-: Performance metrics. 2 2
In this lesson, we're going to talk 3 3
all about performance metrics and how they're used 4 4
to ensure network availability. 5 5
Now, network performance metrics are a large part 6 6
of network monitoring. 7 7
Network performance monitoring is the end-to-end 8 8
network monitoring of your end user experience. 9 9
This differs from traditional monitoring though, 10 10
because traditional monitoring is focused on performance 11 11
between two points, like a switch and a router, 12 12
but with network performance monitoring, 13 13
we're going to look at the overall end user experience 14 14
by monitoring the performance 15 15
from the end user's workstation to the final destination 16 16
that they're trying to reach. 17 17
So to help us monitor network performance, 18 18
there's really going to be three key metrics 19 19
that we're going to use. 20 20
These are latency, bandwidth and jitter. 21 21
The first metric is latency. 22 22
Now, latency is the measure of the time that it takes 23 23
for data to reach its destination across a network. 24 24
Usually we measure network latency as the round trip time 25 25
from a workstation to the distant end 26 26
and back to the workstation. 27 27
We report this time in milliseconds. 28 28
Now, for example, let's say you open up your command prompt 29 29
and you enter the command ping 8.8.8.8, and you hit enter. 30 30
You're going to get a response that tells you 31 31
how long it took for an ICNP packet to leave your computer 32 32
reach the Google DNS server located at eight dot 8.8.8.8 33 33
and return to your computer again. 34 34
In my case, this took an average time of 38.2 milliseconds 35 35
when I did it for four repetitive ping requests. 36 36
Now it's important to measure the round trip delay 37 37
for network latency because the computer that uses 38 38
a TCP IP network can send only a limited amount of data 39 39
to its destination at one time, 40 40
and then it sits and waits for an acknowledgement 41 41
that that data was received before it sends out 42 42
more data across the network. 43 43
So if you have high latency or a long round trip delay, 44 44
this can drastically slow down 45 45
your overall network performance for your end users. 46 46
Now, if you're seeing consistent delays 47 47
or even just spikes in the delay time in your network, 48 48
this could indicate a major performance issue 49 49
that's going to be occurring. 50 50
For regular web traffic these delays 51 51
aren't usually noticeable, 52 52
but if you're using streaming video applications, 53 53
things like voiceover IP, or you're playing video games, 54 54
these delays are extremely noticeable 55 55
and they can cause a lot of problems for your end users. 56 56
Our second metric media monitor is known as bandwidth. 57 57
Now bandwidth is the maximum rate of data transfer 58 58
across a given network. 59 59
Now, technically bandwidth is actually 60 60
a theoretical concept that measures how much data 61 61
could be transferred from a source to a destination 62 62
under ideal conditions. 63 63
But in reality, when we're talking about our networks 64 64
and our connections, they're rarely operating 65 65
at the perfect or ideal conditions. 66 66
Therefore we often measure something known as throughput 67 67
instead of bandwidth to monitor our network performance. 68 68
Throughput is the actual measure of data 69 69
as it's being successfully transferred 70 70
from the source to the destination, 71 71
but you'll often hear people use the terms 72 72
bandwidth and throughput interchangeably, 73 73
not realizing there is a difference. 74 74
Technically, bandwidth is a theoretical limit 75 75
where throughput is the reality of what you're achieving. 76 76
So if you want to a bandwidth speed test 77 77
or more accurately, a throughput test for your network, 78 78
you can go to something like speedtest.net and click on go, 79 79
and you'll have a series of downloads and uploads 80 80
that'll occur from your workstation 81 81
to their server and back. 82 82
Then it will report to you how fast or slow 83 83
your connection was in terms of throughput. 84 84
In this example, you can see my results indicate 85 85
I have a throughput with a top download speed 86 86
of 240 megabits per second, 87 87
and a top upload speed of around 241 megabits per second. 88 88
The problem with that is that my actual bandwidth, 89 89
my theoretical, limit should be 650 megabits per second 90 90
for downloads and 310 megabits per second for uploads. 91 91
So why is my throughput so much less? 92 92
Well, when I was doing this test, 93 93
I connected to my office network using my wifi adapter 94 94
and not directly connecting through a wired switch. 95 95
At the same time, there's other people 96 96
in the office using the connection, 97 97
and all of these factors lead to a less than ideal 98 98
environment and this makes my throughput much lower 99 99
than my expected bandwidth. 100 100
As I make different changes to my network, 101 101
I can retest the throughput to see if those changes 102 102
help or hurt my overall throughput. 103 103
For example, if I switched 104 104
from a wireless internet connection 105 105
to a wired internet connection, 106 106
I'll be able to see a dramatic increase 107 107
in overall throughput that I wouldn't see 108 108
over that wireless connection. 109 109
The third metric we need to monitor is known as jitter. 110 110
Jitter is the network condition that occurs 111 111
when a time delay in the sending of the data packets 112 112
over a network connection is occurring. 113 113
Now jitter is really a big problem 114 114
for any real-time applications that you may be supporting 115 115
on your network. 116 116
If you're doing things like video conferences 117 117
and voiceover IP, and virtual desktop infrastructure, 118 118
all of these are negatively affected by jitter. 119 119
Basically a jitter is simply a variation 120 120
in the delay of the packets. 121 121
And this can cause some really strange side effects, 122 122
especially for your voice and video calls. 123 123
If you've ever been in a video conference 124 124
and somebody starts speaking, 125 125
and then all of a sudden you hear their voice 126 126
start speeding up for about five or 10 seconds, 127 127
and then it returns back to normal speed, 128 128
that usually is because of jitter on their network. 129 129
If you have a good quality of service management in place, 130 130
you shouldn't experience a lot of jitter, 131 131
but if you're not doing QoS properly, 132 132
then jitter will occur. 133 133
You see, when your network suffers from congestion, 134 134
the network devices like your routers and switches 135 135
are going to be unable to send the equivalent amount of traffic 136 136
as what they're receiving. 137 137
This causes their packet buffers to start to fill up, 138 138
and eventually they'll start to drop packets 139 139
if they have too much in the buffers. 140 140
This is known as packet loss. 141 141
Now, when this happens, your TCP packets 142 142
are going to get resent, and this causes 143 143
increased network load again. 144 144
Now on the other hand, if the buffer begins to fill up, 145 145
but then the network congestion eases up 146 146
those buffers will be able to quickly send 147 147
all of their contents to the destination. 148 148
The destination will then try to process them all, 149 149
but usually it can't do that. 150 150
And this leads to delays in processing 151 151
that can result in jitter on the endpoint device as well. 152 152
So to prevent jitter, we want to ensure our network 153 153
is using quality of service properly. 154 154
We want to make sure we're categorizing 155 155
and prioritizing our voice and video traffic over 156 156
the other types of traffic. 157 157
Also, we need to verify our network connections 158 158
and our devices are large enough to support 159 159
the amount of data that we're trying to transfer. 160 160
As a network administrator, 161 161
it's your responsibility to always monitor 162 162
your network's performance and the three key metrics 163 163
you always should be keeping track of 164 164
are latency, bandwidth or throughput and jitter. 165 165
(logo buzzing)