Abstract: A state machine that allows an audible alarm for a given fault condition to be extinguished while allowing subsequent audible alarms for different fault conditions.

Abstract: A line card circuit using a pair of comparators such that the output of the first comparator is coupled to an input of the second comparator through an RC circuit. The RC circuit is tuned such that short transients, such as false pulses and false off hook indications passed by the first comparator are not passed by the RC circuit to the second comparator. The input of the first comparator is coupled to the subscriber line and the output of the second comparator is coupled to the switch's hook status detection circuitry.

Abstract: A state machine that allows an audible alarm for a given fault condition to be extinguished while allowing subsequent audible alarms for different fault conditions.

Abstract: A line card circuit to prevent false off-hook signals resulting from the permanent loss of battery voltage at a line card. In the battery present condition, the 5V operating voltage is connected to the collector lead of an NPN transistor, which also supplies the output signal of the system. The emitter lead of the transistor is connected to ground. The -48V battery voltage is connected to the transistor base lead and biases the base negative with respect to the emitter, maintaining the 5V logic "1" output signal on the collector lead. There is a resistor and capacitor in series, forming an RC circuit, across the 5V collector lead and the -48V base lead. In the battery present condition, there is a significant charge across the capacitor. In the battery absent condition, the -48V battery voltage is lost and the voltage on the base lead rises to a positive voltage in a time interval governed by the discharge time of the RC circuit, thus causing the system output signal to drop to logic "0".

Abstract: A system that provides secure transmission of data between a subscriber's PC and an online service provider (OLS) over an Ethernet WAN. The system includes a remote transceiver unit located at a subscriber site and connected to the subscriber's PC; a central transceiver unit located at a telephone central office and connected to the remote transceiver unit over a twisted pair network and also connected to a WAN; an authorization server that is connected to the WAN; and one or more OLSs, which may include Internet service providers, connected to the WAN. Security of transmission is provided through a method in which only subscriber transmissions directed to a session-specific OLS are allowed to pass through the central transceiver unit onto the WAN, and only unicast transmissions from authorized OLSs are allowed to pass through the central transceiver unit to the subscriber port of the remote transceiver unit. Broadcast transmissions are minimized in favor of unicast messages.