Broadband passive optical network
The initial PON was standardized by the ITU-T as the ATM PON (APON) in 1995. This system uses ATM cells to transport traffic between the head end device (OLT) and the customer devices (ONT). The ATM cells are arranged into frames and assigned as timeslots (big T-1s) for upstream and downstream traffic. The nominal speeds for APONs are 622 Mbps in the downstream direction and 155 Mbps in the upstream direction. The provider community was not accepting of APONs due to the naming and association with ATM services (too complicated and inefficient). The name evolved to broadband passive optical network (BPON) to show the true nature of the service. Another reference from Lucent uses the term broadcast PON to reflect the broadcast nature of the system traffic.
BPONs use wavelength division multiplexing to support multiple channels for services. The downstream channel is assigned in the range of 1480 to 1500 nm while the upstream channel is in the 1260 to 1360 nm range. When video services are added to the mix, they are mapped to the 1550 nm channel.
BPONs support triple play services at the megabit range. Data services are offered on an ATM infrastructure with voice riding time division channels and video on its own wavelength. Video services are linear RF channels on the wavelength.
BPON FTTP Speeds and Feeds
Broadband PON is the PON system used to support the current FTTP architecture. The architecture is standardized in ITU-T recommendation G.983.3 and supports the interfaces below.
- Up to four phone connections
- An asynchronous data interface supporting up to 155 Mbps (OC-3) in the upstream channel and 655 Mbps (OC-12) in the downstream channel (enough bandwidth for a 100 Mbps Ethernet interface)
- An optical wavelength that can support digital video channels; video channels are a mix of linear programming and on-demand titles
The next generation standards (G.984.2) are complete. The Gigabit PON (GPON) architecture supports bidirectional speeds up to 2.4 Gbps and has a logical reach of 20 km.