Tuesday 03 July, 2018 | RSS Feed

What are the differences among OLT, ONU and ONT?

by www.fiber-mart.com

What are the differences among OLT, ONU and ONT?


In recent years, Fiber to the Home (FTTH) is rapidly developing support technologies. The TOLT, ONU and ONT are now widely used in fiber network access in city. It can help efficiently reduce network construction cost, while simultaneously providing a guarantee on high bandwidth and high integration.


Optical Line Terminal (OLT)  


OLT (Optical Line Terminal) is the endpoint hardware device located at the central office in a Passive Optical Network (PON). The OLT contains a central processing unit, a gateway router, voice gateway uplink cards and passive optical network cards. The main functionality of the OLT is to adapt the incoming traffic (voice/data/video) from the metropolitan rings into the PON transport layer. It can transmit a data signal to users at 1490nm wavelength. That signal can serve up to 128 ONTs at a range of up to 12.5 miles by using Optical Splitters.


Optical Network Unit (ONU)


ONU converts optical signals transmitted via fiber to electrical signals. These electrical signals are then sent to individual subscribers. In general, there is a distance or other access network between ONU and end user’s premises. Furthermore, ONU can send, aggregate and groom different types of data coming from customer and send it upstream to the OLT. Grooming is the process that optimises and reorganises the data stream so it would be delivered more efficient. OLT supports bandwidth allocation that allows to make smooth delivery of data float to the OLT, that usually arrives in bursts from customer. ONU could be connected by various methods and cable types, like twisted-pair copper wire, coaxial cable, optical fiber or Wi-Fi.


Optical Network Terminal (ONT)


ONU and ONT are basically the same device – ONT is located at the customer premise, and ONU is located outside the home. ONU can be working in different temperature and weather conditions. It should resist water, winds and vandals. The ONU usually communicates with an optical network terminal (ONT), which may be a separate box that connects the PON to TV sets, telephones, computers, or a wireless router.




OLT is generally employed for terminal connected to the fiber backbone. An OLT has two primary functions:

  • Converting the standard signals use by a FiOS service provider to the frequency and framing used by the PON system;
  • Coordinating the multiplexing between the conversion devices on the optical network terminals (OLTs) located on the customers’ premises.


ONT (Optical Network Terminal), also ONU (Optical Network Unit)


ONT location,is at the customer’s premises. Its purpose is to use optical fiber for connecting to the PON on the one side, while interfacing with customers on the other side. ONT supports wide variety of interfaces, depending on requirements of customer:

  • Digital video formats
  • Analog video formats
  • ATM interfaces (155 Mbps)
  • DS3 or E3 telephone connections (44.736 or 34.368 Mbps)
  • T1 or E1 (1.544 or 2.048 Mbps)
  • Various Ethernet rates


To describe simply, OLT means Optical Line Terminal. ONU is the Optical Network Unit. ONT means Optical Network Terminal.OLT use fiber cables, adapters and others to connect with ONU and ONT, in order to build ODN (Optical Distribution Network).Both of ONU and ONT are client-side devices, no difference in nature, but if you have to distinguish, it can be seen from the name difference.ONT is the optical network terminal, applied to the end user, and ONU refers to the optical network unit, which is with the end user. There may be other networks.give a simple example, such as in a district, ONT is directly on the user’s home equipment, and ONU may be placed in the corridor, each user through the switch and other equipment connected to the ONU.




The development of fiber optic networks, ONT and OLT are indispensable components in the GPON network system. Fiber-Mart provides OLTs for both EPON and GPON systems. Any question pls feel free to contact with us. E-mail: [email protected]

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