PON is a point to multi-point (P2MP) passive optical network. GPON, a type of
PON technology, is defined by ITU-T Recommendation G.984.x. Figure 1 shows a GPON network.
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| IFgpon: GPON interface | SNI: service node interface |
| UNI: user to network interface | CPE: customer premises equipment |
- The optical line terminal (OLT) is an aggregation device located at the central office (CO) for terminating the PON protocol.
- Optical network units (ONUs)/Optical network terminal (ONTs) are located on the user side, providing various ports for connecting to user terminals. The OLT and ONUs are connected using an optical distribution network (ODN) for communication.
- The ODN is composed of passive optical components (POS), such as optical
fibers, and one or more passive optical splitters. The ODN provides optical
channels between the OLT and ONUs. It interconnects the OLT and ONUs and is
highly reliable.
NOTE:
The ODN network is passive, indicating that no optical amplifier or regenerator is deployed on the ODN network, thereby reducing maintenance costs of outdoor devices.
Why Is GPON Required
As the wide use of broadband services and fiber-in and copper-out development, carriers require a longer transmission reach, higher bandwidth, reliability, and lower operating expense (OPEX) on services. GPON supports the following functions to meet these requirements:- Longer transmission distance: The transmission media of optical fibers covers up to 60 km coverage radius on the access layer, resolving transmission distance and bandwidth issues in twisted pair transmission.
- Higher bandwidth: Each GPON port can support a maximum transmission rate of 2.5 Gbit/s in the downstream direction and 1.25 Gbit/s in the upstream direction, meeting the usage requirements of high-bandwidth services, such as high definition television (HDTV) and outside broadcast (OB).
- Better user experience on full services: Flexible QoS measures support traffic control based on users and user services, implementing differentiated service provisioning for different users.
- Higher resource usage with lower costs: GPON supports a split ratio up to 1:128. A feeder fiber from the CO equipment room can be split to up to 128 drop fibers. This economizes on fiber resources and O&M costs.
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