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 document 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. Table 1 shows a map from the IEC designations to the ITU-T recommendations. The table also provides the normative annex in this document that contains the detailed specification as well as the name used to describe this fibre type in IEC 60793-2-50:2015. The ITU-T recommendations as well as the IEC categories/sub-categories within each recommendation are given. In some cases@ as for Recommendation G.652@ a given IEC designation maps to multiple categories in the ITU-T because the ITU-T categories are distinguished by cabled fibre attribute (PMDQ) performance which are not distinguished in the IEC fibre specifications.