-: Why do we need quality of service or QoS? 2 2
Well, nowadays we operate converge networks, 3 3
which means all of our networks are carrying voice, data 4 4
and video content over the same wire. 5 5
We don't have them all separate out like we used to. 6 6
We used to have networks for phones and ones for data 7 7
and ones for video, 8 8
but now everything's riding over the same IP networks. 9 9
So, because of this convergence of mediums, 10 10
we have these networks 11 11
that now have a high level availability 12 12
to ensure proper delivery 13 13
over all of these different medians, 14 14
because we want a phone to work 15 15
every time we pick up the phone, right? 16 16
Well, by using QoS, we can optimize our network 17 17
to efficiently utilize all the bandwidth at the right time 18 18
to deliver the right service to our users 19 19
and give a success and cost savings. 20 20
Now, we want to have an excellent quality of service, 21 21
an excellent service for our customers, 22 22
and that's what we're going to start doing by using QoS. 23 23
So what exactly is QoS? 24 24
Well, quality of service enables us 25 25
to strategically optimize our network performance 26 26
based on different types of traffic. 27 27
Previously, we talked about the fact 28 28
that we want to categorize our different traffic types. 29 29
I might have web traffic and voice traffic and video traffic 30 30
and email traffic. 31 31
And by categorizing it 32 32
and identifying these different types of traffic, 33 33
I can then prioritize that traffic and route it differently. 34 34
So I might determine how much bandwidth is required 35 35
for each of those types of traffic. 36 36
And I can efficiently use my wide area network links 37 37
and all that bandwidth available, for maximum utilization, 38 38
and save me bandwidth costs over time. 39 39
This can help me identify 40 40
the types of traffic that I should drop 41 41
whenever there's going to be some kind of congestion, 42 42
because if you look at the average load, 43 43
there's always going to be some peaks and some valleys. 44 44
And so we want to be able to figure that out. 45 45
So for example, here on the screen, 46 46
you can see the peaks and the valleys. 47 47
The peaks over time, 48 48
and we need to be able to categorize things 49 49
to fit within our bandwidth limitations. 50 50
So for example, if we have things like VoIP, 51 51
or voice over IP, or video service, 52 52
they need to have a higher priority, 53 53
because if I'm talking to you on a phone, 54 54
I don't want a high amount of latency. 55 55
From checking my bank balance, for instance, though, 56 56
I can wait another half a second for the web page to load. 57 57
From listening to you talk, that half a second delay 58 58
starts sending like an echo, 59 59
and it gives me a horrible service level. 60 60
So we want to be able to solve that, 61 61
and to do that, we use quality of service. 62 62
Now there are different categories of quality of service. 63 63
There are three big ones known as delay, jitter and drops. 64 64
When I talk about delay, 65 65
this happens when you look at the time 66 66
that a packet travels from the source to the destination, 67 67
this is measured in milliseconds, 68 68
and it's not a big deal if you're dealing with data traffic, 69 69
but if you're dealing with voice or video, 70 70
delay is an especially big thing, 71 71
especially if you're doing things live, 72 72
like talking on the phone or doing a live stream, 73 73
or something like that. 74 74
Now, jitter is an uneven arrival of packets, 75 75
and this is especially bad in voiceover IP traffic, 76 76
because you're using something like UDP. 77 77
And so if I sing something to you, like, "my name is Jason," 78 78
and you got "Jason my name is," 79 79
it sounds kind of weird, right? 80 80
Now, usually it's not big chunks like that, 81 81
but instead it's little bits 82 82
and you'll hear these glick and glock sounds 83 83
that make it jumble up because of that jitter. 84 84
And this really sounds bad, and it's a bad user experience 85 85
if you're using voiceover IP. 86 86
And so jitter is a really bad thing 87 87
when you're dealing with voice and video. 88 88
Now, the third thing we have is what's known as a drop. 89 89
Drops are going to occur during network congestion. 90 90
When the network becomes too congested, 91 91
the router simply can't keep up with demand, 92 92
and the queue starts overflowing, 93 93
and it'll start dropping packets. 94 94
This is the way it deals with packet loss, 95 95
and if you're using TCP, it'll just send it again. 96 96
But again, if I'm dealing with VoIP, VoIP is usually UDP. 97 97
And so if we're talking 98 98
and all of a sudden my voice cuts out like that, 99 99
that would be bad too. 100 100
That's why we don't want to have packet drop on a VoIP call. 101 101
And so we want to make sure that that doesn't happen. 102 102
These network drops are something that can be avoided 103 103
by doing the proper quality of service as well. 104 104
So when we deal with this, 105 105
we have to think about effective bandwidth. 106 106
What is our effective bandwidth? 107 107
This is an important concept. 108 108
So let's look at this client and this server. 109 109
There's probably a lot more to this network 110 110
than what I'm showing you here on the screen, 111 111
but I've simplified it down for this example. 112 112
Here, you can see I have my client on the left, 113 113
and he wants to talk to the server. 114 114
So he goes up through the switch, 115 115
which uses 100 megabit per second Cat-5 cable. 116 116
Then he goes through a WAN link 117 117
over a 256 kilobit per second connection 118 118
because he's using an old DSL line. 119 119
Then that connects from that ISP over a T1 connection 120 120
to another router. 121 121
That router connects to an E1 connection to another router. 122 122
And from that router, it goes down a WAN link 123 123
over a 512 kilobit per second connection, 124 124
and then down to a switch with a gigabit connection, 125 125
down to the server. 126 126
Now, what is my effective bandwidth? 127 127
Well, it's 256 kilobits per second, 128 128
because no matter how fast any of the other links are, 129 129
whatever the lowest link is inside of this connection, 130 130
that is going to be your effective bandwidth. 131 131
So we talked about quality of service categories, 132 132
in our next lesson, we're going to be talking about 133 133
how we can alleviate this problem 134 134
of this effective bandwidth, and try to get more out of it, 135 135
because we need to be able 136 136
to increase our available bandwidth, but in this example, 137 137
we're limited to 256 kilobits, 138 138
which is going to be really, really slow for us. 139 139
Now, I like to think about effective bandwidth 140 140
like water flowing through pipes. 141 141
I can have big pipes and I can have little pipes. 142 142
And if I have little pipes, 143 143
I'm going to get less water per second through it 144 144
than if I have a really big pipe. 145 145
And so this is the idea, if you think about a big funnel, 146 146
it can start to back up on us, right? 147 147
That's the concept, 148 148
And we have to figure out how we can fix that 149 149
by using quality of service effectively, 150 150
which we're going to discuss more in the next video.