Fibre ONU : definition, functions and types (GPON, EPON, xPON)
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If you follow the world of fibre optics, you will inevitably come across the acronym ONU. Presented as the "equivalent of the ONT" here, as landing-floor equipment there, or as a fibre modem elsewhere, the ONU is a vague term that covers several technical realities.
Yet choosing the right ONU is crucial when you want to : replace your operator's box with third-party equipment, deploy a POL network in a hotel, equip a RIP or simply understand what lies behind the "fibre box". This guide breaks down the definition, functions, types (EPON, GPON, xPON) and models available for each use case.
What is an ONU ?
ONU stands for Optical Network Unit. It is an optical terminal device located on the subscriber side (or in an upstream technical room) within a fibre access network. The ONU :
- Network side : optical interface (SC/APC or LC/APC) towards the splitter and the OLT
- User side : electrical interfaces (Ethernet RJ45, POTS RJ11, WiFi, USB, CATV)
- Bidirectional conversion : optical ↔ electrical continuously
- A/D and D/A conversion : digitises analogue voice signals for VoIP
- Multiplexing : simultaneously manages Internet, TV, VoIP, IoT over the same fibre link
Not to be confused with the ONT (Optical Network Terminal) : in practice, both refer to the same equipment, but the ONT is strictly at the subscriber's premises, whereas the ONU can be further upstream (landing floor, technical room).
Main functions of an ONU
| Function | Description |
|---|---|
| Triple Play | Internet + IPTV (multicast) + VoIP simultaneously over a single fibre |
| Broadcast reception | Receives downstream data sent by the OLT |
| Transmit buffering | Caches Ethernet data awaiting transmission, respects the TDMA window allocated by the OLT |
| OAM administration | Remote management by the OLT : diagnostics, configuration, firmware updates |
| AES encryption | Protects downstream data against eavesdropping by other ONUs on the same PON port |
| IGMP snooping | Filters multicast IPTV traffic : only replicates the requested streams |
| QoS | Prioritises VoIP, then IPTV, then Internet according to the operator profiles |
The ONU is therefore much more than a simple converter : it is an intelligent device remotely administered by the operator OLT.
Position of the ONU in FTTx
Depending on where the ONU is installed in the network, we speak of different FTTx variants :
- FTTC (Fiber To The Curb) : ONU placed in a street cabinet, serves several homes via twisted pairs
- FTTB (Fiber To The Building) : ONU placed at the foot of the building, serves the dwellings via Cat 6 Ethernet
- FTTN (Fiber To The Node) : ONU placed at a neighbourhood node, serves homes via VDSL2
- FTTH (Fiber To The Home) : ONU directly at the subscriber's premises (= ONT). The current French standard.
- FTTO (Fiber To The Office) : ONU at a professional's premises, often with a reinforced SLA
In France, the vast majority of fibre subscribers are on pure FTTH : the ONU (or ONT) is in the home, connected to the wall PTO via an SC/APC patch cord.
To better understand the various acronyms, see our article FTTP, FTTH, FTTC, FTTx explained.
ONU types : GPON, EPON, xPON
1. GPON ONU (ITU-T G.984)
ONU compatible with the ITU-T GPON standard, dominant in France, Europe and the USA. Data rates :
- Downstream : 2.5 Gbps shared between subscribers
- Upstream : 1.25 Gbps shared
- Wavelengths : downstream 1490 nm, upstream 1310 nm
- Splitting up to 1:128
2. EPON ONU (IEEE 802.3ah)
ONU compatible with the IEEE EPON standard, historically dominant in Asia. Data rates :
- Symmetric 1.25 Gbps
- Simpler to deploy (no complex service profiles)
- Common deployment in enterprise POL (IEEE ecosystem)
3. xPON ONU (dual-mode)
ONU compatible with both GPON and EPON, switchable via firmware configuration. Advantages :
- Shared stock for international operators
- Easy migration from an EPON network to GPON
- Maximum compatibility with different OLTs
For a deployment in France, favour GPON (compatible with major operators). For an international POL or an integrator, dual-mode xPON offers more flexibility.
Available Elfcam models
Our ONU range covers all use cases :
Recommended Elfcam ONUs
- V-SOL HGU xPON 4GE+POTS+USB 3.0+WiFi 6 — modern all-in-one FTTH
- V-SOL HGU xPON 4GE+POTS+USB+WiFi 5 — economical WiFi 5 version
- V.SOL ONU GPON/EPON 1GE+2.5GbE — multi-gig SFU for maximum throughput
- V-SOL xPON ONU 2GE+CATV+USB 3.0+WiFi — triple-play with CATV for hotels
- V-SOL xPON ONU 1GE+3FE PoE — reverse PoE to power the ONU via the LAN
- Elfcam ONU 1GE GPON/EPON SC/APC — entry-level SFU for test/lab
Focus on 3 key models
1. xPON HGU WiFi 6 (Ref 7011)
The top of the range : MediaTek WiFi 6 chipset, USB 3.0 for NAS sharing, 4 Gigabit ports, POTS VoIP. WiFi throughput up to 1800 Mbps. IPv4 and IPv6 support. Switchable dual GPON/EPON mode.
2. EPON ONU 1GE+1FE WiFi (economical)
Basic solution : 1 Gigabit port + 1 Fast Ethernet port + WiFi 802.11b/g/n up to 300 Mbps. Optical reach up to 20 km. Ideal for enterprise POL or educational deployment.
3. GPON ONU 4FE reverse PoE (Ref 7025)
Specialised : 4 auto-adaptive 10/100 Mbps Ethernet ports. Reverse PoE +12/+24 V DC function : the ONU can be powered via one of the Ethernet ports instead of a mains supply. Handy for high-mounted installations or weatherproof enclosures.
How to choose your ONU
- PON standard : GPON for France/Europe, xPON for flexibility
- Use : complete box (HGU) or simple terminal (SFU) behind a third-party WiFi 6 mesh router
- Throughput : 1 GE is enough up to a 1 Gbps subscription, 2.5 GE for multi-gig
- Built-in WiFi : WiFi 5 is fine, WiFi 6 recommended in 2026
- POTS : necessary if you keep an operator VoIP landline phone
- Number of LAN ports : 2-4 ports for home use, > 4 for POL
- Power supply : standard 220 V AC or PoE (for wall/outdoor installation)
- Operator compatibility : LOID, SLID, VLAN — check before purchase
Tip : HGU vs SFU + third-party router
For a non-geek consumer, the all-in-one HGU is the simplest : one box, everything works. For an advanced user who wants to manage their WiFi (mesh, OpenWRT updates) or their security (pfSense, OPNsense), an SFU 1GE+2.5GbE paired with a WiFi 6 Mesh AX3000 router or a dedicated firewall offers far more flexibility.
FAQ — Everything about the ONU
1ONU and ONT, what's the difference ?
2Does a dual-mode xPON work everywhere ?
3Does my HGU replace my operator's box ?
- Free (Freebox Ultra/Delta) : yes, third-party SFP ONT allowed
- Orange, SFR, Bouygues : not officially authorised (proprietary LOID)
- Alternative operators, RIP : often yes
4What is a reverse PoE ONU ?
5Can I use several ONUs on the same fibre ?
6Optical receive power of the ONU ?
- Minimum sensitivity : -28 dBm (GPON), -27 dBm (EPON)
- Saturation : -8 dBm
- Optimal operating range : -20 to -12 dBm
7Power consumption of an ONU ?
- Simple SFU : 3-5 W (equivalent to an LED)
- HGU WiFi 5 : 7-10 W
- HGU WiFi 6 with USB 3.0 : 10-15 W
- HGU Premium WiFi 7 multi-gig : 15-25 W
8Elfcam delivery and support ?
In summary
The ONU is the subscriber-side fibre terminal : it converts the optical signal into Ethernet, WiFi, VoIP and IPTV. Three main families : GPON (France, Europe), EPON (Asia, enterprise POL), dual-mode xPON (flexibility).
For domestic FTTH use, the all-in-one HGU WiFi 6 is the optimal choice. For professional or geek use, favour an SFU 2.5GbE combined with a WiFi 6 Mesh router. Always check compatibility with your operator before purchase, and complete the chain with patch cords, PTO and Ethernet cables.
