Why One Access Point Per Classroom is NOT a Universal Solution
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Why One Access Point Per Classroom is NOT a Universal Solution


Hi, everyone. My name is Michael McNamee. I’m a senior network engineer here at SecurEdge
Networks. Today’s topic for our Whiteboard session is
why one AP per classroom is not a universal solution. The first reason is if you’re using enterprise
grade APs, they are fully capable of handling 40 to 50 devices at a time without any issue. And if you think about a K-12 environment,
if we’ve got three rooms with about 30 students or 30 devices per room. That’s really only going to give us about
45 devices actually connected. You’re gonna question my math on that. Hear me out. In the real world, we’re never seeing 100%
of the client devices connected at any one time. We’re only seeing about 50%. 50% would net us about 45 devices connected
to the wireless LAN. So that’s well within the 40 to 50 devices
that the AP can handle without issue. Now, those devices are connected, they’re
not actively through-putting or consuming bandwidth on the wireless LAN. In the real world, what we’re seeing is about
40% actively through-putting on the system. So that puts us somewhere in the range of
about 30 to 35 devices actually through-putting on the system which is still under the 40
to 50 devices that the AP can handle without an issue. Another reason that I want to discuss why
one access point per classroom is not a universal solution is doing a proper wireless LAN design. An enterprise grade AP has no problem getting
neg 65 dB to a client device in a classroom. With the AP set at 25 milliwatt, which is
a symmetrical power setting to, say, an iPad or Chromebook, or some sort of tablet type
device. And that same AP can cover three to four classrooms
with good signal, depending on what the construction materials are. In most K-12 environments, it’s gonna be drywall
with stud construction or potentially even cinder-block, but the AP has no trouble with
that. So having the proper wireless LAN design implemented
just further validates why you don’t have to have one AP per classroom. So, reason number three that I want to talk
about is CCI and ACI, which stand for co-channel interference and adjacent channel interference. In designing wireless LAN, we want to avoid
channel reuse as much as possible. We also want to keep at least 20 to 25 dB
of separation between our channels, we want to keep our retry rates less than 20%. Even with enterprise grade APs, it’s gonna
be very difficult to achieve all these bullet points. It really is an example of too much of a good
thing is a bad thing. And reason four we have is cost. Cost is a big factor. Everybody’s concerned about cost. If a solution provider or a reseller comes
in and does a one AP per classroom design, they’re gonna propose a mid-level AP which
lists about $700. If we’ve got four classrooms with $700 APs,
we’re looking at a cost of $2,800. If we do what we propose, which is proper,
we don’t need these other three APs. We have one AP, and we do a higher end AP
that’s $1,000. We now have a project cost for these four
classrooms of $1,000, which is an $1,800 savings. That’s a big savings. So we get better cost, and we get better performance
from the system.

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1 thought on “Why One Access Point Per Classroom is NOT a Universal Solution

  1. Okay, where to begin. I design WLANs for Schools, Libraries, and health care systems and this is NOT sound advise. I'm not sure your level of experience in designing and implementing WLANs, but assuming you have implemented any with the advise in this video, your customers will not be happy. Yes, most enterprise APs can handle 30-50 clients well, but assuming that "50%" of the clients being authenticated at any one time in your example is piss poor. You always design for density now a days. You mean to tell me that during testing you expect everyone to take turns? Or, better yet when you do have a decent load on the AP from an adjacent room with just one AP serving 3-4 classrooms that these users will have a good experience? What do you think their data rate would be….?

    Designing for -65 is ideal. Forget everything else in your bullet list, as the power requirements change from room to room. What schools have you been to that are predominately drywall? Ive been to literally hundreds and the vast majority are brick/block exterior with mostly block interiors.

    In regards to keeping 20-25 dB of separation between cells…. Just walk it (assuming you have site survey software). If your device can hear your neighboring cell at -85, you're good. It's not so much what other APs hear, it's what the client devices will hear. Usually their chipsets are not tuned (pumped out by the millions daily) and they can often hear a cell at -92 RSSI. You didn't dive in to CCI and ACI at all really. Look, if DFS channels are able to be used, having a 20 MHz wide channel plan offers you 25 usable channels. 25! In an AP per classroom environment this really helps you be flexible. I know that higher throughput rates are achieved using 40 and 80 MHz wide channel plans, but for high density environments this isn't really worth it. Having additional overhead isn't helping, considering those rates are at the mercy of the clients being used. Wanna guess how many 3×3 devices are used by consumers in these school systems? Not many. ACI can be avoided easily. Just dont be a dummy. CCI is mostly only a concern on the 2.4. It can be seen on the 5 GHz band as well, but only at 40 MHz wide channel plans. Dont argue, just look at a spectrum analyzer.

    Yes cost is always an issue, but I sure as shit rather my customer end up with something that works. Especially if I am managing and supporting it. This is honestly mind blowing. For anyone watching this video, do not take this mans advise. It is lazy and piss poor. Also, "you dont really need these other 3 APs"… Look at the fucking AP placement! Jesus man. REALLY?!

    I cannot wait to go through the remaining videos this company has pumped out. Wi-Fi is so misunderstood and I would hope that anyone that has even a CWNA would give better advise than this.

    If your engineers at SecureEdge Networks are certified, they're phonies. They need real knowledge and real world experience. Give me a call. I'll school em.

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