Nima,
this was explained in the paper I presented at the 2nd .LRN Forum Madrid-05 and available in the proceedings
(http://www.dotlrn.org/conferences/Madrid05/):
Paper: http://dotlrn.org/file-storage/view/madrid05/05.pdf
Slides: http://dotlrn.org/file-storage/view/madrid05/alfanet.ppt
which is also linked from the Project Documentation area at aLFanet website (aLFanet architecture).
Olga