Method and circuit to connect ATM/FDDI devices to ATM/SDH devices

摘要

The present invention enables a device using a Fiber Distributed Data Interface protocol in the Asynchronous Transfer Mode to communicate with another device using a Synchronous Digital Hierarchy protocol in the Asynchronous Transfer Mode, according to a method which is implemented in an associated conversion circuit wherein both devices uses different data formats and transmission speeds. When a FDDI receiver receives a data ATM cell, it detects the start_of_cell of the received data ATM cells and writes the data bytes into FIFO buffer at the same frequency. A counter is incremented each time a data ATM cell is stored in the FIFO buffer. As long as the counter is not equal to 0, the data ATM cell is transmitted byte by byte from the FIFO buffer to a SDH Transmitter on its request at another frequency. The counter is decremented each time a data ATM cell is transmitted. When the counter is equal to 0 then empty ATM cells are generated and transmitted to the SDH Transmitter on its request. Therefore, a multiplexer is required to multiplex data cells and empty cells, and to transmit them to the SDH transmitter with respect to the SDH link speed transmission. Conversely, the ATM cells received by a SDH receiver are stored in a dual port memory. In parallel, the header of the received ATM cell is decoded by an empty cell detection circuit. If the ATM cell is an empty cell, it is discarded from the memory. If the ATM cell is a data cell, the ATM cell is stored in the memory and a counter is incremented. As long as this counter is not equal to 0, one data cell is tranmsitted from the memory to a FDDI transmitter, preceded by a byte delimiter 'TT'. At the end of the data cell transmission, the counter is decremented. If the counter is equal to 0, which means that no data ATM cell has been received from the SDH link, then the FDDI transmitter sends idle byte 'JK' on the FDDI link.