Abstract: The method and apparatus to determine if a telephone subscriber line is loaded or non-loaded including circuitry to provide a signal having at least one given frequency which is coupled to a telephone subscriber line under test having a subscriber subset on-hook either directly or through the switching system such that this signal can be received from the subscriber line under test and analyzed to determine the value of at least one parameter of the subscriber line under test to determine whether the subscriber line under test is loaded or non-loaded. When the signal applied to the line has one frequency, the parameter involved is the real part of the on-hook impedance of the subscriber line under test and where a plurality of frequencies are employed, the parameter involved is either the change in the real part of the on-hook impedance of the subscriber line or a change in the phase angle of the on hook impedance of the subscriber line.

Abstract: A line switch for a digital telephone switching system utilizes distributed processing. The line switch comprises one or more switch modules. Each switch module is coupled to a central office switching system via one or more PCM lines which utilize common channel signaling. Each switch module comprises groups of line circuits, each line circuit being coupled to a subscriber line. Three separate distributed processor functions are provided in each line switch module. A first processor is utilized to communicate with the central office switching system is provided to control clock generation and rate conversion circuits. Each group of line circuits includes a third processor to control the operations of the line circuits and to gather information from the line circuit.A test bus is routed to the line circuits. The third processor may be utilized to automatically measure and adjust various transmission parameters.