an error correction encoder inserts redundant parity information into a data stream to improve system reliability . the encoder can generate the redundant parity information using a composite code . dummy bits are inserted into the data stream in locations reserved for parity information generated by subsequent encoding . the error correction code can have a uniform or a non - uniform span . the span corresponds to consecutive channel bits that are within a single block of a smaller parity code that is used to form a composite code . the span lengths can be variant across the whole codeword by inserting dummy bits in less than all of the spans .