(Passive Optical Network) An optical point-to-multipoint access network. There are no optical repeaters or other active devices in a PON, hence the name "passive." PONs are designed for local loop transmission rather than long distance and serve to bring fiber closer to the customer in order to obtain higher speed. PONs began in 1995 when a group of telecom providers organized the Full Service Access Network group (see FSAN).|
An optical line terminal (OLT) device resides in the telco central office or cable company head end. It generates or passes on SONET and DWDM signals via fiber to an optical network unit (ONU) in the field. The ONU provides the optical to electrical (O-E) and electrical to optical (E-O) conversion between the fiber and the copper wires that reach homes and offices in a "fiber to the curb" (FTTC) or "fiber to the neighborhood" (FTTN) scenario. When the optical line goes directly into the building for "fiber to the home" (FTTH), an optical network terminal (ONT) is used to terminate the fiber. Fiber to the home is also called "fiber to the premises" (FTTP).
APON, BPON, EPON and GPON
APON (ATM PON) was the first passive optical network and uses ATM for transport. BPON (Broadband PON) includes APON, Ethernet and video transports. GPON (Gigabit PON), which uses the SONET GPF frame, is designed to be efficient for packets as well as TDM. BPON and GPON are the ITU-T G.983 and G.984 standards respectively. EPON is the IEEE Ethernet standard for PONs.
PONs provide a way to bring high-speed fiber networks closer to the customer in the local loop.
BPON GPON EPON
ITU-T ITU-T IEEE
G.983 G.984 802.3
Supported B,C A,B,C PX10, PX20**
Downstream 155 Mbps 1.25 Gbps 1.25 Gbps
Speeds 622 Mbps 2.5 Gbps
Upstream 155 Mbps 155 Mbps 1.25 Gbps
Speeds 622 Mbps 622 Mbps
Maximum Number of ONTs
Based on Class and Distance
ODN CLASS 7 km 10 km 20 km
Class A 16 13 6
Class B 40 32 15
Class C 101 81 39
** PX10 & PX20 are similar to B and C