Abstract: Measuring the programming resistor in a data jack by placing the resistor in an AC voltage divider circuit via a transformer. An AC voltage (preferably generated by the modem's own transmitter circuitry) is applied to the voltage divider circuit, and an AC voltage measurement (preferably made by the modem's A/D converter) provides the resistance of the programming resistor. Matching the low-pass filter impedance characteristic of a local loop with a network having a matching low-pass filter characteristic, while also compensating the received signal with a compensation network having a high-pass filter characteristic, to reduce the frequency dependent gain effects caused by the matching network and/or the local loop.

Abstract: A digital communications device with a removeable cartridge is disclosed for programming the functions and primary operations into a digital communications device as for example a modem. Examples of programmable functions include data transmission rates, interface protocols and/or full duplex mode of operation.

Abstract: In general the invention features mapping a digital data sequence into a signal point sequence for data transmission over a channel characterized by a non-ideal response, by selecting the signal point sequence from a subset of all possible signal point sequences based on the digital data sequence and upon the response, all possible signal point sequences in the subset lying in a fundamental region of a filtered trellis code, the fundamental region being other than a simple Cartesian product of finite-dimensional regions.

Abstract: A digital data sequence is mapped into a signal point sequence for transmission, by selecting the signal point sequence from a subset of all possible signal point sequences based on the digital data sequence, all possible signal point sequences in the subset lying in a fundamental region of a trellis code, the fundamental region being other than a simple Cartesian product of finite-dimensional regions. In another aspect, a digital data sequence is mapped into a sequence of signal points for transmission, by specifying a class of possible sequences based on the digital data, and selecting the signal point sequence from the class, the selection being based on the respective average powers of the possible sequences of the class, the selection being based on not only a fixed-length block of the digital data.

Abstract: An apparatus for identifying a first tone and a second tone present in a dual-tone signal, the first tone being selected from a group of tones located within a low band and the second tone being selected from a second group of tones located within a high band, the low band and the high band each spanning a frequency range no greater than f.sub.0 wide, the apparatus including a first filter for isolating and downconverting the portion of the dual-tone signal falling within the low band so that it lies within a low frequency range extending from -f.sub.0 to F.sub.0 ; and a second filter for isolating and downconverting the portion of the dual-tone signal falling within the high band so that it lies within the low frequency range.

Abstract: Information encoded by data compression (or another data encoding technique, e.g., encryption, requiring synchronization between the encoder and decoder) is transmitted over an unreliable network by checking for transmission errors after decoding. If an error is detected, the encoder is reset, using a reset protocol which may operate over an unreliable reverse channel by using a timer to generate further reset requests when the receiver does not acknowledge them in a timely fashion.

Abstract: This invention is suited for a packet network that carries bursty data. A mechanism is coupled to an edge node for coding bursty information into a digital format at either a first coding rate of a second coding rate which is less than the first rate. A mechanism senses traffic overload of one or more intermediate nodes carrying the bursty informaton. A mechanism which is responsive to the overload sensing mechanism causes the coding mechanism to switch from the first rate to the second rate while a traffic overload is sensed. Thus, network demand requirements are reduced and the overload will be alleviated.

Abstract: A method and apparatus is provided for determining the lag of a long term filter in a code excited linear prediction speech coder. An open loop lag is first determined using an autocorrelation function. The open loop lag is then utilized to generate a limited range over which a closed loop search is performed. The range for appropriate values includes lags that are harmonically related to the open loop lag as well as adjacent lags.

Abstract: A first set of plated-through holes in the printed circuit board (PCB) are covered by a protective solder mask on the solder side of the PCB while a second set of plated-through holes are exposed. Electrical components are disposed on the component side with leads inserted in the second set of holes. Solder is prevented from flowing into the first set of holes during wave soldering by the mask covering. Conductive pins designed for press fitting into the first set of holes are inserted therethrough to define connecting pins on each side of the PCB following wave soldering. This permits both a wave soldering and press fit operation to be accommodated.

Abstract: A digital decimation filter for receiving a stream of input digital samples at an input sample rate, and for delivering a corresponding stream of output digital samples at a different output sample rate stores a plurality of input digital samples, derives samples of the output stream from the stored input digital samples, and makes an output sample available for inclusion in the output stream at all times, whereby the output sample may be delivered with a selectable phase.

Abstract: A modem for receiving data sent from a remote device over a communication channel by using a single carrier modulated signal, the modem including a receiver for receiving the modulated signal and for receiving a line probing signal sent by the remote device over the channel, the receiver being capable of receiving the modulated signal over any one of a plurality of frequency bands; a line probing processor for measuring characteristics of the channel based upon the received line probing signal; and a selector for selecting one of the plurality of frequency bands, said selection being based upon the measured characteristics of the channel, said selected frequency band to be used for receiving the modulated signal from the remote device.

Abstract: Apparatus for generating a (running digital sum) sequence of digital signals X.sub.k and/or a (partial response coded) sequence of digital signals Y.sub.k, K=1, 2, . . . , such that Y.sub.k =X.sub.k .+-.X.sub.k-l, L and integer, in which the Y.sub.x signals are a sequence in a given modulation code. In one aspect, the signals Y.sub.k are chosen to be congruent to coset representatives specified in accordance with a modulation code, a plurality of code constellations are used, and at least one constellation includes both a point with a positive sum of coordinates and one with a negative sum of coordinates. In another aspect, the signals X.sub.k are chosen to be congruent to a sequence of alternate (precoded) coset representatives. In other aspects, the Y.sub.k alphabet signals are evenly spaced, and a selectable, e.g., an optimal, tradeoff between S.sub.x and S.sub.y is made. An N-dimentional modulation code is generated as a sequence of one-dimensional signals.

Abstract: The frequency of a clock for a receiving terminal is controlled based on a predetermined clock frequency of a terminal that produces a continuous stream of data at a predetermined frequency for transmission to the receiving terminal over a communications network of the kind in which data is transmitted between the terminals in discrete packets that are delayed on the network by possibly different amounts. Arrivals of packets that are sent to the receiving terminal are detected, time intervals between the arrivals of the successive packets are determined, and the time intervals are processed to generate an estimate that is related to the predetermined frequency. The frequency of the receiving terminal clock is controlled in response to the estimate. In one aspect, the time intervals are determined by measuring time differences of arrival between successive packets, and the measured time differences are filtered to generate the estimate.

Abstract: An echo cancellation modem for full-duplex communication over a channel with a remote device in accordance with one of several possible modulation schemes suitable for different channel qualities, respectively. The modem includes an echo canceller for reducing echo components appearing in the channel signal while leaving a residual echo component in the echo reduced channel signal, a monitor for determining the quality of the channel based on an analysis of the residual echo component, and a controller for selecting an acceptable modulation scheme, based on the analysis of the monitor. The modem selects the acceptable modulation scheme prior to data communication and it also requests changes to the appropriate level of modulation during data communication when the monitor indicates that the channel quality has changed significantly. The modem requests the remote device to operate at the selected rate and begins operating at the selected rate only if the remove device concurs.

Abstract: A sample rate converter receives an input stream of samples representative of a time-varying signal and generates a corresponding output stream of samples which is also representative of the time-varying signal and in which each output stream sample appears at a desired time which may differ from the time when a sample appears in the input stream; filter circuitry receives the input stream and generates at least two intermediate samples which appear at different times, and interpolation circuitry combines selected intermediate samples to form a sample of the output stream at the desired time.

Abstract: An echo cancellation modem having a fast training echo canceller in which the echo cancellation coefficients are computed by taking correlations between a complex, periodic training signal sequence and a real component of the corresponding echo signal. The modem includes a receiver circuit for detecting a signal on a channel possibly including an echo; an echo canceller for estimating the real component of the echo signal; training circuitry for applying the complex training sequence to the channel and for taking correlations between the training sequence and the real component of the corresponding echo signal. The modem also includes a computational element for computing the period of the periodic sequence, generating the complex periodic train sequence in real time and for computing a phase roll frequency based upon the computed echo cancellation coefficients.

Abstract: The communications network includes a plurality of interconnected nodes and communication links between nodes. Computing apparatus in provided for determining a shortest path from a starting node to a destination node. The computing apparatus is adapted so that each node forms a routing tree having nodes with indentities, branches with weights, and a distinguished node called a root. The routing tree is the estimated shortest path to all of the nodes and each node communicates its routing tree to each adjacent node. Upon receipt of a routing tree by a reference node from an adjacent node, the reference node stores the routing tree and produces a large tree having roots and branches by placing the reference node as the root of the large tree and creating branches from the reference node to the roots of the routing trees of the adjacent nodes. The lengths of the branches are equal to the lengths of the links from the reference node to the adjacent nodes.

Abstract: Partner modules are assigned to a plurality of primary modules in a communications system, each partner module being adapted to route signals from the primary module to which it is assigned to a spare module in case the primary module fails. The partner modules preferrably also serve as primary modules for receiving signals from their associated communication lines. As a result, redundancy for a failed primary module is provided by a signal routing architecture that is distributed throughout the communications system.

Abstract: A large number (e.g., 20 or more) independent processors are connected by a network that provides high data throughput (e.g., 64 megabits/second). The network has redundant data, arbitration, and status/control buses. The buses extend across a plurality of microstripline backplanes connected together by impedance-matched twisted-pair cables. Data is transmitted in packets, along with status signals that provide error detection information.