In PLDT Fibr, an ONU (Optical Network Unit) is the IEEE term for what is called an Optical Network Terminal in ITU-T terminology.

It is the fiber-optic equivalent of the usual modem used to decode signals into actual data. Many users collectively call the ONU as a modem, since it works similar to one. It is a term often interchanged.

How it worksEdit

In fiber-to-the-premises systems, the signal is transmitted to the customer premises using fiber optic technologies. Unlike many conventional telephone technologies, this does not provide power for premises equipment, nor is it suitable for direct connection to customer equipment. An optical network terminal (ONT) is used to terminate the fiber optic line, demultiplex the signal into its component parts (voice telephone, television, and Internet), and provide power to customer telephones.

Difference between DSL ModemEdit

  • As the ONT must derive its power from the customer premises electrical supply, some ONTs have the option for a battery backup, to maintain service in the event of a power outage. Unfortunately, ONTs provided by PLDT do not have battery backup. However, an Uninterrupted Power Supply (UPS) can be used for this purpose.
  • ONTs have provisions for IPTV, whereas earlier DSL Modems do not.
  • DSL Modems are currently capped at 10 to 20 mbps due to the limits of copper wires. ONTs have been known to go as high as 10 gbps, provided the endpoint supports such speeds.
  • ONTs are virtually invulnerable to interference, except for extreme fiber optic breakage. They do not possess the same limitations as copper wires, where they are vulnerable to crosstalk, electrical interference and heat stress, enabling higher speeds.
  • Unlike copper wires, ONUs use VOIP (Voice over IP) to provide telephony services. Copper wires provide telephony out of the box. This can be a problem if the ONT breaks down or in a power interruption.
  • PLDT landlines over Fibr have questionable results when it comes to Fax. In the same vein, POTS modems are known not to work in the VOIP system from the ONT.