端口扫描，根据TCP的connect连接原理，如果连接成功就说明端口打开，如果连接不成功就说明端口关闭-Port scanning, in accordance with the principle of TCP connection of the connect, if the connection open on that port, if the connection is not successful on that port closed

介绍传输控制协议可靠的、面向连接的字节流服务 -Introduce transmission control protocol (TCP) of a reliable, connection-oriented byte stream service