Fwd: Regarding grgsm voice traffic decoding for downlink hopping channel

[Prajakta Pandit]

Hello,

Good Afternoon!

I am Prajakta Pandit. I am currently working on gsm voice and sms decryption using grgsm tools. I apologise for bothering you.

I was able to do the SMS decryption on downlink. Currently I am facing issues with decoding voice traffic on hopping channel(TCHF).

I would be grateful if you could kindly provide me with your valuable suggestions and inputs.

Kindly find below the details of my experiment.

SDR: USRP N210

Capturing voice traffic: grgsm_capture.py -a 991 -s 2e6 -T 50 -c voice_hopping.cfile

(My sim card is latched to 928.4Mhz freq which gives me arfcn of 991)

Decoding BCCH: grgsm_decode -s 2e6 -c voice_hopping.cfile -m BCCH -t 0 -a 991

(In Immediate assignment --> SDCCH8 timeslot 1)

(In System Information Type 1 --> ARFCNs: 986,991,998,1000,1002)

(In System Information Type 2 --> ARFCNs: 980,983,985,990,997,1003,1007,1008,1016,1020)

After giving encryption key and encryption aalgorithm(A5/3):

(In Assignment command: TCH/F Timeslot:0 Training sequence:4 Hopping: Yes MAIO:0 HSN:36)

Later, I am trying to decode the TCHF channel to obtain the speech.au.gsm file.

I have edited the grgsm_hopping_example.grc file as per the information in System Information and assignment command. But I do not see any output.

I tried to use grgsm_channeliye tool to obtain individual arfcn file and gave those as inputs to the grc as source files:
grgsm_channelize.py -i voice_hopping.cfile -f 924.8e6 980 983 985 990 997 1003 1007 1008 1016 1020

It would be of great help if I could get some information as to how can I proceed or what is it that I am doing wrong.

I tried generating cfiles for each arfcn using the channelize script and also with get_channel script. But I am unable to see any output.

Please find attached the cfile for voice traffic in this mail for your reference.
TMSI-0x71753049
Kc-0xAFE6916D8BF0C47C​

 voice_hopping.cfile

​

Thank You for your time in advance and kindly do let me know if you need any further details from my end.

Warm Regards,

Prajakta

[moemu...@gmail.com]

try to change TCH code mode from FT to AMR