Recommendation ITU-T G.709.3 specifies 100G, 200G and 400G FlexO Beyond 100G (B100G) long-reach interfaces. The Recommendation specifies the structure using forward error correction codes with a higher coding gain suitable for longer reach applications, and references common elements from [ITU-T G.709.1] and FEC structures from [ITU-T G.709.2]. Edition 3 contains the following extensions to Edition 2.1: – Removal of FlexO-1-SC and FOIC1.k-SC interface – Move of OTUCn GMP mapping procedure to G.709.1