This part of IEC 60793 is applicable to optical fibre categories B-652, B-653, B-654, B-655, B-656 and B-657. A map illustrating the connection of IEC designations to ITU-T designations is shown in Table 1. These fibres are used or can be incorporated in information transmission equipment and optical fibre cables. Three types of requirements apply to these fibres: general requirements, as defined in IEC 60793-2; specific requirements common to the class B single-mode fibres covered in this standard and which are given in Clause 5; particular requirements applicable to individual fibre categories or specific applications, which are defined in Annexes A to F. For some fibre categories (shown in the relevant family specifications), there are subcategories that are distinguished on the basis of difference in transmission attribute specifications. The designations for these sub-categories are documented in the individual family specifications.