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Adam Swindell
Beginner

Looking for validation of my high density wireless design.

Hello. 

I'm just looking for some validation of my high density wireless design. 

Based on a lot of documents I've read I'm trying to get the number of users down to around 10 per AP. 

The room in question is a conference / board room that has seating for 42, with the potential for 84 people if it is standing room only. (I know I can't get it down to around 10 people per AP if there are 84 people in there, but I would be assuming they are not on their laptops doing bandwidth intensive things if it is a standing presentation).  My design right now is 5 access points (3502). All of them have the 5 GHz radio enabled and the power levels are at the lowest possible. They are all on different channels and are at least 10 feet apart. They are mounted to the ceiling which is at a regular height. I will have the 802.11n protocol enabled but it will be running in mixed mode so legacy clients can still connect. Out of the 5 access points 2 of them will have the 2.4 GHz radio enabled. However I'll be enabling band steering to try and convince the clients to connect to the 5 GHz radio. 

Attached are a bunch of screens from my Air Magnet predictive survey. There is a .pdf that shows full 5 Ghz coverage, and another that shows full 2.4 Coverage. And then subsequent screens show each channels coverage (to give a good idea of the cell size of each AP) As for the heat map...anything in gray is below -70dBm. Not sure if I should account for signals that are weaker than that or not. I've read mixed information from various sources. 

So is my plan sound, or is it absolutely terrible? Any pointers would be much appreciated. 

 

Thank you. 

7 REPLIES 7
Leo Laohoo
VIP Community Legend

The room in question is a conference / board room that has seating for 42, with the potential for 84 people if it is standing room only. (I know I can't get it down to around 10 people per AP if there are 84 people in there, but I would be assuming they are not on their laptops doing bandwidth intensive things if it is a standing presentation). 

You forgot one culprit:  The wireless client. 

 

At the end of the day, it is the wireless client that makes the ultimate (in some cases, dumb ones) decision to join which AP.  Wireless clients are known to join the nearest AP and have been observed to be joining the FURTHEST AP in the country.  

 

You could try to encourage your clients to ensure the wireless clients used have their wireless drivers updated.  This is particularly important when you are dealing with 802.11n.  In the last two/three years the wireless NIC manufacturers have been releasing updated drivers so their products can play harmoniously with 802.11n network.

Hi,

Just to add to Leo's response maybe is a good idea to disable lower data rates and config a higher mandatory rate like 18,24mbps or higher.

 

Regards.

good idea to disable lower data rates and config a higher mandatory rate like 18,24mbps or higher.

I would not consider disabling data rates 12 Mbps because there are some applications (such as Voice CAC protocol) which requires a minimum of 12 Mbps.  

 

I would disable data rates from 1 Mbps to 11 Mbps, 18 Mbps as Mandatory and the rest are supported.

Abhishek Abhishek
Cisco Employee

Disable lower data rates and config a higher mandatory rate.
jmeachum
Beginner

Adam,

I can see you have put a good deal of thought into your design and I would not say it is terrible, but I would do it quite differently.

  • Believe it or not 2 good access points can handle the load you are looking at so lets look at doing 3
  • Have all of the radios enabled
  • Set the TX power be much higher then the lowest setting, but not above 3 - this will provide a better SNR and a better SNR = lower retries and faster connected data rates - I have also seen some clients not work well with access points that have their power turned down all the way
  • disable all data rates below 12Mbps, and set 12 and 24Mbps to mandatory (both bands) - this will provide good client compatibility and low management frame overhead
  • Enable client link and client band steering
  • If you find that clients tend to load up one radio ensure that the TX powers are all similar or the same and consider configuring Client Load Balancing - If you do, set it weak globally and use default settings or a bit more aggressive in your RF profile 
  • If you have not purchased the access points yet and you have a newer model WLC then I would recommend the 2700 or 3700 access points over the 3500
  • For this scenario I would enable 40Mhz wide channels on the 5Ghz band
  • Ensure you do not have any unnecessary SSIDs broadcasting on the access points - this can be done with AP groups
  • Configure RF groups for the 2.4 and 5Ghz bands - this will become handy when the 8.0 code is released as it will provide the ability to apply the rx-sop command to the group
  • Enable EDRRM to protect yourself from an RF event
  • If you deploy Monitor mode access points you can change the Off Channel Scanning settings on the SSID servicing this room to 1000ms and check all of the priority boxes - this will prevent the access points in this room from spending 5% of their time scanning while serving clients
  • If contending with nearby wireless systems is also an issue then you may want to look at using patch antennas to further improve SNR and reduce the area that your access points will hear packets and noise from

I hope that this helps.

John

Trent Hurt
Beginner
Adam Swindell
Beginner

Thanks for all the input everyone.

I just installed the access points the other day and did some limited testing. 

It looks like for the clients that play nice with the assisted roaming feature (available in 7.4 and higher) the client actually moves to the closest access point very consistently. 

Older clients that don't play nice, just stick to the access point they first connect to. I tried disabling all but the highest data rates, but it looks like even at the lowest power settings the signal is still to good no matter where you go in the room and there is no rate shifting. Not a huge deal, as I expect most clients in this room to be mobile devices or at least newer than the laptop I use. 

Right now I have no 2.4 enabled in the room, but I plan on enabling on just one of the 5 access points. I have band steering enabled so hopefully most devices will still connect to the 5 GHz but there will still be 2.4 there for any old or miss-configured client. I also enabled the 'client load balance' feature, not sure how that is going to work in real life, I can't really test it myself as I only have two clients at my own personal disposal. Just have to wait until the room fills for the first time I think. 

 

Overall the RF in the room looks good. Because of the power settings being used, when directly underneath an access point you get around -50 dBm, as you move away it quickly drops off to around -65 or -70 but by then you are near another AP with -50 dBm. I'm sure more tuning and configuration will be needed in the coming weeks but I think everything is looking okay right now. 

 

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