1 00:00:00,060 --> 00:00:00,960 In this lesson, 2 00:00:00,960 --> 00:00:04,050 we're going to cover digital subscriber line connections. 3 00:00:04,050 --> 00:00:06,870 Now, a digital subscriber line or DSL connection 4 00:00:06,870 --> 00:00:09,420 is a family of technologies that provide internet access 5 00:00:09,420 --> 00:00:11,730 by transmitting digital data over the wires 6 00:00:11,730 --> 00:00:13,740 of a local telephone network. 7 00:00:13,740 --> 00:00:15,150 When I first started building networks 8 00:00:15,150 --> 00:00:17,760 back in the late 1990s and early 2000s, 9 00:00:17,760 --> 00:00:19,740 DSL was all the rage. 10 00:00:19,740 --> 00:00:22,470 It was everywhere, because it was relatively inexpensive 11 00:00:22,470 --> 00:00:24,090 and a great way to get high-speed data 12 00:00:24,090 --> 00:00:26,190 to our end users in small offices 13 00:00:26,190 --> 00:00:28,230 and in home office environments. 14 00:00:28,230 --> 00:00:30,330 Now, instead of having to pay for a dedicated lease line 15 00:00:30,330 --> 00:00:33,990 like a T1, which could cost you 1,000 or $2,000 a month, 16 00:00:33,990 --> 00:00:35,700 you could go ahead and get a DSL connection 17 00:00:35,700 --> 00:00:37,950 for 50 or $100 per month. 18 00:00:37,950 --> 00:00:40,800 Now, back in the day, we had three different types of DSL, 19 00:00:40,800 --> 00:00:43,140 and you may still run into some of these these days. 20 00:00:43,140 --> 00:00:46,950 These are ADSL, SDSL, and VDSL. 21 00:00:46,950 --> 00:00:49,800 ADSL stands for Asymmetric DSL. 22 00:00:49,800 --> 00:00:51,270 That means there's going to be a different speed 23 00:00:51,270 --> 00:00:54,360 on the download versus what you're going to get on the upload. 24 00:00:54,360 --> 00:00:56,730 The maximum download speed on an ADSL line 25 00:00:56,730 --> 00:00:58,440 was about eight megabits per second, 26 00:00:58,440 --> 00:01:00,180 according to our current textbooks, 27 00:01:00,180 --> 00:01:01,013 although there were some 28 00:01:01,013 --> 00:01:03,060 that were getting a little bit faster than that. 29 00:01:03,060 --> 00:01:04,440 The upload speed was equivalent 30 00:01:04,440 --> 00:01:08,400 to about a T1 at 1.544 megabits per second. 31 00:01:08,400 --> 00:01:09,870 Now, why do you think it would be okay 32 00:01:09,870 --> 00:01:12,630 to have two different speeds for downloads and uploads? 33 00:01:12,630 --> 00:01:14,580 Well, when you're online, think about it. 34 00:01:14,580 --> 00:01:16,530 Do you do more uploading or downloading? 35 00:01:16,530 --> 00:01:17,670 If you're like most people, 36 00:01:17,670 --> 00:01:20,010 you download a lot more than you upload. 37 00:01:20,010 --> 00:01:22,020 For example, when you're watching this video, 38 00:01:22,020 --> 00:01:23,400 you selected the video with your mouse 39 00:01:23,400 --> 00:01:25,590 and you told the server what you wanted to watch. 40 00:01:25,590 --> 00:01:27,900 You may have sent just a couple of kilobits in size 41 00:01:27,900 --> 00:01:30,600 up to our server, and then we sent you back a video 42 00:01:30,600 --> 00:01:34,380 that was maybe 100, 200, or 300 megabytes in size. 43 00:01:34,380 --> 00:01:35,460 And it's a really large file, 44 00:01:35,460 --> 00:01:37,020 and you're downloading all of that. 45 00:01:37,020 --> 00:01:39,780 So your upload was very, very small, 46 00:01:39,780 --> 00:01:41,610 but your download was a whole lot. 47 00:01:41,610 --> 00:01:44,040 And for most users, they upload very little, 48 00:01:44,040 --> 00:01:46,710 but they download a ton of information. 49 00:01:46,710 --> 00:01:49,650 This is why ADSL decided to maximize the download 50 00:01:49,650 --> 00:01:51,720 and minimize your upload speeds. 51 00:01:51,720 --> 00:01:53,130 Now, on the other hand, if you're somebody 52 00:01:53,130 --> 00:01:55,530 who needed the same upload and download speeds, 53 00:01:55,530 --> 00:01:57,270 you could get a specialty product known 54 00:01:57,270 --> 00:02:00,300 as SDSL or symmetric DSL. 55 00:02:00,300 --> 00:02:02,550 Now, symmetric DSL works just like a typical 56 00:02:02,550 --> 00:02:04,680 lease line connection, like a T1. 57 00:02:04,680 --> 00:02:06,060 With an SDSL connection, 58 00:02:06,060 --> 00:02:08,789 you have an equal upload and download speed. 59 00:02:08,789 --> 00:02:10,620 Now, the problem here is because you're having 60 00:02:10,620 --> 00:02:12,510 equal upload and download speeds, 61 00:02:12,510 --> 00:02:15,000 you are going to have slower speeds overall. 62 00:02:15,000 --> 00:02:16,590 For example, with ADSL, 63 00:02:16,590 --> 00:02:18,960 we said you can have an eight meg download speed 64 00:02:18,960 --> 00:02:21,720 and a one meg or one and a half meg upload speed. 65 00:02:21,720 --> 00:02:24,810 So you have about 10 megs total to work with. 66 00:02:24,810 --> 00:02:27,840 But if you're using SDSL, you can actually reconfigure that, 67 00:02:27,840 --> 00:02:30,630 so you have five megs upload and five megs download, 68 00:02:30,630 --> 00:02:33,360 or four megs upload and four megs download. 69 00:02:33,360 --> 00:02:34,590 Either way, you're going to have equal 70 00:02:34,590 --> 00:02:37,560 upload and download speeds but at a much slower rate 71 00:02:37,560 --> 00:02:38,820 than the total speed you would get 72 00:02:38,820 --> 00:02:41,010 on an asymmetric connection. 73 00:02:41,010 --> 00:02:43,260 Now, because these were more of a specialized product, 74 00:02:43,260 --> 00:02:44,670 they gave you dedicated access, 75 00:02:44,670 --> 00:02:45,990 and you're guaranteed to pretty much get 76 00:02:45,990 --> 00:02:48,270 all that speed all of the time. 77 00:02:48,270 --> 00:02:50,820 Now, if you're dealing with ADSL, on the other hand though, 78 00:02:50,820 --> 00:02:52,530 if there's a lot of people online at a time, 79 00:02:52,530 --> 00:02:54,480 it actually could slow down your speeds, 80 00:02:54,480 --> 00:02:56,520 because ADSL used a shared pipe 81 00:02:56,520 --> 00:02:57,990 for the entire neighborhood 82 00:02:57,990 --> 00:02:59,640 where you are connected to. 83 00:02:59,640 --> 00:03:01,890 Now, ADSL was very, very popular 84 00:03:01,890 --> 00:03:04,800 with home users back in the '90s and early 2000s, 85 00:03:04,800 --> 00:03:06,000 and so it got a lot of funding 86 00:03:06,000 --> 00:03:07,770 from the telecommunication companies, 87 00:03:07,770 --> 00:03:10,110 and that means ADSL speeds quickly increased 88 00:03:10,110 --> 00:03:12,660 and got into the one and a half megabits per second, 89 00:03:12,660 --> 00:03:14,040 and then four megabits per second, 90 00:03:14,040 --> 00:03:15,540 and then eight megabits per second. 91 00:03:15,540 --> 00:03:17,280 And they kept going up from there. 92 00:03:17,280 --> 00:03:20,700 And these days, ADSL is still out in the marketplace 93 00:03:20,700 --> 00:03:22,440 for some more remote areas, 94 00:03:22,440 --> 00:03:24,780 but most people have now moved into cable modems 95 00:03:24,780 --> 00:03:27,900 or fiber modems in larger city environments. 96 00:03:27,900 --> 00:03:29,970 Now, when DSL first started coming out though, 97 00:03:29,970 --> 00:03:31,770 it was very, very slow. 98 00:03:31,770 --> 00:03:33,480 When we started talking about DSL speeds, 99 00:03:33,480 --> 00:03:36,030 it was in the quarter of a meg per second 100 00:03:36,030 --> 00:03:39,090 or 256 kilobits per second of speed. 101 00:03:39,090 --> 00:03:41,220 As advancements came up, we kept getting more 102 00:03:41,220 --> 00:03:44,730 and more towards ADSL and faster and faster modems. 103 00:03:44,730 --> 00:03:46,740 Now, the last type of DSL that we need to mention 104 00:03:46,740 --> 00:03:51,300 is what's known as VDSL or very high bit rate DSL. 105 00:03:51,300 --> 00:03:52,410 Now, this is where you can actually get 106 00:03:52,410 --> 00:03:54,780 very, very high speeds, and you can have downloads 107 00:03:54,780 --> 00:03:57,330 as high as 50 megabits per second or more, 108 00:03:57,330 --> 00:04:00,450 and uploads of about 10 megabits per second or more. 109 00:04:00,450 --> 00:04:01,830 The big limitation here though 110 00:04:01,830 --> 00:04:04,470 was your distance from what is known as the DSLAM. 111 00:04:04,470 --> 00:04:06,030 Now, what is a DSLAM? 112 00:04:06,030 --> 00:04:07,920 Well, the DSLAM is the point of presence 113 00:04:07,920 --> 00:04:10,020 that's owned by the telephone company. 114 00:04:10,020 --> 00:04:12,720 With very high bit rate DSL, you had to be within 115 00:04:12,720 --> 00:04:16,740 about 4,000 feet of that D-S-L-A-M or DSLAM. 116 00:04:16,740 --> 00:04:18,329 And this is less than a mile. 117 00:04:18,329 --> 00:04:20,550 Now, unfortunately, a lot of home and offices 118 00:04:20,550 --> 00:04:22,980 could not get VDSL, because most of them 119 00:04:22,980 --> 00:04:25,320 were outside that 4,000 foot range. 120 00:04:25,320 --> 00:04:27,690 But they were still within the 18,000 foot range 121 00:04:27,690 --> 00:04:29,670 that you would need to get ADSL. 122 00:04:29,670 --> 00:04:32,790 So if you have to be anywhere between 4,000 and 18,000 feet, 123 00:04:32,790 --> 00:04:34,260 you were stuck with ADSL. 124 00:04:34,260 --> 00:04:35,100 But if you were lucky enough 125 00:04:35,100 --> 00:04:37,170 to be within 4,000 feet of the DSLAM, 126 00:04:37,170 --> 00:04:40,200 you could get VDSL and get those really high speeds. 127 00:04:40,200 --> 00:04:41,850 Again though, at this time, 128 00:04:41,850 --> 00:04:44,160 DSL has really declined in popularity, 129 00:04:44,160 --> 00:04:45,120 and you really won't see it 130 00:04:45,120 --> 00:04:47,700 unless you're working in one of the older areas of town, 131 00:04:47,700 --> 00:04:49,800 or if you're working in more rural area of town, 132 00:04:49,800 --> 00:04:52,920 because VDSL and ADSL were installed 133 00:04:52,920 --> 00:04:54,930 over traditional copper phone lines. 134 00:04:54,930 --> 00:04:56,940 And these days, a lot of those copper phone lines 135 00:04:56,940 --> 00:04:59,100 aren't really being serviced and are being taken out 136 00:04:59,100 --> 00:05:00,210 as most things are starting 137 00:05:00,210 --> 00:05:02,190 to move towards fiber optic connections 138 00:05:02,190 --> 00:05:04,170 and voiceover IP services 139 00:05:04,170 --> 00:05:05,550 where we're just using data packets 140 00:05:05,550 --> 00:05:07,560 over the internet to make our phone calls. 141 00:05:07,560 --> 00:05:09,330 And this is why you're going to see a lot more cable 142 00:05:09,330 --> 00:05:10,680 and fiber modems out there 143 00:05:10,680 --> 00:05:12,933 instead of DSL as you move into the field.