Digital data transmission system having frequency or phase modulated data carrying signals to provide supervisory channel
AssigneeThe Post Office
InventorsPeter Cochrane, James A. Kitchen
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Abstract
A supervisory channel is provided on a digital transmission system by frequency modulation of the data signal transmitted along a transmission link which includes repeaters. The frequency modulation can be carried out using an elastic store. Each repeater includes means for demodulating the frequency modulation so that each repeater can be addressed and interrogated. Each repeater can also phase modulate the data signals on the return link to a terminal station so that signals indicative of an interrogated condition can be transmitted to the terminal station.
Claims16
A digital data transmission system having send and receive equipment at terminal stations connected by a digital data communication link which includes one or more repeaters, wherein the send equipment includes means for frequency or phase modulating the occurrence timing of digital data carrying signals being transmitted along the link with additional information, and the or each repeater includes means for demodulating said frequency or phase modulation thus providing said additional information thereat, said modulation providing a supervisory channel by means of which the repeaters can be addressed and interrogated while simultaneously communicating said digital data carrying signals over said link.
A method of interrogating repeaters on a digital data transmission link connecting terminal stations, said method comprising frequency or phase modulating the occurrence timing of digital data carrying signals being transmitted from a terminal station with additional information to provide a supervisory channel and demodulating said frequency or phase modulation of each repeater thus providing said additional information thereat to obtain signals for interrogating a condition or conditions in the repeater while simultaneously communicating said digital data carrying signals over said link.
A repeater for a digital data transmission link including a logic means arranged to provide signals indicative of the condition of the repeater and means for phase modulating the occurrence timing of digital data carrying signals on the digital data transmission link in accordance with the signals from the logic means.
Dependencies are inferred from the claim text.