Welcome back, guys.
So this is our module seven.
And in module seven, we're going to study the transport layer.
So the transport layer is also called a socket layer.
So in this module we're going to discuss about transport layer goals and the transport layer protocols.
The two most famous transport layer protocols that is used worldwide is UDP protocol, which is also
called user datagram protocol and TCP protocol, which is transmission control protocol.
So we have studied data link layer, we have studied network layer.
Now we will study transport layer.
So transport layer goals.
So after the network layer has verified that packet is not to be forwarded to next hop, that is, the
network layer has made a decision that the packet is actually destined to a local machine on which the
packet is received and it is not supposed to be forwarded.
The packet is destined to its own network layer chop off the network layer header, which is actually
the IP header in IP protocol and hence over the remaining packet to upper layer, which is the transport
layer and the TCP IP stack.
Now transport layer has two standard protocols which are widely used and widely deployed across the
globe.
These two protocols are TCP protocol and UDP protocol.
So what are actually the function of transport layer?
Transport layer function is to identify the correct process or application running above the transport
layer to deliver the packet.
This is done by the transport layer protocols, TCP, UDP, or you can have your own custom protocol
running at the transport layer.
Now among the two protocols that is TCP and UDP, the TCP protocol has more functionality attached to
it.
It also does the congestion control in the network.
That is, whenever the source machine or the destination machine are communicating and whenever there
is a lot of traffic on the network and the network gets overwhelmed or the network is busy or the resources
on the network are are depleting, that state of the network is called congestion.
TCP protocol is complex enough that it also encompasses it within itself the mechanism of congestion
control.
TCP protocol also does reliable delivery of the packets to the application.
Reliable delivery means the packet may get lost in the network due to one reason or the other, or the
packet may get corrupted.
The application running TCP protocol or the application which is using TCP protocol for communication
can recover from all these network issues like packet loss, packet corruption or congestion control.
So all these functionality is done by TCP protocol.
UDP protocol is simple protocol and it is a very simple mechanism of transmitting a packet from source
machine to destination machine and it do not have all these features which TCP has.
So we will discuss that in what scenarios it is beneficial to use TCP as a transport layer protocol
and in what scenario.
The application must use UDP as a transport layer protocol for carrying out communication.
So transport layer, once again, the overall function of the transport layer protocol is the process
to process delivery of the data packet.
And again, transport layer transport layer is not aware of any layer above it or below it.
This is true for every layer in the TCP IP stack.
In fact, for example, in the TCP IP stack, the data link layer do not assume that the layer running
above it is an IP layer.
It could be IPV six protocol, right?
Similarly, IPV six protocol.
Do not assume that the protocol running above it in the TCP IP stack is actually the TCP protocol.
It could be UDP protocol.
So how the layer one, how the layer came to know that the layer running above it or below it is which
running which protocol.
This we will discuss in the next slide when we when we will be studying the stacking of headers.
Now coming back.
The data link layer has the responsibility for the transmission of data packet.
Hop by hop.
So this is Hop by hop.
So it is the job of the data link layer to take the packet from machine A to machine B, whereas Machine
A and machine B are directly connected Machine's network layer.
On the other hand, has the responsibility to take the data packet from source machine to destination
machine.
Now source machine and the destination machine could be present anywhere in the world.
And they and their can can be any number of routers in between the source machine and the destination
machine.
So this is actually internet.
So network Layer is responsible to take the data packet from source machine to destination machine.
And now comes the transport layer.
The transport layer has the responsibility to take the data packet from application, a running on source
machine to application B running on destination machine.
That is the reason the transport layer is.
Concerned with process to process delivery, where a is the process running on source machine and b
is the process running on destination machine?
So you can see that each layer in the TCP IP stack is actually associated with its one particular function.
And the function do not overlap at all.
All these layers combine together and place their own specific role for which they have been designed
in order to establish end to end communication between the application running on source machine with
the application running on destination machine.