[Gta04-owner] Detect Call Hangup / Option Datasheet

Marcel Holtmann marcel at holtmann.org
Sun Jan 1 20:21:23 CET 2012

Hi Mickey,

> > 2) With the help of the ofono guys I added basic support for voicecalls
> > of the GTA04 to ofono (not upstream). Unfortunately this is quite
> > difficult to begin with, making and taking calls works just fine, but it
> > does seem impossible to detect if the call partner hung up, either
> > before accepting (=sending to voicemail and such) or after (hanging up a
> > successful call).
> > The reason is, that the AT interface never reports this (which it
> > should), so software can never known when someone hung up on you.
> > You could in theory work around that by polling with AT+CLCC or
> > something like that, but that's really uncomfortable and messy and the
> > ofono guys really aren't happy with such an approach (which I fully
> > understand).
> Well, it's the way how GSM 07.07 without vendor extensions works. I
> don't see anything more messy in there than the rest of the AT command
> spec ;)

voice call handling with standard 3GPP 27.007 is broken. Everybody knows
that and there is no point in sweet talking that.

That is why every serious voice modem manufacturer adds a vendor command
for call state notifications. And more important why they make ATD123; a
non blocking call where OK is returned right away. However it seems that
nobody told this to Option. Polling via CLCC is still nasty, but doable,
but having a blocking ATD123; is just pure stupid.

The Option modem is a horrible phone modem. So besides not having good
call handling support, the next real issue is that it only seems to
support one active PDP context at a time. Also I am not sure they ever
tested anything other than network connections.

And I have not even tried to do advanced call handling with any of the
Option modems. Mainly since there is no point if they do not even get
the basics right. They even messed up the CLIP and CDIP orders on simple
incoming calls as well. And here 27.007 is pretty clear on how it is
suppose to be done.

The TTY port assignment for voice call related unsolicited notifications
is also fully broken since they only come on the Application port. Even
if they got enabled on a different port. Combined with blocking AT123;
you are in a lot of fun here.

There are some other not so nice parts in 27.007, but the larger
majority is actually perfectly fine. And as soon as people stop trying
to parse AT commands with regular expression it becomes pretty nice and

I personally actually prefer an AT command based modem with 27.010
multiplexer. It was a dream to work with the IFX based modems.

> > Is there some other way I missed? Can you provide a newer firmware from
> > Option that fixes this?
> > 
> > 3) So far I only found the GTA04 handbook, no documentation to the
> > Option modem itself.
> > The AT-Commands in the GTA04 handbook are not really helpful, first of
> > all, there are very few of them, secondly many of them just don't work
> > (i.e. a lot of the option specific stuff).
> > There's really a lot of stuff that would be really needed or could be
> > very useful - and some documentation for other Option calls would be
> > great, too. Is there any documentation available? Can you get one from
> > Option to release?
> Can you give some specific examples for what you're trying to configure?
> There are some non-OPTION documents floating around on the net
> describing some of the qualcomm commands.

The Qualcomm commands are useless when it comes to Option cards. I would
actually prefer if Option starts fixing their stupid bugs in the
Qualcomm firmware.

For example we have a long standing issue with EF reading. For the
Option cards we need to fake the access rights to make it work. In a
real phone modem you need to handle all the EF properly and give the
host proper access to it. Compare this to MBM or IFX and you will see
the difference.

Since this card is Qualcomm based it suffers also from the a bug in the
CBS handling where you need to clear the topic list first before you can
add anything to it. I hope this is not intentional.

For the USSD handling it has some serious issues with its default
character set stuck in IRA. So we have to enforce GSM character set to
handle non-ASCII responses. And even that seems to work just by pure
luck. This is also common for Qualcomm based cards as it seems.

And I think the handling of SMS delivery receipts is still broken and
turns the message handling of modem into an undefined state.

As a conclusion, a direct contact with Option to get the firmware
actually fixed and extended to be used as a voice call modem is the only
way to go. Otherwise you have an expensive data only modem in a phone
form factor. Or you start looking at getting Telit or IFX based modems.



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