1 1 00:00:00,850 --> 00:00:03,510 Layer Five, the Session Layer. 2 2 00:00:03,510 --> 00:00:05,830 Now, layer five is our session layer, 3 3 00:00:05,830 --> 00:00:09,160 and we want to start thinking about what a session is. 4 4 00:00:09,160 --> 00:00:10,790 The way I like to think about a session 5 5 00:00:10,790 --> 00:00:13,140 is that it's a conversation that has to be kept 6 6 00:00:13,140 --> 00:00:15,400 separate from all of the others to prevent 7 7 00:00:15,400 --> 00:00:17,380 the intermingling of data. 8 8 00:00:17,380 --> 00:00:19,880 Now, if you think about yourself in a classroom setting, 9 9 00:00:19,880 --> 00:00:22,160 we might have 20 students sitting here. 10 10 00:00:22,160 --> 00:00:24,658 Now, if I wanted to ask a question to one student only, 11 11 00:00:24,658 --> 00:00:26,740 everyone else can listen to it. 12 12 00:00:26,740 --> 00:00:28,130 Maybe I want to take that student, 13 13 00:00:28,130 --> 00:00:29,960 and we're going to go walk about in to the hallway 14 14 00:00:29,960 --> 00:00:32,130 so we can have our own session, our own private 15 15 00:00:32,130 --> 00:00:34,680 conversation, while all of the other 19 students 16 16 00:00:34,680 --> 00:00:36,140 can talk among themselves. 17 17 00:00:36,140 --> 00:00:38,170 And they're having their own session. 18 18 00:00:38,170 --> 00:00:40,530 That way, we can separate these two sessions apart 19 19 00:00:40,530 --> 00:00:42,790 and each of us can talk at the same time 20 20 00:00:42,790 --> 00:00:44,290 without interfering with the other, 21 21 00:00:44,290 --> 00:00:45,970 me and my student out in the hall 22 22 00:00:45,970 --> 00:00:48,130 and all the other 19 students sitting back 23 23 00:00:48,130 --> 00:00:49,360 in the classroom. 24 24 00:00:49,360 --> 00:00:51,057 Now, that's the idea here when we talk about 25 25 00:00:51,057 --> 00:00:52,460 the session layer. 26 26 00:00:52,460 --> 00:00:54,723 We have all sorts of data flying around our networks 27 27 00:00:54,723 --> 00:00:57,815 all day long, and by establishing these sessions, 28 28 00:00:57,815 --> 00:01:00,212 we can separate them to prevent the intermingling 29 29 00:01:00,212 --> 00:01:03,040 or cross-contamination of that data. 30 30 00:01:03,040 --> 00:01:05,130 Now, what we're going to do is we're going to set up a session, 31 31 00:01:05,130 --> 00:01:06,517 we're going to maintain a session, 32 32 00:01:06,517 --> 00:01:08,270 and we're going to tear down a session 33 33 00:01:08,270 --> 00:01:10,540 here inside the session layer. 34 34 00:01:10,540 --> 00:01:12,820 Now, what is setting up a session? 35 35 00:01:12,820 --> 00:01:15,360 This is where we're going to check our user credentials, 36 36 00:01:15,360 --> 00:01:17,370 and we're going to assign a number to the session 37 37 00:01:17,370 --> 00:01:18,830 to help identify it. 38 38 00:01:18,830 --> 00:01:20,360 It's basically some random number 39 39 00:01:20,360 --> 00:01:22,115 that's going to allow us to negotiate services 40 40 00:01:22,115 --> 00:01:24,364 for that session with the server 41 41 00:01:24,364 --> 00:01:27,080 and then negotiate who's going to talk first, 42 42 00:01:27,080 --> 00:01:29,260 either the server or myself. 43 43 00:01:29,260 --> 00:01:31,800 Now, let's go back to our classroom setting once more. 44 44 00:01:31,800 --> 00:01:33,630 If Johnny asks me a question, he says, 45 45 00:01:33,630 --> 00:01:34,930 hey, professor Dion. 46 46 00:01:34,930 --> 00:01:36,420 I'll say, yes Johnny? 47 47 00:01:36,420 --> 00:01:37,380 And then, guess what? 48 48 00:01:37,380 --> 00:01:38,640 We're going to start talking, 49 49 00:01:38,640 --> 00:01:40,560 because we've established that session. 50 50 00:01:40,560 --> 00:01:42,145 I know that Johnny wants to talk to me, 51 51 00:01:42,145 --> 00:01:44,604 and Johnny knows that I'm ready to talk to him. 52 52 00:01:44,604 --> 00:01:46,460 Now, I know who he is. 53 53 00:01:46,460 --> 00:01:47,590 He knows who I am. 54 54 00:01:47,590 --> 00:01:49,200 And we both know what each other wants. 55 55 00:01:49,200 --> 00:01:50,820 We want to start talking. 56 56 00:01:50,820 --> 00:01:52,732 In a computer network, it's a little bit more difficult 57 57 00:01:52,732 --> 00:01:54,667 but that's really the idea behind it 58 58 00:01:54,667 --> 00:01:57,000 when we start talking about a session. 59 59 00:01:57,000 --> 00:01:58,263 Now, the next thing we have to do 60 60 00:01:58,263 --> 00:02:00,398 is we have to maintain this session. 61 61 00:02:00,398 --> 00:02:02,200 This is where we're going to transfer data 62 62 00:02:02,200 --> 00:02:03,630 back and forth across the network 63 63 00:02:03,630 --> 00:02:05,720 over and over and over again. 64 64 00:02:05,720 --> 00:02:06,991 Going back to my classroom example, 65 65 00:02:06,991 --> 00:02:09,340 if Johnny asks me a question, I'd say, 66 66 00:02:09,340 --> 00:02:11,590 yes, go ahead and ask the question, Johnny. 67 67 00:02:11,590 --> 00:02:13,500 And then, Johnny's going to ask his question. 68 68 00:02:13,500 --> 00:02:15,081 And at this point, we're maintaining a session. 69 69 00:02:15,081 --> 00:02:17,525 So, here we are going back and forth, back and forth, 70 70 00:02:17,525 --> 00:02:19,380 where I can answer their question 71 71 00:02:19,380 --> 00:02:22,347 and see if I can answer everything they have for me, right? 72 72 00:02:22,347 --> 00:02:25,410 Well, the same idea happens here inside our networks. 73 73 00:02:25,410 --> 00:02:27,200 Now that the session has been established, 74 74 00:02:27,200 --> 00:02:29,280 we're going to send all of our data back and forth 75 75 00:02:29,280 --> 00:02:30,530 over and over again. 76 76 00:02:30,530 --> 00:02:32,330 Now, if we have a break in the connection, 77 77 00:02:32,330 --> 00:02:34,520 we're going to have to reestablish our connection. 78 78 00:02:34,520 --> 00:02:36,700 So, for instance, I might say, I'm sorry, 79 79 00:02:36,700 --> 00:02:37,830 I didn't hear you Johnny. 80 80 00:02:37,830 --> 00:02:39,360 Can you repeat your question? 81 81 00:02:39,360 --> 00:02:41,490 Again, I'm maintaining that session. 82 82 00:02:41,490 --> 00:02:43,120 So, that way, I can get what they want to tell me, 83 83 00:02:43,120 --> 00:02:44,630 and then I can answer them. 84 84 00:02:44,630 --> 00:02:47,360 Now, also I'm going to acknowledge the receipt of the data. 85 85 00:02:47,360 --> 00:02:49,660 I'll say, did you understand my answer, Johnny? 86 86 00:02:49,660 --> 00:02:50,840 And they'll say, yeah I did. 87 87 00:02:50,840 --> 00:02:51,970 Or no, I didn't. 88 88 00:02:51,970 --> 00:02:54,450 And if they did, they'll acknowledge the receipt. 89 89 00:02:54,450 --> 00:02:56,090 If they didn't, they're going to tell me, 90 90 00:02:56,090 --> 00:02:57,070 no, I didn't understand. 91 91 00:02:57,070 --> 00:02:59,160 Can you tell me that again a different way? 92 92 00:02:59,160 --> 00:03:01,634 Well, the same thing happens digitally with your networks. 93 93 00:03:01,634 --> 00:03:04,045 And that brings us to the final area. 94 94 00:03:04,045 --> 00:03:05,690 Tearing down a session. 95 95 00:03:05,690 --> 00:03:07,600 So, now that the student's question has been answered 96 96 00:03:07,600 --> 00:03:09,440 in our analogy of the classroom, 97 97 00:03:09,440 --> 00:03:11,737 I'll say, Johnny, does that answer your question? 98 98 00:03:11,737 --> 00:03:13,885 And hopefully, he'll say, yes it does. 99 99 00:03:13,885 --> 00:03:15,780 And at that point, I'll say okay, 100 100 00:03:15,780 --> 00:03:17,501 we're going to move on to the next thing in the course. 101 101 00:03:17,501 --> 00:03:18,816 And as I say that, 102 102 00:03:18,816 --> 00:03:20,850 we're going to move on to the next question. 103 103 00:03:20,850 --> 00:03:22,390 That tears down the session. 104 104 00:03:22,390 --> 00:03:24,490 The session between me and Johnny is done, 105 105 00:03:24,490 --> 00:03:26,020 and I'm going to go back to teaching. 106 106 00:03:26,020 --> 00:03:27,170 And if Johnny has another question, 107 107 00:03:27,170 --> 00:03:28,580 he's going to have to raise his hand again, 108 108 00:03:28,580 --> 00:03:30,980 so that I can go and say, okay Johnny, what's your question? 109 109 00:03:30,980 --> 00:03:32,720 And we'll start a new session, right? 110 110 00:03:32,720 --> 00:03:34,730 That would be the end of that particular session 111 111 00:03:34,730 --> 00:03:37,190 once I answer his question and got confirmation 112 112 00:03:37,190 --> 00:03:38,240 that he has it. 113 113 00:03:38,240 --> 00:03:39,910 Then, we can move on. 114 114 00:03:39,910 --> 00:03:42,509 Now, this is done based on this mutual agreement. 115 115 00:03:42,509 --> 00:03:45,090 Once we've transferred all the data back and forth 116 116 00:03:45,090 --> 00:03:46,631 we wanted to, we're going to verify 117 117 00:03:46,631 --> 00:03:48,504 that I'm ready to tear down the session, 118 118 00:03:48,504 --> 00:03:50,910 you're ready for the session to be torn down, 119 119 00:03:50,910 --> 00:03:53,158 and then, we can tear down that session. 120 120 00:03:53,158 --> 00:03:55,330 The other way we could take down a session 121 121 00:03:55,330 --> 00:03:56,707 is if one of the parties disconnects 122 122 00:03:56,707 --> 00:03:58,505 and we simply can't reconnect to them. 123 123 00:03:58,505 --> 00:04:01,065 For instance let's go back to my classroom example. 124 124 00:04:01,065 --> 00:04:02,790 Johnny asked a question. 125 125 00:04:02,790 --> 00:04:05,260 I go on a 30-minute diatribe trying to explain 126 126 00:04:05,260 --> 00:04:07,930 every possible thing to answer his question. 127 127 00:04:07,930 --> 00:04:09,227 And I look up and guess what? 128 128 00:04:09,227 --> 00:04:10,839 Johnny has his head down on the table 129 129 00:04:10,839 --> 00:04:12,120 and he's fallen asleep. 130 130 00:04:12,120 --> 00:04:13,276 I bored him to death. 131 131 00:04:13,276 --> 00:04:15,820 There's no way for me to maintain that session, 132 132 00:04:15,820 --> 00:04:17,500 because he's not getting the information. 133 133 00:04:17,500 --> 00:04:19,410 He's completely asleep. 134 134 00:04:19,410 --> 00:04:22,220 He is dead asleep and he is not listening anymore. 135 135 00:04:22,220 --> 00:04:24,720 Well, he has disconnected from this conversation. 136 136 00:04:24,720 --> 00:04:27,120 And therefore, I can't re-engage. 137 137 00:04:27,120 --> 00:04:28,920 So, I'm just going to stop teaching 138 138 00:04:28,920 --> 00:04:31,150 and move on to other students who are awake 139 139 00:04:31,150 --> 00:04:32,220 and are paying attention 140 140 00:04:32,220 --> 00:04:33,617 and actually have questions for me. 141 141 00:04:33,617 --> 00:04:35,788 That's the idea here with tearing down a session. 142 142 00:04:35,788 --> 00:04:37,438 This can be done either mutually 143 143 00:04:37,438 --> 00:04:39,560 where we both have finished the communication 144 144 00:04:39,560 --> 00:04:41,120 and we say, yep, I'm done, you're done, 145 145 00:04:41,120 --> 00:04:42,250 we understand each other. 146 146 00:04:42,250 --> 00:04:43,230 We move on. 147 147 00:04:43,230 --> 00:04:45,750 Or the other party simply disappears. 148 148 00:04:45,750 --> 00:04:47,633 In which case, I want to free up my resources 149 149 00:04:47,633 --> 00:04:49,270 so I can go help other people again. 150 150 00:04:49,270 --> 00:04:51,440 And that's what I would do as a computer. 151 151 00:04:51,440 --> 00:04:53,568 So, what are some examples of Layer 5 devices 152 152 00:04:53,568 --> 00:04:56,440 or protocols, or things that you should associate 153 153 00:04:56,440 --> 00:04:57,800 with Layer 5? 154 154 00:04:57,800 --> 00:05:02,000 Well, the two big ones are H.323 and NetBIOS. 155 155 00:05:02,000 --> 00:05:03,879 Let's talk about H.323 first. 156 156 00:05:03,879 --> 00:05:08,010 H.323 is used to set up, maintain, and tear down 157 157 00:05:08,010 --> 00:05:09,880 voice and video connections. 158 158 00:05:09,880 --> 00:05:11,810 If you're using FaceTime or Skype 159 159 00:05:11,810 --> 00:05:13,780 or something like that, you're probably using 160 160 00:05:13,780 --> 00:05:16,370 something like H.323, which operates 161 161 00:05:16,370 --> 00:05:19,580 over the RTP or Real-Time Protocol. 162 162 00:05:19,580 --> 00:05:21,709 Now, I know I just threw out a lot of acronyms for you. 163 163 00:05:21,709 --> 00:05:26,010 For the exam, if you see something like H.323 164 164 00:05:26,010 --> 00:05:29,730 or H.264, I want you to think about streaming audio 165 165 00:05:29,730 --> 00:05:30,940 or streaming video. 166 166 00:05:30,940 --> 00:05:33,070 Something like FaceTime, Skype, YouTube, 167 167 00:05:33,070 --> 00:05:35,655 video teleconference, something like that. 168 168 00:05:35,655 --> 00:05:40,210 These operate over the Real-Time Protocol, known as RTP. 169 169 00:05:40,210 --> 00:05:43,370 Any time you see RTP, I want you to think about 170 170 00:05:43,370 --> 00:05:45,560 streaming audio or streaming video. 171 171 00:05:45,560 --> 00:05:47,530 Generally in a two-way format, 172 172 00:05:47,530 --> 00:05:50,250 like a phone call or a FaceTime session. 173 173 00:05:50,250 --> 00:05:51,720 Keep those in your head, and you're going to do great 174 174 00:05:51,720 --> 00:05:53,810 on the exam cause they do like to throw those in 175 175 00:05:53,810 --> 00:05:55,520 and I want you to see those. 176 176 00:05:55,520 --> 00:05:56,568 Now, the second thing I mentioned 177 177 00:05:56,568 --> 00:05:59,201 is that we have something known as NetBIOS. 178 178 00:05:59,201 --> 00:06:01,646 Now, NetBIOS is used by computers to share files 179 179 00:06:01,646 --> 00:06:03,480 over a network. 180 180 00:06:03,480 --> 00:06:06,120 Windows uses this as the method of its file sharing 181 181 00:06:06,120 --> 00:06:08,400 as well inside, so you're going to see it a lot 182 182 00:06:08,400 --> 00:06:09,620 on your networks. 183 183 00:06:09,620 --> 00:06:12,012 Now, again, when we talk about Layer 5 devices, 184 184 00:06:12,012 --> 00:06:14,410 there's really not a device necessarily, 185 185 00:06:14,410 --> 00:06:16,680 but it's more of these protocols and software. 186 186 00:06:16,680 --> 00:06:20,848 So, if you see something like H.323, RTP, or NetBIOS, 187 187 00:06:20,848 --> 00:06:24,083 I want you to remember, these are all Layer 5 issues.