Sorry, but I have not understood your question so clearly.
The calculation I have made is for 1 cell. Each TRU has 8 channels (8 timeslots). The 1st TRU in the cell caries the BCCH (on the 1st timeslot), so 1st TRU may provide 7 traffic channels. Other TRUs in a cell (if any) provide 8 traffic channels per each.
Pls advise if it is not the answer for your question.