The core of a AN-STM-ETH unit is the SDH processing block implemented in a single FPGA. Its functions include SDH mapping, pointer processing, multiplexing, framing, clock extraction, alarm detections. The Ethernet processing deals with the Ethernet interface functions, such as rate negotiation, CRC processing etc. The E1 interface block converts between TTL level and HDB3 signal format. FO interface converts STM-1 optical signal into electrical format for processing by the FPGA, and vice versa. Orderwire block allows maintenance telephone conversation to be established between two connected AN-STM-ETH units, or between the AN-STM-ETH and the AN-MSPP. A handset is used for orderwire instead of a full functional telephone set. As a CPE equipment, management on AN-STM-ETH is usually done through the management station connected to the AN-MSPP. When used in a point-to-point link, management is through the RS485 management port using TABS protocol. The power conversion block converts input -48V DC or 220V AC power supply to internal voltages for logical operations. | 
