In this lesson,
we're going to talk all about performance
metrics and how they're used to ensure network availability.
Now, network performance metrics are a large
part of network monitoring.
Network performance monitoring is the end-to-end network
monitoring of your end user experience.
This differs from traditional monitoring though,
because traditional monitoring is focused on performance
between two points, like a switch and a router.
But with network performance monitoring,
we're going to look at the overall end user experience
by monitoring the performance from the end user's
workstation to the final destination
that they're trying to reach.
So to help us monitor network performance,
there's really going to be three key
metrics that we're going to use.
These are latency, bandwidth, and jitter.
The first metric is latency.
Now latency is the measure of the time that it takes
for data to reach its destination across a network.
Usually we measure network latency
as the round trip time from a workstation to the destination
and back to the workstation.
We report this time in milliseconds.
Now, for example, let's say you opened up your command
prompt and you enter the command ping 8.8.8.8,
and you hit enter.
You're going to get a response
that tells you how long it took
for an ICMP packet to leave your computer,
reach the Google DNS server located at 8.8.8.8,
and return to your computer again, in my case,
this took an average time of 38.2 milliseconds when I did it
for four repetitive ping requests.
Now, it's important to measure the roundtrip delay
for network latency
because a computer that uses a TCP/IP network can send
only a limited amount of data
to its destination at one time, and then it sits
and waits for an acknowledgement that that data was received
before it sends out more data across the network.
So if you have high latency
or a long roundtrip delay,
this can drastically slow down your overall network
performance for your end users.
Now, if you're seeing consistent delays
or even just spikes in the delay time in your network,
this could indicate a major performance issue
that's going to be occurring.
For regular web traffic,
these delays aren't usually noticeable,
but if you're using streaming video applications,
things like Voice over IP
or you're playing video games,
these delays are extremely noticeable
and they can cause a lot of problems for your end users.
Our second metric medium monitor is known as bandwidth.
Now, bandwidth is the maximum rate
of data transfer across a given network.
Now, technically, bandwidth is actually a theoretical
concept that measures
how much data could be transferred from a source
to a destination under ideal conditions.
But in reality, when we're talking about our networks in our
connections, they're rarely operating at the perfect
or ideal conditions.
Therefore, we often measure something known
as throughput instead of bandwidth
to monitor our network performance.
Throughput is the actual measure of data
as it's being successfully transferred from the
source to the destination.
But you'll often hear people use the terms bandwidth
and throughput interchangeably,
not realizing there is a difference.
Technically, bandwidth is a theoretical limit
where throughput is the reality of what you're achieving.
So if you want to do a bandwidth speed test
or more accurately a throughput test for your network,
you can go to something like speedtest.net and click on go,
and you'll have a series of downloads
and uploads that'll occur from your workstation
to their server and back.
Then it'll report to you how fast
or slow your connection was in terms of throughput.
In this example, you can see my results indicate I have a
throughput with a top download speed
of 240 megabits per second
and a top upload speed of around 241 megabits per second.
The problem with that is that my actual bandwidth,
my theoretical limit should be 650 megabits per second
for downloads and 310 megabits per second for uploads.
So why is my throughput so much less?
Well, when I was doing this test, I connected
to my office network using my wifi adapter
and not directly connecting through a wired switch.
At the same time, there's other people in the office using
the connection and all these factors lead
to a less than ideal environment,
and this makes my throughput much lower than
my expected bandwidth.
As I make different changes to my network,
I can retest the throughput to see if those changes help
or hurt my overall throughput.
For example, if I switch from a wireless internet connection
to a wired internet connection, I'll be able
to see a dramatic increase in overall throughput
that I wouldn't see over that wireless connection.
The third metric we need to monitor is known as jitter.
Jitter is the network condition
that occurs when a time delay in the sending
of the data packets over a network connection is occurring.
Now jitter is really a big problem
for any real time applications
that you may be supporting on your network.
If you're doing things like video conferences
and Voice over IP
and virtual desktop infrastructure, all
of these are negatively affected by jitter.
Basically, a jitter is simply a variation in
the delay of the packets.
And this can cause some really strange side effects,
especially for your voice and video calls.
If you've ever been in a video conference
and somebody starts speaking
and then all of a sudden you hear their voice starts
speeding up for about five or 10 seconds
and then it returns back to normal speed, that usually is
because of jitter on their network.
If you have a good quality of service management in place,
you shouldn't experience a lot of jitter.
But if you're not doing QoS properly,
then jitter will occur.
You see, when your network suffers from congestion,
the network devices like your routers
and switches are going to be unable
to send the equivalent amount of traffic
as what they're receiving.
This causes their packet buffers to start to fill up,
and eventually they'll start
to drop packets if they have too much in the buffers.
This is known as packet loss.
Now, when this happens,
your TCP packets are going to get reset,
and this causes increased network load again.
Now, on the other hand, if the buffer begins to fill up,
but then the network congestion eases up,
those buffers will be able to quickly send all
of their contents to the destination.
The destination will then try to process them all,
but usually it can't do that.
And this leads to delays in processing
that can result in jitter on the endpoint device as well.
So to prevent jitter,
we want to ensure our network is using
quality of service properly.
We want to make sure we're categorizing
and prioritizing our voice
and video traffic over the other types of traffic.
Also, we need to verify our network connections and our
devices are large enough to support the amount of data
that we're trying to transfer.
As a network administrator, it's your responsibility
to always monitor your network's performance.
And the three key metrics you always should be keeping track
of are latency, bandwidth or throughput, and jitter.