A data encoding method for encoding a sequence of N input blocks of bits into an output block for transmission includes adding an L-bit control indicator, indicating whether the sequence contains any control blocks, and if so, producing an output block in which the order of data and control blocks is preserved by deleting a set of bits from the block-type field of at least one control block, adding to the sequence an N-bit position indicator indicating positions of data and control blocks in the sequence, and providing in bit positions of remaining bits of the block-type field of the at least one control block an indication of the type of that control block; wherein the position indicator bits are added at bit-positions such that, in a header-first transmission order of the output block, all data and control blocks succeed the position indicator bits indicating positions of those blocks.