1 00:00:00,150 --> 00:00:00,983 In this video, 2 00:00:00,983 --> 00:00:03,510 we're going to discuss the various issues you may experience 3 00:00:03,510 --> 00:00:06,810 with connectivity that are caused by cable signaling issues. 4 00:00:06,810 --> 00:00:10,620 This includes attenuation, interference, and decibel loss. 5 00:00:10,620 --> 00:00:12,450 First, we have attenuation. 6 00:00:12,450 --> 00:00:15,240 Attenuation is a loss of signal strength on a network cable 7 00:00:15,240 --> 00:00:17,700 or connection over the length of the cable. 8 00:00:17,700 --> 00:00:19,590 This is a common occurrence in both wired 9 00:00:19,590 --> 00:00:20,910 and wireless connections, 10 00:00:20,910 --> 00:00:22,680 but for right now, we're going to focus 11 00:00:22,680 --> 00:00:24,570 on wired connections only. 12 00:00:24,570 --> 00:00:27,120 When we're using a copper cable, such as a twisted pair 13 00:00:27,120 --> 00:00:28,470 or a coaxial cable, 14 00:00:28,470 --> 00:00:30,600 we're going to transmit data across the cable 15 00:00:30,600 --> 00:00:33,120 by sending electrical signals of varying voltages 16 00:00:33,120 --> 00:00:35,340 that represent our binary ones and zeros 17 00:00:35,340 --> 00:00:36,810 of the data being sent. 18 00:00:36,810 --> 00:00:38,760 The copper conduit inside these cables 19 00:00:38,760 --> 00:00:40,050 are going to carry those signals, 20 00:00:40,050 --> 00:00:43,110 but that copper has a natural level of resistance, 21 00:00:43,110 --> 00:00:44,790 and the longer the cable becomes, 22 00:00:44,790 --> 00:00:46,590 the higher that resistance becomes, 23 00:00:46,590 --> 00:00:48,120 and the data has a harder time 24 00:00:48,120 --> 00:00:50,010 traveling down the copper cable. 25 00:00:50,010 --> 00:00:51,690 This causes the signal to weaken 26 00:00:51,690 --> 00:00:55,080 or attenuate as it travels along the distance of the cable. 27 00:00:55,080 --> 00:00:57,660 When you learned about twisted pair cable, I told you 28 00:00:57,660 --> 00:01:00,750 that we had this maximum distance of about a hundred meters. 29 00:01:00,750 --> 00:01:03,120 Now, this is caused because of attenuation. 30 00:01:03,120 --> 00:01:04,980 Once you get further than a hundred meters, 31 00:01:04,980 --> 00:01:07,740 the signal's going to weaken and become unreliable. 32 00:01:07,740 --> 00:01:10,110 With coaxial cables, you have more shielding 33 00:01:10,110 --> 00:01:11,640 or insulation around it. 34 00:01:11,640 --> 00:01:13,320 Therefore, you can reach distances 35 00:01:13,320 --> 00:01:15,150 of up to about 500 meters. 36 00:01:15,150 --> 00:01:16,980 But when you pass that limit, 37 00:01:16,980 --> 00:01:19,140 the attenuation again becomes too much, 38 00:01:19,140 --> 00:01:21,870 and the signal strength weakens to an unusable level. 39 00:01:21,870 --> 00:01:24,510 So distance is going to be our main factor when we're dealing 40 00:01:24,510 --> 00:01:27,150 with attenuation, but there's a couple other factors 41 00:01:27,150 --> 00:01:29,190 that can affect your signal strength too. 42 00:01:29,190 --> 00:01:31,710 This includes frequencies that are used by the connection, 43 00:01:31,710 --> 00:01:33,000 the noise in the environment, 44 00:01:33,000 --> 00:01:35,220 and the physical surroundings near the connection. 45 00:01:35,220 --> 00:01:36,360 You see, all networking 46 00:01:36,360 --> 00:01:39,360 and electrical cables operate at a specific frequency. 47 00:01:39,360 --> 00:01:41,550 For example, power cables in a residential 48 00:01:41,550 --> 00:01:44,520 or office setting are usually going to operate at 60 hertz 49 00:01:44,520 --> 00:01:46,140 in the United States and Canada. 50 00:01:46,140 --> 00:01:47,730 But if you're in another country, 51 00:01:47,730 --> 00:01:49,920 it may operate at 50 hertz. 52 00:01:49,920 --> 00:01:50,940 Ethernet cables though, 53 00:01:50,940 --> 00:01:52,800 operate at different frequencies too. 54 00:01:52,800 --> 00:01:55,020 If you're using a CAT 5e cable, for instance, 55 00:01:55,020 --> 00:01:57,450 it uses a frequency of a hundred megahertz. 56 00:01:57,450 --> 00:01:59,340 Well, a CAT 6 cable is going to use a frequency 57 00:01:59,340 --> 00:02:01,050 of 250 megahertz. 58 00:02:01,050 --> 00:02:04,470 A CAT 6a cable uses a frequency of 500 megahertz, 59 00:02:04,470 --> 00:02:07,980 and a CAT 7 cable uses a frequency of 600 megahertz. 60 00:02:07,980 --> 00:02:10,229 Now, in general, the higher the frequency, 61 00:02:10,229 --> 00:02:11,400 the higher the bandwidth 62 00:02:11,400 --> 00:02:13,830 that a particular cable is going to be able to produce. 63 00:02:13,830 --> 00:02:16,560 This is because each hert is one cycle per second 64 00:02:16,560 --> 00:02:19,740 in frequency, and so the more cycles you have in a second, 65 00:02:19,740 --> 00:02:21,360 the more times you could put a one 66 00:02:21,360 --> 00:02:23,160 or a zero down that cable. 67 00:02:23,160 --> 00:02:24,723 So if you're going to use a network cable 68 00:02:24,723 --> 00:02:26,910 that uses a frequency similar to the frequencies 69 00:02:26,910 --> 00:02:29,460 of the cable surrounding it, you can have something known 70 00:02:29,460 --> 00:02:32,970 as crosstalk or interference that's going to occur. 71 00:02:32,970 --> 00:02:34,470 Now, this brings us to the concept 72 00:02:34,470 --> 00:02:36,300 of noise in your environment. 73 00:02:36,300 --> 00:02:38,070 If there's additional electrical frequency 74 00:02:38,070 --> 00:02:40,560 or radio frequency noise in your area, 75 00:02:40,560 --> 00:02:43,080 this can cause your network cables to have problems 76 00:02:43,080 --> 00:02:45,030 and increase the rate of attenuation 77 00:02:45,030 --> 00:02:47,640 and decreasing your associated signal strength. 78 00:02:47,640 --> 00:02:49,500 For example, if you have a network cable 79 00:02:49,500 --> 00:02:51,720 that's located near an area where heavy machinery 80 00:02:51,720 --> 00:02:54,660 or power generators are being used, this will create noise 81 00:02:54,660 --> 00:02:57,180 and signal interference that will decrease the distance 82 00:02:57,180 --> 00:02:58,980 that cable is going to be able to support 83 00:02:58,980 --> 00:03:00,630 because there's more attenuation 84 00:03:00,630 --> 00:03:03,030 and more noise across that signal. 85 00:03:03,030 --> 00:03:04,590 Finally, the physical surroundings 86 00:03:04,590 --> 00:03:06,000 you're using your copper cables in 87 00:03:06,000 --> 00:03:08,040 can also increase your attenuation. 88 00:03:08,040 --> 00:03:10,440 Things like temperature, the construction of the walls 89 00:03:10,440 --> 00:03:13,290 or other barriers, and the type of wire insulation itself, 90 00:03:13,290 --> 00:03:15,780 can all negatively affect your signal strength. 91 00:03:15,780 --> 00:03:17,700 If you have freezing temperatures, for instance, 92 00:03:17,700 --> 00:03:19,620 your copper cables will become more brittle 93 00:03:19,620 --> 00:03:22,620 and inflexible, which in turn slows down the connection 94 00:03:22,620 --> 00:03:24,270 and attenuates the signal. 95 00:03:24,270 --> 00:03:26,040 When you're experiencing hotter temperatures, 96 00:03:26,040 --> 00:03:27,750 the signals can actually overheat 97 00:03:27,750 --> 00:03:30,180 and the network cable could potentially even catch fire 98 00:03:30,180 --> 00:03:32,070 if the outside plastic melts away 99 00:03:32,070 --> 00:03:35,250 and the inside wire becomes exposed to flammable materials. 100 00:03:35,250 --> 00:03:37,140 For this reason, it's always important 101 00:03:37,140 --> 00:03:38,730 to have well insulated wires 102 00:03:38,730 --> 00:03:41,040 and attempt to maintain the proper temperature control 103 00:03:41,040 --> 00:03:42,690 that your network connection needs 104 00:03:42,690 --> 00:03:45,750 to maintain a strong signal and minimal attenuation. 105 00:03:45,750 --> 00:03:49,020 So, what can you do when you experience attenuation? 106 00:03:49,020 --> 00:03:51,750 First, you can make sure you're using the proper cables 107 00:03:51,750 --> 00:03:54,180 for the physical environment you're operating within. 108 00:03:54,180 --> 00:03:55,470 If you're operating in a hotter 109 00:03:55,470 --> 00:03:57,600 or colder environment, you may need to switch 110 00:03:57,600 --> 00:03:59,250 to shielded twisted pair instead 111 00:03:59,250 --> 00:04:01,470 of unshielded twisted pair, for example. 112 00:04:01,470 --> 00:04:03,690 Second, you can shorten the distance. 113 00:04:03,690 --> 00:04:05,490 While the maximum length is a hundred meters 114 00:04:05,490 --> 00:04:06,390 for these cables, 115 00:04:06,390 --> 00:04:07,950 it's a good idea to use cables 116 00:04:07,950 --> 00:04:09,330 that are a bit shorter than that 117 00:04:09,330 --> 00:04:11,430 to ensure you always have a good, clear signal 118 00:04:11,430 --> 00:04:13,080 on all of your connections. 119 00:04:13,080 --> 00:04:15,930 Personally, I tend to implement an 80 meter limit 120 00:04:15,930 --> 00:04:19,079 on all of my twisted pair cables inside my networks. 121 00:04:19,079 --> 00:04:22,110 Third, you can use an amplifier or a repeater. 122 00:04:22,110 --> 00:04:23,370 These are layer one devices 123 00:04:23,370 --> 00:04:26,280 that take in the signal on one end, boost up the signal 124 00:04:26,280 --> 00:04:28,380 and retransmit it out the other side. 125 00:04:28,380 --> 00:04:29,990 This means if I need to run a twisted pair 126 00:04:29,990 --> 00:04:33,550 of cable over 150 meters, I could use a 75 127 00:04:33,550 --> 00:04:36,390 or 80 meter cable connected to a repeater, 128 00:04:36,390 --> 00:04:39,180 and then I can go the next 75 to 80 meters 129 00:04:39,180 --> 00:04:41,520 to make the total 150 meters. 130 00:04:41,520 --> 00:04:44,220 By using this repeater, there's going to be no signal loss 131 00:04:44,220 --> 00:04:47,250 because we essentially re-broadcast out a new signal again 132 00:04:47,250 --> 00:04:50,760 from that repeater as we start over our distance limitation. 133 00:04:50,760 --> 00:04:52,410 If you're dealing with fiber cables instead 134 00:04:52,410 --> 00:04:55,110 of copper cables, you have a lot of the same issues in terms 135 00:04:55,110 --> 00:04:57,210 of attenuation because of distance, 136 00:04:57,210 --> 00:05:00,480 but they don't begin to occur until much further out. 137 00:05:00,480 --> 00:05:01,920 This is because we're using light 138 00:05:01,920 --> 00:05:03,600 instead of electricity here. 139 00:05:03,600 --> 00:05:06,390 Now, for example, let's say you have a single mode fiber 140 00:05:06,390 --> 00:05:09,000 that is a maximum distance of 40 kilometers. 141 00:05:09,000 --> 00:05:11,010 You're not going to really suffer much signal loss 142 00:05:11,010 --> 00:05:14,400 until you get around 30 to 40 kilometers from your source, 143 00:05:14,400 --> 00:05:16,470 depending on your environmental conditions. 144 00:05:16,470 --> 00:05:18,960 Another cause of attenuation in fiber cables tends 145 00:05:18,960 --> 00:05:21,300 to occur if you have cheaply constructed fiber cables 146 00:05:21,300 --> 00:05:24,210 or you have fiber cables that have dirty connectors. 147 00:05:24,210 --> 00:05:26,070 Let's imagine you have a pair of sunglasses on 148 00:05:26,070 --> 00:05:28,380 and you have fingerprints all over the lenses. 149 00:05:28,380 --> 00:05:30,360 That makes it really hard to see through 'em, right? 150 00:05:30,360 --> 00:05:32,070 Because you have dirty glasses. 151 00:05:32,070 --> 00:05:34,710 Well, the same thing happens with fiber connectors. 152 00:05:34,710 --> 00:05:36,210 When you're dealing with fiber connections 153 00:05:36,210 --> 00:05:38,550 and your fiber connectors are dirty, this can lead 154 00:05:38,550 --> 00:05:40,260 to signal loss and attenuation 155 00:05:40,260 --> 00:05:41,910 because the light can't cleanly pass 156 00:05:41,910 --> 00:05:44,250 through those connectors because it's dirty. 157 00:05:44,250 --> 00:05:47,070 This adds to attenuation and signal loss for you. 158 00:05:47,070 --> 00:05:48,960 Now, if you're experiencing this attenuation 159 00:05:48,960 --> 00:05:51,630 with fiber cables, the first thing I recommend you do 160 00:05:51,630 --> 00:05:54,720 is change up the fiber cable for a higher quality cable, 161 00:05:54,720 --> 00:05:57,780 or you clean and polish both ends of that fiber 162 00:05:57,780 --> 00:06:00,120 and make sure those connectors are really clean. 163 00:06:00,120 --> 00:06:02,250 You want to make sure there is not a dirty connector there 164 00:06:02,250 --> 00:06:03,510 'cause even something as little 165 00:06:03,510 --> 00:06:04,950 as your fingerprints on it 166 00:06:04,950 --> 00:06:07,500 can cause this attenuation to occur. 167 00:06:07,500 --> 00:06:09,210 Next, we have interference. 168 00:06:09,210 --> 00:06:11,400 Interference occurs when multiple cables operate 169 00:06:11,400 --> 00:06:13,560 in the same frequency band and they operate 170 00:06:13,560 --> 00:06:15,480 in close proximity to each other. 171 00:06:15,480 --> 00:06:16,350 To help prevent this, 172 00:06:16,350 --> 00:06:18,690 we want to use high quality twisted pair cables 173 00:06:18,690 --> 00:06:21,060 or use higher category rated cables. 174 00:06:21,060 --> 00:06:23,400 Now, this is because higher category rated cables 175 00:06:23,400 --> 00:06:25,200 are going to have more internal twists per inch 176 00:06:25,200 --> 00:06:27,180 inside their internal twisted pairs. 177 00:06:27,180 --> 00:06:29,640 These internal twists can help overcome the interference 178 00:06:29,640 --> 00:06:32,070 that can occur within a single cable inside 179 00:06:32,070 --> 00:06:33,930 of its own wired twisted pairs. 180 00:06:33,930 --> 00:06:36,720 Now additionally, if you see a twisted pair network cable 181 00:06:36,720 --> 00:06:37,740 that's being run over 182 00:06:37,740 --> 00:06:40,800 or near a high power cable, this can cause interference 183 00:06:40,800 --> 00:06:43,380 as well and a large amount of signal loss. 184 00:06:43,380 --> 00:06:44,520 To solve this problem, 185 00:06:44,520 --> 00:06:47,370 you always want to plan your cable runs to operate in parallel 186 00:06:47,370 --> 00:06:50,400 and not directly next to any high power cables running 187 00:06:50,400 --> 00:06:52,740 in your cable trays or your risers. 188 00:06:52,740 --> 00:06:55,590 Finally, we have decibel or dB loss. 189 00:06:55,590 --> 00:06:57,720 Now, decibel loss is used to measure the amount 190 00:06:57,720 --> 00:06:59,010 of signal deterioration 191 00:06:59,010 --> 00:07:01,440 that we're experiencing on a given connection. 192 00:07:01,440 --> 00:07:03,450 This can be used to measure the signal on a copper 193 00:07:03,450 --> 00:07:04,860 or fiber cable. 194 00:07:04,860 --> 00:07:05,850 For copper cables, 195 00:07:05,850 --> 00:07:08,970 we see this reported as a dB loss to represent the amount 196 00:07:08,970 --> 00:07:10,320 of voltage that is decreased 197 00:07:10,320 --> 00:07:12,090 since we sent the signal out originally 198 00:07:12,090 --> 00:07:13,740 over that twisted pair cable. 199 00:07:13,740 --> 00:07:15,090 For fiber connections though, 200 00:07:15,090 --> 00:07:17,490 this dB loss is instead going to represent the amount 201 00:07:17,490 --> 00:07:18,600 of light that's lost 202 00:07:18,600 --> 00:07:21,540 as it travels across the cable or the connection. 203 00:07:21,540 --> 00:07:22,980 If you're experiencing a high amount 204 00:07:22,980 --> 00:07:26,010 of dB loss on a copper cable, you need to replace that cable 205 00:07:26,010 --> 00:07:27,930 with a higher quality twisted pair cable 206 00:07:27,930 --> 00:07:29,130 with additional shielding 207 00:07:29,130 --> 00:07:31,170 or a higher number of twists per inch. 208 00:07:31,170 --> 00:07:32,550 If you're experiencing a high amount 209 00:07:32,550 --> 00:07:35,820 of dB loss on a fiber cable, you want to replace that cable 210 00:07:35,820 --> 00:07:37,800 with a higher quality fiber cable, such 211 00:07:37,800 --> 00:07:39,990 as a glass one instead of a plastic one. 212 00:07:39,990 --> 00:07:42,960 Or you need to clean and polish both ends of your cable 213 00:07:42,960 --> 00:07:44,760 and the associated connectors. 214 00:07:44,760 --> 00:07:46,170 Alright, we just covered 215 00:07:46,170 --> 00:07:48,150 our three big cable signaling issues 216 00:07:48,150 --> 00:07:49,770 that you are going to experience in the field 217 00:07:49,770 --> 00:07:51,210 as a network technician. 218 00:07:51,210 --> 00:07:53,340 Just a reminder, these are attenuation, 219 00:07:53,340 --> 00:07:55,380 interference, and decibel loss. 220 00:07:55,380 --> 00:07:58,050 When you're testing your network for attenuation conditions, 221 00:07:58,050 --> 00:07:59,520 always use a cable certifier 222 00:07:59,520 --> 00:08:01,410 to measure the amount of attenuation. 223 00:08:01,410 --> 00:08:04,170 For fiber connections, you're going to use a fiber light meter 224 00:08:04,170 --> 00:08:06,210 to test for attenuation as well. 225 00:08:06,210 --> 00:08:08,550 If you need a test a connection for interference, 226 00:08:08,550 --> 00:08:11,040 you can connect a spectrum analyzer to the cable 227 00:08:11,040 --> 00:08:12,390 to see the exact frequencies 228 00:08:12,390 --> 00:08:14,940 and signals that are being sent over that connection. 229 00:08:14,940 --> 00:08:16,800 If you want to test for decibel loss, 230 00:08:16,800 --> 00:08:19,410 you're going to use a cable certifier, a cable analyzer, 231 00:08:19,410 --> 00:08:21,990 or a fiber light meter to measure the signal being sent 232 00:08:21,990 --> 00:08:23,820 and received across a given cable 233 00:08:23,820 --> 00:08:26,280 and report back that loss in decibels. 234 00:08:26,280 --> 00:08:27,120 For the exam, 235 00:08:27,120 --> 00:08:29,130 it's important to understand the tool you might use 236 00:08:29,130 --> 00:08:31,930 to troubleshoot the different cable connectivity issues.