IEC 60794-2-21:2012 presents the detailed requirements specific to this type of cable to ensure compatibility with ISO/IEC 11801, Information technology - Generic cabling for customer premises. The requirements of the Family Specification IEC 60794-2-20:2008 are applicable to cables covered by this standard. Particular requirements detailed in clause 4 either define a specific option relative to the requirements of IEC 60794-2-20:2008 or define additional requirements. This second edition cancels and replaces the first edition published in 2005. It constitutes a technical revision. The main changes are: - Incorporation of the OM4 cabled fibre performance cateory; - Incorporation of the OS2 cables fibre performance category; - Incorporatino of the B6_a1 and B6_a2 bibre category as per IEC 60793-2-50:2008.