Instructor: Now up to this point
I've mentioned a few wireless standards
like B and G, N, and AC.
Next I'm going to provide you with a nice little summary chart
that's going to cover all the wireless networking standards
that you need to memorize for the exam.
This is one that I would print out and memorize.
You need to know the standard and you need to know the band,
and you need to know the maximum bandwidth.
These three pieces of information are very important.
Now, when we started out with wireless networks
all the way back in the early 1990s,
we only had the 802.11 standard.
This standard though, was not commercially viable.
It was essentially a big proof of concept.
It didn't really make it into the marketplace.
It operated in the 2.4 gigahertz spectrum,
but it only operated
at about one to two megabits per second.
Now, for your chart,
I wouldn't even bother writing that one down.
Instead, you need to know about
A, B, G, N, AC and AX for our exam.
Those six Wi-Fi types are the ones you need to memorize
for the exam with those three pieces of critical information
to make sure you're successful on the exam
for wireless networking questions.
Let's talk about each one now.
First, let's talk about Wireless A or 802.11a.
This operated in the 5 gigahertz spectrum,
which was a very expensive radio
to build and manufacturer at that time,
but it did give us a good amount of speed
because it operated at 54 megabits per second.
This was really good in the late nineties,
but again, unfortunately it cost a lot of money.
Because of that high cost
only business users really ended up using it,
and it wasn't really that commercially viable
in the mainstream market.
Now, since it wasn't getting as much traction
in the commercial markets,
they decided to make something cheaper and easier,
so the manufacturers decided to create Wireless B,
which operates in the 2.4 gigahertz spectrum.
Now, this frequency range is commonly used
by a lot of other household devices,
things like security cameras, walkie-talkies,
baby monitors, microwaves, and more.
Now, this made the radios in the 802.11b wireless devices
very cheap and easy to get,
and it led to widespread adoption of Wi-Fi throughout homes,
businesses, and schools, bringing us to where we are today.
Now using this cheaper chipset
and the way the frequencies worked
actually slowed down our networks,
so we went from 54 megabits per second
down to 11 megabits per second,
which today sounds extremely slow,
but again, we're talking about the late 1990s here.
We weren't doing a lot of streaming video,
and so 11 megabits per second was actually fast enough
for most home users.
Now, over time though, networks got faster
and we wanted more speed,
and so Wireless G came out as a replacement for Wireless B.
Now, wireless 802.11g is also in the 2.4 gigahertz spectrum,
but it operates at 54 megabits per second.
Now, eventually we wanted to go even faster than this,
so engineers kept working on new solutions
and new ways to manipulate the frequencies,
and eventually they came up with Wireless N,
which is also called Wi-Fi 4
since it was the fourth generation of Wi-Fi.
Now 802.11n really wanted to increase speed,
so moved back to the 5 gigahertz spectrum again.
And this allowed it to get up to speeds
of 300 to 600 megabits per second.
This allowed for really fast networks,
but the big problem
is that this newer 5 gigahertz spectrum
wasn't compatible with all the existing devices
that were out there
because they were Wireless B and G,
and they operate at 2.4 gigahertz.
So people were resistant to buying Wireless N at first.
Now, to overcome this,
manufacturers started making hybrid devices
that were marketed under the name Wireless N,
and these type of devices had a wireless access point
with two sets of radios in them.
One was for the 2.4 gigahertz spectrum
and one for the 5 gigahertz spectrum.
This way, if you had a mixture of devices
that were 802.11b and G and N,
you could connect to the slower 2.4 gigahertz spectrum,
and it would support Wireless B speeds, Wireless G speeds
or newer Wireless N speeds,
that went up to about 150 megabits per second.
Now, if someone connected
to the more modern Wireless N radios
using the 5 gigahertz spectrum,
they could actually reach speeds
up to 600 megabits per second
by using a technology known as MIMO.
MIMO stands for multiple input and multiple output,
which means that the access point
could use multiple antennas to send and receive data
instead of putting it all through a single antenna.
Essentially, your data was going to be split
across multiple antennas and was received on the other end,
it was multiplexed back into a single data stream
for processing.
This is why you can see Wireless N access points
that have one, two, three, or even 5 antennas
because the more antennas you had,
the more data transfer they could support simultaneously.
Next, we have Wireless AC,
which is also called Wi-Fi 5 or 802.11ac.
This was the fifth generation of Wi-Fi.
Now, Wireless AC operates exclusively
in the 5 gigahertz spectrum,
and technically it does not provide
any kind of backward compatibility.
These 802.11ac networks
can operate at speeds up to 6.9 gigabits per second or more.
These networks are really fast in theory.
Now to achieve these higher speeds,
802.11ac networks uses a technology known as MU-MIMO,
which is multiple user multiple input multiple output.
It's a newer variation of the MIMO technology
that was first developed back with 802.11n networks.
Now, MU-MIMO is a multi-path
wireless communication technology
that allows multiple users to access the wireless network
and access point at the same time.
This is different than a regular MIMO
where a single user support it at one time
and the access point switches between users
to share the bandwidth across all the users
who are requesting services.
So if you only have one person requesting services,
they get a really fast network,
but if you have two or three, it starts slowing down
because you have to share the bandwidth.
Essentially, with MIMO,
the wireless network acts more like a hub,
but with MU-MIMO, it begins to act more like a switch
and helps avoid collisions and congestion.
Now, when it comes to Wireless AC,
some of the original and older AC devices
actually still use the older MIMO technology,
whereas the newer Wireless AC devices
will use the MU-MIMO for faster speeds.
Now, this brings us to the latest generation
of wireless networks, 802.11ax.
Wireless AX is known as Wi-Fi 6
because it's the sixth generation of wireless networks.
This was introduced in 2021,
and it can be used in the 2.4 gigahertz
and 5 gigahertz spectrum under the marketing term Wi-Fi 6
or in the newer and faster 6 gigahertz spectrum
under the marketing term Wi-Fi 6E
or high efficiency Wi-Fi.
Now, these Wi-Fi 6 and Wi-Fi 6E networks,
these 802.11ax networks,
can reach speeds up to 9.6 gigabits per second
using MU-MIMO technology.
Also, because these access points
have both the 2.4 gigahertz
and 5 gigahertz radios inside them,
they're fully backwards compatible with all devices,
including Wireless A, B, G, N, and AC.
All right, for the exam,
I want you to remember
there are different wireless networks out there.
These include A, B, G, N, AC, and AX.
You also need to remember
that if it's A, B, G, N, or AX network,
it's going to support 2.4 gigahertz as a spectrum.
If it's A, N, AC, or AX,
it supports 5 gigahertz as a spectrum.
You also need to remember the relative speeds
of these different wireless devices
going from 11 megabits per second for Wireless B,
all the way up to the gigabits per second
used in AC and AX networks.
This is important for the exam
because on Test A, you may get questions about frequencies,
things like which of these frequencies
do not support 5 gigahertz,
and the answer would have to be either B or G
for Wireless B and Wireless G.
Now you may get a question asking you to select
which wireless standard doesn't support 2.4 gigahertz,
and in this case,
you'd need to select Wireless A or Wireless AC.
If they wanted to make it more difficult for you,
They can ask the question
as more of a troubleshooting scenario.
For example, you are working as a network technician
on an older laptop,
and it's failing to connect to your Wireless AC network.
You check the laptop and see
that it has a Wireless B network card.
What is the problem?
Then you're going to find the answer
that has something to do with the fact
that there's a frequency mismatch
because Wireless AC supports 5 gigahertz
and Wireless B supports 2.4 gigahertz
and therefore you can't connect to the network.
Now, one more thing to keep in mind as you're studying
is that marketers sometimes mislabel things
to make it easier for our consumers,
but on test day, you have to go by the official standards.
A great example of this is Wireless AC,
the 802.11ac standard.
It only specifies operation
in the 5 gigahertz frequency band,
but if you go to the store,
and you find a Wireless AC access point,
the box will tell you
it supports both 5 gigahertz and 2.4 gigahertz.
This is a lie, and you will get in trouble on the exam
if you pick this answer
because you think it's dual band, and it's not.
The truth is Wireless AC
only operates in the 5 gigahertz spectrum.
When you're buying
that Wireless AC access point at the store,
and it says it supports both frequencies,
it's actually a wireless access point with two radios in it.
One radio is 5 gigahertz for Wireless AC
at speeds up to about 1300 megabits per second.
The other one is a 2.4 gigahertz radio for Wireless N
at speeds of up to 600 megabits per second
with a MIMO antenna configuration.
Now while in real life, your users really don't care
and they just say, hey, I have a wireless AC access point,
and they think it supports both 5 gigahertz
and 2.4 gigahertz,
on the exam you will get the question wrong
if you select 2.4 gigahertz for Wireless AC.
Remember, Wireless AC only supports 5 gigahertz
for its operations.
The only dual band standards we have
are Wireless N and Wireless AX.
Both of those support both 2.4 gigahertz
and 5 gigahertz frequency bands per the 802.11 standards.
Now let's talk about radio frequency interference
or RFI for a minute here.
Radio frequency interference is caused
when there are similar frequencies to wireless networks
in your area.
For example, I mentioned earlier
that one of the reasons we went to 2.4 gigahertz for Wi-Fi B
was the fact that there was other radios out there
that already used it.
Things like baby monitors and cordless phones
and microwave ovens and other security devices.
Now, this means that 2.4 gigahertz
as a spectrum is fairly crowded.
This is what made the radios cheap,
but it made it very difficult for us
because it causes a lot of interference.
Over time, as more and more devices
moved into the 5 gigahertz spectrum,
there's also more interference in that area too.
All these other electronics can cause interference
with your wireless networks,
so you have to think about these things
as you're developing your networks
and troubleshooting your networks.
For example,
if you have a 2.4 gigahertz Wireless G network in use
and the access point happens
to be sitting in the break room at the office
and every time somebody turns on the microwave
to reheat their burrito, the network drops,
this is probably because the 2.4 gigahertz frequency
is being interfered with by those microwaves
that are operating in that same frequency band.
In addition to all this frequency interference,
you might also see things like physical interference.
This is where physical things
can block your wireless signals.
For instance, I live in Puerto Rico
and the walls in my house are solid concrete.
I also have a refrigerator inside my kitchen.
I have kitchen cabinets and those block the signal.
All these things can cause signal strength issues for you.
If your signals are too weak,
and it can't make it around a corner
or through a wall, that signal is going to get blocked,
or it suffers what's known as attenuation.
All of these things can lead to interference,
which will slow down your ability
for your network to operate at top speed.
As your signal decreases in strength
or interference increases,
we get a worse signal-to-noise ratio.
This is going to cause additional retransmissions
because most of the time we're sending things over TCP.
When TCP retransmits,
this creates additional network baggage
that's being taken up and bandwidth that's being used
for all these retransmissions,
and this slows down the network even more.
You want to make sure you have good signal
throughout your entire structure
to increase the efficiency of your network.
To do this, you would do what's called a site survey
where you check the signal strength in different areas
and make sure you have the right antennas
and the right repeaters throughout the building.