Do NOT Use Stop and Go Survey

by | Sep 23, 2020 | Blog

Let’s talk about why you should NOT use stop and go surveys

There’s reasons for it and I’m going to show you the answers. Like all rules, if you know what you’re doing and you have a legitimate reason for using stop and go, then go ahead. But just realize there is a cost in data collection and they are inaccurate.

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Do Not Use Stop and Go Surveys

In today's training video, we're going to talk about

why you should not use stop and go surveys

in Ekahau

There's reasons for it and

I'm going to show you the answers

Now of course, like all rules

if you know what you're doing

and you have a legitimate reason

for using stop and go

then go ahead

But just realized the cost

in data collection and inaccuracy

Let's just go jump right into Ekahau,

and first of all, we're going to see is a not stop

and go

This was a continuous mode survey

We're going to look at the data and see what's collected

And then afterwards we're going to come back

and do the same site, but with a stop and go

and then compare the data collected between the two

We're now in a survey on an elementary school

that was conducted using a MacBook on a Segway

so you kind of going fast, as fast as you can go on it

and a Segway inside of a school

And let's go and look detailed in to

what the data collected tells us

We're looking for a couple of things

How far apart are the data collection saving points

Where are they with their distances

Because we know at some point Ekahau's

going to have to take the data that was collected and

interpolate in between the data points

That's how it makes the heat maps we'll be looking at

So let's zoom in here really close and see what's going on

I'm going to zoom in on the screen

And we can see if we turn on survey tab

and then survey inspector tab

I'm going to hide this for a minute

Down below and just zoom in nice and close

And we can see there's a green dot

the green dot is where we clicked

That's the human clicked and said

here's where I'm turning

Now remember the rules for continuous surveys

Click when you stop

Click when you start

Click when you turn

Yeah, and walk a straight lines

so every time you are going to a stop, start or turn,

you're going to drop a data collection point

You're telling the software I am here

and then the software is going to calculate

all the other data points along the way

in between the ones you do

So if you walk at a constant rate

and you click every time you turn and you walk in

straight lines, the software is going to

line them out right where they are

So come in here, look a little closer

There's one right here where I clicked and then

the other one's on here are when the software did

its data collection on the sidekick, there's two NIC

so each of them gets a slightly different colored

when their saved

And let's see how far apart those are

So on average here, if I switch over to the ruler tab

I can say, well, I had one here and

one here

You click and drag it up

An old man eyes put glasses on

That's about four meters between this one and that one

It's about four and a half meters over here

three and a half over here, three point four

It take a couple over on this side

Here's a really long one that got all the way out

to seven meters, some in the middle or really close

some over here about three meters apart

So even though we're allowing the software

to drop those data points

we're collecting the data fast enough

And this by the way is collecting on all channels

If we wanted these to be closer together

we would collect only on the channels that we care about

in this building that would make it go a little faster

which would mean they'd be a little closer

So now let's look at the data that was actually collected

We know these are collected close together

three to four meters

maybe on a worst case, we've got about seven

But you know over here where we had a seven

there was one between here and here

that only was a two

So, yeah, we haven't, they're very close together

Now, let's look with survey inspector and see what we got

At this data point right here

this individual data point

I'm going to go and make the bottom look a little bigger

so we can focus on

but realized each data point

it's going to turn blue up above

but since I only have a single screen to show you

I'm going to kind of minimize that

let you see what's collecting

Over on the left we see we're collecting all the APs

we have to meet in 5 gigahertz

This is a 5 gigahertz APs that are being collected

and they're coming up and down

The horizontal axis is time

Every time we move and collect data

it's time driven

Below that is the 5 gigahertz spectrum

Now one of these

frequencies is going to look stronger than others

And that's

that's an artifact of being in an active mode survey

because the NIC that was in the MacBook

while we were surveying was associated to an

access point and sending data

So the spectrum analyzer there was on the side kick

that was fairly close

would see that signals being much

stronger because they were very far apart

So realized that this isn't interference

It's an artifact of the active survey

And then at the very bottom

down here we can see the active survey and the ping times

that were being collected during that active survey

The top bar is going to say the Mac address of the AP

were associated to the bottom green bars

are showing the ping times

The upper part is showing our SoSci from each of

the individual APs we're collecting

And then on the right side, in the center is the

spectrum analyzer view and currently I have it set

to not show

Actually, it is showing a real time sweeps

so let me turn that off

we don't need to see the sweep

If we happen to hit an interferer

we'll pop it up on the screen

I'm looking at the Max Density Color

That's how it's currently configured

as well as showing the APs

The AP information coming from over here

comes from the Wi-Fi NIC inside the sidekick

the spectrum analyzer is showing the parts inside

So the little box comes from Wi-Fi

The colors underneath come from spec end

And now let's walk through as I'm walking

and because I did a continuous mode survey

I can just go step, step, step and walk

through the entire day

It took an hour to walk, I can replay the entire hour

and you see as I'm replaying the hour

stepping forward, there was an AP that was strong

that was the one I was associated to showing up here

on the spectrum analyzer, a couple of other ones show up

because they're close and they have traffic on them

I can see all of the signals coming up and down

And as you'd think, as you're walking

one AP is going to climb, as you're getting closer to it

as you go away from it's going to lower

another one's going to climb

And we can see that, in this little section up over here

That's what happens when you have

a continuous mode survey

we're collecting all the data

you can see over in the RTFM section, the Mac address

all the information from all the APs

if you hover, you can also even see some more detailed

information that we decoded from beacons

So this is continuous mode survey

It was done with, on a Segway fairly fast

actually really fast

And still our data points are three, four meters apart

Now let's go over and switch surveys

and this time we're going to look at what we capture

walking in the same area, in the same place

but this time we'll be using a stop

and go survey instead

We're back and now we have the stop and go survey data

Same school, same equipment, same sidekick

The only difference is what we're going to be doing

is collecting the data in a different manner

A lot of people like stop and go survey

because it feels like you're in control

You go someplace, you stop, you click the button

you wait five seconds, it collects all the data from all

the channels twice, and then it stops and

then you move on and you do it again

That's true, it does that

and it also fixes a problem that we have seen in the past

if you have a very slow, say you're only having one

data collection and we click in one place

and then you walk, walk, walk, walk, walk, click

all the data saved between those two

get saved at the next point

So there is kind of a shifting of

the actual data you collected over to the next data point

Now, if those only two, three, four meters apart

I can live with that little shift

more than I can live with the lack of data

I hate losing data being on site, collecting data

and throwing away

And that's what stop and go surveys do

they collect data only

when you're standing still

all of that data you collect

I mean, it's coming into the sidekick

the NICs are listening

they hear all the beacons

they're pulling all the data in and then stop and go says

yeah, throw it away

Let's look and see what happens

So here we can see

I'm going to do the same thing I did before

Let's zoom in really close and we don't see the lines

in between where we're walking

We obviously walked in between those locations

but we didn't save where it was

One benefit, it doesn't look like you walk through walls

Well, if you click properly in a continuous

you can't walk through walls because we know

it's humanly impossible

So your continuous mode survey shouldn't ever look like

you walk through a wall if you click correctly

Here's a little data point right here

Stood at the corner of that intersection

collecting collected data

Let's go and look at what that collected data looks like

We can go to that same little spot and click

Now just like before, I'm going to

extend the bottom so we have a little more detail

But you understand, as we're stepping through

point to point to point

we'll now be jumping from each of those locations

I want to be in 5 gig and I'm in the survey mode data

and here we go and I can walk back and forth in time

just like we did before

Oh, but look at right there

I'm collecting data for the five seconds

but what happened in between?

I said we threw it all away

and yes Ekahau did throw all the RSSI data away

Guess what

The spectrum analyzer kept running the entire time

the active survey kept running the entire time

so we did collect that set of data

What we threw away was the data

was happening in between

Another downside of stop and go survey

as you go, stop, go, stop, go, stop, go

right click, save, that saved one group

of stop and go's together

They're not tied contiguously back together

like we do in a continuous mode survey

I could right click and save and save and save and save

through a building and then come back

with survey inspector and see the whole

continuous mode working together

I can easily save that way

Here, it's in little groups so I can walk and say

Oh over this period of time

Oh there I saw some

Oh yeah

Then they went away

Well you can see in the spectrum analyzer

they didn't go away

You can see right here it's there, over in the RTFM

the Real-Time Frequency Monitor

We could see the data was coming in from the device

The active survey is running

We just threw all this data away so that we could

stop right here and collect better data

Pretty obvious what's going on

We're collecting the data and then throwing it away

Let's take another look

Let's go back up here for a second

And let's find another data point

And there's another set of information here

you can see as I go along

Here there is a long stretch over here as you look

there's a long stretch where there was no stop and go's

But obviously I collected data

In fact, if you zoom in way down here you can see

you even roamed and the roaming took place during

the walk in between the stop and go data

that might have been useful information to have

Yeah. So let's get rid of this for a second and come back

and say here's our big stop and go survey

It took a lot longer to do all the stops and go's

because you have to stop

Wait, wait, wait, wait five seconds

Move, stop, compared to a continuous where you can

collect more data faster, closer together

Let's see how far apart these are

using the same method I used before

From here to here

That's 7 meters from here to here, 6.2 from here to here

10 meters from here to here, 8 meters from here to here.

9 meters, 6, 4, 4

On average, we're collecting way less data points

and throwing the data away that's in between

and it took longer

Spectrum analyzer collected all the spectrum data

all the way through

Active survey including roams was collected

all the way through

Stop and Go survey though

you felt like you were in control

because you didn't want to walk and

click properly and follow the rules

click when you start, click when you stop

click when you turn

And you ended up with less data

if you have a legitimate need for stop and go

go ahead and use it

what's not a legitimate need is

well I don't want to click as I go into a room because

I have to go

Yeah just click when you stop.

click when you start, click when you turn

And you can keep all the data being collected

as you're going along

Thanks for listening

We have a lot more training modules, videos, podcast

videos from all the WLPC out on

wlanprofessionals.com or wlanpros.com

Thanks for being part of the community

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