An ONU (Optical Network Unit) is a key device used in FTTH (Fiber to the Home) networks that implement PON (Passive Optical Network) technology. The ONU is located at the subscriber's premises and is connected to the central office OLT (Optical Line Terminal) via fiber optic cabling. The main components of an ONU include:
1. Optical transceiver: This contains a transmitter and receiver that convert electrical signals to optical signals and vice versa. It allows for bidirectional communication over a single fiber between the ONU and OLT. Different optical transceivers are used depending on the type of PON technology - GPON, XG-PON, EPON etc.
2. PON port: This port connects the optical transceiver to the single fiber that runs to the OLT. It contains a wavelength specific filter that separates downstream and upstream wavelengths.
3. Ethernet port(s): Most ONUs provide 1 or 4 Ethernet ports to connect to devices like computers, routers, IP phones etc. The ONU transparently passes Ethernet frames between the subscriber device and OLT.
4. POTS port: Some ONUs like the 1G ONU GPON with POTS provide a Plain Old Telephone Service (POTS) port to connect analog phones. This allows subscribers to make calls over the PON network.
5. CATV port: ONUs like the 1GE 1FE CATV WiFi ONU include a RF coaxial connector to pass cable TV signals to a set-top box or TV. This delivers Triple Play services over the fiber network.
6. WiFi router: Many ONUs integrate 4G/5G WiFi routers. This provides wireless connectivity for client devices like laptops, tablets, phones etc. without needing an external router.
7. Power supply: Supplies power to the ONU either via AC input or PoE. PoE ONUs receive power over the fiber cable from the OLT.
8. Splitter: Splits the downstream GPON signal into multiple ports to connect to Optical Network Terminals or analog phones.
9. Management port: Provides out-of-band management access to the ONU via protocols like Telnet, SSH, HTTP etc.
10. Antenna ports: Some ONUs with integrated antennas provide external antenna ports for better wireless coverage.
11. Backup battery: Provides power backup to the ONU during electricity outages to maintain continuity of services.
In summary, a modern ONU contains optical transceivers, PON port, Ethernet switching capabilities, and optionally CATV, voice, routing and WiFi functionality in a compact device. Advanced ONUs with PoE, antennas, extensive QoS,过滤and management capabilities enable operators to deliver high-speed broadband and multi-play services over PON networks. Careful selection of ONU features allows operators to customize services for each subscriber.
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