Plan GPON and XGS-PON fiber links with confidence.
Calculate optical power budgets for your FTTH deployment. Select your SFP class, configure splitter stages, enter fiber distances, and instantly verify whether your link has sufficient margin for long-term reliable operation.
ITU-T G.984 — 2.5 Gbps down / 1.2 Gbps up
0.5 dB each
0.1 dB each
dB (aging, temperature)
Link Budget Analysis
21.9 dB
32 dB
10.1 dB
PASS-17.9 dBm
-18.4 dBm
30.3 km
78 Mbps ↓ 39 Mbps ↑
1:32 split
Link Diagram (downstream)
Loss Breakdown
* Upstream signal assumes typical ONU Tx power of 2.5 dBm at 1310nm. 1550nm (CATV/RF video overlay) is not calculated — it uses a separate EDFA transmitter, not the OLT SFP module.
| Split Ratio | Insertion Loss |
|---|---|
| 1:2 | 3.5 dB |
| 1:4 | 7.0 dB |
| 1:8 | 10.5 dB |
| 1:16 | 14.0 dB |
| 1:32 | 17.5 dB |
| 1:64 | 21.0 dB |
| Technology | Class | Min Tx Power | Optical Budget |
|---|---|---|---|
| GPON | Class B+ | +1.5 dBm | 28 dB |
| GPON | Class C+ | +3 dBm | 32 dB |
| GPON | Class C++ | +5 dBm | 35 dB |
| GPON | Class C+++ | +7 dBm | 38 dB |
| XGS-PON | Class N1 | +4 dBm | 29 dB |
| XGS-PON | Class N2a | +4 dBm | 31 dB |
| XGS-PON | Class E1 | +3 dBm | 33 dB |
| XGS-PON | Class E2 | +5 dBm | 35 dB |
An optical power budget defines the maximum amount of signal loss a PON link can tolerate between the OLT and the ONU while still maintaining a reliable connection. As specified in ITU-T G.984 (GPON) and ITU-T G.9807.1 (XGS-PON), the budget is determined by the OLT's SFP transceiver class — for example, a GPON Class C+ module provides a 32 dB budget.
Every component in the fiber path consumes part of this budget: the fiber itself (typically 0.35 dB per kilometer at 1310 nm), PLC splitters (the largest loss contributor), connectors, fusion splices, and environmental factors. If the total path loss exceeds the optical budget, the ONU cannot maintain synchronization and subscribers lose service.
Optical Margin = SFP Budget − (Fiber Loss + Splitter Loss + Connector Loss + Splice Loss + Safety Margin)
A positive margin means the link will work. A margin above 3 dB is considered safe for long-term operation, accounting for connector aging, temperature swings, and fiber bending. Between 0 and 3 dB is marginal — the link works initially but may degrade. A negative margin means the link will fail.
The calculator also computes maximum reach — the longest fiber distance where the margin stays above 3 dB given your splitter and connector configuration. This helps you quickly determine whether a customer site is within range.
Splitters are typically the largest source of loss in a PON link. A 1:32 PLC splitter introduces about 17.5 dB of insertion loss — consuming more than half the budget of a Class C+ SFP. Choosing the right split ratio is a trade-off between subscriber density and reach.
Many ISPs use a two-stage splitter architecture: a 1:4 or 1:8 splitter near the OLT (in the central office or distribution cabinet), followed by a 1:4 or 1:8 splitter closer to subscribers (in the fiber distribution terminal). This provides flexibility for subscriber growth while keeping losses predictable.
The SFP transceiver class determines your optical budget. For GPON deployments:
Urban FTTH with short distances and moderate splitting (1:16 or 1:32 under 5 km).
The most common choice. Supports 1:32 splits over 10–15 km — ideal for typical ISP deployments.
Long-reach or high-split deployments. Rural FTTH, 1:64 splits, or distances beyond 15 km.
Extreme-range deployments or heavily cascaded splitter architectures with maximum reach requirements.
For XGS-PON (10G symmetric), Class N2a (31 dB) and E2 (35 dB) are the most common. Both technologies can coexist on the same fiber using wavelength multiplexing.
Planning is only the first step. Once your FTTH network is live, optical power levels drift over time due to connector degradation, environmental changes, and accidental fiber damage. Continuous PON monitoring tracks Rx power at every ONU, alerting you when margins drop below safe thresholds — before subscribers experience issues.
NetSense NMS polls optical power levels every 30 seconds across all ONUs, detects partial PON failures automatically, and provides historical trend analysis to predict future degradation. Combined with smart alert correlation, you can catch fiber issues before they become outages.
Common questions about PON optical power budgets, splitter planning, and FTTH network design.
NetSense NMS tracks Rx power at every ONU with 30-second polling, detects partial PON failures automatically, and alerts you when margins drop below safe thresholds — before subscribers call.
Learn more: PON Monitoring · OLT Monitoring · SLA Calculator
