-
Notifications
You must be signed in to change notification settings - Fork 35
Usage: Decoding
Using the decode you can decode control channels and traffic channels carrying Full-Rate voice traffic.
You can use either a burst file as your data source specified with the parameter --bursts, or a cfile using the --cfile parameter. If you use a cfile source, you have to provide additional parameters: either an ARFCN with the -a option or a frequency with the -f' option, and a GSM band with the -b` option.
Also you have to specify the the mode of the channel you wish to decode using the -m option. For control channels you have BCCH for common control channels CCH, BCCH_SDCCH4 for slow dedicated control channels SDCCH combined with a CCH, and SDCCH8 for standalone SDCCH.
Furthermore you can specify the timeslot using the -t option. On SDCCH channels you can also restrict decoding to a given subslot using the --subslot option.
The decoded messages will be sent to UDP port 4729 using the GSMTAP protocol. Use Wireshark for inspection, you can start a preconfigured session using the GAT command wireshark.
If the transmission you want to decode is encrypted, you can provide a session key Kc using the -k option, and specify the algorithm using the -5 option, such that the transmission will be decrypted in the decoding process. Supported algorithms are A5/1 - A5/4
For decoding voice traffic you have to specify the speech codec of the voice transmission using the option -c. The codec is usually determined in the preceding Assignment command.
The decoded voice traffic is saved to a file, so you have to provide a file path for that using the -o option
The decode command supports printing messages in hex format to the command line using the option --print-messages, and printing bursts in binary format using the --print-bursts option.