The most common passive optical network (PON) standards in current use are Ethernet passive optical network (EPON) and gigabit passive optical network (GPON). GPON is the most widely deployed optical system in today’s fiber-to-the-home (FTTH) networks. Why choose GPON?
GPON network mainly consists of two pieces of active transmission equipment, namely optical line termination (OLT) and optical network unit (ONU) or optical network termination (ONT). GPON adopts two multiplexing mechanisms. One is in downstream direction, from OLT to users. Data packets are transmitted in an broadcast manner, but encryption (AES, advanced encryption standard) is used to prevent eavesdropping. The other is in upstream direction, from users to OLT. Data packets are transmitted in a time division multiple address (TDMA) manner. A single fiber from the OLT runs to a passive optical splitter which is located near the users’ locations. The optical splitter merely divides the optical power into N separate paths to the users. The optical paths can vary between 2 to 128. From the optical splitter, a single mode fiber strand run to each user.
There are several basic services provided by GPON system, such as triple-play, TDM and RF overlay services.
Most FTTH systems are so-called “triple play” systems offering voice (telephone), video (TV) and data (Internet access). To provide all three services over one fiber, signals are sent bidirectionally over a single fiber using several wavelengths of light. As triple play service is becoming popular, more and more cable operators upgrade their coaxial cable network to EPON/GPON network or triple play FTTH network to attract users and satisfy their diversified needs.
Time division multiplexing (TDM) is a method of transmitting and receiving independent signals over a common signal path by means of synchronized switches at each end of the transmission line so that each signal appears on the line only a fraction of time in an alternating pattern. With fixed upstream/downstream frame structure, periodic multiframes are transmitted in GPON line. So GPON can transmit TDM service with first-born advantage. OLT supports processing TDM service in Native and CESoP modes.
The RF (radio frequency) signal is distributed from a standard RF head-end through an E/O 1550 nm laser transmitter. The RF signal is transported by a separate fiber network to the PoP station. Optical protection of the primary and secondary signal routes is optional through a protection switch. A PON coupler combines the RF signal with the data traffic from the PoP OLT, which uses a different wavelength (1490 nm), putting both wavelengths on the same fiber PON and distributing them downstream through the splitters to the customer ONT/ONUs.
The clear advantage of PON networks generally is that a single shared optical fiber can support multiple users through the use of inexpensive passive optical splitters. In GPON networks, up to 64 ONTs can share one fiber connection to the OLT. This makes GPON an attractive option for service providers who want to replace copper networks with fiber networks, particularly in high-density urban areas. Other advantages of GPON networks include:
- GPON specifies management protocols required for triple-play services over the network, providing competitive all-service solution.
- GPON supports high-bandwidth transmission to break down the bandwidth bottleneck of the access over twisted pair cables, so as to satisfy the requirements of high-bandwidth services, such as IPTV and live TV broadcasts.
- GPON supports the long-reach (up to 20 km) service coverage to overcome the obstacle of the access technology over twisted pair cables and reduce the network nodes.
- GPON supports voice in native PCM/TDM format and data in Ethernet format, and employs wavelength division multiplexing (WDM) for downstream transmission.
- GPON offers twice the bandwidth of EPON/GEPON at its downstream speed of 2.5 Gbps, and it also supports twice the split ratio, offering maximum flexibility and cost advantages for service provider deployments.
- GPON was developed by the ITU-T to be an industry-wide interoperable standard.
Current and future demands for Internet access bandwidth have led to extensive deployment of FTTH technologies. Of these technologies, GPON provides the flexibility and cost advantages that service providers need to deliver services profitably to their subscribers. To support the increasing deployment of GPON in access networks worldwide, Fiberstore has developed full-featured ONT devices that can deliver a range of services. These ONT devices offer simple indoor installation in end-user residences and include additional features, such as support for VoIP, integrated WiFi, and CATV overlay.