How the calculator works
ODN loss = fibre length × attenuation + splitters + connector pairs × loss + splices × loss + other elements + reserve, in both directions. Upstream (1310 nm in GPON, 1270 nm in XGS-PON) sees more fibre loss than downstream (1490 / 1577 nm) and is usually the worst case. The loss must stay inside the class window: above the maximum the farthest ONU cannot reach the OLT; below the minimum an ONU close to the OLT may overload.
| Class | ODN loss window | OLT Tx / Rx sensitivity | ONU Tx / Rx sensitivity |
|---|---|---|---|
| GPON B+ | 13–28 dB | +1.5 … +5 / −28 dBm | +0.5 … +5 / −27 dBm |
| GPON C+ | 17–32 dB | +3 … +7 / −32 dBm | +0.5 … +5 / −30 dBm |
| XGS-PON N1 | 14–29 dB | +2 … +6 / −28 dBm | +4 … +9 / −28 dBm |
| XGS-PON N2 | 16–31 dB | +4 … +8 / −30 dBm | +4 … +9 / −28 dBm |
| XGS-PON E1 | 18–33 dB | +6 … +10 / −30 dBm | +4 … +9 / −28 dBm |
| XGS-PON E2 | 20–35 dB | +8 … +12 / −32 dBm | +4 … +9 / −28 dBm |
Splitter loss
| Ratio | 1:2 | 1:4 | 1:8 | 1:16 | 1:32 | 1:64 | 1:128 |
|---|---|---|---|---|---|---|---|
| Typical loss, dB | 3.5 | 7.2 | 10.5 | 13.7 | 17.2 | 20.5 | 24 |
The ideal loss is 10 · log₁₀ N; a real splitter adds 0.5–1.5 dB of excess loss. Each doubling of the split costs about 3.3 dB — roughly 9–13 km of fibre. Two cascaded stages (for example 1:4 and then 1:8) lose 0.5–1 dB more than a single 1:32 but save feeder fibre.
Expected power
The calculator also shows what each end receives: ONU Rx = OLT Tx − downstream loss and OLT Rx = ONU Tx − upstream loss, with the margin above the receiver sensitivity. The overload check uses the maximum Tx power and leaves the reserve out.
Worked example
GPON B+ with 12 km of fibre, one 1:32 splitter, 5 connector pairs and 10 splices at typical values (0.4 and 0.08 dB): 4.2 + 17.2 + 2.0 + 0.8 = 24.2 dB — inside the 13–28 dB window with 3.8 dB to spare. The same network with a 1:64 split loses 27.5 dB and needs C+ or N1 optics.
More in the documentation: ODN classes and the PON link budget, PON wavelengths, PON transceivers.