Question for all you true WiFi Gurus

[panjandrum]

Ok, to keep a long story short: A school network. The school structure is rife with nearly impenetrable walls, combined with a few large open areas and fast spans of glass to boot.

So we've got penetration issues, combined with signal reflection issues.

Primary systems are moved to the 5ghz network and a total of 6 WAPs are in use, that works fine. Plenty of non-operlapping channels. But we also have to use the 2.4ghz spectrum for devices which can't see the 5ghz. spectrum, and for our iPad network for other reasons (50-wireless client limit on Airport Extremes). Unfortunately, two of our WAPS are the newer Airport Extremes which will NOT turn off the damn 2.4ghz signal. Therefore we have those both set to channel 1, so as to consume as little of the valuable 2.4ghz channel range as possible. Leaving 6 and 11 available to us.

Due to the school's construction, we are completely unable to cover the entire building with only 3 WAPS on the 2.4ghz spectrum, which would allow me to physically separate the WAPS enough to use 11, 6, and 11 and be OK. But it leaves dead-zones. So that's a no-go. So (other than the useless Airport Extremes needlessly consuming channel 1), we have to have 4 WAPS, and then need to share channels 6 and 11. With 3 WAPS we get dead-zones, with 4 we get excessive coverage overlap. But 3 own't do it, so we have not choice but to go with all 4. Crazy, but there you have it.

THE QUESTION: We want maximum performance in ONE area of the school (Middle School has additional 40 iPads - so a heavy concentration there) Are we better off using channel 6 in our most congested area and leaving all three of the other WAPS on 11? Or are we better off using 11 , 6, 11, 6, spreading them out as much as possible? Alternatively, our WiFi bleeds out of this building essential 0%. Walk inside, powerful signal, walk outside even 5 feel? Nada, zilch, zero. It's a giant frigging faraday cage apparently. Thus, I *could* use a 4-channel setup without fear of interfering with neighboring networks. Say 1,4,8,11. But that's always touted as such a no-no that I've never even really considered it. Like I said, we need reliable coverage through the building on the 2.4ghz network, but only need maximum performance in physical location. If that helps...

Thanks for any advice you can provide!

- Lost in the signals...

 

[DJLC]

I just finished fighting this at our two campuses (one elementary, one middle). We also have some interesting construction choices. I ended up with roughly 23 Xirrus WAPs across both buildings.

My best advice is to limit channel overlap as much as you can. A very useful tool in this is Wi-fi Explorer (on the App Store), which will show you a visual graph of channel utilization. You can walk around to each area in the building and get a visual idea of what's going on spectrum wise in that area.

So, supposing you have an AP on channel 6 at the front of the building. If you do a scan at the back and the signal on channel 6 is low, you shouldn't have a problem re-using channel 6 in back. Keep an eye on the graph in Wi-fi Explorer; if you have some overlap, make sure there's a significant difference in the strength from each AP and you shouldn't have too much trouble.

I also have to say, depending on the number of students you have, an AirPort is definitely not the right equipment for this job. When it comes to wifi in an enterprise environment, you really do get what you pay for. I'm very satisfied with the Xirrus APs that I've installed in both of our buildings. But granted, I have a total of 540 kids, 300 of which have 1:1 iPad Airs. Plus 60 or so staff members with MacBook Airs and iPad Airs.

 

[Altemose]

THE QUESTION: We want maximum performance in ONE area of the school (Middle School has additional 40 iPads - so a heavy concentration there) Are we better off using channel 6 in our most congested area and leaving all three of the other WAPS on 11? Or are we better off using 11 , 6, 11, 6, spreading them out as much as possible? Alternatively, our WiFi bleeds out of this building essential 0%. Walk inside, powerful signal, walk outside even 5 feel? Nada, zilch, zero. It's a giant frigging faraday cage apparently. Thus, I *could* use a 4-channel setup without fear of interfering with neighboring networks. Say 1,4,8,11. But that's always touted as such a no-no that I've never even really considered it. Like I said, we need reliable coverage through the building on the 2.4ghz network, but only need maximum performance in physical location. If that helps...

I actually managed a network for my high school which had 12 AirPort Expresses and one AirPort Extreme that functioned as the router on the network. Combined, the network served 150+ clients without a hitch daily. In light of your description, I would actually leave the 2.4 GHz network turned on all the APs. The AirPort seamlessly switches clients between 2.4 and 5 GHz as appropriate for their connection. A side note is that you do not want to have the "5 GHz Network" box checked as that would simply create a new SSID as 5 GHz is already enabled. A client gasping for a 5 GHz signal is worse than 2.4 GHz pollution.

The critical part of any wireless network in a school is the back end. I would sincerely hope that you are using Gigabit Ethernet as the back end connection amongst the AirPorts. Are you using an AirPort as the router?

From the sounds of it, I recommend that you do a full site survey. In light of the construction, I doubt you will have much outside signal pollution but internally you need to bear in mind of microwaves. The general rule of 1, 6, 11 on the 2.4 GHz spectrum means nothing if the higher channels are all congested. As referenced by DJLC, Wi-Fi Explorer is a great tool to have as is NetSpot (for mapping APs). You want to have a signal to noise ratio on each AP of at least 30 dB.

Some other tips to keep in mind is AP placement. I cannot tell you how many times I have seen APs sitting right on ceiling tiles or right next to fluorescent lighting with the cables running over those lights or parallel with electrical wiring. Verify that you do not have this issue as it may not appear when dealing with 5-10 clients but when an AP is getting slammed, you will start to see problems appear. On older flat AirPorts and even the current AirPort Expresses, you can turn down the transmit power on the wireless radios using AirPort Utility 5.6.

In essence, get the idea of the 50 client limit out of your head. You want at most 30-35 on the newer Extremes depending on tasks. I have gotten 65 clients on an Express before, but they were mere connections and not really pulling bandwidth. These are just tips with using equipment you already have, but if you were to replace the system then the UniFi line is the perfect balance of manageability, affordability, and simplicity.

 

[things]

we've done hundreds of thousands of wlan design/installs globally in umpteen environments, don't get hung up on non-over-lapping channels

unless you're running high bandwidth real time traffic, wlans are pretty tolerant

i've seen corporate offices where the internal networking people put every ap on the same chanel, with added bleed through from several other companies via an atrium and glass walls, our spectrum monitor showed signal from over a hundred aps in the same and adjacent buildings, but you know what, it all works ok

yes, ideally, try to minimise overlap where possible, but in the real world it's often out of your control

no system is ideal, if you are also faced with mobile devices to secure/manage, as well as wifi then you might do better long term to look at something like cisco meraki where you get single pane of glass management and lots of device management capability, especially good for ios devices, they often have special pricing programs for usa education sector (i'm not based in usa, and i don't work for cisco/meraki but they are one of the vendors we use)

 

[panjandrum]

OK, that's a lot of great info. I didn't want to make the original post too long, so I didn't go into the back-end too much, which is quite robust (Airport Extreme hands off to Mac OS X Server into gigabit switch and entire building is gigabit wired. OS X Server handles dns, dhcp, and a very basic Squid-based HTTP proxy). Overall performance is excellent. All of the Airport extremes are in bridge mode except the main one connecting us to the outside world.

Is WiFi Explorer back on the App Store? I've been using the Cydia version for many years now, after it suffered a case of "Apple thinks iThing users are too stupid to use this app" moment and it was removed from the App Store...

We did, unfortunately, go will Apple Airport extremes through the school for a number of reasons which were perfectly valid at the time (very little $ for a gigabit-capable router, and maximum WiFi client density on any one WAP back then was, maybe, 20). Then the school got a little government $ for iPads for special-needs purposes, plus a huge parent-commitee donation to the Middle School. Then another foundation funds the purchase of 13 MacBook Airs...) And suddenly, in the span of a single school year, we can easily exceed the 50-wifi client limit on any of the Airport Extremes (why the heck did Apple put that limit on them? Their performance is *excellent* in our building. If they didn't have the hard-coded limit our entire situation would be different).

With zero additional funds, our only real solution was to roll-out our older, but enteperise-level (for the day) 802.11 b/g routers (also working in bridge mode) and put the iPads on that separate network. These routers do not have an artificially introduced maximum number of WiFi Clients.

So everything is pretty darn good except for the 2.4ghz issues. I've been cursing Apple a lot recently, and the fact that I can turn-off the 2.4ghz channel completely in the OLDER Airports and can't in the NEWER ones is just frustrating as hell. Every single place I turn anymore, where having Apple equipment used to be a boon, having Apple hardware (or software) is now a hinderance. I may go back and try limiting the signal-strength of the Apple routers on channel 1. I have an old copy of the Airport utility tucked-away just for that, but IIRC Apple has again introduced a "Can't be run on this version of the OS" error for that version. I should be able to get it running on a Lion VM or even pull out an old SL laptop though. So thanks for reminding me about that; it sounds like a good option.

I really appreciate the feedback and thank you! I'm just going to go 6, 11, 6, 11 and adjust the signal strength to keep the overlap as minimal as possible. That's a real problem in this building, with the dense walls and signal-reflection, but I'll do the best I can and hope for the best.

Another question: It's obvious Apple no longer wants our business when it comes to networking hardware. I intend to seek funding for better equipment next year. I can relegate the Airports to speciality tasks, like maybe a guest network. Since there are a few others here working in schools; Do you have recommendations for a good fast capable router at a reasonable price? They would need to support bridge mode of course (I've stayed away from dedicated "bridges" since they are, as far as I can tell, more expensive than simply putting a good router in bridge mode and calling it a day...) We can easily cover the building with 6 good WAPS; that seems to be pretty ideal in our location. - Which model Xirrus APs are you using DJLC?

 

[Altemose]

Do you have recommendations for a good fast capable router at a reasonable price? They would need to support bridge mode of course (I've stayed away from dedicated "bridges" since they are, as far as I can tell, more expensive than simply putting a good router in bridge mode and calling it a day...) We can easily cover the building with 6 good WAPS; that seems to be pretty ideal in our location. - Which model Xirrus APs are you using DJLC?

In our location we currently use a TP-Link business class router that I cannot recall the model of and 15 UniFi APs and AP Pros. The pros of the AP Pros is the affordable price bracket (around the AirPort Extreme) and overall capability when paired with the UniFi software controller. That being said, the AirPort hardware you have now will easily do what you need but you need to get everything configured properly. When you have the money go ahead and upgrade, but for now you can certainly do great with your existing AirPort hardware.

 

[DJLC]

Another question: It's obvious Apple no longer wants our business when it comes to networking hardware. I intend to seek funding for better equipment next year. I can relegate the Airports to speciality tasks, like maybe a guest network. Since there are a few others here working in schools; Do you have recommendations for a good fast capable router at a reasonable price? They would need to support bridge mode of course (I've stayed away from dedicated "bridges" since they are, as far as I can tell, more expensive than simply putting a good router in bridge mode and calling it a day...) We can easily cover the building with 6 good WAPS; that seems to be pretty ideal in our location. - Which model Xirrus APs are you using DJLC?

I did quite a bit of shopping and got quotes from Xirrus, AeroHive, and Meraki. We have a Meraki firewall at our middle school and a Meraki core switch at the elementary (connected together via 100Mbps Metro Ethernet). Meraki seemed great when I ordered those, but the costs of the licenses on their APs quickly inflated their price. Also turns out Meraki firewalls can't handle several industry-standard routing features. So all in all, I can't really recommend Meraki.

AeroHive seemed nice. Good in-the-middle price.

Xirrus ultimately won the bidding war, primarily because there were already Xirrus APs in the building when I was hired and they had a trade-in program at the time. We kept two of our seven old XAPs — the XR4820 model — and just got them into a current software + XMS-C (cloud management) license. Then everywhere else we did the XR620 with 802.11AC. And in our boardroom we went with the slightly beefier XR2426 w/ AC. Total cost for both buildings was around $14k. I did the physical install myself — we're in historic buildings (MS was JC Penney in the 50s, ES was Ford Motors in the early 1900s), and as a result the install quotes were outrageous. For both I did home runs with STP from each AP back to a switch with PoE in each building.

This year we refreshed and expanded our 1:1 program; 330 iPads in grades 4-8. And new MacBook Airs for all staff. With the new APs, we haven't seen any wifi issues at all. The XR620 is only rated for around 50 clients, but they routinely exceed that without much trouble. In more dense areas I put both radios on 5GHz, while in less dense areas one radio is on 5GHz and one on 2.4GHz. Between our two buildings with 22 APs, we support around 400 wireless clients daily (at this exact moment there are 412 connected).

I'll also mention that the Xirrus folks are great about sending people out to look at your environment and make recommendations. Because of our building construction we did more of the smaller APs, but depending on environment it might make more sense to do fewer larger APs. Our K1 area can be supported by one big 4820 while our 4/5 area needed two 620s due to HVAC and wall placement.

Hope this helps!

 

[panjandrum]

OK, thanks again!

Our experience with the Apple Airport Extremes is extremely good right up until they hit that 50 client limit. We have up to 30 MacBooks on WiFi bound to network home-folders on the server all in use simultaneously on a single access point, for example. So we're talking plenty of bandwidth. (Sure, performance drops if suddenly all have huge amounts of network traffic, such as trying to copy large quantities of data to them all simultaneously with ARD, but that's just part of living with how WiFi functions.) In the Airports, however, this is not a "suggestion" but appears to be a hard-coded limit. The second we try to get more than 50 clients on a single Airport Extreme WAP everything goes to hell. I'm pretty sure that the any single Airport (even when in bridge mode) actively rejects any further attempted connections on WiFi. Now start bring up iPads that go to sleep, wake back up, laptops being closed and opened, etc. And suddenly nothing in that area works properly. Clients literally get kicked off the network. So, at least on the Apple hardware, you can't exceed the 50-client limit and simply suffer poor performance - it turns from "everything works great" to "instant chaos" the moment you exceed that limit.

Unfortunately for us (publicly "funded" if it can be called that), we will, maybe, if we are lucky, manage to squeeze out $1000 for computer hardware of any type next year... (We're still running 35+ Macs of 2006/2007 vintage along with a total of only 20ish newer models... To give you an idea...)

 

[DJLC]

Unfortunately for us (publicly "funded" if it can be called that), we will, maybe, if we are lucky, manage to squeeze out $1000 for computer hardware of any type next year... (We're still running 35+ Macs of 2006/2007 vintage along with a total of only 20ish newer models... To give you an idea...)

I know that fight... we're a public charter so we get the short end of the stick when it comes to funding. We were able to use some of our facilities budget to cover the wifi, and we did it toward the end of the last fiscal year since we hadn't had any maintenance emergencies. Got lucky there for sure.

Depending on your free/reduced lunch numbers, you may be able to quality for eRate Priority 2 funding for wifi as well.