Help me with a project about connecting ISDN to GSM network

[dperez79]

www.ihub.com/gsm%20modems.htm

Hi,
In my new project I have to connect to computers by a ISDN network to a GSM network, I am looking for some gateway that I could use to maintain a GSM call and then send data to the other computer. I'm programming in VBasic, but I could do it in VC++.
Could I mix the GSM network the IP protocol?
Thanks.

 

[pisoiu]

modem isdn gsm embedded

Hi,
If you plan to use GSM for IP data, you better choose GPRS. It is easier and faster than standard 9600/14400 gsm modem.

 

[dperez79]

I can't use GPRS, it an railway application based on GSM-r.
Do you know any gateway?

 

[Antharax]

Re: ISDN + GSM

gateway?
What should that so called gateway do?

why don't you open a COM-port and call the gsm with your isdn line?

AT<some initializations depending on your connection needs>
ATD <number>\r
then you receive a "\x0D\x0ACONNECT 9600\x0D\x0A" string
(or BUSY or NO CARRIER or ...)

Now you just have a transparant line and can send any data you want over the connection.

It's not that difficult to talk with a modem

And if you want to connect 2 PC's just install an ISDN modem and a gsm modem driver on the PC's and you can configure a dial-up connection between the 2 PC's. When they're connected through a serial-port you probably can use a regular modem driver (I think nokia talks a strange protocol but there are a lot of gsm's with a plain AT-command interface available)
I guess you can talk tcp/ip to each other then if you install it.

Antharax

 

[Antharax]

Re: ISDN + GSM

Perhaps this helps
**broken link removed**

or use google to search for
gsm modem

 

[dperez79]

Thanks for your answers Antharax

I am wondering if I could implement the TCP in this connection via GSM.
Could you show me some example code of any application that talks with a modem ISDN?
Thanks again.

 

[eYe]

Can you use GSM as PPP/SLIP modem?

 

[Antharax]

Re: ISDN + GSM

If you find the correct drivers for your modem, you probably can use your GSM as a PPP or SLIP modem. PPP is a protocol for sending IP-packets over serial lines. When you make a connection with your gsm, you have a direct serial line so you probably can run any kind of protocol over it!
When you're using a gsm it is possible that you have to use a specific driver to be able to enter the PIN-code. I'm not sure about this when you're using a normal consumer gsm. I only have experience with embedded gsm's where the only interface is the control uart.



And when you want to write a driver/application which talks to the modem directly you can do it like this (you can easily test in using hyperterminal!!!):

Open a serial Port (preferably the one connected to your gsm/isdn modem ;-))

Check communication with the modem by sending "AT"
Modem should respond with "<0x0D><0x0A>OK<0x0D><0x0A>"
(in hyperterminal you won't see the <0x0D><0x0A> since they are Carriage Return and Line Feed characters)

You can send all kind of controll commands to your gsm/isdn modem
see https://www.traud.de/gsm/atex.htm for a reference
or search google for "AT Commands"

Some commands i use for GSM are
(all responses are enclosed by "<0x0D><0x0A>"):

ATE1
Now you see what you send, Echo back

ATE0
Now you don't see what you've send

AT+CBST=71,0
The answer should be "OK"
this puts the modem in data mode

Should we enter the Pin Code
AT+CPIN?
when the answer is "+CPIN: SIM PIN" then the pin code isn't inserted yet
AT+CPIN="xxxx" enters the pin and the answer should be "OK"
when the answer is "+CPIN: READY" then the pin code has been inserted

now we can dial out with
ATD+0123456789
"CONNECTED 9600" means you're connected with a 9600 baudrate.
"NO CARRIER" means the other side is no number (or a GSM which isn't registred to the network.
"BUSY" means the other side is making a call
...

Just install google on you PC and search for more information
And use Hyperterminal to try your stuff

 

[dperez79]

Now, I can connect with another computer via serial port, creating a transparent connection.
I'm wondering if I could include TCP to this connection.
Do you know some Activex control?

 

[Antharax]

Re: ISDN + GSM

I guess it's possible to use a socket to serial and serial to socket solution.
This should not be that dificult to write.
Then you can send the data you wanna send to the other side to localhostortYouWannaUse
Your socket to serial solution gets the data from the socket and forwards it over the serial line.
The other side receives the serial data and forwards it again to the correct destination socket.

You can implement an application which listens on the socket for data.
Get the data (this is without the TCP-IP) overhead and forwards it over the serial connection. This means that you loose all TCP-IP controll and guaranteed delivery so you'll have to implement this yourself over the serial link. It's like building your own proxy to forward stuff! You can forward anything you want (and don't need knowledge on what you're forwarding)

If you've got experience with driver programming you could write a modemdriver for your gsm. With some luck you can find one available. Then you can use your gsm as a normal modem and talk any protocol you install.

Have you (or someone else) tried to install you gsm as a modem?
I installed a generic modemdriver and it seemed to work (I had to put the AT+CPIN=xxxx as extra command but you can de-activate the ask for pin on your sim card which solves this issue.)

Antharax

 

[eeklac]

Re: ISDN + GSM

Actually, you can use the GSM as a modem, such that you can use it to dial-up to any ISP as a normal modem do.

However, you need to activate your sim card for the data transmission. Ask your mobile operator for help.

 

[dperez79]

Several RAS connections

Now, I have to do several RAS connections between GSM modems as clients and my server with a BRI ISDN line (2 Connections).
Could I get both connections with wXP in my server? or I must install W Server 2003.
I have only a phone number in my ISDN line, when I try the second connection, The Gsm modems can't call the ISDN modem. How could I solve this problem? Must I use ISDN MSN numbers for each connection?
Thanks.

 

[Antharax]

Re: ISDN + GSM

It works with a PRA card (32 ISDN lines) configuered with 1 number.
Perhaps you should configure your ISDN card or contact your provider?

each ISDN line appears as another COM port (meaning that you have 2 comports in your case)
The server should monitor all COM ports for incomming connections. When the first is in use, the modem will decide to send the call to the second. I've seen this working with 2 ISDN modems configuered on 1 number too (but i have no idea how to configure it)