The PDU, The protocol data unit in each layer contains the payload data that is being transmitted,
and it's a common to prefix a header which contains information required for the payload data to be
transmitted, such as the addresses of the source and destination nodes on the network to the payload
data.
So sometimes the protocol data unit PDU also has a footer here that is suffixed to the payload data
and contains values needed to ensure correct transmission, such as error checking information.
And here in this diagram I created how pdus are laid out in the eips.
Remember from the previous lectures IPS means Internet protocol suite.
So let's get started with the application layer here.
So you can see here we have layer four, we have application session, um, internet layer and the link
layer.
Now I will explain all of these layers and their payloads heaters one by one.
So the TCP header contains a source and destination port number which is here.
Source and destination port number here.
And these port numbers allow a single node to have a multiple unique network.
Connections and port numbers for TCP and UDP ranges from 0 to 65,500.
35.
And the most port numbers are assigned as needed to new connections.
But some numbers have been given a special assignment such as the Port 80 for HTTP.
You can find the current list of assigned port numbers in the ATC services file on the most Unix like
operating system, but you can also check in from the Wikipedia from internet and TCP payload and header
are commonly called the segment where the UDP payload and header are commonly called a datagram.
The IPA protocol uses a source and destination headers.
The destination address lost the data to be sent to a specific node on the network and the source address.
Lost the receiver of the data to know which node sent the data and lost the receiver to reply to the
sender.
IPv4 uses 32 bit addresses, which you will typically see written as a four numbers separated by dots
such as this.
192168.
Here.
Ten and one.
So this is an example.
IP version four, IP address and IPv6 actually let me notify their IP version four.
So.
But the IPV six here.
IPv6 uses 128 bit addresses.
Because 32 bit addresses aren't sufficient for the numbers of nodes on the modern networks.
IPv6 addresses are usually written as a hexadecimal number separated by colons such as.
For example, if a 80 0004 times zero here, actually let me increase the size it here.
000.
And.
So this is an example.
IPV four IPV six address.
Long strings of four times zero.
As you can see here, we've written like that.
Long strings of 000 numbers are collapsed into two columns.
For example, if you want to read, write this IPV IP version six number easily.
You can also write like that.
For example.
One, two, three.
So one.
Two, three.
The Internet also contains source and destination address.
Source and destination address.
Ethernet uses a 64 bit value called a media access control address, which is typically set during a
manufacture of the Ethernet adapter.
And you will usually see MAC addresses written as a series of hexadecimal numbers separated by dashes
or colons.
For example, Mac Address three writes like this.
Example zero.
A.
With dashes.
We will separate here.
28 and nine.
For a five.
So this is an example media access control address and the Ethernet payload, including the header and
footer is commonly referred as frame.