1 1 00:00:00,140 --> 00:00:02,060 Cable signal issues. 2 2 00:00:02,060 --> 00:00:04,670 In this video, we're going to discuss the various issues 3 3 00:00:04,670 --> 00:00:06,610 you may experience with connectivity 4 4 00:00:06,610 --> 00:00:08,840 that are caused by cable signaling issues. 5 5 00:00:08,840 --> 00:00:12,610 This includes attenuation, interference, and decibel loss. 6 6 00:00:12,610 --> 00:00:14,490 First, we have attenuation. 7 7 00:00:14,490 --> 00:00:16,330 Attenuation is the loss of signal strength 8 8 00:00:16,330 --> 00:00:18,130 on a network cable or connection 9 9 00:00:18,130 --> 00:00:19,740 over the length of the cable. 10 10 00:00:19,740 --> 00:00:21,610 This is a common occurrence in both wired 11 11 00:00:21,610 --> 00:00:22,930 and wireless connections. 12 12 00:00:22,930 --> 00:00:24,740 But for right now, we're going to focus 13 13 00:00:24,740 --> 00:00:26,600 on wired connections only. 14 14 00:00:26,600 --> 00:00:28,110 When we're using a copper cable, 15 15 00:00:28,110 --> 00:00:30,470 such as a twisted pair or a coaxial cable, 16 16 00:00:30,470 --> 00:00:32,600 we're going to transmit data across the cable 17 17 00:00:32,600 --> 00:00:35,150 by sending electrical signals of varying voltages 18 18 00:00:35,150 --> 00:00:37,370 that represent our binary ones and zeros 19 19 00:00:37,370 --> 00:00:38,850 of the data being sent. 20 20 00:00:38,850 --> 00:00:40,780 The copper conduit inside these cables 21 21 00:00:40,780 --> 00:00:42,090 are going to carry those signals, 22 22 00:00:42,090 --> 00:00:45,120 but that copper has a natural level of resistance, 23 23 00:00:45,120 --> 00:00:46,790 and the longer the cable becomes 24 24 00:00:46,790 --> 00:00:48,580 the higher that resistance becomes 25 25 00:00:48,580 --> 00:00:50,160 and the data has a harder time 26 26 00:00:50,160 --> 00:00:52,040 traveling down the copper cable. 27 27 00:00:52,040 --> 00:00:54,780 This causes the signal to weaken or attenuate 28 28 00:00:54,780 --> 00:00:57,080 as it travels along the distance of the cable. 29 29 00:00:57,080 --> 00:00:58,900 When you learned about twisted pair cables 30 30 00:00:58,900 --> 00:01:01,020 in our ethernet connections, I told you 31 31 00:01:01,020 --> 00:01:04,120 that we had this maximum distance of about 100 meters. 32 32 00:01:04,120 --> 00:01:06,490 Now, this is caused because of attenuation. 33 33 00:01:06,490 --> 00:01:08,350 Once you get further than 100 meters, 34 34 00:01:08,350 --> 00:01:11,100 the signal is going to weaken and become unreliable. 35 35 00:01:11,100 --> 00:01:13,480 With coaxial cables, you have more shielding 36 36 00:01:13,480 --> 00:01:16,680 or insulation around it, therefore you can reach distances 37 37 00:01:16,680 --> 00:01:18,530 of up to about 500 meters. 38 38 00:01:18,530 --> 00:01:21,390 But when you pass that limit, the attenuation again 39 39 00:01:21,390 --> 00:01:23,800 becomes too much and the signal strength weekends 40 40 00:01:23,800 --> 00:01:25,220 to an unusable level. 41 41 00:01:25,220 --> 00:01:27,380 So, distance is going to be our main factor 42 42 00:01:27,380 --> 00:01:29,000 when we're dealing with attenuation. 43 43 00:01:29,000 --> 00:01:30,520 But there's a couple other factors 44 44 00:01:30,520 --> 00:01:32,550 that can affect your signal strength too. 45 45 00:01:32,550 --> 00:01:35,070 This includes frequencies that are used by the connection, 46 46 00:01:35,070 --> 00:01:36,340 the noise in the environment 47 47 00:01:36,340 --> 00:01:38,600 and the physical surroundings near the connection. 48 48 00:01:38,600 --> 00:01:41,060 You see, all networking and electrical cables operate 49 49 00:01:41,060 --> 00:01:42,730 at a specific frequency. 50 50 00:01:42,730 --> 00:01:45,940 For example, power cables in a residential or office setting 51 51 00:01:45,940 --> 00:01:47,870 are usually going to operate at 60 Hertz 52 52 00:01:47,870 --> 00:01:49,500 in the United States and Canada. 53 53 00:01:49,500 --> 00:01:51,120 But, if you're in another country, 54 54 00:01:51,120 --> 00:01:53,290 it may operate at 50 Hertz. 55 55 00:01:53,290 --> 00:01:56,170 Ethernet cables though operate at different frequencies too. 56 56 00:01:56,170 --> 00:01:58,380 If you're using a CAT 5e cable, for instance, 57 57 00:01:58,380 --> 00:02:00,810 it uses a frequency of 100 megahertz, 58 58 00:02:00,810 --> 00:02:02,700 while a CAT 6 cable is going to use a frequency 59 59 00:02:02,700 --> 00:02:04,440 of 250 megahertz. 60 60 00:02:04,440 --> 00:02:07,690 A CAT 6a cable uses a frequency of 500 megahertz, 61 61 00:02:07,690 --> 00:02:11,340 and a CAT 7 cable uses a frequency of 600 megahertz. 62 62 00:02:11,340 --> 00:02:13,590 Now, in general, the higher the frequency 63 63 00:02:13,590 --> 00:02:15,660 the higher the bandwidth that your particular cable 64 64 00:02:15,660 --> 00:02:17,210 is going to be able to produce. 65 65 00:02:17,210 --> 00:02:18,660 This is because each hertz 66 66 00:02:18,660 --> 00:02:20,780 is one cycle per second in frequency. 67 67 00:02:20,780 --> 00:02:23,110 And so, the more cycles you have in a second, 68 68 00:02:23,110 --> 00:02:26,520 the more times you can put a one or a zero down that cable. 69 69 00:02:26,520 --> 00:02:28,370 So, if you're going to use a network cable 70 70 00:02:28,370 --> 00:02:30,270 that uses a frequency similar to the frequencies 71 71 00:02:30,270 --> 00:02:31,790 of the cables surrounding it, 72 72 00:02:31,790 --> 00:02:33,960 you can have something known as crosstalk 73 73 00:02:33,960 --> 00:02:36,350 or interference that's going to occur. 74 74 00:02:36,350 --> 00:02:37,850 Now, this brings us to the concept 75 75 00:02:37,850 --> 00:02:39,640 of noise in your environment. 76 76 00:02:39,640 --> 00:02:41,440 If there's additional electrical frequency 77 77 00:02:41,440 --> 00:02:43,930 or radio-frequency noise in your area, 78 78 00:02:43,930 --> 00:02:46,430 this can cause your network cables to have problems 79 79 00:02:46,430 --> 00:02:48,290 and increase the rate of attenuation 80 80 00:02:48,290 --> 00:02:51,020 and decrease in your associated signal strength. 81 81 00:02:51,020 --> 00:02:52,860 For example, if you have a network cable 82 82 00:02:52,860 --> 00:02:55,100 that's located near an area where heavy machinery 83 83 00:02:55,100 --> 00:02:56,920 or power generators are being used, 84 84 00:02:56,920 --> 00:02:59,200 this will create noise and signal interference 85 85 00:02:59,200 --> 00:03:00,560 that will decrease the distance 86 86 00:03:00,560 --> 00:03:02,350 that cable is going to be able to support 87 87 00:03:02,350 --> 00:03:04,920 because there's more attenuation and more noise 88 88 00:03:04,920 --> 00:03:06,370 across that signal. 89 89 00:03:06,370 --> 00:03:07,940 Finally, the physical surroundings 90 90 00:03:07,940 --> 00:03:09,350 you're using your copper cables in 91 91 00:03:09,350 --> 00:03:11,400 can also increase your attenuation. 92 92 00:03:11,400 --> 00:03:13,760 Things like temperature, the construction of the walls 93 93 00:03:13,760 --> 00:03:16,650 or other barriers, and the type of wire installation itself 94 94 00:03:16,650 --> 00:03:19,130 can all negatively affect your signal strength. 95 95 00:03:19,130 --> 00:03:21,070 If you have freezing temperatures for instance, 96 96 00:03:21,070 --> 00:03:23,960 your copper cables will become more brittle and inflexible, 97 97 00:03:23,960 --> 00:03:25,970 which in turn slows down the connection 98 98 00:03:25,970 --> 00:03:27,610 and attenuates the signal. 99 99 00:03:27,610 --> 00:03:29,420 When you're experiencing hotter temperatures, 100 100 00:03:29,420 --> 00:03:31,840 the signals can actually overheat and the network cable 101 101 00:03:31,840 --> 00:03:33,560 could potentially even catch fire 102 102 00:03:33,560 --> 00:03:36,330 if the outside plastic melts away and the inside wire 103 103 00:03:36,330 --> 00:03:38,550 becomes exposed to flammable materials. 104 104 00:03:38,550 --> 00:03:40,500 For this reason, it's always important 105 105 00:03:40,500 --> 00:03:42,950 to have well-insulated wires and attempt to maintain 106 106 00:03:42,950 --> 00:03:44,400 the proper temperature control 107 107 00:03:44,400 --> 00:03:46,040 that your network connection needs 108 108 00:03:46,040 --> 00:03:49,120 to maintain a strong signal and minimal attenuation. 109 109 00:03:49,120 --> 00:03:52,350 So, what can you do when you experience attenuation? 110 110 00:03:52,350 --> 00:03:55,100 First, you can make sure you're using the proper cables 111 111 00:03:55,100 --> 00:03:57,530 for the physical environment you're operating within. 112 112 00:03:57,530 --> 00:04:00,030 If you're operating in a hotter or colder environment, 113 113 00:04:00,030 --> 00:04:02,310 you may need to switch to shielded twisted pair 114 114 00:04:02,310 --> 00:04:04,840 instead of unshielded twisted pair for example. 115 115 00:04:04,840 --> 00:04:07,040 Second, you can shorten the distance. 116 116 00:04:07,040 --> 00:04:09,740 While the maximum length is 100 meters for these cables, 117 117 00:04:09,740 --> 00:04:11,300 it's a good idea to use cables 118 118 00:04:11,300 --> 00:04:12,690 that are a bit shorter than that 119 119 00:04:12,690 --> 00:04:14,800 to ensure you always have a good, clear signal 120 120 00:04:14,800 --> 00:04:16,440 on all of your connections. 121 121 00:04:16,440 --> 00:04:19,290 Personally, I tend to implement an 80 meter limit 122 122 00:04:19,290 --> 00:04:22,440 on all of my twisted pair cables inside my networks. 123 123 00:04:22,440 --> 00:04:25,480 Third, you can use an amplifier or a repeater. 124 124 00:04:25,480 --> 00:04:26,730 These are layer one devices 125 125 00:04:26,730 --> 00:04:29,650 that take in the signal on one end, boost up the signal, 126 126 00:04:29,650 --> 00:04:31,750 and retransmit it out the other side. 127 127 00:04:31,750 --> 00:04:34,130 This means if I need to run a twisted pair cable 128 128 00:04:34,130 --> 00:04:38,350 over 150 meters, I could use a 75 or a 80 meter cable 129 129 00:04:38,350 --> 00:04:41,802 connected to a repeater, and then I can go the next 75 130 130 00:04:41,802 --> 00:04:44,880 to 80 meters to make the total 150 meters. 131 131 00:04:44,880 --> 00:04:47,570 By using this repeater, there's going to be no signal loss 132 132 00:04:47,570 --> 00:04:50,580 because we essentially rebroadcast out a new signal again 133 133 00:04:50,580 --> 00:04:54,120 from that repeater as we start over our distance limitation. 134 134 00:04:54,120 --> 00:04:55,510 If you're dealing with fiber cables 135 135 00:04:55,510 --> 00:04:58,120 instead of copper cables, you have a lot of the same issues 136 136 00:04:58,120 --> 00:05:00,570 in terms of attenuation because of distance, 137 137 00:05:00,570 --> 00:05:03,850 but, they don't begin to occur until much further out. 138 138 00:05:03,850 --> 00:05:05,290 This is because we're using light 139 139 00:05:05,290 --> 00:05:06,980 instead of electricity here. 140 140 00:05:06,980 --> 00:05:09,780 Now, for example, let's say you have a single mode fiber 141 141 00:05:09,780 --> 00:05:12,390 that has a maximum distance of 40 kilometers. 142 142 00:05:12,390 --> 00:05:14,370 You're not going to really suffer much signal loss 143 143 00:05:14,370 --> 00:05:17,760 until you get around 30 to 40 kilometers from your source 144 144 00:05:17,760 --> 00:05:19,820 depending on your environmental conditions. 145 145 00:05:19,820 --> 00:05:22,060 Another cause of attenuation in fiber cables 146 146 00:05:22,060 --> 00:05:24,680 tends to occur if you have cheaply constructed fiber cables 147 147 00:05:24,680 --> 00:05:27,550 or you have fiber cables that have dirty connectors. 148 148 00:05:27,550 --> 00:05:29,450 Let's imagine you have a pair of sunglasses on, 149 149 00:05:29,450 --> 00:05:31,760 and you have fingerprints all over the lenses, 150 150 00:05:31,760 --> 00:05:33,720 that makes it really hard to see through them, right? 151 151 00:05:33,720 --> 00:05:35,430 Because you have dirty glasses. 152 152 00:05:35,430 --> 00:05:38,090 Well, the same thing happens with fiber connectors. 153 153 00:05:38,090 --> 00:05:39,580 When you're dealing with fiber connections 154 154 00:05:39,580 --> 00:05:41,350 and your fiber connectors are dirty, 155 155 00:05:41,350 --> 00:05:43,610 this can lead to signal loss and attenuation 156 156 00:05:43,610 --> 00:05:45,280 because the light can't cleanly pass 157 157 00:05:45,280 --> 00:05:47,610 through those connectors because it's dirty. 158 158 00:05:47,610 --> 00:05:50,420 This adds to attenuation and signal loss for you. 159 159 00:05:50,420 --> 00:05:52,330 Now, if you're experiencing this attenuation 160 160 00:05:52,330 --> 00:05:54,970 with fiber cables, the first thing I recommend you do 161 161 00:05:54,970 --> 00:05:58,090 is change out the fiber cable for a higher quality cable 162 162 00:05:58,090 --> 00:06:01,150 or you clean and polish both ends of that fiber 163 163 00:06:01,150 --> 00:06:03,470 and make sure those connectors are really clean. 164 164 00:06:03,470 --> 00:06:05,590 You want to make sure there is not a dirty connector there 165 165 00:06:05,590 --> 00:06:08,310 because even something as little as your fingerprints on it 166 166 00:06:08,310 --> 00:06:10,860 can cause this attenuation to occur. 167 167 00:06:10,860 --> 00:06:12,580 Next, we have interference. 168 168 00:06:12,580 --> 00:06:14,780 Interference occurs when multiple cables operate 169 169 00:06:14,780 --> 00:06:16,280 in the same frequency band 170 170 00:06:16,280 --> 00:06:18,840 and they operate in close proximity to each other. 171 171 00:06:18,840 --> 00:06:19,750 To help prevent this, 172 172 00:06:19,750 --> 00:06:22,050 we want to use high quality twisted pair cables 173 173 00:06:22,050 --> 00:06:24,440 or use higher category rated cables. 174 174 00:06:24,440 --> 00:06:26,740 Now, this is because higher category rated cables 175 175 00:06:26,740 --> 00:06:28,580 are going to have more internal twist per inch 176 176 00:06:28,580 --> 00:06:30,550 inside their internal twisted pairs. 177 177 00:06:30,550 --> 00:06:33,030 These internal twists can help overcome the interference 178 178 00:06:33,030 --> 00:06:34,980 that can occur within a single cable 179 179 00:06:34,980 --> 00:06:37,300 inside of its own wired twisted pairs. 180 180 00:06:37,300 --> 00:06:38,990 Now additionally, if you see a twisted pair 181 181 00:06:38,990 --> 00:06:41,100 of network cable that's being run over 182 182 00:06:41,100 --> 00:06:43,030 or near a high power cable, 183 183 00:06:43,030 --> 00:06:44,710 this can cause interference as well 184 184 00:06:44,710 --> 00:06:46,740 and a large amount of signal loss. 185 185 00:06:46,740 --> 00:06:49,370 To solve this problem, you always want to plan your cable runs 186 186 00:06:49,370 --> 00:06:51,840 to operate in parallel and not directly next 187 187 00:06:51,840 --> 00:06:54,670 to any high power cables running in your cable trays 188 188 00:06:54,670 --> 00:06:56,070 or your risers. 189 189 00:06:56,070 --> 00:06:58,960 Finally, we have decibel or dB loss. 190 190 00:06:58,960 --> 00:07:00,760 Now, decibel loss is used to measure 191 191 00:07:00,760 --> 00:07:03,390 the amount of signal deterioration that we're experiencing 192 192 00:07:03,390 --> 00:07:04,800 on a given connection. 193 193 00:07:04,800 --> 00:07:06,140 This can be used to measure the signal 194 194 00:07:06,140 --> 00:07:08,230 on a copper or fiber cable. 195 195 00:07:08,230 --> 00:07:11,460 For copper cables, we see this reported as a dB loss, 196 196 00:07:11,460 --> 00:07:13,700 to represent the amount of voltage that has decreased 197 197 00:07:13,700 --> 00:07:15,450 since we sent the signal out originally 198 198 00:07:15,450 --> 00:07:17,090 over that twisted pair cable. 199 199 00:07:17,090 --> 00:07:18,460 For fiber connections though, 200 200 00:07:18,460 --> 00:07:20,530 this dB loss is instead going to represent 201 201 00:07:20,530 --> 00:07:22,720 the amount of light that's lost as it travels 202 202 00:07:22,720 --> 00:07:24,900 across the cable or the connection. 203 203 00:07:24,900 --> 00:07:27,010 If you're experiencing a high amount of dB loss 204 204 00:07:27,010 --> 00:07:29,380 on a copper cable, you need to replace that cable 205 205 00:07:29,380 --> 00:07:31,280 with a higher quality twisted pair cable 206 206 00:07:31,280 --> 00:07:32,530 with additional shielding 207 207 00:07:32,530 --> 00:07:34,530 or a higher number of twists per inch. 208 208 00:07:34,530 --> 00:07:36,610 If you're experiencing a high amount of dB loss 209 209 00:07:36,610 --> 00:07:39,190 on a fiber cable, you want to replace that cable 210 210 00:07:39,190 --> 00:07:40,940 with a higher quality fiber cable, 211 211 00:07:40,940 --> 00:07:43,340 such as a glass one instead of a plastic one. 212 212 00:07:43,340 --> 00:07:46,330 Or you need to clean and polish both ends of your cable 213 213 00:07:46,330 --> 00:07:48,140 and the associated connectors. 214 214 00:07:48,140 --> 00:07:50,280 All right, we just covered our three big 215 215 00:07:50,280 --> 00:07:52,520 cable signaling issues that you're going to experience 216 216 00:07:52,520 --> 00:07:54,560 in the field as a network technician. 217 217 00:07:54,560 --> 00:07:56,700 Just a reminder, these are attenuation, 218 218 00:07:56,700 --> 00:07:58,750 interference, and decibel loss. 219 219 00:07:58,750 --> 00:08:01,400 When you're testing your network for attenuation conditions, 220 220 00:08:01,400 --> 00:08:02,860 always use a cable certifier 221 221 00:08:02,860 --> 00:08:04,760 to measure the amount of attenuation. 222 222 00:08:04,760 --> 00:08:07,530 For fiber connections, you're going to use a fiber light meter 223 223 00:08:07,530 --> 00:08:09,560 to test for attenuation as well. 224 224 00:08:09,560 --> 00:08:11,930 If you need to test a connection for interference, 225 225 00:08:11,930 --> 00:08:14,410 you can connect a spectrum analyzer to the cable 226 226 00:08:14,410 --> 00:08:16,360 to see the exact frequencies and signals 227 227 00:08:16,360 --> 00:08:18,300 that are being sent over that connection. 228 228 00:08:18,300 --> 00:08:20,140 If you want to test for decibel loss, 229 229 00:08:20,140 --> 00:08:22,820 you're going to use a cable certifier, a cable analyzer, 230 230 00:08:22,820 --> 00:08:25,350 or a fiber light meter to measure the signal being sent 231 231 00:08:25,350 --> 00:08:27,200 and received across a given cable 232 232 00:08:27,200 --> 00:08:29,610 and report back that loss in decibels. 233 233 00:08:29,610 --> 00:08:31,440 For the exam, it's important to understand 234 234 00:08:31,440 --> 00:08:33,100 the tool you might use to troubleshoot 235 235 00:08:33,100 --> 00:08:35,100 the different cable connectivity issues.