Corrigendum 1 to Recommendation ITU-T G.709/Y.1331 (2016) corrects the following items: - Delete references to virtual concatenation (7, 15.9.1, 15.9.2.1, 15.9.2.2) - Add a note to describe that OSC signals designed prior to Edition 5.0 may not support the added OTSiA trail and payload overhead (15.1.8) - Change number of OPU3 Tributary Slots necessary to carry an ODUflex(IB DDR) signal from "4" to "5" in Table 7-9 (7-4) - Change the second instance of "OCh-FDI-P" to "OTSiA-FDI-P" in the first paragraph of clause 16.3.1 - Add a new paragraph to clause 16.3.2 that defines the OTSiA-FDI-O signal - Change "ODTUC.ts" into "ODTUCn.ts" in the third dash item in clause 20.4.1.1. - Change "2M-byte word" to "16M-byte word" in the last paragraph of clause 20.4.3.1 - Change the description of "Inputs = C14, II, DI, CRC" at the top left in Figure D.8 into "Inputs = C14, II, and DI for the 14 bit count" plus "Inputs = C10, II, and DI for the 10-bit count". Delete the text at the bottom of the figure; this text is part of figure D.9. (annex D.3)