Wireless Access

Hi I am currently completing RF plans for my company using the VisualRF planner auto provisioner and although I have completed my CCNA bringing everything together has brought up against a fair few questions and I was hoping you could verify what I am saying and clarify some points.

All my questions are hypothetical to verify my understanding,

So hypothetically if I have 1 Aruba 93 access point what are its capabilities, I know it has one radio which can operate on either the 2.4ghz band or the 5ghz, so for this purpose, say I choose to operate my device at the 2.4ghz band. The 2.4ghz band has 13channels with 3 of them being non overlapping.

1. Now my belief Is that my one AP device is only using one of the 13 available channels, and so all clients connected to that AP will be communicating across that same channel however many clients that may be ? –is this correct?

2.If 1 is correct then hypothetically I could have 3 Aruba 93 access points stacked directly on top of each other on different non overlapping channels and increase the throughput and quantity of client devices threefold without experiencing any intererence? –do you agree?

3.Furthermore could you also have 13 Aruba 93 access points lined up accordingly so that each one is a separate channel  1,5,9,13,2,6,10,3,7,11,4,8,12 and spaced far enough apart so that say chanels 1,5,9,13 overlap each other but 1 is far enough away from channel 2 to avoid interference.? –is this correct

thanks for you input in advance

Rob

1. Now my belief Is that my one AP device is only using one of the 13 available channels, and so all clients connected to that AP will be communicating across that same channel however many clients that may be ? –is this correct?

Correctt all the clients connecting to that AP will be using that channel

How many clients can connect? well you can connect as much you want but remenber that  wireless is a shared medium so you are sharing the BW you got between ALL the devices connecting to that AP... so basically you dont want like 100 users connected to one AP... recommended maybe like 25 or 30 if you using voice then that number would drop to 15

2.If 1 is correct then hypothetically I could have 3 Aruba 93 access points stacked directly on top of each other on different non overlapping channels and increase the throughput and quantity of client devices threefold without experiencing any intererence? –do you agree?

Yes you can have 3 AP 93 in one room and they would no overlap one will pick channel 1 the other channel 6 and the other one chanel 11

3.Furthermore could you also have 13 Aruba 93 access points lined up accordingly so that each one is a separate channel  1,5,9,13,2,6,10,3,7,11,4,8,12 and spaced far enough apart so that say chanels 1,5,9,13 overlap each other but 1 is far enough away from channel 2 to avoid interference.? –is this correct

I dont undesrtand this quetions but illl try to asnwer to see if i got what you asking..

Well if you got one AP 93 on channel 1 and one ap 93 on channel 5 that would overlap and will have interference...

You normally just use channel 1 6 and 11 and thats it... you actuallly dont use channel 2 because that overlaps channel 1 and channel 6 and so on...

You would reallly want to have always if you cant dual band APS and send all the clietns you can to the 5ghz channel... 23 non overlapping channels = Win  :)

Hope it helps

Cheers
Carlos

Hello Rob,

Some answers to your hypothetical questions:

1. Correct. The AP may change channel dynamically depending on RF conditions, but at any given time it's operating on one particular channel (typically 1, 6 or 11) and the channel is shared among all connected devices. the maximum number of clients connected to a single AP depends on AP type, per-client throughput expectations, client density, etc. The hard limit in our SW is 255, but for an AP-93 we recommend not to exceed 25 concurrent active clients or so.

2. No. Even though the APs all operate on a different channel, AP radios can only deal with a specific amount of "adjacent channel interference" (ACI). The RF energy transmitted by one AP on channel 1 will still hit the receivers of the other radios, even if those are tuned to channels 6 and 11, and if the APs are close together, that will saturate the receiver. If you stack three APs together as you suggest, you'll effectively share the medium and end up with rouhly the same total capacity as with just one AP. In order to avoid this, we recommend a minimum AP-to-AP spacing of 10m (but that's admittedly somewhat conservative).

3. It is best to avoid partially overlapping channels and stick with the common 1, 6, 11 channel plan. Given that in Europe you have 2 more channels, and you really just need 20MHz spacing, you could use 1, 5, 9, 13, but you should use either set consistently and avoid channels with center frequencies in between. Channel 4 overlaps only partially with channel 1, but the impact of a transmission on channel 4 on an AP operating on channel 1 is just as bad as a transmission on the same channel. In both cases, this would effectively be "co-channel interference" (CCI), and AP radios are even more susceptible to CCI than they are to ACI

Hope this helps. Let me know if you have further questions.

/Onno Harms, Product Manager, Aruba

Good info Oharms didnt really know about the second one....

My mistake

Cheers

Carlos

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oharms wrote:

3. It is best to avoid partially overlapping channels and stick with the common 1, 6, 11 channel plan. Given that in Europe you have 2 more channels, and you really just need 20MHz spacing, you could use 1, 5, 9, 13, but you should use either set consistently and avoid channels with center frequencies in between.

 

Please be advised that while you can use the 1, 5, 9, 13 channel plan in Europe, the customers that tried this to my knowledge most reverted to the 1, 6, 11 channel plan.

 

The reason for reverting is that some client equipment refuses to use channel 13. It might be never tested on those devices, driver settings, but several customers experienced this problem and reverted to old channel schemes. At least when APs are deployed for coverage (lowest AP count for full coverage), there may appear coverage holes in places where only channel 13 is availabe (for only some devices).

 

Another issue may occur when other networks in the neigbourhood use 1, 6, 11 channeling; as your channel 9 interferes with 6 and 11, and 13 with 11.

 

So theory dictates that a 1, 5, 9, 13 channel plan should work fine, practice may prove otherwise.