How many clients can overload an AP MR-52

[AldoCar]

This is my scenario: I have 3 classrooms next to each other, each with their own AP but same SSID. Clients are laptops permanently set in each classroom except for teacher's client which moves around these 3 different rooms and APs. Why would half of the clients in one room connect to an AP in a different room instead of all connecting to the AP in their own room?

Would appreciate any feedback as to how many clients does it take to overload an AP. I'm talking about basic Dell laptops.

[MerakiDave]

Hi @AldoCar there are many variables that will determine if and when a client roams from one AP to another and/or which one they will connect to in the first place.  And those variables are constantly changing, possibly from second to second, for example as people (attenuators) move around the environment, doors open and close, etc.  It is always the clients decision.  We can configure the network and try to fine tune the RF environment and leverage 802.11k and 802.11v to try to influence client decisions and get them behaving as expected, but even still, the decision ultimately rests with the client. 

Generally speaking, yes, most of the clients should get the best RSSI from the AP in the same room, but again, the RF environment can change second by second in time, and foot by foot in distance.  In addition, different client devices will have different roaming behaviors, and sometimes even the same brand of client devices, like you mentioned Dell laptops, can have different behaviors based on operating system, wireless NIC and even driver versions. 

So lots of variables and every deployment is going to be unique from an RF perspective.  Still, if something just seems plain wrong with the client/AP balance, definitely open a case with Meraki Support for a deeper look and to scrub through your config settings.  

Also, I'm assuming the APs in the 3 rooms are the same model, with the same capabilities?  Because if you had an 8x8 AP in one room and a 2x2 or 3x3 in another, that could also explain more clients sticking with the 8x8 AP, even from another room, because that's where they perceive the best SNR, that's just one of a few variables.  Have a look at your radio settings page for example, see if the transmit powers are relatively balanced, or perhaps not, and perhaps adjust them.  Also look at your minimum bit rates, which should typically be 12 or 18Mbps, but make sure it's not much lower, which would create much larger coverage cells and leave clients happily connected to an AP in another room and be stubborn about roaming.  Also look over your Wireless Health page and see if anything jumps out, like if one AP is having many more issues than another.  You could also try toggling Client Balancing on and off, and allow that time to settle and re-check and that result could be another data point to open a case with.  

Hope that helps!

[AldoCar]

Thank you. @PhilipDAth @MerakiDave 

Right now I am getting 75% of clients connected to the MR52 AP  located in this room. Your input help me understand that perhaps this is not an AP issue but that it is ultimately the client's sole decision to choose to connect to this or the AP next door. These student clients are staying in one room the whole day though. Due to Covid-19 students aren't allowed to move around/ between classrooms - instead, instructors come to their classrooms.

In my attempt to rule out issues with this MR52 AP (by the way, we only have MR52s in the building), I created an SSID and tagged it to that specific AP in this classroom. I adjusted the bitrate by assigning a classroom profile already provided by Meraki. The majority of the clients are maintaining connectivity to this dedicated classroom SSID.

I still see about 25-30 % of clients disassociate from this particular AP and wanna go back to the AP next door. All of these clients are running zoom meeting as well as clients next door. Based on the literature, I don't think we are overloading these APs.

I'll try focusing on client behavior for now. Hope is not client power issues switching off connections.

[cmr]

@AldoCar we have a mix of APs in our venues and a fair few are MR52s, I've seen over a hundred clients on one many a time and they were working.  On the other side I have an MR56 and MR55 at home and I often find clients connected to the further AP and on 2.4GHz which has loads of interference, when 5GHz is empty.  The only way to force clients to connect to a particular AP is to have one SSID per AP.

What I'd ask, is does it matter if some clients go to a further AP?

[AldoCar]

Well, my concern to have clients connecting to the AP farthest away instead of the one in their room was that these

clients kept disconnecting from the students’ SSID broadcasted across the building - users had to reconnect to this SSID from their own interface.  The AP next door would associate these clients even though there’s two concrete walls in between. But after so many minutes, signal from room next door wasn’t strong enough and users had to troubleshoot connectivity.  In all this mess I noticed that the AP in the desired room did not have that many clients associated to it even though clients were physical located underneath.

I think right now I’ve ruled out problems with the AP and started looking at power settings in clients. I’m also going to look at DHCP range on my server - Win2016 BTW. I have DHCP enabled in these SSIDs, maybe I switch this off.

[GIdenJoe]

You should certainly check the channels the AP's are on if there is an unacceptable airtime issue or some interference for the channels on the classroom AP's.
Maybe also disable load balancing on all AP's if that feature is on so it does not push clients off.

Is the SSID 5GHz only or dual band? In case of dual band, can you correlate the misroamers to a certain band?

Are the AP's in the classrooms functioning properly ( = can you test with your own devices you can always succesfully connect without having dhcp, dns issues ) Clients can sometimes bounce back if they don't have full network connectivity within a certain time.

I hope you don't have an AP in the hallway, that could cause the signal to stretch in the hallway causing clients to stick because conditions are not bad enough inside the classrooms.

Are you running a powerlevel no higher than 14 dBm on all AP's?

[Bossnine]

It may have been mentioned, and I know it was an issue in the past so it might still be.........but the 'client balancing' option in the radio settings has caused me issues previously.  The AP would kick some clients over to a neighboring AP even if the current AP really wasnt overloaded.  Once I turned that off my problems went away.

[AldoCar]

whoa. So the "client balancing" option which is supposed to keep your clients associated to the best - in my case, nearest- available AP does not actually do that? 

Would turning this off create problems to clients moving around from room to room?

[cmr]

@AldoCar best is not necessarily closest in the eyes of the AP...

[Bossnine]

@AldoCar 

He is correct, 'best' doesn't' always mean closest but no, disabling this did not affect clients roaming from room to room in my setting, which is a school environment.  

My scenario was a typical classroom setting and the AP would kick clients off after say, 20 clients attached and try to move them over to another AP, even if the traffic going over the AP wasn't detrimental.  Once I disabled it clients would stay on the AP in their classroom. 

Again, this was just my experience and it has been some time since this was first introduced so the issue may be resolved now but its still disabled in my networks.

[MerakiDave]

Oh, and I realized I never answered the actual question in the title of your post, as far as how many clients. That is always an "it depends" answer, many variables there too, one of which is the applications in use and what's going to drive the duty cycle.  Depending on the client capabilities, the applications in use, the RF environment and airtime utilization, the client density and spread, etc, you could find this to be 60 clients, 100 clients, or more.  The theoretical max on the acW2 MR52 AP is 256 clients per radio, but please do not ever design for that or attempt to achieve that 😁 

[PhilipDAth]

Start reading from the capacity planning section.

https://documentation.meraki.com/Architectures_and_Best_Practices/Cisco_Meraki_Best_Practice_Design/... 

[PhilipDAth]

Do by any chance the students have to walk past the other classrooms to get to the one they are in?  You might be finding they are locking onto the first AP as they walk past, and then the signal strength is strong enough they stay connected to that one.

I'd increase the minimum bitrate to 12Mb/s.

https://documentation.meraki.com/MR/Radio_Settings/Minimum_Bitrate_Control 

[GIdenJoe]

I think if you not only have more than 50 clients on one access point but even cross your beams towards it, the thing will overload and might actually explode!

Sorry, the title just begged for this answer 😜

[GIdenJoe]

And now the serious response:

You're more likely to run out of airtime on your channel than actually trouble the cpu of the AP.
This will depend on a multitude of factors:
How wide is your channel, what traffic is flying through the air and is there any channel interference (co channel or adjacent), what is your amount of management frame overhead.

If you have the ability to run a test with one AP, you should use a tool like an Ekahau Sidekick that measures the RF energy and shows you the channel utilisation.  If normal traffic pushes you towards 80% then you are at the maximum of usable airtime.

You can improve design by focusing signals (by using external antennas or clever usage of walls blocking signals) so you can add a few more AP's.
Or you can tackle the usage of the air by lowering per client speeds but allowing short bursts.

However if the applications require said amount of bandwidth, go with the former solution.

[RobinGanderton]

Good day Gentlemen and ladies.

I am running into a similar problem.  I did a high level network scan of all AP's, clients, and generally RF saturation for a College Campus environment.

We have many AP's.  Some of which are MR33's and a smattering of MR52's

Clients keep getting kicked off, or simply time out trying to authenticate.    It is quite un-usable for our clients, at least at times.

Here is what I found.

With the RF Scan, using Kismet, I found the APs being simply overwhelmed by requests to connect, and/or data volume issues.

This was easily demonstrated thusly.

One class, of Many BYOD's, including a mobile lab.  Machine/device count came out to about 42 devices, for a class of 16.   Our MR33, right outside the classroom door, was simply overwelmed.  I finally read the actual specifications of the MR33 and with the 2 Bands (+BLE), 2.4 and 5.2 Ghz.   Just not able to keep up with that many requests.

Even the traffic volume was huge.  > 1.2 Gb (or trying) over the single 1 Gb line (PoE)   I cannot see 16 clients, each receiving streaming video, to keep up.   Kismet confirmed this.  (Delays, simple drops, Interference (Quite a bit))

I had one extra port in the room.  Confirmed it was good to serve as an PoE AP line, and simply put in a second MR33.   

That worked perfectly.  All clients, still slow, were connecting.

Further investigation and MR33/52 specs tells the story why.

So, for some of the other troublesome areas, I've put in a MR52, where the client experience has improved by leaps and bounds.   People are still having a little less issue connecting, but once they do, it's usually pretty good.  As long as they do not all stream at the same time.

That being said;  The MR33 has the 2 radios (2.4/5.2/BLE) the MR52 has 4 (2X2.4 2X5.2;  BLE ?)  and importantly, two trunkable ports.  (one of which is NOT PoE)

These MR33s and MR52's are a little older, do we have newer hardware to help out with this issue ?

I've noted that Meshing is NOT enabled, or responding at all.    I would love suggestions on that as well.

I hope that helps!

[cmr]

@RobinGanderton if you're looking for more powerful APs then the MR56 has 4x4:4 on the 2.4GH band, but more importantly 8x8:8 on the 5GHz band with a 5Gb uplink.

However depending on the situation two MR44s might give a better experience than one MR56 as though each radio has half as many chains, you have twice as many radios (as you have two APs).