TCP 协议学习笔记——三次握手 参考资料: * RFC 793 - TRANSMISSION CONTROL PROTOCOL 状态编码 LISTEN SYN-SENT SYN-RECEIVED ESTABLISHED FIN-WAIT-1 FIN-WAIT-2 CLOSE-WAIT CLOSING LAST-ACK TIME-WAIT CLOSED 三次握手 四次挥手