Data call (aka CSD) with QtExtended

Al Johnson openmoko at
Wed May 6 00:31:10 CEST 2009

On Tuesday 05 May 2009, Franky Van Liedekerke wrote:
> On Tue, 5 May 2009 22:44:49 +0200
> Mile Davidovic <david.moko.comunity at> wrote:
> > Hello
> >
> > My understanding is next:
> > - qt extended have support for CSD but quite rudimentary (these words
> > are from qt extended documentation)
> > - sample qt application works fine with CSD but only first time (they
> > have problem with releasing resources)
> >
> > In general, OpenMoko is capable of working with CSD but my
> > understanding is that CSD (at least on Qt) is not preferable working
> > scenario.
> >
> > Regards
> > Mile
> Hi Mile,
> I'm sorry, but I'm not really familiar with CSD calls, could you
> ellaborate?

Circuit Switched Data, the original GSM data mode where the phone acts as a 
slow (9600) conventional modem. Later HSCSD increased the speed a bit by 
channel bonding. My k700i will let you select between analogue and ISDN modem 
behaviour, handy when calling an ISDN line as it doesn't need all the time 
consuming analogue negotiation when it connects.

In theory it should be really simple to use; just configure ppp as if you were 
connecting to a serial modem. gsm0710muxd or equivalent may complicate this 
slightly, but I wouldn't expect it to be any worse than the current use of ppp 
for GPRS. That said, I haven't tried it.

While GPRS is faster CSD has other advantages which may be critical in some 
cases. You can call into it, which may not be possible with GPRS as it is 
often hidden behind NAT. CDS also has lower, predictable latency whch made it 
the transport of choice for a GSM cryptophone.

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