Abstract: A novel packet switch architecture is disclosed. The packet switch utilizes internal queuing (i.e. recirculation loops) and output queuing (i.e. multiple paths to each destination) to provide a packet switch which offers superior performance in comparison to a packet switch which utilizes either of these queuing strategies alone. The combination of recirculation and output queues have complimentary effects. The output queuing reduces the number of recirculation loops needed and recirculation reduces the bandwidth requirements for an output buffered switch.

Abstract: A high capacity metropolitan area network (MAN) is described. Data traffic from users is connected to data concentrators at the edge of the network, and is transmitted over fiber optic data links to a hub where the data is switched. The hub includes a plurality of data switching modules, each having a control means, and each connected to a distributed control space division switch. Advantageously, the data switching modules, whose inputs are connected to the concentrators, perform all checking and routing functions, while the 1024.times.1024 maximum size space division switch, whose outputs are connected to the concentrators, provides a large fan-out distribution network for reaching many concentrators from each data switching module.

Abstract: A multi-port (multiplexed) modem for implementing automatic reconfiguration of the ports so that transmission bandwidth can be optimized. The modem utilizes a sequence of communications and acknowledgments transmitted over the donor port donating the bandwidth and the recipient port receiving the bandwidth. This allows reconfiguration of the modem ports without need for interruption of the unaffected ports and requires no secondary channel to implement. Only the port going idle and the port receiving the bandwidth are affected so that communication channel throughput is maximized and unaffected ports are not interrupted.

Abstract: A key telephone system includes a plurality of ports being linked by port associated bidirectional communication channels which are synchronously switched by transferring bit states between ones of the channels to provide communication paths between the ports as directed by a central processor. The ports are also linkable to and via the central processor by port associated message channels. An interface circuit is responsive to the central processor and message channel signals for regulating flow of messages received by the central processor and for effecting single and plural channel distribution of messages from the central processor. The message channels permit telephony operating features and functions to be provided either within the central processor or by appropriate apparatus means being connected at any of the ports.

Abstract: A method and apparatus for assigning time slots in a frame of time slots used for time division multiplexing, the time slots being representable as a position within the frame, in which it is determined what quantity of the time slots are required to provide a needed amount of bandwidth. A random number generator (40) generates (92) a uniformly distributed random number which is scaled (94) to represent a position in the first portion of the frame. A first of the positions within the frame is assigned based upon the value of the randon number. The remaining positions are assigned by fitting (64) the remaining required positions to the available positions in the frame spacing them at approximately equally spaced intervals as available. This prevents bunching of the used time solts which would otherwise prevent dynamic allocation of large blocks of bandwidth in the frame without complete recalculation of the frame.

Abstract: A method of providing an inband secondary channel for a data modem includes encoding the main channel data using a convolutional encoder so that main channel data symbols are selected from a first constellation. The secondary channel data are encoded using a differential encoder and secondary channel data symbols are selected from a second constellation. The transmission of the main channel symbols takes place during 48 frames of a 49 frame master frame. The differentially encoded secondary channel data symbols are transmitted during the remaining frame. The symbols of the secondary channel constellation are selected to have a higher average energy than those of the main channel data so that the secondary channel is easily detected and may be used to obtain frame synchronization for the modem after brief dropouts without having to retrain the modem.

Abstract: High transmission and reception quality is achieved in a high definition television system, with minimum intra-channel interference, by digitally encoding the enhancement information and employing spread-spectrum modulation techniques.

Abstract: In an integrated digital network with at least three nodes, A, B, and C, a call placed at node A to be transmitted through the network from node A to node B to node C, is compressed in multiple modes. In response to the path selected, the speech signal in node A is compressed in a first mode for transmission to node B. In node B, the speech signal is compressed in a second mode for transmission to node C, where the first and second modes involve dissimilar algorithms for compression of speech signals. At node C, the speech signal would again be adapted for supply to a receiving station. The system can accommodate as many modes of compression as desired.

Abstract: A unique packet-switched cellular telephone system includes a cellular switch (140) and base sites (110) for providing packet-switched data services to cellular data telephones (102). Cellular switch (140) includes packet access points (152, 153) coupled to a packet network and T1 span lines (160, 161) coupled to the landline telephone network. Base sites (110) are coupled to cellular switch (140) by T1 span lines (164, 165) in which all time slots are clear channels and one time slot is dedicated for common channel signalling. Multiple data calls are assigned to each packet-mode radi channel thereby conserving valuable radio channel spectrum. Data calls are handed off from one packet-mode radio channel to another on the basis of cellular data telephone movement, signal strength, and/or bit-error rate, or on the basis of radio channel data packet capacity, data packet traffic, and/or data packet throughout.

Abstract: In a communication system having first and second ring transmission lines for connecting a plurality of stations and for providing opposite signal transmission direction, a first station, which is located just downstream side of a failure point occurred in the first transmission line, sends out a beacon signal along said first transmission line while causing an intentional failure in the second transmission line on its downstream side and a second station, which is located just upstream side of the failure point on the first transmission line, forms a first loop-back path (WRAPA) by detecting the intentional failure on the second transmission line if the second station has received the beacon signal. The first station forms a second loop-back path (WRAPB) by receiving the beacon from the second transmission line which is sent back by the second station.

Abstract: A method and arrangement for transmitting a digital signal with a low bit rate in a time section, provided for higher bit rates, of a time division multiplexed signal. At a transmitting end the first digital signal with a low bit rate is over-sampled with a first clock signal assigned to this time section. A second digital signal which results is transmitted in the time division multiplexed signal to a receiving end. Following the demultiplexing of the time division multiplexed signal, this second digital signal is sampled with a second clock signal, corresponding to its bit rate, omitting forbidden phase position zones, and results in a fifth digital signal. The forbidden phase position zones are defined by a shift register, an exclusive-NOR-gate, an upwards/downwards counter and a logic unit. Double samplings are prevented in that the phase of the second clock signal is shifted via the resetting of a frequency divider.

Abstract: Messages consisting of an arbitration field followed by a data field circulate in a single-channel bus system. The stations comprise a storage element for an intended delay time between a locally formed signal transition and a resultant detectable signal transition. The stations also comprise a continuous sequencer for the successive bit cells. When a signal transition is detected, the sequencers are loaded with the position of the storage element, so that they are synchronized. In the case of a transmission operation, the delay is measured, so as to update the contents of the storage element.

Abstract: A stuff (or dummy) pulse and a stuff designation pulse which indicates existence of nonexistence of the dummy pulse are inserted in a multiplexed pulse code modulation signal to convert an input signal frequency to a higher frequency. The frame synchronization pulse is used as the stuff designation pulse. Therefore, stuff designation is possible even when the frequency difference between the input signal frequency and output signal frequency is small.

Abstract: A digital switch for selectively interconnecting a plurality of devices, including microcomputers, in a network comprises a plurality of inputs, a plurality of outputs and selectively operable interconnections which include decoding means for decoding data and acknowledgement bit packets, clock means, and means for generating under control of clock signals output bit packets having bit signals corresponding to bits of input bit packets.

Abstract: A node apparatus is used in a communication network having a hierarchical structure and transmission paths each coupling one node apparatus to another node apparatus or a terminal device. The node apparatus has at least one high order direction port, low order direction ports, and a control unit for controlling the coupling of the high order direction port and the low order direction ports. When signals are transmitted from the terminal devices approximately at the same time, one of the signals which first reaches the node apparatus provided in a highest order layer is broadcasted within the communication network and remaining signals are eliminated.

Abstract: A communication system for connecting a telephone switching office to a data processing center is described. A telephone trunk line from the switching office carries data which is digitally encoded and may be in a compressed format, for example mu-law PCM, and which is derived from remote data terminals. A novel type of modem is connected between the trunk and the data processing center. This is a direct synthesis device which converts the modulated digital data directly to a non-modulated digital format readable by the data processing center and, for digital data originating at the data processing center, produces modulated digital data which is transmitted along the trunk to the switching office. The direct synthesis modem is a single, purely digital device which replaces many separate digital/analog modems which are required in conventional systems.

Abstract: A method and apparatus for allowing ISDN devices to communicate over an analog telephone line is shown. A first interface (12) accepts ISDN formatted data from an ISDN terminal equipment (TE) device (10), removes the D channel data from the ISDN data, and provides the D channel data to a synchronous modem (14). The modem (14) places onto an analog telephone line (15) a modulated carrier corresponding to the D channel data. The modulated carrier is passed through a telephone switch (16)onto another analog telephone line (17). A second synchronous modem (20) accepts the modulated carrier, demodulates the modulated carrier to recover the data, and provides the data to a second interface (22). The second interface (22) accepts the data from the modem (20), inserts the data into the D channel information in ISDN data stream, and provides the ISDN data stream to an ISDN network termination (NT) device or ISDN switch (24).

Abstract: An improved digital demodulator capable of demodulating a frequency multiplexed input signal is disclosed. The frequency division multiplexed input signal is sampled in an analog-to-digital converter. The samples are translated by mixing with base band frequency signals to yield real and imaginary values corresponding to phase information in the original modulation signals. After translation, the translated samples are filtered in real and imaginary digital filters. After filtering, the original modulation information is recovered by analysis of the position of vectors in the complex plane represented by the real and imaginary values. In the preferred embodiment, a successive approximation technique is used to determine the angle of the vectors to the real axis. Low pass output filtering may be employed after recovery of the modulation signal for improvements in signal to noise ratio.

Abstract: A local area network is disclosed including apparatus and methods for transmitting data between a plurality of data processing resources (agents) coupled to a cable. An agent desiring to send data to a receiving agent transmits a request to send (RTS) data packet which includes a control character requesting to either high or low speed data communication. Utilizing the teachings of the present invention, absent other predefined conditions a transmitting agent capable of high speed communication requests a high speed data exchange with the receiving agent. The RTS data packet itself is transmitted at low speed. Upon receiving the RTS packet, the receiving agent must transmit a clear to send (CTS) packet to the transmitting agent within a predetermined time after the receipt of the RTS packet.

Abstract: A pair of full duplex modems are connected and each is designed to transmit to the other at the same predetermined band rates. One modem is connected to receive data bits for transmission over the channel at a predetermined first (and fast) rate and to transmit its received data bits at a integral number of first transmission bits per band. The other modem is connected to receive data bits for transmission over the channel at a rate slower than the band rate and is designed to sequentially encode blocks of said slower rate data bits into a larger number of second transmission bits for transmission over said channel at an integral number of second transmission bits per band. Means forming part of said one modem for converting said second transmission bits into the slower rate data bits.