ONT/ONU Terminals – End Devices for PON Fibre Optic Networks
ONT/ONU terminals offered by Senetic are designed for operators and installers building fibre optic networks, resellers, and IT departments launching fibre connections in commercial and public facilities. The choice of a terminal compatible with the operator's OLT and supporting remote management directly affects the stability of the connection and the costs of maintaining the network. In this guide, we discuss the most important selection criteria: PON standards, optical budget classes, connector types, operating modes, and management via OMCI.
How ONT/ONU Works
ONT (Optical Network Terminal) is an end device that converts the optical signal transmitted through fibre into an electrical signal used by local network devices – computers, VoIP phones, Wi-Fi access points – and performs transmission in the reverse direction. The terminal is installed at the customer's location, near the fibre entry point, in a place with access to power and providing easy service access.
ONU (Optical Network Unit) is a broader term that encompasses any termination device in a PON network – both serving a single subscriber and multiple users (e.g., an entire building).
In a PON network, the signal from the operator's device – OLT (Optical Line Terminal) – reaches multiple ONT/ONU terminals through passive optical splitters that do not require power. In the downstream direction, the OLT distributes data to all terminals on a given branch, and each terminal receives only the traffic intended for it. In the upstream direction, terminals transmit in time slots allocated by the OLT (TDMA), allowing multiple devices to share a single fibre. The terminal provides services through Ethernet ports, and in HGU models, also via Wi-Fi. Through the ONT, the operator can provide internet access, telephony (VoIP), and IPTV services.
Types of ONT/ONU Terminals
The choice of terminal type depends on the network architecture, end customer requirements, and the range of services provided at a given location. We distinguish two basic types of devices – SFU and HGU – available in many equipment variants.
SFU Terminals (Single Family Unit)
SFU is the simplest type of ONT terminal, intended for a single subscriber. It typically features 1–4 Ethernet ports, and in some versions, also an FXS port for connecting an analogue telephone in VoIP service. The SFU terminal does not have router or Wi-Fi functions – it operates in bridge mode, forwarding traffic to an external router, firewall, or switch, which are responsible for routing, NAT, and security. This solution is preferred by companies that want to maintain full control over their edge device.
HGU Terminals (Home Gateway Unit)
HGU combines the functions of an ONT terminal and a gateway in one device. It offers a built-in router with NAT, DHCP, and a firewall, LAN ports, most often Wi-Fi (including Wi-Fi 6 and newer standards), and FXS ports for voice services. HGU is the right choice when the operator provides a service package – internet, telephony, and IPTV – and the customer expects a complete solution without an additional router. Many HGU models can also be switched to bridge mode.
Variants of ONT/ONU Terminals
Regardless of type, ONT/ONU terminals differ in supported PON standard, number and throughput of ports, and operating mode (bridge or router). The choice of variant depends on the standard used by the operator, required bandwidth, and network management method. Before purchasing, it is essential to verify the terminal's compatibility with the operator's requirements and the OLT compatibility list.
How to Choose an ONT/ONU Terminal
The terminal parameters should be matched to the operator's infrastructure and the requirements of the specific location. When selecting, it is worth considering the following criteria:
- PON Standard
- Optical Budget Class
- Interfaces and Services
- Operating Mode and Management Model
- Connector Type
- Power Supply and Installation
Manufacturers of ONT/ONU Terminals Available
The offer of ONT/ONU terminals at Senetic includes devices from the following manufacturers, each addressing slightly different design needs.
Ubiquiti
Ubiquiti offers compact GPON terminals designed to work with the manufacturer's OLT and centrally managed from the UISP platform. The devices are characterised by small dimensions, low power consumption, and easy deployment, which facilitates network management with a large number of subscribers.
PLANET
PLANET is a manufacturer of networking solutions, whose portfolio includes ONT/ONU terminals with extensive port configurations.
TP-Link
TP-Link provides ONT terminals with a favourable functionality-to-price ratio. The devices offer GbE LAN ports and operate in bridge or router mode, with selected models also featuring Wi-Fi. This solution is suitable for projects where quick deployment and simple configuration are priorities.
Extralink
Extralink is a brand known for its wide range of fibre optic cables and accessories. In the terminal category, it offers SFU and HGU devices for GPON and EPON networks, with declared compatibility with popular OLT platforms. This is a practical choice for operators building large-scale networks where the cost of the terminal per subscriber is crucial.
Frequently Asked Questions
What is the difference between ONT and ONU?
ONT is a terminal designed for a single subscriber, typically installed in an apartment or office in FTTH architecture. ONU is a broader term – it encompasses any termination device in a PON network, including those serving multiple users, such as an entire floor of a building in FTTB architecture. In practice, manufacturers and operators often use both terms interchangeably. ONT and router are usually separate devices, although HGU terminals combine both functions.
What do classes B+ and C+ mean in an ONT terminal?
The optical budget class defines the range of attenuation that may occur on the path between the OLT and ONT while maintaining proper transmission. Class B+ includes attenuation of about 13–28 dB, which is sufficient for typical installations. Class C+ includes about 17–32 dB and allows operation over longer distances or with a greater number of split stages. Classes B+ and C+ pertain to GPON networks and must be supported by both the terminal and the optical module of the OLT.
Will every ONT terminal work with any OLT?
No. The cooperation of a terminal with an OLT requires compliance with the PON standard, optical budget class, connector type, and management protocol. OLT manufacturers also use their own OMCI extensions, so a terminal compliant with the standard may not always support all services. Before purchasing, it is essential to check the compatibility list of the terminal with the OLT used in the network, provided by the terminal manufacturer or operator.
Can an ONT terminal function as a router?
Yes, but only in the case of HGU terminals, which have a built-in router with NAT, DHCP, and a firewall, and often also Wi-Fi. The role of the ONT is to convert the optical signal into electrical, while the router's role is to manage traffic in the local network and distribute internet access. An HGU terminal with Wi-Fi combines both functions, eliminating the need for an additional device.
What is OMCI and what is it used for?
OMCI (ONU Management and Control Interface) is a protocol defined in ITU-T recommendation G.988, used for remote management of ONT/ONU terminals from the operator's OLT. It allows for service configuration, monitoring of optical parameters, collecting statistics, handling alarms, and updating software without physical access to the terminal. OMCI is used in GPON, XG-PON, and XGS-PON networks.
