Sending Multipart PDU SMS by AT Command

Question

I have successfully sent a multipart pdu sms,

The problem is when i try to send this SMS to a number on a different network it gives me the following error :

+CMGS ERROR:500

Please can any one tell me what should i do.

        atCommandStr = "AT+CMGF=0\r";
        comPort.WriteLine(atCommandStr + (char)13);
        Console.WriteLine(comPort.ReadExisting());

        Thread.Sleep(2000);

        for (int i = 0; i < number_of_parts; i++)
        {
            int oct = (messagesParts[i].ToCharArray().Count() / 2) -1;

            atCommandStr = "AT+CMGS=" + oct + "\r";
            comPort.WriteLine(atCommandStr + (char)13);
            Console.WriteLine(comPort.ReadExisting());

            Thread.Sleep(2000);

            string path;
            path = messagesParts[i] + Char.ConvertFromUtf32(26);
            comPort.WriteLine(path + (char)13);

            for (int a = 0; a < 100; a++)
            {
                Thread.Sleep(2000);

                string t = comPort.ReadExisting();
                Console.WriteLine(t);

                if (t != "" && t.Contains("CMGS") || t.Contains("ERROR"))
                {

                    break;
                }
            }

            //Console.WriteLine(comPort.ReadExisting());
        }

Answer 1

Did the modem really return +CMGS ERROR:500 and not +CMS ERROR: 500? Because in that case, your modem is not compliant with the 27.005 standard which specifies if sending fails: +CMS ERROR: <err>.

Error code 500 means unknown error, so that does not help very much. But I would guess that your length calculation is wrong. From the standard:

<length> must indicate the number of octets coded in the TP layer data unit
to be given (i.e. SMSC address octets are excluded).

Is it correct to subtract 1 after dividing by 2? Try to decode exactly what will be sent on TP layer. Try to increase/decrease the length a bit and see if it makes any difference.

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Also, since atCommandStr already contains \r you should not include the + (char)13 in

comPort.WriteLine(atCommandStr + (char)13);