1 1 00:00:00,421 --> 00:00:03,150 If we start on the bottom of the OSI Model, 2 2 00:00:03,150 --> 00:00:05,875 we'll find our first layer, the physical layer. 3 3 00:00:05,875 --> 00:00:09,110 Now, this is where bits are transmitted across the network 4 4 00:00:09,110 --> 00:00:10,570 and includes all of the physical 5 5 00:00:10,570 --> 00:00:13,090 and electrical characteristics of this network. 6 6 00:00:13,090 --> 00:00:14,120 So, this is going to tell us 7 7 00:00:14,120 --> 00:00:16,030 whether we're using an Ethernet network, 8 8 00:00:16,030 --> 00:00:18,440 whether we're using fiber or copper cables, 9 9 00:00:18,440 --> 00:00:20,800 whether we're using Cat5 or Cat6, 10 10 00:00:20,800 --> 00:00:22,830 and even if we're using radio frequency 11 11 00:00:22,830 --> 00:00:24,490 in the case of Wi-Fi. 12 12 00:00:24,490 --> 00:00:26,210 Regardless of which method we're using 13 13 00:00:26,210 --> 00:00:28,430 to send our data across this first layer, 14 14 00:00:28,430 --> 00:00:30,420 it's always going to occur as bits, 15 15 00:00:30,420 --> 00:00:31,890 and these are binary bits. 16 16 00:00:31,890 --> 00:00:35,000 These are going to be a series of ones and zeros. 17 17 00:00:35,000 --> 00:00:36,960 Now, each media has a different way 18 18 00:00:36,960 --> 00:00:40,140 of representing these bits, these series of ones and zeros, 19 19 00:00:40,140 --> 00:00:41,970 because these series of ones and zeros 20 20 00:00:41,970 --> 00:00:44,780 are the basic building blocks of all of our data. 21 21 00:00:44,780 --> 00:00:46,890 For example, if I'm using a copper wire, 22 22 00:00:46,890 --> 00:00:49,169 such as in a Cat5 or a Cat6 network, 23 23 00:00:49,169 --> 00:00:51,870 you may see that there's zero voltage on the wire 24 24 00:00:51,870 --> 00:00:53,200 when you have a zero bit, 25 25 00:00:53,200 --> 00:00:55,010 and then if you want to represent a one, 26 26 00:00:55,010 --> 00:00:57,520 you might use plus 5 or negative five volts 27 27 00:00:57,520 --> 00:00:58,803 on that copper wire. 28 28 00:00:58,803 --> 00:01:01,220 Now, when we switch between these two modes, 29 29 00:01:01,220 --> 00:01:03,160 this tells us whether we should read a one 30 30 00:01:03,160 --> 00:01:04,640 or a zero on the network, 31 31 00:01:04,640 --> 00:01:06,854 and this is called transition modulation. 32 32 00:01:06,854 --> 00:01:09,190 Now, for the exam, you don't need to understand 33 33 00:01:09,190 --> 00:01:11,780 the specifics of transition modulation. 34 34 00:01:11,780 --> 00:01:14,090 But you should understand this basic concept 35 35 00:01:14,090 --> 00:01:15,180 that on this wire, 36 36 00:01:15,180 --> 00:01:17,590 we're going to have one level that represents a one 37 37 00:01:17,590 --> 00:01:19,841 and another level that represents a zero. 38 38 00:01:19,841 --> 00:01:21,800 Let me give you another example. 39 39 00:01:21,800 --> 00:01:24,820 This time, let's pretend we're using a fiber optic cable. 40 40 00:01:24,820 --> 00:01:26,150 Now, with fiber optic cables, 41 41 00:01:26,150 --> 00:01:28,610 we're going to use light instead of voltages. 42 42 00:01:28,610 --> 00:01:30,470 Now, it's similar to the way we did voltages, 43 43 00:01:30,470 --> 00:01:32,530 but instead, when we want to represent a one, 44 44 00:01:32,530 --> 00:01:33,940 we turn the light on. 45 45 00:01:33,940 --> 00:01:36,470 If we want to represent a zero, we turn the light off. 46 46 00:01:36,470 --> 00:01:38,400 Now, we can just read the state of light. 47 47 00:01:38,400 --> 00:01:39,233 Is it on? 48 48 00:01:39,233 --> 00:01:40,066 That's a one. 49 49 00:01:40,066 --> 00:01:40,899 Is it off? 50 50 00:01:40,899 --> 00:01:41,732 That's a zero. 51 51 00:01:41,732 --> 00:01:43,430 And when there's a transition between, 52 52 00:01:43,430 --> 00:01:45,610 that tells us between these two modes 53 53 00:01:45,610 --> 00:01:48,103 whether we should be reading this as a one or zero. 54 54 00:01:48,103 --> 00:01:50,090 Now, as we start understanding that, 55 55 00:01:50,090 --> 00:01:52,100 we then have to look at the cables themself 56 56 00:01:52,100 --> 00:01:54,490 because this is also part of our physical layer. 57 57 00:01:54,490 --> 00:01:57,680 If we're using something like a Cat5 or a Cat6 cable, 58 58 00:01:57,680 --> 00:01:59,870 we may have a certain connector on the end 59 59 00:01:59,870 --> 00:02:03,020 called an RJ45, which allows us to plug that cable 60 60 00:02:03,020 --> 00:02:05,396 into the back of a computer or into a switch. 61 61 00:02:05,396 --> 00:02:07,860 Now, the way that connector is wired 62 62 00:02:07,860 --> 00:02:09,760 is based on a certain standard. 63 63 00:02:09,760 --> 00:02:12,180 We use two standards inside our network: 64 64 00:02:12,180 --> 00:02:16,910 TIA/EIA-568A and TIA/EIA-568B. 65 65 00:02:18,050 --> 00:02:19,310 Now, we'll talk about these 66 66 00:02:19,310 --> 00:02:21,510 and which way these pins actually are set up 67 67 00:02:21,510 --> 00:02:24,190 inside, this connector in a future lesson. 68 68 00:02:24,190 --> 00:02:25,370 This is going to be important 69 69 00:02:25,370 --> 00:02:27,400 because as we start talking about these, 70 70 00:02:27,400 --> 00:02:29,150 this is going to tell us whether or not we're using 71 71 00:02:29,150 --> 00:02:31,960 crossover cables or straight-thru cables. 72 72 00:02:31,960 --> 00:02:33,460 If we use a crossover cable, 73 73 00:02:33,460 --> 00:02:35,340 we're actually going to flip the transmission 74 74 00:02:35,340 --> 00:02:37,460 and receive bits on the end of the cable. 75 75 00:02:37,460 --> 00:02:39,560 So, one end will be the A standard 76 76 00:02:39,560 --> 00:02:41,420 and one end will be the B standard. 77 77 00:02:41,420 --> 00:02:44,280 But if we're using a straight-thru cable or a patch cable, 78 78 00:02:44,280 --> 00:02:46,824 we're going to have the B standard on both sides. 79 79 00:02:46,824 --> 00:02:48,880 Now, again, it's important to understand 80 80 00:02:48,880 --> 00:02:50,090 these wiring standards, 81 81 00:02:50,090 --> 00:02:52,670 so, we're going to spend some time on them in a future lesson 82 82 00:02:52,670 --> 00:02:55,220 because on the exam, you may be asked 83 83 00:02:55,220 --> 00:02:57,166 to wire up an Ethernet jack. 84 84 00:02:57,166 --> 00:02:59,950 Maybe they're going to tell you to make a crossover cable 85 85 00:02:59,950 --> 00:03:02,496 and you have to drag the right colors to the right pins. 86 86 00:03:02,496 --> 00:03:03,880 That kind of a thing. 87 87 00:03:03,880 --> 00:03:05,240 And so, to make sure you're ready for that, 88 88 00:03:05,240 --> 00:03:07,720 we're going to cover that in a separate lesson. 89 89 00:03:07,720 --> 00:03:10,500 Now, at this point, we've talked about having our cables, 90 90 00:03:10,500 --> 00:03:13,140 we've talked about how we represent bits on those cables, 91 91 00:03:13,140 --> 00:03:14,610 and we talked about how we're going to set up 92 92 00:03:14,610 --> 00:03:16,170 the connectors of those cables. 93 93 00:03:16,170 --> 00:03:17,560 But there's another thing we have to think about 94 94 00:03:17,560 --> 00:03:18,780 at the physical layer, 95 95 00:03:18,780 --> 00:03:21,100 and that's the topology of the network. 96 96 00:03:21,100 --> 00:03:22,840 How are we actually running these cables 97 97 00:03:22,840 --> 00:03:25,266 to physically connect the different devices together? 98 98 00:03:25,266 --> 00:03:28,270 Well, we look at this from a Layer 1 perspective, 99 99 00:03:28,270 --> 00:03:30,460 we can look at this based on the things we talked about 100 100 00:03:30,460 --> 00:03:32,090 in the last section of the course. 101 101 00:03:32,090 --> 00:03:35,020 Is it a bus, is it a ring, is it a star? 102 102 00:03:35,020 --> 00:03:36,290 Is it a hub and spoke? 103 103 00:03:36,290 --> 00:03:38,510 How about a full mesh, a partial mesh, 104 104 00:03:38,510 --> 00:03:40,605 or any other topology that we discussed. 105 105 00:03:40,605 --> 00:03:42,440 When it comes to figuring this out, 106 106 00:03:42,440 --> 00:03:44,730 you're going to look at how they're physically cabled, 107 107 00:03:44,730 --> 00:03:46,050 and if you drew them out, 108 108 00:03:46,050 --> 00:03:48,420 does it make a line like a bus, 109 109 00:03:48,420 --> 00:03:50,090 a ring, going in a circle, 110 110 00:03:50,090 --> 00:03:51,170 or a star pattern? 111 111 00:03:51,170 --> 00:03:53,780 And that will tell you what physical topology you have. 112 112 00:03:53,780 --> 00:03:56,045 This, again, is a Layer 1 issue. 113 113 00:03:56,045 --> 00:03:58,390 Another issue that we have to concern ourself with 114 114 00:03:58,390 --> 00:04:01,360 at Layer 1 is synchronizing our communications. 115 115 00:04:01,360 --> 00:04:04,630 We have to ask ourself how does the receiving end know 116 116 00:04:04,630 --> 00:04:06,500 if it's ready to accept ones and zeros 117 117 00:04:06,500 --> 00:04:07,940 that we're going to send it? 118 118 00:04:07,940 --> 00:04:10,150 Now, this sounds like a really easy thing to do 119 119 00:04:10,150 --> 00:04:11,210 if we're talking to each other, 120 120 00:04:11,210 --> 00:04:14,020 but with computers, this can get much more complicated. 121 121 00:04:14,020 --> 00:04:15,860 So, to make sure that we understand this, 122 122 00:04:15,860 --> 00:04:17,640 we have two things that can happen. 123 123 00:04:17,640 --> 00:04:20,010 It can either be transmitted asynchronously 124 124 00:04:20,010 --> 00:04:21,319 or synchronously. 125 125 00:04:21,319 --> 00:04:24,220 Now, when I'm looking at asynchronous communication, 126 126 00:04:24,220 --> 00:04:26,780 you should be able to consider something like a voice mail. 127 127 00:04:26,780 --> 00:04:28,630 You call up your friend, they don't answer, 128 128 00:04:28,630 --> 00:04:31,340 and so, you leave a message so they can listen to it later. 129 129 00:04:31,340 --> 00:04:34,470 The communication happens out of sync or out of time. 130 130 00:04:34,470 --> 00:04:36,010 You do it and then later on, 131 131 00:04:36,010 --> 00:04:37,870 they can go back and listen to it. 132 132 00:04:37,870 --> 00:04:41,470 Now, in networks, this happens via a start and stop bit. 133 133 00:04:41,470 --> 00:04:43,270 Similarly to how your friend can press Play 134 134 00:04:43,270 --> 00:04:45,530 on their voicemail system to listen to their message, 135 135 00:04:45,530 --> 00:04:47,350 a network can send a start bit 136 136 00:04:47,350 --> 00:04:49,430 when it wants to start beginning the transmission 137 137 00:04:49,430 --> 00:04:51,670 and then a stop bit to tell the other side, 138 138 00:04:51,670 --> 00:04:53,330 hey, I'm done transmitting, 139 139 00:04:53,330 --> 00:04:55,550 you've gotten everything I'm going to send. 140 140 00:04:55,550 --> 00:04:56,700 Now, if we decide to go 141 141 00:04:56,700 --> 00:04:59,430 and do communications synchronously, on the other hand, 142 142 00:04:59,430 --> 00:05:02,240 we have to be in the same place at the same time. 143 143 00:05:02,240 --> 00:05:03,820 So, in our previous example, 144 144 00:05:03,820 --> 00:05:05,360 if your friend picked up the phone 145 145 00:05:05,360 --> 00:05:06,860 and you had a conversation, 146 146 00:05:06,860 --> 00:05:08,930 you could talk to them and they could talk to you, 147 147 00:05:08,930 --> 00:05:10,800 this is a synchronized conversation 148 148 00:05:10,800 --> 00:05:13,590 because you're both talking at the same time. 149 149 00:05:13,590 --> 00:05:15,690 Now, this communication happens in real time. 150 150 00:05:15,690 --> 00:05:17,940 That's what's great about synchronization. 151 151 00:05:17,940 --> 00:05:19,840 Now, as far as when we start talking about this 152 152 00:05:19,840 --> 00:05:21,390 from a network perspective, 153 153 00:05:21,390 --> 00:05:24,730 instead of using a start and a stop bit for synchronizing, 154 154 00:05:24,730 --> 00:05:27,680 we would use some sort of common time source. 155 155 00:05:27,680 --> 00:05:29,820 And so, maybe we're all going to use a clock, 156 156 00:05:29,820 --> 00:05:32,250 and every time a second passes, 157 157 00:05:32,250 --> 00:05:34,170 we can transmit and receive, 158 158 00:05:34,170 --> 00:05:35,890 and that tells us that we're going to do it 159 159 00:05:35,890 --> 00:05:37,740 on the cadence of the bit. 160 160 00:05:37,740 --> 00:05:39,960 That would be something that is synchronous. 161 161 00:05:39,960 --> 00:05:41,260 Now, in addition to figuring out 162 162 00:05:41,260 --> 00:05:43,510 if it's going to be asynchronous or synchronous, 163 163 00:05:43,510 --> 00:05:45,770 you also have to figure out how you're going to utilize 164 164 00:05:45,770 --> 00:05:47,400 the bandwidth of the cable, 165 165 00:05:47,400 --> 00:05:49,530 and there's two main ways that you can do this. 166 166 00:05:49,530 --> 00:05:52,520 One is called broadband and one is called baseband. 167 167 00:05:52,520 --> 00:05:54,690 Now, broadband is going to divide our bandwidth 168 168 00:05:54,690 --> 00:05:56,210 into separate channels. 169 169 00:05:56,210 --> 00:05:58,120 If you have a TV service at your house, 170 170 00:05:58,120 --> 00:05:59,530 you're probably familiar with this 171 171 00:05:59,530 --> 00:06:01,860 because you have a single cable coming into your house, 172 172 00:06:01,860 --> 00:06:04,330 but it carries 200 or more channels. 173 173 00:06:04,330 --> 00:06:06,470 The user, then, is going to choose a single channel 174 174 00:06:06,470 --> 00:06:08,470 and the rest are going to be filtered out. 175 175 00:06:08,470 --> 00:06:10,730 In opposition to this, we have baseband, 176 176 00:06:10,730 --> 00:06:12,910 where you're going to use all of the frequency of the cable 177 177 00:06:12,910 --> 00:06:14,270 all of the time. 178 178 00:06:14,270 --> 00:06:17,750 So, a telephone, for instance, uses baseband communication, 179 179 00:06:17,750 --> 00:06:19,470 which means that when you pick up the phone, 180 180 00:06:19,470 --> 00:06:20,780 you're using all of the bandwidth 181 181 00:06:20,780 --> 00:06:22,770 allocated to that phone line. 182 182 00:06:22,770 --> 00:06:25,140 This doesn't hold true with the cable TV signal, right? 183 183 00:06:25,140 --> 00:06:26,500 Because we had 200 channels 184 184 00:06:26,500 --> 00:06:28,350 all using some of that bandwidth, 185 185 00:06:28,350 --> 00:06:30,640 but we only pulled out the ones we wanted. 186 186 00:06:30,640 --> 00:06:31,740 For this reason, 187 187 00:06:31,740 --> 00:06:34,320 we can only make one call at a time when using a phone, 188 188 00:06:34,320 --> 00:06:37,136 but we can have 200 channels or more on our TV. 189 189 00:06:37,136 --> 00:06:38,980 Now, when we use baseband, 190 190 00:06:38,980 --> 00:06:40,880 we're going to use a reference clock 191 191 00:06:40,880 --> 00:06:42,600 that allows us to send the information 192 192 00:06:42,600 --> 00:06:45,740 for both the sender and the receiver at the certain time. 193 193 00:06:45,740 --> 00:06:47,380 By using this reference clock, 194 194 00:06:47,380 --> 00:06:50,730 this is an example of using a synchronous communication. 195 195 00:06:50,730 --> 00:06:53,010 Another good example of a baseband network 196 196 00:06:53,010 --> 00:06:55,160 is a wired home Ethernet network 197 197 00:06:55,160 --> 00:06:57,590 because this is going to use all of the frequency 198 198 00:06:57,590 --> 00:07:00,970 that's available on your cable, giving you more bandwidth 199 199 00:07:00,970 --> 00:07:03,830 than you would if you had a broadband area. 200 200 00:07:03,830 --> 00:07:06,380 Now, in this case, if we have a single baseband 201 201 00:07:06,380 --> 00:07:08,060 using up all of the bandwidth, 202 202 00:07:08,060 --> 00:07:10,390 we need to figure out how to get more out of it. 203 203 00:07:10,390 --> 00:07:11,240 And so, to do this, 204 204 00:07:11,240 --> 00:07:13,427 we have a couple of different mechanisms we can do. 205 205 00:07:13,427 --> 00:07:14,600 And the first one of these 206 206 00:07:14,600 --> 00:07:17,150 is what's known as time-division multiplexing. 207 207 00:07:17,150 --> 00:07:19,570 In this mode, each session is going to take turns 208 208 00:07:19,570 --> 00:07:21,281 using a dedicated time slot 209 209 00:07:21,281 --> 00:07:24,570 to get part of that bandwidth from the baseband. 210 210 00:07:24,570 --> 00:07:26,080 Now, an easy analogy of this 211 211 00:07:26,080 --> 00:07:28,360 is if you have a house with a single TV in it 212 212 00:07:28,360 --> 00:07:30,300 but you have four family members. 213 213 00:07:30,300 --> 00:07:33,510 Everyone wants to watch TV, but there's only one TV, 214 214 00:07:33,510 --> 00:07:34,710 so they're going to have to take turns 215 215 00:07:34,710 --> 00:07:36,810 picking what program is going to be on. 216 216 00:07:36,810 --> 00:07:39,670 Now, in a pure time-division multiplexing environment, 217 217 00:07:39,670 --> 00:07:42,400 each person is going to be assigned a time slot 218 218 00:07:42,400 --> 00:07:44,240 and they can pick whatever TV show they want 219 219 00:07:44,240 --> 00:07:45,630 during that time slot. 220 220 00:07:45,630 --> 00:07:47,240 Now, this may or may not line up 221 221 00:07:47,240 --> 00:07:49,190 with the time that their show is actually on 222 222 00:07:49,190 --> 00:07:51,030 and that could cause a problem, right? 223 223 00:07:51,030 --> 00:07:52,460 So, we have the second method 224 224 00:07:52,460 --> 00:07:56,650 called statistical time-division multiplexing or StatTDM. 225 225 00:07:56,650 --> 00:07:58,100 This is a more efficient version 226 226 00:07:58,100 --> 00:07:59,780 of time-division multiplexing 227 227 00:07:59,780 --> 00:08:02,700 because it's going to dynamically allocate these time slots 228 228 00:08:02,700 --> 00:08:04,690 based on when people need it. 229 229 00:08:04,690 --> 00:08:06,365 So, if we take our TV example, 230 230 00:08:06,365 --> 00:08:08,680 maybe, for example, I want to go down 231 231 00:08:08,680 --> 00:08:10,750 and nobody is watching TV at eight o'clock, 232 232 00:08:10,750 --> 00:08:12,490 but it wasn't my time slot. 233 233 00:08:12,490 --> 00:08:14,470 Well, under time-division multiplexing, 234 234 00:08:14,470 --> 00:08:15,880 I couldn't turn on the TV 235 235 00:08:15,880 --> 00:08:17,520 because it wasn't my time slot. 236 236 00:08:17,520 --> 00:08:19,770 But with StatTDM, I can, 237 237 00:08:19,770 --> 00:08:21,950 because as long as nobody is using the TV, 238 238 00:08:21,950 --> 00:08:23,560 anyone is free to use it. 239 239 00:08:23,560 --> 00:08:26,060 Everyone is going to take turns based on their necessity, 240 240 00:08:26,060 --> 00:08:27,920 not based on the time itself. 241 241 00:08:27,920 --> 00:08:30,730 So, instead, when I start watching the TV at eighth o'clock, 242 242 00:08:30,730 --> 00:08:32,100 then after my 30 minutes is up, 243 243 00:08:32,100 --> 00:08:34,770 I'm going to get off at 8:30 so somebody else can get on 244 244 00:08:34,770 --> 00:08:37,440 even though my assigned time slot under TDM 245 245 00:08:37,440 --> 00:08:39,812 might have been something like nine to 9:30. 246 246 00:08:39,812 --> 00:08:41,870 Now, our last method is what's known 247 247 00:08:41,870 --> 00:08:44,932 as frequency-division multiplexing or FDM. 248 248 00:08:44,932 --> 00:08:48,050 This is going to involve taking the medium, that cable, 249 249 00:08:48,050 --> 00:08:49,690 and splitting it up into channels 250 250 00:08:49,690 --> 00:08:51,890 similar to the way we do in broadband. 251 251 00:08:51,890 --> 00:08:54,030 So, if I take a single cable and I break it up 252 252 00:08:54,030 --> 00:08:56,935 into 50, 100, or 200 different frequencies, 253 253 00:08:56,935 --> 00:08:59,350 then each person can get a small portion 254 254 00:08:59,350 --> 00:09:01,030 of frequency allotted to them 255 255 00:09:01,030 --> 00:09:03,390 and they can use it as much as they want. 256 256 00:09:03,390 --> 00:09:05,410 Now, for the exam, the good news 257 257 00:09:05,410 --> 00:09:09,223 is you don't need to memorize TDM, StatTDM, and FDM, 258 258 00:09:09,223 --> 00:09:12,430 but rather, you just need to understand that multiplexing 259 259 00:09:12,430 --> 00:09:15,500 involves taking some limited amount of resource 260 260 00:09:15,500 --> 00:09:17,380 and using it more efficiently. 261 261 00:09:17,380 --> 00:09:19,340 In the real world, you may come across 262 262 00:09:19,340 --> 00:09:20,800 these multiplexing techniques, 263 263 00:09:20,800 --> 00:09:22,140 especially if you start working 264 264 00:09:22,140 --> 00:09:24,520 as a network engineer or a network architect, 265 265 00:09:24,520 --> 00:09:26,410 and that's why I want to introduce them to you. 266 266 00:09:26,410 --> 00:09:28,200 But for the Network+ Exam, 267 267 00:09:28,200 --> 00:09:31,890 just remember, multiplexing allows multiple people 268 268 00:09:31,890 --> 00:09:35,404 to use a baseband connection at the same time. 269 269 00:09:35,404 --> 00:09:38,430 The final thing we need to talk about in this lesson 270 270 00:09:38,430 --> 00:09:42,170 is some examples of physical or Layer 1 devices. 271 271 00:09:42,170 --> 00:09:44,520 The most common one is going to be a cable. 272 272 00:09:44,520 --> 00:09:46,200 So, if I have a fiber optic cable 273 273 00:09:46,200 --> 00:09:49,040 or an Ethernet cable or a coaxial cable, 274 274 00:09:49,040 --> 00:09:51,180 these are all different types of media. 275 275 00:09:51,180 --> 00:09:52,550 And if I have different types of media, 276 276 00:09:52,550 --> 00:09:55,060 that's considered a Layer 1 device. 277 277 00:09:55,060 --> 00:09:57,540 The reason is whatever goes in one end of the cable 278 278 00:09:57,540 --> 00:09:59,410 is going to come out the other end of the cable. 279 279 00:09:59,410 --> 00:10:00,690 So, if I have a fiber optic cable 280 280 00:10:00,690 --> 00:10:02,020 and I put light in one end, 281 281 00:10:02,020 --> 00:10:03,730 I'm going to get light out the other end. 282 282 00:10:03,730 --> 00:10:05,430 That's a physical response, 283 283 00:10:05,430 --> 00:10:07,890 a physical layer of the OSI Model. 284 284 00:10:07,890 --> 00:10:09,950 Additionally, beyond wired cables, 285 285 00:10:09,950 --> 00:10:11,720 we also have wireless things, 286 286 00:10:11,720 --> 00:10:13,740 things like Bluetooth and Wi-Fi 287 287 00:10:13,740 --> 00:10:15,390 and near field communication. 288 288 00:10:15,390 --> 00:10:17,926 All of these radio frequencies make up the media 289 289 00:10:17,926 --> 00:10:21,304 at Layer 1 for those type of networks. 290 290 00:10:21,304 --> 00:10:24,290 The final example is infrastructure devices, 291 291 00:10:24,290 --> 00:10:26,880 and that will be things like hubs, access points, 292 292 00:10:26,880 --> 00:10:28,162 and media converters. 293 293 00:10:28,162 --> 00:10:31,830 All of these devices operate at the bit layer. 294 294 00:10:31,830 --> 00:10:33,190 This is going to be a function 295 295 00:10:33,190 --> 00:10:35,000 to just simply repeat what they get. 296 296 00:10:35,000 --> 00:10:37,530 So, if I have a hub, whatever goes in port one of the hub 297 297 00:10:37,530 --> 00:10:40,130 is coming out of ports two, three, and four. 298 298 00:10:40,130 --> 00:10:42,220 Whatever comes in gets repeated out. 299 299 00:10:42,220 --> 00:10:43,860 The same thing with the media converter. 300 300 00:10:43,860 --> 00:10:46,370 If I have something coming in over coaxial, 301 301 00:10:46,370 --> 00:10:48,060 it's going to get converted through media 302 302 00:10:48,060 --> 00:10:50,020 and pushed out over fiber optic. 303 303 00:10:50,020 --> 00:10:53,570 That device is simply doing it at the physical layer. 304 304 00:10:53,570 --> 00:10:55,260 Whatever comes in is going to go out. 305 305 00:10:55,260 --> 00:10:58,090 There's no logic to it, there's no intelligence to it. 306 306 00:10:58,090 --> 00:11:01,370 Layer 1 devices simply repeat whatever they're told. 307 307 00:11:01,370 --> 00:11:03,890 Now, we'll talk about some other infrastructure devices 308 308 00:11:03,890 --> 00:11:06,550 as we get into Layers 2 and 3 and 4 309 309 00:11:06,550 --> 00:11:08,290 but for right now, I want you to remember 310 310 00:11:08,290 --> 00:11:10,730 Layer 1 is dumb devices. 311 311 00:11:10,730 --> 00:11:12,200 They're simply repeaters. 312 312 00:11:12,200 --> 00:11:14,750 Whatever they take in, they send it right back out.