I have to design a passive optical network that uses WDM technology ( CWDM in particular ) for triple play broadband services including HDTV to residential and buisness customers.

There is also a hospital which provides long distance medical imaging and 2 colleges that has distance learning (live video broadcasts and video conferencing with other multi media options are used). 2 schools with wireless LAN , video conferencing, multimedia and educational video feed ( live and VoD) options.

A map was given that showed the area that the PON has to servuce and the max distance of the Central office to the end of the town ( furthest distance) is 10km.

the first step is to calculate the BW requirements of the users .

After that I am confused on what I should do. How do i determine what topology to use ( ring or star). I have read the ITU standards but they do not have established guidelines for CWDM PON.Do i use one fiber or more?. How do you get upstream and downstream data flow on the same fiber. for instances like the hospitals should a wavelength be given to them for use?.

how much bandwidth do a single wavelength (channel ) on a fiber support?

All link calculations and justifications for the equipment choosen has to be shown. The only hint that was given was that the transmitter / receiver / equpment specs should give you the losses and BER.
Help!!