1 00:00:00,330 --> 00:00:01,589 We've finally made it. 2 00:00:01,589 --> 00:00:04,980 We've gotten to layer 7, the application layer. 3 00:00:04,980 --> 00:00:07,890 We've gone through seven different layers of the OSI model, 4 00:00:07,890 --> 00:00:10,440 starting all the way down with physical, then going up 5 00:00:10,440 --> 00:00:14,970 to data link, network, transport, session, presentation, 6 00:00:14,970 --> 00:00:17,700 and now we're here at application. 7 00:00:17,700 --> 00:00:19,560 The application layer is going to provide 8 00:00:19,560 --> 00:00:22,020 all of your application-level services, 9 00:00:22,020 --> 00:00:24,390 which makes sense since it's the application layer. 10 00:00:24,390 --> 00:00:26,340 But I don't want you to think about an application like 11 00:00:26,340 --> 00:00:28,860 Internet Explorer or Chrome or Word 12 00:00:28,860 --> 00:00:30,690 or PowerPoint or Notepad. 13 00:00:30,690 --> 00:00:33,510 That's not the kind of application we're talking about. 14 00:00:33,510 --> 00:00:34,680 We're actually going to be talking about 15 00:00:34,680 --> 00:00:36,690 more lower-level applications. 16 00:00:36,690 --> 00:00:39,840 When we talk about applications in the OSI context, 17 00:00:39,840 --> 00:00:42,180 we're really talking about things like file transfer 18 00:00:42,180 --> 00:00:43,770 or network transfer. 19 00:00:43,770 --> 00:00:46,320 This is the layer where the user is going to communicate 20 00:00:46,320 --> 00:00:48,810 with the computer and the computer can then take 21 00:00:48,810 --> 00:00:51,750 that information and pass it across the network. 22 00:00:51,750 --> 00:00:54,120 These are functions like application services 23 00:00:54,120 --> 00:00:56,910 and service advertisement, and we're going to talk about those 24 00:00:56,910 --> 00:00:59,340 as we go through this short lecture. 25 00:00:59,340 --> 00:01:00,960 Application services are the thing 26 00:01:00,960 --> 00:01:02,940 that unites communicating components 27 00:01:02,940 --> 00:01:05,190 for more than one network application. 28 00:01:05,190 --> 00:01:08,670 If I have a file transfer and file sharing, email, 29 00:01:08,670 --> 00:01:11,280 remote access, network management activities, 30 00:01:11,280 --> 00:01:13,050 and client server processes, 31 00:01:13,050 --> 00:01:16,380 these are all different types of application services. 32 00:01:16,380 --> 00:01:18,300 Now, again, I want to caution you. 33 00:01:18,300 --> 00:01:19,560 When I talk about email, 34 00:01:19,560 --> 00:01:21,900 I'm not talking about Microsoft Outlook. 35 00:01:21,900 --> 00:01:24,540 Instead, I'm talking about the low-level protocol 36 00:01:24,540 --> 00:01:25,800 that's used by email. 37 00:01:25,800 --> 00:01:29,190 Things like POP3 or Post Office Protocol 3, 38 00:01:29,190 --> 00:01:32,130 or Internet Message Access Protocol, an IMAP, 39 00:01:32,130 --> 00:01:36,180 or something like SMTP, the Simple Mail Transfer Protocol, 40 00:01:36,180 --> 00:01:37,320 things of this nature. 41 00:01:37,320 --> 00:01:39,510 And we're going to talk about these as we go through our ports 42 00:01:39,510 --> 00:01:42,540 and protocols in a future lesson when you have to memorize 43 00:01:42,540 --> 00:01:43,920 the different port numbers for each 44 00:01:43,920 --> 00:01:45,840 of these three types of services. 45 00:01:45,840 --> 00:01:47,370 Now, the other thing we want to talk about 46 00:01:47,370 --> 00:01:48,840 is service advertisement. 47 00:01:48,840 --> 00:01:51,180 This is where applications can send out announcements 48 00:01:51,180 --> 00:01:53,947 to other devices on the network, and they can say, 49 00:01:53,947 --> 00:01:56,250 "These are the different services that I offer." 50 00:01:56,250 --> 00:01:57,780 If you have something like a printer 51 00:01:57,780 --> 00:02:00,000 that is essentially managed by your active directory 52 00:02:00,000 --> 00:02:02,670 or a file server that's managed by active directory, 53 00:02:02,670 --> 00:02:04,980 it can do those advertisements for you. 54 00:02:04,980 --> 00:02:07,290 If not though, your files and your printers 55 00:02:07,290 --> 00:02:09,870 can actually advertise for themselves. 56 00:02:09,870 --> 00:02:12,480 And that's the idea of a service advertisement. 57 00:02:12,480 --> 00:02:14,940 For example, let's say you have a nice wireless printer 58 00:02:14,940 --> 00:02:16,230 that's on your network. 59 00:02:16,230 --> 00:02:18,240 Anytime you connect to the wireless network, 60 00:02:18,240 --> 00:02:20,077 it actually sits out there and the printer goes, 61 00:02:20,077 --> 00:02:22,050 "Hey, brand new device that I don't know 62 00:02:22,050 --> 00:02:24,390 that just joined my network, I'm a printer. 63 00:02:24,390 --> 00:02:25,223 And guess what? 64 00:02:25,223 --> 00:02:28,047 You can use me to print things because I'm a printer." 65 00:02:28,047 --> 00:02:31,020 And that's what it does, it advertises itself. 66 00:02:31,020 --> 00:02:32,940 And all this is done under this concept 67 00:02:32,940 --> 00:02:36,090 of service advertisement here in layer 7. 68 00:02:36,090 --> 00:02:38,820 Now, when we talk about layer 7, what are some examples 69 00:02:38,820 --> 00:02:40,380 of layer 7 things? 70 00:02:40,380 --> 00:02:43,170 Well, these are email applications like POP3, 71 00:02:43,170 --> 00:02:45,000 IMAP, and SMTP. 72 00:02:45,000 --> 00:02:49,500 This would be web browsing applications like HTTP or HTTPS. 73 00:02:49,500 --> 00:02:52,410 This could be things like DNS, the Domain Name Service, 74 00:02:52,410 --> 00:02:54,480 which is going to translate our names to numbers 75 00:02:54,480 --> 00:02:55,980 and our numbers to names. 76 00:02:55,980 --> 00:02:59,119 It can be things like File Transfer Protocols like FTP 77 00:02:59,119 --> 00:03:01,440 and FTPS and SFTP. 78 00:03:01,440 --> 00:03:04,830 It could be things like remote access like Telnet and SSH 79 00:03:04,830 --> 00:03:08,400 and Simple Network Management Protocol or SNMP. 80 00:03:08,400 --> 00:03:10,680 All of these things are layer 7. 81 00:03:10,680 --> 00:03:11,940 And if it sounds like I just threw out 82 00:03:11,940 --> 00:03:14,670 a lot of acronyms to you, I know I did. 83 00:03:14,670 --> 00:03:15,630 Don't worry about it. 84 00:03:15,630 --> 00:03:17,820 We are going to talk about each and every one of those 85 00:03:17,820 --> 00:03:20,370 as we go through the future lessons in this course. 86 00:03:20,370 --> 00:03:22,680 So just hang with me, and by the end of this, 87 00:03:22,680 --> 00:03:25,320 you are going to know all of those like the back of your hand. 88 00:03:25,320 --> 00:03:27,180 You're going to know what the acronyms are, 89 00:03:27,180 --> 00:03:30,000 what they stand for, and what ports they operate on, 90 00:03:30,000 --> 00:03:32,753 because that is going to be important for the exam as well.