This part of IEC 60793 is applicable to optical fibre categories B1.1, B1.2, B1.3, B2, B4, B5 and B6. A map illustrating the connection of IEC designations to ITU-T designations is shown in Annex I. 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 3; – particular requirements applicable to individual fibre categories or specific applications, which are defined in Annexes A to G. For some fibre categories (shown in the relevant family specifications), there are sub - categories 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.