Recommendations for a data-only GSM/UMTS device in USB stick ff

Dr. H. Nikolaus Schaller hns at
Sun Nov 20 11:18:11 CET 2011

Am 19.11.2011 um 22:51 schrieb David Pottage:

> On 15/11/11 01:24, Michael Sokolov wrote:
>> Hello Om community,
>> Given that the GTA04 contains an off-the-shelf UMTS module and, if my
>> understanding is correct, truly off-the-shelf GSM/GPRS/UMTS modems in
>> the consumer USB stick form factor have been used during the
>> BeagleBoard prototyping phase for the GTA04, I've figured that someone
>> here might have some experience with / knowledge of these USB sticks,
>> hence me asking here...
> [snip]
>> * I need this device to be capable of placing old-fashioned data calls,
>>  not just Internet access.  By old-fashioned data calls I mean the
>>  arrangement where one dials a number from the mobile device with
>>  ATD<number> (no semicolon at the end, making it a data rather than
>>  voice call), and the number being dialed is a POTS land line with a
>>  plain old analog modem answering the call.  I want to be able to
>>  connect to my personal data center from remote locations bypassing
>>  the Internet.
> I think you will find that it is imposible to make data calls to an
> analoge modem. The reason is that GSM and it's sucessor standards are
> inherently digital, and are derived from ISDN telephone standards, so
> nothing in your phone or in the phone network will create tones that
> will be understood by an analogue modem.

The service he is looking for is called CSD:

There is indeed a (DSP based) modem in the network that converts your
digital data to analog tones. The same principle is used if you send DMTF
or a Fax through (digital) GSM. It will be transported through efficiently
encoded through digital networks until it comes close to the destination.

There, it is converted into analog signals (maybe PCM encoded) so
that your Plain Old analog Telephone or Fax modem can finally receive it.
And you can hear the tones or beeps.

It should be listed in the data sheet of the USB modem if it supports
this mode on the mobile end. And, the network operator should be
able to tell if he still operates such a gateway to analog/PCM phone

-- hns

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