what important networking-troubleshooting tool is part of icmp
HartJohnson,United States,Professional
Published Date:02-08-2017
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3 tools and troubleshooting
Into the Wire
Doesn’t she
get my signal?
Oh I do, but you’re not
understanding my signal.
How do you know when a network signal isn’t getting through
a network cable? Often the first thing you’ll hear about it is when the network stops
working effectively, but the trouble is, it’s hard to tell what’s wrong by just looking at a cable.
Fortunately, there’s a raft of tools you can use that let you see deep into the heart of your
network cables, down to the signal itself. Keep reading, and we’ll show you how to use these
tools to troubleshoot your networks, and how to interpret the secrets of the signal.
this is a new chapter 85
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Mighty Gumball won the Super Bowl contract
Mighty Gumball is the leading vendor of a wide variety of candies and chocolates,
and they’ve just won an exclusive contract to sell their products at the next Super
Bowl. With sales on the day and all the extra publicity, Mighty Gumball stands to
make millions.
There’s just one problem. Mighty Gumball has recently been plagued by network
problems, and it’s hitting gumball production. If they don’t get their network errors
fixed soon, they won’t be able to produce enough gumballs in time for the Super
Bowl, and they’ll lose the contract.
We can’t lose this contract; we’ve got to
get our network sorted. I’ll give 5,000
to whoever finds out what’s wrong. I’ll
even throw in a year’s supply of gumballs.
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Mighty Gumball CEOtools & troubleshooting
Am I missing the point
here? Can’t we just use
a toner and tracer? Won’t
that find the problems?
Toner and tracer sets can’t find every problem.
So far, we’ve only looked at network problems that toner and
tracers can help us find, and while they’re extremely useful,
they can’t root out every kind of network problem.
Here are some of the potential network problems that might be
affecting Mighty Gumball. Can you see which ones a toner and
tracer might not be able to detect?
Why is each of these a problem? Why do you think you can’t use a toner and
tracer set to detect all of these?
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Potential network cable problems
Broken cables.
Bad connectors.
Mis-wired connectors.
Too close to a power cable.
Too long a cable.
Wrong type of cable used.signal but not quality
A toner and tracer can check for a signal...
As we saw earlier, we can use a toner and tracer to listen out for signs of life
from electrons. The toner sends a signal along the cable, and provided you
hook it up to the same cable, the tracer picks up the signal from the electrons.
If the tracer can’t pick up the signal at any point along the cable, this means
there’s a break at that point.
There’s no way
I’m gonna jump
that break.
...but can’t check for signal quality
If there’s a connected wire going all the way through the cable,
then the tracer will be able to pick up the signal along the entire
length of the cable. The trouble is, it can’t tell you anything about
the quality of the signal, or the speed with which it moves along
the cable. All it can tell you is that the wire is continuous.
So if the network problem’s down to signal quality, you need
something more than a toner and tracer. But what?
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When there’s a break in continuity,
the electrons can’t get through, so
the tracer can’t pick up the signal.
If the wire’s continuous, the tracer
will pick up a signal all the way along
the cable. What it can’t tell you is
anything about the signal quality.tools & troubleshooting
BE the Toner & Tracer
Your job is to play like you’re the toner &
tracer and imagine that you are facing the
problems shown below. Say if you can help
or not, and why or why not.
Problem Can you help? Tell us more
Yes
The wrong cable is plugged
into a device.
No
Yes
The cable is wired
improperly.
No
Yes
The cable is longer than the
recommended maximum for
Ethernet (100 meters).
No
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BE the Toner & Tracer Solution
Your job is to play like you’re the toner & tracer and
imagine that you are facing the problems shown below.
Say if you can help or not, and why or why not.
Problem Can you help? Tell us more
You can hook the tracer on the correct
Yes
wire and use the toner to find the correct
The cable is plugged to the
plug on the opposite end.
wrong end.
No
You can trace each wire of a cable and
Yes
find the incorrect wires and fix them.
The cable is wired
improperly.
No
A simple toner & tracer set will only tell
Yes
you if there is a connected wire or not. You
The cable is longer than the
recommended maximum for
cannot tell the length with just a toner
Ethernet (100 meters).
No
and tracer.
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tools & troubleshooting
Well, I don’t know
about you guys, but
I’m going after that
5,000 bonus.
Joe: Yeah? Me too. There must be some pretty hairy
problems if the toner and tracer can’t find them all.
Jim: Well, I’m going to set my multimeter to work on the
cables. I’ll soon be 5,000 richer.
Frank: A multimeter? Are you crazy? What’s a
multimeter going to tell you about the state of the cables?
Jim: Just wait and see. You might learn something.
Q: Q:
Can a toner and tracer find a cable What signals can a toner send? Q: Does a tracer have to touch a
that is too long? cable to hear the warbling signal?
A: Generally, a toner can send a
A:
A: No. A toner and tracer can only check warbling type of signal that is used to trace No, that is the nice thing about it. You
for whether there is a electrical connection. or find the end of a cable. can run it quickly over some wires and
To check for the length, you need to actually hear as you get closer to the wire
measure the resistance of the cable. A second signal is just a voltage that the that the toner is connected to.
tracer checks for on the other end. This is
used to check a cable for breaks. This is
called continuity.
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Joe
JimUse the selector knob
to select what you
want to measure.
measure resistance
Introducing the multimeter
As you can probably tell from its name, a multimeter
is a versatile tool that measures multiple things, such
as voltage and resistance along a cable. To use it, turn
the selector knob on the multimeter to whatever it is
you want to to measure, and then touch the probes to
opposite ends of the wire you’re testing. You then read
the measurement off the multimeter display.
Use a multimeter to measure resistance
The thing that makes the multimeter really useful in networking
is its ability to measure resistance along a cable. This is something
that a toner and tracer can’t tell you, and it can shed important
light on how a cable is functioning.
So what’s resistance, and what effect does it have on your network?
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An analog multimeter
A digital multimeter
Read off the
measurements from the
output screen.
You touch the probes
to the opposite ends
of a wire to test it.0
0
1
1
2
2
5
5
0
0
1
1
Here’s the readout from
the multimeter where
the resistance is low.
tools & troubleshooting
So what’s resistance?
Resistance is a measurement of how hard it is for electrons to
move through a wire. It’s measured in ohms, and represented by the
Greek letter omega, Ω. The higher the number of ohms, the harder
it is for electrons to move through the wire.
When resistance is low
When a cable has low resistance, this means that it’s easy for
electrons to pass through the conductor. There’s very little stopping
the electrons from flowing, and so they move quickly and easily
along the cable.
ΩΩ
When resistance is high
When a cable has resistance that’s high, this means that it’s difficult
for electrons to move through the wire. And if the electrons can’t
move well, your signal can’t either.
ΩΩ
Oh man, this is like
molasses; it’s gonna
take forever.
So if you’re having network problems, you can use a multimeter to
check out whether high resistance along the cable is slowing down
your signal.
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0
0
When resistance is low, electrons can
move quickly and easily along the wire.
When resistance is
high, the electrons
can’t move as quickly.
2
2
0
0
0
0
1
1
k
k
1
1
∞
∞which tool?
Tonight’s talk: Toner & Tracer vs. Multimeter
Toner & Tracer: Multimeter:
Whoa, what are you doing here, Multimeter?
What do you mean? I do networking too, you know.
I guess, like a screwdriver has uses in networking
as well. We’re made for finding broken cables and
tracing cables. What can you possible add?
Well I can tell how long a cable is by measuring its
resistance. I can find broken cables as well
That resistance thing is nice, but we don’t think it’s
used very much. Your biggest problem is that both
ends of the cable must be right next to you, how
lame’s that?
You kind of got me there.
We even work on cables where the ends are in
different buildings. Tracer doesn’t even need to be
touching the cable; we can keep tabs on each other
with magnetic induction.
But I have ways to measure cables like that. I can
create a loop and then make measurements on that.
Notice I said measurements.
What is that supposed to mean? Just because you
give some number readout doesn’t make you more
useful. We’re simple and effective at our job.
Yeah, your job. Notice my name has multi in it. That
means I can do multiple things, not like you. I can
also measure how fast the electrons are flowing, or
current. Can you do that? Can you?
Well...
Anyway, gotta dash, I’m needed for some resistance
training. See you around, guys.
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0
0
0
1
1
1
1
2
2
2
2
5
5
5
5
0
0
0
0
1
1
1
1
tools & troubleshooting
Match up the wire with the resistance than an electron moving through these wires would feel.
A really long wire
ΩΩ
A really thick wire
ΩΩ
ΩΩ
A broken wire
ΩΩ
A short wire
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0
0
0
0
2
2
2
2
0
0
0
0
0
0
0
0
1
1
1
1
k
k
k
k
1
1
1
1
∞
∞
∞
∞0
0
0
0
1
1
1
1
2
2
2
2
5
5
5
5
0
0
0
0
1
1
1
1
which resistance?
Match up the wire with the resistance than an electron moving through these wires would feel.
A really long wire
ΩΩ
A really thick wireΩΩ
ΩΩ
A broken wire
ΩΩ
A short wire
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0
0
0
0
2
2
2
2
0
0
0
0
0
0
0
0
1
1
1
1
k
k
k
k
1
1
1
1
∞
∞
∞
∞tools & troubleshooting
BE the Multimeter
Your job is to play like you’re the
multimeter and imagine that you
are facing the problems shown
below. Say if you
can help or not,
and why or why not.
Problem Can you help? Tell us more
Yes
The cable is longer than the
recommended maximum for
Ethernet (100 meters).
No
Yes
Noise on the cable
produced by power, RF,
loose connector, bare
No
cables, and shorts.
Yes
Connector is mis-wired.
No
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BE the Multimeter Solution
Your job is to play like you’re the
multimeter and imagine that you are
facing the problems shown below. Say if
you can help or not, and why
or why not.
Problem Can you help? Tell us more
You can use the resistance setting on the
Yes
multimeter to read the resistance of the
The cable is longer than the
recommended maximum for
cable. A longer cable will have a higher
Ethernet (100 meters).
No
resistance.
The multimeter will not show noise on a line,
Yes
Noise on the cable
with the exception of a higher than normal
produced by power, RF,
voltage.
loose connector, bare
No
cables, and shorts.
You can use the resistance setting on a
Yes
multimeter to check for continuity, just
Connector is mis-wired.
like a toner and tracer, but with a readout
No
instead of a tone.
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So how well did the multimeter do?
Jim tested the cables at Mighty Gumball, and found six with
mis-wired connectors, and twelve that were too long. So does
this mean that Jim takes away the 5,000 bonus?
You’re kidding me,
right? We’ve still got a
ton of network problems,
and nobody’s getting any
money til they’re all fixed.
So what’s next?
Q: Q: Q:
So, it’s called a multimeter. What What is current then? Is a multimeter used that much by
else does it measure? network people?
A: If you think about voltage like the
A: Great question Most multimeters can pressure in a water line, current is how fast A: Not that much. We are using it here to
measure voltages, both AC and DC, as well the water flows. So electrical current is how show how to check cables and to show how
a current. fast the electrons are flowing in the wire. resistance measurements work.
Sometimes, you will need to check for a
Q: Q:
What’s AC & DC voltage? Are there any big differences
specific voltage, and then they come in real
between digital and analog multimeters?
handy.
A: DC stands for direct current. That is
the type of voltage you get from a battery. It A: Not really. In most cases, an analog
is just steady at one voltage, like 9 volts. multimeter uses just electrical components
such as resistors, capacitors, and inductors.
AC stands for alternating current. This
current alternates in the direction it is The digital multimeters use integrated
flowing. Your house current is AC. circuits along with the electrical components.
This is why they are more expensive.
you are here4 99
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the right tool for the job...
So, still feeling
confident about
multimeters, Jim?
Jim: Yeah, well maybe the problems are a bit bigger than
I thought.
Frank: I still think I have a shot at the 5,000, though.
I’m sure my oscilloscope will be able to sniff out the
remaining problems.
Jim: A what?
Frank: An oscilloscope. You see, if you use a multimeter
to track down resistance problems, you’ll only be able to
troubleshoot cables with that sort of problem. I think we
need to look a bit wider than that.
Jim: Such as...
Frank: Well, I think we need to look for voltage
problems too.
Joe: And you think an oscilloscope will find everything?
Frank: Of course it will. You just wait and see.
So what’s an oscilloscope?
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Joe
JimTime base
Screen where the
adjustment
signal shows up
tools & troubleshooting
An oscilloscope shows voltage changes
An oscilloscope is another tool you can use to help you
troubleshoot your network. It shows you the voltage changes on a
wire over time, measured in milliseconds.
Here’s an example readout from the oscilloscope showing you the voltage
changes in a cable over time.
Being able to analyze the voltage changes in this way gives you
important troubleshooting information about your cables. Let’s see how.
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An oscilloscope
takes some
training to use
properly.
An oscilloscope is a
complex piece of test equipment
requiring advanced training and
some knowledge of electrical
principles to use properly.
Channel 1
signal input
The highs and lows on the
display correspond to the
highs and lows of the voltage.
Channel 1
voltage level
adjustmentResistance is anything that might
slow down the electrons, like the
width of the garden hose.
voltage is electrical pressure
Voltage is really electrical pressure
Let’s start by taking a look at what voltage is.
In simple terms, voltage is the pressure that tries to make electrons flow.
It’s the push felt by the electrons. Think of voltage as the force that
moves the electrons in a circuit, and resistance as anything that might
slow them down, such as a broken wire.
If we compare electron flow in a cable to water flow down a garden
hose, voltage is like the pressure of the water coming out the faucet,
and resistance is like the width of the garden hose.
So how does this help us troubleshoot problems?
As we’ve seen, an oscilloscope allows us to see voltage changes over time.
The signal on a network cable is just the change in voltage
over time. This means that an oscilloscope effectively allows us to
see a network signal. More importantly, it allows us to see how clear
and distinct the network signal is, or whether there are any extraneous
voltages changing the signal and causing network problems. We call
extraneous voltages noise.
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...and a network signal
A clear clean network signal...
distorted by noise on the wire.
Voltage is electrical pressure, like
the pressure of water coming out
a faucet. T here are ways to take
care of noise.
First make sure that you
don’t untwist your cable
too much, that twist takes care of a lot of
noise. Also, keep some distance between your
network cables and things that create noise.
tools & troubleshooting
Where does noise on network
cables come from?
Noise is unwanted signals on your network cables.
It comes from lots of different sources of electronic
energy. Most things that use electricity leak
electromagnetic energy. This is especially true of
electric things that move or have moving parts.
Match up the things that create noise on network lines with how they create noise.
I cause noise when I do not have a connection to
Bad Grounding
what I am plugged into.
I cause noise when I move cables.
Radio Frequency Interference
I cause noise because I have revolving magnets.
Cable Crosstalk
I cause noise by broadcasting waves of
Bad Connector
electromagnetic energy.
I cause noise when signals from me cable creep on to
Physical Vibration
another cable next to me.
I cause noise with voltage differences.
Electric Motor
Answers on page 107.
you are here 4 103
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Tonight’s talk: Multimeter vs. Oscilloscope
Multimeter: Oscilloscope:
Hey Oscilloscope, it is good to see another real
electrical tool here.
Did you have a bad morning or something?
No, I just got done talking with Toner & Tracer.
They were wondering why I was here. I guess you’re
in the same boat. We pretty much do the same thing.
Hold your horses now. I think we do some different
stuff. I mean, you can’t really see a signal now, can
you?
I guess it’s “pick on Multimeter” day. No, I can’t
do that trick of seeing the signal on a cable. I can
measure the voltage, but that’s about it. But I can
tell how long a cable is, can you? It goes down well
at parties.
That resistance thing you do is cool. But seeing
the signal is more than a trick. If there’s noise or
extraneous power on a cable I can help see that.
Well, I can measure extraneous power as well, even
AC power which is how noise shows up, right?
True, but if it’s transient or very quick, you won’t
catch it. I will.
Well, only when you’re setup correctly. Isn’t it true
that it takes some pretty special training to run you?
I wouldn’t say special training as such. But yes,
someone using me will have to spend some time
understanding all of my powerful skills. You’re just
a toy by comparison.
I think I would rather be a “pick up and use” type
of portable tool. Anyway, gotta go.
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