so

like I was telling you guys the OSI

model is more of a reference a guideline

to help us delegate responsibilities to

help us understand what the

communication process entails and so I

had you guys just list them out from top

to bottom but remember the communication

process entails both directions

going down the stack is what we call

encapsulating and going up the stack we

call decapsulation

and today I hope to explain why the

encapsulation process is very critical

to the communication

that is to get the message from the

sender to the receiver

layer six sorry layer seven layer six

and layer 5 can be grouped in in fact

the sole responsibly for the three of

these is to produce what for the

transport layer

yeah so by the time we get down to the

transport layer

the pdu

to look something like this it should be

in a binary format so these three layers

produce a pdu

that we will call data

pdu is short for what protocol data unit

depending on the application all the

encryptions in the compressions

these zeros and ones are going to be

something that's really trivial I mean

that's what network people see all the

time or just zeros and ones they don't

know if it's an email or it's a voice

communication or whether it's a video

stream in fact that's what we call the

converging Network right the digital

converging Network this is why Time

Warner and all the other companies can

offer you phone internet TV all in the

same line it's all zeros and ones once

you get into zeros and ones you need to

identify that typically on the

application layer we identify zeros and

ones

by a file extension

a DOT EXE

represents zeros and ones used to

execute instructions a DOT jpeg jpg

represents those zeros and once to

display a picture

likewise we have identifications used in

networking sometimes we call these

addresses

to identify the application of the

service

that's the first thing that the

transport layer is going to do

the transport layer is going to identify

what applications make in the request

and what app sorry what service is going

to receive this

applications make requests

Services receive them

all right

so the way we identify them is to report

addresses

it's going to be a source

and there's going to be a destination

we stamp each and every one

of the pdu for the transport layer with

the source and destination what is the

pdu call of the transport layer

segment

and why is it called a segment because

what is the second thing or I should say

technically this would be the first

thing

yeah it takes the date and breaks up

into pieces hence we call those pieces

segments right so the pdu for the

transport layer

it's called a segment

why do we segment our data

security performance

and we can also allow multiple

Communications to occur relatively at

the same time which we call multiplexing

right

what was the one of the protocols

that defined

the segment because remember protocol

data unit right so if we're producing a

pdu there's got to be a protocol that

told me how to produce that pdu correct

so what was one of the protocols

TCP was one of them absolutely

and TCP we said time's irrelevant I'm

going to sacrifice time over reliability

okay this is why those big fat Cadillacs

I've launched a bunch of luxury items in

there that add weight to the car but a

sports car which is going to cost more

than a Cadillac I mean if you're getting

like a high-end sports car probably

going to trim all that fat because they

want speed correct

so what was the other protocol designed

UDP

TCP is the most popular one

all right we passed that segment down to

the network layer

and what is that Network layer going to

produce what are we going to take that

segment and make it into

packet

and what is one of the most popular

protocols on this layer that tells the

operating system how to take a segment

and make it into a packet

IP

and with IP

we have a source

and a destination address

much much bigger than Port addresses but

nevertheless same principle

but what's the difference between these

addresses what does the transport layer

use addresses for

they're both logical but which one does

the Tran what does the transport layer

use addresses for to identify what

they're called Port addresses but what

do they use to identify

services or applications

because look above the transport layer

the transport layer is looking up and

says okay who's getting this data who's

getting that data the way they know that

is through Port addresses okay so what

are the addresses used at the network

layer what do they use to identify

the key is Network what is the

definition of a network

to where more devices connected together

so they got to identify the devices on

the network

so the sender

and the receiver's IP address goes here

into the packet

all right so the packet gets passed down

and that becomes what

so we're in a data link layer

and we're going to produce what we call

a frame

remember the frame is the only time we

add a header and a trailer

and that frame

uses well we could use all kinds of

different protocols

I always like to talk to data link layer

with the physical layer because its idea

is to connect all that logical stuff

now the way I explained in my last class

and I got a kick out of it but I think

it clicked can you guys tell me what

Internet Explorer smells like

I know you guys are gonna say it smells

like because it's a piece of

but what about Firefox what about Chrome

what do they smell like what do they

feel like when you guys touch Internet

Explorer what does it feel like

felt a little heavy squishy

it doesn't have

smell

it doesn't have texture because it's all

virtual

it's abstract right

if I tell you what a nine if I ask you

what a nine volt battery feels like you

guys can tell me right

that's down here the physical stuff is

what we touch what we work with so this

layer is to take that abstract stuff and

make it into something real

and we need standards

we need standards that tell me okay I

can work with all that logical stuff

give me all those zeros and ones and I'm

going to convert into something that

people can touch taste hear feel it's

see

all depends on your interface card

now I say here because if you could hear

like my dog or Beyond

you can hear the Wi-Fi network sending

messages

and they operate a 2.4 gigahertz

Spectrum that's well beyond our hearing

and you guys are going to be glad for

that

I mean the way we listen to FM radios

which are in the megahertz is you need a

tuner to tune into that frequency and

then to

tone it down to a range that you can

hear correct

networks we call them modems

but nevertheless those signals are all

over us they're in this classroom all

time I'm sending one from this

microphone to my phone

drive me nuts if you guys heard or saw

all those things

but they do exist

the question is

how do I know that the interface card

that I bought

is going to work

with my other devices on my network

there's got to be standards like when

you go shopping for a hard drive it says

USB or a flash drive it says USB you

know you have a USB port and you expect

it to work

so when you guys go shopping for

interface cards or network devices what

are you looking for when you guys go

shopping for wireless cards or wireless

routers what do you look for

says Wi-Fi maybe but more importantly it

says 802.11

followed by a letter

so where the latest one is 802.11 AC

in order to use all that bandwidth to

use that wireless router to its full

potential what kind of interface card

are you going to need

an 802.11 AC interface card

so don't stop halfway and buy just a

wireless router

go the extra mile and buy the interface

card that uses the full potential out of

that wireless router

clear about that if I was setting up a

wired Network like we've been doing in

Packet Tracer you click on the computer

it says what for the interface card

fast

ether and that is a protocol or a

standard

that happens

right here the data link

ethernet has source

and destination addresses

but they're physical

that means the company that made that

interface card

burned an address into that card that

you cannot change

we'll get more into the difference

between physical and logical

right physical just takes those bits

and produces a signal

they carry them

that's it

now I tell my students

there are other models that explain the

same process

some are less elaborate as this

one of the most popular models

that we used as a substitute

to the OSI model is called the TCP slash

IP model and if you want to take a guess

why it's called TCP slash IP

because the persons that develop the

internet

focused on two protocols and only two

protocols TCP slash IP

they need to make sure data is reliable

because went back when it was called

arpanet

everything was very sensitive

with all this research

there wasn't any like voice or video or

any of that kind of crap

in fact the reason why the Internet was

developed was because a cold war

situation that we've connected are

missile silos so when Washington DC was

attacked we could still give the launch

codes over in Alaska

or turkey or wherever so we had

developed a very reliable Network so if

pathway gets disconnected we have

another way to get there another route

and that's what IP

says

so they said you know what

we developed this thing

let's create a model

that shows a grand overview of how this

behaves

and they said in order to use our

network if you want to send a web page

you need a web browser

and so they said

the first three layers are going to be

accomplished

under the application layer

so I just grouped the first three in

fact we've looked at layer 7 6 and 5

didn't I say that's all software stuff

OSI models a little bit more thorough

and said you know what I don't want a

cartographer writing the user interface

for my web browser

and thank God for that because if the

cryptographer did do that they would

hide the OK button it's a secret

likewise I wouldn't want a programmer

Who develops user interfaces

to write the cryptography program

because they would say oh it's real easy

passwords password

because their job is to make the

application user friendly

the cryptographer's job is to make it

very unfriendly

so that when you see it it doesn't make

any sense

very thorough and so what I like to see

is does that happen over here absolutely

because so there's like a division and

probably in that division there are

these departments because they need to

be accomplished

we do need session stuff we do need

presentation stuff but TCP was like yeah

that's all in the software

and that's we're going to do and it too

will produce data

and it too is interconnected and it's

going to connect to

the transport layer

and it two would produce segments

because I don't care

how you communicate but eventually in

your communication process you're going

to need to identify

what you're talking about the subject

right

have you ever talk to somebody then out

of the blue they bring something up and

you're like we were just talking about

uh Hell on Wheels why are you talking

about the weather next week what did it

have anything to do with the topic right

so in there you're gonna need some way

to identify what application or what

service you're talking with

so transport layer transport layer all

the same

remember these are the people that

developed the Internet

so their layer isn't going to be called

the network layer or rather they're

going to call it the inner Network layer

and what does inner mean anyway enter

it's just abbreviated from

interconnected

so just a bunch of networks connected

together

networks are networks whether they're

dropped together or not they all need to

behave the same way and it too is going

to produce

a packet

all right this is a very simple model so

it's going to take the last two

and group them together

and they're going to call this the

network access layer and oh hell does

that cause problems so far I have a 99

failure rate on my exam

when I give a multiple choice question

and I say

uh which

layer on the OSI model

is the same as the network access layer

and I will only give you one it'll be

like Network layer Network transport and

session something like that and students

want to say this one

network network it's got to be the same

thing

and it's not

the key here is access

going on to the network we're talking

about the physical stuff

so it takes both the data link and the

physical stuff in here

and it too

cause it's pdu a frame now let me give

you an example away from networks into

Hardware because I'm a hardware guy I

love reading Hardware magazines I love

staying on latest edge with CPUs gpus

and all that stuff especially the stuff

with the phones like iPhone just

released a new processor they're called

their motion processor and I'm just like

oh wow just another processor great what

does it do and so I'm looking at this

and I remember back in the 90s you know

we get into little geek fights and say

oh Nvidia is better than ATI or some

crap like that and then somebody would

say well no ATI has gotten great

processors and their gpus are excellent

they have more transistors and they have

more shaders and everything and I'm like

oh yeah whippy do and just like you guys

might be getting a pissing contest with

about Xbox 360 versus the PlayStation 3.

oh yeah PlayStation 3 has a lot of

muscle

compared to the Xbox

but what drives us to

these game consoles

content

likewise

I was so discouraged with ATI because

they had shitty Developers

the people at the valve drivers

didn't know what they were doing because

ATI needed to save money so they said

you know what you're an engineer you're

also going to develop the driver

what is a software driver it acts as a

translator between the hardware and the

operating system right

if you're a translator isn't doing a

good job translating you could find

yourself in prison right

likewise if your driver isn't using the

hardware to its full potential

you wasted all your money on all that

muscle and what you have is a dumb jock

I can't read and so you've paid a

millions of dollars to play football

well you guys understand a game plan and

so now he's running to the opposite

field goal or running to the opposite

end zone and you're like well you're big

and strong well you're pretty stupid

so I'm gonna get rid of you don't bring

out any teams I kept it Loose likewise

so what happened is over here Nvidia

decided to follow a model like this and

said we'll pay for engineers

and we'll also pay for software

developers that do nothing but developed

drivers

you need them

but they just have more levels

which might cost them more but hopefully

they produce a better product

over here the same process has to be

done the communication process has to

happen

however

how we group them and organize or

delegate responsibility is our business

model