Section overhead Called regenerator section overhead (RSOH) in SDH terminology: 27 octets containing information about the frame structure required by the terminal equipment. Line overhead Called multiplex section overhead (MSOH) in SDH: 45 octets containing information about error correction and Automatic Protection Switching messages (e.g., alarms and maintenance messages) as may be required within the network. The error correction is included for STM-16 and above.[9] Administrative unit (AU) pointer Points to the location of the J1 byte in the payload (the first byte in the virtual container).[10]