Why do we need quality of service, or QoS?
Well, nowadays, we operate converged networks,
which means all of our networks are carrying voice, data,
and video content over the same wire.
We don't have them all separated out, like we used to.
We used to have networks for phones
and one's for data and one's for video.
But now, everything's riding over the same IP networks.
So because of this convergence of mediums,
we have these networks
that now have a high level of availability
to ensure proper delivery
over all of these different mediums
because we want a phone to work
every time we pick up the phone, right?
Well, by using QoS, we can optimize our network
to efficiently utilize all the bandwidth at the right time
to deliver the right service to our users
and give us success and cost savings.
Now, we want to have an excellent quality of service,
an excellent service for our customers,
and that's what we're going to start doing by using QoS.
So what exactly is QoS?
Well, Quality of Service enables us
to strategically optimize our network performance
based on different types of traffic.
Previously, we talked about the fact
that we want to categorize our different traffic types.
I might have web traffic and voice traffic
and video traffic and email traffic.
And by categorizing it
and identifying these different types of traffic,
I can then prioritize that traffic and route it differently.
So I might determine how much bandwidth is required
for each of those types of traffic.
And I can efficiently use my Wide Area Network links
and all that bandwidth available for maximum utilization
and save me bandwidth cost over time.
This can help me identify the types of traffic
that I should drop whenever there's going to be some kind
of congestion, because if you look at the average load,
there's always going to be some peaks and some valleys.
And so we want to be able to figure that out,
and we need to be able to categorize things
to fit within our bandwidth limitations.
So for example, if we have things like VoIP, or Voiceover IP
or video service, they need to have a higher priority
because if I'm talking to you on a phone,
I don't want a high amount of latency.
If I'm checking my bank balances, for instance, though,
I can wait another half a second for the webpage to load.
If I'm listening to you talk,
that half a second delay starts sounding like an echo,
and it gives me a horrible service level.
So we want to be able to solve that.
And to do that, we use Quality of Service.
Now, there are different categories of Quality of Service.
There are three big ones known as Delay, Jitter and Drops.
When I talk about Delay,
this happens when you look at the time
that a packet travels from the source to the destination.
This is measured in milliseconds,
and it's not a big deal if you're dealing with data traffic,
but if you're dealing with voice or video,
Delay is an especially big thing,
especially if you're doing things live,
like talking on the phone
or doing a livestream or something like that.
Now, Jitter is an uneven arrival of packets,
and this is especially bad in Voiceover IP traffic
because you're using something like UDP.
And so if I was saying something to you like,
"My name is Jason," and you got, "Jason, my name is,"
it sounds kind of weird, right?
Now, usually, it's not big chunks like that,
but instead, it's little bits, and you'll hear these glick
and glock sounds that kind of make it jumble up
because of that Jitter, and this really sounds bad,
and it's a bad user experience if you're using Voiceover IP.
And so Jitter is a really bad thing
when you're dealing with voice and video.
Now, the third thing we have is what's known as a Drop.
Drops are going to occur during network congestion.
When the network becomes too congested,
the router simply can't keep up with demand
and the queue starts overflowing
and it'll start dropping packets.
This is the way it deals with packet loss,
and if you're using TCP, it'll just send it again.
But again, if I'm dealing with VoIP, VoIP is usually UDP.
And so if we're talking and, all of a sudden,
my voice cuts out like that, that would be bad too.
That's why we don't want to have packet Drop on a VoIP call,
and so we want to make sure that that doesn't happen.
These network Drops are something that can be avoided
by doing the proper Quality of Service as well.
So when we deal with this,
we have to think about effective bandwidth.
What is our effective bandwidth?
This is an important concept.
So let's look at this client and this server.
There's probably a lot more to this network
than what I'm showing you here on the screen,
but I simplified it down for this example.
Here, you can see, I have my client on the left
and he wants to talk to the server.
So he goes up through the switch,
which uses 100 megabit per second CAT-5 cable.
Then he goes through a WAN link over a 256 kilobit
per second connection because he is using an old DSL line.
Then that connects from that ISP over a T-1 connection
to another router.
That router connects through an E-1 connection
to another router, and from that router,
it goes down a WAN link over a 512 kilobit per second
connection, and then down to a switch
with a gigabit connection down to the server.
Now, what is my effective bandwidth?
Well, it's 256 kilobits per second,
because no matter how fast any of the other links are,
whatever the lowest link is inside of this connection,
that is going to be your effective bandwidth.
So when we talk about Quality of Service categories
in our next lesson, we're going to be talking
about how we can alleviate this problem
of this effective bandwidth and try to get more out of it
because we need to be able to increase
our available bandwidth.
But in this example, we're limited to 256 kilobits,
which is going to be really, really slow for us.
Now, I like to think about effective bandwidth
like water flowing through pipes.
I can have big pipes and I can have little pipes,
and if I have little pipes,
I'm going to get less water per second through it
than if I have a really big pipe.
And so this is the idea.
If you think about a big funnel,
it can start to back up on us, right?
That's the concept, and we have to figure out
how we can fix that by using Quality of Service effectively,
which we're going to discuss more in the next video.