T-Mobile TCP problem

Our friend trying to set up our modem in Germany. He provided us APN name of the sim card. We saved the APN configuration on modem. Then the modem established gprs connection, got a dynamic ip address then connected to our server machine as TCP client.
From our server side, we obtained the ip address of the modem. Then we try to connect to that ip address over TCP port 3000 but we can not establish any connection.
Does anyone know about a similar issue with T-Mobile sim cards? Should we obtain a static ip address or should we use a different apn name? Or do they block the inbound port number of 3000 which we try to connect? Or do they have any NAT rule behind the modem ip address?
Any idea?

Currently used Apn names : both “internet” and “internet.t-mobile” were tried.
Module configuration: Airprime Q2687RD, R7.46 FW


Probably because it’s a Private IP address :question:

You cannot connect from any server to a client with a Private IP address :exclamation:

The Client needs to intiate the connection to the Server - or you need to get a Public IP address.

Static won’t help - it’s Public IP that you need!

Yes, i think you are right. The term must be private/public ip insead of dynamic/static ip. We try to contact with t-mobile stuff and try to get a public ip address which we can connect to.

Maybe in forum, someone who uses t-mobile sim card in Germany already knows an apn name that makes modem to obtain a public ip address automaticly? i dont think this is realted to apn settings we can do on our own but any information may help.

That will be a special service, at extra cost.

If you’re going to rely upon having a Public IP address, you should probably be using a proper M2M Service provider…

Alternatively, rethink your system architecture so that it does not rely upon the device having a Public IP address!

Normally, in a Client-Server system, it is the Client which initiates connections to the Server - not the other way around. In that way, the Client doesn’t need a Public IP address.
This is how you can browse the web from a PC with a Private IP address!

Correct - as noted above, it’s a special service that you have to specifically request and pay for.

Even with public IP, the operator may block incoming connections.

You are right. We implemented this way too. But while modem connects to server as a client, the server has to wait for the modem to send any data or order to modem. When server needs to connect to modem anytime needed, it will have to wait for the modem to establish a connection. This one way communication style makes our application missing. In our case, we need both way both “from server to modem” and “from modem to server”.

This is also what i am afraid of. I think the operators have to consider easy solutions for M2M applications. At least they can give more information on their web sites.

That’s true - so you design your system such that the modem contacts the server frequently enough for this not to be a problem.
And/or you provide some alternative means for the server to “prompt” the client to connect…

This is why I say you should be using a proper M2M service provider :exclamation:

Or talking to T-Mobile’s specialist M2M team - this stuff is not going to be on their consumer website!

I learned that the sim operator is not T-Mobile actually it is Mobilcom.
My friend talked to the specialist of the operator and he told him that static ip/public ip costed 20.000 Euro :confused:
I think there is a misunderstanding. He also said that static/public ip is used by only big firms such as Banks. I dont believe that any application dont use “Server to Modem” connection logic. There must be a way of using this feature or there must be a way to obtain public ip with low cost.
We will try to talk them again. By the way, any M2M user in Germany would be helpful here.