This part of IEC 60793 contains the general specifications for both multimode and single - mode optical fibres. Sectional specifications for each of the four multimode categories: A1, A2, A3, and A4 contain requirements specific to each category. Sectional specifications for each of the two single-mode classes, B and C, contain requirements common to each class. Each sectional specification includes family specifications (in normative annexes) that contain requirements for the applicable category or sub-categories. These sub-categories are distinguished on the basis of different fibre types or applications. The requirements of this standard apply to all class. Each sectional specification contains the requirements that are common to all the family specifications that are within it. These common requirements are copied to the family specification for ease of reference. Tests or measurement methods are defined for each specified attribute. Where possible, these definitions are by reference to an IEC standard - otherwise the test or measurement method is outlined in the relevant sectional specification. The following table defines the sectional specifications. The relevant family specifications are defined within the sectional specifications as normative annexes (see Tables 2 to 5) Annexes A and B summarizes the existing Fibres specifications.