# GPON vs XGS-PON: Speeds, Wavelengths, OLT and ONU Explained

> GPON (ITU-T G.984) vs XGS-PON (G.9807.1): line rates, wavelengths, optical classes, split ratios, OLT/ONU choices and how both coexist on one ODN.

GPON (ITU-T G.984) shares 2.488 Gbit/s downstream and 1.244 Gbit/s upstream among all subscribers on a PON port, while XGS-PON (ITU-T G.9807.1) runs at about 9.953 Gbit/s in both directions. The two use different wavelengths, so both can run on the same passive fiber plant (ODN). GPON is still the most economical option for residential plans up to around 1 Gbit/s, and XGS-PON suits symmetrical business services, multi-gigabit plans and dense subscriber areas.

## How PON works: OLT, ODN and ONU/ONT

A passive optical network (PON) is a point-to-multipoint access network. One fiber port on the operator side is split optically to serve dozens of premises. GPON and XGS-PON use the same three building blocks:

- **OLT (Optical Line Terminal):** the active device in the central office or POP. It has the PON ports and uplinks, registers ONUs, applies VLAN and QoS policy and runs dynamic bandwidth allocation (DBA) to assign upstream time slots.
- **ODN (Optical Distribution Network):** the passive part of the network, made up of cables, splice closures, connectors and splitters. It needs no power.
- **ONU / ONT (Optical Network Unit / Terminal):** the customer-side device. In ITU-T terms an ONT is an ONU that serves a single subscriber, and in practice the two terms are used interchangeably. Common form factors are bridge-mode SFUs, HGUs with routing and Wi-Fi, SFP "ONU sticks" that plug into a router or switch, and MDU units for apartment buildings.

Downstream, the OLT broadcasts the same signal to every ONU, and each ONU processes only its own frames. Upstream, ONUs take turns transmitting in time slots granted by the OLT (TDMA). The capacity of a PON port is therefore shared by everyone connected to it. In both technologies, ONUs are configured remotely over OMCI, defined in ITU-T G.988.

## GPON vs XGS-PON at a glance

| Parameter | GPON | XGS-PON |
|---|---|---|
| Standard | ITU-T G.984 series | ITU-T G.9807.1 |
| Downstream line rate | 2.48832 Gbit/s | 9.95328 Gbit/s |
| Upstream line rate | 1.24416 Gbit/s | 9.95328 Gbit/s |
| Downstream wavelength | 1480–1500 nm (nominal 1490 nm) | 1575–1580 nm (nominal 1577 nm) |
| Upstream wavelength | 1260–1360 nm, or reduced 1290–1330 nm for coexistence (nominal 1310 nm) | 1260–1280 nm (nominal 1270 nm) |
| Optical budget classes | B+ (13–28 dB), C+ (17–32 dB) | N1 (14–29 dB), N2 (16–31 dB), E1 (18–33 dB), E2 (20–35 dB) |
| Logical split supported by the standard | Up to 1:128 | Up to 1:256 |
| Common split in the field | 1:32 – 1:64 | 1:32 – 1:64, 1:128 where the budget allows |
| Typical fiber distance | 20 km | 20 km, longer with a suitable optical class |
| Framing | GTC / GEM | XGTC / XGEM |
| ONU management | OMCI (G.988) | OMCI (G.988) |

Line rates are quoted before protocol overhead such as framing, FEC and line coding. Usable throughput is roughly 2.3 Gbit/s for GPON and around 8.5 Gbit/s for XGS-PON. Exact figures depend on configuration and vendor.

## Wavelength plan: why both fit on one fiber

GPON and XGS-PON wavelengths do not overlap. GPON uses 1490 nm downstream and 1310 nm upstream. XGS-PON uses 1577 nm downstream and 1270 nm upstream. Cable-TV style RF video overlay sits at 1550–1560 nm. Because of this separation, both technologies can use the same fiber and the same splitters at the same time.

Two details matter in practice:

1. **ONU filtering.** For coexistence, GPON ONUs need a wavelength blocking filter (WBF) that rejects neighbouring bands such as 1577 nm. Some older ONUs don't have one. Before you add XGS-PON, confirm that the ONU models already in the field comply with ITU-T G.984.5.
2. **Attenuation at 1270 nm.** Single-mode fiber loses more at shorter wavelengths. XGS-PON's 1270 nm upstream signal sees slightly more loss per kilometre than GPON's 1310 nm signal. On long routes that are already close to their budget, this difference counts.

## Split ratio and capacity per subscriber

The split ratio decides two things: how many subscribers share a port and how much optical loss the path has. The table shows the worst case, with the line rate divided evenly:

| Split | GPON downstream per subscriber | XGS-PON per subscriber |
|---|---|---|
| 1:16 | ~155 Mbit/s | ~622 Mbit/s |
| 1:32 | ~78 Mbit/s | ~311 Mbit/s |
| 1:64 | ~39 Mbit/s | ~156 Mbit/s |

These numbers assume every subscriber uses full capacity at the same time. Real traffic is statistically multiplexed, which is why operators can sell 1 Gbit/s plans on GPON ports. As more gigabit subscribers land on a port, however, busy-hour congestion shows up quickly. Per-port traffic graphs on the OLT are the most reliable indicator of when a port should move to XGS-PON.

The optical budget is the second limit. Each two-way split adds roughly 3–3.5 dB once splitter excess loss is included. GPON B+ optics with a 1:64 split on a long route therefore usually run out of margin. On such routes, use C+ optics for GPON or N2/E1 optics for XGS-PON.

## Coexistence and migrating from GPON to XGS-PON

ITU-T designed XGS-PON so it can be added to existing GPON ODNs. Operators typically use one of two approaches:

- **Coexistence element (CEx / WDM).** A passive WDM unit at the OLT site combines GPON and XGS-PON ports onto one feeder fiber. It is flexible, but it adds another loss point. That loss is typically around 1–1.5 dB (check the vendor's datasheet) and has to be subtracted from the budgets of both technologies.
- **Combo PON (Multi-PON Module).** GPON and XGS-PON optics and the WDM filter are built into a single OLT port module. Existing GPON ONUs and new XGS-PON ONUs work on the same port, and no separate passive unit is needed in the central office or in the field.

A typical phased migration:

1. **Validate the ODN.** Compare measured path losses with the XGS-PON classes, and add the extra attenuation at 1270 nm.
2. **Check splitter types.** PLC splitters are broadband across 1260–1650 nm. Older dual-window FBT splitters may show unexpected loss at 1270 or 1577 nm.
3. **Scale the uplinks.** A 16-port XGS-PON card can in theory carry 160 Gbit/s, so 10G uplinks quickly become the bottleneck.
4. **Move priority subscribers first.** Put high-tier and business customers on XGS-PON ONUs and leave everyone else on GPON.
5. **Update operations tooling.** Adjust OMCI profiles, TR-069/ACS configuration and the subscriber management integration for the new ONU models.

## Choosing an OLT and ONUs

- **Optical class.** Match the module class (B+, C+, N1, N2, E1) to measured ODN loss. Use your longest and most heavily split route as the reference.
- **Interoperability.** If the ONUs and the OLT come from different vendors, test OMCI compatibility, VLAN designs and IPTV multicast before rollout.
- **ONU LAN ports.** An XGS-PON ONU with only 1 Gbit/s Ethernet ports cannot pass the extra capacity on to the customer. Look for 2.5G or 10G LAN ports and Wi-Fi 6/7.
- **Dual-mode support.** Some XGS-PON ONUs fall back to GPON automatically when connected to a GPON OLT. That simplifies inventory during migration.
- **Large-scale management.** Bulk provisioning, alarm handling, dying-gasp notifications and API/SNMP integration directly affect operating cost.

We are the Türkiye distributor for [V-SOL](/en/brands/v-sol) GPON and XGS-PON OLTs and ONUs. They are available through [wi.com.tr](/en/solutions/wi-com-tr) together with WINET-branded SFP modules and splitters. For planning, [WiMap](/en/solutions/wimap) covers fiber route and duct design as well as splice and core matching. OLT → splitter → ONU topology and optical budget design are on its roadmap.

## GPON or XGS-PON: recommendations by scenario

| Scenario | Recommendation |
|---|---|
| Rural or low-density residential, 100–500 Mbit/s plans | GPON: lower ONU cost, mature product range |
| Urban residential where 1 Gbit/s plans are becoming standard | Keep GPON and migrate port by port with Combo PON |
| Symmetrical business lines, data center access | XGS-PON |
| Mobile cell site or Wi-Fi 6/7 access point backhaul | XGS-PON |
| New greenfield FTTH build | Start with XGS-PON or Combo PON |

For new builds, look past today's plan speeds and decide based on the traffic the ODN is expected to carry over its long service life. The most reliable comparison is cost per subscriber for both options, calculated with current OLT port and ONU prices.

## Frequently asked questions

### Is XGS-PON the same as XG-PON?

No. XG-PON (ITU-T G.987) is asymmetrical, with 10 Gbit/s downstream and 2.5 Gbit/s upstream. XGS-PON (G.9807.1) uses the same wavelengths but runs at 10 Gbit/s in both directions. Most 10G PON investment today goes into XGS-PON.

### Can existing GPON fiber be reused for XGS-PON?

Usually, yes. Fiber, splitters and connectors stay in place, and only the OLT ports and ONUs change. Before migrating, recalculate path loss against the XGS-PON class, including attenuation at 1270 nm and any CEx loss. Inspect and clean the connectors as well.

### Will an XGS-PON ONU work on a GPON OLT?

A standard XGS-PON ONU cannot talk to a GPON OLT, because both the wavelengths and the line rates are different. Only ONUs designed as dual-mode (GPON/XGS-PON auto-sensing) work with both OLT types.

### Does it make sense to sell 1 Gbit/s plans on GPON?

It works because of statistical multiplexing: subscribers rarely use full capacity at the same moment. The more gigabit subscribers share a port, though, the higher the risk of busy-hour congestion. If a port's peak-hour utilisation stays consistently high, reduce the split or move that port to XGS-PON.

### How is 10G-EPON different from XGS-PON?

10G-EPON is the IEEE 802.3av Ethernet PON standard. XGS-PON belongs to the ITU-T family. Speeds and wavelengths are similar, but framing, management and the available ONU ranges differ, and the two do not interoperate on the same PON port.

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Canonical: https://internetten.com.tr/en/knowledge-base/gpon-vs-xgs-pon-olt-onu-explained