Automatic self-test system for a digital multiplexed telecommunication system

Apparatus in a terminal of a telephone system for testing a voice channel within said terminal of said telephone system carrying plural audio channels, each said channel having a line card interface circuit coupling said terminal to a telephone line each said line card interface circuit including a digital-to-analog converter for carrying data toward said telephone line, and an analog-to-digital converter for carrying data toward said terminal and audio circuitry for the analog side of said interface circuit, comprising:

• means for periodically, automatically monitoring each of said plural audio channels to select an audio channel which is not in use;
• means for generating a test signal and for connecting said test signal to said line card interface circuit so that said test signal propagates through said digital-to-analog converter, said audio circuitry and said analog-to-digital converter of said audio channel which is not in use;
• and
• means for detecting whether said line card interface circuit which is not in use is operative by detecting the presence of said test signal at the output of said analog-to-digital converter.

A self-diagnosing telephone terminal for use in a digital multiplexed span line telephone system for coupling a plurality of telephone lines to said span line, comprising:

• a digital-to-analog converter for coupling digital signals from said span line to a telephone;
• an analog-to-digital converter for coupling analog signals from said telephone to said span line;
• means for sensing whether said telephone is on hook;
• audio signal processing means for driving analog signals from said digital-to-analog converter onto said telephone lines and for receiving analog signals from said telephone lines and for driving them into the input of said analog-to-digital converter;
• means responsive to said sensing means for periodically, automatically injecting a digital test signal into said digital-to-analog converter when said telephone is on hook;
• means for looping output signals from said digital-to-analog converter to the input of said analog-to-digital converter through said audio signal processing means;
• and
• means responsive to said sensing means for detecting said digital test signals from the output of said analog-to-digital converter.

Apparatus for testing an audio channel within a terminal of a telephone system in which plural audio channels share a common span line, where said system includes at least two terminals connected by said common span line, comprising:

• plural line termination means including per line audio amplifier circuits for connecting said terminal with plural telephone lines, said line termination means superimposing said plural audio channels of said plural telephone lines on said common span line;
• a maintenance circuit comprising:
• means for sensing which of said plural telephone lines is not in use, for automatically generating a test signal, and for coupling said test signal to line termination means of said telephone line which is not in use;
• means in said line termination means for looping said test signal back to said maintenance circuit through said per line audio amplifier circuits;
• and
• means in said maintenance circuit for detecting said test signal.

Apparatus for testing a voice channel within a terminal of a multiplexed digital telephone system, where said system includes at least two terminals connected by a span line, comprising:

• plural line termination circuits for connecting said terminal with plural telephone lines, said circuits converting between analog signals on said telephone lines and digital signals in said terminal and including per line audio amplifiers to drive said telephone lines with analog signals and receive analog signals from said telephone lines;
• means for multiplexing between digital signals in said plural line termination circuits and said span line to provide simultaneous transmission on said span line for a selected group of said plural telephone lines;
• test circuit comprising:
• means for sensing which of said plural telephone lines is not in use, for automatically generating a digital test signal, and for coupling said test signal through said multiplexing means to the line termination circuit of said telephone line which is not in use;
• means in said line termination circuits for looping said test signal through said per line audio amplifiers and back through said multiplexing means to said test circuit;
• and
• means in said test circuit for detecting said test signal.

An apparatus for self-testing a digital multiplexed communication system, comprising:

• a data bus for carrying digital data describing an analog waveform;
• a plurality of line interface means coupled to said data bus, said plurality of line interface means including a plurality of per line A/D and D/A conversion circuits and a plurality of audio line driver and line receiver amplifiers coupling a plurality of telephone lines to said data bus;
• a test signal generator coupled to said data bus, generating a plurality of digital test words, and placing said digital test words on said data bus;
• a detector coupled to said data bus, detecting said digital test words on said data bus;
• a multiplexer coupled to said data bus, transferring said digital test words from said test signal generator to a selected one of said plural line interface means, and transferring said digital test words from said selected one of said line interface means to said detector on said data bus during selected time slots;
• and
• a controller coupled to said test signal generator, said detector, said multiplexer and said plural line interface means, said controller for selecting the line interface means for said transfer, and to cause said multiplexer to transfer said digital test words from said test signal generator to a selected line interface means where said digital test signals propagate through said per line conversion and audio amplifier circuits and to transfer said digital test signal from said selected line interface means to said detector.

A maintenance circuit for a digital multiplexed communication system coupling a plurality of analog telephone lines coupled to telephones to a digital data transmission line, comprising:

• line interface means having a digital-to-analog converter and an analog-to-digital converter and audio interface circuits for each telephone line to interface said analog telephone lines to said data bus and for indicating when said telephones coupled to said telephone lines are on-hook and not in use;
• a PCM data bus for carrying digital representations of analog waveforms;
• a toner generator coupled to said PCM data bus for generating a plurality of words of digital test data which, in combination, describe an analog test signal and for placing said plurality of digital words on said data bus;
• a detector coupled to said PCM data bus for detecting said test signal and for generating an output signal when said test signal is present;
• an alarm circuit coupled to said main data bus;
• a multiplexer having a line receiver coupled to a serial data input for converting serial format input data on said digital data transmission line to parallel format data for outputting on said PCM data bus and having a line transmitter coupled to a serial data output for converting parallel format data from said PCM data bus to serial format data for outputting on said digital data transmission line, said multiplexer coupled to said line interface means, said tone generator, and said detector by said PCM data bus, and having a control word input coupled to said main data bus for receiving a digital control word, said multiplexer for establishing a plurality of time slots and for establishing a data link for each time slot via said PCM data bus between one of said line interface means and said line receiver and said line transmitter or for establishing a data link between said detector and said tone generator and one of said line interface means, the selection of circuits to be linked and assignment of time slots controlled by said digital control word data;
• and
• a controller coupled to said main data bus, and having address and control lines coupled to said multiplexer, said controller for generating a control word for each time slot established by said multiplexer, said controller also coupled to said line interface means by said data, address and control lines, said controller programmed to test each line interface means to determine which telephones are on-hook and not in use and to generate a control word for a self-test time slot, said control word causing said multiplexer to transfer said digital test data from said tone generator to said line interface means for any telephone line not in use and to cause said multiplexer to transfer digital data from said line interface means, which data has been converted to an analog test signal, propagated through said audio interface circuits and reconverted to digital test data, to said detector during the assigned time slot, said main data bus, address and control lines of said controller also coupled to said detector for controlling when said detector is enabled, and said controller programmed to read said output signal from said detector to determine when said line interface circuitry is functioning properly, and to cause said alarm circuit to indicate a failure on the tested line when no test signal is detected and said controller programmed to continuously so test idle line interface means.

A maintenance circuit for a digital multiplexed communication system having a central office terminal and a remote terminal with a plurality of digital-to-analog and analog-to-digital line card interface circuits for individual telephone lines, said maintenance circuit located in said central office terminal to automatically, continuously test said line card interface circuits whenever they are idle, comprising:

• a data bus coupled to said line card interface circuits for carrying digital data;
• a generator means coupled to said data bus for generating a plurality of words of digital test data;
• a detector means coupled to said data bus for detecting test data and for generating an output signal;
• and
• means to automatically, continuously determine which said line card interface circuits are idle and for causing said generator means to send digital test data to said idle line card interface circuits and for causing said detector means to be coupled to said idle line card interface circuits to detect the presence of said digital test data after it has been converted to analog form and then back to digital form by said idle line card interface circuits.

A self-testing digital multiplexed telephone system for coupling a plurality of telephone lines from a central office switching network to a plurality of remotely located telephone lines, comprising:

• first means for converting analog signals from said central office telephone lines to digital data for transmission to said remote telephone lines and for converting incoming digital data from said remote telephone lines into analog data for application to said telephone lines from said central office, and including audio circuitry for driving the analog signals in both directions;
• second means for carrying digital data between said first means and said remote telephone lines;
• third means for multiplexing digital data from said first means onto said second means and for demultiplexing data from said second means for coupling by said first means to said telephone lines from said central terminal;
• and
• fourth means for continuously selecting idle telephone line channels in said first means and for applying a digital test signal to said idle channels through a self-test time slot in said third means, and for detecting a digital test signal after it has passed through said third means and said first means after being converted to an analog test signal, passed through said audio driver circuitry of said first means and reconverted to digital test signal.

A self-testing multiplexed telephone system for carrying signals between a plurality of telephone lines from a central office switching network and a plurality of remote telephone lines, comprising:

• a first means including audio line driver and receiver amplifiers for converting analog signals from said telephone lines from said central office switching network to digital data and for converting digital data to analog signals to drive said central office telephone lines;
• a second means for carrying digital data;
• a third means including audio line driver and receiver amplifiers to convert digital data from said first means to analog signals to drive said remote telephone lines and to convert analog signals from said remote telephone lines to digital data;
• a fourth means for multiplexing said digital data from said first means onto said second means and for demultiplexing data from said second means for use by said first means in driving said central office telephone lines;
• a fifth means for demultiplexing data from said second means for use by said third means to drive said remote telephone lines and for multiplexing digital data from said third means onto said second means;
• a sixth means for continuously selecting telephone lines from said central office which are not in use and for causing a test signal to be propagated through all the audio and conversion circuits of said first means interfacing with the idle lines only and for detecting said test signal after it has propagated through said first means to determine the operability of the interface circuits of said idle lines.