1 1 00:00:00,480 --> 00:00:01,740 We finally made it, 2 2 00:00:01,740 --> 00:00:05,130 we've gotten to layer 7, the application layer. 3 3 00:00:05,130 --> 00:00:08,050 We've gone through seven different layers of the OSI model, 4 4 00:00:08,050 --> 00:00:09,960 starting all the way down with physical, 5 5 00:00:09,960 --> 00:00:13,320 and then going up to data link, network, transport, 6 6 00:00:13,320 --> 00:00:17,840 session, presentation, and now we're here at application. 7 7 00:00:17,840 --> 00:00:19,700 The application layer is going to provide 8 8 00:00:19,700 --> 00:00:22,140 all of your application-level services, 9 9 00:00:22,140 --> 00:00:24,510 which makes sense since it's the application layer. 10 10 00:00:24,510 --> 00:00:25,343 But I don't want you to think 11 11 00:00:25,343 --> 00:00:28,290 about an application like Internet Explorer, or Chrome, 12 12 00:00:28,290 --> 00:00:30,840 or Word, or PowerPoint, or Notepad. 13 13 00:00:30,840 --> 00:00:33,670 That's not the kind of application we're talking about. 14 14 00:00:33,670 --> 00:00:34,710 We're actually going to be talking 15 15 00:00:34,710 --> 00:00:36,850 about more lower-level applications. 16 16 00:00:36,850 --> 00:00:39,980 When we talk about applications in the OSI context, 17 17 00:00:39,980 --> 00:00:41,100 we're really talking about things 18 18 00:00:41,100 --> 00:00:43,920 like file transfer or network transfer. 19 19 00:00:43,920 --> 00:00:45,540 This is the layer where the user 20 20 00:00:45,540 --> 00:00:47,560 is going to communicate with the computer, 21 21 00:00:47,560 --> 00:00:49,910 and the computer can then take that information 22 22 00:00:49,910 --> 00:00:51,890 and pass it across the network. 23 23 00:00:51,890 --> 00:00:54,250 These are functions like application services 24 24 00:00:54,250 --> 00:00:57,050 and service advertisement, and we're going to talk about those 25 25 00:00:57,050 --> 00:00:59,340 as we go through this short lecture. 26 26 00:00:59,340 --> 00:01:00,970 Application services are the thing 27 27 00:01:00,970 --> 00:01:02,950 that unites communicating components 28 28 00:01:02,950 --> 00:01:05,210 from more than one network application. 29 29 00:01:05,210 --> 00:01:08,700 If I have a file transfer and file sharing, email, 30 30 00:01:08,700 --> 00:01:11,280 remote access, network management activities, 31 31 00:01:11,280 --> 00:01:13,070 and client server processes, 32 32 00:01:13,070 --> 00:01:16,380 these are all different types of application services. 33 33 00:01:16,380 --> 00:01:19,560 Now, again, I want to caution you, when I talk about email, 34 34 00:01:19,560 --> 00:01:21,930 I'm not talking about Microsoft Outlook. 35 35 00:01:21,930 --> 00:01:23,060 Instead, I'm talking about 36 36 00:01:23,060 --> 00:01:25,830 the low-level protocol that's used by email, 37 37 00:01:25,830 --> 00:01:29,200 things like POP3 or Post Office Protocol 3, 38 38 00:01:29,200 --> 00:01:32,510 or Internet Message Application Protocol, IMAP, 39 39 00:01:32,510 --> 00:01:36,550 or something like SMTP, the Simple Mail Transfer Protocol, 40 40 00:01:36,550 --> 00:01:38,890 things of this nature, and we're going to talk about these 41 41 00:01:38,890 --> 00:01:42,060 as we go through our ports and protocols in a future lesson 42 42 00:01:42,060 --> 00:01:43,850 when you have to memorize the different port numbers 43 43 00:01:43,850 --> 00:01:46,240 for each of these three types of services. 44 44 00:01:46,240 --> 00:01:47,760 Now, the other thing we want to talk about 45 45 00:01:47,760 --> 00:01:49,370 is service advisement. 46 46 00:01:49,370 --> 00:01:51,700 This is where applications can send out announcements 47 47 00:01:51,700 --> 00:01:53,520 to other devices on the network, 48 48 00:01:53,520 --> 00:01:54,880 and they can say these are 49 49 00:01:54,880 --> 00:01:56,770 the different services that I offer. 50 50 00:01:56,770 --> 00:01:58,300 If you have something like a printer 51 51 00:01:58,300 --> 00:02:00,530 that is essentially managed by your active directory, 52 52 00:02:00,530 --> 00:02:03,170 or a file server that's managed by an active directory, 53 53 00:02:03,170 --> 00:02:05,500 it can do those advertisements for you. 54 54 00:02:05,500 --> 00:02:07,810 If not though, your files and your printers 55 55 00:02:07,810 --> 00:02:10,300 can actually advertise for themselves, 56 56 00:02:10,300 --> 00:02:13,000 and that's the idea of a service advertisement. 57 57 00:02:13,000 --> 00:02:14,310 For example, let's say you have 58 58 00:02:14,310 --> 00:02:16,760 a nice wireless printer that's on your network. 59 59 00:02:16,760 --> 00:02:18,760 Any time you connect to the wireless network, 60 60 00:02:18,760 --> 00:02:21,300 it actually sits out there and the printer goes hey, 61 61 00:02:21,300 --> 00:02:22,550 brand new device that I don't know 62 62 00:02:22,550 --> 00:02:24,930 that just joined my network, I'm a printer. 63 63 00:02:24,930 --> 00:02:25,763 And guess what? 64 64 00:02:25,763 --> 00:02:28,900 You can use me to print things, cause I'm a printer! 65 65 00:02:28,900 --> 00:02:31,540 That's what it does, it advertises itself. 66 66 00:02:31,540 --> 00:02:33,490 And all of this is done under this concept 67 67 00:02:33,490 --> 00:02:36,600 of service advertisement here in layer 7. 68 68 00:02:36,600 --> 00:02:38,350 Now, when we talk about layer 7, 69 69 00:02:38,350 --> 00:02:40,900 what are some examples of layer 7 things? 70 70 00:02:40,900 --> 00:02:42,713 Well, these are email applications 71 71 00:02:42,713 --> 00:02:45,530 like POP3, IMAP, and SMTP. 72 72 00:02:45,530 --> 00:02:50,020 This would be web browsing applications like HTTP or HTTPS. 73 73 00:02:50,020 --> 00:02:52,930 This could be things like DNS, the Domain Name Service, 74 74 00:02:52,930 --> 00:02:53,870 which is going to translate 75 75 00:02:53,870 --> 00:02:56,520 our names to numbers and our numbers to names. 76 76 00:02:56,520 --> 00:02:58,710 It can be things like file transfer protocols 77 77 00:02:58,710 --> 00:03:02,320 like FTP, and FTPS, and SFTP. 78 78 00:03:02,320 --> 00:03:05,670 It could be things like remote access like TELNET and SSH, 79 79 00:03:05,670 --> 00:03:09,290 and Simple Network Management Protocol, or SNMP. 80 80 00:03:09,290 --> 00:03:11,570 All of these things are layer 7. 81 81 00:03:11,570 --> 00:03:12,820 And if it sounds like I just dropped 82 82 00:03:12,820 --> 00:03:15,580 a lot of acronyms to you, I know I did. 83 83 00:03:15,580 --> 00:03:17,400 Don't worry about it, we're going to talk about 84 84 00:03:17,400 --> 00:03:18,710 each and every one of those 85 85 00:03:18,710 --> 00:03:21,260 as we go through the future lessons in this course. 86 86 00:03:21,260 --> 00:03:23,560 So, just hang with me, and by the end of this, 87 87 00:03:23,560 --> 00:03:26,210 you are going to know all of those like the back of your hand. 88 88 00:03:26,210 --> 00:03:28,070 You're going to know what the acronyms are, 89 89 00:03:28,070 --> 00:03:30,870 what they stand for, and what ports they operate on, 90 90 00:03:30,870 --> 00:03:33,670 because that is going to be important for the exam, as well.