GPON networks use specific wavelengths for upstream and downstream transmission:
Downstream (OLT to ONU) : 1490 nm.
Upstream (ONU to OLT) : 1310 nm.
Optional CATV overlay : 1550 nm (used for video services).
Why 1490 nm?
The ITU-T G.984.x standards specify 1490 nm as the wavelength for downstream data transmission in GPON networks. This wavelength is chosen for optimal performance in fiber-optic communication.
Other Options :
850 nm : Used in multimode fiber for short-distance communication, not in GPON.
1310 nm : Used for upstream transmission in GPON.
1550 nm : Optional wavelength for CATV overlay, not for standard downstream data.
Thus, the correct answer is A .
References:
HCIA Huawei ACCESS Official Documentation , Chapter: GPON Wavelengths.
ITU-T G.984.x Standards for GPON .
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