My experience with secure phones is that they work by starting a CSD call; there may be (and it sounds like there are) anomalies to this trend.

It is my current understanding that there is no CSD support in O.BTS; although I have never tried to make a CSD call I would expect it to fail since there are at least a few things missing that would be needed to make it run.

Although running a CSD call provides a lower bit-rate than the GSM vocoder would over the same channel, the CSD call guarantees nothing gets broken if the call crosses a boundary on the network that would re-code the audio (and thus jumble the bits as: [encrypted GSM] <--(vocoder)--> [ulaw] is not a bit-preserving reversible transformation.

Most old secure phone implementations run their own codec at a rate to fit within the envelope of a CSD call; with encryption of course.

I heard some of the modern Secteras and the like are going all-IP; but I'm a tad out of touch.

While many of these phones will connect to rouge networks and hope to carry traffic over them (after all, the GSM infrastructure is treated as an untrusted pipe on these guys) , cracking their connection-level traffic is a task not to be taken lightly.

//AA

On Tue, Dec 28, 2010 at 3:55 PM, David A. Burgess <dburgess@jcis.net> wrote:

I don't know about the Sectera, but I do know that some so-called
secure phones will attach to OpenBTS systems and make calls with no
trouble.  (The people who supplied those phones didn't understand why
I thought that was so funny.)


On Dec 28, 2010, at 2:44 PM, Mike Chapman wrote:

> Hi,
>
> Does anyone know if a Sectera Secure GSM cell phone will work with
> OpenBTS?
>
> Thanks,
>
> Mike
>
> Sent from my iPhone
>
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David A. Burgess
Kestrel Signal Processing, Inc.





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