1
00:00:04,160 --> 00:00:07,160
Speaker 1: Get in text with technology with tech Stuff from how

2
00:00:07,240 --> 00:00:13,280
Speaker 1: stuff works dot com. Hey there, and welcome to tech Stuff.

3
00:00:13,320 --> 00:00:15,920
Speaker 1: I am your host, Jonathan Strickland. I'm an executive producer

4
00:00:15,960 --> 00:00:20,680
Speaker 1: at how stuff Works and I love technology. You guys,

5
00:00:21,200 --> 00:00:23,640
Speaker 1: you may or may not be aware that I live

6
00:00:23,760 --> 00:00:27,160
Speaker 1: stream text stuff whenever it's just me and I don't

7
00:00:27,160 --> 00:00:30,240
Speaker 1: have a guest or or a co host. I live

8
00:00:30,280 --> 00:00:34,040
Speaker 1: stream out on twitch dot tv slash tech stuff, and

9
00:00:34,159 --> 00:00:36,800
Speaker 1: one of the features that Twitch has is a chat room,

10
00:00:36,880 --> 00:00:41,000
Speaker 1: so I often engage in chat in said chat room,

11
00:00:41,040 --> 00:00:44,000
Speaker 1: and occasionally I asked people, Hey, is there anything you

12
00:00:44,040 --> 00:00:46,240
Speaker 1: would like me to talk about in a future episode

13
00:00:46,280 --> 00:00:49,640
Speaker 1: of tech Stuff And Nick k a k A dirt

14
00:00:49,640 --> 00:00:53,519
Speaker 1: burr over at the Twitch chat room suggested the os

15
00:00:53,600 --> 00:00:56,720
Speaker 1: I model, the seven layers of the O S I model,

16
00:00:57,160 --> 00:00:59,400
Speaker 1: and I thought, you know what, I have never actually

17
00:00:59,520 --> 00:01:04,120
Speaker 1: done an episode about the O SI model, and challenge

18
00:01:04,160 --> 00:01:07,040
Speaker 1: has been accepted. The gauntlet was thrown picked up, and

19
00:01:07,120 --> 00:01:10,920
Speaker 1: here we go. The seven layer O SI model is

20
00:01:10,959 --> 00:01:15,600
Speaker 1: an interesting topic. It's typically one that's taught in computer

21
00:01:15,680 --> 00:01:19,920
Speaker 1: science and telecommunications classes. It's it's a networking thing. It's

22
00:01:20,040 --> 00:01:22,880
Speaker 1: not necessarily internet. You would usually talk about t c

23
00:01:23,000 --> 00:01:26,440
Speaker 1: P i P protocols for Internet models of networking, but

24
00:01:26,480 --> 00:01:31,240
Speaker 1: it is for computer networks in general. And before I

25
00:01:31,319 --> 00:01:34,800
Speaker 1: get into this too far with this whole concept of

26
00:01:34,840 --> 00:01:37,520
Speaker 1: the seven layers of the O SI model, I gotta

27
00:01:37,560 --> 00:01:41,720
Speaker 1: make something very very clear. The seven layers are not

28
00:01:41,880 --> 00:01:46,280
Speaker 1: actual physical layers. Even though there is one layer called

29
00:01:46,319 --> 00:01:49,320
Speaker 1: the physical layer, they are not physical layers to any

30
00:01:49,320 --> 00:01:51,920
Speaker 1: sort of system. This is not some sort of seven

31
00:01:52,040 --> 00:01:54,880
Speaker 1: layer DIP situation, which is too bad because that stuff

32
00:01:54,960 --> 00:01:59,840
Speaker 1: is of course delicious. This is a conceptual model, and

33
00:02:00,320 --> 00:02:03,920
Speaker 1: it's a way to imagine the interactions, the rules, the

34
00:02:03,960 --> 00:02:09,359
Speaker 1: protocols between various elements within a telecommunications network to make

35
00:02:09,400 --> 00:02:13,000
Speaker 1: it easier to comprehend what is actually going on. Or,

36
00:02:14,200 --> 00:02:17,960
Speaker 1: as Eli the Computer Guy said in an incredibly useful

37
00:02:18,040 --> 00:02:20,440
Speaker 1: video on YouTube, you can actually search for Eli the

38
00:02:20,440 --> 00:02:22,680
Speaker 1: Computer Guy and look for the us I model. You

39
00:02:22,680 --> 00:02:26,080
Speaker 1: can actually watch this video. Uh. The model breaks down

40
00:02:26,440 --> 00:02:30,680
Speaker 1: the components of network communication into layers to make it

41
00:02:30,720 --> 00:02:33,000
Speaker 1: easier to understand what is actually going on. So, in

42
00:02:33,000 --> 00:02:36,480
Speaker 1: a way, the seven layer O SI model is sort

43
00:02:36,520 --> 00:02:39,160
Speaker 1: of like the analogies I tend to use on this

44
00:02:39,280 --> 00:02:42,920
Speaker 1: show in order to explain various concepts. It's meant to

45
00:02:42,960 --> 00:02:47,280
Speaker 1: clarify the purposes of various design elements and different protocols

46
00:02:47,400 --> 00:02:50,280
Speaker 1: and and tasks. By the way, there will be many

47
00:02:50,320 --> 00:02:53,840
Speaker 1: analogies in this episode because I love them. I was

48
00:02:53,880 --> 00:02:56,160
Speaker 1: an English major, so that's kind of my go too.

49
00:02:56,560 --> 00:02:58,880
Speaker 1: There are also other models, Like I said, there's the

50
00:02:58,919 --> 00:03:02,680
Speaker 1: Internet Protocol Suite. That's the other standard model of computer networking.

51
00:03:02,960 --> 00:03:05,200
Speaker 1: But we're going to focus on the O SI model

52
00:03:05,240 --> 00:03:08,079
Speaker 1: for this episode. Maybe someday I'll do an episode about

53
00:03:08,120 --> 00:03:10,119
Speaker 1: the t C P I P model, but that will

54
00:03:10,160 --> 00:03:13,360
Speaker 1: not be this episode. They are similar in many ways,

55
00:03:13,400 --> 00:03:16,080
Speaker 1: but there are distinctions between the two. But it's really

56
00:03:16,120 --> 00:03:20,200
Speaker 1: just a way of thinking about how these communication networks

57
00:03:20,280 --> 00:03:23,440
Speaker 1: handle tasks. The OSI model, by the way, did not

58
00:03:23,600 --> 00:03:26,320
Speaker 1: just spring up out of whole cloth either. It's the

59
00:03:26,320 --> 00:03:31,200
Speaker 1: product of an organization called the International Standards Organization or ISO,

60
00:03:31,400 --> 00:03:35,880
Speaker 1: not I S o IO. So let's learn about that

61
00:03:36,000 --> 00:03:38,880
Speaker 1: group first before we talk about the model. Is SO

62
00:03:39,120 --> 00:03:43,840
Speaker 1: is a non governmental international organization that is completely independent

63
00:03:43,880 --> 00:03:46,920
Speaker 1: of any state authority, so it doesn't fall under the

64
00:03:46,920 --> 00:03:51,240
Speaker 1: purview of any one nation's government. Uh. The membership of

65
00:03:51,280 --> 00:03:55,800
Speaker 1: the of ISO includes a hundred sixty two national standards bodies,

66
00:03:56,360 --> 00:04:00,320
Speaker 1: there's only one is a member per country, so you

67
00:04:00,400 --> 00:04:05,360
Speaker 1: can't have multiple standards organizations from one country in ISO's roster.

68
00:04:05,880 --> 00:04:10,240
Speaker 1: It has to be the foremost standards organization of that country.

69
00:04:10,600 --> 00:04:15,440
Speaker 1: The United States, for example, has a member. Or there's

70
00:04:15,440 --> 00:04:19,000
Speaker 1: an organization that is in ISO is the American National

71
00:04:19,120 --> 00:04:23,640
Speaker 1: Standards Institute or and C. And C actually predates ISO.

72
00:04:23,760 --> 00:04:27,480
Speaker 1: Has and C was founded in nineteen eighteen. IO began

73
00:04:27,520 --> 00:04:30,680
Speaker 1: in nineteen More on the founding of ISO in just

74
00:04:30,760 --> 00:04:34,880
Speaker 1: a second. And c's purpose is to accredit standards that

75
00:04:34,920 --> 00:04:38,440
Speaker 1: are created by quote qualified groups in the quote. So,

76
00:04:38,480 --> 00:04:41,599
Speaker 1: in other words, this organization the United States does not

77
00:04:41,800 --> 00:04:45,280
Speaker 1: create standards. It's not the one that says, this is

78
00:04:45,400 --> 00:04:50,520
Speaker 1: what the standard X is from now on, you all

79
00:04:50,560 --> 00:04:52,919
Speaker 1: have to follow it. This is the X by which

80
00:04:52,960 --> 00:04:56,159
Speaker 1: all other x is must be measured. They don't do that.

81
00:04:56,400 --> 00:04:58,480
Speaker 1: What they do is they look at the work of

82
00:04:58,960 --> 00:05:03,200
Speaker 1: qualified groups and say, yes, this example of whatever that

83
00:05:03,279 --> 00:05:07,719
Speaker 1: thing is is the standard against which all others shall

84
00:05:07,760 --> 00:05:12,320
Speaker 1: be judged. So mote it be at this point it

85
00:05:12,400 --> 00:05:14,720
Speaker 1: might even be good for us to just consider what

86
00:05:14,760 --> 00:05:17,360
Speaker 1: the heck a standard is in the first place, because

87
00:05:17,360 --> 00:05:20,760
Speaker 1: otherwise this just becomes a jumble of words, and I

88
00:05:20,760 --> 00:05:24,680
Speaker 1: start using phrases that don't really mean anything to you,

89
00:05:24,680 --> 00:05:27,520
Speaker 1: You're gonna totally tune out. So the definition of standard

90
00:05:27,600 --> 00:05:32,359
Speaker 1: is according to the Miriam Webster Dictionary. Your definitions may

91
00:05:32,480 --> 00:05:35,680
Speaker 1: vary depending on the dictionary of use. It includes the

92
00:05:35,880 --> 00:05:40,480
Speaker 1: definition of something established by authority, custom or general consent

93
00:05:40,640 --> 00:05:44,480
Speaker 1: as a model or example, or something set up and

94
00:05:44,640 --> 00:05:50,080
Speaker 1: established by authority as a rule for the measure of quantity, weight, extent, value,

95
00:05:50,279 --> 00:05:54,080
Speaker 1: or quality. It could also be a giant flag that

96
00:05:54,120 --> 00:05:57,919
Speaker 1: you carry into battle. But that definition probably doesn't really

97
00:05:57,960 --> 00:06:00,279
Speaker 1: apply when it comes to the O S. I'm also

98
00:06:00,279 --> 00:06:03,560
Speaker 1: we're not gonna think about it right now. Standards are

99
00:06:03,640 --> 00:06:07,520
Speaker 1: an agreed upon model upon which all other instances of

100
00:06:07,560 --> 00:06:12,320
Speaker 1: that concept or physical object should be measured. Uh So,

101
00:06:12,760 --> 00:06:16,760
Speaker 1: units of measurements are standards that are easy to understand. Right.

102
00:06:16,800 --> 00:06:18,840
Speaker 1: An inch is an inch no matter where you go.

103
00:06:20,040 --> 00:06:22,640
Speaker 1: A kilogram is a kilogram no matter where you go.

104
00:06:23,400 --> 00:06:26,400
Speaker 1: That sort of thing. So organizations like ants and is

105
00:06:26,600 --> 00:06:29,880
Speaker 1: so help establish these standards. They don't necessarily come up

106
00:06:29,880 --> 00:06:32,760
Speaker 1: with them, but they might accredit them, they might endorse them,

107
00:06:32,760 --> 00:06:37,120
Speaker 1: and thus get widespread acceptance of that as a standard,

108
00:06:37,720 --> 00:06:40,640
Speaker 1: this becomes sort of a generally agreed upon common concept

109
00:06:40,680 --> 00:06:44,680
Speaker 1: across multiple nations. The need for standards was apparent from

110
00:06:44,680 --> 00:06:47,680
Speaker 1: the early days of trade, because merchants had to create

111
00:06:47,760 --> 00:06:50,880
Speaker 1: standards so that trade systems could actually work across different

112
00:06:50,880 --> 00:06:54,880
Speaker 1: currencies and regions, not to mention, create standards of measurements

113
00:06:54,960 --> 00:06:56,880
Speaker 1: so they could make sure they were talking about the

114
00:06:56,880 --> 00:07:00,000
Speaker 1: same amount of stuff they were selling from place to play.

115
00:07:00,560 --> 00:07:03,360
Speaker 1: If you're a if you're a spice merchant, you want

116
00:07:03,400 --> 00:07:06,479
Speaker 1: to make sure the people you're selling to understand the

117
00:07:06,560 --> 00:07:08,960
Speaker 1: quantities you're talking about. So you had to set up

118
00:07:08,960 --> 00:07:12,400
Speaker 1: these standards that people would generally agree to in order

119
00:07:12,440 --> 00:07:14,920
Speaker 1: to actually make trade work. It was necessary for that

120
00:07:15,000 --> 00:07:17,560
Speaker 1: sort of thing. Well, the same thing is true in

121
00:07:17,720 --> 00:07:20,760
Speaker 1: technology in general, not just with units of measurement things

122
00:07:20,760 --> 00:07:24,720
Speaker 1: that are more kind of ultimately tangible, but with general

123
00:07:24,760 --> 00:07:27,360
Speaker 1: concepts where you're gonna have lots of different people from

124
00:07:27,400 --> 00:07:30,440
Speaker 1: all over the world working within those sort of concepts,

125
00:07:30,680 --> 00:07:33,760
Speaker 1: and you want there to be interoperability between all of

126
00:07:33,760 --> 00:07:37,160
Speaker 1: those people. You have to create these standards so that

127
00:07:37,600 --> 00:07:40,120
Speaker 1: everyone is kind of working from the same basic set

128
00:07:40,120 --> 00:07:42,920
Speaker 1: of rules, and by working from the same basic, basic

129
00:07:42,960 --> 00:07:50,040
Speaker 1: set of rules. You you reduce the possibility of incompatibilities.

130
00:07:51,080 --> 00:07:55,160
Speaker 1: There will always be incompatibilities just because technology doesn't always

131
00:07:55,160 --> 00:07:57,160
Speaker 1: work the way we intended it to. But you can

132
00:07:57,200 --> 00:07:59,560
Speaker 1: at least remove some of those barriers early on in

133
00:07:59,600 --> 00:08:02,640
Speaker 1: the des line process by agreeing upon a basic set

134
00:08:02,640 --> 00:08:05,880
Speaker 1: of rules from the start. That's the whole purpose of

135
00:08:06,040 --> 00:08:12,360
Speaker 1: organizations like ISO SO. This extends to telecommunication and networking layers.

136
00:08:13,000 --> 00:08:16,720
Speaker 1: As ISSO states on its web page, international standards make

137
00:08:17,000 --> 00:08:22,080
Speaker 1: things work. They give world class specifications for products, services,

138
00:08:22,120 --> 00:08:26,800
Speaker 1: and systems to ensure quality, safety, and efficiency. Now, i

139
00:08:26,920 --> 00:08:29,400
Speaker 1: SO got its start back in nineteen forty six during

140
00:08:29,400 --> 00:08:32,920
Speaker 1: a meeting of the Institute of Civil Engineers in London, England,

141
00:08:32,960 --> 00:08:35,840
Speaker 1: and there were representatives from twenty five different countries that

142
00:08:35,880 --> 00:08:39,200
Speaker 1: attended that meeting, and they concluded that they needed an

143
00:08:39,240 --> 00:08:44,520
Speaker 1: official but independent organization to help coordinate and unify industrial standards.

144
00:08:44,520 --> 00:08:48,960
Speaker 1: I would become an official entity on February twenty third,

145
00:08:49,080 --> 00:08:52,719
Speaker 1: nineteen forty seven, and according to ISO, the organization has

146
00:08:52,720 --> 00:08:58,280
Speaker 1: published nearly twenty two thousand international standards since it was founded.

147
00:08:58,840 --> 00:09:01,720
Speaker 1: Oh and uh ice SO is not an acronym. It

148
00:09:01,840 --> 00:09:04,319
Speaker 1: is not I s O. It is ISO. It is

149
00:09:04,360 --> 00:09:08,559
Speaker 1: all capitalized, but still it's ISO. And it's because if

150
00:09:08,559 --> 00:09:11,040
Speaker 1: you translate the name of the organization into the different

151
00:09:11,120 --> 00:09:14,559
Speaker 1: languages of all the different countries that have a an

152
00:09:14,679 --> 00:09:18,000
Speaker 1: organization that's a member of ISO, you don't end up

153
00:09:18,080 --> 00:09:21,960
Speaker 1: with words that start with I, S and O with

154
00:09:22,080 --> 00:09:25,800
Speaker 1: every translation. Right. That's just the English version. So the

155
00:09:25,800 --> 00:09:30,160
Speaker 1: English version is International Standards Organization. But other languages have

156
00:09:30,360 --> 00:09:33,600
Speaker 1: it in different orders or even different words. So you

157
00:09:33,640 --> 00:09:36,600
Speaker 1: can't just call it an acronym because not every country

158
00:09:37,559 --> 00:09:42,160
Speaker 1: uses the same the same language, right, So they decided

159
00:09:42,200 --> 00:09:44,480
Speaker 1: instead they would take their name from a Greek word

160
00:09:44,559 --> 00:09:49,559
Speaker 1: ISOs i S O s which means equal so is

161
00:09:49,800 --> 00:09:52,400
Speaker 1: so is always is so no matter what language you

162
00:09:52,440 --> 00:09:55,719
Speaker 1: are speaking. As for the O S I model, now,

163
00:09:55,760 --> 00:09:58,720
Speaker 1: that actually emerged from a couple of different projects that

164
00:09:58,800 --> 00:10:02,840
Speaker 1: we're trying to ablish a framework for network systems. This

165
00:10:02,880 --> 00:10:06,160
Speaker 1: would be in the seventies when networks were really starting

166
00:10:06,200 --> 00:10:10,640
Speaker 1: to become a possibility. You may remember that ARPA net

167
00:10:10,720 --> 00:10:13,960
Speaker 1: had been in the development stages in the sixties and seventies,

168
00:10:14,400 --> 00:10:17,480
Speaker 1: and that was a precursor to the Internet. It was

169
00:10:17,520 --> 00:10:22,320
Speaker 1: also those early early days of networking different devices together

170
00:10:22,440 --> 00:10:25,120
Speaker 1: so that they could communicate directly to one another instead

171
00:10:25,120 --> 00:10:29,439
Speaker 1: of having to work on one machine, save your work

172
00:10:29,559 --> 00:10:33,599
Speaker 1: on some form of physical media, maybe it's a magnetic

173
00:10:33,679 --> 00:10:36,640
Speaker 1: disc or real to real tape or whatever, taking that

174
00:10:36,760 --> 00:10:40,160
Speaker 1: physical media over to another and I guess I should

175
00:10:40,200 --> 00:10:44,000
Speaker 1: say medium over to another device and then loading it

176
00:10:44,080 --> 00:10:46,040
Speaker 1: up there. Instead of doing that, you can have them

177
00:10:46,120 --> 00:10:49,200
Speaker 1: communicate directly to one another using a network solution. But

178
00:10:49,240 --> 00:10:54,040
Speaker 1: you had to establish those standards, particularly since there were

179
00:10:54,080 --> 00:10:57,600
Speaker 1: lots of different computers that were being produced and lots

180
00:10:57,600 --> 00:11:00,160
Speaker 1: of other devices that you also would want to net

181
00:11:00,200 --> 00:11:03,840
Speaker 1: computers too, and they didn't all use the same sort

182
00:11:03,880 --> 00:11:07,240
Speaker 1: of operating systems, they didn't communicate in the same way,

183
00:11:07,800 --> 00:11:10,680
Speaker 1: So you had to create a set of standards that

184
00:11:10,720 --> 00:11:16,320
Speaker 1: would work across multiple instances of networked machines so that

185
00:11:16,400 --> 00:11:21,640
Speaker 1: you didn't just end up with different specific network protocols

186
00:11:21,800 --> 00:11:25,439
Speaker 1: for very specific instances. Let's say that one place has

187
00:11:25,559 --> 00:11:28,719
Speaker 1: all the same sort of mainframe style computers, so they

188
00:11:28,760 --> 00:11:31,800
Speaker 1: design a network that only works with those. That's not

189
00:11:31,840 --> 00:11:34,880
Speaker 1: any use to somebody who's trying to create a network

190
00:11:34,960 --> 00:11:37,400
Speaker 1: for a totally different type of machines. So they wanted

191
00:11:37,400 --> 00:11:39,880
Speaker 1: to create this basic set standards. In the seventies, you

192
00:11:39,880 --> 00:11:42,800
Speaker 1: had two different groups doing that, and eventually those two

193
00:11:42,840 --> 00:11:46,240
Speaker 1: groups they got their work kind of merged together, and

194
00:11:46,360 --> 00:11:49,880
Speaker 1: in nineteen eighty three they published this, or at least

195
00:11:49,880 --> 00:11:53,320
Speaker 1: they they submitted this to ISO. UH. It was called

196
00:11:53,360 --> 00:11:57,599
Speaker 1: the Basic Reference Model for Open Systems Interconnection, and i

197
00:11:57,720 --> 00:11:59,920
Speaker 1: SO would publish that model the following year, in nineteen

198
00:12:00,000 --> 00:12:04,280
Speaker 1: eight four. This would be the UH the ISO publication

199
00:12:04,360 --> 00:12:09,280
Speaker 1: number seven thousand. So next time you're at pub trivia

200
00:12:09,559 --> 00:12:13,200
Speaker 1: and someone says, what's the ISO publication number of the

201
00:12:13,200 --> 00:12:16,400
Speaker 1: os I model, you can just pipe up seven and

202
00:12:16,480 --> 00:12:21,319
Speaker 1: you will win great acclaim. I don't know why you're

203
00:12:21,360 --> 00:12:25,600
Speaker 1: going to I T professional pub trivia, but that's you know,

204
00:12:25,840 --> 00:12:29,840
Speaker 1: I'm not judging. So I SO created the O s

205
00:12:29,880 --> 00:12:32,920
Speaker 1: I seven layers model. This again was to create a

206
00:12:32,960 --> 00:12:36,079
Speaker 1: sort of common lexicon across the world for the purposes

207
00:12:36,120 --> 00:12:40,960
Speaker 1: of discussing telecommunication systems. And let's take a high level

208
00:12:40,960 --> 00:12:46,359
Speaker 1: look at what this means. Those seven layers to this model, AH,

209
00:12:46,800 --> 00:12:51,040
Speaker 1: they represent different tasks sort of or or different layers

210
00:12:51,160 --> 00:12:55,000
Speaker 1: of responsibility within a communications network. The bottom most layer,

211
00:12:55,200 --> 00:12:59,080
Speaker 1: layer one is what we call the physical layer, the

212
00:12:59,120 --> 00:13:03,320
Speaker 1: top layer. Lay year seven is the application layer, and

213
00:13:03,480 --> 00:13:05,480
Speaker 1: if you'd like to visualize this in a practical way,

214
00:13:05,600 --> 00:13:08,520
Speaker 1: layer seven is the one that the end user comes

215
00:13:08,559 --> 00:13:12,840
Speaker 1: into contact with. Layer seven is the part of an

216
00:13:12,840 --> 00:13:17,400
Speaker 1: application or program that that you can see. Now it's

217
00:13:17,440 --> 00:13:21,120
Speaker 1: not Layer seven is not an application in of itself,

218
00:13:21,160 --> 00:13:25,880
Speaker 1: although some applications can exist entirely in layer seven. Layer

219
00:13:25,920 --> 00:13:30,280
Speaker 1: seven is the group of services within a communications network

220
00:13:31,040 --> 00:13:33,800
Speaker 1: that interact directly with whatever is going on with the

221
00:13:33,840 --> 00:13:38,839
Speaker 1: application and send that further down the stack. So while

222
00:13:38,880 --> 00:13:42,880
Speaker 1: a web browser is not in itself a layer seven,

223
00:13:43,760 --> 00:13:49,760
Speaker 1: it uses elements that do tie into layer seven. In

224
00:13:49,760 --> 00:13:52,760
Speaker 1: other words, uh, it's it's kind of like the the

225
00:13:54,200 --> 00:13:58,920
Speaker 1: just under the surface layer for whatever application you have

226
00:13:58,960 --> 00:14:03,760
Speaker 1: opened that has this network communication aspect to it, whether

227
00:14:03,840 --> 00:14:07,320
Speaker 1: that's with a phone or a computer or a printer,

228
00:14:07,559 --> 00:14:11,120
Speaker 1: really any device that's connected to a network. This is

229
00:14:11,160 --> 00:14:13,720
Speaker 1: the one that's closest to you. So it's the one

230
00:14:13,800 --> 00:14:16,360
Speaker 1: that's easiest for us to kind of understand because it's

231
00:14:16,360 --> 00:14:19,840
Speaker 1: the stuff that we interact with. You interact with this interface,

232
00:14:20,000 --> 00:14:23,680
Speaker 1: you send commands. Those commands get pushed down the stack

233
00:14:24,000 --> 00:14:26,440
Speaker 1: and depending it depends on what the command is about

234
00:14:26,480 --> 00:14:29,480
Speaker 1: where that ends up going on the other end of

235
00:14:29,480 --> 00:14:31,840
Speaker 1: the model, and we'll go through all the layers in

236
00:14:31,840 --> 00:14:33,920
Speaker 1: this episode, but right now I'm just looking at the top.

237
00:14:33,960 --> 00:14:36,120
Speaker 1: In the very bottom on the other end, the bottom

238
00:14:36,160 --> 00:14:40,200
Speaker 1: of the stack is layer one. That's the physical layer

239
00:14:40,240 --> 00:14:44,120
Speaker 1: of the networking process. This is the basic bit stream.

240
00:14:44,200 --> 00:14:46,840
Speaker 1: This is the zeros and ones that are being carried

241
00:14:47,080 --> 00:14:51,320
Speaker 1: by some means. You could even argue that it's not

242
00:14:51,360 --> 00:14:54,840
Speaker 1: even zeros and ones, it's the stuff that represents those

243
00:14:54,920 --> 00:14:58,800
Speaker 1: zeros and ones. It's the actual electrical impulses or rays

244
00:14:58,840 --> 00:15:03,800
Speaker 1: of light or radio signals that are carrying information. So

245
00:15:03,880 --> 00:15:08,720
Speaker 1: this is the conveyance of data. So that depends upon

246
00:15:08,840 --> 00:15:14,080
Speaker 1: actual physical properties like physical components like cables or Wi

247
00:15:14,240 --> 00:15:18,200
Speaker 1: Fi cards or things of that nature. That is why

248
00:15:18,240 --> 00:15:21,240
Speaker 1: it's called the physical layer. It is completely dependent upon that.

249
00:15:21,360 --> 00:15:25,120
Speaker 1: It does not care about protocols. None of that stuff matters.

250
00:15:25,160 --> 00:15:32,000
Speaker 1: This is just carrying the signal. Uh So, between layers seven,

251
00:15:32,440 --> 00:15:35,000
Speaker 1: the one that we interact with directly, and layer one,

252
00:15:35,120 --> 00:15:38,920
Speaker 1: that physical layer, are all the intervening levels that handle

253
00:15:39,000 --> 00:15:42,520
Speaker 1: protocols for network communication. Again, this these are not physical,

254
00:15:42,720 --> 00:15:45,680
Speaker 1: literal layers, but rather a way to divide up those

255
00:15:45,720 --> 00:15:49,200
Speaker 1: protocols for the purposes of understanding which layers hand tasks

256
00:15:49,240 --> 00:15:53,360
Speaker 1: off to other layers or accept tasks from other layers.

257
00:15:53,920 --> 00:15:56,440
Speaker 1: So I'm gonna explain this conceptual model with an analogy.

258
00:15:56,760 --> 00:15:58,920
Speaker 1: So we're gonna get even more abstract because that's what

259
00:15:58,960 --> 00:16:00,880
Speaker 1: I do, and you can't stop me. It's my show.

260
00:16:01,440 --> 00:16:03,680
Speaker 1: The O S I seven layer model is like a

261
00:16:03,680 --> 00:16:08,320
Speaker 1: metaphorical bucket brigade fighting a fire. So let's say that

262
00:16:08,440 --> 00:16:11,600
Speaker 1: layer one, that physical layer, that's the person in the

263
00:16:11,640 --> 00:16:14,800
Speaker 1: bucket brigade who is closest to the water spigot. Water

264
00:16:14,960 --> 00:16:18,800
Speaker 1: is pouring out of the water spigot. Now, the person

265
00:16:18,840 --> 00:16:23,240
Speaker 1: who's representing layer one can do a couple of different things.

266
00:16:23,240 --> 00:16:25,920
Speaker 1: They can fill up a bucket with water. They can

267
00:16:25,960 --> 00:16:29,080
Speaker 1: hand a full bucket of water over to the person

268
00:16:29,120 --> 00:16:32,280
Speaker 1: who is representing layer two, or they can accept an

269
00:16:32,280 --> 00:16:34,960
Speaker 1: empty bucket from layer two so that they can then

270
00:16:35,000 --> 00:16:37,560
Speaker 1: fill up the bucket of to make it a bucket

271
00:16:37,560 --> 00:16:41,200
Speaker 1: of water. Again, Layer two can really only do a

272
00:16:41,240 --> 00:16:44,040
Speaker 1: couple of things in this particular analogy. They can accept

273
00:16:44,080 --> 00:16:47,280
Speaker 1: an empty bucket from layer three, or they can accept

274
00:16:47,360 --> 00:16:50,760
Speaker 1: a full bucket from layer one and they pass it

275
00:16:50,840 --> 00:16:53,760
Speaker 1: on in continuing in the direction that it was traveling.

276
00:16:54,120 --> 00:16:55,880
Speaker 1: When you get all the way down to layer seven,

277
00:16:56,320 --> 00:16:59,480
Speaker 1: they can accept a full bucket of water from layer six,

278
00:17:00,160 --> 00:17:03,520
Speaker 1: can splash that water onto a fire, and they can

279
00:17:03,720 --> 00:17:08,359
Speaker 1: send a empty bucket down to layer six. That's kind

280
00:17:08,400 --> 00:17:11,000
Speaker 1: of what's going on here from a conceptual level with

281
00:17:11,160 --> 00:17:18,119
Speaker 1: network communication, it's instead of water communication tasks and different

282
00:17:18,200 --> 00:17:20,560
Speaker 1: layers are responsible for different parts of the task. So

283
00:17:20,600 --> 00:17:22,600
Speaker 1: it gets a little more complicated because it's not just

284
00:17:23,240 --> 00:17:26,280
Speaker 1: accept something and pass it on. That's it's not as

285
00:17:26,280 --> 00:17:28,040
Speaker 1: simple as that. There's a little bit more to it.

286
00:17:28,080 --> 00:17:29,960
Speaker 1: But I wanted to start big so you can kind

287
00:17:29,960 --> 00:17:34,240
Speaker 1: of understand that these layers are all dependent upon one another.

288
00:17:36,040 --> 00:17:40,119
Speaker 1: So I hope that analogy makes some sense to you.

289
00:17:40,240 --> 00:17:42,520
Speaker 1: I really liked it because while I was trying to

290
00:17:42,600 --> 00:17:45,119
Speaker 1: kind of digest the OSI model, that's kind of how

291
00:17:45,160 --> 00:17:48,639
Speaker 1: I imagined it was this process of passing down a

292
00:17:48,760 --> 00:17:52,639
Speaker 1: task so that it goes down the chain until it

293
00:17:52,680 --> 00:17:54,399
Speaker 1: hits where it needs to go, comes back up the

294
00:17:54,480 --> 00:17:57,720
Speaker 1: chain with whatever the response is. Now, the reason the

295
00:17:57,800 --> 00:18:00,240
Speaker 1: whole model is important. Why are we even talking about

296
00:18:00,240 --> 00:18:02,680
Speaker 1: the OSI model in the first place, beyond just giving

297
00:18:02,760 --> 00:18:04,879
Speaker 1: us an idea of what's going on behind the scenes

298
00:18:04,960 --> 00:18:09,880
Speaker 1: when you are using devices on a networked system. It's

299
00:18:09,920 --> 00:18:13,160
Speaker 1: because it provides a guide for developers. For one thing,

300
00:18:13,359 --> 00:18:16,359
Speaker 1: if you're developing programs or applications that are meant to

301
00:18:16,400 --> 00:18:19,600
Speaker 1: be networked, it is really good to have an understanding

302
00:18:19,840 --> 00:18:23,080
Speaker 1: of the OSI model so that you can focus on

303
00:18:23,160 --> 00:18:27,359
Speaker 1: the proper way to implement your your program. Uh. And

304
00:18:27,400 --> 00:18:30,280
Speaker 1: it's also important for you to adhere to the standard

305
00:18:30,359 --> 00:18:33,400
Speaker 1: that's been established. That's what standards are for, after all.

306
00:18:33,640 --> 00:18:35,680
Speaker 1: So you might even wonder why is this even important,

307
00:18:35,720 --> 00:18:38,040
Speaker 1: why are we even talking about OSI models? Well, I

308
00:18:38,040 --> 00:18:40,120
Speaker 1: mean beyond just giving us an idea of what's going

309
00:18:40,160 --> 00:18:43,159
Speaker 1: on behind the scenes of devices that are running on

310
00:18:43,160 --> 00:18:46,520
Speaker 1: a network and how that communication is supposed to work

311
00:18:46,560 --> 00:18:50,280
Speaker 1: from a conceptual level, it provides a guide for developers

312
00:18:50,280 --> 00:18:53,439
Speaker 1: who are creating applications and programs that will run on

313
00:18:53,560 --> 00:18:57,879
Speaker 1: networked devices. It's really important that their processes adhere to

314
00:18:57,920 --> 00:19:00,840
Speaker 1: the standard. I mean, that's why we of standards. It's

315
00:19:00,880 --> 00:19:04,680
Speaker 1: to make sure that things are falling in line so

316
00:19:04,720 --> 00:19:07,480
Speaker 1: that the everything is as smooth as it possibly can be,

317
00:19:07,560 --> 00:19:11,720
Speaker 1: especially when you get into interoperability where you have programs

318
00:19:11,760 --> 00:19:15,680
Speaker 1: operating with other programs. If you have that happening, they

319
00:19:15,720 --> 00:19:18,600
Speaker 1: need to agree upon the same basic set of rules.

320
00:19:19,560 --> 00:19:23,240
Speaker 1: Otherwise it's like getting two people together who speak completely

321
00:19:23,280 --> 00:19:27,640
Speaker 1: different languages that have no basis, like there's no shared

322
00:19:28,119 --> 00:19:32,200
Speaker 1: origin for the two languages. They both arose completely independently,

323
00:19:32,480 --> 00:19:35,960
Speaker 1: and then try to have them have a conversation without

324
00:19:36,160 --> 00:19:38,719
Speaker 1: using gestures or anything else to kind of get their

325
00:19:38,760 --> 00:19:43,320
Speaker 1: meeting across. It's it's practically impossible. So this is very

326
00:19:43,359 --> 00:19:46,800
Speaker 1: important for programmers in order to make sure that their

327
00:19:47,320 --> 00:19:53,719
Speaker 1: approach will be interoperable for other types of processes and programs. Uh.

328
00:19:54,400 --> 00:19:57,080
Speaker 1: This could be as simple as making sure that your

329
00:19:57,160 --> 00:19:59,639
Speaker 1: program is not going to make an entire framework on

330
00:19:59,720 --> 00:20:02,560
Speaker 1: stay will and cause potential crashes or other issues, to

331
00:20:02,680 --> 00:20:05,600
Speaker 1: something more complicated such as apps being able to share

332
00:20:05,600 --> 00:20:09,119
Speaker 1: the same data across each other or access each other's

333
00:20:09,119 --> 00:20:11,720
Speaker 1: functionality in some way. And it's only because we have

334
00:20:11,760 --> 00:20:13,760
Speaker 1: these standards in place at such an approach is really

335
00:20:13,800 --> 00:20:16,840
Speaker 1: possible without having different teams worked very tightly with one

336
00:20:16,840 --> 00:20:19,600
Speaker 1: another from the first place. It's also really useful if

337
00:20:19,600 --> 00:20:22,520
Speaker 1: you're a network specialist like an I T network guy

338
00:20:23,000 --> 00:20:26,560
Speaker 1: or a lady because you've got a problem happening in

339
00:20:26,600 --> 00:20:28,480
Speaker 1: a network that you manage, you want to be able

340
00:20:28,520 --> 00:20:31,560
Speaker 1: to identify where that problem is and how you would

341
00:20:31,560 --> 00:20:34,800
Speaker 1: go about solving it, and being able to figure out

342
00:20:34,840 --> 00:20:38,359
Speaker 1: conceptually where in the OSI model that problem may be arising,

343
00:20:38,400 --> 00:20:40,959
Speaker 1: tells you what approach you may need to take in

344
00:20:41,080 --> 00:20:45,400
Speaker 1: order to fix the problem. I've heard that problems fall

345
00:20:45,440 --> 00:20:48,360
Speaker 1: on the physical layer, which essentially means that someone has

346
00:20:48,359 --> 00:20:50,920
Speaker 1: not plugged something in. It sounds like an I T.

347
00:20:51,080 --> 00:20:53,920
Speaker 1: Crowd kind of joke, but apparently it's absolutely true that

348
00:20:54,000 --> 00:20:56,760
Speaker 1: you know, there's folks who just there's a cable that's

349
00:20:56,760 --> 00:20:59,399
Speaker 1: not fully plugged into a port, or someone forgot to

350
00:20:59,400 --> 00:21:02,240
Speaker 1: turn a switch John or something, and a lot of

351
00:21:02,240 --> 00:21:04,199
Speaker 1: the problems do stem from that. And then once you

352
00:21:04,240 --> 00:21:06,640
Speaker 1: get beyond the physical layer, things get real tricky because

353
00:21:06,640 --> 00:21:09,439
Speaker 1: you got to figure out where is the breakdown happening

354
00:21:09,440 --> 00:21:11,720
Speaker 1: and what can you potentially do about it. So it

355
00:21:11,760 --> 00:21:14,840
Speaker 1: does have a practical application outside of of just a

356
00:21:14,880 --> 00:21:17,879
Speaker 1: general information The model is also obviously used as a

357
00:21:17,880 --> 00:21:22,800
Speaker 1: teaching tool to explain computer network architecture and communication protocols,

358
00:21:23,200 --> 00:21:25,560
Speaker 1: and it gives computer science students a foundation and the

359
00:21:25,640 --> 00:21:29,240
Speaker 1: logic they'll need to understand to work within computer network architecture.

360
00:21:29,640 --> 00:21:32,600
Speaker 1: So that's the overview. Now we're gonna take a quick break,

361
00:21:32,960 --> 00:21:34,919
Speaker 1: and then when we come back, we're gonna start waiting

362
00:21:34,920 --> 00:21:38,200
Speaker 1: into what all these layers actually mean. So let's take

363
00:21:38,320 --> 00:21:47,639
Speaker 1: a quick break to thank our sponsor. All right, let's

364
00:21:47,720 --> 00:21:49,639
Speaker 1: look at these layers. Now, we're gonna start at that

365
00:21:49,720 --> 00:21:52,320
Speaker 1: highest layer and work downwards since I think that makes

366
00:21:52,359 --> 00:21:55,080
Speaker 1: the most sense for the average person. Here's a quick overview,

367
00:21:55,119 --> 00:21:58,159
Speaker 1: and then we're gonna dive further into detail. All right.

368
00:21:58,240 --> 00:22:00,600
Speaker 1: Layer seven is the application layer. That's where the end

369
00:22:00,680 --> 00:22:04,040
Speaker 1: user applications live, or at least where they touch. That's

370
00:22:04,400 --> 00:22:08,200
Speaker 1: where they make contact with this OSI model. This would

371
00:22:08,200 --> 00:22:10,800
Speaker 1: be the stuff that we interact with, like whether you're

372
00:22:10,800 --> 00:22:14,439
Speaker 1: playing Pokemon, or you're using a web browser to surf

373
00:22:14,440 --> 00:22:16,880
Speaker 1: the web, or you're checking a fitness app or anything

374
00:22:16,920 --> 00:22:20,080
Speaker 1: that's along those lines where it's tapping into this network.

375
00:22:20,680 --> 00:22:24,240
Speaker 1: You are interfacing with something that is touching on this layer.

376
00:22:24,640 --> 00:22:26,520
Speaker 1: There's a lot more going down below the surface, but

377
00:22:27,000 --> 00:22:29,800
Speaker 1: we'll jump into that in a minute. Next is layer six.

378
00:22:30,240 --> 00:22:34,879
Speaker 1: That's the presentation layer. That layer handles syntax processing. Don't worry.

379
00:22:34,920 --> 00:22:36,840
Speaker 1: I'll explain that in a little bit. It's sort of

380
00:22:36,880 --> 00:22:40,240
Speaker 1: like a translator in many ways, so hold on to

381
00:22:40,359 --> 00:22:43,879
Speaker 1: that idea. Layer five is the session layer. This layer

382
00:22:43,920 --> 00:22:48,000
Speaker 1: manages the flow of events that establish and terminate network connections,

383
00:22:48,320 --> 00:22:53,720
Speaker 1: communication channels, if you will, between applications or devices. Layers

384
00:22:53,720 --> 00:22:56,359
Speaker 1: five through seven, so the ones we just talked about,

385
00:22:56,520 --> 00:23:02,159
Speaker 1: are considered application level data layers. Everything below those layers

386
00:23:02,280 --> 00:23:06,320
Speaker 1: gets into more fundamental aspects of moving data around, where

387
00:23:06,359 --> 00:23:09,199
Speaker 1: it's not so much concerned with it being identified as

388
00:23:09,200 --> 00:23:14,000
Speaker 1: an application. It's more basic than that. It reaches progressively

389
00:23:14,040 --> 00:23:16,720
Speaker 1: more abstract concepts and moving further away from anything we

390
00:23:16,760 --> 00:23:20,800
Speaker 1: would think of as an application. Level four is the

391
00:23:20,840 --> 00:23:25,560
Speaker 1: transport layer that provides transfer of data between end systems

392
00:23:25,560 --> 00:23:28,200
Speaker 1: and is responsible for end to end recovery. Again, we'll

393
00:23:28,359 --> 00:23:30,680
Speaker 1: go into this in more detail in a minute. Level

394
00:23:30,760 --> 00:23:33,600
Speaker 1: three is the network layer that's the domain of things

395
00:23:33,600 --> 00:23:37,520
Speaker 1: like switches and routers. Level two is the data link layer,

396
00:23:37,800 --> 00:23:42,720
Speaker 1: in which all information we've been talking about the packets

397
00:23:42,920 --> 00:23:47,440
Speaker 1: of information getting coded into bits. This layer technically as

398
00:23:47,440 --> 00:23:51,439
Speaker 1: two sub layers. There's the Media Access control or MAC layer.

399
00:23:51,520 --> 00:23:54,040
Speaker 1: If you've heard of MAC addresses, that's what this refers to.

400
00:23:54,600 --> 00:23:58,679
Speaker 1: And there's the logical Link Control or l C layers,

401
00:23:58,680 --> 00:24:00,840
Speaker 1: so it's not a limited liability company. It is the

402
00:24:00,880 --> 00:24:04,400
Speaker 1: logical link control. More on all of that again just

403
00:24:04,440 --> 00:24:06,600
Speaker 1: a minute. And then finally we get to layer one,

404
00:24:06,680 --> 00:24:09,399
Speaker 1: that physical layer I mentioned earlier. That is the bitstream

405
00:24:09,440 --> 00:24:13,200
Speaker 1: conveyance layer. So all that sounds really technical, but we'll

406
00:24:13,240 --> 00:24:15,879
Speaker 1: break it down layer by layer, and we'll start with

407
00:24:16,000 --> 00:24:19,840
Speaker 1: layer seven, that application layer. It identifies the protocols and

408
00:24:20,040 --> 00:24:23,840
Speaker 1: interface that hosts in a communications network have that the

409
00:24:23,920 --> 00:24:27,240
Speaker 1: end user uses. A host, by the way, is any

410
00:24:27,280 --> 00:24:29,960
Speaker 1: network device. So it could be a computer, it could

411
00:24:29,960 --> 00:24:33,040
Speaker 1: be a smartphone, it could be printer, it could be

412
00:24:33,080 --> 00:24:39,920
Speaker 1: really any networked device that is connected to a computer network. Uh. Really,

413
00:24:39,960 --> 00:24:43,359
Speaker 1: it's anything. It's not just servers. You might think a

414
00:24:43,400 --> 00:24:45,639
Speaker 1: host has to be a server because the name host

415
00:24:45,680 --> 00:24:48,919
Speaker 1: and server seem really related. Um, a server is a

416
00:24:48,960 --> 00:24:52,720
Speaker 1: device that accepts network connections from other devices, and those

417
00:24:52,760 --> 00:24:56,040
Speaker 1: other devices we call clients. So if you use a

418
00:24:56,040 --> 00:25:01,000
Speaker 1: web browser to connect to a web page, the computer

419
00:25:01,200 --> 00:25:03,840
Speaker 1: that has that web page saved on it, because that

420
00:25:03,880 --> 00:25:08,000
Speaker 1: web web page actually exists somewhere. The computer that has

421
00:25:08,040 --> 00:25:11,560
Speaker 1: that web page on it is a server. Your browser

422
00:25:11,840 --> 00:25:14,880
Speaker 1: is acting as the client. It is asking for that

423
00:25:14,880 --> 00:25:18,199
Speaker 1: that web page to be served to it. So that

424
00:25:18,359 --> 00:25:20,680
Speaker 1: is a case of a server. It is allowing the

425
00:25:20,880 --> 00:25:25,000
Speaker 1: web browser to access it. So all servers are hosts,

426
00:25:25,119 --> 00:25:29,160
Speaker 1: but not all hosts are servers. Host is a larger term.

427
00:25:29,200 --> 00:25:33,680
Speaker 1: It includes servers, but includes all the other devices connected

428
00:25:33,720 --> 00:25:35,520
Speaker 1: to the network as well, or at least all the

429
00:25:35,520 --> 00:25:39,520
Speaker 1: computer style devices. So this is the stuff we as

430
00:25:39,600 --> 00:25:43,000
Speaker 1: users encounter when we're working with an application or a program,

431
00:25:43,240 --> 00:25:47,320
Speaker 1: and as long as that program is accessing the network,

432
00:25:47,359 --> 00:25:50,120
Speaker 1: if it's a self contained program, it's kind of separate

433
00:25:50,119 --> 00:25:53,960
Speaker 1: from this OSI model. It's really considered concerned with network communications.

434
00:25:54,320 --> 00:25:56,400
Speaker 1: So let's take a real world example and talk about

435
00:25:56,400 --> 00:26:00,200
Speaker 1: web browsers. The application layer would be the interface ace

436
00:26:00,240 --> 00:26:03,320
Speaker 1: that we rely upon, uh or at least it would

437
00:26:03,320 --> 00:26:05,560
Speaker 1: be touching upon the interface we rely upon when we're

438
00:26:05,600 --> 00:26:08,320
Speaker 1: interacting with our web browser. These are the rules that

439
00:26:08,359 --> 00:26:11,800
Speaker 1: dictate how we can select links, how it instructs the

440
00:26:11,840 --> 00:26:15,119
Speaker 1: app on how to display information to the user in

441
00:26:15,200 --> 00:26:18,280
Speaker 1: response to commands. This is all front of the curtain

442
00:26:18,440 --> 00:26:21,000
Speaker 1: stuff as far as users are concerned. For the os

443
00:26:21,080 --> 00:26:24,600
Speaker 1: I model, this bit also includes aspects like user authentication

444
00:26:24,680 --> 00:26:28,920
Speaker 1: and quality of service. Everything on this layer is application specific,

445
00:26:29,720 --> 00:26:33,600
Speaker 1: so uh, very specific to whatever instance you're looking at.

446
00:26:33,680 --> 00:26:37,360
Speaker 1: It also provides the application services for email, file transfers

447
00:26:37,359 --> 00:26:41,639
Speaker 1: and other network software services. So some services that exist

448
00:26:41,640 --> 00:26:45,280
Speaker 1: at this level are FTP, which is filed Transfer protocol

449
00:26:45,640 --> 00:26:48,040
Speaker 1: and tell net. That's the service that allows you to

450
00:26:48,119 --> 00:26:50,800
Speaker 1: use your computer as if it were a terminal for

451
00:26:50,960 --> 00:26:54,560
Speaker 1: remote server. So, in other words, tell net lets you

452
00:26:54,640 --> 00:26:59,520
Speaker 1: log into a virtual terminal for another machine and execute

453
00:26:59,520 --> 00:27:02,560
Speaker 1: commands as if you were working on that computer directly.

454
00:27:02,680 --> 00:27:06,080
Speaker 1: So there's some computer that's out there in the wild,

455
00:27:06,640 --> 00:27:09,919
Speaker 1: you use tell neet to log into that computer, and

456
00:27:09,920 --> 00:27:13,639
Speaker 1: suddenly your computer, the one you're typing on, it's acting

457
00:27:13,680 --> 00:27:17,200
Speaker 1: as if it is directly connected, like it is part

458
00:27:17,520 --> 00:27:20,000
Speaker 1: of the machine that you are tapping into. When you

459
00:27:20,080 --> 00:27:24,000
Speaker 1: type a command in through your virtual terminal, it's executed

460
00:27:24,320 --> 00:27:27,480
Speaker 1: on the other machine, not on your computer. Telling that

461
00:27:27,880 --> 00:27:32,840
Speaker 1: is bi directional. It's an eight bit bite oriented communications specification,

462
00:27:33,240 --> 00:27:37,000
Speaker 1: and it exists at this layer seven that is the

463
00:27:37,040 --> 00:27:40,240
Speaker 1: domain of tell neet. Some other examples of stuff you'd

464
00:27:40,240 --> 00:27:42,359
Speaker 1: find in layer seven, apart from telling neet, an FTP

465
00:27:42,560 --> 00:27:47,160
Speaker 1: and web browsers are the HTTP protocol and Simple Network

466
00:27:47,240 --> 00:27:51,040
Speaker 1: Management Protocol or s n MP. That's a standard for

467
00:27:51,119 --> 00:27:54,119
Speaker 1: organizing information about devices on IP networks and also the

468
00:27:54,200 --> 00:27:58,280
Speaker 1: rules for modifying that data in order to change device behavior. Now,

469
00:27:58,320 --> 00:28:01,800
Speaker 1: one thing the layer is not is the application itself. Right,

470
00:28:01,960 --> 00:28:05,880
Speaker 1: Applications are separate from the OSI model. They touch on it,

471
00:28:06,160 --> 00:28:08,520
Speaker 1: but they are their own thing. So this is this

472
00:28:08,560 --> 00:28:11,520
Speaker 1: would really be the services that applications can make use

473
00:28:11,560 --> 00:28:16,840
Speaker 1: of that are universal for communications networks. So you can't

474
00:28:17,240 --> 00:28:20,720
Speaker 1: get to applications specific and layer seven because then you

475
00:28:20,720 --> 00:28:23,040
Speaker 1: you depart from the concept of standard. You have to

476
00:28:23,080 --> 00:28:27,159
Speaker 1: have a list of different services that layer seven handles

477
00:28:27,840 --> 00:28:31,320
Speaker 1: that applications can tap into. Right, So it'd be like

478
00:28:31,400 --> 00:28:35,600
Speaker 1: walking into a business that offers certain services. You can't

479
00:28:35,800 --> 00:28:39,600
Speaker 1: order anything off of that list. You can only accept

480
00:28:39,640 --> 00:28:42,320
Speaker 1: the ones that are on that list. Same sort of

481
00:28:42,320 --> 00:28:46,760
Speaker 1: thing for this os I model. H Anything that would

482
00:28:46,800 --> 00:28:49,760
Speaker 1: require the application to reference information on the network, or

483
00:28:49,840 --> 00:28:52,200
Speaker 1: send data to the network, or otherwise interact with the

484
00:28:52,240 --> 00:28:56,320
Speaker 1: network is part of this layer. Layer six. That presentation

485
00:28:56,400 --> 00:29:00,880
Speaker 1: layer handles format conversions and encryption and decrypt shin. So,

486
00:29:00,960 --> 00:29:02,719
Speaker 1: like I said earlier, This is sort of like a

487
00:29:02,760 --> 00:29:06,960
Speaker 1: translator between different forms of data, and it's usually part

488
00:29:07,040 --> 00:29:09,640
Speaker 1: of an operating system. So an example of a layer

489
00:29:09,720 --> 00:29:12,920
Speaker 1: six task is to take clear text that is sent

490
00:29:13,040 --> 00:29:16,800
Speaker 1: from an application and encrypt it before moving it further

491
00:29:17,000 --> 00:29:20,520
Speaker 1: down the layers, or doing the reverse of that and

492
00:29:20,600 --> 00:29:24,400
Speaker 1: taking encrypted information from further down the chain and translating

493
00:29:24,440 --> 00:29:27,200
Speaker 1: it into clear text for the use of the application

494
00:29:27,320 --> 00:29:31,520
Speaker 1: in the layer above. Because of this feature, the presentation

495
00:29:31,600 --> 00:29:35,840
Speaker 1: layer is sometimes referred to as the syntax layer. Syntax

496
00:29:35,920 --> 00:29:38,520
Speaker 1: refers to the set of rules for the arrangement of

497
00:29:38,600 --> 00:29:43,560
Speaker 1: words and phrases to create something of meaning. Syntax allows

498
00:29:43,560 --> 00:29:46,840
Speaker 1: for clear communication, whether in human languages or machine ones.

499
00:29:46,920 --> 00:29:50,520
Speaker 1: So if I tell you later today, I'm going to

500
00:29:50,560 --> 00:29:52,360
Speaker 1: go to the store so that i can buy some

501
00:29:52,400 --> 00:29:56,440
Speaker 1: salted caramel pringles because they taste like golden grams, you'll

502
00:29:56,520 --> 00:29:59,600
Speaker 1: understand what I'm saying. You might not understand why I'm

503
00:29:59,640 --> 00:30:01,760
Speaker 1: saying it, or why I would bother to do such

504
00:30:01,800 --> 00:30:03,360
Speaker 1: a thing. By the way, they really do taste like

505
00:30:03,400 --> 00:30:05,720
Speaker 1: golden grams, and it's not necessarily a good thing. But

506
00:30:05,800 --> 00:30:10,480
Speaker 1: let's say I've said that you would understand what I meant.

507
00:30:10,840 --> 00:30:13,400
Speaker 1: But let's say I rewarded that sentence. I'm using the

508
00:30:13,400 --> 00:30:15,960
Speaker 1: same words, but I've completely changed the order. So it's

509
00:30:15,960 --> 00:30:19,000
Speaker 1: now to the store so that i can buy because

510
00:30:19,080 --> 00:30:22,080
Speaker 1: they taste like golden grams some salted caramel pringles. I'm

511
00:30:22,120 --> 00:30:24,960
Speaker 1: going to go later today. You might have to take

512
00:30:25,000 --> 00:30:27,080
Speaker 1: some time to suss out what the heck I'm saying

513
00:30:27,120 --> 00:30:29,960
Speaker 1: because I'm not using the correct syntax. I'm not following

514
00:30:29,960 --> 00:30:34,160
Speaker 1: the rules of English language to communicate clearly. Syntax is

515
00:30:34,200 --> 00:30:36,120
Speaker 1: really important so that we can be understood. And for

516
00:30:36,200 --> 00:30:39,760
Speaker 1: machines it's extra important because we typically programmed them to

517
00:30:39,840 --> 00:30:44,200
Speaker 1: accept very specific formats and anything that departs from that

518
00:30:44,280 --> 00:30:49,840
Speaker 1: format is essentially nonsense to a machine, so syntax is

519
00:30:49,960 --> 00:30:53,360
Speaker 1: key now. Examples of concepts and protocols that belong in

520
00:30:53,440 --> 00:30:59,040
Speaker 1: layer six include encryption methods of encoding such as JPEG's impegs, MIDI,

521
00:30:59,160 --> 00:31:01,760
Speaker 1: or as key tag. All of that belongs in level six.

522
00:31:02,760 --> 00:31:06,360
Speaker 1: Moving on down to layer five, the session layer. This

523
00:31:06,560 --> 00:31:10,240
Speaker 1: encompasses all the ways that the system enables or terminates

524
00:31:10,280 --> 00:31:16,640
Speaker 1: connections between applications. At this layer, the network allows conversations, exchanges,

525
00:31:16,720 --> 00:31:20,080
Speaker 1: and other transmissions between applications to occur, and it's all

526
00:31:20,120 --> 00:31:23,960
Speaker 1: about session and connection coordination. Another way to think about

527
00:31:23,960 --> 00:31:27,280
Speaker 1: this is the layer is the one that allows one

528
00:31:27,400 --> 00:31:31,480
Speaker 1: machine to chat with another machine across the network. It

529
00:31:31,560 --> 00:31:34,960
Speaker 1: creates that communication channel, also known as a session, So

530
00:31:35,280 --> 00:31:37,880
Speaker 1: it creates the session between the two machines, It maintains

531
00:31:37,920 --> 00:31:41,760
Speaker 1: the channel, and it most importantly, you could argue, terminates

532
00:31:41,800 --> 00:31:44,240
Speaker 1: the channel once the session has ended, so you don't

533
00:31:44,280 --> 00:31:48,680
Speaker 1: have a continuation of data exchange once you have indicated

534
00:31:48,760 --> 00:31:52,680
Speaker 1: that that communication is over. Otherwise you would have a

535
00:31:52,680 --> 00:31:56,680
Speaker 1: situation where it's kind of like listening in on somebody

536
00:31:56,760 --> 00:31:59,080
Speaker 1: when they thought they hung up the phone, but they didn't.

537
00:31:59,480 --> 00:32:02,280
Speaker 1: It would be a end to that from a data standpoint.

538
00:32:02,560 --> 00:32:05,520
Speaker 1: So that concludes all the layers that are on the

539
00:32:05,560 --> 00:32:09,400
Speaker 1: application side, the application layers of the os I model.

540
00:32:09,600 --> 00:32:13,440
Speaker 1: It's all about moving that data around at the application level.

541
00:32:13,880 --> 00:32:17,200
Speaker 1: Below that are the layers where we descend into the

542
00:32:17,240 --> 00:32:20,080
Speaker 1: real guts of the OSI model. And before I do that,

543
00:32:20,320 --> 00:32:23,480
Speaker 1: I need to take a rest. I gotta regain some

544
00:32:23,560 --> 00:32:26,760
Speaker 1: spell slots because I burned a couple in that last section. Also,

545
00:32:26,760 --> 00:32:28,960
Speaker 1: I've been listening to The Adventure Zone a lot. It's

546
00:32:29,000 --> 00:32:31,920
Speaker 1: a show that if you haven't listened to it. You

547
00:32:31,920 --> 00:32:34,080
Speaker 1: should check it out. It's kind of neat, has nothing

548
00:32:34,160 --> 00:32:35,800
Speaker 1: to do with how stuff works. That's just a free

549
00:32:35,840 --> 00:32:38,760
Speaker 1: plug for the adventure zone. Let's take a quick break

550
00:32:39,400 --> 00:32:49,040
Speaker 1: and thank our sponsor. All right, we're down to layer four.

551
00:32:49,120 --> 00:32:51,800
Speaker 1: We've been digging down. We've hut the topmost layer in

552
00:32:51,840 --> 00:32:53,840
Speaker 1: the group of layers that are all about just moving

553
00:32:53,920 --> 00:32:56,720
Speaker 1: data around in general. That it's kind of more abstract

554
00:32:56,800 --> 00:33:00,640
Speaker 1: than the application level. Layer four is the transport layer.

555
00:33:00,720 --> 00:33:04,720
Speaker 1: This is the layer that handles packet ization of data

556
00:33:04,880 --> 00:33:07,600
Speaker 1: and the delivery of packets, as well as checking incoming

557
00:33:07,600 --> 00:33:11,960
Speaker 1: packets for errors when the packets arrive. Packets, packets, packets.

558
00:33:12,320 --> 00:33:14,320
Speaker 1: But wait, I hear you cry out, what the heck

559
00:33:14,360 --> 00:33:17,040
Speaker 1: is a packet? All right? So a packet is a

560
00:33:17,040 --> 00:33:20,120
Speaker 1: basic unit of communication across the network, and there are

561
00:33:20,160 --> 00:33:23,520
Speaker 1: lots of different kinds of packets. There are the kinds

562
00:33:23,560 --> 00:33:26,200
Speaker 1: that are most people I think are familiar with. If

563
00:33:26,240 --> 00:33:29,520
Speaker 1: they've heard the term packet, they're thinking of the um

564
00:33:29,680 --> 00:33:32,680
Speaker 1: Internet Protocol version of packets. But packets can take other

565
00:33:32,720 --> 00:33:38,520
Speaker 1: forms as well. It's really structures within which data can exist.

566
00:33:39,560 --> 00:33:42,160
Speaker 1: Think of it like an envelope. It's very similar to

567
00:33:42,240 --> 00:33:46,000
Speaker 1: that From a conceptual level, an envelope is something that

568
00:33:46,080 --> 00:33:48,680
Speaker 1: you put letters into, or pieces of paper into, and

569
00:33:48,720 --> 00:33:51,239
Speaker 1: then you can send that through the mail. That's kind

570
00:33:51,240 --> 00:33:54,760
Speaker 1: of what packets are, except there for data, like raw data,

571
00:33:54,880 --> 00:33:57,960
Speaker 1: or at least for information that you're going to send

572
00:33:58,000 --> 00:34:02,840
Speaker 1: across a network, not a sequal letter. But let's say

573
00:34:02,840 --> 00:34:06,000
Speaker 1: that you have an envelope you have you bought a

574
00:34:06,080 --> 00:34:10,240
Speaker 1: box of envelopes, and you discover that each envelope has

575
00:34:10,320 --> 00:34:14,240
Speaker 1: a certain capacity. It can hold ten pages of paper.

576
00:34:14,960 --> 00:34:17,839
Speaker 1: But no matter what, you cannot shove eleven or more

577
00:34:17,880 --> 00:34:20,279
Speaker 1: pages into a single envelope. You just can't. You can

578
00:34:20,320 --> 00:34:23,480
Speaker 1: only shove up to ten pages in. So if you

579
00:34:23,560 --> 00:34:25,680
Speaker 1: had a longer document than ten pages, you would need

580
00:34:25,719 --> 00:34:28,840
Speaker 1: to divide it up into smaller groups so as you

581
00:34:28,840 --> 00:34:31,600
Speaker 1: could fit it into several envelopes. So let's say you've

582
00:34:31,640 --> 00:34:36,160
Speaker 1: just completed a two page manuscript during Nano Rimo, that's

583
00:34:36,160 --> 00:34:40,280
Speaker 1: a national novel writing month, and you're going to send

584
00:34:40,600 --> 00:34:44,280
Speaker 1: your physical copy of this manuscript off to a friend

585
00:34:44,400 --> 00:34:47,000
Speaker 1: for proof reading. But your friend lives very far away.

586
00:34:47,480 --> 00:34:49,680
Speaker 1: You're not in a real rush, so you're just gonna

587
00:34:49,719 --> 00:34:51,440
Speaker 1: send it through post. You don't happen to have a

588
00:34:51,480 --> 00:34:54,560
Speaker 1: digital copy because you typed it out on an old typewriter.

589
00:34:54,760 --> 00:34:57,080
Speaker 1: It doesn't really matter. So all you have are these

590
00:34:57,080 --> 00:35:00,120
Speaker 1: normal envelopes that can hold ten pages each. How you

591
00:35:00,160 --> 00:35:03,319
Speaker 1: get your document to your distant friend. Well, if you're

592
00:35:03,360 --> 00:35:06,120
Speaker 1: a machine on a network system, you would divide up

593
00:35:06,160 --> 00:35:09,840
Speaker 1: the job into manageable chunks and pack each chunk of

594
00:35:09,920 --> 00:35:14,360
Speaker 1: information into its own packet. So for our real world example,

595
00:35:14,640 --> 00:35:17,600
Speaker 1: you would have to divide your two page manuscript into

596
00:35:17,680 --> 00:35:23,160
Speaker 1: twenty ten page chunks and put each ten pages into

597
00:35:23,200 --> 00:35:26,719
Speaker 1: a different envelope. Now you would realize, because you were

598
00:35:26,719 --> 00:35:29,480
Speaker 1: a bit of a doof you sealed all the envelopes,

599
00:35:29,960 --> 00:35:33,839
Speaker 1: but you forgot to include page numbers on the individual pages. Well,

600
00:35:33,880 --> 00:35:36,319
Speaker 1: fortunately you still have all the envelopes in the right order,

601
00:35:36,840 --> 00:35:40,720
Speaker 1: So you include information on the envelope itself to indicate

602
00:35:40,760 --> 00:35:45,439
Speaker 1: to the recipient where those pages fit within the entire manuscript.

603
00:35:45,640 --> 00:35:49,080
Speaker 1: So the first envelope says pages one through ten, for example,

604
00:35:49,360 --> 00:35:53,480
Speaker 1: and envelope two says pages eleven through twenty. You dump

605
00:35:53,560 --> 00:35:57,680
Speaker 1: all twenty envelopes in the mail and the postal service

606
00:35:57,719 --> 00:36:00,400
Speaker 1: picks them up. Now it's a busy time at the

607
00:36:00,400 --> 00:36:03,319
Speaker 1: post office, and the destination for these envelopes is quite

608
00:36:03,360 --> 00:36:06,160
Speaker 1: a far way away, and the various envelopes get a

609
00:36:06,160 --> 00:36:08,799
Speaker 1: little divided up. They get put into different bags, and

610
00:36:08,960 --> 00:36:12,160
Speaker 1: they get distributed to different trucks and different planes. As

611
00:36:12,160 --> 00:36:14,200
Speaker 1: they travel to their destination. They're all going to the

612
00:36:14,239 --> 00:36:17,319
Speaker 1: same place, they're each taking a slightly different pathway there,

613
00:36:17,600 --> 00:36:19,600
Speaker 1: your friends starts to get the envelopes in the mail

614
00:36:19,760 --> 00:36:22,080
Speaker 1: and is able to put the pages in order because

615
00:36:22,120 --> 00:36:26,480
Speaker 1: you included information on those envelopes themselves, And eventually your

616
00:36:26,480 --> 00:36:29,279
Speaker 1: friend has the whole manuscript. Well, that's sort of how

617
00:36:29,360 --> 00:36:33,160
Speaker 1: data transmission across a network happens, except there are a

618
00:36:33,200 --> 00:36:37,520
Speaker 1: few extra considerations. One is that devices will typically send

619
00:36:37,560 --> 00:36:41,360
Speaker 1: more than one of each packet. Sometimes packets will encounter

620
00:36:41,400 --> 00:36:44,160
Speaker 1: problems as they travel across the network. Maybe a node

621
00:36:44,360 --> 00:36:47,880
Speaker 1: in the network goes offline without warning, or something else happens.

622
00:36:47,880 --> 00:36:51,760
Speaker 1: Maybe there's some traffic congestion at that section of the network.

623
00:36:52,280 --> 00:36:55,200
Speaker 1: So if you send multiple copies of each packet, there's

624
00:36:55,200 --> 00:36:57,000
Speaker 1: a better chance that the whole thing will get to

625
00:36:57,000 --> 00:36:59,680
Speaker 1: the destination. Even if you don't send multiple copies, what

626
00:36:59,760 --> 00:37:03,480
Speaker 1: will happen is there will be an acknowledgement on the

627
00:37:03,480 --> 00:37:07,200
Speaker 1: recipient side of receiving a packet, and if there's a

628
00:37:07,200 --> 00:37:10,960
Speaker 1: packet missing, that message gets sent across and then the

629
00:37:11,160 --> 00:37:15,080
Speaker 1: sender can send that specific packet again and it can

630
00:37:15,120 --> 00:37:18,000
Speaker 1: travel across the network to the recipient. On the receiving end,

631
00:37:18,000 --> 00:37:21,279
Speaker 1: the transport layer takes in these packets and consults the

632
00:37:21,360 --> 00:37:25,239
Speaker 1: data in the header of that packet to assemble the

633
00:37:25,320 --> 00:37:28,160
Speaker 1: data properly. That's kind of like those page numbers on

634
00:37:28,239 --> 00:37:30,920
Speaker 1: the envelopes I was talking about. It's the equivalent of

635
00:37:30,920 --> 00:37:34,640
Speaker 1: that saying, here's where this data fits in context with

636
00:37:34,719 --> 00:37:37,400
Speaker 1: all the other information that's coming in that is related

637
00:37:37,440 --> 00:37:41,040
Speaker 1: to this particular file. Uh, there's a bit more to

638
00:37:41,120 --> 00:37:43,120
Speaker 1: it than that, but the nature of the packets are

639
00:37:43,160 --> 00:37:45,840
Speaker 1: dependent upon the type of packet it is and the

640
00:37:45,840 --> 00:37:48,480
Speaker 1: protocol in question. And I think you get the general

641
00:37:48,520 --> 00:37:52,279
Speaker 1: idea here now. As Eli the computer guy explains it,

642
00:37:52,640 --> 00:37:55,960
Speaker 1: the session layer opens up communication channels, but the transport

643
00:37:56,040 --> 00:37:58,520
Speaker 1: layer is the one that decides how much data is

644
00:37:58,560 --> 00:38:02,080
Speaker 1: actually exchanged. Betwe lean those different devices that are in

645
00:38:02,160 --> 00:38:06,600
Speaker 1: communication with each other, so they're very tightly bound together,

646
00:38:06,719 --> 00:38:08,719
Speaker 1: so much so that some people put them in the

647
00:38:08,760 --> 00:38:11,880
Speaker 1: same layer. They say that session and transport a kind

648
00:38:11,920 --> 00:38:14,839
Speaker 1: of related closely enough where you can think of them

649
00:38:14,880 --> 00:38:18,200
Speaker 1: as a single layer as opposed to to separate ones.

650
00:38:19,120 --> 00:38:21,880
Speaker 1: Let's move down to layer three. That's the network layer.

651
00:38:22,120 --> 00:38:25,840
Speaker 1: This is the logical pathway layer or the virtual circuit layer.

652
00:38:26,360 --> 00:38:29,160
Speaker 1: This is the layer of switching and routing where data

653
00:38:29,200 --> 00:38:32,200
Speaker 1: transmits from one note to the network to another. And

654
00:38:32,239 --> 00:38:35,800
Speaker 1: at this layer a network performs all of the internetworking,

655
00:38:35,920 --> 00:38:39,440
Speaker 1: all the congestion control, all the addressing features, as well

656
00:38:39,480 --> 00:38:42,399
Speaker 1: as packet sequencing. So another way to think of this

657
00:38:42,480 --> 00:38:44,960
Speaker 1: is that this is the layer in the network where

658
00:38:45,239 --> 00:38:48,320
Speaker 1: network protocols that are in charge of making sure data

659
00:38:48,360 --> 00:38:52,239
Speaker 1: gets from the sender to the recipient does so. Like

660
00:38:52,320 --> 00:38:55,600
Speaker 1: it's all the rules that will guide data along the

661
00:38:55,640 --> 00:38:59,200
Speaker 1: network to get to their destination. That means that it's

662
00:38:59,280 --> 00:39:01,799
Speaker 1: kind of like a road system with all the road

663
00:39:01,840 --> 00:39:05,560
Speaker 1: signs and traffic instructions included. Right, the IP address of

664
00:39:05,560 --> 00:39:07,799
Speaker 1: a machine is at the network level. Now we get

665
00:39:07,840 --> 00:39:10,600
Speaker 1: down to layer two, that is the data link layer,

666
00:39:10,760 --> 00:39:13,560
Speaker 1: and this is where data packets getting coded into bits

667
00:39:13,800 --> 00:39:17,680
Speaker 1: or decoded from bits into packets. At this layer you

668
00:39:17,840 --> 00:39:21,480
Speaker 1: also have transmission protocols and management as well as error

669
00:39:21,560 --> 00:39:25,520
Speaker 1: detection and response from errors in the physical layer below.

670
00:39:26,239 --> 00:39:28,560
Speaker 1: So if something goes wrong in the physical layer below,

671
00:39:28,600 --> 00:39:32,640
Speaker 1: it is the data link layer that is important. Is

672
00:39:32,680 --> 00:39:35,560
Speaker 1: the data link layer that actually detects those errors and

673
00:39:35,640 --> 00:39:38,480
Speaker 1: sends the information up the chain so that someone can

674
00:39:38,520 --> 00:39:41,000
Speaker 1: do something about it. So if there's a switch that's

675
00:39:41,000 --> 00:39:44,279
Speaker 1: not on or a cable that's not plugged in, that

676
00:39:44,400 --> 00:39:46,799
Speaker 1: ends up being detected at layer two and then sent

677
00:39:47,000 --> 00:39:51,480
Speaker 1: up the stack. Uh. There are two sub layers in

678
00:39:51,520 --> 00:39:54,560
Speaker 1: the data link layer. The Media Access control or MAC

679
00:39:54,640 --> 00:39:57,040
Speaker 1: layer is the first one, and you probably have heard

680
00:39:57,080 --> 00:39:59,359
Speaker 1: the term MAC address. You might wonder what the heck

681
00:39:59,440 --> 00:40:04,600
Speaker 1: that means. It's a hardware addresses unique to every node

682
00:40:04,800 --> 00:40:08,080
Speaker 1: within a network. The MAC layer has a direct interface

683
00:40:08,120 --> 00:40:11,040
Speaker 1: with a network medium, and every device that is connected

684
00:40:11,080 --> 00:40:14,040
Speaker 1: to a network has its own MAC address, and it's

685
00:40:14,040 --> 00:40:16,960
Speaker 1: actually burned or recorded on every devices network card. It

686
00:40:17,080 --> 00:40:20,080
Speaker 1: is unique to that And of course the purpose of

687
00:40:20,120 --> 00:40:22,680
Speaker 1: an address is so that a network has to know

688
00:40:22,719 --> 00:40:25,520
Speaker 1: where to send information. Otherwise the whole system wouldn't work

689
00:40:26,080 --> 00:40:28,279
Speaker 1: because if you had a network that didn't use addresses,

690
00:40:28,440 --> 00:40:30,440
Speaker 1: it would be like shouting into the void and getting

691
00:40:30,480 --> 00:40:33,560
Speaker 1: nothing back, or worse, it would be like getting everything back,

692
00:40:33,600 --> 00:40:36,960
Speaker 1: including the stuff you wanted, but also everything else, so

693
00:40:37,080 --> 00:40:38,759
Speaker 1: it would just be a big jumbled mess and you

694
00:40:38,800 --> 00:40:40,600
Speaker 1: wouldn't be able to make sense out of anything. So

695
00:40:40,640 --> 00:40:43,240
Speaker 1: you've got to have the addresses for this to work properly.

696
00:40:43,960 --> 00:40:47,680
Speaker 1: The other sub level of this layer, or sub layer

697
00:40:47,880 --> 00:40:52,280
Speaker 1: I guess of this layer is the logical link control layer. Uh.

698
00:40:52,320 --> 00:40:55,960
Speaker 1: That is the sub layer that controls frame synchronization and

699
00:40:56,040 --> 00:40:58,680
Speaker 1: flow control as well as error checking. So that error

700
00:40:58,719 --> 00:41:00,760
Speaker 1: checking was talking about with the physical air that belongs

701
00:41:00,800 --> 00:41:03,319
Speaker 1: to the I'll see. Yeah, those are some new terms,

702
00:41:03,320 --> 00:41:05,200
Speaker 1: and I guess we needed to find some of them.

703
00:41:05,239 --> 00:41:09,080
Speaker 1: So in telecommunications, which is different from video because there's

704
00:41:09,080 --> 00:41:12,560
Speaker 1: frame synchronization and video as well, but in telecommunications it

705
00:41:12,560 --> 00:41:16,239
Speaker 1: means something slightly different. Frame synchronization is the process in

706
00:41:16,280 --> 00:41:21,359
Speaker 1: which incoming framed data gets extracted for decoding with the

707
00:41:21,400 --> 00:41:25,520
Speaker 1: help of frame alignment signals. Frame synchronization is necessary because

708
00:41:25,560 --> 00:41:29,080
Speaker 1: sometimes data sent to a receiver encounters issues, and frame

709
00:41:29,080 --> 00:41:33,080
Speaker 1: synchronization can identify and correct for those issues, synchronizing between

710
00:41:33,080 --> 00:41:35,640
Speaker 1: the sender and receiver so that you get the full

711
00:41:35,680 --> 00:41:38,880
Speaker 1: amount of information that you expect. Flow control is the

712
00:41:38,880 --> 00:41:42,040
Speaker 1: management of data flow between nodes on a network, and

713
00:41:42,120 --> 00:41:45,400
Speaker 1: it's important so that data can be handled efficiently. So

714
00:41:45,440 --> 00:41:47,960
Speaker 1: you don't want to send more data than a recipient

715
00:41:48,000 --> 00:41:52,520
Speaker 1: can accept at any given time, because you'll hit data overflow,

716
00:41:52,680 --> 00:41:55,480
Speaker 1: and that means that not all the information you're sending

717
00:41:55,520 --> 00:41:56,920
Speaker 1: is going to go through. You're gonna have to re

718
00:41:57,040 --> 00:41:59,279
Speaker 1: send it anyway. So it's better to go ahead and

719
00:41:59,320 --> 00:42:03,480
Speaker 1: make the system more efficient and control that flow of

720
00:42:03,600 --> 00:42:07,240
Speaker 1: data in order to avoid that problem in the first place.

721
00:42:07,320 --> 00:42:10,480
Speaker 1: In this case, the analogy I always think of is

722
00:42:10,520 --> 00:42:13,399
Speaker 1: that classic Christmas episode of I Love Lucy in which

723
00:42:13,480 --> 00:42:16,640
Speaker 1: Lucile Ball is trying to wrap candies along an assembly

724
00:42:16,680 --> 00:42:19,839
Speaker 1: line and the candies start coming faster and faster, so

725
00:42:19,920 --> 00:42:23,239
Speaker 1: she's frantically shoving pieces down her shirt and in her

726
00:42:23,480 --> 00:42:25,759
Speaker 1: hat and in her mouth so that they don't get

727
00:42:25,800 --> 00:42:28,920
Speaker 1: past her. You want to make sure that the data

728
00:42:29,640 --> 00:42:33,319
Speaker 1: like sweet Sweet candy gets sent at just the right

729
00:42:33,360 --> 00:42:35,799
Speaker 1: pace so that it can be handled properly instead of

730
00:42:35,800 --> 00:42:39,960
Speaker 1: shoved into Lucile Ball's mouth or something. And too much

731
00:42:40,040 --> 00:42:42,440
Speaker 1: data is sent to any particular node in the network,

732
00:42:42,480 --> 00:42:45,440
Speaker 1: you get that data overflow situation, and finally we get

733
00:42:45,520 --> 00:42:48,680
Speaker 1: down to layer one. That physical layer. This is the

734
00:42:48,760 --> 00:42:51,759
Speaker 1: layer that handles the actual method of conveyance of data. Now,

735
00:42:51,760 --> 00:42:54,799
Speaker 1: earlier we were talking about data in various formats such

736
00:42:54,840 --> 00:42:58,120
Speaker 1: as clear text or encrypted data, or ultimately as bits.

737
00:42:58,760 --> 00:43:00,400
Speaker 1: But even as we break all that down to the

738
00:43:00,400 --> 00:43:02,919
Speaker 1: basic units of information, there has to be some way

739
00:43:02,960 --> 00:43:07,160
Speaker 1: to actually send that information somewhere. You have to get

740
00:43:07,160 --> 00:43:11,680
Speaker 1: beyond this concept of information. How do you get that

741
00:43:11,719 --> 00:43:14,560
Speaker 1: information somewhere else? It has to travel through some sort

742
00:43:14,560 --> 00:43:18,880
Speaker 1: of medium. Typically it would take the form of something

743
00:43:18,920 --> 00:43:24,200
Speaker 1: like radio signals or light pulses of light, or electrical impulses.

744
00:43:24,800 --> 00:43:27,319
Speaker 1: So this would be the electrical or mechanical part of

745
00:43:27,320 --> 00:43:30,480
Speaker 1: the system that allows for that transmission. That includes physical

746
00:43:30,520 --> 00:43:35,280
Speaker 1: components like cables and computer cards. It also includes information

747
00:43:35,280 --> 00:43:38,120
Speaker 1: about the nature of that conveyance, such as the radio

748
00:43:38,200 --> 00:43:41,719
Speaker 1: frequency you're going to use for wireless transmission, or the

749
00:43:41,760 --> 00:43:45,720
Speaker 1: actual electrical characteristics of various components, like how many pens

750
00:43:46,160 --> 00:43:49,040
Speaker 1: are in any particular connector, or the voltages that you

751
00:43:49,040 --> 00:43:53,160
Speaker 1: need to use for physical components. Layer one. It's so

752
00:43:53,239 --> 00:43:57,680
Speaker 1: basic that's beneath the realm of protocols. It's completely unconcerned

753
00:43:57,680 --> 00:44:01,080
Speaker 1: with protocols. It's literally us the layer that creates the

754
00:44:01,120 --> 00:44:05,200
Speaker 1: actual connection, whether it's physical or wireless. That's all the

755
00:44:05,239 --> 00:44:08,560
Speaker 1: connections between the different devices on a network, and that's it.

756
00:44:09,560 --> 00:44:12,520
Speaker 1: Those are the layers in the OSI model and what

757
00:44:12,560 --> 00:44:14,640
Speaker 1: they mean now, I know I got a little fuzzy

758
00:44:14,640 --> 00:44:17,319
Speaker 1: in there, largely because so many of those layers depend

759
00:44:17,360 --> 00:44:21,080
Speaker 1: upon an understanding of other topics and computer science and telecommunications.

760
00:44:21,120 --> 00:44:23,920
Speaker 1: But really, when you break it down, you're just talking

761
00:44:23,920 --> 00:44:28,560
Speaker 1: about the combination of all the components of network communication

762
00:44:29,160 --> 00:44:32,040
Speaker 1: and then breaking those down into logical layers to make

763
00:44:32,080 --> 00:44:34,960
Speaker 1: it less overwhelming, right, because you think about all the

764
00:44:35,000 --> 00:44:39,000
Speaker 1: things that have to happen for network communication to actually work.

765
00:44:39,360 --> 00:44:41,240
Speaker 1: Then you say, well, that's too big of a picture.

766
00:44:41,480 --> 00:44:43,400
Speaker 1: What if I divide this up into slices and I

767
00:44:43,440 --> 00:44:46,120
Speaker 1: group stuff together in ways that just kind of logically

768
00:44:46,600 --> 00:44:49,880
Speaker 1: are related to one another. Even if when you break

769
00:44:49,920 --> 00:44:54,560
Speaker 1: down physical components it may be a different story. Complementary

770
00:44:54,600 --> 00:44:57,240
Speaker 1: components tend to be in the same layer in this model,

771
00:44:57,360 --> 00:44:59,960
Speaker 1: and some of these layers are in practice often combine

772
00:45:00,000 --> 00:45:02,240
Speaker 1: and like I said, layers four and five, those transport

773
00:45:02,280 --> 00:45:04,560
Speaker 1: and session layers can sometimes be combined with one another.

774
00:45:05,680 --> 00:45:08,839
Speaker 1: Thank you so much, Nick for the suggestion of the

775
00:45:08,840 --> 00:45:11,480
Speaker 1: OSI model. I hope I didn't gum it up too

776
00:45:11,600 --> 00:45:14,920
Speaker 1: much because I wanted to keep it fairly high level

777
00:45:15,400 --> 00:45:19,319
Speaker 1: so that people who are completely unfamiliar when network communications

778
00:45:19,320 --> 00:45:22,120
Speaker 1: could follow it without getting so high leveled that it

779
00:45:22,200 --> 00:45:26,279
Speaker 1: was not a useful conversation. If you guys have suggestions

780
00:45:26,320 --> 00:45:28,719
Speaker 1: for future topics of tech Stuff, there are a lot

781
00:45:28,760 --> 00:45:30,600
Speaker 1: of ways you can get in touch with me. One

782
00:45:30,640 --> 00:45:34,160
Speaker 1: of those is through something called email, which, as you recall,

783
00:45:34,280 --> 00:45:36,720
Speaker 1: is handled by layers seven of the O SI model.

784
00:45:37,560 --> 00:45:40,440
Speaker 1: Send me an email message the addresses tech Stuff at

785
00:45:40,480 --> 00:45:42,359
Speaker 1: house stuffworks dot com. Let me know what you would

786
00:45:42,400 --> 00:45:45,000
Speaker 1: like me to cover, or what sort of guests you

787
00:45:45,000 --> 00:45:46,759
Speaker 1: would like on the show, or maybe a guest co

788
00:45:46,840 --> 00:45:49,279
Speaker 1: host you would love to hear on the show. Let

789
00:45:49,280 --> 00:45:51,360
Speaker 1: me know that. You can also get in touch with

790
00:45:51,400 --> 00:45:53,759
Speaker 1: me via Twitter or Facebook. The handle of both of

791
00:45:53,800 --> 00:45:57,319
Speaker 1: those is tech Stuff h s W or like Nick,

792
00:45:57,640 --> 00:46:00,120
Speaker 1: you can join us over at twitch dot tv e

793
00:46:00,239 --> 00:46:04,600
Speaker 1: slash text stuff. On Wednesdays and Fridays, we record new episodes.

794
00:46:05,000 --> 00:46:08,160
Speaker 1: You can watch live as I mess things up and

795
00:46:08,320 --> 00:46:10,640
Speaker 1: chat with the chat room, and you can even suggest

796
00:46:10,760 --> 00:46:13,520
Speaker 1: future topics right then, and they're just as Nick did.

797
00:46:14,280 --> 00:46:17,960
Speaker 1: And that's it for today's episode. I'll talk to you

798
00:46:17,960 --> 00:46:26,400
Speaker 1: guys again, really say. For more on this and thousands

799
00:46:26,400 --> 00:46:38,520
Speaker 1: of other topics, is how staff Works dot com