Abstract: A method and apparatus for generating first and second tree topologies for any source node in a network which can be represented as a node or an edge redundant graph, such that any node in the graph remains connected to the source node via at least one tree even after the failure of a node or an edge. This technique provides a recovery mechanism upon detection of a failure in a network.

Abstract: There is disclosed the architecture for an all optic network which employs a three level hierarchy using wavelength vision multiplexing. At the lowest level of the hierarchy are Level-0 all optical networks. The Level-0 networks are "local" broadcast networks each of which supports a plurality of access ports and each access port can hear all the local traffic transmitted by all other access ports in the same Level-0 network. Each Level-0 network shares wavelengths internally, but there is extensive reuse of wavelengths among different Level-0 networks. The next higher level, which is the intermediate level, Level-1, is essentially a wavelength router coupled with one or more of the Level-0 networks to provide a wavelength path to one or more directly connect Level-0 networks or, in combination with a Level-2 network, a light path to one or more Level-0 network outside itself.

Abstract: In a modulation system for sending digital symbols over a band-limited channel in accordance with a sequence of multi-dimensional points each composed of a plurality of two-dimensional modulation signal points, and each selected from an available alphabet of the multi-dimensional points by an encoder on the basis of a group of the digital symbols, the improvement which includes circuitry for accumulating the symbols of each group, and circuitry for thereafter selecting the multi-dimensional point for the group, and in which the available alphabet includes a plurality of subsets of the multi-dimensional points, and the subset from which the multi-dimensional point is selected for each group depends on the subset from which the multi-dimensional point is selected for another one of the groups.

Abstract: In a modulation system for sending digital symbols over a band-limited channel in accordance with a sequence of multi-dimensional points each composed of a plurality of two-dimensional modulation signal points, and each selected from an available alphabet of the multi-dimensional points by an encoder on the basis of a group of the digital symbols, the improvement which includes circuitry for accumulating the symbols of each group, and circuitry for thereafter selecting the multi-dimensional point for the group, and in which the available alphabet includes a plurality of subsets of the multi-dimensional points, and the subset from which the multi-dimensional point is selected for each group depends on the subset from which the multi-dimensional point is selected for another one of the groups.

Abstract: Apparatus for sending bits of information over a band-limited channel by modulating a carrier in accordance with a sequence of signal points drawn from a constellation of available signal points, in which the apparatus includes circuitry for accumulating groups of the information bits for encoding into the signal points, different groups having different numbers of information bits from a primary data source, and an encoder for encoding at least the bits of each said group into at least one signal point drawn from the constellation, the encoder being arranged to draw different available signal points with different probabilities.

Abstract: Double side band-quadrature carrier modulation signal points as mapped on the complex plane are drawn from an alphabet consisting of at least 8 points, and are set up in concentric rings each rotated by 45.degree. with respect to adjacent rings. Differential encoding is shown encoding the phase components of the transmitted signals.