I. Introduction
Even though distributed fiber optic sensing (DFOS) technology has been around for decades, and many applications, such as pipeline leakage detection [1], security monitoring [2], fire monitoring and prevention [3], and structure change reporting [4], have been developed based on fundamental sensing features of optical fiber: acoustic effect/vibration, temperature and strain [5], but now, the technology has a new play area: optical network infrastructure, where fiber used for communication traditionally will be used as sensing medium as well.