socket concept

Socket:
Socket=Ip address+TCP/UDP+port.
Socket Socket= (IP address: port number), the representation method of socket is to write the port number after the IP address in dotted decimal.
Each transport layer connection is uniquely connected by two communication ends.The endpoints (that is, the two sockets) are determined.For example: if the IP address is 210.37.145.1 and the port number is 23, then the resulting socket is (210.37.145.1:23)
To communicate over the Internet, you need at least one pair of sockets, one running onThe client, we call it Client Socket, and the other running on the server side, we call it Server Socket [3] .
According to the way the connection is started and the target to be connected to the local socket, the connection process between sockets can be divided into three steps [3]:
(1) Server monitoring.
(2) Client request.
(3) Connection confirmation
1. Server monitoring
The so-called server monitoring means that the server-side socket does not locate the specific client socket, but is in a state of waiting for connection, and real-time monitoringNetwork status [3].
2. Client request
The so-called client request refers to the connection request made by the client's socket, and the target to be connected is the server-side socket.To do this, the client's socket must first describe the server's socket to which it wants to connect, point out the address and port number of the server-side socket, and then make a connection request to the server-side socket [3] .
3. Connection confirmation
The so-called connection confirmation means that when the server-side socket monitors or receives the connection request of the client-side socket, it will respond to the request of the client-side socket and establish anew thread and send the description of the server-side socket to the client.Once the client has confirmed this description, the connection is established.The server-side socket continues to be in a listening state, receiving connection requests from other client-side sockets