Controllerless Networks

Hi All,

 

I got called out to school yesterday who have been experiencing some issues with their wireless slowing down when allot of devices are connected. The school has 12 IAP 93's, 8 in their main building and 4 in a new building. The WiFi was installed about 18 months ago but back then they only had 10-15 laptops for the students. They have recently purchased another 100 or so laptops for the students and are now experiencing problems.

 

I logged in to the virtual controller and it was showing that 25 devices were connected to 1 AP while the 4 surrounding AP's only had 2-3 devices connected which is obviously not ideal. I started by upgrading to the latest version of code to see if it was a bug in the ARM as they hadn't upgraded them since they were installed. This didn't resolve the Issue so I rebooted the AP all of the devices were connected to to try and force them on to other AP's within range, which they did but they all started to flag as poor signal as soon as they did. When the AP came back online they all started to re-associate with that AP. I left them running for a bit and then went through the clients association history and I could see some of them were jumping between different AP's but they always ended up reconnecting to the first one. It seems like ARM is pointing all of the clients towards this one AP as it is the only one with viable signal but would it continue to do this even if the AP is struggling?

 

I checked the AP stats on the virtual controller and the CPU & memory for the AP looked ok so it didn't appear to be struggling that way, the AP also showed 5 neighboring valid AP's which ties in with the physical locations onsite and reasonably close by so I would expect them to be able to hand off to each other.

 

While on site I did notice two things that could be contributing to the issues. Firstly the AP's are not mounted on the ceiling, they are mounted on the walls and all of the surrounding AP's are mounted with what should be the bottom of the AP (hopefully that makes sense) facing away from the area with the issues. Also because the school has no POE on their switches the AP's are going in to a number of 4 port POE hubs (3 AP's in each hub) and then the hub is connected to the schools network, the problem is the hub is only a 100Mb and the schools switches are gig so I'm thinking instant bottleneck. If we could eliminate the 100Mb and have all of the AP's connected to the network on a gig link could they handle 25 devices or would it still struggle?

 

Basically what I'm asking is.

 

1. Will Arm keep associating clients to an AP even if its struggling if the other surrounding AP's don't have the signal strength to support them in order to keep them all connected?

 

2. How many devices will a IAP93 comfortably support before it starts to struggle? I've seen some test doc's where 60 devices have been hooked up to a AP135 without any major problems but obviously the AP93 & 135 are two very different bits of kit.

 

If it’s a case of relocating the existing AP's to be ceiling mounted, swapping the AP's to dual band units or simply installing more AP's then that’s fine but I don't want to suggest a course of action that isn't going to fix the issues they are having.

 

Any thought's suggestions would be greatly appreciated.

#AP135

Are the wireless clients being placed on the same subnet as wired clients?

 

Wall mounting with the APs pointing away from the clients can certaintly contribute to the problem.   The RF signal falls off sharply behind the AP-9x as well as the AP-10x and -13x.   See the AP-9x antenna pattern in the spec sheet here:  AP-9x spec sheet .  Is it possible to temporarily mount the APs on the ceiling and re-test?

 

ARM attempts to steer clients to the best AP, however, it is ultimately up to the client which AP to join.  Some clients tend to be stick and really want to connect to whatever they saw first.   ClientMatch can help with this, however, ClientMatch is not available in Instant yet.

 

How many clients per AP is very subjective.  You can have more if the clients are all relatively low bandwidth or 8 - 10 concurrently connected clients if they are VoIP handsets.

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@Marcus wrote:

Wall mounting with the APs pointing away from the clients can certaintly contribute to the problem.   The RF signal falls off sharply behind the AP-9x as well as the AP-10x and -13x.   See the AP-9x antenna pattern in the spec sheet here:  AP-9x spec sheet .  Is it possible to temporarily mount the APs on the ceiling and re-test?

 

ARM attempts to steer clients to the best AP, however, it is ultimately up to the client which AP to join.  Some clients tend to be stick and really want to connect to whatever they saw first.   ClientMatch can help with this, however, ClientMatch is not available in Instant yet.

 

How many clients per AP is very subjective.  You can have more if the clients are all relatively low bandwidth or 8 - 10 concurrently connected clients if they are VoIP handsets.

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Hi Marcus,

 

I was going to suggest tweaking the AP's but buy the time i noticed it yesterday their technician had to leave to go and pick up his son so couldn't try it while I was there.

 

I know you get sticky clients but these are relativly new laptops and I can see some of them moving between AP's in the client history so it would seem like ARM is trying to spread the load but the clients are just going back to the same AP due to poor signal from the others.

 

I'll try temporarily mounting the AP's on the ceiling and hopefully that will fix the issue.

The new laptops could still be using old drivers if they are the original drivers provided in Windows. This is worth checking.

ok I'll add it to the list, thanks.

I believe so, all of the addresses the clients recieve are coming from the schools DHCP server and they only have one SSID so the student laptops are connecting to the same one as the teachers ect

In reality ARM won't steer you to an AP but if you load balancing enabled that could . That will be possible once ClientMatch makes it to the instant OS .

ARM will adjust the power/channel changes .

You can do the following :

- as Marcus suggested make sure drivers have been updated
- if those are windows laptop there's certain wireless drivers that allow you to configure the roaming settings
- make sure that the power levels are not set too high
- possibly consider looking at IAP deployment setup are the IAPs too close or far from each other.
- make sure band steering is enabled too

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@vfabian wrote:
In reality ARM won't steer you to an AP but if you load balancing enabled that could . That will be possible once ClientMatch makes it to the instant OS .

ARM will adjust the power/channel changes .

You can do the following :

- as Marcus suggested make sure drivers have been updated
- if those are windows laptop there's certain wireless drivers that allow you to configure the roaming settings
- make sure that the power levels are not set too high
- possibly consider looking at IAP deployment setup are the IAPs too close or far from each other.
- make sure band steering is enabled too

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The laptops are running windows 7 but I will get the drivers checked. The system didn't have load balancing enable as the version of firmware firmware they were running didn't have it, once I had upgraded them I made sure this was enabled but it still didn't seem to help. I'll check on the band steering but would this need to be enabled as they are only single band AP's?

 

Thanks,

Mike.

Hi all, I went back to the school yesterday and I've looked a bit deeper in to the problems they are having.

 

As previously mentioned when a class of children are using laptops (20-30) almost all of them are connecting to the closest AP, general web browsing appears to be fine. When they are initially logging in to their profiles (hosted and downloaded from the server every time they log in) some of them take a little longer to log in than the others but that is not a major problem. All of the clients are showing good signal strength and a 54Mb (all of the devices are connected on G not N) connection speed.

 

However while I was there yesterday they had 2 classes (60 laptops) at opposite ends of the school logging on at the same time and that's when they started to experience major problems. A number of the laptops failed to receive the profiles and needed to be rebooted and logged on again, by this time the others had finished downloading their profiles so they went through ok.

 

I looked on the virtual controller and it did have 2 AP's with 25+ AP's logged on to each but when reviewing the AP stats it didn't seem to be struggling. The CPU went up to around 70%, the Ram have around 50% free and the network throughput was peaking at around 8-10Mb so from the looks of that its making me think it's not the AP's causing the problems. They have a gig network so that's shouldn't be a problem either.

 

So my question is not knowing enough windows servers and the way they work could their server be struggling with all the laptops trying to simultaneously download profiles as this seems to be the only time they encounter problems but from the virtual controller the AP's are not struggling. I'm not sure if given everything else the server is running (DHCP, DNS, emails etc) if it will only allocate a certain amount of bandwidth for profile downloads?

 

Also the laptops are using Intel centrino advanced-n 6235 WiFi card which from googling are notoriously unreliable so I'm not sure if anyone else has run across problems with these cards?

 

I'm scheduled to get back in touch with the technician next week so any thoughts would be great.

 

Thanks,

Mike.