A data segmentation circuit is disclosed for use in DS3/STS-1 mapping. The data segmentation circuit uses a circular data buffer to store data for mapping. A recirculating barrel shifter is used for extracting data from within the buffer. A counter moves the barrel shifter window zero, one, five, or eight bits to align the barrel shifter output as necessary to extract a next datum for a next payload envelope location. Data stuffing is then performed. Control circuitry for providing throttling and bit stuffiing as required in an STS-1 information payload is disclosed.