The "digi_tlm.ini" file contains all required information for the APRS client such as WinAPRS to deal with the telemetry information broadcasted. The contens of the file is exactly what to be broadcasted. The telemetry frames are discribed in the APRS specifications.
Also DIGI_NED uses this file to configure it's telemetry function properly.
NOTE: every position in the file is important for the transmission of this information in a proper way. The APRS specified frame is composed here. This frame meets the APRS specifications. If you don't know what you are doing: just keep out. Or read the APRS specifications at http://www.tapr.org
:PE1DNN-2 :BITS.11111111,DIGI_NED Telemetry