Troubleshooting Wifi in a Crowded Environment

[HCHTech]

I did a walk-thru for a new customer today. There is a large-ish rectangular showroom, maybe 100'x100', with offices in an L-shaped hallway behind two of the sides. They have a Cisco setup, using 4 of the business 240ac access points. The APs are in the corners - about 15 feet or so from each corner towards the center of the space. They are currently configured as a mesh (=all APs on the same channel for 2.4GHz and 5GHz) and they are in a very crowded wifi environment, bottom floor of a 3-story building in a business park. In 2.4GHz, channels 1.6 & 11 all have 3 or more neighboring networks visible. 5GHz is less crowded, of course, but there are several other networks there as well. Complicating matters, they have wireless IP phones on a separate internet connection & router.

Their main issue is unstable wireless (clients getting dropped), what a shock. They have several wireless printers, as only some of the office space is wired for ethernet. The printers regularly fall off the network as well.

I'll be collecting logs from the Cisco controller and I'm reading up on just what adjustments are possible, but it strikes me as kind of a no-win situation. I don't get why they setup a mesh in the first place, as all APs have home run wires to the switch, it may have just been the default way these things come up unless you change it. The setup was done by an IT "friend of the business", but they don't have any ongoing IT support.

In my initial discussion, I recommended running network drops for all of the printers and non-wired computers and just getting them off wifi altogether. Several of the employees use laptops that they carry around with them to meet with clients in the showroom, so some wifi usage is inevitable.

What do you think - would ditching the mesh help? I've never found a situation yet where I thought mesh was the right answer, so that's where I'm leaning, but because the environment is so crowded, I'm not sure there is any hope for good 2.4GHz performance...

 

[Markverhyden]

This is my experience with wireless printers at several locations. If they are those cheap ones their power management causes them to drop the connection but you have no way to turn that off. It's the you get what you pay for syndrome.

As far as other devices? I know it sounds like finger pointing but one tack I would take would be getting the problematic devices identified. I wouldn't be surprised if some were ancient in computer life terms.

What were you using @HCHTech to look at the spectrum?

 

[YeOldeStonecat]

So is only 1x of the APs wired....and the other 3x are doing wireless uplinks? (mesh)
Or....are all 4x of the APs wired? If so...having both radios on the same channel does not mean "mesh"..it's just not a good setup.

What you want to do is walk around taking measurements of wireless signals.
With the 2.4 radios you just have the 3x non overlapping channels to work with, 1, 6, and 11. So....by default, 2x of the 4 radios will interfere with each other. And we're not accounting for the neighbors noise.
With the 5 radios, on the common default of 40 wide, you'll have 4x non overlapping, non DFS channels to work with, but if you lower the 5 radios to 20 wide, you'll get 9 to work with...better penetration, better stability, better range, at a cost of a little less speed.

Walk around doing a survey, adjust TX strength of radios so that, when you're under the cell (coverage) of one particular AP, the other APs are not coming in too strong...you generally want to keep them weaker than ...eh, depends on the setup, but lets start with around -65. You want your selected AP for that area to be the strongest signal there by far...ideally stronger than -55. This way clients easily select the AP that they are closest to.

Since the 2.4 radio typically has twice the range of the 5.0 radios, in denser environments I'll often disable the 2.4 radio on 1/2 or 1/3 of the APs.

Adjusting RSSI helps encourage clients to leave an AP as they walk over to the cell of another AP..it's like a "soft kick". Wireless roaming is a client sided decision, clients should be smart...but adjusting RSSI encourages them to leave sooner if they find an AP stronger than the value you put in. I often start this setting at -67...and based on the environment..may lower than or raise it.

How many clients total that might be on this whole network? Nothing wrong with lots of wireless clients if the wifi is setup to handle it.

 

[HCHTech]

So is only 1x of the APs wired....and the other 3x are doing wireless uplinks? (mesh)
Or....are all 4x of the APs wired? If so...having both radios on the same channel does not mean "mesh"..it's just not a good setup.

No, all 4 APs are wired to the switch. The Controller clearly has them setup as mesh - it's an A/B choice in the configuration - so when you do that, they all get on the same channel for 2.4 and all on the same channel for 5GHz as well. This seems likely to be a problem - just cause the setup guy is a sysadmin somewhere doesn't mean he knew about wifi - haha.

In looking around in the controller, it's not obvious you can turn down the signal strength for 2.4 either, like you can do with Ubiquiti's. I supposed it had to be in there somewhere, but didn't find it. Maybe it's a CLI adjustment. My inclination is go back to a regular non-mesh setup with separate channels for each AP, but A, they are fairly close together, and B, the environment is so crowded there just isn't a "less used" channel for any of them. I think I counted 23 visible 2.4 networks when I was standing in the middle of their space (including theirs). Logically when there is such a crowded airspace, it seems the right answer is not to reduce the signal, but to boost it to screw your neighbors in exchange for better performance. I guess it's probably a good thing you can't do >100% without illegal firmwares.

I only used wifi analyzer on my phone for the initial walk-thru, and only spent 15 minutes or so digging around the controller. The controller lives on one of the APs, and it designated as the "master". I'm not sure if that changes if you don't do a mesh, so I need to get into their setup docs a bit to see what the choices are. I think it makes sense to disable 2.4 on two of the APs, I hadn't thought of that.

 

[HCHTech]

Adjusting RSSI helps encourage clients to leave an AP as they walk over to the cell of another AP..it's like a "soft kick". Wireless roaming is a client sided decision, clients should be smart...but adjusting RSSI encourages them to leave sooner if they find an AP stronger than the value you put in. I often start this setting at -67...and based on the environment..may lower than or raise it.

@YeOldeStonecat - Just so I understand the RSSI adjustment, the range is -1 to -94. Signal strengths closer to zero are better. So when you set a minimum of -67, the APs are encouraging any clients with signal strengths of less than that (-68 to -94) to leave by sending back special packets. When you want clients to roam more easily, you must have to make that number higher (closer to zero), right? When you want them to stick around and NOT roam as easily, you must have to make that number lower (farther from zero). Do I have that right?

I'm sure it's more complicated than that as roaming to an AP with a better signal but that happens to be more crowded with clients, might not produce a better experience - just playing devil's advocate...

 

[HCHTech]

As far as other devices? I know it sounds like finger pointing but one tack I would take would be getting the problematic devices identified. I wouldn't be surprised if some were ancient in computer life terms.

What were you using @HCHTech to look at the spectrum?

This is also a good point. One of the printers with more problems is 2 weeks old, but it is a $300 Brother Laser MFP, so not a high-end device.
I took network reports from each of the printers. They've got a list of problems that result from no real IT management - we'll start knocking those out once we get in there for some real work.

I used Wifi Analyzer on my phone to measure the signal strengths. I should probably get a fancier setup, but could never justify the cost - for the same reason I don't have a nice Fluke network analyzer - haha.

 

[YeOldeStonecat]

Usually with Mesh you're just using 1x of the radios for the backhaul (wireless uplink)...so having both radios on the same channel for all 4x APs doesn't make sense. Yup, I'd flip that switch to "non mesh"...and manually change things.

Regarding the dense environment of neighbors...yeah it may takes some planning on the 5 radio side of things. This is where flipping them from 40 wide to 20 wide can help...open up a lot more options for you. Narrowing the channel width gives you more stability.

For signal strength, yeah in dense environments you'll pick up a lot of channels of nearby wireless networks....BUT, as long as you tune yours, you can work around them. Who cares if you pick up 6 or 10 other wifi networks when they come in weaker than -70dBm....your focus is on making your wifi in the room(s) be stronger than the neighbors...but not TOO strong so that your own APs overlap each others cells too much.

Signal strengths...
*If you're standing like...5 feet from an AP...you'll have a good strong signal of around -35dBm. I think the theoretical "best" is -30, but..due to overhead and many factors, figure the best you get in the real world is -35. Get a dozen people in the room, furniture, etc...and you'll weaken to around the low to mid -40's.

*You generally want an APs area of cell coverage to be stronger than... -55dBm,.

*Once you get weaker than -55dBm, like -60, -65...things like streaming HD video can suffer. As you get into the higher -60's...towards -70....things like streaming music might begin to stutter.

*Generally once you get weaker than -70....officially around -75 it begins to become a poor quality connection. Your email may still work fine, you can still (slowly) bring up websites. But you won't be streaming music well, or watching videos.,,,,not so well.

*Once you get weaker than -80dBm....-85...you'll start to get dead in the water for a connection. Most devices will drop once they get into the high -80's or -90.

So....RSSI...what it does, is tell the client "Hey, if you get as weak as -67dBm (for example)...start looking for other APs...and if you find one stronger than -67...please...go to it! Feel free to leave me..and go to it! By default, most wireless clients will latch onto the first AP that they find...but if you go walk from one room to another room that is closer to a different AP, that wireless client may still be latched onto that first AP, even if you're standing under the next AP. The client had a death grip on the first AP. So RSSI is a good value to manage...when you have an environment of multiple access points. It encourages roaming better. Not all wireless clients are created equal...yes roaming is a client based decision, different products may have different default values built into their smarts. So...RSSI is a nice way to "encourage" roaming better. I once read that Apple devices have some default value of -75dBm built into them. Not sure if that's true or not

 

[YeOldeStonecat]

I used Wifi Analyzer on my phone to measure the signal strengths. I should probably get a fancier setup, but could never justify the cost - for the same reason I don't have a nice Fluke network analyzer - haha.

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Along with a subscription to their design software....and it's useful when doing LARGE setups...like schools, etc. Because you can load a map, walk around, and take measurements...that give great detail, and it can save those and print out verification reports. It's like getting expensive ethernet testing devices that can actually "verify" it. Much more involved than just an ethernet test that has link lights.

But for...homes, small businesses...to be honest, I'll do just fine using an old version of inSSIDer on my laptop. Some time ago MetaGeek took away some of the functions in the free version. I have version 3.1.2.1 installed on my laptop that has the latest version of Windows 10...and it works fine.

Using my cell phone with Ubiquitis WiFiMAN is pretty useful too...however from what I've seen, most smart phone wifi apps don't list all of the APs broadcasting in the same row. They'll show you first a row of SSIDs...and you have to click into each SSID to see each AP broadcasting it. It will work, but...you do a lot of back 'n forth.

Versus...using inSSIDer....I can see one big row of each and every AP it sees....along with the SSIDs each AP is broadcasting., the channel, and the signal strength. Much more useful to see all of that on the same page. So I can slowly walk around an office....going around each room, from room to room, up 'n down hallways, etc...and watch things change, and adjust as necessary.

Right now sitting at my desk, my laptop sees the AP outside my door at -37, and it sees the other AP down the hall and around the corner at -59/-60. (it was -59 when I first looked and then someone walked down the hall..and caused it to drop to -60 in the blink of an eye).

Which brings to point, don't forget to factor in people...if you're designing for an environment that may fill with people. Human bodies can be big sponges for wireless signals. You can do a survey of school, tune a classroom to have an average of -40 across the classroom when it's empty. But fill the classroom with 25 booger pickers.....and now an average reading around the room may weaken to -55.