Serial port ReadTo timeout exception

Question

Hello.
I am communicating with modem using serial port.
The fist time I open serial port and start sending AT commands everything works fine.
Then I wait for a couple of seconds and repeat procedure...
Second time it opens port and sends first command and waits port.ReadTo("\r\n") -> and here is operation timed out exception.
If I close the program and start again it works fine... its like serial port wasnt disposed properly?
Here is the program:
class Program
static void Main(string[] args)
SendATcommands();
Thread.Sleep(5000);
SendATcommands();
static void SendATcommands()
SerialPort port = new SerialPort();
port.RtsEnable = true;
port.BaudRate = 9600;
port.DataBits = 8;
port.Handshake = Handshake.None;
port.Parity = Parity.None;
port.PortName = "COM9";
port.StopBits = StopBits.One;
port.WriteTimeout = 20000;
port.ReadTimeout = 30000;
port.NewLine = "\r";
port.Open();
Thread.Sleep(1000);
port.WriteLine("+++");
Thread.Sleep(1000);
port.WriteLine("AT\r\n");
port.ReadTo("\r\n");
port.WriteLine("ATH\r\n");
port.ReadTo("OK\r\n");
port.WriteLine("AT\r\n");
port.ReadTo("OK\r\n");
port.WriteLine("AT&D2\r\n");
port.ReadTo("OK\r\n");
port.WriteLine("AT\r\n");
port.ReadTo("OK\r\n");
port.WriteLine("ATE0V1Q0\r\n");
port.ReadTo("OK\r\n");
port.WriteLine("AT\r\n");
port.ReadTo("OK\r\n");
port.WriteLine("ATDT040111222"); //phone number
port.ReadTo("CONNECT 9600/RLP\r\n");
port.WriteLine("ATH");
Thread.Sleep(1000);
port.WriteLine("+++");
Thread.Sleep(1000);
port.Close();
port.Dispose();

Answer 1

Closing the serial port makes normal no sense, when you want a contious communication. Also using sleep to time your commands is pretty useless as the modem may need longer to prepare for the next command. Thus you need to read the answer from your modem
and continue when sent an OK.