Abstract: The invention provides a method and apparatus for providing hitless protection switching in a synchronous transmission system. A switching apparatus is arranged to receive data signals on at least two transmission paths and to output data from a selected one of said transmission paths. The apparatus is arranged to align the respective received data signals so that a selector mechanism can select between corresponding elements of the received data signals. This arrangement allows hitless switching to be performed since there is no loss or repetition of signal elements when switching occurs. In a preferred embodiment, data in respect of each frame of each data signal is stored and the selector mechanism selects between paths on a frame-by-frame basis by comparing quality information carried by the data signals. This arrangement offers a very low end to end Bit Error Rate (BER) performance.

Abstract: The invention concerns a switching apparatus comprising a low order switch subtended from a high order switch. In order to compensate for delays incurred by passing a data frame through the high order switch to the low order switch and delays incurred by the operation of the low order switch, the apparatus is arranged to advance the payload of a received data frame with respect to the fixed overhead of the data frame by an amount corresponding to the incurred delays. The low order switch uses the advanced payload to create an output frame, for sending to the high order switch, which is advanced with respect to the data frame that it receives. The apparatus, which is particularly suitable for use in SDH and/or SONET systems, obviates the need to provide an alignment apparatus, such as a VT/TU aligner between the high order switch and the subtended low order switch.

Abstract: In order to allow geographically separate SONET/SDH networks to be interconnected transparently without changes in clock content, payload and overhead, it has conventionally necessary to use dark fiber. For relatively low bandwidth operators this is prohibitively expensive. The present invention proposes a scheme using a mapping and virtual concatenation scheme to allow SONET/SDH to be carried in a bandwidth efficient manner over a SONET/SDH link whilst maintaining clock integrity.

Abstract: A high capacity switch for switching communications traffic. The high capacity switch has a plurality of differing granularity switching levels, each switching level having at least one switch node capable of performing a switching operation at the granularity of the switching level and at least two primary connections, each connecting one of the switching levels to another one of the switching levels. At one of the switching levels, at least one switch node is capable of switching communications traffic along at least one switch connection path established along one of the primary connections, and is also capable of switching communications traffic along at least one secondary connection to another switch node within the same switching level, such that each of the at least one switch connection paths established is filled to a predetermined level.

Abstract: The invention relates to message signalling in a synchronous transmission apparatus using redundant pointer bits as a signalling channel within the apparatus. The preferred embodiment uses one or more of the new data flag (NDF) pointer bits as a signalling channel. The invention has particular, but not exclusive, application in the field of performance monitoring in a path protected telecommunications network, where the pointer bit signalling channel is used to communicate between data ports which transmission path is selected.

Abstract: An interface for converting a variety of incoming digital signals into SDH/SONET format for transmission on a synchronous digital network, by identifying the line code of the incoming digital signal, without identifying the information for OSI layer 2 or 3 processing, i.e. format of each packet. Headers are used to encapsulate incoming packets, and enable packets to be discriminated at the receiver. Advantages of performance monitoring capability and transparency are combined. Identifying line codes enables a greater degree of error detection, than a bit based interface. Also synchronisation can be simpler since line codes for padding can be added or deleted more easily than adding or subtracting bits. The interface is semi-transparent in the sense that identification of line codes limits the interface to those formats that use identifiable line codes, but without limiting to a particular OSI layer 2 or 3 frame format.

Abstract: A synchronous digital communications network incorporating a number of nodes arranged in path protected rings and has two or more timing reference sources. The reference sources each allocated an artificial ranking of unique quality level values and these quality level values are transmitted as a section overhead message to provide a unique identifier for each source. Identification of the source to a node enables that node to be aware of a synchronization signal that has in fact originated from that node so as to prevent the setting up of synchronization loops. In a further embodiment the technique is extended to protection path identification for signals coupled between adjacent rings in a network having ring topology.

Abstract: In order to allow geographically separate SONET/SDH networks to be interconnected transparently without changes in clock content, payload and overhead, it has conventionally necessary to use dark fiber. For relatively low bandwidth operators this is prohibitively expensive. The present invention proposes a scheme using a mapping and virtual concatenation scheme to allow SONET/SDH to be carried in a bandwidth efficient manner over a SONET/SDH link whilst maintaining clock integrity.

Abstract: The invention provides a method and apparatus for providing hitless protection switching in a synchronous transmission system. A switching apparatus is arranged to receive data signals on at least two transmission paths and to output data from a selected one of said transmission paths. The apparatus is arranged to align the respective received data signals so that a selector mechanism can select between corresponding elements of the received data signals. This arrangement allows hitless switching to be performed since there is no loss or repetition of signal elements when switching occurs. In a preferred embodiment, data in respect of each frame of each data signal is stored and the selector mechanism selects between paths on a frame-by-frame basis by comparing quality information carried by the data signals. This arrangement offers a very low end to end Bit Error Rate (BER) performance.

Abstract: A multi-master serial bus system supporting, for example, up to 32 masters, and usable in applications requiring high-speed communications within a shelf. A plurality of nodes (2, 3, 4, 5) are interconnected by a highway (1) over which data is transmitted between the nodes. Each node has access control means (6) which ensures only one node accesses the highway at a time by means of an arbitration scheme. Data transmission involves an arbitration phase and a transmission phase and the highway comprises three lines, two of which are shared and perform respective functions in the arbitration and transmission phases (FIG. 1).

Abstract: Programmable power supplies are made responsive to beam-index and timing signals in order to automatically control the size and position of the display on a cathode ray tube. The high voltage power supply is also made programmable, responsive to video signal content, to reduce the energy stored in the high voltage circuits. Savings in energy consumption are also obtained by efficiently modulating the target screen of a beam-index type color cathode ray tube. Energy lost at the target screen is less than 10% compared to approximately 70% for a conventional color tube, an improvement factor of 7:1 or more. Taking advantage of the above features, a multi-color display apparatus is disclosed which employs dual excitation of a planar target screen to provide high resolution information in monochrome together with a wide range of colors for enhancement of contrast and for improved information discrimination.

Abstract: Programmable power supplies are made responsive to beam-index and timing signals in order to automatically control the size and position of the display on a cathode ray tube. The high voltage power supply is also made programmable, responsive to video signal content, to reduce the energy stored in the high voltage circuits. Savings in energy consumption are also obtained by efficiently modulating the target screen of a beam-index type color cathode ray tube. Energy lost at the target screen is less than 10% compared to approximately 70% for a conventional color tube, an improvement factor of 7:1 or more.

Abstract: Beam-index line-screen television display systems are disclosed for generating multi-color images throughout the size range from small direct view cathode ray tubes to projection type wall screen configurations. The image in the small screen display is generated by a scanning electron beam whereas the image generated in the large screen configuration is developed bY a scanning optical beam. In both cases the excitation of the image producing target screen is synchronized by beam-indexing features which utilize optical index signals transmitted across the target screen.