I am trying to send a string from a Huawei MU509 GPRS modem to a Linux server over the internet. I am using an AT command tester to simulate AT commands. After giving the ipinit (AT^IPINIT="airtelgprs.com") and ipopen (AT+IPOPEN=1,"TCP","",7869) commands, the module indicates that the data connection was established successfully. While sending data using the ipsend command (AT^IPSEND=1,"cgfcgcgs,1100.8683,07656.7037"), no data is received server side.

I also checked the server side program, and it reports no errors. When using a piece of software called Packet Sender, I got an empty response. I've searched some hours in net and I haven't got any possible solution. What is the issue with the module and/or server?

  • \$\begingroup\$ What exact cell modem are you using? Do you see any connection attempt in the server logs? \$\endgroup\$
    – tcrosley
    Apr 2, 2014 at 13:04
  • \$\begingroup\$ Huawei MU509 gsm modem. Ya i got empty response while using a software named Packet Sender. \$\endgroup\$
    – gzix
    Apr 2, 2014 at 13:08

1 Answer 1


I think you'll need some further testing and debugging to determine whether this is a GPRS network and/or server firewall problem, or possibly a problem with your SIM card. Some suggestions would be:

  • Insert the SIM card into a consumer GPRS modem and see if you can connect to port 7869 on that server from a laptop or PC using the connection. A free program like Tera Term will allow you to connect to any TCP/IP port.

  • If you don't have a GPRS modem maybe try a cell phone and make sure at least you have basic Internet connectivity.

  • Instead of port 7869 try connecting to a well known port such as 80 on the same server.

  • Make sure you can connect to port 7869 from outside the network using a different Internet connection (home / friend's place etc) and once again a program like Tera Term may be useful.

Some mobile providers block lesser used TCP ports in unusual ways and if the connection looks OK but doesn't seem to arrive anywhere it might just be a problem with port fowarding and routing on the server end.

  • \$\begingroup\$ Yes it did need some debugging. \$\endgroup\$
    – gzix
    Apr 4, 2014 at 7:23

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