PON — passive optical network: introduction, types and applications

PON (Passive Optical Network) is the fibre optic network architecture on which the entire global FTTH deployment relies. Its principle — distributing the signal from a central point to numerous subscribers via fully passive splitters — revolutionised the economics of access networks. This introductory guide presents how PON works, its evolution from APON to 10G XGS-PON, and the criteria for choosing the right standard for your project.

What is PON?

A passive optical network is a fibre optic telecommunications network that links a central piece of equipment (the OLT) to multiple subscriber devices (the ONU) without any electrically powered component in the transmission path. The signal is distributed via passive optical splitters — purely mechanical components that physically divide the light beam.

The adjective "passive" is the key property of PON: between the operator's central office and the subscriber's home, there is no switch, no amplifier, and no equipment requiring a power supply or active maintenance. Only glass fibres and optical splitters occupy this segment — with a typical lifespan of 25 to 30 years without intervention.

The PON topology is described as point-to-multipoint (P2MP): a single fibre from the OLT is progressively divided via cascaded splitters to reach each subscriber individually. This is the opposite of a point-to-point (P2P) network where each subscriber would require their own dedicated fibre back to the central office.

A PON deployment can serve 64 subscribers with a single transport fibre instead of 64 — a 98% reduction in the fibre needed between the central office and the first distribution node.

PON vs AON: passive network against active network

The alternative to PON is AON (Active Optical Network) — a point-to-point network where each subscriber has a dedicated fibre and a powered active switch at each distribution node. Here are the fundamental differences:

In practice, PON dominates residential FTTH deployments and campus networks for its economic advantages. AON is reserved for critical links requiring guaranteed dedicated bandwidth — datacenter-to-datacenter links, industrial or military infrastructures.

The components of a PON network

A standard PON network comprises three categories of equipment:

The OLT (Optical Line Terminal) — the only active equipment on the operator side. Located in the central office or server room, it manages all transmissions: TDMA synchronisation, bandwidth allocation (DBA), ONU authentication and service routing (Internet, VoIP, IPTV). A 16-port PON OLT can serve up to 1,024 subscribers simultaneously.

Passive optical splitters (PLC) — the heart of the PON architecture. These dividers based on planar technology (Planar Lightwave Circuit) split the optical signal into N identical streams without electrical conversion. The most common configurations: 1×4, 1×8, 1×16, 1×32, 1×64. Two cascaded splitter levels make it possible to reach ratios of 1:128 (e.g. 1×8 + 1×16). Their lifespan is unlimited — no power supply, no wear.

The ONU / ONT (Optical Network Unit / Terminal) — active equipment on the subscriber side. It receives the optical signal from the fibre via its SC/APC port, decodes it and distributes it as Ethernet, WiFi, telephony or CATV signal depending on its configuration. It is the only active equipment that the subscriber (or installer) has to manage in the field.

Evolution of standards: APON, BPON, EPON, GPON, XGS-PON

PON technology has evolved over several generations since the 1990s, each new standard multiplying the available data rates:

APON — ATM PON (late 1990s)

The first PON standardisation, defined by ITU-T G.983. Based on the ATM protocol (Asynchronous Transfer Mode), it offered data rates of 155 Mbps or 622 Mbps. Now obsolete technology, replaced in all active deployments.

BPON — Broadband PON (early 2000s)

An evolution of APON, still ATM-based, but with data rates rising to 622 Mbps and support for additional services (CATV, Ethernet access, leased lines). Also obsolete, but still present in a few legacy infrastructures.

EPON — Ethernet PON (2004, IEEE 802.3ah)

A technological break: abandoning ATM in favour of native Ethernet. Symmetric 1.25 Gbps data rates, split ratio up to 1:64. Dominant in Asia (Japan, Korea, China), still deployed in Europe in some enterprise networks. Read our guide: ONU EPON GEPON — functions and types.

GPON — Gigabit PON (2004, ITU-T G.984)

The reference standard in Europe. Data rates of 2.5 Gbps downstream / 1.25 Gbps upstream, ratio up to 1:128, proprietary GEM protocol. Standard imposed by Orange, SFR and Bouygues for all FTTH deployments in France. Read our guide: GPON networks — architecture and deployment.

XG-PON / XGS-PON (2010–2016, ITU-T G.987 / G.9807)

The 10G generation of PON. XG-PON: 10G downstream / 2.5G upstream (asymmetric). XGS-PON: symmetric 10G — the version becoming standard in new deployments. It coexists with GPON on the same infrastructure thanks to distinct wavelengths. Freebox Ultra has used XGS-PON since 2024.

NG-PON2 (2015, ITU-T G.989)

Next Generation PON 2: combines 4 XGS-PON wavelengths to reach 40 Gbps per fibre. Deployments are underway in datacenters and 5G mobile networks (fronthaul). Still marginal in residential access networks.

PON standards comparison table

PON applications: FTTH, enterprise and campus

PON was designed for residential FTTH, but its qualities — low cost, passive infrastructure, long reach — have extended it to many other contexts:

Residential FTTH / FTTB — the historic and dominant application. Operators deploy OLTs in central offices and serve entire neighbourhoods via passive GPON networks. Each home has an ONT or a box integrating the GPON interface. In France: Orange, SFR, Bouygues and Free have all migrated to GPON/XGS-PON.

Enterprise and campus networks — PON advantageously replaces floor switches in large buildings. A central-rack OLT feeds each office, meeting room and common area via compact ONU. The result: zero active equipment to maintain in intermediate technical rooms.

Hospitality and serviced residences — each room has its own ONU (broadband Internet, telephony, IPTV), with centralised management from the OLT's EMS software. Passive fibre on the riser replaces dozens of floor switches.

Rural and public-initiative networks (RIP) — the 20 km reach of GPON makes it possible to serve remote villages and hamlets from a single central office without any powered intermediate equipment.

5G fronthaul — 5G mobile networks use PON links (XGS-PON, NG-PON2) to connect Radio Access Network (RAN) antennas to the base station. The bandwidth and low latency of PON make it a suitable medium for this critical use case.

How to choose your PON standard?

The choice of a PON standard depends on three main factors:

1. The geographical and operator context

In France and Europe, if you connect to a public operator's network (Orange, SFR, Bouygues, Free), the standard is imposed: GPON or XGS-PON. You have no choice — your ONU equipment must be compatible with the operator's OLT. In Asia, EPON remains common.

2. The data rates required now and in 5 years

For standard residential uses (streaming, gaming, remote work): GPON is more than enough in the short term. For professional applications (intensive cloud, remote backup, multi-site videoconferencing) or to futureproof the infrastructure: choose XGS-PON directly, which coexists with GPON on the same fibre.

3. The number of subscribers and the budget

A private network (building, campus, hotel) with fewer than 64 subscribers will be well served by a 4-port GPON OLT. Beyond that, an 8- or 16-port OLT. The cost of GPON OLT equipment is now very accessible — from €1,700 for a 4-port OLT capable of serving 256 subscribers.

Frequently asked questions — PON passive optical network