XGS-PON (10-Gigabit Symmetric Passive Optical Network) uses specific wavelengths for upstream and downstream transmission:
Downstream (OLT to ONU) : 1577 nm.
Upstream (ONU to OLT) : 1270 nm.
Why 1577 nm?
The ITU-T G.9807.1 standard specifies 1577 nm as the downstream wavelength for XGS-PON. This wavelength is chosen to avoid interference with GPON, which uses 1490 nm for downstream transmission.
Other Options :
1490 nm : Used for downstream transmission in GPON, not XGS-PON.
1310 nm : Used for upstream transmission in GPON, not XGS-PON.
1290 nm : Not a standard wavelength in PON technologies.
Thus, the correct answer is C .
References:
HCIA Huawei ACCESS Official Documentation , Chapter: XGS-PON Wavelengths.
ITU-T G.9807.1 Standards for XGS-PON .
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