Find gsm modem port in c#

Question

I want to loop through the available ports: System.IO.Ports.SerialPort.GetPortNames() to find if a port is used by a gsm modem. Any idea please.

Answer 1

What I did in my application for one similar task:

1. To check that a modem is connected to particular port you can send AT command into this port. This function below returns true if we found a modem on the current COM port:

   private bool CheckExistingModemOnComPort(SerialPort serialPort)
   {
       if ((serialPort == null) || !serialPort.IsOpen)
           return false;
   
       // Commands for modem checking
       string[] modemCommands = new string[] { "AT",       // Check connected modem. After 'AT' command some modems autobaud their speed.
                                               "ATQ0" };   // Switch on confirmations
       serialPort.DtrEnable = true;    // Set Data Terminal Ready (DTR) signal 
       serialPort.RtsEnable = true;    // Set Request to Send (RTS) signal
   
       string answer = "";
       bool retOk = false;
       for (int rtsInd = 0; rtsInd < 2; rtsInd++)
       {
           foreach (string command in modemCommands)
           {
               serialPort.Write(command + serialPort.NewLine);
               retOk = false;
               answer = "";
               int timeout = (command == "AT") ? 10 : 20;
   
               // Waiting for response 1-2 sec
               for (int i = 0; i < timeout; i++)
               {
                   Thread.Sleep(100);
                   answer += serialPort.ReadExisting();
                   if (answer.IndexOf("OK") >= 0)
                   {
                       retOk = true;
                       break;
                   }
               }
           }
           // If got responses, we found a modem
           if (retOk)
               return true;
   
           // Trying to execute the commands without RTS
           serialPort.RtsEnable = false;
       }
       return false;
   }
   

2. On the next stage we can collect some data from the modem. I used the following commands:

   • ATQ0 - switch on confirmations (receive OK on each request)
   • ATE0 - switch on echo
   • ATI - get modem details
   • ATI3 - get extended modem details (not all modems supports this command)