This Recommendation describes a single-mode fibre with a chromatic dispersion coefficient (absolute value) that is greater than some non-zero value throughout the wavelengths larger than 1530 nm. This dispersion reduces the growth of non-linear effects that can be particularly deleterious in dense wavelength division multiplexing (DWDM) systems. At lower wavelengths@ the dispersion coefficient can cross zero@ but chromatic dispersion coefficient values at these wavelengths may be specified to support coarse wavelength division multiplexing (CWDM) systems that do not have significant impairments due to non-linear effects. These fibres were originally intended for use at wavelengths in a prescribed region between 1530 nm and 1565 nm. Provisions have been made to support transmission at higher wavelengths of up to 1625 nm and lower wavelengths down to 1460 nm. In clause 7@ Tables 2 and 3 distinguish the two main families of ITU-T G.655 fibre implementations that are supported by multiple vendors. The G.655.A@ G.655.B and G.655.C attributes tables can be used to define other implementations. The G.655.A and G.655.B attributes tables of the 2003 edition are not included in the current version of this Recommendation. The geometrical@ optical@ transmission and mechanical parameters are described below in three categories of attributes: ? fibre attributes are those attributes that are retained throughout cabling and installation; ? cable attributes that are recommended for cables as they are delivered; ? link attributes that are characteristics of concatenated cables@ describing estimation methods of system interface parameters based on measurements@ modelling@ or other considerations. Information for link attributes and system design are in Appendix I. This Recommendation@ and the different performance categories found in the tables of clause 7@ is intended to support the following related system Recommendations: ? ITU-T G.691; ? ITU-T G.692; ? ITU-T G.693; ? ITU-T G.695; ? ITU-T G.696.1; ? ITU-T G.698.1; ? ITU-T G.957 ? ITU-T G.959.1. This Recommendation contains a combination of fibre designs able to cover a broad spectrum of applications. Some re-arrangement might be considered in the future. However@ the system compatibility of fibres with different characteristics is not proved and@ in general@ their simultaneous use in one system might be questioned and should be agreed in advance between the user and manufacturers. The meaning of the terms used in this Recommendation and the guidelines to be followed in the measurement to verify the various characteristics are given in [ITU-T G.650.1] and [ITU-T G.650.2]. The characteristics of this fibre@ including the definitions of the relevant parameters@ their test methods and relevant values@ will be refined as studies and experience progress.