The user uses the telnet user program to establish a connection with the service process. The user program writes information to the service process, the service process reads the information and sends out a response, and the user program reads the response and reports it to the user. Therefore, this connection is duplex and can be used for reading and writing.

Tcp or udp connections are uniquely acknowledged using the following four items in each message:

Source ip address

The Ip address of the sending packet.

Target ip address

Ip address of the received packet.

Source port

The connection port on the source system.

Port of destination

The connection port on the target system.

Port refers to the communication protocol port used for super busy connection service and connectionless service in the network. It is an abstract software structure, including some data structures and i/o buffers. It is a software structure used by client programs or service processes to send and receive information. One port corresponds to 16 bits.