Now in this slide, we will going to discuss that Each layer in the TCP IP stack has its own isolated
non-overlapping responsibilities.
For example, when the packet travels in the network from, say, router A to router B and router A
and router B are directly connected routers, then it is the responsibility of the data link layer to
take the packet from Node A to its directly connected neighbor node B.
So data link layer is concerned with node to node delivery.
That is datalink layer is concerned.
For data delivery from Node to its adjacent node only.
This is also called L2 routing.
Similarly, Network Layer is responsible for the delivery of the packet from the source machine to destination
machine.
Now remember, source machine and destination machine can be present anywhere in the network.
They can be.
There can be any number of intermediate routers between source machine and destination machine.
So Network Layer is responsible for the data delivery from source node to destination node.
Transport layer, on the other hand, is responsible for the data delivery.
Between processes.
So let us say you have the process X or application X running on the source machine and you have application
y running on destination machine.
So transport layer will be responsible for the data delivery between X and Y.
Where X is the application running on source machine and y is the application running on destination
machine.
Application layer, on the other hand, could be any generic application which implements networking
functions.
So let us say X is a WhatsApp application.
The application Y running on the destination machine is also WhatsApp.
So the application X and Y could be any applications.
Which implements networking communication.
Physical layer, on the other hand, is responsible to transmit the data on the wire in the form of
electrical signals.
And as I have already mentioned, the physical layer is out of the scope of this course.
So no layer is aware of layer above it or below it.
Now what does it mean?
You can see on the right hand side that the most famous protocols at each layer is listed.
The application layer, the most famous protocols are ping, Http, WhatsApp, all mobile apps, and
there are thousands of applications which falls under application layer.
So any application which communicates.
Over the network falls under the application layer.
The most famous transport layer protocols are UDP and TCP protocol.
Of course there are other protocols, but we are talking only about the famous ones.
So the network layer protocols are IP protocol.
99% of the machines in the world are running IP protocol, and the other protocol is IPV six protocol,
which is now becoming famous.
And data link layer.
The most famous protocol is Ethernet protocol.
So we will going to discuss all these protocols in detail that how they function.
Now coming back to the point that no layer is aware of the layer above it or below it.
What does it mean?
It simply means that, for example, let the network layer is running IP protocol.
So the IP protocol will not assume that the transport layer protocol is UDP or TCP.
The IP layer protocol has to function without knowing what protocol is running as the transport layer
protocol.
Similarly, IP layer has to function without knowing or without assuming that the data link layer protocol
is the Ethernet protocol.
It means that each protocol in a particular layer of the TCP IP stack runs without assuming anything
about the protocol running in the layer above it or below it in the TCP IP stack.
So this is the reason I said that each layer works in complete isolation and has their own set of responsibilities.
So once again, in the diagram below, the transport layer is responsible for the data delivery between
applications.
Network Layer is responsible for the data delivery between source machine and the destination machine,
and the data link layer is responsible for the data delivery from a node to its adjacent node in the
network that is Hop by Hop.
So that's all with the OSI model Introduction of the OSI model.
Since it's a complete theory, therefore I am wrapping it up fast.
Otherwise you guys will feel sleepy.
I want to cover the theoretical part as fast as possible so that you guys can start off with the assignments
as soon as possible.
Because networking by its nature is very theoretical subject.
So I don't want you guys to feel sleepy and getting bored that you are learning a lot of theory and
without doing any practical.
So I will keep the theory portion of this course short, but at the same time comprehensive and complete.
So next we will going to discuss data encapsulation and decapsulation, which is another theory portion
of the subject, but very important.