- This flag is used to synchronized the sequence numbers between two hosts who wants to communicate, each host start their segment with random initial sequence number (RISN) When SYN flag is set it means ,that this is the first segment, and its used for connection establishment. ACK : - this flag is used to acknowledge the received segment When ACK =1 then it means that Acknowledgement field is valid and it contains the acknowledge no FIN : - This flag is used to terminate the TCP connection when FIN =1 this means that it wants to close the connection RST :- This field is used to Reset the connection when RST =1 means that there is something wrong and the host wants to reset the connection. PSH : -This flag is used to push the data immediately on the network tcp waits for the data from application layer upto the maximum segment size (MSS) then it send the data. but some application like chatting they need to send their data immediately then it uses PSH flag URG :- This flag is used to send the urgent data out of bound. means that if there are many segments but if some data is urgent then it should go first (high priority) Urgent Pointer : - this is a 16 bit field used to indicate how many bytes of data is urgent , and and its from first byte that is (from seq no) Difference between PSH and URG is in push all the data is pushed immediately and in URG only the urgent data is sent first rest of the data will come after