A Gigabit-capable Passive Optical Network (GPON) is a fiber access technology that connects one port in a provider’s facility to many homes or businesses through unpowered optical splitters. “Passive” means there is no powered equipment between the provider’s site and the customer: the splitters simply divide the light. GPON is standardized by the ITU-T in the G.984 series and is often called a “Gigabit Passive Optical Network” informally. It is one of the most widely deployed ways to deliver fiber to the premises. Because every customer on a splitter shares the same port, GPON service is shared capacity, not a dedicated circuit.
At a glance
- One provider port and fiber are split, typically among 32 or 64 endpoints, with no powered equipment in between.
- Capacity is about 2.5 Gbps down and 1.25 Gbps up per port, shared by everyone on that port.
- Many residential and small-business fiber plans use GPON or its faster successor, XGS-PON.
- Shared, usually best-effort service: speeds can dip at busy times and SLAs are typically limited.
- Some large campuses use the same technology internally as a passive optical LAN.
What problem it solves
Running a separate fiber from a provider’s facility to every customer, with powered switches along the way, is expensive to build and maintain. GPON lets a provider run one fiber into a neighborhood or building and split it passively to many customers. Fewer fibers, no powered cabinets in the field and simpler maintenance make fiber to homes and small businesses affordable at scale.
For buyers, that is why fiber broadband offers can be much cheaper than dedicated internet access. The trade-off is sharing: the capacity is pooled among everyone on the splitter.
How it works
A GPON network has three main parts:
- Optical line terminal (OLT). Provider equipment in a central office or hub. Each OLT port serves one passive network.
- Optical distribution network. Single-mode fiber and passive splitters that divide one fiber among many endpoints. Common split ratios are 1:32 and 1:64, and typical reach is up to about 20 km.
- Optical network terminal (ONT). A small box at the customer site that converts the light into Ethernet, and sometimes Wi-Fi or phone ports.
Downstream, the OLT sends one stream to every ONT on the network, using one wavelength; each ONT reads only the traffic addressed to it. The standard supports encrypting that downstream traffic so customers can’t read each other’s data. Upstream, ONTs use a different wavelength and take turns, sending in time slots the OLT assigns, so their signals don’t collide.
The roughly 2.5 Gbps down and 1.25 Gbps up is shared by every ONT on the port. Providers sell plans below that total and rely on the fact that customers don’t all use their full speed at once, the same oversubscription principle used in cable and other shared networks.
Newer standards raise capacity. XGS-PON offers about 10 Gbps in each direction and uses different wavelengths, so providers can usually run it over the same fiber and splitters as GPON and upgrade customers by changing the equipment at each end. Even faster PON standards are also in deployment.
When it matters for buyers
- Comparing fiber quotes. A quote for “gigabit fiber” at a broadband price is often GPON or XGS-PON. Ask whether it is shared or dedicated, what the upload speed is, and what the SLA covers.
- Critical sites. For voice, contact centers, and sites that need committed speeds and fast repair commitments, a dedicated circuit is usually the better primary connection. Shared fiber makes a good, inexpensive secondary path, if it takes a different physical route.
- Small offices and branches. GPON-based business fiber can be a cost-effective choice for general internet and cloud use, paired with SD-WAN and a backup link.
- Large campuses. Some hotels, hospitals, universities and office campuses deploy passive optical LANs, using the same technology to replace many floor switches with splitters and ONTs. That is a design choice for your own network, with trade-offs in vendor choice and features.
Our internet access page covers the business internet options to compare.
Questions to ask vendors
- Is this service delivered over a shared PON (GPON or XGS-PON) or a dedicated fiber circuit?
- What are the download and upload speeds, and is any part of that speed committed?
- How many customers share the PON port, and how do you manage congestion?
- What SLA applies: availability, repair time, and any latency or packet-loss commitments?
- Is a static IP address available, and what does the ONT hand off to our router?
- Can we upgrade to a faster PON or a dedicated circuit later without new construction?
- Does this circuit take a different physical path from our other connection?
How it differs from fiber to the premises (FTTP)
Fiber to the premises (FTTP) describes where the fiber goes: all the way to your building rather than stopping at a cabinet and switching to copper. GPON is one of the technologies used to build it. An FTTP service may run over GPON, XGS-PON or a point-to-point fiber dedicated to your site. Knowing that a service is FTTP tells you the medium; knowing it is GPON tells you the capacity is shared and how much there is to share.
Problems this helps with
- Fiber internet that slows down at busy times
- Upload speeds far lower than download on a fiber plan
- Not knowing whether a fiber quote is shared or dedicated
- Running separate switches in every closet across a large campus
