The technique of variable frames with HEC (header error control) and frame length information is being studied widely for transporting IP packets efficiently in layer 2. The HEC and frame length information are used for frame alignment. This paper investigates the frame alignment performance and finds that the conventional frame alignment method allows a misframe, the framer declares out-of-sync falsely due to bit error corruption of the header, to occur frequently. We propose a method for reducing the misframe frequency that is based on forced two-bit error correction. We show that the proposed method has a much better performance than the conventional method.

The authors propose and describe an original feedback banyan switching network topology and control algorithm. This feedback banyan network prevents congestion even at high throughput. It does so by establishing a feedback route for the output packets from the output port to the input port of the banyan switching network. Input accommodated logical channels that do not encounter congestion within the switching network are output directly from the intended output port. Other packets are returned to the input port via the feedback route, then rerouted.>

Future subscriber loops will provide various services including broad-band video. Fiber optic technology is the key for introducing these services. The Electrical Communication Laboratories (ECL) of Nippon Telegraph and Telephone Public Corporation (NTT) have been promoting research and development on basic technology of fiber optic subscriber loops, and studying the ways to use fiber optic subscriber loops for new services. As one of the programs, a field trial of fiber optic subscriber loops was planned and conducted in the Yokosuka area from April 1980 until May 1981. This paper first describes fiber optic transmission technologies for subscriber loops. Then, the system configuration and experimental results of the Yokosuka field trial are presented.