1 1 00:00:00,331 --> 00:00:02,630 Wide Area Network Technologies. 2 2 00:00:02,630 --> 00:00:05,250 Now, I'm going to break this lesson into two parts 3 3 00:00:05,250 --> 00:00:06,820 because there are so many technologies 4 4 00:00:06,820 --> 00:00:08,120 that we have to talk about, 5 5 00:00:08,120 --> 00:00:10,780 and so, it's going to be this lesson and the next one. 6 6 00:00:10,780 --> 00:00:12,190 Now, the first one we want to talk about 7 7 00:00:12,190 --> 00:00:13,830 is a dedicated leased line. 8 8 00:00:13,830 --> 00:00:15,740 I mentioned this in the last lesson. 9 9 00:00:15,740 --> 00:00:18,400 This is a point-to-point connection between two sites, 10 10 00:00:18,400 --> 00:00:20,610 and you're going to get all the bandwidth all of the time 11 11 00:00:20,610 --> 00:00:21,970 which is really good. 12 12 00:00:21,970 --> 00:00:25,200 If you see something like a T1, an E1, a T3, 13 13 00:00:25,200 --> 00:00:27,550 or an E3, or other dedicated circuits, 14 14 00:00:27,550 --> 00:00:29,260 that's what we're talking about. 15 15 00:00:29,260 --> 00:00:30,990 Now, when you get this digital circuit, 16 16 00:00:30,990 --> 00:00:34,340 it's going to be measured in 64 kilobit per second channels 17 17 00:00:34,340 --> 00:00:38,190 called a DS0, or a Digital Signal 0. 18 18 00:00:38,190 --> 00:00:40,600 Based on the type of connection you buy, for example, 19 19 00:00:40,600 --> 00:00:43,350 you're going to get more or less of these DS0s. 20 20 00:00:43,350 --> 00:00:45,760 So, if you buy a T1, you're going to get 24 21 21 00:00:45,760 --> 00:00:48,190 of these 64-kilobit channels. 22 22 00:00:48,190 --> 00:00:49,460 Now, on your location, 23 23 00:00:49,460 --> 00:00:51,830 you're going to get a device that looks like a modem, 24 24 00:00:51,830 --> 00:00:54,450 and this is actually called a CSU/DSU, 25 25 00:00:54,450 --> 00:00:57,460 a channel service unit/data service unit. 26 26 00:00:57,460 --> 00:00:59,320 It's used to terminate the digital signal 27 27 00:00:59,320 --> 00:01:01,480 in your location from the phone company, 28 28 00:01:01,480 --> 00:01:03,060 and then, you tie that into your router 29 29 00:01:03,060 --> 00:01:05,010 to be able to connect it to your network. 30 30 00:01:05,010 --> 00:01:07,320 Now, for exam day, I want you to remember 31 31 00:01:07,320 --> 00:01:10,150 T1s and E1s are dedicated leased lines 32 32 00:01:10,150 --> 00:01:14,000 and they use CSUs and DSUs to connect to your network. 33 33 00:01:14,000 --> 00:01:15,907 Now, some students say, "Why do I have to learn this? 34 34 00:01:15,907 --> 00:01:16,807 It's really old. 35 35 00:01:16,807 --> 00:01:18,400 Nobody uses them anymore." 36 36 00:01:18,400 --> 00:01:20,620 Well, there's still a lot of people that do use these, 37 37 00:01:20,620 --> 00:01:22,260 and as a network technician, 38 38 00:01:22,260 --> 00:01:25,270 you may come across a CSU/DSU in the field. 39 39 00:01:25,270 --> 00:01:27,400 Just last year, I came across a couple of them 40 40 00:01:27,400 --> 00:01:29,130 as I was doing some consulting work. 41 41 00:01:29,130 --> 00:01:31,160 So they do still exist even though most people 42 42 00:01:31,160 --> 00:01:33,170 are migrating away from them. 43 43 00:01:33,170 --> 00:01:36,170 Now, what are some examples of digital signal levels? 44 44 00:01:36,170 --> 00:01:37,210 Well, this is going to depend 45 45 00:01:37,210 --> 00:01:39,180 on the carrier signal you're using. 46 46 00:01:39,180 --> 00:01:40,790 If you're using something like a T1, 47 47 00:01:40,790 --> 00:01:43,300 or a T3, or an E1, or an E3, 48 48 00:01:43,300 --> 00:01:45,710 then, you're going to have an associated signal with it. 49 49 00:01:45,710 --> 00:01:47,680 A T1 is going to be a DS1. 50 50 00:01:47,680 --> 00:01:49,989 A T3 is going to be a DS3. 51 51 00:01:49,989 --> 00:01:52,560 Now, E1 and E3, those are European standards, 52 52 00:01:52,560 --> 00:01:55,410 where T1 and T3 are American standards. 53 53 00:01:55,410 --> 00:01:58,250 Now, these don't fall into this digital signaling measurement 54 54 00:01:58,250 --> 00:02:00,480 when you're dealing with those European standards, though. 55 55 00:02:00,480 --> 00:02:01,840 You're going to see the number of channels 56 56 00:02:01,840 --> 00:02:02,673 that you're going to get, 57 57 00:02:02,673 --> 00:02:04,970 and how many voice channels or data channels 58 58 00:02:04,970 --> 00:02:07,490 of 64 kilobits each that you're going to have 59 59 00:02:07,490 --> 00:02:09,180 and the speed is right there. 60 60 00:02:09,180 --> 00:02:11,520 Now, what from this chart should you memorize? 61 61 00:02:11,520 --> 00:02:13,850 Well, you should know that a T1 and a T3 62 62 00:02:13,850 --> 00:02:16,590 and an E1 speed are important to know. 63 63 00:02:16,590 --> 00:02:20,790 So, if you remember a 1.544 megabit per second, that is a T1. 64 64 00:02:20,790 --> 00:02:25,790 44.736 megabits per second, or about 45 megabits per second, 65 65 00:02:26,330 --> 00:02:27,720 is a T3. 66 66 00:02:27,720 --> 00:02:28,880 And if you have an E1, 67 67 00:02:28,880 --> 00:02:31,280 that's going to be a two-megabit connection. 68 68 00:02:31,280 --> 00:02:33,390 Now, if you remember that, you're going to do fine on test day. 69 69 00:02:33,390 --> 00:02:35,870 And remember, this is a multiple choice exam, 70 70 00:02:35,870 --> 00:02:40,300 so, if you remember 1.5-ish, 45-ish, and two-ish, 71 71 00:02:40,300 --> 00:02:42,880 that's going to be close enough to get you the right answer. 72 72 00:02:42,880 --> 00:02:44,870 Next, we have metro ethernet. 73 73 00:02:44,870 --> 00:02:46,810 Now, service providers are beginning to get away 74 74 00:02:46,810 --> 00:02:49,940 from these T1s, and E1s, and T3 connections 75 75 00:02:49,940 --> 00:02:51,970 because those CSU/DSUs are just 76 76 00:02:51,970 --> 00:02:53,290 kind of cumbersome to work with, 77 77 00:02:53,290 --> 00:02:55,500 and it's a really old technology. 78 78 00:02:55,500 --> 00:02:56,660 So, they've been starting to migrate 79 79 00:02:56,660 --> 00:02:58,630 towards what's called metro ethernet. 80 80 00:02:58,630 --> 00:02:59,880 This is where the service provider 81 81 00:02:59,880 --> 00:03:01,900 gives you an ethernet jack in your building, 82 82 00:03:01,900 --> 00:03:03,890 and you simply plug it into your router. 83 83 00:03:03,890 --> 00:03:06,190 Now, these are less expensive and much more common 84 84 00:03:06,190 --> 00:03:08,040 than using a specialized serial port 85 85 00:03:08,040 --> 00:03:10,300 like you'd see in a CSU and DSU. 86 86 00:03:10,300 --> 00:03:11,940 The technology used by the service provider 87 87 00:03:11,940 --> 00:03:14,100 really doesn't matter to me as a customer, right? 88 88 00:03:14,100 --> 00:03:16,320 All I care about is the fact that I have this ethernet jack 89 89 00:03:16,320 --> 00:03:17,960 that I can plug into my router, 90 90 00:03:17,960 --> 00:03:19,010 and as long as I can do that, 91 91 00:03:19,010 --> 00:03:20,340 I don't really care what's behind it 92 92 00:03:20,340 --> 00:03:22,250 and I let the service provider worry about it. 93 93 00:03:22,250 --> 00:03:25,010 So, give me something as simple as an RJ45, 94 94 00:03:25,010 --> 00:03:27,190 I plug it in my router, and I get online. 95 95 00:03:27,190 --> 00:03:28,750 It's a win for me as a customer, 96 96 00:03:28,750 --> 00:03:30,590 and it allows the service provider 97 97 00:03:30,590 --> 00:03:32,850 to change the backbone anytime they want 98 98 00:03:32,850 --> 00:03:34,240 and I don't even have to see it. 99 99 00:03:34,240 --> 00:03:37,070 That's one of the big benefits of metro ethernet. 100 100 00:03:37,070 --> 00:03:39,470 Next, we have a PPP connection, 101 101 00:03:39,470 --> 00:03:41,610 which is the Point-to-Point Protocol. 102 102 00:03:41,610 --> 00:03:44,130 This is commonly used as a Layer 2 protocol 103 103 00:03:44,130 --> 00:03:47,090 that we use on top of one of these dedicated leased lines. 104 104 00:03:47,090 --> 00:03:49,000 So, whether we're using metro ethernet, 105 105 00:03:49,000 --> 00:03:53,060 a T1, an E1, T3, an E3, a cable modem, 106 106 00:03:53,060 --> 00:03:55,240 a DSL, any of these things, 107 107 00:03:55,240 --> 00:03:57,180 we can actually use these other 108 108 00:03:57,180 --> 00:03:59,010 different protocols on top of it, 109 109 00:03:59,010 --> 00:04:01,520 and PPP is what we use at Layer 2. 110 110 00:04:01,520 --> 00:04:04,370 Then, we can use other protocols at Layer 3, 111 111 00:04:04,370 --> 00:04:07,200 like IPX or IP, on top of them. 112 112 00:04:07,200 --> 00:04:08,750 Now, most of the time in your networks, 113 113 00:04:08,750 --> 00:04:10,720 you're probably going to be using IP 114 114 00:04:10,720 --> 00:04:13,570 because TCP/IP is what we all use these days, 115 115 00:04:13,570 --> 00:04:15,850 but each Layer 3 protocol could run 116 116 00:04:15,850 --> 00:04:19,710 its own instance of PPP under the Link Control Protocol, 117 117 00:04:19,710 --> 00:04:21,700 which manages the link and does some basic 118 118 00:04:21,700 --> 00:04:22,980 error-checking for you. 119 119 00:04:22,980 --> 00:04:26,450 So, I can run different levels and different IP or IPXs 120 120 00:04:26,450 --> 00:04:28,220 over the same connection. 121 121 00:04:28,220 --> 00:04:30,090 Now, this is also going to do what we call 122 122 00:04:30,090 --> 00:04:31,900 a multilink interface for you, 123 123 00:04:31,900 --> 00:04:34,110 and that will allow multiple physical connections 124 124 00:04:34,110 --> 00:04:35,380 to be bounded together 125 125 00:04:35,380 --> 00:04:37,720 to give you a single, logical interface. 126 126 00:04:37,720 --> 00:04:40,470 So, much like I could do link aggregation in my switches, 127 127 00:04:40,470 --> 00:04:43,730 I could do the same thing where I buy two or three T1s, 128 128 00:04:43,730 --> 00:04:46,380 bind them together, and that will give me more speed. 129 129 00:04:46,380 --> 00:04:49,750 So, a single T1 is about 1.5 megabits per second. 130 130 00:04:49,750 --> 00:04:53,400 If I buy three of them, I have 4.5 megabits per second. 131 131 00:04:53,400 --> 00:04:55,950 And I can put them all together using this aggregation, 132 132 00:04:55,950 --> 00:04:57,010 and bind them all together 133 133 00:04:57,010 --> 00:04:59,100 under a single, logical interface. 134 134 00:04:59,100 --> 00:05:01,570 It'll also allow me to do looped link detection 135 135 00:05:01,570 --> 00:05:03,600 to find any kind of errors that I have. 136 136 00:05:03,600 --> 00:05:05,050 It also allows me to do error detection 137 137 00:05:05,050 --> 00:05:06,310 by checking my frames 138 138 00:05:06,310 --> 00:05:08,780 and perform basic authentication over the link 139 139 00:05:08,780 --> 00:05:10,230 to make sure I'm authorized to use 140 140 00:05:10,230 --> 00:05:11,900 this point-to-point connection. 141 141 00:05:11,900 --> 00:05:14,700 These are all some of the benefits of PPP. 142 142 00:05:14,700 --> 00:05:17,710 Now, the way it does this is with three different mechanisms, 143 143 00:05:17,710 --> 00:05:19,880 depending on which one you're going to choose. 144 144 00:05:19,880 --> 00:05:22,630 Now, the authentication can be done using PAP, 145 145 00:05:22,630 --> 00:05:25,200 which is the Password Authentication Protocol. 146 146 00:05:25,200 --> 00:05:27,020 You could also be using the Challenge-Handshake 147 147 00:05:27,020 --> 00:05:29,130 Authentication Protocol, or CHAP. 148 148 00:05:29,130 --> 00:05:31,710 Or you could be using Microsoft CHAP, which is their version 149 149 00:05:31,710 --> 00:05:34,210 of the Challenge-Handshake Authentication Protocol. 150 150 00:05:34,210 --> 00:05:36,120 Now, because Microsoft seems to not follow 151 151 00:05:36,120 --> 00:05:37,430 the standards everybody else does, 152 152 00:05:37,430 --> 00:05:40,390 they make up their own, and this is known as MS-CHAP. 153 153 00:05:40,390 --> 00:05:43,120 Now, I like to say a little tongue-in-cheek about Microsoft 154 154 00:05:43,120 --> 00:05:45,390 but Microsoft actually made a better implementation 155 155 00:05:45,390 --> 00:05:46,910 of the old CHAP protocol, 156 156 00:05:46,910 --> 00:05:49,560 which is why they have MS-CHAP, instead. 157 157 00:05:49,560 --> 00:05:51,970 Now, when we talk about PAP, how does it work? 158 158 00:05:51,970 --> 00:05:54,680 Well, PAP performs a one-way authentication 159 159 00:05:54,680 --> 00:05:56,640 between the client and the server. 160 160 00:05:56,640 --> 00:05:57,830 On my basic diagram, 161 161 00:05:57,830 --> 00:05:59,620 you're going to see I have a client on one side 162 162 00:05:59,620 --> 00:06:01,640 and a server right around the other. 163 163 00:06:01,640 --> 00:06:03,470 line:15% Now, the credentials are sent in the clear, 164 164 00:06:03,470 --> 00:06:05,360 line:15% from the client to the server. 165 165 00:06:05,360 --> 00:06:08,430 line:15% Basically it says, "Here's my username and my password." 166 166 00:06:08,430 --> 00:06:09,717 line:15% The server then comes back and says, 167 167 00:06:09,717 --> 00:06:11,880 line:15% "I acknowledge it and I let you in." 168 168 00:06:11,880 --> 00:06:13,300 line:15% Now, the bad thing about PAP 169 169 00:06:13,300 --> 00:06:14,880 line:15% is that it was sent in clear-text, 170 170 00:06:14,880 --> 00:06:16,550 line:15% which means anybody on that network 171 171 00:06:16,550 --> 00:06:19,100 line:15% could read the authentication and steal it from you. 172 172 00:06:19,100 --> 00:06:21,120 line:15% So, there had to be a better way, 173 173 00:06:21,120 --> 00:06:22,900 and that's where CHAP came in. 174 174 00:06:22,900 --> 00:06:25,620 CHAP is the Challenge-Handshake Authentication Protocol, 175 175 00:06:25,620 --> 00:06:27,730 and it performs a one-way authentication 176 176 00:06:27,730 --> 00:06:29,810 using a three-way handshake. 177 177 00:06:29,810 --> 00:06:32,060 Essentially, when you want to connect to a router, 178 178 00:06:32,060 --> 00:06:33,750 in this case the server's router, 179 179 00:06:33,750 --> 00:06:35,180 it starts doing a challenge. 180 180 00:06:35,180 --> 00:06:36,980 It essentially says, "Hey, who are you?" 181 181 00:06:36,980 --> 00:06:39,707 and then the client says, "Well, I'm this person, 182 182 00:06:39,707 --> 00:06:41,680 and here's my username and password." 183 183 00:06:41,680 --> 00:06:43,820 And then the router checks the hash credentials 184 184 00:06:43,820 --> 00:06:45,650 sent as the username and password, 185 185 00:06:45,650 --> 00:06:48,480 and if that matches its stored version in the server, 186 186 00:06:48,480 --> 00:06:51,290 it's going to send a success or failure message. 187 187 00:06:51,290 --> 00:06:54,100 The benefit of this is that there was no password sent 188 188 00:06:54,100 --> 00:06:55,430 in clear-text over the network. 189 189 00:06:55,430 --> 00:06:58,640 Instead, it just sent a hash of that credential. 190 190 00:06:58,640 --> 00:07:01,380 Now, Microsoft server does essentially the same thing 191 191 00:07:01,380 --> 00:07:04,020 except there's also a two-way authentication here, 192 192 00:07:04,020 --> 00:07:05,830 so, the client has to verify the server 193 193 00:07:05,830 --> 00:07:07,920 and the server verifies the client. 194 194 00:07:07,920 --> 00:07:09,710 For the exam, I want you to remember 195 195 00:07:09,710 --> 00:07:11,340 that PAP is sent in the clear, 196 196 00:07:11,340 --> 00:07:13,170 which is a huge security risk. 197 197 00:07:13,170 --> 00:07:15,430 CHAP and Microsoft CHAP are actually 198 198 00:07:15,430 --> 00:07:17,560 going to have the credentials hashed first, 199 199 00:07:17,560 --> 00:07:20,000 and they're going to make it a more secure way of doing PAP, 200 200 00:07:20,000 --> 00:07:22,740 with Microsoft CHAP being the most secure. 201 201 00:07:22,740 --> 00:07:24,290 Now, the next thing we need to talk about 202 202 00:07:24,290 --> 00:07:26,690 is PPP over ethernet, 203 203 00:07:26,690 --> 00:07:29,390 or Point-to-Point Protocol over ethernet. 204 204 00:07:29,390 --> 00:07:31,340 This was commonly used with DSL modems, 205 205 00:07:31,340 --> 00:07:33,670 and it actually took your PPP protocol 206 206 00:07:33,670 --> 00:07:35,660 that we would use over a T1 connection 207 207 00:07:35,660 --> 00:07:37,660 and encapsulates those with frames 208 208 00:07:37,660 --> 00:07:40,580 so it can use it over ethernet at layer two. 209 209 00:07:40,580 --> 00:07:42,410 Now, if you're using metro ethernet, 210 210 00:07:42,410 --> 00:07:44,810 this is likely what you're going to be using, as well. 211 211 00:07:44,810 --> 00:07:47,270 This allows authentication to occur over ethernet, 212 212 00:07:47,270 --> 00:07:50,690 using something like PAP, CHAP, or MS-CHAP. 213 213 00:07:50,690 --> 00:07:54,090 Next, we have DSL which is a digital subscriber line. 214 214 00:07:54,090 --> 00:07:55,610 Now, when I first started building networks 215 215 00:07:55,610 --> 00:07:58,390 back in the late 1990s and early 2000s, 216 216 00:07:58,390 --> 00:08:00,230 DSL was all the rage. 217 217 00:08:00,230 --> 00:08:03,430 It was everywhere because it was a really inexpensive way 218 218 00:08:03,430 --> 00:08:05,660 to get high-speed data to our end users, 219 219 00:08:05,660 --> 00:08:08,250 and small offices, and home offices. 220 220 00:08:08,250 --> 00:08:10,220 Now, instead of having to pay for a T1 connection, 221 221 00:08:10,220 --> 00:08:12,900 which could cost you 1,000 or $2,000 a month, 222 222 00:08:12,900 --> 00:08:15,120 you could actually go ahead and get a DSL connection 223 223 00:08:15,120 --> 00:08:17,460 for 50 or $100 a month. 224 224 00:08:17,460 --> 00:08:19,820 Now, there is three different types of DSL. 225 225 00:08:19,820 --> 00:08:23,540 You have ADSL, SDSL, and VDSL. 226 226 00:08:23,540 --> 00:08:26,210 ADSL is Asymmetric DSL. 227 227 00:08:26,210 --> 00:08:27,870 That means there's a different speed 228 228 00:08:27,870 --> 00:08:30,150 on the download versus the upload. 229 229 00:08:30,150 --> 00:08:31,520 The maximum download speed 230 230 00:08:31,520 --> 00:08:33,350 was about eight megabits per second 231 231 00:08:33,350 --> 00:08:34,870 according to the current textbooks, 232 232 00:08:34,870 --> 00:08:35,880 although there were some that were getting 233 233 00:08:35,880 --> 00:08:37,470 a little bit faster than that. 234 234 00:08:37,470 --> 00:08:39,720 The upload speed was equivalent to a T1, 235 235 00:08:39,720 --> 00:08:42,770 at about 1.544 megabits per second. 236 236 00:08:42,770 --> 00:08:45,660 So, I have eight megs down, one and a half up. 237 237 00:08:45,660 --> 00:08:46,880 Now, why would it be okay 238 238 00:08:46,880 --> 00:08:49,170 to have different uploads and download speeds? 239 239 00:08:49,170 --> 00:08:51,630 Well, this went back to the 80/20 rule. 240 240 00:08:51,630 --> 00:08:54,900 When you're online, do you upload more or download more? 241 241 00:08:54,900 --> 00:08:55,980 If you're like most people, 242 242 00:08:55,980 --> 00:08:58,610 you download a lot more than you upload. 243 243 00:08:58,610 --> 00:09:00,910 For example, when you're watching this video, 244 244 00:09:00,910 --> 00:09:02,370 you selected the video with your mouse, 245 245 00:09:02,370 --> 00:09:04,500 and you told the server what you wanted to watch. 246 246 00:09:04,500 --> 00:09:07,630 That may have been just a couple of kilobits in size. 247 247 00:09:07,630 --> 00:09:09,854 Then the video sent you back 100, 248 248 00:09:09,854 --> 00:09:12,220 or 200, or 300 megabytes in size, 249 249 00:09:12,220 --> 00:09:13,360 and it's a really large file 250 250 00:09:13,360 --> 00:09:14,920 and you're downloading all of that. 251 251 00:09:14,920 --> 00:09:17,020 So, your upload was very, very small, 252 252 00:09:17,020 --> 00:09:18,380 but your download was a lot, 253 253 00:09:18,380 --> 00:09:20,970 and for most users, they upload very little, 254 254 00:09:20,970 --> 00:09:22,920 but they download a lot of information. 255 255 00:09:22,920 --> 00:09:25,430 And so, ADSL maximizes the download 256 256 00:09:25,430 --> 00:09:27,470 and minimizes your uploads. 257 257 00:09:27,470 --> 00:09:31,850 Now SDSL, or Symmetric DSL, works just like a T1. 258 258 00:09:31,850 --> 00:09:34,560 You'd have an equal upload and download speed. 259 259 00:09:34,560 --> 00:09:36,750 The speeds are much slower here for symmetric, 260 260 00:09:36,750 --> 00:09:38,530 but they were dedicated access 261 261 00:09:38,530 --> 00:09:39,620 so you're pretty much guaranteed 262 262 00:09:39,620 --> 00:09:41,570 to get that speed all of the time. 263 263 00:09:41,570 --> 00:09:44,380 With ADSL, if there is a lot of people online at the time, 264 264 00:09:44,380 --> 00:09:46,390 it could slow down your speeds. 265 265 00:09:46,390 --> 00:09:48,527 Now, ADSL is very popular with home users, 266 266 00:09:48,527 --> 00:09:50,660 and it started getting a lot more funding, 267 267 00:09:50,660 --> 00:09:53,490 and because of that, ADSL speeds increased quickly 268 268 00:09:53,490 --> 00:09:56,010 and got into those one and a half megabits per second, 269 269 00:09:56,010 --> 00:09:57,207 and then four megabits per second, 270 270 00:09:57,207 --> 00:09:59,040 and then eight megabits per second, 271 271 00:09:59,040 --> 00:10:00,780 and they kept going up from there. 272 272 00:10:00,780 --> 00:10:03,390 When they first came out, all of this was very slow. 273 273 00:10:03,390 --> 00:10:04,709 We were talking about DSL speeds 274 274 00:10:04,709 --> 00:10:09,270 of 256 kilobits per second, or half a meg per second. 275 275 00:10:09,270 --> 00:10:11,300 As advancements in technology went though, 276 276 00:10:11,300 --> 00:10:13,690 they kept moving more and more towards ADSL, 277 277 00:10:13,690 --> 00:10:16,890 and most people abandoned the symmetric DSL. 278 278 00:10:16,890 --> 00:10:18,610 Now, the last type of DSL we have 279 279 00:10:18,610 --> 00:10:21,330 is known as the Very High Bit-Rate DSL. 280 280 00:10:21,330 --> 00:10:23,910 This is where you could get very, very high speeds. 281 281 00:10:23,910 --> 00:10:25,280 In fact, you could have downloads 282 282 00:10:25,280 --> 00:10:27,590 as high as 50 megabits per second or more 283 283 00:10:27,590 --> 00:10:30,580 and uploads over 10 megabits per second or more. 284 284 00:10:30,580 --> 00:10:32,050 The big limitation here though 285 285 00:10:32,050 --> 00:10:35,060 was your distance from what's known as the DSLAM. 286 286 00:10:35,060 --> 00:10:36,650 Now, what is a DSLAM? 287 287 00:10:36,650 --> 00:10:38,260 Well, this is the point of presence 288 288 00:10:38,260 --> 00:10:40,400 that's owned by the telephone company. 289 289 00:10:40,400 --> 00:10:44,640 With Variable DSL, you had to be within 4,000 feet 290 290 00:10:44,640 --> 00:10:47,300 from that DSLAM, which is less than a mile. 291 291 00:10:47,300 --> 00:10:50,820 Now, not all home users or offices could get VDSL 292 292 00:10:50,820 --> 00:10:53,794 because most of them were within 18,000 feet, 293 293 00:10:53,794 --> 00:10:57,157 and if you're within 18,000 feet, you could get ADSL. 294 294 00:10:57,157 --> 00:10:59,720 But, if you are lucky and you're within 4,000 feet, 295 295 00:10:59,720 --> 00:11:02,700 you could then use VDSL and get those higher speeds. 296 296 00:11:02,700 --> 00:11:04,690 Again, because DSL started declining 297 297 00:11:04,690 --> 00:11:06,420 in popularity in recent years 298 298 00:11:06,420 --> 00:11:08,920 as more people moved towards cable and fiber, 299 299 00:11:08,920 --> 00:11:10,110 that's what ended up happening. 300 300 00:11:10,110 --> 00:11:12,980 And so, DSL didn't get a lot more DSLAMS put in, 301 301 00:11:12,980 --> 00:11:14,680 and it ended up fading away 302 302 00:11:14,680 --> 00:11:16,750 as we started moving towards cable and fiber, 303 303 00:11:16,750 --> 00:11:19,150 which we're going to talk about in the next lesson.