Instructor: In this lesson we're going to talk about
wireless connectivity issues.
Now, when we deal with wireless connectivity issues
there are lots of different things that could affect us,
including intermittent wireless connectivity,
signal interference, low signal strength,
or standards mismatch.
First, we have intermittent wireless connectivity.
Now, when we talk about intermittent wireless connectivity
this means that your wireless connection
is going from an up to downstate and back again.
When we talk about intermittent wired connectivity,
we talk about things like port flapping,
where we go from an upstate to a downstate
on that particular switch port.
Well, the same type of thing can happen
when you're dealing with a wireless network,
but instead of having this port flapping
that occurs with a physical device,
we instead get connected or disconnected
from the wireless network.
And there's lots of different reasons for it
and as we talk about some of the other issues
that we experience with wireless connectivity,
all of these will tie back to being the cause
of intermittent wireless connectivity on your network.
Now, the second main cause of wireless connectivity issues,
and these can lead
to intermittent wireless connectivity as well,
is what's known as signal interference.
Now, signal interference means that there is something
that is causing issues with our signal.
Remember, when we're dealing with something like wifi,
or 802.11, we are primarily operating inside
the 2.4 gigahertz range and the 5 gigahertz range.
Now, the reason that those two frequency bands were chosen
is because the FCC, or Federal Communications Commission,
has those as open frequencies that anyone can use
for their consumer electronic devices
in a certain power range.
So this made it very inexpensive
to be able to use these ranges,
but it also means there's a lot of other devices
that are using these ranges too.
For example, in our older networks,
like wireless b, wireless g, and wireless n,
if you're operating in the 2.4 gigahertz spectrum
you're actually using the same frequency band
that microwave ovens do.
So if your wireless access point
happens to be located your office's break room
and every time somebody reheats their burrito
your wireless network goes down,
this could be because of signal interference
being caused by the microwave oven
because it's using that same 2.4 gigahertz spectrum
to be able to heat up that burrito.
Now in addition to things like microwaves,
we also have lots of other communication devices
that are operating in this 2.4 gigahertz
and 5 gigahertz spectrum.
For example, you might have a wireless security system
and those are operating in that same frequency band.
You might have wireless cameras or other IoT devices
and all of these operate inside of that same band
and this can actually cause signal interference.
In addition to all of that,
if you happen to be in an area that's very congested,
like an apartment building, a condo,
or a small office park,
you can actually have signal interference
from other wireless networks
that are located next door to you.
For example, if you're operating
in the 2.4 gigahertz spectrum
and you're using wireless b, g, or n,
you're actually competing for the same 11 channels
that everybody else is
and so we see a lot of channel overlap
and that causes signal interference.
To be able to spread out your networks
and avoid interference, you should always operate
on channels 1, 6, and 11
in the wireless b, g, or n spectrums.
Conversely, if you're operating
with wireless a, n, ac and ax,
there are more channels available
and therefore you are less prone to signal interference.
But again, if there's a lot of wireless networks
in your area those networks may experience
intermittent connections or slower speeds
because of the different interference
from the other networks in the area.
Now, one other area of signal interference
is actually physical interference.
If you happen to be located in a building
that uses a lot of steel or concrete,
this will actually block wireless signals
and this is a type of interference as well.
Now, the next issue you may come across
is what's known as a low signal strength.
Now, we measure this by using a thing called the RSSI.
The RSSI stands for the Received Signal Strength Indicator
and this RSSI is used to measure the signal strength
according to an index level and it gives us a value
in what's known as decibels, or dB.
Now, when we deal with
the received signal strength indicator,
anytime we have a higher value
this means we have a higher signal and less noise.
But if we have a lower value
this means we have more noise and less signal.
Now, one thing to keep in mind
is that RSSI is normally displayed in negative decibels.
So when I talk about having a lower value
this means you're going to have more noise and less signal.
Normally, this is going to be a number like negative 90
or negative 100, or something like that.
On the other hand, if you have a very strong RSSI
this is going to be something like negative 30, negative 40,
negative 50 and this means you have a very good
and strong wireless connection.
Now notice when I talk about a large number
I was actually using smaller numerical values
but that's because we're talking about negative numbers.
So when you're dealing with negative 30 to negative 50
we talk about having a strong signal or a larger number
than we do when we have something like
negative 90 to negative 100,
which is considered a very small number
or a very high noise environment for an RSSI.
So if you look at your RSSI and you have a very low number
what are you going to do to increase your signal strength?
Well, there's a couple things you can do.
First, you can increase the power being used
by your wireless device,
but in most wireless devices
this is not user configurable
because the Federal Communications Commission
puts limits on how much power you can use.
The second thing you can do is increase your antenna size.
If you're using a larger antenna,
you should be able to pick up a signal from further away
or relatively you're giving it more strength or more signal.
Now, the third thing you can do
is you can actually move closer to the source.
For example, if I'm in an office
and there's only one wireless hotspot
and that's sitting in the break room and my office
is all the way in the other side of the building,
I'm going to have a very weak RSSI.
To increase that I need to give it a bigger antenna
or I need to move closer to that source.
So if I'm sitting in the break room
I may have a value of negative 30 or negative 40,
but if I'm sitting in my office,
that's all the way on the other side of the building,
I might have have a value of negative 90 or negative 100
and that is considered a very weak signal.
When you have a weak signal two things are going to happen.
If the signal is extremely weak
you can have intermittent connectivity issues
because you can't maintain a connection with that network.
On the other hand,
if you can maintain a connection to the network
but you're in the weaker signal area
you're going to actually see speed decreases.
So instead of being able to get
the full 54 megabits per second with wireless g,
or 108, or 300, or 600 megabits per second with wireless n,
you're going to be getting much slower speeds.
So for example, instead of getting 54 with wireless g
you might only be getting one, or five,
or 10 megabits per second
depending on that signal strength.
So the goal here is to get a higher RSSI
by moving you closer to the access point,
increasing your antenna size,
or increasing the power of the transmission.
The final thing we need to consider
is when you have a standards mismatch.
Now remember, there are lots of different variations
to wireless networking.
We started out with wireless a, then we moved to b,
then g, then n, then ac, and now ax.
When you're dealing with these different networks
you can mix and match different clients
with those different access points
and many of the different access points have dual radios
so they can support all of these different bands.
Remember, wireless a, wireless n,
wireless ac, and wireless ax
all operate in the 5 gigahertz spectrum.
When you're dealing with wireless b, wireless g,
or wireless n, they operate in the 2.4 gigahertz spectrum.
Now these two spectrums are not compatible
and if you have a radio that only supports wireless g
it has to operate in 2.4 gigahertz mode.
It will not have the ability to communicate
in the 5 gigahertz band.
Similarly, if you have a modern device,
you probably have an 802.11 ac or ax network interface card.
These network interface cards only actually support
5 gigahertz for wireless ac and ax,
but many of them have a dual radio setup
where they put in a 2.4 gigahertz capable radio as well
so you can use backwards compatibility
and connect to wireless b, g, or n access points as well.
So let's say for example at your home
you have a wireless n access point.
That wireless n access point has two radios in it,
one at 2.4 gigahertz to support wireless b, g, and n,
and the other one at 5 gigahertz
to support wireless a, n, ac and ax.
Now let's talk about what happens
when three different clients connect to this access point.
The first client is going to be my iPhone
and my iPhone has an 802.11 ac wireless card inside of it
so when I connect to that wireless n router
I'm going to connect over 5 gigahertz,
but I'm going to downgrade into wireless n speeds
so I'm going to get a top speed of about
108 to 300 megabits per second
and I'm using the 5 gigahertz spectrum.
Second, I'm going to connect an old tablet to it.
This old tablet only has a wireless g network card in it
so when it connects to this access point
it's going to connect to the 2.4 gigahertz radio.
When it does this, that is now going to make the top speed
of that wireless connection at 54 megabits per second.
Now this is because my device only supports wireless g
so the access point is going to downgrade itself
and start talking at wireless g speeds
over that 2.4 gigahertz radio.
Now, that's not going to affect my iPhone
because my iPhone is on the 5 gigahertz radio
so it's still going to be operating at wireless n speeds
in the 5 gigahertz spectrum
and we'll be able to have that faster speed.
But this older client
that's now connecting at wireless g speeds
is going to be slowing down anything that's connecting
over that 2.4 gigahertz radio.
So now it's time to take out the third device.
I'm going to take an old wireless printer
that uses wireless n to be able to connect to this network.
Now unfortunately, the radio inside of this printer
is only going to operate at 2.4 gigahertz
because it's the older style of wireless n
but it could go up to a speed of 108 megabits per second.
Now, as it connects it's going to see
that that wireless access point is supporting somebody else
who's operating at wireless g though and because of this
it's going to have to downgrade itself
in a backwards compatibility mode to wireless g speeds.
So even though the printer is capable
of going up to 108 megabits per second
it can't actually reach those speeds
and will only reach 54 megabits per second
because everything connected to that 2.4 gigahertz section
of this wireless access point
is now going to be operating at wireless g speeds
and if I took a really old device that was wireless b
and connected it to it, it's going to drop from wireless g
down to wireless b at 11 megabits per second,
drastically decreasing our network performance.
So it's really important when you're troubleshooting
network performance issues on a wireless network
that you consider what frequency is being used,
what the maximum speed of that frequency is,
and which particular versions of wireless networking
is being used when they're connecting
to that wireless access point.
Remember, your wireless access points
can support older devices but when you do that
and you add that backwards compatibility
it will have that wireless access point
drop its speed to those lower levels.
So if you want to maintain the highest level of performance
you can configure your wireless access points
to only support the most modern versions of those protocols,
such as wireless n on the 2.4 gigahertz spectrum
and wireless ac or ax on the 5 gigahertz spectrum.
Or you can allow backwards compatibility
but you're going to have to understand
that you're going to take a huge network performance hit
anytime somebody with one of those older devices
connects to your network
and it's going to drag down the speeds
of every client that's connected
on that particular frequency.