Are you ready for some networking theory I know, I know!
Try to control your excitement on this I know it's difficult. But really, seriously
if you want a job or career in the field of computer networking you're going to
have to know all about the OSI model. OSI stands for Open Systems
Interconnection. The Open Systems Interconnection model is a structured
model developed for computer networking in the 1970's and it was developed by the
International Organization for Standardization (ISO). (And I know
this can get confusing because the OSI was developed by the ISO, but I digress).
It was basically developed as a way, it was developed and adopted really
as a way of standardizing network technologies. The first and most
important thing this did - this model did - was it allowed computers from different
manufacturers to communicate with each other. Because it modeled networking
hardware software and protocols and modeled them in such a way that they
could communicate with each other. Manufacturers had a model to work under
which allowed them all to kind of leverage off of each other by being
compatible with each other's devices. They had kind of a standardized model to
work with. The OSI model is divided into 7 Layers or groupings of
standardization that makes up kind of a hierarchy of sorts. I'm going to cover
these 7 Layers here in this video lesson of this Level 1 "New to Networking" Course.
But if you want to delve deeper into the OSI Model and the TCP/IP Model which I
haven't even talked about yet and how they are similar and different as well
as more thorough detail on what each layer does you'll want to check out the
Level 2 Course on this same chapter lesson. There are also other study
materials out there that kind of go into deeper detail about the OSI Model.
Also keep in mind just as a side note that most of what is done in each of
these Layers is actually done on the actual networking card (the NIC) of a
computer. Not all of it but for all intents and purposes we can say that at
this level of understanding networking. So what are the 7 Layers? The top
layer is the Application Layer. Now this is the layer where
users communicate and interact with the computer and applications, as well as
where the applications interact with all the other layers of the OSI Model. Over a
network the Presentation Layer is the next layer down. This layer presents data
coming from the other layers to the Application Layer. Now it
also translates data as needed from the Application Layer down to the Session
Layer below it. And obviously the next layer is the Session Layer. This is the
layer that is responsible for each networking session between this computer
and the other devices on a network. This is also the layer - this Session Layer -
is also the layer where Presentation Layer data is set up managed and
dismantled. Then you have the Transport Layer. This layer - the Transport Layer -
takes data from the upper layers the Session the Presentation the Application
Layers it takes data from those and it combines it into a data stream for
end-to-end transport between devices. So the Transport Layer kind of makes sure
that it is transported from this device to the other, and from the other device
to this device correctly. It also takes data received from other
devices and delivers it up to the Session Layer to go back up the
hierarchy if it needs to. That's data that it received FROM the network. Then
you get into the Network Layer. Now this is also known as Layer 3. So when we're
talking about "Layer 3" in networking we're talking about the Network Layer.
This Network Layer is the layer where device addressing (see IP addresses as a
side note) where network addressing and data packet tracking actually takes
place. This is where Routers tend to do their magic...at the Network Layer.
Anything dealing with IP addresses and network addresses, this is the Network
Layer that's involved. Next you have Layer 2 which is the Data Link Layer.
Now this Data Link Layer is responsible for transmitting the data from the upper
layers out ONTO the Physical Layer and the network. It also receives data from
other devices on the network from that Physical Layer below it and takes it up
into the upper layers of the OSI Model. You also see at the Data Link Layer
you also see flow control and error notification. Those things are done at
this Data Link Layer - this Layer 2. Last but not least you have the Physical
Layer. Now the Physical Layer is the actual physical media or medium used to
transmit and receive data in bits...either zeros or ones. Now this is essentially
the physical hardware that the NIC interface, the cables, the antennae, any
physical hardware that makes up the network is basically in the realm of the
physical layer. So that's the 7 Layers of the OSI Model. And again it's
just a structured standardized model that manufactures of all these different
devices and contraptions on a network can kind of stick to to make sure that
they're on the same page, so to speak, with all the other manufacturers of all
of the other devices out there for networking so that they can all be used
together on the same network or networks.