Abstract: In an Optical Transport Network (OTN) system, methods and devices are provided for communicating rate-adaptive OTUk frames. One method determines channel statistics for a fiber span connecting a transmitter to a receiver. A client input data rate is determined that is sufficient to meet a minimum communication threshold, and a rate-adaptive OTUk frame format is determined sufficient to carry the client input data rate. The format comprises a set of (n) allocated slots of client input data in a rate-adaptive OTUk frame comprising (m) slots, where (n) is less than or equal to (m). The method then fills the rate-adaptive OTUk frame, including (m?n) unallocated slots, using one of two processes. The first process fills the rate-adaptive OTUk frame with parity bits computed from client input data. The second process fills at least a portion of the rate-adaptive OTUk frame with and dummy bits.