Apparently “boggits” over at Think Broadband believes this system is based on GPON, which if true would mean it works on a similar principle to how Virgin Medias cable network works, albeit with allot more bandwidth per UBR to play with. Verizon in the US appear to be using the same system, so I have no reason to doubt this.
http://en.wikipedia.org/wiki/Passive_optical_network