TCP/IP details -- Role of the TCP Header option field -- TCP Header

TCP/IP details -- Role of the TCP Header option field -- TCP Header
1. Set the option field of the TCP header to 40B and write down some common items:

2. The Option END field (EOP, 0x00) occupies 1B, and only one packet segment is used once. It is placed at the end to indicate that there are no more messages in the header, and the Application Data starts at the next 32-bit character.

3. No operation field (NOP, 0x01), which accounts for 1B. It is also used for filling and placed at the beginning of the option.

4. MSS (maximum packet segment length). Format: type (1B, value: 2), length (1B, value: 4), value: (2B)

This parameter is used to determine the size of the MSS at the start of the connection. If it is not determined, the default value is used (generally 536B)

5. Window expansion factor, in the following format: type (1B, value: 3), length (1B, value: 3), value (1B)

New window value = power of the first window value * 2 (expansion factor)

When both Parties consider that the header window value is not big enough, use this to define a larger window at the beginning of the connection. Valid only when the connection starts. Once defined, it cannot be changed during communication.

6. Time cut (RTT for application testing and serial number bypass prevention), omitted, supplemented later

7. Allow SACK and SACK options