In Huawei's 10G GPON (Gigabit-capable Passive Optical Network) system, different optical wavelengths are used for upstream and downstream transmission to ensure bidirectional communication over a single fiber.
According to the ITU-T G.987.x series and Huawei's Access Network Technical Documentation, the wavelength plan for 10G GPON (XG-PON) is as follows:
Downstream (OLT # ONU): 1577 nm
Upstream (ONU # OLT): 1270 nm
This separation of wavelengths allows both transmission directions to occur simultaneously using WDM (Wavelength Division Multiplexing) on the same optical fiber, minimizing interference.
Huawei OLTs such as the MA5800 and EA5800 series follow this standard exactly - supporting 10G GPON (XG-PON) with downstream at 1577 nm and upstream at 1270 nm.Hence, the correct answer is 1577 nm.
References (Aligned with HCIP-Access V2.5 and Huawei Technical Sources):
HCIP-Access V2.5 Study Guide - "Huawei Campus Network Overview" Chapter, Section: PON Technology Overview Huawei 10G GPON (XG-PON) Technical White Paper ITU-T G.987.2: 10-Gigabit-capable Passive Optical Networks (XG-PON): Physical Media Dependent (PMD) Layer Specification Huawei MA5800 Product Description - 10G GPON Port Wavelength Specifications