657 are ITU-T standardized singlemode fiber types used across long-haul, metro, ODN, and FTTH networks. 65x series is a commonly known single mode fiber standard category, which can be further divided into G. 655 are the two options commonly used. Each fiber type is engineered with different refractive index profiles, dispersion properties, and bending performance to support specific applications—from long-distance. Two commonly used single mode fiber specifications are G. 652 is the most widely deployed single mode. This Recommendation describes the geometrical, mechanical, and transmission attributes of a single-mode optical fibre which has the absolute value of the chromatic dispersion coefficient greater than some non-zero value throughout the wavelength range from 1530 nm to 1565 nm.