Mapping six (6) eight (8) mbit/s signals to a sonet frame

[Means for Solution] A system (104) is provided in order to fill up SONET SPE (204, 300, 500, 600, 700) with a byte of digital information. A system has the data input port (1*6) constituted so that a payload signal which has payload information might be received. A system has the data-processing circuit constituted so that a byte of payload information might be transmitted in an order from a payload signal. A data-processing circuit decomposes payload information into a byte segment. A data-processing circuit carries out the map of the byte segment to 1 byte of SONET SPE for every byte. SONET SPE has a cell. In each sequence, it fills up with a cell for every line from the left downward from a top on the right. A method of filling up SONET SPE with a byte of digital information corresponding to a payload signal is provided similarly.