Abstract: In a data communications network comprising a series of nodes connected by optical fiber links providing direct bidirectional communication between adjacent nodes, and communication between non-adjacent nodes in both directions through the same set of intermediate nodes, failure of a single link or of a single node is overcome by protection switching to a standby transmisison loop, including a standby link connecting the head end and tail end nodes of the series. The network provides survivability while also taking advantage of the ability of add/drop multiplexers to allow reuse of bandwidth. Rapid switchover to the protection loop is achieved by providing each node with the capability of detecting and responding to adjacent faults and, in normal operation, maintaining a high-speed by-pass path for the protection loop through all of the nodes except the head end node.

Abstract: In a digital communications system comprising a plurality of modules plugged into slots, the backplane provides a private five-conductor data bus for each module slot so that data from the modules are transmitted over separate busses. Each of the data busses is split into separately driven branches extending to the right and to the left of its corresponding module, so that the drivers are located at the ends of the branches rather than connected to an intermediate point on a bus. Pairs of slots are connected through the backplane so that, instead of having one module in each slot driving a five conductor data bus, the system can alternatively have a double-bandwidth module in every other slot driving a ten-conductor data bus made up of two five-conductor busses. Clock and synchronization signals provided by control modules are conducted to device modules over separate conductors on the backplane.

Abstract: In a bridge for interconnecting local area networks, the decision on whether or not to forward a frame is based on the frame's destination address. This is made possible in a practical bridge by a hardware-based prefilter which causes an abbreviated representation of the destination address of each frame to be generated, and uses the representation to address a global address table or "GAT" memory. Each cell of the GAT memory may correspond to more than one destination address. If any destination address, corresponding to the cell addressed by the prefilter, is active on a remote local area network, the prefilter allows the frame to be forwarded for further filtering by a software-controlled processor. Otherwise, the frame is discarded.

Abstract: A packaging scheme for an expandable electronic system or sub-system unit which minimizes cabinet interconnection structure whereby electrical signal connections are bifurcated and may be made to and from electronic component carrying printed circuit boards, whereof, inter-board connections may be made off of one edge of each board while input/output interface connections may be made off of another edge of each board.