Possible causes include: The connector attenuation of the optical fiber exceeds the attenuation threshold, or the optical fiber is bent seriously. If not, the original optical module is faulty. from transceivers Check “Alarm information” section for warnings, LOS Alarm means no inbound signal, execute display this to check shutdown mode, execute undo shutdown if necessary. The optical module type does not. Optical Signal Attenuation is the single greatest factor limiting the distance and performance of your network. This guide will demystify signal loss, explore its causes, and show you how. Description: Huawei switches must use Huawei-certified optical modules.