yes. Epic? No.

<http://www.thebestpageintheuniverse.net/c.cgi?u=epic>

Pardon the title.

~~~
memset
Interestingly, this downvoted link resulted in 63 hits to Maddox's page from
this referer. <http://maddox.xmission.com/statistics/statistics.html>

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Alex3917
The problem is that if your event only has 100 people, that means that every
attendee has to be willing to pay an extra $50 in order to have someone
guarantee that the WiFi will work. That's why most event organizers just take
their chances.

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ismarc
How many attendees were there? I tried to find some numbers real quick and
couldn't manage to find them. For conferences (or any high density user
environment), the density of users has a massive impact on how the network
needs to be designed (omni vs. directional antennas, output power, individual
channel selection, switching infrastructure, etc.). There reaches a point
where the device density is so high that even narrow beam antennas at the
lowest power setting can easily be hitting max associations. Really the only
way to provide good coverage at any sort of event is to plan ahead (months in
advance, especially for tech-heavy conferences) and not trust that the IT
department of the venue will know how to properly set up the access.

~~~
cramforce
At the last JSConf, 370 attendees, ~1000 devices online. You are absolutely
right. At a certain density all bets are off. We were pretty close to this
point at several points in time. The problem gets much harder with more
people.

The blog post is very much not about technical details. Having people who
actually care is what really counts. This is all, of course, presented in term
of not-for-profit-conf where paying people to get it right is usually not an
option.

~~~
ismarc
Yeah, that's definitely in the "too small to pay a company but big enough to
have real problems to solve" range. I completely agree that just having people
who care (and plan ahead) goes the furthest.

At a previous employer, the number of "Oh, we have a conference going on and
the internet access sucks, please fix it" or "Yeah, we have a conference this
weekend with <ABSURD NUMBER OF ATTENDEES>, can you get it built out for us?"
calls we got were absolutely insane.

------
idan
I wish the conferences I go to could have a team of network ninjas like this.

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dpapathanasiou
Another solution is to use your own hardware, a la Pirate Box:
<http://wiki.daviddarts.com/PirateBox>

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morganpyne
Is it really wise to suggest "Don't use encryption." ?

Even your grandmother can steal sessions with Firecookie these days.

~~~
incant
Most conferences that have encrypted WiFi will use PSK. Given the pre-shared
key and observation of the handshake, you can calculate the session key and
decrypt all traffic between a user and the access point. Compiling aircrack is
no longer "grandmother" territory, but it is certainly "average linux geek"
territory. Aircrack creates a virtual network interface, so you can even use
it with Firesheep with no extra modification.

So turning off encryption is really not that bad when you consider that all it
did was hog CPU and give people a false sense of security.

~~~
morganpyne
These are good points. (And indeed, I intended to write 'Firesheep' and not
'Firecookie').

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bdwalter
At the risk of sounding like a plug... Xirrus can do this. They kept up at
interop just fine this year.

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mightyMike
q: i've never attended such a conference. when the users move from room to
room they would have to reconnect to another SSID ? or did you setup something
like a mesh setup ?

~~~
cramforce
No Mesh magic involved. Just set them all to the same SSID and it will
magically work.

~~~
mightyMike
this would only work if you aren't using encryption, like in your case ? (or
encryption won't change a thing, except a lot heavier on CPU and there goes
all down the drain)

~~~
cramforce
Also works with encryption.

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carterschonwald
heres a link to the slides: <http://social-
traffic.streamie.org/preso/static/#slide1>

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zbowling
Would love to know the hardware they were running and their monitor software.

~~~
cramforce
Hardware: <http://www.ubnt.com/unifi> Monitor software: tail -f

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theschwa
Can anyone link to some good 101 info on wifi networks like this?

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mightyMike
yep. what hardware you guys used ?

~~~
cramforce
<http://www.ubnt.com/unifi>

~~~
Adaptive
Upvoting. I realize this is a single vendor link, but I recently spent a long
time redesigning my home network and settled on the same unifi system.

It's really worth looking at commercial grade access points if you are looking
for a more robust networking solution, even at home. There are other good
manufacturers besides ubnt, but their 3 unit unifi price point is pretty good.
2.4 ghz only however.

~~~
trafficlight
All around, Ubiquiti makes some pretty decent stuff for the prices they
charge.

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wglb
Good article. Hardcore.

