Google Grotto Networking Huawei Ericsson This document describes requirements for, and the use of, the Generalized Multi-Protocol Label Switching (GMPLS) control plane in support of the Virtual Concatenation (VCAT) layer 1 inverse multiplexing data plane mechanism and its companion Link Capacity Adjustment Scheme (LCAS). LCAS can be used for hitless dynamic resizing of the inverse multiplex group. These techniques apply to Optical Transport Network (OTN), Synchronous Optical Network (SONET), Synchronous Digital Hierarchy (SDH), and Plesiochronous Digital Hierarchy (PDH) signals. This document updates RFC 4606 by making modifications to the procedures for supporting virtual concatenation. [STANDARDS-TRACK]