Abstract: A succession of (k+n)-bit input words are coded for transmission over a (1 - D) partial response channel by applying n of the bits of each word to a trellis coder which, in turn, selects one of a plurality of 2.sup.m cosets from a predefined lattice, where M>n. A signal point, or "seed," is then selected as a function of both (a) the values of the other k bits and (b) the value, referred to as the "channel state", of the last pulse in the previous signalling interval, in such a way as to ensure that the signal point presented to the receiver is a point in the selected cost. Viterbi decoding on the cosets is then used in the receiver to recover the most likely sequence of transmitted signal points and, in turn, the (k+n)-bit input words.

Abstract: A personal computer or workstation is provided with an arrangement whereby the workstation keyboard and printer can be made to emulate the operation of a standard typewriter. The printer associated with the workstation is adapted to receive the workstation keyboard and to hold it in front of the platen and print head at an angle that approximates the angle of a standard typewriter keyboard, while software within the workstation, when called into operation, causes the printer to respond to the keyboard on a keystroke-by-keystroke basis.

Abstract: A combined electrical/lightwave connection arrangement provides electrical connections via conventional contact blades and ground post and a lightwave connection via a lightwave transmission line carried within the ground post.

Abstract: The UNIX.RTM. and MS-DOS.RTM. operating systems are supported in a multi-tasking computer. At the heart of the computer is a microprocessor having protected and non-protected modes. The computer includes special-purpose hardware which prevents the MS-DOS system and its applications, which execute in the non-protected mode, from interfering with the UNIX system and its applications, which execute in the protected mode. In particular, this hardware monitors addresses generated by the computer and, by selectively inhibiting the associated control pulses, prevents the MS-DOS system from, for example, writing in UNIX-system-allocated memory, or accessing I/O devices that the UNIX system is currently using. In addition, a context switching feature is provided whereby the user can select, via a keyboard operation, to have displayed on the computer video monitor at any given time the image generated from the current UNIX system screen data or the image generated from the current MS-DOS system screen data.

Abstract: The UNIX.RTM. and $MS-DOS sup R $ operating systems are supported in a multi-tasking computer. At the heart of the computer is a microprocessor having protected and non-protected modes. The computer includes special-purpose hardware which prevents the MS-DOS system and its applications, which execute in the non-protected mode, from interfering with the UNIX system and its applications, which execute in the protected mode. In particular, this hardware monitors addresses generated by the computer and, by selectively inhibiting the associated control pulses, prevents the MS-DOS system from, for example, writing in UNIX-system-allocated memory, or accessing I/O devices that the UNIX system is currently using. In addition, a context switching feature is provided whereby the user can select, via a keyboard operation, to have displayed on the computer video monitor at any given time the image generated from the current UNIX system screen data or the image generated from the current MS-DOS system screen data.

Abstract: An adaptive equalizer for data signals is allowed to start up and train in a wholly decision-directed mode but is precluded from converging to an incorrect state by inhibiting equalizer updating for equalizer output values which fall within a predetermined null zone.

Abstract: An integrated data processing and communication service is provided by a system which comprises a plurality of nodes interconnected via a packet-switched transport network. Each node includes a database processor and at least one node processor, with a number of terminals and hosts being connected to the latter via at least one front-end processor. Processes existing with each node processor are two types--application layer processes which perform "useful work" on behalf of the customers and the vendor of the service, and control layer processes, each of which manages, or provides some part of, the service itself. The processors are virtual memory processors and the program region of the virtual address space of each process includes both a process-specific image and shared image.

Abstract: Apparatus and a technique for echo cancellation is described in which the real and imaginary parts of an echo replica signal can evolve independently of each other. By removing the coupling heretofore found in cross coupled echo canceller structures, the echo replica obtained in conjunction with carrier-phase tracking circuitry can be a more exact duplicate of the real and imaginary components of a received echo containing signal. The echo canceller may include a plurality of subcancellers, each including at least four adaptive filters. Alternatively the filters within each subcanceller can be implemented by a suitably programmed digital signal processor.

Abstract: A multi-stage time division switch interconnects a plurality of processors that individually communicate over one or more channels at various signalling rates. Any processor may initiate a call and request that a connection be set by the switch. The switch assigns one or more time slots to the call and gathers or distributes data over the interconnecting channels through the utilization of polling techniques, thereby creating a virtual circuit through the combination of a time division switch and a polled communication line.

Abstract: In a system for communicating primary and secondary data from a transmitter to a receiver, each of a first plurality of primary data word values is communicated by the transmitter by transmitting an individual channel symbol associated with that value, while each of at least two other primary data word values are communicated by transmitting a selected one of at least two other channel symbols associated with that primary data word value. A predetermined one of the two channel symbols associated with the first primary data word value is transmitted only when secondary data having a first value is to be communicated, and a predetermined one of the two channel symbols associated with the second primary data word value is transmitted only when secondary data having a second value is to be communicated. In the receiver, both the primary and secondary data word values are recovered from the channel symbols thus transmitted.

Abstract: In a system for communicating primary and secondary data from a transmitter to a receiver, each of a first plurality of primary data word values is communicated by transmitting an individual channel symbol associated with that value, while at least one other primary data word value is communicated by transmitting a selected one of at least two other channel symbols associated with that one other value. The selected symbol is a function of the value of an individual secondary data word. In the receiver, both the primary and secondary data word values are recovered from the channel symbols thus transmitted.

Abstract: In a cryptographic communication system, a first encryptor transmits to a first decryptor and a second encryptor, co-located with the first decryptor, transmits to a second decryptor, which is co-located with the first encryptor. Each encryptor/decryptor pair is adapted to communicate using a selected non-self-synchronizing cryptographic mode. Whenever it is determined that synchronization between, say, the first encryptor and the first decryptor has been lost, both the first decryptor and the co-located, second encryptor are switched from the non-self-synchronizing mode to the self-synchronizing mode. This causes a loss of synchronization between the second encryptor and second decryptor since the latter is still operating in the non-self-synchronizing mode. Upon detection of this loss of synchronization, the second decryptor and the co-located, first encryptor are also switched from the non-self-synchronizing mode to the self-synchronizing mode.

Abstract: A multi-stage time division switch interconnects processors communicating over one or more channels on time division lines. One of the processors is designated as a common processor to provide the switching "mapping" information for the various stages of the switch sending the switching information to the memory and logic of each switched stage over dedicated channels which include channels on the time division line emanating from the common processor and time division channels which pass through several switches until the memory of the applicable switch is accessed.

Abstract: A geographically distributed multiprocessor system is implemented by locating groups of processors at nodes which are interconnected by way of a transport network and which are connected by way of local lines to customer terminals and hosts. Each processor supports a plurality of processes including certain process executing programs "customized" for the customers and other processes executing programs having "universal capabilities" which serve common needs of a plurality of customers. Processes communicate with other processes in the same processor by way of internal links and with other processes in other processors by way of combinations of internal links and external communication links. Interface processes exchange data between the internal and external links.

Abstract: A light-transmissive device, illustratively a glass plate, is disposed adjacent to a plurality of light-emissive pixel locations, illustratively the pixel locations of a cathode ray tube (CRT). The glass plate entraps light originating from the CRT at least when an object, such as a document, is placed on one of the surfaces of the light-transmissive device, the amount of light that is entrapped being a function of the reflectivity characteristics of the document. The pixel locations are successively energized and a light detection signal indicative of the level of the entrapped light is generated by photodetection circuitry disposed adjacent to the edge of the glass plate. A pixel signal is stored for each energized pixel location, that signal being a function of the level of the light detection signal during the time that that pixel location was energized. The ensemble of stored pixel signals can then, for example, be displayed.

Abstract: Voice signals are transmitted over a voiceband telephone channel with a high degree of security and good voice quality by applying to the transmission channel a first signal which includes digital information derived from the vocal tract response of the signal and a second signal which includes continuous information derived from the excitation component of the voice signal.