谁可以讲解一下telnet的工作原理？？？？？

试试这个TcpClient telnet = new TcpClient(172.27.98.253,23);
NetworkStream writeStream = telnet.GetStream();
StreamReader readStream = new StreamReader(telnet.GetStream());
// sending username to the server
string sendString = "username" + txtUserName.Text + "\r\n";
byte[] dataToSend = Encoding.ASCII.GetBytes(sendString);
writeStream.Write(dataToSend,0,dataToSend.Length);
// sending password
sendString = "password " + txtpass.Text + "\r\n";
dataToSend = Encoding.ASCII.GetBytes(sendString);
writeStream.Write(dataToSend,0,dataToSend.Length);//send command
sendString = "show mac-add\r\n";
dataToSend = Encoding.ASCII.GetBytes(sendString);
writeStream.Write(dataToSend,0,dataToSend.Length);//read return string
string receiveData = readStream.ReadLine();