As shown in the figure, the TCP header is ***20 bytes, and the option (if any) is 4 bytes. The prototype definitions of headers and options are as follows: /*TCP header definition, * * 20 bytes */typedefstruct _ TCP _ header {short m _ source port; //Source port number 16bit short m _ sDestPort// Destination port number 16-bit unsigned int m _ uisequenum///Serial number 32-bit unsigned int m _ uiacknowlegenum// Confirmation number 32-bit short m _ shearlenandflag//First 4 bits: TCP header length; Middle 6 digits: reserved; Last 6 bits: flag bit short m _ sWindowSize// window size16 bit short m _ s checksum; //test and16 bitshort m _ SurgentPointer; //Emergency data offset16bit} _ _ attribute _ ((packed)) TCP _ header, * PTCP _ header/* The option definition in TCP header is kind(8bit)+Length(8bit, the length of the whole option, including the first two parts) +content (if any) kind =/kl. Part 2 without the back indicates that the length after the maximum segment is the length of the maximum segment option (in bytes, 1+ 1+ content part length) 3 indicates that the length after windows scale is the length of windows scale option (in bytes,1+/kloc-0+content part length) 4 indicates the allowable length of SACK. No content part 5 indicates that this is a SACK packet with length 2, and no content part 8 indicates a time stamp with length 10 and an 8-byte time stamp */typedefstruct _ TCP _ options {charm _ ckind; Char m _ cLengthChar m_cCo, bear muscle Cao Ke, Jiujian Xuechang mill ntext [32]; }__attribute__ ((packaging)) TCP_OPTIONS, * PTCP _ OPTIONS