- Let's take a look in this video at how we can do
quality of service in a wireless LAN environment.
Wireless LAN's often support a feature called WMM,
or Wi-Fi Multimedia.
And what WMM does is it gives us four different categories
for accessing the wireless network.
It gives us four access categories
and here are their names.
We have one for the background traffic,
that's low priority.
Best effort, just average priority.
We've got a class, or a category, for video
and a category for voice.
And on screen you see the different names
given to those different categories.
And how we put traffic in the categories
is we take a .1P marking map from a client.
And we put it in one of the categories,
based on that .1P marking map.
Now an 802.1P marking is supported by some network clients
and what we're doing is,
we're adding four bytes onto our frames.
It's a lot like adding four bytes on a .1Q truck.
In fact, it looks almost identical to that.
The big difference is the VLAN field is all zeros.
We're not identifying a VLAN membership,
we're just adding those four bytes
so that we can use three bits in those bytes
to identify the priority of a frame.
So, we've got three bits at our disposal.
How many possible values is that?
It's eight.
Two raised over a third power is eight.
So, we've got values in the range of zero through seven.
And on screen you'll see how
the .1P markings in the range zero through seven
map to these different access categories.
Now, if we're in one category versus another,
what exactly does that mean?
Well, your category membership influences
Interframe Space and the Random Backoff Timer
that you're going to be using.
Here's what I mean.
When we're sending frames out in a wireless network
there is a gap that we have between those frames,
that's called the IFS.
The Interframe Space.
Well, for higher priority traffic,
for example the voice, the video categories,
we start to use smaller and smaller Interframe Spaces.
So, we're sending more aggressively.
Also, wireless networks can use CSMA/CA,
Carrier-Sense Multiple Access with Collision Avoidance.
What that's going to do,
is it's going to listen to the airwaves
to see if it's free to send right now.
Now this is prior to Wi-Fi six.
With Wi-Fi Six, or 802.11ax,
we start to move away from this a little bit
and we're given time slots in which we can send
so we don't have this contention issue.
But traditional wireless LAN's
would listen to the airwaves
to see if it's free to send right now.
And if it is, they'll send.
If not, they'll wait a random amount of time
and they'll try again.
Well, that random amount of time gets smaller and smaller
as we increase our priorities,
as we go up in the stack that you see on screen.
Again, the idea is the higher the access category,
the more aggressively we're trying to send our traffic.
And that's the way that we can take a .1P marking
on a network client
and translate that into how aggressively
we're going to be trying to send it
on the wireless network.
Now let's go out to a CISCO Wireless LAN Controller
and take a look
at how we could assign one of these WMM categories perhaps,
to an entire wireless LAN.
What we can do with the CISCO Wireless LAN Controller,
and we're sitting at the management screen
of one of those controllers here.
What we can do is assign different wireless LAN's
for different traffic types.
We might put video in one wireless LAN,
voice in another,
and so on.
And for the wireless LAN that I have.
Let's go in to WLAN's.
And I've got one called CCNA
that I use for my CCNA training.
Notice that there's a tab that says QoS.
If we go to that tab
we see that we can specify the quality of service
for this wireless LAN.
And these are the four categories we talked about.
Background, Best Effort, Video and Voice.
And right now, this CCNA wireless LAN
is just set to Best Effort.
But that's a look at how we can go in
and set the access category for a particular
wireless LAN on a CISCO Wireless LAN Controller.