"Computer network" Wireshark Capture Packet Analysis 2

In Analysis 1, you probably see the information in a package. Here, look at what these bags are doing.

This is the first 4 packages that my computer interacts with a website.

The first three packets can be clearly seen as TCP three handshake.

So, here's the question:

Why is the third package shorter than the first two? What information was exchanged in the process of building a handshake?

(My own understanding, not necessarily right, please correct me)

We analyze the information of the first three packets, we can find that only the TCP header length is different, the first two packets to 12 bytes of TCP option field, and the third package does not.

More in the circle of places, in the options field, both sides pass their own maximum message length (MSS), Window enlargement options (Windows scale) and selectable confirmation options (SACK). In fact, for both sides after the size of the transmission of data, confirm the way to do the exchange of information, to ensure that both sides can communicate properly.

"Computer network" Wireshark Capture Packet Analysis 2