Amendment 2 to Recommendation ITU-T G.709/Y.1331 (2012) contains extensions related to the: - addition of a low latency 1.25G OTU0 for deployment at the edge of an optical transport network (clauses 2, 3.2, 4, 11.1 and Annex G) - addition of OCh OH trail trace identifier and nominal central frequency overhead and transport of this overhead plus OCh FDI-P, FDI-O and OCI overhead within a PDU over a multi-vendor IaDI (clauses 10.1, 15.5, 15.5.4, 15.5.5)