GPON: Gigabit Passive Optical Network
FiOS networks are built upon Passive Optical Networks.
BPON conforms to the ITU-T G983.1 specification which is capable of 622 Mbps download and 155 Mbps upload. Each BPON fiber is split using an optical splitter to serve 16 or 32 users.
GPON conforms to the ITU-T G984.1 specification. Verizon's GPON implementation uses Gig-E instead of ATM that was used with BPON. A 2.4 Gbps download speed coupled with a 1.2 Gbps upload speed. Each GPON fiber is split to serve 16 or typically 32 users. Verizon's next phase of GPON will support 64 users per fiber.
Verizon is building new networks with GPON technology, while existing BPON systems will only be upgraded when capacity limits are reached.