Communication circuit loopback test apparatus

The method of remotely localizing the area of failure in a multiple repeater station communication link between two end terminals comprising the steps of:

• interrupting the transmission of signal long enough for detection of a "null" by receiving equipment in the repeater station;
• transmitting N+1 pulses of a predetermined length and of a frequency distinguishable from the frequency of data signals with predetermined "null" signal times between the transmitted pulses from one of said end terminals;
• detecting the frequency of signals received after initialization and setting each receiver stage to a data or test condition in accordance with the frequency of the detected signal;
• retransmitting one less pulse than received, by each repeater station that receives more than two pulses, to the following repeater station in the communication link wherein the retransmitted pulses have the same timing characteristics as the originally transmitted pulses;
• reconnecting the repeater station that receives only two pulses in a loopback configuration;
• transmitting a test signal from said terminal and checking for receipt of same by said terminal due to the loopback connection at said remote repeater station;
• and
• repeating the above steps for repeater stations further away by incrementing the number of pulses N until the test signal is not returned from a requested remote repeater station.

The method of signaling a specific repeater station "N", in a communication link having more than N repeater stations wherein the station N is the Nth station in the communication link, to change modes of operation comprising the steps of:

• establishing an initializing set of conditions on said communication link through a "null" signal;
• transmitting a set of N+1 pulses having predetermined characteristics distinguishable from data signal characteristics over said communication link;
• detecting the characteristics of the signal received at each repeater station after establishment of the initialized condition for setting an operational mode in said repeater station in accordance with the characteristics of the received signal to a data or test mode;
• removing one of said pulses from the received set of pulses, by each repeater station that receives more than two pulses, and forwarding the remaining pulses to the next successive repeater station in said communication link;
• providing a specific configuration in the repeater station that receives only two pulses in response to those two pulses and their predetermined characteristics;
• and
• maintaining the condition of said mode and said specific configuarion until an initializing set of conditions is again provided on said communication link.

Apparatus for testing a communication link including at least an end terminal transmitter, a remote end terminal receiver and a plurality of intermediate repeater stages for localizing the section of the communication link having transmission problems comprising, in combination:

• communication link end terminal transmitter first means for interrupting the flow of information from transmitter to remote receiver with a "null" signal for a time sufficient to cause all intermediate receiver stages to reset to an initialized condition;
• second means, comprising a part of said first means, for transmitting N+1 pulses of predetermined length and of a frequency distinguishable from that used in data transmission;
• a plurality of repeater stations connected in series in said communication between end terminals, each repeater station including;
• "null" signal detection means for reinitializing each repeater station upon reception and detection of the "null" signal and for setting said repeater station to a test or a data condition in accordance with the frequency of the next received signal;
• third means for receiving transmitted pulses at each intermediate receiver stage in succession and for transmitting one less pulse than received when more than two pulses are received;
• and
• fourth means for altering the signal path condition, in the intermediate repeater stage receiving only two pulses, to a loopback configuration;
• fifth means, comprising a part of said end terminal means, for transmitting a test signal through said looped communication link;
• sixth means, comprising a part of said end terminal means, for clearing the communication link by transmitting a null signal for initializing each intermediate receiver and returning same to normal signal transmission conditions between the transmitter of said end terminal and a remote end terminal receiver at the other end of said communication link, if no faults are detected;
• and
• seventh means for providing an indication that no faults were detected in a given N+1 pulse transmission test.

Apparatus for remotely localizing the area of failure in a multiple repeater station communication link between two end terminals comprising, in combination:

• end terminal first means for interrupting the transmission of data signals long enough for detection of an initializing "null" signal by receiving equipment in the repeater stations;
• end terminal second means for transmitting N+1 pulses of a predetermined frequency and length with predetermined "null" signal times between the transmitted pulses from one of said end terminals;
• a plurality of repeater station third means connected in series in the communication link between end terminals, each of said third means including retransmitting fourth means, reconnecting fifth means, "null" signal detecting and initializing sixth means and further means to set the station to test or data transmission modes in accordance with signals first received after receipt of an initializing "null" signal;
• said fourth means portion of each of said third means retransmitting one less pulse than received to the following repeater station in the communication link wherein the retransmitted pulses have the same timing characteristics as the originally transmitted pulses;
• said fifth means reconnecting the repeater station that receives only two pulses in a loopback configuration;
• and
• end terminal seventh means for transmitting a test signal from said end terminal and checking for receipt of same by said end terminal due to the loopback connection at said remote repeater station.

The method of eliminating the requirement for data stream decoding to detect test signal interrupts in a repeater station intermediate end terminals in a communication link normally transmitting data at a first frequency comprising the steps of:

• interrupting normal data being transmitted at said first frequency from one end terminal to the other with a "null" signal for a time sufficient to cause a reset of the intermediate repeater stations to an initialized condition;
• transmitting a test interrupt signal at a second frequency distinguishable from said first frequency;
• detecting the frequency of the signal being received at the repeater station and setting the station to one of test or data transmission conditions based on the frequency of the signals detected;
• and
• maintaining the set condition at said repeater station until a further "null" signal is received causing a return of said repeater station to an initialized condition.

Repeater station apparatus for use in a communication link sending data at a first frequency between end terminals comprising, in combination:

• a pair of signal detection receiver means for receiving signals from the east and the west;
• a pair of signal transmission means for transmitting, to both the east and the west, amplified versions of signals received by a connected receiver means;
• signal detection first means for resetting the circuitry to an initialized condition where the east receiver is connected to the west transmitter and the west receiver is connected to the east transmitter whenever a null signal is received;
• and
• signal detection second means for reconnecting a given receiver means in a loopback condition to the complementary transmitter means whenever a predetermined signal of a second frequency, where said second frequency is distinguishable from said first frequency, is received immediately after a null signal has been detected and the circuitry has been reset to an initialized condition.