unable to connect - CD didn't go high...???

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Garret - 17 Sep 2003 15:17 GMT

I'm trying to dial a Siemens Tc35 terminal (a gsm card) from a laptop
on a phone number "087 AAAAAAA". The laptop uses a vodafone mobile
connect card (a gsm/gprs card) as it's modem.

When I dial from a regular pc modem (landline) the connection is
succefully made to 087 AAAAAAAA

When I dial from the laptop I get the error message "unable to connect
to other modem - CD didn't go high"

I called the terminal direct from two phones:

when I dial 087 AAAAAAAA from a landline phone I get the terminal
answering and trying to handshake as expected. (as per regular modem
scenario)

when I dial 087 AAAAAAAA from my mobile phone, I get through to the
voicemail of 087 BBBBBBB! (as per gsm modem scenario?) I don't know if
redirects are set up, or even how they work, I didn't set up the
original sim cards.

Any ideas why I can't make a straight gsm - gsm connection? My laptop
call is getting directed to a voicemail because it's gsm?? I'm not
initialising my modem to make a data only call??

Any help appreciated

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John Henderson - 17 Sep 2003 15:58 GMT

> I'm trying to dial a Siemens Tc35 terminal (a gsm card) from a
> laptop on a phone number "087 AAAAAAA". The laptop uses a
[quoted text clipped - 20 lines]
> laptop call is getting directed to a voicemail because it's
> gsm?? I'm not initialising my modem to make a data only call??

How are you dialling from the laptop and GSM card? If you're
using some version of the "ATD..." command, what syntax are you
using? "ATD087AAAAAAAA<cr>" or "ATD087AAAAAAAA;<cr>"? The first
requests a data circuit, while the second requests a voice
circuit.

Is the laptop GSM card being given an initialisation string prior
to dialling, and if so, what?

Is the TC35 set up in the usual way for GSM data, with 2 phone
numbers? The usual (default) phone number is voice, and the
second number is the one to ring to specifically request a data
circuit on the BTS to receiver leg. The fact that you're
connecting from the landline modem strongly suggests that you're
dialling a data number.

Usually, the data circuit needs to be specified at both ends of a
GSM call - the dialling syntax has to be the "data" syntax, and
the number dialled has to be the data number. This is because
there're two distinct "air interface" legs to the circuit that
need to be set up as "data". Some carriers automatically set up
the second leg as data if the first leg is, but I believe they're
in the minority.

John

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John Henderson - 17 Sep 2003 22:53 GMT

Adding a few more comments to my previous reply:

A dedicated data number is not required to instigate a data call,
just (in most cases) to receive one. Any data-capable GSM phone
can make a data call, other things being equal.

Which brings me to the next point. Not all carriers support data
calls. And of those that do, some require you to subscribe to a
data plan in order to make such calls.

You mention that you're trying to make the data call from a
Vodafone service. At least here in Australia, phones with
Vodafone SIMs can make data calls "by default".

Lastly, you mention that you can establish a data call from a
landline modem to the TC35. This means that you might be able to
use the landline modem to test your GSM dialling setup.
Specifically, if you can establish a data call to that modem from
your laptop GSM card, then you should have no problems reaching
the TC35 also.

Without further info, it looks to me like the laptop modem is
requesting an air-interface voice circuit (which will have
characteristics incompatible with data transfer).

John

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