Controller Based WLANs

How to calculate number of AP's for a high density deployment

by on ‎07-04-2014 12:35 AM

How to calculate number of APS for High Density
In this tutorial I will guide you in how and what you need to calculate the total number of APS in a High Density scenario, such as an Auditorium, Conference Room etc
Information needed
In order to calculate this you need to get some information of your client which is the following:
Total of devices expected to be  connected
Minimum BW needed for each device
Type of Devices expected(Laptops, Smartphones, Tablets)
Formula components
MBW = Minimum BW Needed for each device
RBW = Real BW of the Device
ND = Number of Devices
AP = Airtime Percentage
Real BW of the Devices is the real TCP/IP Throughput which is around haft of the total raw speed
Example 1  
A laptop with a wireless card of 3x3:3 the raw speed of it is 450Mbps
The TCP/IP Throughput would be haft of it which is 225Mbps
Example 2
A smartphone with a wireless card of 1x1 the raw speed normally is = 65Mbps
The TCP/IP Throughput would be haft of it which is 30Mbps
Formula 1
(MBW/RBW)*100 = AP
Formula 2
(AP*ND)/80 = Total of Radios
Remember that most of Aruba APS are dual radio which mean that each AP got 2 radios!(one 2.4ghz and the 5ghz Radio)
Example with real Aruba Deployment

Let take this scenario and fill the information we need by reading the document above:
Filling basic information
Total of devices expected to be  connected = 100
Minimum BW needed for each device = 3 Mbps(2Mbps for apps and 1Mbps for Video)
Type of Devices expected(Laptops, Smartphones, Tablets) = IPADS with a maximum raw speed of 100Mbps and TCP/IP Throughput of 50Mbps(In the document implies that the IPAD provides 100Mbps Wireless speed Connection)
Formula 1
AP = (MBW/RBW)*100
Let’s substitute the values
AP = (3Mbps/50Mbps)*100
AP = 6%
Formula 2
(AP*ND)/80 = Total of radios
Let’s substitute the values
Total of Radios = (6*100)/80
Total of Radios = 7.5 Radios
Total Amount of Aps 4( In this case 4 AP 135)
As you see the total APS is the exact number used on the Aruba Deployment.
With this formula you will be able to calculate the approximate number of APS needed in a High Density deployment such as an auditorium.  
Remenber also that this will give you just the total of radios needed,  as in the auditoriums you sometimes or at least i do, turn off the 2.4ghz band of some of the AP because of the overlapping.  So for example 10 radios could be  7 APS,  3 of them with 2.4ghz and 5ghz on, and  4 on just 5ghz which give a total of 10 Radios.
 I'd add a few more design considerations:-
You may get away with fewer APs because...
I'd suggest that it is worth considering the real-world utilization of any particular device or user. In your Auditorium, do you expect 100% of users to be using the bandwidth at once? If not you could consider contending the bandwith provisioning at more than 1:1
If it's possible, can you get any usage statistics to quantify likely usage?
You may on the other hand need more because...
It is important to consider overhead from SSID beaconing. Although an approximation, the examples given do not account for bandwidth lost to beaconing by APs. (Good design and consideration to increasing basic rates can minimise this.)
You probably don't want to re-use any 2.4 channels. Even given a highly engineered design with respect to APs, the client broadcasts are going to be omni-directional.
The approximation assumes that all cients will associate at top rate. In reality a good proportion will rate shift down and send data at lower rates. Aruba's ClientMatch can help  to some extent with this by shifting clients to the most suitable AP.

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