The SDH/STM-1 trunk card is a high density multiplex/demultiplex trunk card that demultiplexes the SDH/STM-1 trunk down to 1890 DS0 channels at 64 Kbps each. The SDH/STM-1 trunk card allows the Cisco AS5850 to interface to a SDH network at 155 Mbps with a single mode, intermediate reach fiber.