One possible source of randomness is the frequency offset correction loop
From
https://groups.google.com/d/msg/gr-gsm/gve4CcJubgw/3l_xZAr9AAAJ > It can happen if you use frequency offset correction loop in gr-gsm.
> Messages that control correction are currently asynchronous so timing of
> correction isn't currently deterministic. You can disable frequency
> correction loop if you have device that doesn't require it. For
> grgsm_decode you do this by not giving carrier frequency parameter.
Could you try the following command
grgsm_decode -c ./vf_call6_a725_d174_g5_Kc1EF00BAB3BAC7002.cfile -s $((100000000/174)) -m SDCCH8 -t 1 -k 0x1E,0xF0,0x0B,0xAB,0x3B,0xAC,0x70,0x02 -v --ppm -10 | grep "13 05 1e 02 ea 81 5c 08 11 83 94 03 98 93 92 49 81"
The expected result is
> 862363 1331349: 03 42 45 13 05 1e 02 ea 81 5c 08 11 83 94 03 98 93 92 49 81 2b 2b 2b