To answer the previous question of why there wasn't a data section, it's
important to understand how sessions are formed within TCP.
Let's take a closer look at TCP session formation. As we learned earlier,
by reviewing our flags in the TCP datagram, the source computer initiates
a three‑way handshake through the use of the SYN flag to a destination
computer to start communication.
If all goes well,
the destination computer will respond with a SYN/ACK
acknowledging the receipt of the SYN.
The source computer will then respond with a final ACK,
at which point the data can then begin to flow.
Please note,
this is just a primer to get you ready for the
module, TCP and UDP Ready Set Action, as during the module,
we'll actually decompose a three‑way handshake.
Let's drop to a diagram to gain a better visual representation of this process.
Let's say we have a computer with the source address of 192.168.1.1. The
user behind the source PC would like to access a website on the server of
192.168.1.100. The computer of 192.168 first sends a SYN to the web server
of 192.168.1.100. After receiving the SYN,
the web server responds with a SYN/ACK acknowledging
the SYN. Upon receipt of the SYN/ACK,
the source computer will send one final ACK upon the
successful receipt of the SYN.
The three‑way handshake has then been completed, at which point the data can then begin to flow.