The PD98411 NEASCOT-P40 is one of ATM-LAN LSIs and provides the functions of the TC sublayer of the SONET/SDH-base physical layer of the ATM protocol specified by the ATM Forum. Its main functions include a transmission function to map an ATM cell passed from an ATM layer to the payload of 155M-bps SONET STS3c/SDH STM-1 frame and transmit the cell to the PMD (Physical Media Dependent) sublayer of the physical layer, and a reception function to separate the overhead and ATM cell from the data string received from the PMD device and transmit the ATM cell to the ATM layer.