1 00:00:00,910 --> 00:00:05,830 Telcos or service providers offer leased lines with different speeds. 2 00:00:06,160 --> 00:00:10,390 However, you as a customer conscious pick some arbitrary speed. 3 00:00:10,570 --> 00:00:15,430 The speeds of lease lines follow the standards of older technology. 4 00:00:15,460 --> 00:00:23,110 In the US it's called the carrier system and in other parts of the world it's called the EE carrier 5 00:00:23,110 --> 00:00:23,800 system. 6 00:00:24,130 --> 00:00:31,330 This comes originally from Alexander Graham Bell and the way that analog voice is digitized. 7 00:00:31,570 --> 00:00:37,510 So as an example, when you speak, it's an analog signal and you're sending sound waves through the 8 00:00:37,510 --> 00:00:38,070 air. 9 00:00:38,080 --> 00:00:42,400 But that gets digitized using something called the Nyquist Theorem. 10 00:00:42,580 --> 00:00:49,930 And your analog voice is converted into a 64 kilobits per second stream using a technology called Time 11 00:00:49,930 --> 00:00:51,370 Division multiplexing. 12 00:00:51,520 --> 00:00:59,260 A single voice call in most parts of the world using older technology, such as ISDN, use a 64 kilobits 13 00:00:59,260 --> 00:01:00,100 per second. 14 00:01:00,310 --> 00:01:06,640 In the US, you'll typically find 56 kilobits per second when bonded together. 15 00:01:06,670 --> 00:01:08,530 Speeds can be increased. 16 00:01:08,530 --> 00:01:17,380 So as an example, a popular one is a PT one, which consists of 2464 kilobits per second sessions, 17 00:01:17,380 --> 00:01:23,740 plus eight kilobits per second for overhead in a single connection or single lease line, which provides 18 00:01:23,740 --> 00:01:26,410 1.54 megabits per second. 19 00:01:26,680 --> 00:01:35,020 Don't worry too much about the details, but for example, a zero or digital signal level of zero provides 20 00:01:35,020 --> 00:01:36,940 64 kilobits per second. 21 00:01:37,330 --> 00:01:44,830 A T1 consists of 2464 kilobits per second sessions plus eight kilobits per second overhead, giving 22 00:01:44,830 --> 00:01:47,740 you 1.54 megabits per second. 23 00:01:47,770 --> 00:01:56,560 So this is 24 D zeros plus eight kilobits overhead, giving you at1 speed of 1.54 megabits per second. 24 00:01:56,920 --> 00:01:59,080 That's a standard used in the US. 25 00:01:59,440 --> 00:02:06,940 In Europe, as an example, we have an E one rather than at1, which gives you just over two megabits 26 00:02:06,940 --> 00:02:07,780 per second. 27 00:02:07,780 --> 00:02:16,600 So 2.048 and that consists of 32 D zeros or 3264 kilobits per second. 28 00:02:16,600 --> 00:02:25,600 Channels Ideas zero or digital signal level zero is a 64 kilobits per second channel. 29 00:02:25,810 --> 00:02:32,620 A T1 consists of 24 channels each providing 64 kilobits per second. 30 00:02:32,920 --> 00:02:34,900 Some other US examples. 31 00:02:34,990 --> 00:02:44,770 at2 is for t one lines provide six megabits per second at3 is 20 8t1 lines providing 48 megabits per 32 00:02:44,770 --> 00:02:45,460 second. 33 00:02:45,790 --> 00:02:52,240 at4 consists of 168 T1 lines, giving you 274 megabits per second. 34 00:02:52,510 --> 00:02:56,860 In Europe, an E one is just over two megabits per second. 35 00:02:57,100 --> 00:02:59,350 E two is eight megabits per second. 36 00:02:59,380 --> 00:03:05,230 E three is 34 megabits per second and an E four is 140 megabits per second. 37 00:03:05,380 --> 00:03:16,210 If you're going to remember any 1at1 is 1.54 four megabits per second and an E one is 2.048 megabits 38 00:03:16,210 --> 00:03:17,050 per second. 39 00:03:17,320 --> 00:03:26,410 So the CSU DSU, which is acting as the DCE, is using, clocking to control when the router sends data 40 00:03:26,410 --> 00:03:31,060 and it also is configured for the relevant speed of the connection. 41 00:03:31,300 --> 00:03:38,560 So the DCI controls the speed of the serial connection and the router is controlled by the clocking 42 00:03:38,560 --> 00:03:41,290 signals that it receives from the DCE. 43 00:03:41,440 --> 00:03:45,160 The CQ tells Router when to send and receive bits. 44 00:03:45,370 --> 00:03:52,780 The router will only send and receive bits when instructed to by the DCE because of the clocking that 45 00:03:52,780 --> 00:03:55,270 the DCE is providing on the cable.