Harald Welte laforge at
Sun Jul 25 18:09:08 UTC 2010


On Sat, Jul 24, 2010 at 01:29:23PM -0700, Dev Purohit wrote:

> I just want to elaborate it my question is  is there is some down link
> traffic between MS and a testing BTS , let say on ARFCN # 13 and Time slot 3
> this traffic channel is non encrypted A5/0 , is osmocom BB or airprob is
> become to capable to tune to that particular ARFC in this case ARFCN no. 13
> and time slot 3 and fetch the traffic channel data process it and convert it
> to pure voice or encode speech signals ( (CELP) or PCM format ) i
> specifically request to Harald as he is taking care for airprob also.

For airprobe: you will have to touch the source code to configure it correctly.
However, I am aware that somebody has  been working on this and will post
patches shortly.

For OsmocomBB: We have not worked a lot on TCH yet.  Dieter has some preliminary
work done and has stated he can see the TCH/F frames of unencrypted full-rate
calls in the downlink already.  All he needed to do is create the respective
multiframe scheduler tables and set the correct DSP task for Full-Rate TCH/F
processing (in the source code).  If you want this data on the host pc,
you will have to create a new HDLC/Sercomm channel and send it over to the PC.

On the PC, you will then run a GSM FR codec and convert it to PCM.

> i feel reception of  voice , then transition of voice is very basic
> requirement of any mobile software, then we can add on other features like
> channel hoping , cell handovers, other UI features , various multimedia and
> messaging features..   

well, that's your personal opinion.  To me, voice is relatively insignificant,
and it will more or less automatically fall into place once the other parts
are finished.  Only after we can establish encrypted, hopping channels to
a real-world BTS, we will have the need to switch to a TCH...

> thanks for your great work and wish to contribute at my best abilities..

Thanks for wanting to help us out!
- Harald Welte <laforge at> 
"Privacy in residential applications is a desirable marketing option."
                                                  (ETSI EN 300 175-7 Ch. A6)

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