1 00:00:00,710 --> 00:00:01,040 All right. 2 00:00:01,040 --> 00:00:08,150 So since there's really nothing much to say about the physical layer, I mean, because in this course, 3 00:00:08,150 --> 00:00:11,090 we're really looking at the digital side of networking. 4 00:00:11,090 --> 00:00:16,250 I'd like to just skip that and start with the second one, the data link layer. 5 00:00:17,160 --> 00:00:25,530 The data link layer is the second layer in the OSI Open Systems Interconnection seven layer reference 6 00:00:25,530 --> 00:00:26,250 model. 7 00:00:26,280 --> 00:00:34,560 Now it responds to service requests from the network layer above it and issues service requests to the 8 00:00:34,560 --> 00:00:36,390 physical layer below it. 9 00:00:36,510 --> 00:00:37,320 Right. 10 00:00:37,560 --> 00:00:44,850 So the data link layer is responsible for encoding bits into packets prior to transmission and then 11 00:00:44,850 --> 00:00:48,090 decoding the packets back into bits at the destination. 12 00:00:48,850 --> 00:00:54,430 And bits, by the way, are the most basic unit of information in computing and communications. 13 00:00:55,030 --> 00:01:03,520 Packets are the fundamental unit of information transport in all modern computer networks and increasingly 14 00:01:03,520 --> 00:01:06,010 in other communications networks as well. 15 00:01:07,430 --> 00:01:10,820 So the data link layer is also responsible for. 16 00:01:11,910 --> 00:01:13,650 Logical link Control. 17 00:01:13,950 --> 00:01:16,050 Media Access Control. 18 00:01:16,350 --> 00:01:17,970 Hardware Addressing. 19 00:01:18,330 --> 00:01:24,510 Error Detection and handling and defining physical layer standards. 20 00:01:25,440 --> 00:01:32,670 It provides reliable data transfer by transmitting packets with a necessary synchronization error control 21 00:01:32,670 --> 00:01:34,080 and flow control. 22 00:01:34,720 --> 00:01:38,470 The data link layer is divided into two sub layers. 23 00:01:39,060 --> 00:01:48,390 First, the Media Access Control Mac Sublayer that governs protocol access to the physical network medium 24 00:01:48,690 --> 00:01:53,190 through the Mac addresses that are typically assigned to all ports on a router. 25 00:01:53,490 --> 00:02:00,210 Multiple devices on the same physical link can uniquely identify one another at the data link layer. 26 00:02:00,830 --> 00:02:06,500 Mac addresses are used in addition to the network addresses that are typically configured manually on 27 00:02:06,500 --> 00:02:08,030 ports within a network. 28 00:02:09,800 --> 00:02:09,979 Now. 29 00:02:09,979 --> 00:02:18,290 Secondly, the logical Link control or LLC Sublayer manages communications between devices over a single 30 00:02:18,290 --> 00:02:19,670 link of a network. 31 00:02:19,820 --> 00:02:28,340 This sublayer supports fields in link layer frames that enable multiple higher layer protocols to share 32 00:02:28,340 --> 00:02:30,110 a single physical link. 33 00:02:31,350 --> 00:02:38,490 So here we have some protocols and the data link layer and some physical media and connection methodologies 34 00:02:38,490 --> 00:02:39,900 in the physical layer. 35 00:02:41,080 --> 00:02:47,740 Ethernet and 802.11 Wireless LAN are the best known protocols of the data link layer. 36 00:02:49,660 --> 00:02:55,750 Ethernet is the name of the most commonly used network protocol that controls how data is transmitted 37 00:02:55,750 --> 00:02:58,990 over a LAN, which is a local area network. 38 00:02:59,770 --> 00:03:06,520 Now you need to have a network interface card in the device that you want to connect to the network. 39 00:03:07,640 --> 00:03:12,020 I know it probably seems pretty obvious to you, but I just wanted to make sure that we're all on the 40 00:03:12,020 --> 00:03:12,860 same page. 41 00:03:13,970 --> 00:03:21,770 A wireless local area network or LAN is a wireless computer network protocol that links two or more 42 00:03:21,770 --> 00:03:28,850 devices using wireless communication within a limited area such as a home or school computer lab or 43 00:03:28,850 --> 00:03:29,870 office building. 44 00:03:31,290 --> 00:03:37,500 And this gives users the ability to move around within a local coverage area and still be connected 45 00:03:37,500 --> 00:03:38,550 to the network. 46 00:03:39,410 --> 00:03:49,070 Most modern plans are based on the IEEE 802.11 standard and are marketed under the Wi-Fi brand name.