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Vehicle Tracking System- Loss of SMS

Posted on 2004-10-16
Medium Priority
Last Modified: 2013-12-09
Dear Friends,
I have developed an apllication for Vehicle Tracking using Short Messaging service(SMS). I have installed a TC35i module with a computer as modem and the vehicle unit has also been developed around TC35i module with GPS along with it. the computer programming is in VB6.0
The problem I facing is that when I install my Vehicle unit in a vehicle I lose a number of SMS (for example if the vehicle unit sends 50 SMS to the modem, the modem receives only about 40 SMS and the rest are lost). However, if I install the vehicle unit in the same or adjacent room as the modem there is no loss of SMS.
Can somebody help???
Question by:jasneetdua
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LVL 13

Expert Comment

ID: 12345346
There could be three reasons......

1) Your Unit is not sending all the messages..... Suppose your UNIT sends AT commands to the modem and the modem tries to send the message.....Maybe due to Low signal strength your message is not delivered....Are you checking this case ? Are you making sure that your message is send from the Unit ? Reading the OK after sending is very necessary....... Also you should check for Signal Strength before sending SMS.....If the Signal Strength is < 12 then most probably your SMS will not be send.......

2) Your GSM provider is chocking the messages.....Although the chances are very remote as you are receiving the messages from your UNIT in the Lab test....

3) Your SMS reading program might be missing some SMS......Again the chances of this happening is remote as your application works well when you are doing Lab Test......Still I will like to know what technique you are using to read SMS..... My preferred is AT+CMGL=4 (PDU Mode) and AT+CMGL="ALL" (Text Mode) and then deleting the SMS one by one......There is absolutely no chance of not reding an SMS in this way......

So I reckon your Unit is not making sure that the SMS is delivered or not......Just I want to know how you can say that the vehicle has send 50 SMS ????? Maybe it has send 40 SMS........

I hope this info is helpful........


Author Comment

ID: 12356308
Dear Imran,
I will answer all your questions point by point

1)Your point regarding signal strength may hold true, because initially we were using antenna with 3db gain. now we are using an antenna with 6db gain and are able to receive complete data from the vehicle unit even when it is installed in a vehicle. With the 3 db gain antenna signal stenght (AT+CSQ) was arount 10 but with 6db antenna we are getting a signal strength of 30.

2) GSM provider is not choking the messages

3)we are already using the technique suggested by you. AT+CMGL=ALL (Text mode) and then delete the SMS one by one. The vehicle unit has a message ID which is incremented only when it gets response <+CMGS "mr" OK>. this message ID is sent with all the SMS and received and displayed at the computer.

One clarification that I would like at this point is that after receiving the response <+CMGS "mr" OK>, is there still a possibility of losing a SMS? Is there something else which has to be done/checked to ensure that no SMS is lost. Does the vehicle unit need to check for some other response also?

LVL 13

Accepted Solution

imarshad earned 1500 total points
ID: 12367824
>>One clarification that I would like at this point is that after receiving the response <+CMGS "mr" OK>, is there still a possibility of losing a SMS? Is there something
>>else which has to be done/checked to ensure that no SMS is lost. Does the vehicle unit need to check for some other response also?

After receiving <+CMGS "mr" OK> you are almost sure that the message will be send.......Just a few things that might cause the message to not to be delivered....
The number in the AT+CMGS="xxxxxxxxxxx" might not be correct......If you send the SMS on a wrong number then you still will receive the same <+CMGS "mr" OK> message though the message is not delivered.....
I suggest you to check your Hardware code again and again..........I think there is some condition in it that is increasing the messageID even when the message is not send......

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