1 1 00:00:00,550 --> 00:00:02,430 Ethernet fundamentals. 2 2 00:00:02,430 --> 00:00:03,740 In this section of the course, 3 3 00:00:03,740 --> 00:00:06,470 we're going to cover Layer 2 of the OSI Model 4 4 00:00:06,470 --> 00:00:10,300 in much more depth by digging into Ethernet fundamentals. 5 5 00:00:10,300 --> 00:00:11,670 As we go through this section, 6 6 00:00:11,670 --> 00:00:13,400 we're going to be touching on domain one, 7 7 00:00:13,400 --> 00:00:14,700 networking fundamentals, 8 8 00:00:14,700 --> 00:00:16,940 domain two, network implementations, 9 9 00:00:16,940 --> 00:00:18,820 domain four, network security, 10 10 00:00:18,820 --> 00:00:21,260 and domain five, network troubleshooting. 11 11 00:00:21,260 --> 00:00:22,670 We're going to cover a lot of stuff 12 12 00:00:22,670 --> 00:00:24,600 across a lot of domains here. 13 13 00:00:24,600 --> 00:00:26,713 Now we're going to cover objectives 1.3, 2.1, 2.3, 14 14 00:00:28,919 --> 00:00:31,480 4.4, and 5.5. 15 15 00:00:31,480 --> 00:00:34,230 Objective 1.3, is to summarize the types of cables 16 16 00:00:34,230 --> 00:00:35,080 and connectors, 17 17 00:00:35,080 --> 00:00:37,990 and explain which is the appropriate type for a solution, 18 18 00:00:37,990 --> 00:00:40,420 as we talk about our Ethernet standards. 19 19 00:00:40,420 --> 00:00:43,080 Objective 2.1, is going to be to compare and contrast 20 20 00:00:43,080 --> 00:00:44,760 various devices, their features, 21 21 00:00:44,760 --> 00:00:47,020 and their appropriate placement on the network. 22 22 00:00:47,020 --> 00:00:49,490 Objective 2.3, is given a scenario, 23 23 00:00:49,490 --> 00:00:52,460 configure and deploy common Ethernet switching features. 24 24 00:00:52,460 --> 00:00:55,500 And objective 4.4, is to compare and contrast 25 25 00:00:55,500 --> 00:00:58,450 remote access methods and security implementations. 26 26 00:00:58,450 --> 00:01:01,640 Finally, objective 5.5 is given a scenario, 27 27 00:01:01,640 --> 00:01:03,900 troubleshoot general networking issues. 28 28 00:01:03,900 --> 00:01:06,830 So without further delay, let's dive right into 29 29 00:01:06,830 --> 00:01:09,230 Ethernet fundamentals, and I'm going to warn you, 30 30 00:01:09,230 --> 00:01:11,310 this is a bit of a longer video, 31 31 00:01:11,310 --> 00:01:13,530 because there's a lot of stuff we need to know. 32 32 00:01:13,530 --> 00:01:15,080 Now in early computer networks, 33 33 00:01:15,080 --> 00:01:17,440 there were so many different networking technologies 34 34 00:01:17,440 --> 00:01:19,150 out there, and each of them was competing 35 35 00:01:19,150 --> 00:01:20,730 for a piece in the market share. 36 36 00:01:20,730 --> 00:01:22,090 There wasn't much standardization 37 37 00:01:22,090 --> 00:01:23,440 among the different types either, 38 38 00:01:23,440 --> 00:01:24,840 and so if you were using Ethernet, 39 39 00:01:24,840 --> 00:01:26,980 it didn't talk with other types of networks. 40 40 00:01:26,980 --> 00:01:29,370 Now, when I first started working with computer networks, 41 41 00:01:29,370 --> 00:01:31,190 we had lots of different things out there, 42 42 00:01:31,190 --> 00:01:33,230 including Ethernet, Token Bus, 43 43 00:01:33,230 --> 00:01:36,870 Token Ring, Fiber Distributed Data Interface or FDDI, 44 44 00:01:36,870 --> 00:01:38,963 Local Talk, Apple Talk, as well as others 45 45 00:01:38,963 --> 00:01:41,940 that were all fighting to be the dominant market leader. 46 46 00:01:41,940 --> 00:01:45,070 Well, there was one clear winner in these Layer 2 wars, 47 47 00:01:45,070 --> 00:01:47,800 and that was Ethernet for our local area networks. 48 48 00:01:47,800 --> 00:01:49,460 In this entire section of the course, 49 49 00:01:49,460 --> 00:01:51,670 we're going to focus specifically on Ethernet, 50 50 00:01:51,670 --> 00:01:53,610 because it's just that important. 51 51 00:01:53,610 --> 00:01:56,160 Now Ethernet has gotten extremely popular, 52 52 00:01:56,160 --> 00:01:58,680 so much so that if you don't understand Ethernet, 53 53 00:01:58,680 --> 00:01:59,900 you really don't understand the way 54 54 00:01:59,900 --> 00:02:02,050 today's modern networks operate. 55 55 00:02:02,050 --> 00:02:04,490 Ethernet has been with us a long time. 56 56 00:02:04,490 --> 00:02:06,790 Originally, it was run over coaxial cables, 57 57 00:02:06,790 --> 00:02:09,250 using BNC connectors and vampire taps. 58 58 00:02:09,250 --> 00:02:12,280 And these networks were called 10BASE2 and 10BASE5 59 59 00:02:12,280 --> 00:02:15,340 Ethernet networks, also nicknamed ThinNet and ThickNet, 60 60 00:02:15,340 --> 00:02:18,150 because of the relative size of their coaxial cables. 61 61 00:02:18,150 --> 00:02:19,750 Now, the great thing about these networks 62 62 00:02:19,750 --> 00:02:21,810 is they could cover a really long distance, 63 63 00:02:21,810 --> 00:02:24,820 up to 200 meters with the 10BASE2 networks, 64 64 00:02:24,820 --> 00:02:27,780 and 500 meters with a 10BASE5 networks. 65 65 00:02:27,780 --> 00:02:29,500 Now for the Network Plus exam, 66 66 00:02:29,500 --> 00:02:32,140 you don't need to memorize anything about 10BASE2 67 67 00:02:32,140 --> 00:02:33,780 or 10BASE5 networks anymore, 68 68 00:02:33,780 --> 00:02:36,240 because they're old and antiquated and likely, 69 69 00:02:36,240 --> 00:02:37,700 you're never going to see them. 70 70 00:02:37,700 --> 00:02:39,860 Now, the only reason I'm even talking about them, 71 71 00:02:39,860 --> 00:02:41,140 is because I want you to understand 72 72 00:02:41,140 --> 00:02:42,330 where Ethernet came from, 73 73 00:02:42,330 --> 00:02:45,000 because these were the first networks that used Ethernet 74 74 00:02:45,000 --> 00:02:47,380 and it was introduced in the early 1980s. 75 75 00:02:47,380 --> 00:02:48,240 Over time, though, 76 76 00:02:48,240 --> 00:02:51,230 we migrate to what is known as 10BASE-T Ethernet, 77 77 00:02:51,230 --> 00:02:52,860 and Ethernet became associated 78 78 00:02:52,860 --> 00:02:54,740 with this twisted pair cabling 79 79 00:02:54,740 --> 00:02:57,830 that could run 10 megabit per second networks over it. 80 80 00:02:57,830 --> 00:02:59,110 Now this twisted pair cabling, 81 81 00:02:59,110 --> 00:03:02,120 is known as Cat 3 or Category 3 wiring. 82 82 00:03:02,120 --> 00:03:04,904 These twisted pairs could be unshielded or shielded, 83 83 00:03:04,904 --> 00:03:06,720 and they were cheaper and easier to use 84 84 00:03:06,720 --> 00:03:10,227 than the older 10BASE2 or 10BASE5 coaxial networks. 85 85 00:03:10,227 --> 00:03:13,380 The only real disadvantage to the new 10BASE-T network, 86 86 00:03:13,380 --> 00:03:16,200 was it could only cover distance of up to 100 meters, 87 87 00:03:16,200 --> 00:03:18,050 before they need to have their signal repeated 88 88 00:03:18,050 --> 00:03:19,940 by a switch or a hub. 89 89 00:03:19,940 --> 00:03:21,960 Now I know that 10 megabits per second here, 90 90 00:03:21,960 --> 00:03:23,650 doesn't sound like a lot of speed. 91 91 00:03:23,650 --> 00:03:27,420 But back in the 1980s, this was super fast. 92 92 00:03:27,420 --> 00:03:29,690 After all, a dial-up modem in those days 93 93 00:03:29,690 --> 00:03:32,740 was lucky to reach speeds of 300 bits per second. 94 94 00:03:32,740 --> 00:03:35,670 So this internal network of 10 megabits per second, 95 95 00:03:35,670 --> 00:03:37,220 was a really fast speed. 96 96 00:03:37,220 --> 00:03:39,230 That's 10,000 bits per second. 97 97 00:03:39,230 --> 00:03:41,800 It was lightning fast to users back then. 98 98 00:03:41,800 --> 00:03:44,260 Now the big question, when it comes to network devices, 99 99 00:03:44,260 --> 00:03:46,570 especially when they start operating at these speeds, 100 100 00:03:46,570 --> 00:03:49,650 is how are they going to access the network and communicate? 101 101 00:03:49,650 --> 00:03:51,370 And this is really one of the core questions 102 102 00:03:51,370 --> 00:03:53,170 that Ethernet had to answer. 103 103 00:03:53,170 --> 00:03:54,970 Should the network be deterministic 104 104 00:03:54,970 --> 00:03:57,090 or should it be contention-based? 105 105 00:03:57,090 --> 00:03:59,440 Now, if you're going to use deterministic means, 106 106 00:03:59,440 --> 00:04:01,380 this is going to be where network access 107 107 00:04:01,380 --> 00:04:03,890 is going to be very organized and orderly. 108 108 00:04:03,890 --> 00:04:06,270 Some of the competing technologies like token bus 109 109 00:04:06,270 --> 00:04:07,580 and token ring networks, 110 110 00:04:07,580 --> 00:04:10,460 use this deterministic style of network access. 111 111 00:04:10,460 --> 00:04:12,800 If a device wanted to transmit data under the network, 112 112 00:04:12,800 --> 00:04:14,450 the device had to wait its turn, 113 113 00:04:14,450 --> 00:04:16,830 waiting for an electronic token to get to it, 114 114 00:04:16,830 --> 00:04:19,650 and that way they would know it was its turned to transmit. 115 115 00:04:19,650 --> 00:04:20,830 Now let's pretend for a moment, 116 116 00:04:20,830 --> 00:04:22,770 we're all sitting in a classroom together. 117 117 00:04:22,770 --> 00:04:23,603 There we are, 118 118 00:04:23,603 --> 00:04:26,250 you, me, and 20 to 25 other students, 119 119 00:04:26,250 --> 00:04:27,720 all sitting in this room. 120 120 00:04:27,720 --> 00:04:30,370 Now, if everybody talked at once, what would happen? 121 121 00:04:30,370 --> 00:04:32,770 Nobody could hear or understand anything. 122 122 00:04:32,770 --> 00:04:34,190 We'd have a whole bunch of collisions 123 123 00:04:34,190 --> 00:04:35,600 as we call them in the networking world, 124 124 00:04:35,600 --> 00:04:37,910 as everyone tries to talk over each other. 125 125 00:04:37,910 --> 00:04:40,730 Instead, we need to create a deterministic system 126 126 00:04:40,730 --> 00:04:43,040 to determine who's going to speak at any given time 127 127 00:04:43,040 --> 00:04:44,350 in my classroom. 128 128 00:04:44,350 --> 00:04:46,230 So, whenever I was teaching in a classroom, 129 129 00:04:46,230 --> 00:04:48,560 I would tell my students, you have to raise your hand, 130 130 00:04:48,560 --> 00:04:49,980 and then I'm going to call on you, 131 131 00:04:49,980 --> 00:04:51,640 and then it's your turn to talk, 132 132 00:04:51,640 --> 00:04:52,980 that's deterministic. 133 133 00:04:52,980 --> 00:04:54,220 Since I was the instructor, 134 134 00:04:54,220 --> 00:04:56,470 I was handing out the token, in this case, 135 135 00:04:56,470 --> 00:04:57,760 calling on somebody, 136 136 00:04:57,760 --> 00:04:59,660 and then they were given this virtual token 137 137 00:04:59,660 --> 00:05:01,770 and they could speak until they gave that virtual token 138 138 00:05:01,770 --> 00:05:03,690 back to me and said they were done, 139 139 00:05:03,690 --> 00:05:06,317 or at any time, I could tell them to stop talking, 140 140 00:05:06,317 --> 00:05:09,470 and I could take back that virtual token and speak myself, 141 141 00:05:09,470 --> 00:05:11,220 because again, I'm the instructor, 142 142 00:05:11,220 --> 00:05:13,030 I'm the one in charge in the room. 143 143 00:05:13,030 --> 00:05:16,130 Now, if you use the token ring or a token bus network, 144 144 00:05:16,130 --> 00:05:18,150 that is essentially how they operated. 145 145 00:05:18,150 --> 00:05:20,670 The great thing about this is there are zero collisions, 146 146 00:05:20,670 --> 00:05:22,530 because nobody's going to talk over each other. 147 147 00:05:22,530 --> 00:05:24,080 They all wait their turn. 148 148 00:05:24,080 --> 00:05:27,120 That's the great thing about using a deterministic network. 149 149 00:05:27,120 --> 00:05:28,540 Now, the other way we can determine 150 150 00:05:28,540 --> 00:05:30,060 who gets access to the network, 151 151 00:05:30,060 --> 00:05:32,950 is by using what's known as contention-based networks. 152 152 00:05:32,950 --> 00:05:35,660 Now contention-based networks are very chaotic. 153 153 00:05:35,660 --> 00:05:38,620 Unlike my classroom example, which was very deterministic, 154 154 00:05:38,620 --> 00:05:40,070 and I get to be in charge of telling everyone 155 155 00:05:40,070 --> 00:05:41,930 when and how long they can talk, 156 156 00:05:41,930 --> 00:05:43,280 a contention-based model, 157 157 00:05:43,280 --> 00:05:45,070 is more like when you go to the pub on Friday night 158 158 00:05:45,070 --> 00:05:46,190 with your friends. 159 159 00:05:46,190 --> 00:05:48,010 Maybe you're hanging out with five of your friends, 160 160 00:05:48,010 --> 00:05:49,140 and you're sitting around a table there 161 161 00:05:49,140 --> 00:05:50,380 and you're having some drinks. 162 162 00:05:50,380 --> 00:05:52,500 Now normally, people know how to interact 163 163 00:05:52,500 --> 00:05:55,210 in these situations and they carry on a conversation, right? 164 164 00:05:55,210 --> 00:05:56,570 We've all been there before. 165 165 00:05:56,570 --> 00:05:57,940 There isn't somebody in your group who says, 166 166 00:05:57,940 --> 00:06:00,280 hold on, Alex, it's Tamara's turn to talk now, 167 167 00:06:00,280 --> 00:06:02,550 or okay Tamara, you have 90 seconds, 168 168 00:06:02,550 --> 00:06:04,640 now, it's John's turn, let's switch. 169 169 00:06:04,640 --> 00:06:05,780 It doesn't work that way. 170 170 00:06:05,780 --> 00:06:07,650 I don't know about you, but if I had friends like that, 171 171 00:06:07,650 --> 00:06:09,160 I think I would leave that conversation 172 172 00:06:09,160 --> 00:06:10,720 and find me some new friends. 173 173 00:06:10,720 --> 00:06:13,890 Now, instead, we actually have a natural way of talking 174 174 00:06:13,890 --> 00:06:14,920 with each other, right? 175 175 00:06:14,920 --> 00:06:16,150 Each of us, more or less, 176 176 00:06:16,150 --> 00:06:18,080 take some time to tell our stories, 177 177 00:06:18,080 --> 00:06:21,070 and the flow of conversation naturally just happens. 178 178 00:06:21,070 --> 00:06:23,060 I pick up the conversation when there's a space, 179 179 00:06:23,060 --> 00:06:24,810 and I fill it in with some of my stories, 180 180 00:06:24,810 --> 00:06:26,300 and then somebody else picks up the conversation, 181 181 00:06:26,300 --> 00:06:28,750 and says their stories or what they want to talk about. 182 182 00:06:28,750 --> 00:06:30,300 This is contention-based. 183 183 00:06:30,300 --> 00:06:32,110 Essentially, as you're sitting there, 184 184 00:06:32,110 --> 00:06:35,010 you hear a gap in the conversation and you begin to speak. 185 185 00:06:35,010 --> 00:06:36,380 If somebody else is speaking, 186 186 00:06:36,380 --> 00:06:38,470 you listen until you find an appropriate time 187 187 00:06:38,470 --> 00:06:40,770 for you to transmit, or in this case say, 188 188 00:06:40,770 --> 00:06:43,380 whatever it is you wanted to add to that conversation. 189 189 00:06:43,380 --> 00:06:44,500 Now, the problem with using 190 190 00:06:44,500 --> 00:06:46,080 a contention-based method like this, 191 191 00:06:46,080 --> 00:06:47,900 is that you can have collisions. 192 192 00:06:47,900 --> 00:06:48,920 Have you ever been at the pub, 193 193 00:06:48,920 --> 00:06:50,790 and you're having a conversation with some friends 194 194 00:06:50,790 --> 00:06:52,960 and all of a sudden you hear that gap in the conversation, 195 195 00:06:52,960 --> 00:06:55,580 and you go to speak and you find that somebody else speaks 196 196 00:06:55,580 --> 00:06:57,080 at the exact same time as you? 197 197 00:06:57,080 --> 00:06:58,230 Well, that's a collision. 198 198 00:06:58,230 --> 00:07:00,370 You both transmit at the same time. 199 199 00:07:00,370 --> 00:07:02,610 When that occurs, you both spoke over each other 200 200 00:07:02,610 --> 00:07:04,920 and nobody around you could hear what was being said, 201 201 00:07:04,920 --> 00:07:06,540 because it mumbled together. 202 202 00:07:06,540 --> 00:07:08,900 So likely, one of you paused, 203 203 00:07:08,900 --> 00:07:10,520 let the other one finish their story, 204 204 00:07:10,520 --> 00:07:12,690 and then try talking again. 205 205 00:07:12,690 --> 00:07:15,330 Now, because of this natural way of having a conversation 206 206 00:07:15,330 --> 00:07:17,360 can lead to people talking over each other, 207 207 00:07:17,360 --> 00:07:18,980 and therefore creating collisions, 208 208 00:07:18,980 --> 00:07:21,280 some people also might take up more time than others. 209 209 00:07:21,280 --> 00:07:22,113 And there's other issues like that 210 210 00:07:22,113 --> 00:07:24,570 when we deal with these contention-based models. 211 211 00:07:24,570 --> 00:07:26,310 They can be very chaotic. 212 212 00:07:26,310 --> 00:07:29,780 And oddly enough, this is how Ethernet chose to work. 213 213 00:07:29,780 --> 00:07:31,390 Ethernet, unlike token ring, 214 214 00:07:31,390 --> 00:07:34,040 actually chose to use a contention-based network. 215 215 00:07:34,040 --> 00:07:35,640 Now, why would they do that? 216 216 00:07:35,640 --> 00:07:39,230 Well, because contention-based networks have lower overhead. 217 217 00:07:39,230 --> 00:07:40,440 This means you don't have to pass around 218 218 00:07:40,440 --> 00:07:41,680 this electronic token, 219 219 00:07:41,680 --> 00:07:43,420 and this way you can make full use 220 220 00:07:43,420 --> 00:07:45,080 of all the bandwidth in the network, 221 221 00:07:45,080 --> 00:07:47,720 because anyone can talk at any time. 222 222 00:07:47,720 --> 00:07:49,100 Now I know this may seem odd, 223 223 00:07:49,100 --> 00:07:50,900 but it's actually a good thing. 224 224 00:07:50,900 --> 00:07:52,450 You see, in some of these traditional 225 225 00:07:52,450 --> 00:07:53,740 deterministic networks, 226 226 00:07:53,740 --> 00:07:55,340 you would actually split up the communication 227 227 00:07:55,340 --> 00:07:56,790 into chunks of time. 228 228 00:07:56,790 --> 00:07:57,623 For instance, 229 229 00:07:57,623 --> 00:07:59,720 let's say we have eight devices on our network. 230 230 00:07:59,720 --> 00:08:01,980 We could say that everybody gets one-eighth of a second 231 231 00:08:01,980 --> 00:08:02,910 to communicate. 232 232 00:08:02,910 --> 00:08:04,090 And then they're going to pass the token 233 233 00:08:04,090 --> 00:08:05,430 to the next network's device. 234 234 00:08:05,430 --> 00:08:06,560 That device is going to communicate 235 235 00:08:06,560 --> 00:08:07,620 for their eighth of a second, 236 236 00:08:07,620 --> 00:08:09,680 and we keep doing that as we go in a circle. 237 237 00:08:09,680 --> 00:08:11,220 So if every one second, 238 238 00:08:11,220 --> 00:08:13,760 you can only transmit one-eighth of a second. 239 239 00:08:13,760 --> 00:08:16,020 That is it for a 10 megabit per second network, 240 240 00:08:16,020 --> 00:08:19,160 you're going to get to transmit 1.25 megabits per second, 241 241 00:08:19,160 --> 00:08:20,600 not the full 10. 242 242 00:08:20,600 --> 00:08:22,970 Now effectively, we've just cut down the network speed 243 243 00:08:22,970 --> 00:08:25,640 by a factor of eight, because most of the time, 244 244 00:08:25,640 --> 00:08:27,780 these devices don't have anything to communicate, 245 245 00:08:27,780 --> 00:08:29,930 but we still gave them the time period. 246 246 00:08:29,930 --> 00:08:31,020 Think about when you and your friends 247 247 00:08:31,020 --> 00:08:32,447 are sitting around the table at the pub again. 248 248 00:08:32,447 --> 00:08:34,410 And if I said that each you had to take turns 249 249 00:08:34,410 --> 00:08:36,230 and can only speak for one minute, 250 250 00:08:36,230 --> 00:08:38,140 some of your friends will be able to fill that minute 251 251 00:08:38,140 --> 00:08:39,390 and then run out of time, 252 252 00:08:39,390 --> 00:08:41,880 and others wouldn't be able to fill them in at all. 253 253 00:08:41,880 --> 00:08:43,120 They would tell a quick one-line joke, 254 254 00:08:43,120 --> 00:08:45,500 and then sit there for 45 seconds of silence. 255 255 00:08:45,500 --> 00:08:47,930 This is the difference between the way people communicate. 256 256 00:08:47,930 --> 00:08:50,230 For that reason, deterministic models 257 257 00:08:50,230 --> 00:08:53,560 can waste a lot of resources and we'd be sitting in silence. 258 258 00:08:53,560 --> 00:08:54,960 So Ethernet chose instead, 259 259 00:08:54,960 --> 00:08:56,480 to use contention-based networks, 260 260 00:08:56,480 --> 00:08:58,620 to maximize the efficiency of the network, 261 261 00:08:58,620 --> 00:09:01,730 by allowing anyone to use all the bandwidth at any time 262 262 00:09:01,730 --> 00:09:03,340 for as long as they need it. 263 263 00:09:03,340 --> 00:09:05,750 But if any network device can transmit at any time 264 264 00:09:05,750 --> 00:09:08,460 on the network, how are we going to prevent collisions? 265 265 00:09:08,460 --> 00:09:10,230 Well, the way Ethernet approaches this, 266 266 00:09:10,230 --> 00:09:13,960 is by using something known as CSMA/CD. 267 267 00:09:13,960 --> 00:09:16,350 This stands for Carrier Sense Multiple Access 268 268 00:09:16,350 --> 00:09:17,890 with Collision Detection. 269 269 00:09:17,890 --> 00:09:19,620 Now, what exactly is that? 270 270 00:09:19,620 --> 00:09:21,970 Well, just like when you're sitting around the table 271 271 00:09:21,970 --> 00:09:23,710 at the pub, with all your friends, 272 272 00:09:23,710 --> 00:09:26,900 you first listened and waited for the gap in conversation. 273 273 00:09:26,900 --> 00:09:29,430 Once you heard that, you then tried to speak. 274 274 00:09:29,430 --> 00:09:32,140 Now, if two of you spoke at the same time, you simply say, 275 275 00:09:32,140 --> 00:09:34,770 oh, I'm sorry, we must have spoken over each other. 276 276 00:09:34,770 --> 00:09:37,920 Let's try again, and then we wait and we try again. 277 277 00:09:37,920 --> 00:09:39,210 That's the idea here. 278 278 00:09:39,210 --> 00:09:42,910 Well, in Ethernet, we do the same thing using CSMA/CD. 279 279 00:09:42,910 --> 00:09:44,290 Let's break down each part of this 280 280 00:09:44,290 --> 00:09:45,550 and explain it a little bit. 281 281 00:09:45,550 --> 00:09:47,780 The CS or carrier sense part of this, 282 282 00:09:47,780 --> 00:09:48,950 means that the Ethernet 283 283 00:09:48,950 --> 00:09:51,190 needs to be able to do carrier sensing. 284 284 00:09:51,190 --> 00:09:52,980 Now, a carrier is essentially the line 285 285 00:09:52,980 --> 00:09:54,340 we're going to communicate on. 286 286 00:09:54,340 --> 00:09:56,090 This means that it's going to listen to the network 287 287 00:09:56,090 --> 00:09:59,010 and determine if there's a signal already being transmitted. 288 288 00:09:59,010 --> 00:10:01,130 Now, this is known as carrier sensing. 289 289 00:10:01,130 --> 00:10:03,370 Carrier is just this fancy word in electronics 290 290 00:10:03,370 --> 00:10:05,800 for a signal that carries information or data. 291 291 00:10:05,800 --> 00:10:07,930 So we're going to try to sense if that data 292 292 00:10:07,930 --> 00:10:09,350 is currently being transmitted, 293 293 00:10:09,350 --> 00:10:11,120 or to use our pub example, 294 294 00:10:11,120 --> 00:10:14,050 we're going to see, is there a gap in the conversation? 295 295 00:10:14,050 --> 00:10:15,640 Now, if there is a gap, 296 296 00:10:15,640 --> 00:10:19,730 this is where the MA part of CSMA/CD comes into play. 297 297 00:10:19,730 --> 00:10:21,830 MA stands for multiple access. 298 298 00:10:21,830 --> 00:10:24,220 All that means is that there are many different devices 299 299 00:10:24,220 --> 00:10:26,600 that all have the ability to access, listen to, 300 300 00:10:26,600 --> 00:10:29,720 and transmit to that network at the same time. 301 301 00:10:29,720 --> 00:10:32,590 So Ethernet is going to have lots of devices on the network, 302 302 00:10:32,590 --> 00:10:35,180 and they're all going to be able to listen before they speak. 303 303 00:10:35,180 --> 00:10:39,760 That is the CSMA part of CSMA/CD. 304 304 00:10:39,760 --> 00:10:42,340 Now we get to the important part, the CD part, 305 305 00:10:42,340 --> 00:10:43,830 collision detection. 306 306 00:10:43,830 --> 00:10:46,200 Since of all these devices are listening to the network, 307 307 00:10:46,200 --> 00:10:48,090 if they detect a collision has occurred, 308 308 00:10:48,090 --> 00:10:49,880 when they are transmitting something, 309 309 00:10:49,880 --> 00:10:53,050 then those two devices who are both talking over each other 310 310 00:10:53,050 --> 00:10:55,400 can decide who's going to transmit their data now, 311 311 00:10:55,400 --> 00:10:57,594 and who's going to wait to retransmit. 312 312 00:10:57,594 --> 00:10:58,730 To simplify this process, 313 313 00:10:58,730 --> 00:11:00,610 Ethernet uses a clever method to determine 314 314 00:11:00,610 --> 00:11:02,630 who gets to transmit first. 315 315 00:11:02,630 --> 00:11:04,840 Essentially, if a collision is detected, 316 316 00:11:04,840 --> 00:11:07,250 both Ethernet devices will stop transmitting 317 317 00:11:07,250 --> 00:11:10,120 and pick a random number and then wait to retransmit. 318 318 00:11:10,120 --> 00:11:12,090 So if you and your friend both talk over each other 319 319 00:11:12,090 --> 00:11:13,900 at the pub, you might have a standing rule 320 320 00:11:13,900 --> 00:11:15,600 that you both will stop what you're doing, 321 321 00:11:15,600 --> 00:11:16,670 pick a random number, 322 322 00:11:16,670 --> 00:11:18,530 and then count up to that number in your head, 323 323 00:11:18,530 --> 00:11:21,900 and if nobody is speaking yet, you can then start to talk. 324 324 00:11:21,900 --> 00:11:23,830 This is exactly what Ethernet devices do 325 325 00:11:23,830 --> 00:11:25,170 when they detect a collision. 326 326 00:11:25,170 --> 00:11:26,460 They stop transmitting, 327 327 00:11:26,460 --> 00:11:28,650 they pick a random number, and they count. 328 328 00:11:28,650 --> 00:11:30,960 This is known as a random back-off timer, 329 329 00:11:30,960 --> 00:11:32,170 and it allows the two devices 330 330 00:11:32,170 --> 00:11:33,810 to attempt to retransmit again, 331 331 00:11:33,810 --> 00:11:35,420 when their timers hit zero. 332 332 00:11:35,420 --> 00:11:36,420 Think of it this way. 333 333 00:11:36,420 --> 00:11:38,380 Have you ever been walking down a hallway at work 334 334 00:11:38,380 --> 00:11:39,900 and somebody is coming from the other direction, 335 335 00:11:39,900 --> 00:11:42,337 it might be a small hallway and you walk up to each other, 336 336 00:11:42,337 --> 00:11:43,760 and you kind of do that little dance 337 337 00:11:43,760 --> 00:11:45,540 where I go left and you go right, 338 338 00:11:45,540 --> 00:11:47,180 and you go right and I'll go left, 339 339 00:11:47,180 --> 00:11:48,120 and you really don't say anything, 340 340 00:11:48,120 --> 00:11:49,550 but you just kind of figure it out? 341 341 00:11:49,550 --> 00:11:51,590 Well, if so, you're smack dab in the middle 342 342 00:11:51,590 --> 00:11:53,690 of a CSMA/CD collision. 343 343 00:11:53,690 --> 00:11:55,430 So what should you do? 344 344 00:11:55,430 --> 00:11:58,360 Well, what I usually do, is exactly what Ethernet does. 345 345 00:11:58,360 --> 00:12:00,370 I stop and I count to three, 346 346 00:12:00,370 --> 00:12:01,940 and then I look and see if the other person 347 347 00:12:01,940 --> 00:12:04,240 has walked around me, or if they're still in front of me. 348 348 00:12:04,240 --> 00:12:06,800 If they haven't walked around me, I'll walk around them. 349 349 00:12:06,800 --> 00:12:08,630 It effectively ends that little dance, 350 350 00:12:08,630 --> 00:12:11,150 and the collision is over inside the hallway. 351 351 00:12:11,150 --> 00:12:14,030 That's the same idea here with Carrier Sense Multiple Access 352 352 00:12:14,030 --> 00:12:15,250 Collision Detection. 353 353 00:12:15,250 --> 00:12:18,320 So let's take a look at how this looks on a network. 354 354 00:12:18,320 --> 00:12:20,830 Here's the example where I have six devices on the network 355 355 00:12:20,830 --> 00:12:23,530 using a bus, just to make it easier for us to see. 356 356 00:12:23,530 --> 00:12:26,300 Yes, you could use a star, a bus, a ring, 357 357 00:12:26,300 --> 00:12:28,720 or any topology you really want with Ethernet. 358 358 00:12:28,720 --> 00:12:31,290 So from my illustration, and to make it graphically easy, 359 359 00:12:31,290 --> 00:12:32,750 we're going to use a bus. 360 360 00:12:32,750 --> 00:12:34,210 Now here we have six devices 361 361 00:12:34,210 --> 00:12:36,220 and they're all sharing the same wire. 362 362 00:12:36,220 --> 00:12:38,430 If your number four wants to talk to number five, 363 363 00:12:38,430 --> 00:12:40,610 and they want to communicate over this network segment, 364 364 00:12:40,610 --> 00:12:41,970 that means there's no problem, 365 365 00:12:41,970 --> 00:12:43,860 because nobody else is talking right now. 366 366 00:12:43,860 --> 00:12:45,660 But what happens if number two 367 367 00:12:45,660 --> 00:12:47,520 wants to talk to number one right now? 368 368 00:12:47,520 --> 00:12:50,570 Well, carrier sensing shows us that the line is clear. 369 369 00:12:50,570 --> 00:12:52,850 So two transmits and one receives. 370 370 00:12:52,850 --> 00:12:54,300 There's no problem here. 371 371 00:12:54,300 --> 00:12:57,140 Now, what happens if both three and number five 372 372 00:12:57,140 --> 00:12:59,680 are both going to try talking at the same time? 373 373 00:12:59,680 --> 00:13:00,920 They listen to the carrier, 374 374 00:13:00,920 --> 00:13:02,400 they didn't hear anybody else talking, 375 375 00:13:02,400 --> 00:13:04,230 and they both started transmitting. 376 376 00:13:04,230 --> 00:13:06,180 Well, this causes a collision, 377 377 00:13:06,180 --> 00:13:08,520 just as we can see here with the red X. 378 378 00:13:08,520 --> 00:13:10,970 So now we've detected a collision. 379 379 00:13:10,970 --> 00:13:12,100 What do we do? 380 380 00:13:12,100 --> 00:13:14,200 Well, three and five are both going to stop, 381 381 00:13:14,200 --> 00:13:15,860 and they're going to pick a random number 382 382 00:13:15,860 --> 00:13:18,000 to serve as their random back-off timer. 383 383 00:13:18,000 --> 00:13:21,120 Now, in the case of three, it chose to wait 30 milliseconds. 384 384 00:13:21,120 --> 00:13:24,200 In the case of five, it chose 150 milliseconds. 385 385 00:13:24,200 --> 00:13:25,550 So what happens next? 386 386 00:13:25,550 --> 00:13:27,670 Well, 30 milliseconds goes by, 387 387 00:13:27,670 --> 00:13:29,110 number three listens to the carrier, 388 388 00:13:29,110 --> 00:13:31,230 and it doesn't detect anybody else transmitting, 389 389 00:13:31,230 --> 00:13:33,140 so it starts to transmit. 390 390 00:13:33,140 --> 00:13:35,600 At the same time, number five is still waiting, 391 391 00:13:35,600 --> 00:13:37,780 because only 30 milliseconds have passed 392 392 00:13:37,780 --> 00:13:40,300 and they chose to wait 150 milliseconds. 393 393 00:13:40,300 --> 00:13:44,110 So they still have 120 milliseconds on their back-off timer. 394 394 00:13:44,110 --> 00:13:46,260 Now, what happens if it takes number three, 395 395 00:13:46,260 --> 00:13:48,720 300 milliseconds to transmit everything? 396 396 00:13:48,720 --> 00:13:51,740 Well, number five is going to wait for its back-off timer 397 397 00:13:51,740 --> 00:13:55,220 of 150 milliseconds, and then when its timer hit zero, 398 398 00:13:55,220 --> 00:13:57,150 it listens to the carrier again. 399 399 00:13:57,150 --> 00:13:59,610 This time though, it hears somebody transmitting, 400 400 00:13:59,610 --> 00:14:01,220 in this case, it's number three. 401 401 00:14:01,220 --> 00:14:03,660 So it's just going to wait until it hears an open spot 402 402 00:14:03,660 --> 00:14:06,370 in the conversation, and then it will transmit, 403 403 00:14:06,370 --> 00:14:08,180 in this case, it should be when number three 404 404 00:14:08,180 --> 00:14:11,530 is done transmitting about 180 milliseconds from now. 405 405 00:14:11,530 --> 00:14:13,410 Now when number three is done communicating 406 406 00:14:13,410 --> 00:14:15,400 and the carrier seems clear for transmission, 407 407 00:14:15,400 --> 00:14:16,950 number five will transmit. 408 408 00:14:16,950 --> 00:14:19,500 If someone else happens to be transmitting at the same time, 409 409 00:14:19,500 --> 00:14:21,070 again, we have a collision, 410 410 00:14:21,070 --> 00:14:22,740 both choose a random back-off timer, 411 411 00:14:22,740 --> 00:14:24,360 they wait and the cycle repeats, 412 412 00:14:24,360 --> 00:14:27,100 until everybody transmits everything they want to send. 413 413 00:14:27,100 --> 00:14:29,740 Now, I know this may seem like a bad way of doing things, 414 414 00:14:29,740 --> 00:14:31,760 because as networks get busier and busier 415 415 00:14:31,760 --> 00:14:32,760 and you have more clients, 416 416 00:14:32,760 --> 00:14:34,630 you're going to have a lot more collisions. 417 417 00:14:34,630 --> 00:14:37,510 And guess what, you would be exactly right. 418 418 00:14:37,510 --> 00:14:39,290 The more devices you have communicating 419 419 00:14:39,290 --> 00:14:40,810 on a single network segment, 420 420 00:14:40,810 --> 00:14:43,050 the more collisions you're going to have. 421 421 00:14:43,050 --> 00:14:45,600 Each area of the network that shares a single segment 422 422 00:14:45,600 --> 00:14:47,600 is known as a collision domain. 423 423 00:14:47,600 --> 00:14:48,630 In this example, 424 424 00:14:48,630 --> 00:14:51,780 we had six devices all sharing a single bus cable. 425 425 00:14:51,780 --> 00:14:53,660 That made up our collision domain. 426 426 00:14:53,660 --> 00:14:56,710 With Ethernet, anytime you have devices on the same cable, 427 427 00:14:56,710 --> 00:14:59,070 or they're all connected to the same hub, 428 428 00:14:59,070 --> 00:15:01,340 you are sharing the same collision domain. 429 429 00:15:01,340 --> 00:15:03,800 Because of this, all of the devices need to operate 430 430 00:15:03,800 --> 00:15:05,280 in half duplex mode, 431 431 00:15:05,280 --> 00:15:07,510 because they have to listen and then talk. 432 432 00:15:07,510 --> 00:15:09,600 They can't do both at the same time. 433 433 00:15:09,600 --> 00:15:11,840 If a device talks and listens at the same time, 434 434 00:15:11,840 --> 00:15:12,930 they simply hear themselves, 435 435 00:15:12,930 --> 00:15:14,580 and think somebody else is transmitting. 436 436 00:15:14,580 --> 00:15:17,390 So they cannot operate in full duplex, 437 437 00:15:17,390 --> 00:15:19,910 where they can listen and talk at the same time. 438 438 00:15:19,910 --> 00:15:22,210 If you're using a hub or a shared network segment, 439 439 00:15:22,210 --> 00:15:25,180 you have to be able to listen to prevent those collisions. 440 440 00:15:25,180 --> 00:15:27,900 For this reason, we need to keep collision domains 441 441 00:15:27,900 --> 00:15:29,710 very small inside our networks. 442 442 00:15:29,710 --> 00:15:31,320 If you have a large collision domain, 443 443 00:15:31,320 --> 00:15:33,150 there is a high probability of collisions, 444 444 00:15:33,150 --> 00:15:36,200 and each collision requires that data to be retransmitted 445 445 00:15:36,200 --> 00:15:38,580 again, waiting for a back-off timer to pass, 446 446 00:15:38,580 --> 00:15:40,790 and this is going to minimize your bandwidth. 447 447 00:15:40,790 --> 00:15:43,660 This is going to slow down the entire network segment. 448 448 00:15:43,660 --> 00:15:45,880 Now, if you have a hub with four devices, 449 449 00:15:45,880 --> 00:15:47,630 it probably won't be a major issue, 450 450 00:15:47,630 --> 00:15:50,830 but if you're using a hub with 24 or 48 ports, 451 451 00:15:50,830 --> 00:15:53,970 the collisions can bring your network to a screeching halt. 452 452 00:15:53,970 --> 00:15:54,980 Think about it this way. 453 453 00:15:54,980 --> 00:15:56,160 If we're going to go to the pub 454 454 00:15:56,160 --> 00:15:58,080 and we take a group of four friends, 455 455 00:15:58,080 --> 00:15:59,930 we can make that conversation work. 456 456 00:15:59,930 --> 00:16:02,310 Everyone can listen for the gaps and they can transmit, 457 457 00:16:02,310 --> 00:16:04,540 and we won't have too many people talking over each other. 458 458 00:16:04,540 --> 00:16:07,810 But if we go at the same time with 20 to 25 people, 459 459 00:16:07,810 --> 00:16:10,230 we're going to have entirely too many collisions 460 460 00:16:10,230 --> 00:16:11,660 and it just won't work. 461 461 00:16:11,660 --> 00:16:14,710 So we need to break that larger group into smaller groups. 462 462 00:16:14,710 --> 00:16:15,920 For my pub example, 463 463 00:16:15,920 --> 00:16:18,670 we may do this by breaking up our 20 to 25 friends 464 464 00:16:18,670 --> 00:16:20,380 into groups of four or five people 465 465 00:16:20,380 --> 00:16:22,380 and sit them each at a different table. 466 466 00:16:22,380 --> 00:16:23,213 This breaks down 467 467 00:16:23,213 --> 00:16:26,200 our large single collision domain of 20 to 25 people 468 468 00:16:26,200 --> 00:16:28,310 into five to six smaller collision domains 469 469 00:16:28,310 --> 00:16:30,060 of four to five people each. 470 470 00:16:30,060 --> 00:16:32,240 In our networks, we do the exact same thing 471 471 00:16:32,240 --> 00:16:35,420 to break down collision domains by using Ethernet switches. 472 472 00:16:35,420 --> 00:16:38,100 This drastically increases the scalability of our networks 473 473 00:16:38,100 --> 00:16:40,430 by creating a lot of different collision domains. 474 474 00:16:40,430 --> 00:16:42,870 Remember, lots of collision domains is good, 475 475 00:16:42,870 --> 00:16:45,240 because you have less people in each one. 476 476 00:16:45,240 --> 00:16:46,390 Every single switch port 477 477 00:16:46,390 --> 00:16:49,000 is actually considered its own collision domain. 478 478 00:16:49,000 --> 00:16:50,850 You can see here with my switch in the center, 479 479 00:16:50,850 --> 00:16:52,540 I have four collision domains. 480 480 00:16:52,540 --> 00:16:55,520 There is one in between each computer and the switch itself. 481 481 00:16:55,520 --> 00:16:57,150 Now, if I was using a hub, 482 482 00:16:57,150 --> 00:16:58,820 all four devices and the hub 483 483 00:16:58,820 --> 00:17:01,270 are all part of that single collision domain. 484 484 00:17:01,270 --> 00:17:03,810 So I have five devices in one collision domain. 485 485 00:17:03,810 --> 00:17:06,070 But by simply replacing the hub with a switch, 486 486 00:17:06,070 --> 00:17:07,640 I can increase the speed of my network, 487 487 00:17:07,640 --> 00:17:10,370 because now nobody else is talking on that switch port, 488 488 00:17:10,370 --> 00:17:12,540 except the device that I cabled to it. 489 489 00:17:12,540 --> 00:17:14,910 Therefore, the switch port now can operate 490 490 00:17:14,910 --> 00:17:16,720 in full duplex mode. 491 491 00:17:16,720 --> 00:17:19,770 After all, it's my only device on that network segment, 492 492 00:17:19,770 --> 00:17:21,640 so there's no chance of collision. 493 493 00:17:21,640 --> 00:17:24,400 It's like I can just ignore the fact that I had to listen. 494 494 00:17:24,400 --> 00:17:25,730 If I'm sitting in my room alone, 495 495 00:17:25,730 --> 00:17:28,850 I can talk all I want and I will never have a collision, 496 496 00:17:28,850 --> 00:17:30,550 because nobody's here to interrupt me. 497 497 00:17:30,550 --> 00:17:32,130 I don't have to listen before I transmit. 498 498 00:17:32,130 --> 00:17:33,630 I can just keep talking. 499 499 00:17:33,630 --> 00:17:35,540 I have a full-time dedicated channel 500 500 00:17:35,540 --> 00:17:37,830 between my device and my switch. 501 501 00:17:37,830 --> 00:17:40,940 So I'm allowed to now operate in full duplex mode, 502 502 00:17:40,940 --> 00:17:42,520 transmitting my data faster, 503 503 00:17:42,520 --> 00:17:44,060 getting more bandwidth out of this connection, 504 504 00:17:44,060 --> 00:17:46,280 and ensuring there are no collisions. 505 505 00:17:46,280 --> 00:17:47,830 All right, now that we covered 506 506 00:17:47,830 --> 00:17:49,570 the basics about Ethernet networks, 507 507 00:17:49,570 --> 00:17:50,930 let's dive into the different ways 508 508 00:17:50,930 --> 00:17:52,660 that we classify Ethernet. 509 509 00:17:52,660 --> 00:17:54,540 These are known as the Ethernet standards, 510 510 00:17:54,540 --> 00:17:56,480 and they take the form of a number, 511 511 00:17:56,480 --> 00:17:59,140 the word base, and then one or two letters. 512 512 00:17:59,140 --> 00:18:02,310 For example, earlier I mentioned that we use 10BASE-T 513 513 00:18:02,310 --> 00:18:04,460 for our Cat 3 Ethernet networks. 514 514 00:18:04,460 --> 00:18:06,830 10BASE-T is the slowest version of Ethernet, 515 515 00:18:06,830 --> 00:18:09,090 and only operates at 10 megabits per second, 516 516 00:18:09,090 --> 00:18:11,610 and for up to a distance of 100 meters. 517 517 00:18:11,610 --> 00:18:13,880 I already covered the basics of copper Ethernet standards 518 518 00:18:13,880 --> 00:18:16,770 in the lesson on copper cabling, but in this lesson, 519 519 00:18:16,770 --> 00:18:19,040 we're going to do a quick review of those standards, 520 520 00:18:19,040 --> 00:18:22,160 as we say, which Ethernet standard goes for each one, 521 521 00:18:22,160 --> 00:18:24,130 and then we're going to talk about the Ethernet standards 522 522 00:18:24,130 --> 00:18:25,810 for fiber optic cables too. 523 523 00:18:25,810 --> 00:18:28,480 So let's do a quick review of copper Ethernet standards. 524 524 00:18:28,480 --> 00:18:29,740 We're going to start with the slowest 525 525 00:18:29,740 --> 00:18:31,840 and move our way upward to the fastest. 526 526 00:18:31,840 --> 00:18:33,560 First, we have 10BASE-T, 527 527 00:18:33,560 --> 00:18:35,380 which operates at 10 megabits per second, 528 528 00:18:35,380 --> 00:18:36,930 over Cat 3 cables. 529 529 00:18:36,930 --> 00:18:38,690 This is known as Ethernet. 530 530 00:18:38,690 --> 00:18:40,890 Second, we have 100BASE-TX, 531 531 00:18:40,890 --> 00:18:42,840 which operates at 100 megabits per second, 532 532 00:18:42,840 --> 00:18:44,380 over Cat 5 cables. 533 533 00:18:44,380 --> 00:18:46,530 This is known as fast Ethernet. 534 534 00:18:46,530 --> 00:18:48,570 Third, we have 1000BASE-T, 535 535 00:18:48,570 --> 00:18:50,620 which operates at 1000 megabits per second 536 536 00:18:50,620 --> 00:18:52,120 or one gigabit per second, 537 537 00:18:52,120 --> 00:18:54,920 over either Cat 5e or Cat 6 cables. 538 538 00:18:54,920 --> 00:18:57,280 This is called gigabit Ethernet. 539 539 00:18:57,280 --> 00:18:59,570 Fourth, we have 10GBASE-T, 540 540 00:18:59,570 --> 00:19:02,410 which operates at 10 gigabits per second over Cat 6, 541 541 00:19:02,410 --> 00:19:04,580 Cat 6a, and Cat 7 cables. 542 542 00:19:04,580 --> 00:19:07,830 This is known as 10 gigabit Ethernet, go figure. 543 543 00:19:07,830 --> 00:19:10,400 And fifth, and finally, we have 40GBASE-T, 544 544 00:19:10,400 --> 00:19:13,740 which operates at 40 gigabits per second over Cat 8 cables. 545 545 00:19:13,740 --> 00:19:16,350 This of course is known as 40 gigabit Ethernet. 546 546 00:19:16,350 --> 00:19:17,183 As you can see, 547 547 00:19:17,183 --> 00:19:19,930 they stopped getting creative with the names after Cat 5. 548 548 00:19:19,930 --> 00:19:21,440 Now, when it comes to distances, 549 549 00:19:21,440 --> 00:19:23,900 remember most copper cabling used by Ethernet 550 550 00:19:23,900 --> 00:19:27,140 can only go up to 100 meters before the signal attenuates, 551 551 00:19:27,140 --> 00:19:29,620 and you can no longer maintain signal integrity. 552 552 00:19:29,620 --> 00:19:32,200 The only two exceptions to this rule are Cat 8, 553 553 00:19:32,200 --> 00:19:33,670 which only goes 30 meters, 554 554 00:19:33,670 --> 00:19:36,360 and Cat 6, which only goes 55 meters, 555 555 00:19:36,360 --> 00:19:37,510 if you want to reach the full 556 556 00:19:37,510 --> 00:19:39,210 10 gigabits per second of speed, 557 557 00:19:39,210 --> 00:19:42,130 otherwise, you can go up to 100 meters with Cat 6, 558 558 00:19:42,130 --> 00:19:44,770 if you stick to a one gigabit per second speed. 559 559 00:19:44,770 --> 00:19:46,480 Now, remember when I say speed, 560 560 00:19:46,480 --> 00:19:48,300 I'm really talking about bandwidth. 561 561 00:19:48,300 --> 00:19:50,190 Bandwidth is measured about how many bits 562 562 00:19:50,190 --> 00:19:52,250 the network can transmit in one second, 563 563 00:19:52,250 --> 00:19:54,110 known as a bit per second. 564 564 00:19:54,110 --> 00:19:55,400 We can get up to megabits, 565 565 00:19:55,400 --> 00:19:57,410 and then that's millions of bits per second, 566 566 00:19:57,410 --> 00:20:00,460 or gigabits, which is billions of bits per second, as well. 567 567 00:20:00,460 --> 00:20:01,970 Depending on the type of cable, 568 568 00:20:01,970 --> 00:20:03,520 this is going to determine the capacity 569 569 00:20:03,520 --> 00:20:05,130 for the bandwidth of your network. 570 570 00:20:05,130 --> 00:20:07,860 So if you replace all your old Cat 3 cables and switches, 571 571 00:20:07,860 --> 00:20:09,420 with newer Cat 7 ones, 572 572 00:20:09,420 --> 00:20:10,580 you're going to increase your bandwidth 573 573 00:20:10,580 --> 00:20:13,840 from 10 megabits per second to 10 gigabits per second, 574 574 00:20:13,840 --> 00:20:16,070 making it 1000 times faster. 575 575 00:20:16,070 --> 00:20:17,930 Now, let's switch from copper to fiber 576 576 00:20:17,930 --> 00:20:20,290 and talk about the different Ethernet standards that we use 577 577 00:20:20,290 --> 00:20:21,660 with fiber cables. 578 578 00:20:21,660 --> 00:20:25,130 Unlike copper, fiber can go further than just 100 meters. 579 579 00:20:25,130 --> 00:20:27,200 Now multi-mode fibers can reach distances 580 580 00:20:27,200 --> 00:20:29,510 of 200 to 500 meters or more, 581 581 00:20:29,510 --> 00:20:31,560 and single-mode fibers can reach distances 582 582 00:20:31,560 --> 00:20:33,080 of up to 40 kilometers, 583 583 00:20:33,080 --> 00:20:35,130 before you have to repeat that signal. 584 584 00:20:35,130 --> 00:20:37,790 First, we have 100BASE-FX. 585 585 00:20:37,790 --> 00:20:40,200 This is going to operate at 100 megabits per second, 586 586 00:20:40,200 --> 00:20:41,570 over multi-mode fiber, 587 587 00:20:41,570 --> 00:20:44,060 and it can reach a distance up to two kilometers. 588 588 00:20:44,060 --> 00:20:46,150 Now this is a bit special because normally, 589 589 00:20:46,150 --> 00:20:48,440 multi-mode isn't going to be able to go this far, 590 590 00:20:48,440 --> 00:20:51,460 but this particular multi-mode range that's being used, 591 591 00:20:51,460 --> 00:20:53,780 is actually going to border on the single-mode range 592 592 00:20:53,780 --> 00:20:55,550 when we talk about the actual light source, 593 593 00:20:55,550 --> 00:20:58,840 and this is why the distance is longer for 100BASE-FX 594 594 00:20:58,840 --> 00:21:01,580 even though it technically uses multi-mode fibers. 595 595 00:21:01,580 --> 00:21:04,240 Now second, we have 100BASE-SX, 596 596 00:21:04,240 --> 00:21:06,490 which is going to operate at 100 megabits per second, 597 597 00:21:06,490 --> 00:21:08,050 over single-mode fiber, 598 598 00:21:08,050 --> 00:21:11,820 but it's going to use a shorter wavelength than 100BASE-FX, 599 599 00:21:11,820 --> 00:21:13,290 which makes it cheaper to produce, 600 600 00:21:13,290 --> 00:21:15,400 because it's going to use LEDs as the light source 601 601 00:21:15,400 --> 00:21:16,650 instead of a laser. 602 602 00:21:16,650 --> 00:21:20,380 100BASE-SX is going to operate at 100 megabits per second 603 603 00:21:20,380 --> 00:21:24,260 at distance of up to 300 meters using a multi-mode fiber. 604 604 00:21:24,260 --> 00:21:26,670 Third, we have 1000BASE-SX, 605 605 00:21:26,670 --> 00:21:28,940 which operates at 1000 megabits per second, 606 606 00:21:28,940 --> 00:21:32,010 or one gigabit per second, over multi-mode fiber, 607 607 00:21:32,010 --> 00:21:34,930 using nanometer near-infrared wavelengths. 608 608 00:21:34,930 --> 00:21:39,930 1000BASE-SX can reach distances of 200 to about 550 meters. 609 609 00:21:40,050 --> 00:21:42,480 Fourth, we have 1000BASE-LX, 610 610 00:21:42,480 --> 00:21:44,940 which is going to operate at 1000 megabits per second, 611 611 00:21:44,940 --> 00:21:48,310 or one gigabit per second, over a single-mode fiber. 612 612 00:21:48,310 --> 00:21:51,960 Now, 1000BASE-LX is going to use a long wavelength laser 613 613 00:21:51,960 --> 00:21:53,040 as its light source, 614 614 00:21:53,040 --> 00:21:55,110 and this means it can go further distances 615 615 00:21:55,110 --> 00:21:57,040 of up to five kilometers. 616 616 00:21:57,040 --> 00:21:59,470 1000BASE-LX is a bit strange though, 617 617 00:21:59,470 --> 00:22:00,510 because you can also use it 618 618 00:22:00,510 --> 00:22:02,610 with multi-mode fibers if you want to. 619 619 00:22:02,610 --> 00:22:04,800 If you use it with the cheaper multi-mode fiber, 620 620 00:22:04,800 --> 00:22:06,440 then the speed is going to remain the same, 621 621 00:22:06,440 --> 00:22:10,730 but your distance is going to drop down to about 550 meters. 622 622 00:22:10,730 --> 00:22:13,340 Fifth, we have 10GBASE-SR. 623 623 00:22:13,340 --> 00:22:15,540 Now, this is going to operate at 10 gigabits per second 624 624 00:22:15,540 --> 00:22:17,300 over multi-mode fiber. 625 625 00:22:17,300 --> 00:22:19,190 SR stands for short range. 626 626 00:22:19,190 --> 00:22:21,130 Because this uses a multi-mode fiber, 627 627 00:22:21,130 --> 00:22:22,700 it's going to limit your maximum distance 628 628 00:22:22,700 --> 00:22:24,430 to about 400 meters. 629 629 00:22:24,430 --> 00:22:26,930 And sixth, we have 10GBASE-LR, 630 630 00:22:26,930 --> 00:22:28,790 which operates at 10 gigabits per second, 631 631 00:22:28,790 --> 00:22:30,450 over a single-mode fiber. 632 632 00:22:30,450 --> 00:22:32,430 Now, LR stands for long reach, 633 633 00:22:32,430 --> 00:22:34,230 because it uses a single-mode fiber 634 634 00:22:34,230 --> 00:22:37,000 that can reach distances of up to 10 kilometers. 635 635 00:22:37,000 --> 00:22:39,140 All right, when it comes to fiber Ethernet standards, 636 636 00:22:39,140 --> 00:22:40,830 you don't have to memorize the fact 637 637 00:22:40,830 --> 00:22:43,000 that there are 200 meters, or 500 meters, 638 638 00:22:43,000 --> 00:22:46,100 or five kilometers, or 10 kilometers, or 40 kilometers. 639 639 00:22:46,100 --> 00:22:49,180 What is important is to remember their relative distances. 640 640 00:22:49,180 --> 00:22:50,450 When it comes to distances, 641 641 00:22:50,450 --> 00:22:52,870 you really need to memorize just a few key things. 642 642 00:22:52,870 --> 00:22:56,730 First, copper cables have a maximum distance of 100 meters. 643 643 00:22:56,730 --> 00:22:58,890 Second, if you're using Cat 6, 644 644 00:22:58,890 --> 00:23:00,570 you're going to be using it at 100 meters, 645 645 00:23:00,570 --> 00:23:03,470 then you need to limit your speed to one gigabit per second, 646 646 00:23:03,470 --> 00:23:05,470 instead of 10 gigabits per second. 647 647 00:23:05,470 --> 00:23:08,890 Third, if you're using Cat 6 and you're under 55 meters, 648 648 00:23:08,890 --> 00:23:11,230 you can increase your speed to 10 gigabits per second, 649 649 00:23:11,230 --> 00:23:13,300 instead of one gigabit per second. 650 650 00:23:13,300 --> 00:23:15,700 Fourth, if you're dealing with multi-mode fiber, 651 651 00:23:15,700 --> 00:23:17,760 you're going to be dealing with shorter distances. 652 652 00:23:17,760 --> 00:23:20,880 That means something around 200 to 500 meters. 653 653 00:23:20,880 --> 00:23:22,900 Fifth, if you need longer distances, 654 654 00:23:22,900 --> 00:23:24,820 you have to use single-mode fibers. 655 655 00:23:24,820 --> 00:23:26,110 This is where we start talking about things 656 656 00:23:26,110 --> 00:23:28,600 in kilometers and distance instead of meters. 657 657 00:23:28,600 --> 00:23:31,760 So we're talking two or 10 or 40 kilometers. 658 658 00:23:31,760 --> 00:23:32,720 For the exam, 659 659 00:23:32,720 --> 00:23:34,820 you may see questions about specific cable lengths 660 660 00:23:34,820 --> 00:23:37,020 or limitations when it comes to copper. 661 661 00:23:37,020 --> 00:23:39,650 But for fiber, they're only going to ask you about the fact 662 662 00:23:39,650 --> 00:23:42,600 that multi-mode distances are longer than copper, 663 663 00:23:42,600 --> 00:23:44,780 but shorter than single-mode. 664 664 00:23:44,780 --> 00:23:46,160 Now this is where you have to figure out 665 665 00:23:46,160 --> 00:23:47,500 which cable you're going to use. 666 666 00:23:47,500 --> 00:23:49,490 Copper is great for short distances. 667 667 00:23:49,490 --> 00:23:51,210 Fiber, if you need short distances, 668 668 00:23:51,210 --> 00:23:52,360 you're going to use multi-mode, 669 669 00:23:52,360 --> 00:23:53,880 and if you need long distances, 670 670 00:23:53,880 --> 00:23:55,850 you're going to use single-mode. 671 671 00:23:55,850 --> 00:23:57,430 Now, another thing they're going to test you on 672 672 00:23:57,430 --> 00:23:58,360 in regards to fiber, 673 673 00:23:58,360 --> 00:24:00,100 is whether a fiber Ethernet standard 674 674 00:24:00,100 --> 00:24:02,740 is going to use multi-mode or single-mode fibers. 675 675 00:24:02,740 --> 00:24:05,180 For example, you might see a question like this. 676 676 00:24:05,180 --> 00:24:06,210 You're a network technician, 677 677 00:24:06,210 --> 00:24:08,080 and you need to select an Ethernet standard 678 678 00:24:08,080 --> 00:24:09,730 that will allow you to connect your main office 679 679 00:24:09,730 --> 00:24:12,820 to your branch office that's located at 35 kilometers away, 680 680 00:24:12,820 --> 00:24:14,560 which of the following should you use? 681 681 00:24:14,560 --> 00:24:15,840 10GBASE-T, 682 682 00:24:15,840 --> 00:24:16,753 1000BASE-SX, 683 683 00:24:16,753 --> 00:24:18,810 10GBASE-LR, 684 684 00:24:18,810 --> 00:24:20,560 or 1000BASE-T? 685 685 00:24:20,560 --> 00:24:21,970 So is this question really asking 686 686 00:24:21,970 --> 00:24:24,890 about the length of the cable and memorizing the distances? 687 687 00:24:24,890 --> 00:24:26,210 Well no, not really. 688 688 00:24:26,210 --> 00:24:28,760 Instead, it's asking you about a single-mode cable 689 689 00:24:28,760 --> 00:24:31,040 and being able to figure out which of these is single-mode, 690 690 00:24:31,040 --> 00:24:33,860 because we know copper cables are less than 100 meters 691 691 00:24:33,860 --> 00:24:36,260 and multi-mode cables are less than 500 meters 692 692 00:24:36,260 --> 00:24:37,900 with modern fiber cables. 693 693 00:24:37,900 --> 00:24:40,440 So if you can remember that 1000BASE-LR 694 694 00:24:40,440 --> 00:24:43,210 is a single-mode cable, you've got your answer. 695 695 00:24:43,210 --> 00:24:45,410 Now, is there an easy way to memorize which cables 696 696 00:24:45,410 --> 00:24:47,220 are single-mode and which are multi-mode? 697 697 00:24:47,220 --> 00:24:50,060 Well, I personally use a little memory to help me do this. 698 698 00:24:50,060 --> 00:24:52,630 Remember, we covered six different types of fiber cables 699 699 00:24:52,630 --> 00:24:53,890 in this lesson, right? 700 700 00:24:53,890 --> 00:24:57,487 We covered 100BASE-FX, 100BASE-SX, 1000BASE-SX, 701 701 00:24:58,330 --> 00:25:02,790 1000BASE-LX, 10GBASE-SR, and 10GBASE-LR. 702 702 00:25:02,790 --> 00:25:03,900 Now, you may remember, 703 703 00:25:03,900 --> 00:25:06,980 that I said that 100BASE-LX was special, right? 704 704 00:25:06,980 --> 00:25:08,050 The reason it was special, 705 705 00:25:08,050 --> 00:25:09,610 is because you could use either single-mode 706 706 00:25:09,610 --> 00:25:11,330 or multi-mode fiber with it. 707 707 00:25:11,330 --> 00:25:12,940 So the rest of them though, 708 708 00:25:12,940 --> 00:25:14,740 we have a really simple little saying 709 709 00:25:14,740 --> 00:25:16,510 that'll help us remember which ones are single, 710 710 00:25:16,510 --> 00:25:18,010 and which ones are multi-mode, 711 711 00:25:18,010 --> 00:25:19,370 and it goes like this, 712 712 00:25:19,370 --> 00:25:20,960 S is not single. 713 713 00:25:20,960 --> 00:25:21,793 That's it. 714 714 00:25:21,793 --> 00:25:23,380 If you remember that S is not single, 715 715 00:25:23,380 --> 00:25:25,170 it will tell you whether or not that fiber 716 716 00:25:25,170 --> 00:25:28,510 is a single-mode or multi-mode fiber based on its name. 717 717 00:25:28,510 --> 00:25:31,370 So if you see an S there in the fiber Ethernet standard, 718 718 00:25:31,370 --> 00:25:36,120 like 100BASE-SX, 1000BASE-SX, 10GBASE-SR, 719 719 00:25:36,120 --> 00:25:38,230 you know it's using a multi-mode fiber, 720 720 00:25:38,230 --> 00:25:40,020 because it's short range. 721 721 00:25:40,020 --> 00:25:42,100 So every time you see S in the name, 722 722 00:25:42,100 --> 00:25:44,380 remember S is not single. 723 723 00:25:44,380 --> 00:25:45,890 Therefore, if there's an S in the name, 724 724 00:25:45,890 --> 00:25:47,750 it must be a multi-mode fiber. 725 725 00:25:47,750 --> 00:25:50,910 If you don't see the S, it's used for longer distances. 726 726 00:25:50,910 --> 00:25:53,510 This rule holds true for most everything out there, 727 727 00:25:53,510 --> 00:25:55,600 except the 1000BASE-LX, 728 728 00:25:55,600 --> 00:25:57,690 because this one works with both single-mode 729 729 00:25:57,690 --> 00:25:59,500 and multi-mode fibers. 730 730 00:25:59,500 --> 00:26:00,720 All right, in this lesson, 731 731 00:26:00,720 --> 00:26:03,440 we covered just a few of the Ethernet fiber standards, 732 732 00:26:03,440 --> 00:26:05,410 specifically, the ones you're going to be asked about 733 733 00:26:05,410 --> 00:26:06,810 on the Network Plus exam, 734 734 00:26:06,810 --> 00:26:09,170 but be aware there are many others out there, 735 735 00:26:09,170 --> 00:26:11,773 including things like 1000BASE-EX, 10GBASE-ER, 736 736 00:26:12,899 --> 00:26:14,377 100GBASE-LR4, 100GBASE-ER4, and many others. 737 737 00:26:18,050 --> 00:26:20,370 But for the exam, you only need to know 738 738 00:26:20,370 --> 00:26:22,320 the six that we covered in this lesson.