Ground start

Abstract: A credit card authorization network which, among other advantages, allows telephone charges to be reduced. A credit card company, operating as an Interexchange Customer, provides trunk-protocol executing modems at a Feature Group B access facility. The modems are interfaced to the trunks, on a T1 digital link, by adapting FXS channel bank cards with a ground start option to translate between E&M signaling and ground start loop signaling.

Abstract: A system and method for providing Feature group B or Feature Group D access to the public data network for effecting point of sale transactions such as credit card authorization. The credit card authorization device includes a modem and auto-dialing mechanism which is connected by a station line to an originating central office switch. The originating central office switch is connected via Feature Group B or Feature Group D trunks to a designated destination central office including a stored program control (SPC) switch. The destination central office is a functioning central office connected to other central offices by non-Feature Group trunks. The Feature Group trunks are connected by the switch in the destination central office to a designated line which is connected to a line side modem which is connected via the public data network to a host computer for effecting the credit card authorization. The SPC switch at the destination central office converts the Feature Group number on the Feature Group trunk to a line side number for the station containing the line side modem. Common channel signaling and quick start or ground start are preferably utilized to optimize speed.

Abstract: A telephone test instrument permits voice communications with and monitoring of a telephone circuit to be tested. The instrument includes a microprocessor used in controlling various functions of the instrument. The microprocessor and other circuits of the instrument are energized from a connected telephone circuit and/or an internal energy supply which is automatically recharged from the telephone circuit. The microprocessor continually checks the voltage of the internal energy supply and automatically turns off a loudspeaker of the instrument, or prevents it from being turned on, if the voltage is too low. The instrument includes circuitry which, in combination with the microprocessor, measures loop current or line voltage while the instrument is connected for making voice communications with the telephone circuit. When the loudspeaker within the instrument is energized, the earpiece receiver remains active. A belt hook connected to a housing of the instrument can connect an electrical ground through a switch in the instrument to the telephone circuit for providing a ground start. The instrument also includes a "crow-bar" circuit which effectively open-circuits the instrument from a connected telephone circuit if too high of a loop current flows.

Abstract: A ground start loop current detector is used to monitor the loop current in a telephone subscriber loop when the subscriber requests service by grounding one line of the loop (ground start), when a busy subscriber discontinues use by opening the loop, and when a called subscriber answers in response to ringing by closing the loop. In order to operate in the presence of longitudinal (common mode) interference currents in the loop, especially in the ground start situation where only one line is monitored, the detector incorporates a differential amplifier which has its inputs connected to the loop through transformer windings that are phased so as to equalize the effects of longitudinal currents on the inputs of the differential amplifier.