Abstract: An improved computer network which utilizes the communication lines of a telephone system to provide connections between computing equipment in geographically mode area is described. The network utilizes a plurality of network units which are coupled by communication links within a telephone system. Each of the network units transmits user data and commands directed to other network units. Each of the network units monitors transmission errors within the telephone system. The data transmission rate within the network can be automatically varied in response to the observed error rate in a manner which reduces transmission errors within the network. When the transmission errors subside, the transmission rate is automatically increased to provide greater data throughput. The network includes features that allow it to be topologically altered without the need to send telephone technicians to the various locations serviced thereby.

Abstract: An apparatus for coupling data processing equipment to subscriber loops in a telephone system based computer network is disclosed. The multipoint communication network includes a plurality of network units with at least two of the network units comprising the apparatus in question. The network units are coupled to telephone system communication links. The network units transmit and receive digital data in a frame mode in which the data is organized into frames on the communication links. The network units also communicate with each other in a manner which allows the configuration and speed of the network to varied in response to the time of day and error rates observed on the telephone system communcation links.

Abstract: An apparatus for transferring digital data between time-domain multiplexed communication links of a telephone system which forms part of a computer network. A time-domain multiplexed communication link interface unit for transferring digital data between a first channel on a first time-domain multiplexed communication link and a second channel on a second time-domain multiplexed communication link of a multipoint communication network is disclosed. The multipoint communication network includes a plurality of network units with at least two of the network units comprising said time-domain multiplexed communication link interface units. The network units are coupled to telephone system communication links. The network units transmit and receive digital data in a frame mode in which the data is organized into frames on the communication links.

Abstract: An office control unit apparatus for transferring digital data between subscriber loops and the time-domain multiplexed communication channels of a multipoint telephone communication network is described. The office control unit receives digital data at its time-domain multiplexed input port and at its loop data input port. In addition to user data, the digital data can include network commands which are processed by the office control unit and acted upon if appropriate. The office control unit is assigned a unique address and can communicate with other network units in response to predefined commands. Data transmitted on the time-domain multiplexed communication channels can be encrypted and the office control unit can process that encrypted data, noting transmission errors and performing majority decision logic where appropriate. Data can be injected into the outgoing data stream at the time-domain multiplexed and loop output ports.

Abstract: An improved error correcting circuit that is adapted for correcting errors in data to be transmitted over communication links which require a minimum density of 1's to preserve timing on the transmission link is described. The circuit utilizes an error correcting code which converts a data word into two encoded words. Neither of the encoded data words is 0 for any of the possible values of the data word.

Abstract: Disclosed is an adaptive multijunction unit apparatus for multiplexing data streams between a master computer and a plurality of slave computers coupled through telephone system communication lines. The apparatus receives and processes both user data and network data which can include commands instructing the apparatus to change the operating modes of its various circuit components. For example, the adaptive multijunction unit apparatus can respond to commands to raise or lower its data transmission rate or to switch between dual channel and single channel data transmission. The apparatus includes a splitter/combiner function which copies data received from the master computer, onto output ports directed to multiple slave computers.

Abstract: An improved computer network multiplexer is disclosed. In a computer network based on the multiplexer, a master computer can communicate with a plurality of slave computers such that each slave computer receives all data sent by other slave computers to the master computer.

Abstract: A method and apparatus for modulating and demodulating information for bandlimited communication is disclosed. Serialized digital data is divided into equal segments which are arranged in parallel. Each data segment is converted into a digital representation of a modulating value (either frequency, phase, amplitude or some combination). Each such digital representation is then combined in a particular manner with a number of digital representations of different carrier frequencies. This overlapping, whereby each digital representation of a carrier frequency is combined with several digital words in such a way that the corresponding analog carrier frequency would be modulated, and each digital word so "modulates" several carrier frequency representations, is called shoring. The resulting digital signals are processed to construct a digital representation of an analog signal which is the superposition, or amplitude sum over time, of all the different modulated carrier frequencies.