-: Cable signal issues. 2 2
In this video, we're going to discuss the various issues 3 3
you may experience with connectivity 4 4
that are caused by cable signaling issues. 5 5
This includes attenuation, interference, and decibel loss. 6 6
First, we have attenuation. 7 7
Attenuation is the loss of signal strength 8 8
on a network cable or connection 9 9
over the length of the cable. 10 10
This is a common occurrence in both wired 11 11
and wireless connections. 12 12
But for right now, we're going to focus 13 13
on wired connections only. 14 14
When we're using a copper cable, 15 15
such as a twisted pair or a coaxial cable, 16 16
we're going to transmit data across the cable 17 17
by sending electrical signals of varying voltages 18 18
that represent our binary ones and zeros 19 19
of the data being sent. 20 20
The copper conduit inside these cables 21 21
are going to carry those signals, 22 22
but that copper has a natural level of resistance, 23 23
and the longer the cable becomes 24 24
the higher that resistance becomes 25 25
and the data has a harder time 26 26
traveling down the copper cable. 27 27
This causes the signal to weaken or attenuate 28 28
as it travels along the distance of the cable. 29 29
When you learned about twisted pair cables 30 30
in our ethernet connections, I told you 31 31
that we had this maximum distance of about 100 meters. 32 32
Now, this is caused because of attenuation. 33 33
Once you get further than 100 meters, 34 34
the signal is going to weaken and become unreliable. 35 35
With coaxial cables, you have more shielding 36 36
or insulation around it, therefore you can reach distances 37 37
of up to about 500 meters. 38 38
But when you pass that limit, the attenuation again 39 39
becomes too much and the signal strength weekends 40 40
to an unusable level. 41 41
So, distance is going to be our main factor 42 42
when we're dealing with attenuation. 43 43
But there's a couple other factors 44 44
that can affect your signal strength too. 45 45
This includes frequencies that are used by the connection, 46 46
the noise in the environment 47 47
and the physical surroundings near the connection. 48 48
You see, all networking and electrical cables operate 49 49
at a specific frequency. 50 50
For example, power cables in a residential or office setting 51 51
are usually going to operate at 60 Hertz 52 52
in the United States and Canada. 53 53
But, if you're in another country, 54 54
it may operate at 50 Hertz. 55 55
Ethernet cables though operate at different frequencies too. 56 56
If you're using a CAT 5e cable, for instance, 57 57
it uses a frequency of 100 megahertz, 58 58
while a CAT 6 cable is going to use a frequency 59 59
of 250 megahertz. 60 60
A CAT 6a cable uses a frequency of 500 megahertz, 61 61
and a CAT 7 cable uses a frequency of 600 megahertz. 62 62
Now, in general, the higher the frequency 63 63
the higher the bandwidth that your particular cable 64 64
is going to be able to produce. 65 65
This is because each hertz 66 66
is one cycle per second in frequency. 67 67
And so, the more cycles you have in a second, 68 68
the more times you can put a one or a zero down that cable. 69 69
So, if you're going to use a network cable 70 70
that uses a frequency similar to the frequencies 71 71
of the cables surrounding it, 72 72
you can have something known as crosstalk 73 73
or interference that's going to occur. 74 74
Now, this brings us to the concept 75 75
of noise in your environment. 76 76
If there's additional electrical frequency 77 77
or radio-frequency noise in your area, 78 78
this can cause your network cables to have problems 79 79
and increase the rate of attenuation 80 80
and decrease in your associated signal strength. 81 81
For example, if you have a network cable 82 82
that's located near an area where heavy machinery 83 83
or power generators are being used, 84 84
this will create noise and signal interference 85 85
that will decrease the distance 86 86
that cable is going to be able to support 87 87
because there's more attenuation and more noise 88 88
across that signal. 89 89
Finally, the physical surroundings 90 90
you're using your copper cables in 91 91
can also increase your attenuation. 92 92
Things like temperature, the construction of the walls 93 93
or other barriers, and the type of wire installation itself 94 94
can all negatively affect your signal strength. 95 95
If you have freezing temperatures for instance, 96 96
your copper cables will become more brittle and inflexible, 97 97
which in turn slows down the connection 98 98
and attenuates the signal. 99 99
When you're experiencing hotter temperatures, 100 100
the signals can actually overheat and the network cable 101 101
could potentially even catch fire 102 102
if the outside plastic melts away and the inside wire 103 103
becomes exposed to flammable materials. 104 104
For this reason, it's always important 105 105
to have well-insulated wires and attempt to maintain 106 106
the proper temperature control 107 107
that your network connection needs 108 108
to maintain a strong signal and minimal attenuation. 109 109
So, what can you do when you experience attenuation? 110 110
First, you can make sure you're using the proper cables 111 111
for the physical environment you're operating within. 112 112
If you're operating in a hotter or colder environment, 113 113
you may need to switch to shielded twisted pair 114 114
instead of unshielded twisted pair for example. 115 115
Second, you can shorten the distance. 116 116
While the maximum length is 100 meters for these cables, 117 117
it's a good idea to use cables 118 118
that are a bit shorter than that 119 119
to ensure you always have a good, clear signal 120 120
on all of your connections. 121 121
Personally, I tend to implement an 80 meter limit 122 122
on all of my twisted pair cables inside my networks. 123 123
Third, you can use an amplifier or a repeater. 124 124
These are layer one devices 125 125
that take in the signal on one end, boost up the signal, 126 126
and retransmit it out the other side. 127 127
This means if I need to run a twisted pair cable 128 128
over 150 meters, I could use a 75 or a 80 meter cable 129 129
connected to a repeater, and then I can go the next 75 130 130
to 80 meters to make the total 150 meters. 131 131
By using this repeater, there's going to be no signal loss 132 132
because we essentially rebroadcast out a new signal again 133 133
from that repeater as we start over our distance limitation. 134 134
If you're dealing with fiber cables 135 135
instead of copper cables, you have a lot of the same issues 136 136
in terms of attenuation because of distance, 137 137
but, they don't begin to occur until much further out. 138 138
This is because we're using light 139 139
instead of electricity here. 140 140
Now, for example, let's say you have a single mode fiber 141 141
that has a maximum distance of 40 kilometers. 142 142
You're not going to really suffer much signal loss 143 143
until you get around 30 to 40 kilometers from your source 144 144
depending on your environmental conditions. 145 145
Another cause of attenuation in fiber cables 146 146
tends to occur if you have cheaply constructed fiber cables 147 147
or you have fiber cables that have dirty connectors. 148 148
Let's imagine you have a pair of sunglasses on, 149 149
and you have fingerprints all over the lenses, 150 150
that makes it really hard to see through them, right? 151 151
Because you have dirty glasses. 152 152
Well, the same thing happens with fiber connectors. 153 153
When you're dealing with fiber connections 154 154
and your fiber connectors are dirty, 155 155
this can lead to signal loss and attenuation 156 156
because the light can't cleanly pass 157 157
through those connectors because it's dirty. 158 158
This adds to attenuation and signal loss for you. 159 159
Now, if you're experiencing this attenuation 160 160
with fiber cables, the first thing I recommend you do 161 161
is change out the fiber cable for a higher quality cable 162 162
or you clean and polish both ends of that fiber 163 163
and make sure those connectors are really clean. 164 164
You want to make sure there is not a dirty connector there 165 165
because even something as little as your fingerprints on it 166 166
can cause this attenuation to occur. 167 167
Next, we have interference. 168 168
Interference occurs when multiple cables operate 169 169
in the same frequency band 170 170
and they operate in close proximity to each other. 171 171
To help prevent this, 172 172
we want to use high quality twisted pair cables 173 173
or use higher category rated cables. 174 174
Now, this is because higher category rated cables 175 175
are going to have more internal twist per inch 176 176
inside their internal twisted pairs. 177 177
These internal twists can help overcome the interference 178 178
that can occur within a single cable 179 179
inside of its own wired twisted pairs. 180 180
Now additionally, if you see a twisted pair 181 181
of network cable that's being run over 182 182
or near a high power cable, 183 183
this can cause interference as well 184 184
and a large amount of signal loss. 185 185
To solve this problem, you always want to plan your cable runs 186 186
to operate in parallel and not directly next 187 187
to any high power cables running in your cable trays 188 188
or your risers. 189 189
Finally, we have decibel or dB loss. 190 190
Now, decibel loss is used to measure 191 191
the amount of signal deterioration that we're experiencing 192 192
on a given connection. 193 193
This can be used to measure the signal 194 194
on a copper or fiber cable. 195 195
For copper cables, we see this reported as a dB loss, 196 196
to represent the amount of voltage that has decreased 197 197
since we sent the signal out originally 198 198
over that twisted pair cable. 199 199
For fiber connections though, 200 200
this dB loss is instead going to represent 201 201
the amount of light that's lost as it travels 202 202
across the cable or the connection. 203 203
If you're experiencing a high amount of dB loss 204 204
on a copper cable, you need to replace that cable 205 205
with a higher quality twisted pair cable 206 206
with additional shielding 207 207
or a higher number of twists per inch. 208 208
If you're experiencing a high amount of dB loss 209 209
on a fiber cable, you want to replace that cable 210 210
with a higher quality fiber cable, 211 211
such as a glass one instead of a plastic one. 212 212
Or you need to clean and polish both ends of your cable 213 213
and the associated connectors. 214 214
All right, we just covered our three big 215 215
cable signaling issues that you're going to experience 216 216
in the field as a network technician. 217 217
Just a reminder, these are attenuation, 218 218
interference, and decibel loss. 219 219
When you're testing your network for attenuation conditions, 220 220
always use a cable certifier 221 221
to measure the amount of attenuation. 222 222
For fiber connections, you're going to use a fiber light meter 223 223
to test for attenuation as well. 224 224
If you need to test a connection for interference, 225 225
you can connect a spectrum analyzer to the cable 226 226
to see the exact frequencies and signals 227 227
that are being sent over that connection. 228 228
If you want to test for decibel loss, 229 229
you're going to use a cable certifier, a cable analyzer, 230 230
or a fiber light meter to measure the signal being sent 231 231
and received across a given cable 232 232
and report back that loss in decibels. 233 233
For the exam, it's important to understand 234 234
the tool you might use to troubleshoot 235 235
the different cable connectivity issues.