Abstract: The present invention provides a solution for interleaving data frames, in a digital subscriber line system in which the data frames are divided into first and second codewords such that the first codeword comprises an even number of data bytes and the second codeword comprises an odd number of data bytes. With an interleaver depth (D) greater than a number of data bytes in the codewords (N), the codewords are written to a first matrix (51) in a predetermined manner (220), and read from the first matrix (51) in a predetermined manner (240 or 250) in which the data bytes of the codewords are delayed by a number of bytes. The codeword data bytes (defined by: B0, B1, . . . , BN−1) are delayed by an amount that varies linearly with a byte index, where byte Bi (with index i) is delayed by (D−1)×i bytes. Further, de-interleaving the interleaved data frames can be implemented by a reverse interleaving writing (340 or 350) and reading (320) in a second matrix (52).