Digital data is transmitted in a block-based hyperframe that consists of N frames. Each frame carries multiplexed data from one or more user data channels and a control channel. Control channel information is unequally allocated among the N frames, the amount of information carried in each frame varying according to the frame's position in the hyperframe. All of the user data channels except one carry a predetermined number of transmission units in each frame. The excepted user data channel carries a calculated amount needed to round out the particular frame. Following multiplexing, a block encoder defines the frames and adds error detection or error correction information. The number of frames per hyperframe and the total number of transmission units for the control channel are available to a receiver, which can then demultiplex the hyperframe.