How To Send and Receive SMS using GSM Modem

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Introduction

SMS client and server is an application software which is used for sending and receiving messages(SMS). It listens for incoming messages to arrive, processes the message if it's in a valid format. Note the processing of arrived messages depends on the application which will be discussed later. I am going to explain the following things:

1. Communication Port Settings
2. Receive Incoming Message
3. Send Messages
4. Read All Messages (Sent by the users)
5. Delete Messages (One or All)

I have used the GSMComm Library for Sending and Receiving SMS. You require a GSM modem or phone for sending an SMS.

Using the code

1) Communication Port Settings

CommSetting class is used for storing comm port settings:

public class CommSetting
{
    public static int Comm_Port=0;
    public static Int64 Comm_BaudRate=0;
    public static Int64 Comm_TimeOut=0;
    public static GsmCommMain comm;

    public CommSetting()
    {
        //
        // TODO: Add constructor logic here
        //
    }
}

Comm is an object of type GsmCommMain which is required for sending and receiving messages. We have to set the Comm port, Baud rate and time out for our comm object of type GsmCommMain. Then try to open with the above settings. We can test the Comm port settings by clicking on the Test button after selecting the Comm port, baud rate and Time out. Sometimes if the comm port is unable to open, you will get a message "No phone connected". This is mainly due to Baud rate settings. Change the baud rate and check again by clicking the Test button until you get a message "Successfully connected to the phone."

Before creating a GSMComm object with settings, we need to validate the port number, baud rate and Timeout.

The EnterNewSettings() does validation, returns true if valid, and will invoke SetData(port,baud,timeout) for comm setting.

The following block of code will try to connect. If any problem occurs "Phone not connected" message appears and you can either retry by clicking on the Retry button or else Cancel.

GsmCommMain comm = new GsmCommMain(port, baudRate, timeout);
try
{
        comm.Open();
        while (!comm.IsConnected())
        {
            Cursor.Current = Cursors.Default;
            if (MessageBox.Show(this, "No phone connected.",
               "Connection setup", MessageBoxButtons.RetryCancel,
                 MessageBoxIcon.Exclamation) == DialogResult.Cancel)
            {
                comm.Close();
                return;
            }
            Cursor.Current = Cursors.WaitCursor;
        }

        // Close Comm port connection (Since it's just for testing
        // connection)
        comm.Close();
}
catch(Exception ex)
{
    MessageBox.Show(this, "Connection error: " + ex.Message,
    "Connection setup", MessageBoxButtons.OK, MessageBoxIcon.Warning);
    return;
}

// display message if connection is a success.
MessageBox.Show(this, "Successfully connected to the phone.",
"Connection setup", MessageBoxButtons.OK, MessageBoxIcon.Information);

2) Receive Incoming Message

We are going to register the following events for GSMComm object comm.

1. PhoneConnected
   This event is invoked when you try to open the Comm port. The event handler for Phone connected is comm_PhoneConnected which will invoke OnPhoneConnectionChange(bool connected) with the help of Delegate ConnectedHandler.
2. MessageReceived
   This event is invoked when a message arrives at the GSM phone. We will register with MessageReceivedEventHandler. When the incoming message arrives, the comm_MessageReceived method will be invoked which in turn calls the MessageReceived() method in order to process the unread message. GSMComm object comm has a method ReadMessages which will be used for reading messages. It accepts the following parameters phone status (All, ReceivedRead, ReceivedUnread, StoredSent, and StoredUnsent) and storage type: SIM memory or Phone memory.

private void MessageReceived()
{
    Cursor.Current = Cursors.WaitCursor;
    string storage = GetMessageStorage();
    DecodedShortMessage[] messages = CommSetting.comm.ReadMessages
                   (PhoneMessageStatus.ReceivedUnread, storage);
    foreach(DecodedShortMessage message in messages)
    {
         Output(string.Format("Message status = {0},
     Location =  {1}/{2}",
         StatusToString(message.Status),
         message.Storage, message.Index));
         ShowMessage(message.Data);
         Output("");
    }

    Output(string.Format("{0,9} messages read.",
                messages.Length.ToString()));
    Output("");
}   

The above code will read all unread messages from SIM memory. The method ShowMessage is used for displaying the read message. The message may be a status report, stored message sent/un sent, or a received message.

3) Send Message

You can send an SMS by keying in the destination phone number and text message.

If you want to send a message in your native language (Unicode), you need to check in Send as Unicode(UCS2). GSMComm object comm has a SendMessage method which will be used for sending SMS to any phone. Create a PDU for sending messages. We can create a PDU in straight forward version as:

SmsSubmitPdu pdu = new SmsSubmitPdu
        (txt_message.Text,txt_destination_numbers.Text,"");

An extended version of PDU is used when you are sending a message in Unicode.

 try
{
    // Send an SMS message
    SmsSubmitPdu pdu;
    bool alert = chkAlert.Checked;
    bool unicode = chkUnicode.Checked;

    if (!alert && !unicode)
    {
        // The straightforward version
        pdu = new SmsSubmitPdu
        (txt_message.Text, txt_destination_numbers.Text,"");
    }
    else
    {
        // The extended version with dcs
        byte dcs;
        if (!alert && unicode)
            dcs = DataCodingScheme.NoClass_16Bit;
        else
        if (alert && !unicode)
            dcs = DataCodingScheme.Class0_7Bit;
        else
        if (alert && unicode)
            dcs = DataCodingScheme.Class0_16Bit;
        else
            dcs = DataCodingScheme.NoClass_7Bit;

        pdu = new SmsSubmitPdu
        (txt_message.Text, txt_destination_numbers.Text, "", dcs);
    }

    // Send the same message multiple times if this is set
        int times = chkMultipleTimes.Checked ?
                int.Parse(txtSendTimes.Text) : 1;

    // Send the message the specified number of times
    for (int i=0;i<times;i++)
    {
        CommSetting.comm.SendMessage(pdu);
        Output("Message {0} of {1} sent.", i+1, times);
        Output("");
    }
}
catch(Exception ex)
{
    MessageBox.Show(ex.Message);
}

Cursor.Current = Cursors.Default;

4) Read All Messages

You can read all messages from the phone memory of SIM memory. Just click on "Read All Messages" button. The message details such as sender, date-time, text message will be displayed on the Data Grid. Create a new row for each read message, add to Data table and assign the Data table to datagrid's source

private void BindGrid(SmsPdu pdu)
{
    DataRow dr=dt.NewRow();
    SmsDeliverPdu data = (SmsDeliverPdu)pdu;

    dr[0]=data.OriginatingAddress.ToString();
    dr[1]=data.SCTimestamp.ToString();
    dr[2]=data.UserDataText;
    dt.Rows.Add(dr);

    dataGrid1.DataSource=dt;
}

The above code will read all unread messages from SIM memory. The method ShowMessage is used for displaying the read message. The message may be a status report, stored message sent/un sent, or a received message. The only change in processing Received message and Read message is the first parameter.

For received message

DecodedShortMessage[] messages =
  CommSetting.comm.ReadMessages(PhoneMessageStatus.ReceivedUnread, storage);

For read all messages

DecodedShortMessage[] messages =
   CommSetting.comm.ReadMessages(PhoneMessageStatus.All, storage);

5) Delete Messages (One or All)

All messages which are sent by the users will be stored in SIM memory and we are going to display them in the Data grid. We can delete a single message by specifying the message index number. We can delete all messages from SIM memory by clicking on "Delete All" button. Messages are deleted based on the index. Every message will be stored in memory with a unique index.

The following code will delete a message based on index:

// Delete the message with the specified index from storage
CommSetting.comm.DeleteMessage(index, storage);

To delete all messages from memory( SIM/Phone)

// Delete all messages from phone memory
CommSetting.comm.DeleteMessages(DeleteScope.All, storage); 

The DeleteScope is an Enum which contains:

1. All
2. Read
3. ReadAndSent
4. ReadSentAndUnsent

Applications

Here are some interesting applications where you can use and modify this software.

1) Pre paid Electricity

Scenario (Customer)

The customer has agreed for pre paid electricity recharges with the help of recharge coupons. The coupon is made available at shops. The customer will first buy the coupons from shops; every coupon consists of Coupon PIN which will be masked, the customer needs to scratch to view the PIN number. The customer will send an SMS to the SMS Server with a specified message format for recharging.

Message Format for Recharging:
RECHARGE <Coupon No> <Customer ID>

Scenario (Server Database)

On the Server, the Database consists of Customer information along with his telephone number, there will a field named Amount which will be used and updated when the customer recharged with some amount. This application becomes somewhat complex, an automatic meter reading software along with hardware needs to be integrated with this. Automatic meter reading systems will read all meter readings and calculate the amount to be deducted for the customer.

2) Astrology

You can implement as astrology software. The user will send an SMS with his zodiac sign. The SMS server will maintain an Astrology Database with zodiac sign and a text description which contains a message for the day. The Database is required to be updated daily for all zodiac signs.

Message Format which will be used by the user to get message of the day:
Zodiac Sign

3) Remote Controlling System

We can implement a remote controlling system, for example you need to:

1. Shutdown
2. Restart
3. Log off system

You can send an SMS. The SMS server will listen and then process the message. Based on the message format sent by the user we can take action.
Example if message format is:
SHUTDOWN
Send to SMS phone number.

Conclusion

This project wouldn't be completed unless I thank the GSMComm Lib developer "Stefan Mayr". I customized my application using this Library. You can download the sample project, library from the web link which I provided under the Reference section.

Reference

• http://www.scampers.org/steve/sms/index.htm