How-to setup High density WLAN area's

Unanswered Question
Sep 29th, 2009

What is the best way to setup a very high density WLAN area.

Such a a conferencing room with 300+ users, which all will be using WLAN connectivity.

Is it possible to use several 'g/n' AP's in close range, eg with directional antenna's ? Maybe by antennas every few yards in the ceiling?

I'm aware that 'a/n' will give better performance to more users.

Is this an good alternative towards the Xirrus WLAN array's? They contain up to 16 AP (integrated) in one enclosure.

They pretent very good perormance and specs but they also are limited to the WLAN standards. ...

I have this problem too.
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jeff.kish Tue, 09/29/2009 - 05:16

The Xirrus arrays are geared more towards providing large coverage areas, not supporting a larger density of clients (at least not larger than Cisco).

Cisco APs would be a great fit for this scenario. I would advise against directional antennas, as this could create unexpected RF shadows. I would recommend 1140s with internal omnidirectional antennas.

Channels are going to overlap in this space, so we'll want to minimize the effects of that as much as possible. You'll want to do several things here:

1. Plan out a realistic number of active clients at a time

2. Plan for each AP to cover 25-30 clients

3. Install the appropriate number of APs around the room, keeping them as separated as possible

4. Eliminate as many low data rates as possible. At minimum, disable the 1, 2, and 5.5Mbps data rate. Eliminate 11 and 12 if possible (this will make it so 802.11b devices cannot connect)

5. Reduce the radios to minimum power levels

Finally, run a test with as many clients as possible. Increase the power if needed, but only on a few select APs.

If this is a professional environment, push the powers that be to install 802.11n cards in the clients. If this is a public environment, the vast majority of devices will be in the 2.4GHz space.

If anyone else has any advice, please don't hesitate to post.

polthuis Tue, 09/29/2009 - 05:23

Jeff,

do you have real experience with these large setup's?

Any one else ?

Peter

alexfrench666 Mon, 03/29/2010 - 08:04

Thanks Jeff! Do you recommend lowering the client power levels ("power client xxx") or just the AP power?

Also, is it worth lowering TX power on an A radio?

Leo Laohoo Tue, 09/29/2009 - 15:03

I have and I have no questions or objections to Jeff's recommendation. A few things to consider, though, if you are using 1140, you'll need to think about getting a WLC because the (long delayed) release of the autonomous IOS is not ready. If you plan to get a WLC, make sure it's has Gig links (same with your switch).

Before the AP installation, do a site survey (you can use the 1130 for this). In placing your APs, because I don't know the dimension of the area, place them about 10ft (3.5m) away from each other and let the WLC calibrate and signals strengths. After the installation, it's optional to perform another site survey to verify the placement of the APs.

Hope this helps.

+5 to you Jeff.

polthuis Tue, 09/29/2009 - 23:10

The setup will be done within a exsiting environemnt. There are allready 300+ AP's in place.

Two WiSM's are used as WLC (with failover) , probaly a 3rd one will be used.

At some area's more AP's are needed.

+1 for you all.

Peter.

zhenningx Tue, 10/06/2009 - 17:13

When placing APs about 10ft away from each other, will that cause co-channel interference between APs when using 2.4G even with the lowest power level?

ericgarnel Wed, 09/30/2009 - 08:29

There are some very good pointers in this thread, but since we do this all the time, I would like to add my input.

1) Ping your Cisco SE: there is an internal Cisco doc exactly for this scenario

2) use Rf absorption to your advantage: place lots of APs down low (under chairs) and build lots of smaller cells for better client to AP ratios

3) I disagree with the "avoidance of directional antennae" tip. Directionals are great for narrow corridors and also for APs on stages & platforms.

4) "Steer" clients to 802.11a when possible by tweaking the WLC rrm values on both bands

petnugen Wed, 09/30/2009 - 10:30

You may consider a pico cell deployment, not used it but it is there, I think you need to engage with Cisco as though.

polthuis Mon, 10/05/2009 - 01:48

Now there is an evironment with about 300 Ap's ij place. This provides total coverage. In some conferencing rooms much more capacity is needed !

wessepj Mon, 08/22/2011 - 12:26

I have the situation about to be configured. I have a large room that will contain about 125 clients. I have read the Cisco documentation conerning high-density designs and can concur that co-channel interface is critical. Cutting down the data rates will definetly help. However, in a WLC environment I can't see a way to adjust just those APs in the room. It looks like this is a global configuration on the controller. Is this something at AP grouping can be used to control? I don't want to change all the APs on this controller.

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