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Cellular forums Home > Archive > Cellular GSM Technology > February 2007 > problems with data calls
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problems with data calls
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| Dear All,
I'm currently trying to get a GPRS module to make data calls. For this
I use a microcontroller that sends various AT commands to it. So to
make the data call, I send ATD followed by the mobile phone number I
want to make a data call to. The GPRS module that I'm using, has a
Vodafone UK SIM card.
Once the ATD command has been issued, it should be possible for me to
know when the receiving mobile phone is ringing as well as whether or
not the data call has been answered.
I'm able to get a ringing response back but even though I can see on
the receiving mobile that the data call has been successful, the GPRS
module that I'm using, doesn't return any connect message, once the
phone has been answered. For example:
ATD "number"
DIALING
RINGING
DISCONNECTED
I've been in touch with the GPRS module manufacturers and I'm told that
it might be a problem with my SIM card.
Does anybody have any explanation to why I'm not getting a connect
message back from my GPRS module?
Thanks in advance for your help,
Regards,
Alan
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| "Alan" <alan_ball007@yahoo.co.uk> wrote in message
news:1168880958.817892.159030@l53g2000cwa.googlegroups.com...
> Dear All,
>
> I'm currently trying to get a GPRS module to make data calls. For this
> I use a microcontroller that sends various AT commands to it. So to
> make the data call, I send ATD followed by the mobile phone number I
> want to make a data call to. The GPRS module that I'm using, has a
> Vodafone UK SIM card.
>
> Once the ATD command has been issued, it should be possible for me to
> know when the receiving mobile phone is ringing as well as whether or
> not the data call has been answered.
>
> I'm able to get a ringing response back but even though I can see on
> the receiving mobile that the data call has been successful, the GPRS
> module that I'm using, doesn't return any connect message, once the
> phone has been answered. For example:
>
> ATD "number"
> DIALING
>
> RINGING
>
> DISCONNECTED
>
>
> I've been in touch with the GPRS module manufacturers and I'm told that
> it might be a problem with my SIM card.
>
> Does anybody have any explanation to why I'm not getting a connect
> message back from my GPRS module?
>
> Thanks in advance for your help,
>
> Regards,
>
> Alan
>
Do I understand right: you are trying to establish a CS data connection from
the GPRS module to another GSM phone? If you are calling the mobile number
(not *99#), you are not using GPRS but your GPRS module most likely supports
CS data too.
When the other phone rings, how do you actually answer it? The phone number
you are dialling should not be the voice call number of the other phone
(again assuming the other phone was a GSM phone) but you should dial an
incoming data call number. If you don't have one, you may not have
subscribed for mobile terminated data calls.
The other end should have a true PSTN modem or a GSM modem answering for a
data call, otherwise you do not get any data connection and no "connect" at
the dialling end.
A few more details about your setup would be useful, and comments if the
above assumptions were right or wrong.
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| John Henderson 2007-01-15, 3:33 pm |
| Alan wrote:
> I'm currently trying to get a GPRS module to make data calls.
> For this I use a microcontroller that sends various AT
> commands to it. So to make the data call, I send ATD followed
> by the mobile phone number I want to make a data call to. The
> GPRS module that I'm using, has a Vodafone UK SIM card.
>
> Once the ATD command has been issued, it should be possible
> for me to know when the receiving mobile phone is ringing as
> well as whether or not the data call has been answered.
>
> I'm able to get a ringing response back but even though I can
> see on the receiving mobile that the data call has been
> successful, the GPRS module that I'm using, doesn't return any
> connect message, once the phone has been answered. For
> example:
>
> ATD "number"
> DIALING
>
> RINGING
>
> DISCONNECTED
>
>
> I've been in touch with the GPRS module manufacturers and I'm
> told that it might be a problem with my SIM card.
>
> Does anybody have any explanation to why I'm not getting a
> connect message back from my GPRS module?
>
> Thanks in advance for your help,
I presume you don't imagine that you're able to establish a GPRS
session with the other mobile.
As you're probably aware, a voice call is of no use to you for
attempting to pass data to or from a mobile. Because a data
call has OTA (over-the-air) characteristics incompatible with
those of voice calls, when establishing a CS (circuit switched)
data call you must tell all entities involved that you want to
make a data call.
When dialing mobile-to-mobile, you must do two things to achieve
this.
Firstly, you must make the OTA circuit from your mobile to your
network a data call. You're probably already doing this, as
you'd need to append a semi-colon to the end of the "ATD"
command (after the number) if you wanted to make a voice call
using "ATD".
Secondly, and independently, you need to specify that the OTA
leg from the called party's network to their mobile is also a
data call. You do this by calling their _data_ number, not
their voice number. Inevitably, the owner of that number will
need to pay extra for this additional service (the second, data
number for the SIM). Unfortunately, not all carriers offer
data calls, either for the making or the receiving, especially
for pre-paid services. And those who do may also charge extra
for the privilege of being able to make data calls (separately
from the ability to receive them).
We need to know that you've taken the above into account before
we look for other possible causes of the failed connection.
Having said all that, there's a remote possibility that you can
unexpectedly manipulate your way through these obstacles by
simply asking for an ISDN (V.110) connection and dialing a
voice number. So
AT+CBST=71
is always worth a try prior to dialing.
John
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| Björn Öman 2007-02-12, 3:33 pm |
| Try to end with a ";"
ATD "number" ;
/BÖ
"Alan" <alan_ball007@yahoo.co.uk> wrote in message
news:1168880958.817892.159030@l53g2000cwa.googlegroups.com...
> Dear All,
>
> I'm currently trying to get a GPRS module to make data calls. For this
> I use a microcontroller that sends various AT commands to it. So to
> make the data call, I send ATD followed by the mobile phone number I
> want to make a data call to. The GPRS module that I'm using, has a
> Vodafone UK SIM card.
>
> Once the ATD command has been issued, it should be possible for me to
> know when the receiving mobile phone is ringing as well as whether or
> not the data call has been answered.
>
> I'm able to get a ringing response back but even though I can see on
> the receiving mobile that the data call has been successful, the GPRS
> module that I'm using, doesn't return any connect message, once the
> phone has been answered. For example:
>
> ATD "number"
> DIALING
>
> RINGING
>
> DISCONNECTED
>
>
> I've been in touch with the GPRS module manufacturers and I'm told that
> it might be a problem with my SIM card.
>
> Does anybody have any explanation to why I'm not getting a connect
> message back from my GPRS module?
>
> Thanks in advance for your help,
>
> Regards,
>
> Alan
>
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| John Henderson 2007-02-12, 3:33 pm |
| Björn Öman wrote:
> Try to end with a ";"
> ATD "number" ;
By all means try it. But that's the syntax specified to request
a voice call, and not a data call. Refer GSM 07.07 for
examples.
John
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