The integration of communication and sensing (ICAS) in optical networks is an effective design based on optical cable resources, and is in line with the development trend of communication system resource integration. The use of this integrated system will not only facilitate the intelligent operation and maintenance of optical networks and improve network quality, but will also expedite intensive acquisition of sensor data and innovation of new applications, effectively revitalizing the optical fiber assets of operators. In this paper, the key technologies of optical-network ICAS system are described. Sensing technologies based on the principles of Rayleigh, Raman, and Brillouin scattering are compared and analyzed. Combined with relevant research, several potential application scenarios of optical-network ICAS technology are discussed, thus providing ideas for the popularization and application of this technology.