Abstract: Apparatus for facilitating the transport and switching of synchronous and asynchronous digital data signals presented by data terminal or data communication equipments to a voice switching network such as a PBX advantageously without the use of modems. The clock rate of the PBX user's digital data is multiplied by a variable factor to define a synchronous transmission clock rate on a data link between a pair of interfaces, one locally connecting to the data terminal or data communications equipment and the other appearing as a port of the PBX switching equipment. The higher rate on the data link permits both the digital data as well as a control channel to be provided. Variations in the data terminal or data communications equipment clock rate do not affect the control channel. Variations in the voice sampling rate of switching modules serving different groups of ports through which the digital data is transported are accommodated.

Abstract: In a PAM bus switching bus which normally handles analog voice signals, the different DC offsets caused by the different buffing, summing and distribution amplifiers cause no ill effects because DC voltages are not passed by the remainder of the support elements. However, when it is attempted to switch logic level DC signals through such a PAM bus network, the DC offset which is an indeterminate function of the particular switching path established, makes it impossible to establish a uniform slicing level. In the illustrative embodiment a uniform slicing level is achieved by clamping the summing bus of the PAM system during a preamble of the time slot, measuring the offset on the distribution bus and then applying the measured offset to compensate the distribution bus during the remainder of the time slot when the actual data signal is allowed to be applied to the summing bus.

Abstract: A loop network is disclosed in which the ports have access to time slots on each of two buses. The buses carry the time slots in opposite directions. Ports are addressed by marking a bit of a time slot word on one bus and a bit of a time slot word on the other bus so that the two marked bits will arrive within a predetermined number of bit intervals of each other at the addressed port. Time slots are seized by an upstream port writing a predetermined pattern into an arriving idle time slot and by the downstream port recognizing the arrival of that predetermined pattern. A time slot may be reused during the remainder of its passage around the loop after it is rendered idle by the downstream port of a connection.

Abstract: A speech scrambling system using discrete prolate spheroidal sequence coefficients (PC). The problem is to provide high fidelity and high security in a scrambling system while limiting the bandwidth of the scrambled signal to the bandwidth of the original speech signal. The disclosed system uses PC to solve this problem. The analog speech signal is digitally sampled (100), converted to PC (203, 204, 205), scrambled (208, 209), and converted to scrambled samples (211, 212, 213). The scrambled samples are transmitted using pulse amplitude modulation (102) in the same bandwidth as the original signal. At the receiving end, the inverse steps are performed to recover the original speech. The scrambling is periodically modified (220, 320) to improve security.

Abstract: A nodal switching network is disclosed wherein each node is connected to distant nodes by groups of links whose lengths are ordered to span distances definable by powers of a finite (preferably binary) integer. Starting at the calling node, a single idle link in a preferred coordinate direction is attempted to be seized to extend the connection as far as possible by a direct path. If a direct path link spanning the most of the distance in the preferred coordinate direction cannot be seized, a direct path link is attempted to be seized in another coordinate direction. If no link which would extend the connection most efficiently in either coordinate direction can be seized, links of less direct length in the coordinate directions are tested. If the call is still blocked, the procedure is repeated in the direction from the called node toward the calling node.

Abstract: A switching network containing a plurality of nodal crosspoint configurations (NCCs) through which connection paths may be established to link together a plurality of different pairs of calling and called terminating circuits is disclosed. This space division nodal network is reconfigured on each of a plurality of repetitive time slots so that the same crosspoint of a given NCC (except the crosspoints associated with the nodes's terminating circuits) may serve a different call on each time slot. Four wire paths are provided, however, to each terminating circuit by assigning separate "going" and "return" time slots to each direction of transmission. A usage count is accrued showing how many independent calls are contained in the network on each time slot. When a path for a new call is to be established, the least busy time slot is selected, and then a link path to connect calling and called terminating circuits is chosen using the least busy intervening NCCs lying in the most direct available path.

Abstract: An electronic key telephone system is disclosed in which connections among the station sets and telephone lines are made in a central time division switching network remote from the station sets. Each station set and line is equipped with a port circuit having an individual shift register for defining the time slot interval during which a connection may take place. To assign a time slot to a port circuit, the main controller interrogates the network to find an idle time slot and then furnishes that time slot number to the network controller. In order to save central memory and to increase system reliability, the main activity memory which stores an indication of which ports are or should be interconnected in the network need not contain any reference to the time slot number assigned for the particular connection. In order periodically to verify that actual network connections reflect the state of the activity memory, two types of audits are performed.

Abstract: A lamp rate generator is disclosed which generates signals for controlling the illumination of key lamps at key telephone sets so that they may be illuminated at wink or flash rates. In addition, a "zero-crossing" signal is generated to determine the onset of conduction in a PNPN switch in the ungrounded side of the lamp power lead to ensure that the rise time of current delivered to the lamp load shall follow the rectified ac waveform of the power source. The circuit is most advantageously employed in time division PBXs which must be rendered secure against transient noise signals that could be induced by current surges having steep wave fronts.

Abstract: Port circuits in a time division switching system that have their outputs connected to a common summing bus by respective summing resistors have their output signals attenuated when the conversation is among port circuits on the same bus: the simultaneous closure of the respective time slot switches causes the summing resistor of one port to shunt the output from the other port. However, when the connection involves port circuits served by different summing buses, there is usually sufficient isolation between the buses to mask the shunting effect. The present disclosure shows an arrangement for selectively adding a compensating amplifier and an attenuating resistor to each distribution bus. When the call involves port circuits served by the same summing and distribution bus pair the amplifier completely compensates for all attenuation.