So going forward in this diagram, I have shown the TCP IP stack.
On the left hand side, you can see that the incoming packet journey and on the right hand side shows
the outgoing packet journey in the TCP IP stack.
So you can see that in the incoming packet journey, the data link layer examine the destination Mac
address and the TCP IP layer that is the network layer.
Examine the destination IP address and the transport layer examines the port number.
So we will discuss in detail about this port number.
Need not worry.
And in the outgoing packet journey each layer appends its own header.
So the thing to note here is that you can see this bracket in yellow.
That.
All these layers are the part of operating system and all these layers are combined together is called
TCP IP suit.
So in your operating system, whether it is Linux or Windows, the transport layer, the TCP IP layer
and the data link layer together with the system call interface are implemented inside the operating
system.
Now, we will talk a little bit here that what actually system call interface is.
You can see that there are a bunch of APIs specified here.
These are the actually these are actually the APIs or function calls, which is used by the application.
To invoke the service of the operating system.
That is why it is called system call interface, because it is an interface between the application
and the operating system.
So you can see on the right hand side, you have many applications running on the top of the operating
system.
The application could be A1, the application could be a two, the application could be a three.
These applications communicate with the operating system using system call interface.
Let me give you one common example of system call interface.
If you have ever written a C program and you have allocated dynamic memory using malloc or system call,
then these are actually the system calls which is invoked by the API, which is invoked by your application
to request a memory from the operating system.
So this is an example of system call interface.
So system call interface enables the application to talk to the operating system.
Using system call interface.
Application can request the services of the operating system.
For example, using malloc, the application can request the memory from the operating system.
So you can see that all the system call interfaces and the transport layer, network layer and the data
link layer, these are all the parts of the operating system.
They are implemented inside the operating system.
And below the operating system there is a hardware.
Which comprises of various device drivers.
These are these hardwares may include CPU.
This may include GPUs.
This may include memory.
These may include various USB ports and many other hardwares.
So operating system interact with the hardware using drivers.
Which sits, which sits between operating system and hardware.
So in this slide, I have tried to show you the networking subsystem of the operating system.