Recalling the TCP three-way handshake

In the TCP / IP protocol, TCP protocol provides a reliable connection service, three-way handshake to establish a connection.
The first handshake: a connection is established, the client sends syn packets (syn = j) to the server, and enters SYN_SEND state, waiting confirmation server; 
SYN: synchronization sequence number (synchronize sequence numbers)
second handshake: server receives syn packets, must confirm the customer SYN (ack = j + 1) , while themselves sends a SYN packet (syn = k), i.e. SYN + ACK packet, then the server enters a state SYN_RECV; 
third handshake: the client receives the SYN + ACK packet to the server, the server sends an acknowledgment packet ACK (ack = k + 1) , this packet is sent, the client and server enter ESTABLISHED state, complete the three-way handshake.