1 00:00:00,090 --> 00:00:05,820 ‫I don't want to spend too much time on theoretical information, but to understand the packets sent 2 00:00:05,820 --> 00:00:12,540 ‫to the destination systems and the reply packets as well, we should talk about the TCP IP Internet 3 00:00:12,540 --> 00:00:13,530 ‫Protocol suite. 4 00:00:14,400 --> 00:00:17,250 ‫OCI open systems interconnection. 5 00:00:18,200 --> 00:00:25,040 ‫Is a reference model for how applications can communicate over a network, a reference model is a conceptual 6 00:00:25,040 --> 00:00:27,440 ‫framework for understanding relationships. 7 00:00:28,410 --> 00:00:34,680 ‫The purpose of the OCI reference model is to guide vendors and developers so that the digital communication 8 00:00:34,680 --> 00:00:41,760 ‫products and software programs they create will interoperate and to facilitate clear comparisons among 9 00:00:41,760 --> 00:00:42,990 ‫communications tools. 10 00:00:43,530 --> 00:00:49,680 ‫Most vendors involved in the telecommunications make an attempt to describe their products and services 11 00:00:49,680 --> 00:00:52,020 ‫in relation to the OCI model. 12 00:00:52,620 --> 00:00:59,640 ‫And although useful for guiding discussion and evaluation, OCI is rarely actually implemented. 13 00:01:00,460 --> 00:01:07,180 ‫As few network products or standard tools keep all related functions together in well-defined layers 14 00:01:07,210 --> 00:01:13,990 ‫as related to the model developed by representatives of major computer and telecommunication companies 15 00:01:13,990 --> 00:01:21,850 ‫beginning in 1983, Osai was originally intended to be a detailed specification of actual interfaces. 16 00:01:22,150 --> 00:01:28,900 ‫Instead, the committee decided to establish a common reference model for which others could then develop 17 00:01:28,900 --> 00:01:32,770 ‫detailed interfaces, which in turn could become standards. 18 00:01:33,550 --> 00:01:39,100 ‫Osai was officially adopted as the international standard by the International Organization of Standards 19 00:01:39,520 --> 00:01:40,240 ‫ISO. 20 00:01:41,290 --> 00:01:44,230 ‫So what about the Oh as I layers? 21 00:01:45,230 --> 00:01:52,460 ‫The main concept of Osai is that the process of communication between two end points in a telecommunication 22 00:01:52,460 --> 00:01:58,400 ‫network can be divided into seven distinct groups of related functions or layers. 23 00:01:59,400 --> 00:02:06,390 ‫Each communicating user, a program is at a computer that can provide those seven layers a function. 24 00:02:06,780 --> 00:02:13,020 ‫So in a given message between users, there will be a flow of data down through the layers in the source 25 00:02:13,020 --> 00:02:18,300 ‫computer across the network and then up through the layers in the receiving computer. 26 00:02:18,750 --> 00:02:24,960 ‫The seven layers of function are provided by a combination of applications, operating systems, network 27 00:02:24,960 --> 00:02:31,890 ‫card device drivers and networking hardware that enable a system to put a signal on a network cable 28 00:02:31,890 --> 00:02:35,640 ‫or out over Wi-Fi or any other wireless protocol. 29 00:02:36,360 --> 00:02:39,720 ‫The seven open systems interconnection layers are. 30 00:02:41,250 --> 00:02:43,200 ‫Layer seven, the application layer. 31 00:02:43,950 --> 00:02:47,340 ‫This is a layer at which communication partners are identified. 32 00:02:47,790 --> 00:02:49,200 ‫Is there someone to talk to? 33 00:02:50,640 --> 00:02:52,500 ‫Network capacity is assessed. 34 00:02:52,980 --> 00:02:56,730 ‫Will the network let me talk to them right now and. 35 00:02:57,720 --> 00:03:01,740 ‫That creates a thing to send or opens the thing received. 36 00:03:02,550 --> 00:03:05,850 ‫Please note that this layer is not the application itself. 37 00:03:06,240 --> 00:03:13,410 ‫It is this set of services and applications should be able to make use of directly, although some applications 38 00:03:13,410 --> 00:03:15,630 ‫may perform application layer functions. 39 00:03:16,690 --> 00:03:23,680 ‫Layer six, the presentation layer, this layer is usually part of an operating system and converts 40 00:03:23,680 --> 00:03:28,120 ‫incoming and outgoing data from one presentation format to another. 41 00:03:28,690 --> 00:03:35,650 ‫For example, from clear text to encrypted text at one end and back to clear text at the other. 42 00:03:36,930 --> 00:03:43,350 ‫Layer five, the session layer, this layer sets up coordinates and terminates conversations. 43 00:03:44,280 --> 00:03:47,280 ‫Services include authentication and reconnection. 44 00:03:47,280 --> 00:03:54,240 ‫After an interruption on the Internet Transmission Control Protocol, TCP and user data Graham Protocol 45 00:03:54,600 --> 00:03:57,750 ‫UDP provide these services for most applications. 46 00:03:59,150 --> 00:04:05,900 ‫Layer four, the transport layer, this layer manages packet ization of data, then the delivery of 47 00:04:05,900 --> 00:04:10,190 ‫the packet, including checking for errors and the data once it arrives. 48 00:04:11,280 --> 00:04:15,840 ‫On the Internet, TCP and UDP provide services for most applications as well. 49 00:04:17,090 --> 00:04:23,300 ‫Layer three, the network layer, this layer handles the addressing and routing of the data, sending 50 00:04:23,300 --> 00:04:29,450 ‫it in the right direction to the right destination on outgoing transmissions and receiving incoming 51 00:04:29,450 --> 00:04:31,520 ‫transmissions at the packet level. 52 00:04:32,360 --> 00:04:35,060 ‫IB is a network layer for the internet. 53 00:04:36,270 --> 00:04:38,250 ‫Layer two, the data link layer. 54 00:04:39,190 --> 00:04:44,800 ‫This layer sets up links across the physical network, putting packets into network frames. 55 00:04:45,640 --> 00:04:52,090 ‫This layer has two sub layers, the logical link control layer and the media access control layer. 56 00:04:52,150 --> 00:04:54,580 ‫Ethernet is the main data link, layer and use. 57 00:04:55,620 --> 00:05:01,650 ‫Layer one, the physical layer, this layer conveys the bitstream stream through the network at the 58 00:05:01,650 --> 00:05:03,990 ‫electrical, optical or radio level. 59 00:05:04,800 --> 00:05:09,240 ‫It provides the hardware means of sending and receiving data on a carrier network. 60 00:05:10,080 --> 00:05:12,810 ‫Let's see some of the most famous protocols of the layers. 61 00:05:13,910 --> 00:05:18,500 ‫For ease of use, it's better to talk about physical layer and data link layer together. 62 00:05:19,510 --> 00:05:24,910 ‫Here we have some protocols and data link layer and some physical media and connection methodologies 63 00:05:25,060 --> 00:05:32,320 ‫in physical layer Ethernet and 8.2.1 one wireless LAN are the most known protocols of the data link 64 00:05:32,320 --> 00:05:32,650 ‫layer. 65 00:05:33,620 --> 00:05:38,660 ‫Ethernet is the name of the most commonly used network protocol that controls how data is transmitted 66 00:05:38,660 --> 00:05:41,450 ‫over land, which is a local area network. 67 00:05:42,610 --> 00:05:47,800 ‫You need to have network interface cards in the devices that you want to connect to the network. 68 00:05:48,660 --> 00:05:55,710 ‫A wireless local area network, W LAN is a wireless computer network protocol that links two or more 69 00:05:55,710 --> 00:06:02,610 ‫devices using wireless communication within a limited area such as a home school, computer, laboratory 70 00:06:02,610 --> 00:06:03,630 ‫or office building. 71 00:06:04,200 --> 00:06:10,410 ‫This gives users the ability to move around with a local coverage area and yet still be connected to 72 00:06:10,410 --> 00:06:11,040 ‫the network. 73 00:06:11,550 --> 00:06:18,720 ‫Most modern LANs are based on I Tripoli 8.2.1 one standards and are marketed under the Wi-Fi brand name. 74 00:06:20,220 --> 00:06:28,380 ‫IP Internet Protocol is responsible for addressing host encapsulating data into transferred packet and 75 00:06:28,380 --> 00:06:34,380 ‫routing packets from a source host to a destination host across one or more IP networks. 76 00:06:35,800 --> 00:06:41,500 ‫The best known transport protocol is the transmission control protocol, or TCP. 77 00:06:41,770 --> 00:06:47,770 ‫It's used for connection oriented transmissions, whereas the connection less user data grand protocol 78 00:06:47,770 --> 00:06:51,430 ‫UDP is used for simpler messaging transmissions. 79 00:06:51,850 --> 00:06:55,240 ‫We're going to talk more in-depth about these protocols in the next lecture. 80 00:06:56,730 --> 00:07:02,490 ‫Again, for ease of use, the last three layers session, layer, presentation, layer and application 81 00:07:02,490 --> 00:07:06,270 ‫layer are thought of together as the application layer. 82 00:07:08,330 --> 00:07:09,890 ‫Let me put another parenthesis here. 83 00:07:10,820 --> 00:07:14,210 ‫We're talking about the OSAI reference model here. 84 00:07:14,510 --> 00:07:21,740 ‫In addition, there is another reference model called TCP IP reference model and instead of OSAI models 85 00:07:21,740 --> 00:07:22,760 ‫last three layers. 86 00:07:23,120 --> 00:07:27,770 ‫There is only a single application layer in the TCP IP reference model. 87 00:07:27,950 --> 00:07:29,570 ‫Just keep that in the back of your mind. 88 00:07:31,260 --> 00:07:32,180 ‫And back to our subject. 89 00:07:33,340 --> 00:07:40,300 ‫The application layer protocols are classified according to the protocol they are using in the transport 90 00:07:40,300 --> 00:07:45,370 ‫layer and these protocols in Iraq with the end user via applications. 91 00:07:45,490 --> 00:07:49,840 ‫Therefore, they are the most known protocols by just about everybody. 92 00:07:51,400 --> 00:07:55,390 ‫Some of the most well-known TCP based application layer protocols are. 93 00:07:56,680 --> 00:08:04,370 ‫HTP Hypertext Transfer Protocol, simply a communications protocol used to send and receive Web pages 94 00:08:04,370 --> 00:08:05,720 ‫and files on the internet. 95 00:08:06,630 --> 00:08:10,950 ‫Telnet is one of the simplest ways to exchange data between two computers. 96 00:08:11,820 --> 00:08:18,210 ‫It allows two computers anywhere on a computer network, including the worldwide internet, to exchange 97 00:08:18,210 --> 00:08:21,030 ‫text and, well, other data in real time. 98 00:08:22,680 --> 00:08:28,890 ‫FTP file transfer protocol is a communication protocol for the rapid, simple transmission of files 99 00:08:28,890 --> 00:08:29,850 ‫across a network. 100 00:08:31,560 --> 00:08:32,400 ‫SMTP. 101 00:08:32,490 --> 00:08:38,760 ‫Simple Mail Transfer Protocol is used to send and relay an e-mail message between e-mail servers. 102 00:08:39,240 --> 00:08:42,900 ‫Note that it is not used to retrieve email messages from a server. 103 00:08:42,900 --> 00:08:47,010 ‫Instead, either IMAP or Pop is used to retrieve email messages. 104 00:08:48,740 --> 00:08:55,700 ‫DNS, the domain name system is a system used to convert a computer's hostname into an IP address on 105 00:08:55,700 --> 00:08:56,180 ‫the internet. 106 00:08:56,900 --> 00:09:03,230 ‫For example, if a computer needs to communicate with a web server, NHS Dot UK, your computer needs 107 00:09:03,230 --> 00:09:05,180 ‫the IP address of the web server. 108 00:09:05,210 --> 00:09:12,860 ‫NHS Dot UK It is the job of the DNS to convert the hostname to the IP address of the web server. 109 00:09:13,010 --> 00:09:16,580 ‫The DNS uses both the UDP and TCP. 110 00:09:17,630 --> 00:09:24,440 ‫SNMP Simple Network Management Protocol is used in network management systems to monitor status of devices 111 00:09:24,440 --> 00:09:26,060 ‫and also spot problems.