If you're connecting a wireless device for the first time,
simply choosing a random frequency
and plugging into the network is probably not
going to be your best course of action.
You may find that you're conflicting with other devices
and other frequencies that are in use,
and therefore the performance of your wireless network
is going to suffer.
The first thing you should do is to perform a site survey.
You need to understand exactly what frequencies are in use
and how you could best configure your access point to work
optimally in that environment.
There are many different tools you
can use to help find all of these different access points.
It might be a free piece of software, or something
commercial that you can purchase.
Or you're getting a full blown spectrum analyzer
and really trying to understand exactly what frequencies
are in use at that location.
Once you have that information, you
can then start determining what particular frequencies are
open or available or which ones are not being used
as much as other frequencies.
This way you can plan where you want to put an access point
and then decide what frequencies should
be used by that particular access point.
Of course, not everybody's going to follow this formal process
when they start setting up their wireless network.
And if there are other organizations
in the same general area as you, you
may find that they are now conflicting with your network
configuration.
So you may want to plan to do ongoing site surveys.
Come back every month or every three months or every six
months, and make sure that the wireless environment is running
as optimally as possible.
One thing you can do is to perform something
like this, a heat map.
This is a piece of software I downloaded
that allowed me to walk around a particular area.
You could even put the diagram of the area as the background.
And as you move, it knows exactly where
you are in relation to the access point.
And it can start to show you in color view
exactly where the signal is very good
and where the signal is very bad.
And you could walk inside of your building, outside
of your building, and get a better understanding
of exactly where the frequencies are in use
for your wireless network.
There are so many different wireless frequencies that we
use for our wireless network.
It is a subset of the 2.4 gigahertz and 5 gigahertz
frequency ranges.
And they are very standardized for all
of the different wireless types.
The IEEE standards will dictate what frequencies are in use,
and governments also control exactly how much
of those particular frequencies are
available in a particular country.
We are going to look at 802.11 a, 802.11 b, g, n, and ac.
There are a lot of different standards in between that,
but those are the main wireless standards
that you will run into.
And you need to understand what frequencies
each one of these particular standards use.
You'll need to understand, therefore,
that each one of these standards uses different speeds.
There's going to be different distances that
are supported because of the frequencies and the type
of modulation in use.
They're using different channels,
which is how we block out the different frequencies in all
these different standards.
And the frequencies, themselves, are
controlled by governmental agencies, which
may limit exactly which frequencies you can
use in a particular country.
Let's look at how 802.11 b uses the 2.4 gigahertz range.
802.11 b uses a modulation type over this wireless network
of direct sequence spread spectrum or DSSS.
This is how it sends the wireless signal from one device
to another over this 802.11 b network.
It uses this mechanism called chipping.
It takes a certain chunk of data,
chips it, and sends it out over a number
of different frequencies.
It's a very pre-defined order.
As this information is being sent,
it's expected to be received in a very pre-defined order
on the other side.
That is the spread spectrum part of the DSSS.
There are generally 14 channels that you can use.
These channels correlate to very specific 2.4 gigahertz
frequencies.
For example, channel one is 2412, megahertz,
channel 11 is 2462 megahertz.
So there's a gap between these different channels
and they overlap themselves quite a bit.
Each channel is about 22 megahertz wide,
and they're spaced at 5 megahertz intervals.
So by simply looking at that, you
can see there is extensive overlap
for each one of these frequency ranges.
That's why we have certain channels that do not
overlap with 2.4 gigahertz.
On 802.11 b, channel one, channel six, and channel 11,
for instance, do not overlap with each other,
at least not here in the United States.
In the US, we can't use any frequencies above that channel
11, but it can go all the way up to channel
14, which may be in use in your particular country.
So you need to look at the different frequencies
that are being used, and what you'll generally
find is if it is an 802.11 b network,
it is running on channel one, channel six, or channel 11.
The 2.4 gigahertz range is also used
by a 802.11 g and 802.11 n.
It uses a different modulation type
to send the information though.
It uses orthogonal frequency division multiplexing, or OFDM.
This is the same modulation type we use for 802.11 a.
It's using the same frequencies as we were just
looking at in the 802.11 b.
It's just using that different modulation type of OFDM,
instead of using DSSS.
So if we start looking at the overlap of channels,
it's exactly the same for 802.11 g and 802.11 in.
We have channels one channel six, and channel 11.
If it needs to use slower speeds,
it effectively reverts back to the 802.11 b mechanism.
So you may see also modulations DSSS
if you're using these slower speeds on 802.11 g or 802.11 n.
In a later video, we'll look at the details of speeds
between all of these different wireless standards,
but one important thing to know is
that 802.11 n provides for much higher speeds than 802.11 g,
and it does that in part by using
much more of the frequency.
You can see that 802.11 n uses a 40 megahertz wide channel.
You can see it's about twice as wide as what we saw with 802.11
b or 802.11 g.
And you can really only have one particular frequency,
so that you're not overlapping with any others
in this particular frequency range.
So channel three is generally what you'll see for 802.11 n,
but of course you can adjust things
depending on what other frequencies may be
in use in your particular area.
Here's a better view of all these non-overlapping channels.
You can see with 802.11 b is our channel one,
our channel six, channel 11, and then the channel
14 at the very top.
These channels are 22 megahertz wide.
For 802.11 g and n, the channels are 20 megahertz wide,
but still we have that non-overlapping channel
at channel one, channel six, and channel 11.
And as I mentioned 802.11 n has twice the size of the channel
width at 40 megahertz, so you can have the higher speeds
for those 802.11 n networks.
Another section or frequencies available for our wireless
networks are the five gigahertz frequencies.
We see these being used for 802.11 a.
802.11 n, and 802.11 ac.
Five gigahertz frequencies are not used for 802.11 b or g.
For 802.11 a, were using dynamic frequency selection
to determine what frequencies to use.
There are a number of military uses for these five megahertz
frequencies.
So by using DFS, were able to avoid conflicting
with radar that's being used for weather or military satellite
use.
This is using that same frequency modulation we
were looking at before of OFDM.
It allows us to send multiple data streams
even though we're using a fixed type of bandwidth.
There are 23 non-overlapping channels available in this five
gigahertz range.
And of course, the availability of the frequencies
will differ depending on what country you're in.
To get some of these higher speeds in 802.11 n,
we take advantage of something called MIMO.
This stands for multiple input and multiple output.
There's a single receiver in 802.11 n,
but you can have more than one antenna,
So you can send and receive on different channels
at the same time.
You can support up to four transmit and four received.
So there's four separate data streams
that can all be communicating at the same time with 802.11 n.
802.11 ac takes this another step farther
with multi-user MIMO, or MUMIMO.
With multi-user MIMO in 802.11 ac,
you can have up to four separate receivers
inside of an access point with multiple antennas
on each of those.
And with that particular architecture,
you're able to get multi gigabit speeds out
of these wireless networks on 802.11 ac.
There's a large emphasis for backwards compatibility
when you start using these wireless networks.
That way you could have an older 802.11 b device, but still
have it communicate even though you have an 802.11 n access
point.
It uses a mechanism called high throughput mode
to determine how it's going to work
and how backwards compatible it's going to be.
For 802.11 n, this high throughput mode
is also called a greenfield mode,
because it doesn't support any of the legacy devices.
You have to have everything running at 802.11 n.
This is also going to give you the highest throughput
for the 802.11 n networks, because it doesn't have
to be the older backwards compatible and slower network
communication used in the older standards.
If you do have legacy devices, you
might want to consider running your 802.11 n access
point in legacy mode.
This is a non-high throughput mode.
It uses those 20 megahertz channels,
so you're not getting the larger 40 megahertz channels.
So you're not going to get the 802.11 n speeds,
but if you have older equipment that can't run at those higher
speeds, this may be a good way to configure your access point,
at least until you get everyone upgraded.
You might also have an option inside
of your access point for a high throughput mixed mode.
And in mixed mode you're able to run 802.11 n and 802.11 b
and g at the same time.
You're n devices are not going to run
at the full capabilities of n.
And your b and g devices obviously won't run at n speeds
either, but this does allow you to have
all of those devices running on your network at the same time.
With goodput, you are defining how fast the application
can transfer the information.
You're not worried about the network mechanisms
or how fast the network is running.
You're only interested in knowing the maximum throughput
for your application.
And when you look at throughput from an application level,
we always refer to that as goodput.