Cannot send SMS more then 140 via HUAWEI USB stick modem

Question

I use HUAWEI USB stick modem and code below to send SMS successfully but under 140 of length (see the code pls -- double lenMes = textsms.Length / 2; ).

But nowdays I see the really big SMS messages.

So I am wondering what's wrong with AT commnds or may me hardware is old so I cannot send big SMS.

Please any clue?

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.IO.Ports;


namespace sendSMSPDU
{
    class Program
    {
        static SerialPort port;

        static void Main(string[] args)
        {
            port = new SerialPort();

            Console.WriteLine("Sending SMS");

            OpenPort();
            bool result;

            result = sendSMS("Some text that less 140 is gonna sending OK", " +75434355544");

            if (result == true)
            {
                Console.WriteLine("OK");
            }
            else
            {
                Console.WriteLine("ERROR");
            }
            Console.ReadLine();

            port.Close();
        }



        private static bool sendSMS(string textsms, string telnumber)
        {
            if (!port.IsOpen) return false;

            try
            {
                System.Threading.Thread.Sleep(500);
                port.WriteLine("AT\r\n");  
                System.Threading.Thread.Sleep(500);

                port.Write("AT+CMGF=0\r\n"); 
                System.Threading.Thread.Sleep(500);
            }
            catch
            {
                return false;
            }

            try
            {
                telnumber = telnumber.Replace("-", "").Replace(" ", "").Replace("+", "");


                telnumber = "01" + "00" + telnumber.Length.ToString("X2") + "91" + EncodePhoneNumber(telnumber);

                textsms = StringToUCS2(textsms);

                string leninByte = (textsms.Length / 2).ToString("X2");
                textsms = telnumber + "00" + "08" + leninByte + textsms;


                double lenMes = textsms.Length / 2;

                if (lenMes < 140) // It sends OK
                {
                    port.Write("AT+CMGS=" + (Math.Ceiling(lenMes)).ToString() + "\r\n");
                    System.Threading.Thread.Sleep(500);


                    textsms = "00" + textsms;

                    port.Write(textsms + char.ConvertFromUtf32(26) + "\r\n");
                    System.Threading.Thread.Sleep(500);
                }
                else
                {
                    return false;
                }
            }
            catch
            {
                return false;
            }

            try
            {
                string recievedData;
                recievedData = port.ReadExisting();

                if (recievedData.Contains("ERROR"))
                {
                    return false;
                }

            }
            catch { }

            return true;
        }


        private static void OpenPort()
        {

            port.BaudRate = 9600;  
            port.DataBits = 7;  

            port.StopBits = StopBits.One;          
            port.Parity = Parity.Odd;  

            port.ReadTimeout = 500;  
            port.WriteTimeout = 500;  

            //port.Handshake = Handshake.RequestToSend;
            //port.DtrEnable = true;
            //port.RtsEnable = true;
            //port.NewLine = Environment.NewLine;

            port.Encoding = Encoding.GetEncoding("windows-1252");

            port.PortName = "COM7";


            if (port.IsOpen)
                port.Close();
            try
            {
                port.Open();
            }
            catch { }

        }




        public static string EncodePhoneNumber(string PhoneNumber)
        {
            string result = "";
            if ((PhoneNumber.Length % 2) > 0) PhoneNumber += "F";

            int i = 0;
            while (i < PhoneNumber.Length)
            {
                result += PhoneNumber[i + 1].ToString() + PhoneNumber[i].ToString();
                i += 2;
            }
            return result.Trim();
        }



        public static string StringToUCS2(string str)
        {
            UnicodeEncoding ue = new UnicodeEncoding();
            byte[] ucs2 = ue.GetBytes(str);

            int i = 0;
            while (i < ucs2.Length)
            {
                byte b = ucs2[i + 1];
                ucs2[i + 1] = ucs2[i];
                ucs2[i] = b;
                i += 2;
            }
            return BitConverter.ToString(ucs2).Replace("-", "");
        }


    }
}

Answer 1

Single SMS message is limited to 160 (or 152 in PDU mode) symbols in GSM-7 encoding. More than that, if there is any symbol not listed here you need to use UCS-2 encoding and your messages now limit to 67 symbols. If you need to send longer messages, you are welcome to the "bright and shiny world" of SMS PDU mode .

So sending a long sms is as easy as:

1. Split it to parts of 67 (or 152) symbols;
2. Convert this parts to UCS-2 or GSM-7 encoding;
3. Transform them to PDU messages;
4. Send them sequentially with use of additional AT-command ( AT+CMGF=0 )

Edit

The one who designed a PDU format is a true evil person. It is really mind breaking thing and I don't want to write a convertion code, sorry. But, I can point you with this stub:

protected void SendMessage(string phoneNumber, string message)
{
    const char CR = '\r'; // "Carage Return"
    const char CtrlZ = (char)26; // Ctrl+Z character

    var header = GeneratePDUHeader(phoneNumber);
    foreach (var messagePart in SplitSMSMessage(message))
    {
        SendToCOM("AT+CMGF=0" + CR);
        SendToCOM("AT+CMGS=42" + CR);
        SendToCOM($"{header}{messagePart}" + CtrlZ);
    }
}

// should return something like "0041000B910000000000F000088C"
protected string GeneratePDUHeader(string phoneNumber) { }

// split long message to parts
protected IEnumerable<string> SplitSMSMessage(string message)
{
    var useUCSEncoding = IsUCSEncodingNeeded(message);
    var partLength = useUCSEncoding ? 67 : 152;

    var messageParts = Enumerable.Range(0, message.Length / partLength)
        .Select(i => message.Substring(i * partLength, partLength))
        .ToArray();

    var referenceNumber = $"{GenerateReferenceNumber():X2}"; // convert to HEX, i.e. "01"
    var totalMessagesCount = $"{messageParts.Length:X2}";    // convert to HEX, i.e. "01"
    var udhBase = $"050003{referenceNumber}{totalMessagesCount}";

    var messageNumber = (char)0;
    foreach (var messagePart in messageParts)
    {
        var udh = $"{udhBase}{++messageNumber}";
        var messagePartText = useUCSEncoding ? StringToUCS(messagePart) : StringToGSM7(messagePart);
        yield return $"{udh}{messagePartText}";
    }
}

private void SendToCOM(string message) { } // writes message to COM port
private bool IsUCSEncodingNeeded(string message) { } // determine if UCS-2 convert is required
private char GenerateReferenceNumber() { } // random number 0-255
private string StringToUCS(string message) { } // convert string to UCS encoding
private string StringToGSM7(string message) { } // convert string to GSM7 encoding (don't forget about padding!)

You may also find this links are useful:

• https://en.wikipedia.org/wiki/Concatenated_SMS
• https://www.developershome.com/sms/cmgsCommand4.asp

Answer 2

The best answer to my question is here

How to concat long SMS in GSMComm Library?

https://github.com/welly87/GSMComm

https://www.nuget.org/packages/GSMComm/

It work fine with my HUAWEI GSM modem! WOW!