Do NOT Put APs in Hallways

by | Sep 21, 2020 | Blog

You should not put access points in hallways. It’s a rule.

In today’s rules for efficient Wireless LAN design, we’re going to talk about why you should not put access points in hallways and give you some examples.

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Do not place access points in hallways

It's a rule

In this little short training video, we're going to

talk about why you should not

put access points in hallways

and give you some examples

It's part of the Wireless LAN Design Rules series

Let's get started and just talk

about why people want to put access points in hallways

Part of the reason was a long time ago

decades ago actually

people want to put APs in hallways because

what we thought Wi-Fi needed was a lot of coverage

We wanted to cover a big area

and we put them in the hallway

we could see that AP from a long ways away

and we thought we were getting something really good

and they were easy to do

It was easy to put in hallways, easy to get access

The problem is it doesn't work as good

as you think it should

We're going to give you some examples inside Ekahau

so you can see the difference of what happens when

you use an AP in a hallway or

when you don't use an AP in a hallway

Hopefully at the end of this little video

you'll feel a lot better about not

putting your APs in hallways

Well to start, we have an access point

and it's sitting on top of a football field

Now, I picked an American football field

because a pretty easy to do work in

You can go and take an access point, put it in the middle

and every line is about 10 meters, 10 yards apart

And so you can see if we take an access point

that's an omni access point and it covers in all directions

That's where it's supposed to do

If you look at the coverage pattern

and I'll come over here and do so

And we can come over here and detail out

and see that the coverage pattern here,

you can see that it's omni in the azimuth plain

It's putting out a circle

We can also see on the football field

when you place it there in proper orientation

It covers the entire football field

60, 70 meters in every direction

that's where this access points been designed

So starting here with no walls and nothing around

you can see it covers a long way

Next up, we're going to switch up and look at

what happens if we take that exact same access point

and put it in a small medical clinic

Here's one access point in the medical clinic

I've already added walls in areas

and I just want to show you that it's no longer circle

It was, you saw the exact same access point

Same height, same power, nothing changed,

and I moved it and just put it here

Now what we're seeing is Ekahau is doing this little math

What it's doing is it's taking the signal strength

coming from the AP, pushing it through the

pattern of the antenna and then doing

freespace loss calculations, covering distance

And then when it hits a wall, looking at the wall material

looking at its RF loss and changing the angle of how that

degradation or attenuation is taking place

So we have both freespace loss, degradation

and you saw on the football field

there's not a lot of that

But here in the Medical Clinic, you can see

the walls are controlling it as well

So if you put an AP in this medical clinic

and you put it in the hall, it's going to have a long tail

We used to think what we wanted was a lot of coverage

What we really want is controlled coverage

So if I take this exact same access point and I just move it

so it's not in this hall and it's not in this hall

I'm just going to move it up and over out of the way

Now, it still covers the area that it was covering before

these rooms in the corner, but it lost its tails

Now, here's one of the reasons we don't want tails

We move it back into the corner and you'll see that it has tails

That's, you know, like that coverage

Or you might say, well, I have voice over AP

And so I walk down the hall, I want to have good coverage

And then when I turn the corner

I want coverage from a different AP

That's true

But if we walk down here and say, I was right here

at the end of the hall about to turn

and right now you're getting oh, sorry

little glass this time we're getting a 58

So right there, there is absolutely

no reason whatsoever for you to roam

You're getting a great meg 58

But if I just walk a little bit further

and if I bring in my ruler tool, you can see that

where I was getting a 58 if I walk 1.3 meters away

What's that take half a second to walk

maybe a second at the top

If I just move 1.3 meters away from here

and now I'm over here

and now my signal dropped down to 68

Do I need to roam?

No, depending on how the client's been programmed?

Maybe, maybe not.

As I turn that corner, though, there is probably another

AP that's going to have better signal there

And as I turn the corner

I'm going to have to have a quick change

How about if we look up over here

right here before I turn the corner

I'm getting, a 54

Again, no reason whatsoever to change

If I again just walk from this corner and I go down

let's say I walked 2, 2 1/2 meters down

and look at the coverage

Now, I was a 54 and within 2 meters away I dropped to a 78

At a 78, I've got to roam

Well, how much time did I have to do that roam

As I turned the corner, boom, I instantly have to roam

Watch what happens when we just move the AP

out of the hallway and back over here

Now, right here, as I'm nearing the corner, I'm getting 66

I walk a little further, I'm getting a 68

And as I turn the corner,

I have this slow loss, not instantaneous

I have enough time to let the client device go

Oh, I'm lowering my signal

Perhaps I should start looking

and then I start looking and then I have some time

I don't have the quick instant loss

as you turn around the corner

Every time you put a AP in a hallway

you're going to get that kind of effect

Now, let's look at some other places

where you might put in AP in hallways

Because that's what you've always done

Let's look at a Hotel

So here's a hotel

And if we only put in two access points

One bottom left, the other one up at the upper right

We have fantastic coverage in the hallways

APs in the hall give great holiday coverage

The problem is that's not

where the people use Wi-Fi in a hotel

They need to use Wi-Fi in their rooms

Well, this doesn't do a very good job

It barely covers two rooms

So if we look at it and say

well let me come and add some more APs

Let's go and add an AP and let's put one right here

And see if, oh, I can get one more room and right here

and get another room and right here

I can get another room

And if I did this continually and I have so let me jump ahead

and show you this is what it looks like

if you put AP in hallways

You can get really decent coverage

Let's come over here and look at the statistics

and you can see statistically

We've got, what, 98 percent coverage

of the areas of all the rooms by sticking with the halls

You can use a AP in the hallway to cover signal in the rooms

That's not like all the Wi-Fi rules, if you break the rule

it doesn't mean Wi-Fi doesn't work

it's just not a matter of efficiency

So let's come back and say

I don't want to do AP in the hallway

How could I do it more efficiently?

Now, in this one, with all these AP in the hallways

we used a total of 24 AP

So you can see up and left corner here

we use twenty four APs

If I switch up and say no, I don't want that

I want to put AP in the room

Now, we have only used 10 APs, less than half the APs,

and we achieved a better result

Now, the reason for that, and this is true not just in hotels

but in many hospitals, schools, other places

the walls on both sides of a hallway

are usually load-bearing

Meaning they're more dense material

meaning they stop the RF more

The walls between rooms, between classrooms

between hall room, hotel rooms

or hospital rooms are less dense

They have lower RF attenuation, so it's easier and cleaner

to allow a single AP to go through multiple rooms

And as you can see, we really used

less than half the APs and achieved a better result

Now, when I've talked to hotel operators

like put them in the hallways, why?

Because we always did it, because we have access

and we don't want you to have to go back in the hotel room

You know what if the AP breaks

we don't want to lock in the hotel room

And I asked them, what's the Mean Time Between Failure?

That's a IT term, MTBF

Of I don't know, a dirty towel and the like

Well, once I explained MTBF after when they go well

we change the towels every day

So you're going in the hotel room every day

and you want me to not put the AP in the hotel room

because our APs have a

Mean Time Between Failure measured in decades?

I don't think that's a legitimate reason

And once you explain that, they kind of get over that one

But they're like, but we've done it in hallways before

And as soon as I show them the difference between 24 APs

And I've been in hotels, have these happen to be around

5 meters apart or 10 APs

Amazing how fast they switch their mind up and go

Oh, APs in hotel rooms make a lot of sense

So just to recap, if you want to have efficient Wi-Fi

don't put your apps in hallways and we've had some

examples here today to show you live directly in the software

You can see the results

So you can take your own copy of Ekahau

Try this, do a design in the halls, do design, not in halls

And you will see you can achieve better results

Now, there may be times like you're on a cruise ship

and the walls are made of steel and the only place

you can not, you cannot get access in the rooms

then you might want to put one on a hall

and use a direction antenna and aim it across the hall

and shoot it into the room

There might be reasons to break this rule

Most of the time though, follow rule

Don't put AP in hallways

If you have more questions

come to WLANPros.com we have a lot more videos

and a lot more training, podcasts, videos, WLPC videos

Glad to have you as part of the community

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