How to capture data Packets from GPRS Modem Sim Card

Posted on 2007-08-12
Medium Priority
Last Modified: 2013-12-21
Hello Experts:

I have written a Client Server application in C sharp. My application is using GPRS modem connected through USB port to send and receive data.

I want to capture the traffic of my Client Server application but When I tried WireShark  I could not found any of my actual data messages transferring over my application. The reason I found for this is that my messages only reside in the modem memory or Sim card and WireShark is unable to read the messages until and unless the message come over to computer memory.

 Does anyone  can tell me please how can I capture the data packets in this situation.



Question by:babubhai
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LVL 57

Expert Comment

ID: 19680651
Wireshark, and products like wireshark are tools that caputer datapackets as they get transfered over a network.

It sounds like the type of connection between the modem and your computer does not appear as a network connection.

Author Comment

ID: 19682257

what do u mean by transfered over a network. ? Does the messages resides on the sim card means that they are already transfered? If so why I am unable to capture those packets?

Yes, I usually donot dial a connection but my modem still receive the message from the client because
when i dial the connection and then run my application it gives me an error message that "unable to connect to Port,it  is busy".Does it means that I am receiving the messages on GSM mode?
If so how can I receive the data packets on GSM mode and secondly how can I fix the problem of my application that port is busy error.

giltjr :sorry boss I ask so many questions in one questions I hope you dont mind as I am just beginner.


LVL 57

Expert Comment

ID: 19682800
It sounds like you really do not understand networking.

Wireshark, and other applications like it, are setup to capture data going to from things like Ethernet, Token Ring, ATM, and some serial interfaces that appear to the Operating system as a "network device".  A USB port may or may not appear as a network device.

Typically when connecting from a computer to a GPRS modem, there are special program involved and the USB device does not appear as a networking device to the operating system and thus does not appear as a networking device to Wireshark.

If there are messages on the GPRS modem that are in the SIM card, then yes they have been transfered to the cell phone already.  You can't capture the packets that were used to transfer the messages to the cell phone because the packets don't exist any more.  

Its like trying to tape a phone conversation after the conversation has ended.  The information that was exchanged during the conversation still exists, but there is no way to tape the conversation afterwards.

You need to see what the GPRS modem appears to be to the operating system of the computer.

After you have "dialed" into the Internet with the GPRS modem, start wireshark, then click on capture, then select interfaces.  If the GPRS modem appears to be a serial port type connection, then you should have an option for a PPP/SLIP type interface.  This COULD be the GPRS modem.  If you start tracing on that interface you might see traffic flowing.

Author Comment

ID: 19682925
Thanks very much for such a detailed explanation. I really appreciate the way u have explain the things to me.
Yes When I dialed into the internet with the GPRS modem I can capture the data packets of GPRS but my problem is how can I capture those packets (messages) which the modem recieves in its GSM stateI mean the messages which modem receives through my application without using the dial up connection.
thanks very much for your time.
LVL 57

Accepted Solution

giltjr earned 2000 total points
ID: 19683485
If I understand that you are asking, you can't.  

     COMPUTER <-- USB Cable --> GPRS Modem <-- wireless connection to GPRS network --> GPRS Network

I believe you are attempting to capture packets on the wireless side of the GPRS modem.  If that is what you are doing, then you will not be able to do this, as nothing on the computer can see the data as it passes between the GPRS modem and GPRS network.  

The computer will only see traffic that flows over the USB connection.

It has no visibility to what is going on inside the GPRS modem.

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