Question about Trellis/Viterbi in GRC


in the course of a student research project i am going to realize a slim
implementation of the WLAN 802.11a standard (consists of
scrambler->trellis->interleaver->ofdm-modulator) based on gnuradio and

in this case i tested (as a start) every single step for itself. so i
get the scrambler, interleaver and ofdm-modulator working.

and here is my problem:
the idea is, to read out a text-file, send it over trellis encoder then
over trellis viterbi an write back a text file with same content.
i tried to build the following flow graph:
[file_source]->[trellis encoder]->[trellis viterbi]->[file_sink]
unfortunately the text_out file has not the same content as the text_in
file (i am not even able to open the text-file).
besides i do not know, what i must insert in the fsm line in
configuration window.
is there any documentation about generating fsm files and which one i
have to enter for my application?

i hope someone had the same problem and could help.

best regards
christoph b.