cisco 1602i AP and 2504 solution. If I have 2 AP in same area, will number of conncurrent connections to both APs will be automatically load balanced between two APs

Posted on 2014-11-09
Last Modified: 2014-11-17
cisco 1602i AP and 2504 solution. If I have 2 AP in same area, Will number of concurrent connections to both APs will be automatically load balanced between two APs?

We have deployed APs in various conference rooms in a venue. As we are concerned about number of maximum concurrent connections a 1602i can handle, we are thinking if adding a another AP is same area will allow for load balancing concurrent connections between two APs
Question by:Syed Hashmi
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LVL 46

Expert Comment

by:Craig Beck
ID: 40431108
There is a load-balancing feature which is disabled by default on the WLC.  I would advise that you don't use it though - it's not an exact science and it isn't actually enforced.  Some clients don't support the feature very well either, if at all.

Author Comment

by:Syed Hashmi
ID: 40431534
is it then correct that even without WLC load balancing feature in use, clients connections will be distributed between APs automatically, in this case of 2504 wlc and 1602i APs.

My presumption is that even without switching the feature on, two APs in same room will result in some degree of automatic load balancing?
LVL 46

Expert Comment

by:Craig Beck
ID: 40431563
My presumption is that even without switching the feature on, two APs in same room will result in some degree of automatic load balancing?
The law of averages says this is likely, but it will actually be more a case of clients choosing whichever AP's probe response they receive first is the one the client will choose to associate with.  Whether association is successful is another matter.

If one AP is transmitting at full power and the other is transmitting at lowest power the received signal from each AP may dictate that the strongest AP is the only viable candidate to use anyway as RF thresholds are usually used to help the decision.
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Author Comment

by:Syed Hashmi
ID: 40442417
it will be great if someone with 2504 experience can confirm if this is what usually happens;that two AP in same conference room will usually result in some degree of load balancing
LVL 46

Expert Comment

by:Craig Beck
ID: 40443165
someone with experience

I'm a Cisco WLAN Consultant!  I have ample experience... Probably more than some of Cisco's engineers.

Author Comment

by:Syed Hashmi
ID: 40445974
Craig sorry - did not mean to offend u..  thanks for replying to our question

what i meant to say me get to a conclusion here please ... something more credible then law of average

do we deploy more then one 1602i in same area to spread the load or not...
i am not a cisco guy..what i need to know is how do we mover forward with this...

i was expecting an answer like "yes it will" or "it will but you need to make these change...etc"
LVL 46

Accepted Solution

Craig Beck earned 500 total points
ID: 40446251
No problem.  For info, I've worked extensively with every WLC (including the 2504) and AP (including the 1602) that Cisco has produced.  I work for one of Cisco's largest global Gold partners and have been designing and installing Cisco WLAN solutions in small and large-scale deployments since around 2002.

Put simply, wireless isn't as straight-forward as "let's put 2 APs here to share the load" unfortunately, and the client load-balancing feature is not enabled by default on the WLC therefore there isn't even a sniff of load-balancing by default.

I understand that you want a solution and that you're expecting to hear good news, but I have really told you what happens already.  Client load-balancing isn't all it's supposed to be, and simply doesn't work well.  Similarly no load-balancing at all is potentially just going to give the same result in theory.  Let me explain...

A client will associate to the first AP that responds to its probe request usually.  If the first responding AP is not the only one to respond the client will decide which AP to attempt to connect to based on the signal strength and SNR (amongst other thresholds and parameters).  The thing to remember is that the first AP to respond usually ends up with the client associated, hence referring to the law of averages (which itself is entirely credible).

However, that's not where it ends... The client has a set of thresholds that triggers its roaming process, so it may be that the client associates to an AP with a weaker signal [than another AP] initially purely because it responded first, but then after the association happens and the client sees the AP with the stronger signal it will roam (or attempt to) to the AP with the stronger signal, providing the SSID, authentication, encryption, etc, all match on the other AP.  That's great.  To complicate things though, clients may all try to then associate to the stronger AP which in-turn would tell the client that it's too busy and to try to associate to another AP.  This causes the client to bounce around (excessive roaming).

All this means that the science is not exact.  Many clients have different thresholds even when client load-balancing is not used on the WLC and therefore it's quite common for an uneven split of clients across APs to occur.

Even if you do turn on client load-balancing, the client has to actually support the load-balancing feature too.  When the WLC tells the client that the AP is too busy and to try a different AP the client doesn't have to listen to that instruction (status code 17), and may not even support the instruction, so it is simply ignored.  On the WLC there is a set of thresholds that control how and when load-balancing is triggered, and by default the client can attempt 3 times to associate with an AP before the WLC decides to stop telling it to try another AP - at that point the client just associates anyway.  The load-balancing feature is a soft-option if you like.

In any case, client load-balancing is one feature which I would stay away from.  It's (obviously) not perfect and it can be ignored by the client.  It can also cause excessive roaming issues by its very nature (as I've already explained) and it doesn't work at all if you have 2 APs in the vicinity which are connected to different WLCs in the same mobility group.  You may end up just turning it off because it's more of a hindrance than a help.

Here's a bit more to back this up...

Hope that helps!

Author Closing Comment

by:Syed Hashmi
ID: 40447001
I accept this as solution for the question asked.
However, i would like to know about a practical solution here in relation to current installation of 2504 and 1602i
In a situation where we have more people in a room then a single 1602i can handle?

I know that putting it down a fix number does not help as what AP can support at any given time will vary significantly with exactly what type of clients its serving and exactly what those clients are doing.

However, i would like to come out of this discussion with something that helps us progress the solution

Thanks for your help

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