Abstract: A data link access unit for insertion into a T1 span supporting the extended superframe (ESF) format includes an interface for accessing the frames of digital data carried by the T1 span in ESF format (including the data link bits) and calculating performance monitoring data for the T1 span. The interface is controlled by a processor that can access this performance monitoring data and also communicate message data over the data link channel via the interface. Additionally, the unit can provide an ESF/SF interface when inserted into a T1 span between a first channel bank supporting ESF and a second channel bank that does not support ESF.

Abstract: The universal channel unit includes a channel interface circuit that uses a pair of fixed ratio transformers to terminate both two wire and four wire analog transmission facilities on a selectable basis. The universal channel unit also includes a plurality of signalling circuits, each of which is switchably connectable via the channel interface unit to provide a DC signalling interface to match the signalling format required by the associated analog transmission facility. The signalling circuits include: DX, FXO, FXS, and other DC signalling circuits. The AC component of the signals carried by the analog transmission facility is output to an adaptive impedance and balance circuit which functions to closely match the impedance of the analog transmission facility and minimize signal reflections under control of a microprocessor. This impedance and balance network is connected to a PCM interface that includes an adaptive echo canceller circuit as well as equalization and gain control circuits.

Abstract: A telephone switching system comprising a central office switching unit and a remote field switching unit controlled by the central office unit. The field unit provides controlled connections between a number of trunks extending from the central office unit and a greater number of subscribers connected to the field unit. The field unit additionally contains a number of intracall lines for establishing a connection between two subscribers without the need for sustained trunk connection after the call is established. The central office unit includes a system controller comprising a microprocessor and associated memory units. The system controller receives information interrupts from both the central office unit and the remote field unit as to subscriber calls, subscriber identity, trunk availability and overall system condition alarms. Appropriate control signals are sent from the central office unit to the remote unit to establish the appropriate connections between the units for subscriber connections.