Data Transmission Telemonitoring Equipment and System

1. Technical Field

The present invention relates to telemonitoring systems for digital signal repeaters sequentially disposed along a data transmission line.

2. Discussion of the Prior Art

The use of data transmission lines for transmitting coded digital signal, and particularly data transmission lines employing a sequence of interposed signal repeaters, is well known in the prior art. In view of the importance of transmission accuracy, repeater telemonitoring must be employed and must possess a high degree of effectiveness, rapidity, flexibility, standardization and economy. There are many telemonitoring systems in use, and among them is a relatively recent system which provides for the forward transmission of an interrogation signal from a remote terminal to a repeater which answers with a status information signal that is transmitted toward the next repeater. When there is no interrogation signal, the repeater itself forwards the interrogation signal to the following repeaters, although no telemonitoring signal is forwarded when a check of the information quality fails. The information quality test of the repeaters yields information about only a few specific repeater parameters, namely: faulty repeater; degraded repeater operation; and normally operating repeater. There are numerous disadvantages inherent in such a system. For example, for the telemetry signal of the transmitter in a first terminal (e.g., a remote terminal), the system requires the interrogation signal plus a signal which detects answers in a second terminal (e.g., a next terminal). Further, although a remote transmitter is of itself simple, it must be duly protected at the time of telemetry failures or else it can pollute the telemonitoring signal and thereby prevent automatic reading of telemetry circuit failures. In addition, the number of repeaters which can be meaningfully monitored with such a system is defined by the alternation of the interrogation signals. Still further, the information concerning repeater status represents only three parameters, namely fault, normal operation and degraded operation. In such a system it is not possible to detect either micro-failures (e.g., on-line bursts) or error storage (e.g., error accumulation). A further disadvantage is that the technology has become obsolete and therefore does not permit reduction in either cost and power consumption. Finally, the aforesaid prior art system results in different or non-standard construction of a terminal when the terminal must act as a buffer to the telemetry signal.

It is therefore an object of the present invention to provide a system which lacks the aforementioned disadvantages, permits an effective utilization of the newest circuitry technology and provides a significant range of information while substantially reducing the cost of the system.

Another object of the present invention is to provide a system which effects sequential telemonitoring of data transmission line repeaters, wherein control is centralized in a single supervisory terminal, and wherein multiple parameters may be processed for each repeater.

A further object of the present invention is to provide advanced technology equipment for implementing a telemonitoring system, particularly with respect to the single supervisory terminal and the repeater regenerating circuitry.

These and other objects of the invention are accomplished by a system according to the present invention which is characterized in that an interrogation signal is periodically forwarded from a single telemonitoring supervisory terminal to a next repeater in sequence which, after recognition of the interrogation signal, sequentially provides a repeater status answer to the single interrogating terminal. In addition, the "next" repeater transmits the interrogation signal to the subsequent repeater in the repeater sequence. In accordance with one of the features of the present invention, the only supervisory terminal: carries out an automatic diagnosis or check of its operating performance; selects the desired telemonitoring operation mode; forwards the interrogation signal to the first repeater in the line; receives the answer signals from the repeaters on the telemetry channel; stores and processes the received answer data; displays the status of the line repeaters; detects failures in the telemetry channel; and, if desired, permits interfacing to a printer and presents a serial interface for data transmission to a maintenance center.

In accordance with an advantageous feature of the present invention, the processing in the supervisory or telemonitoring terminal can be preset for a plurality of different operating modes. In an automatic mode of operation, the first piece of information displayed represents the "worst" parameter status of the interrogated system and the error rate for the repeater having that "worst" status. The operator can immediately perform a test and evaluation on other repeaters and preset a fixed error rate threshold so that the supervisory terminal displays the identity of the first repeater to exceed that threshold. In a manual operating mode, the operator presets for the system, as well as for each repeater, the detection of the error rate, the maximum permissible error rate, and the error storage or accumulation. In a test mode of operation, the supervisory terminal provides an interrogation enable signal and inserts an error in the PCM (Pulse Code Modulation) signal without altering the information content of the signal. During the short interval of this operating mode, the supervisory terminal checks whether or not the error counters in the repeaters are operating correctly.

In a particular embodiment, the status message from the repeaters contains information for more than five parameters (for example, eight parameters, such as absence of pulse, error rate equal to or in excess of 10.sup.-3, error counter overflow, 64-640 errors, 8-63 errors, 4-7 errors, 1-3 errors and 0 errors). The centralized supervisory terminal includes: a clock generator, a receiver-transmitter interface, an information computer or microprocessor, a display and, optionally, a digital selector and a bus interface. The telemetry device connected to each repeater includes at least: a local oscillator, an error detector and error counter, a detector of the counter status, an interrogation transceiver, an answer signal generator, an answer transceiver, and an automonitoring unit.

The various features and advantages of the present invention will be better understood through the preferred (but not limiting) embodiments illustrated in the accompanying drawings, wherein:

FIG. 1 is a functional block diagram of a supervisory terminal and telemetry equipment in a repeater in accordance with the present invention;

FIG. 2 is an expanded functional block diagram of the repeater telemetry equipment of FIG. 1;

FIG. 3 is an expanded functional block diagram of the supervisory terminal;

FIG. 4 is a functional block diagram of the telemetry signal interface portion of the supervisory terminal;

FIG. 5 is a timing diagram of the interrogation and answer sequence employed in the present invention;

FIG. 6 is a timing diagram of the answer portion of the sequence illustrated in FIG. 5;

FIGS. 7(a), 7(b) and 7(c) are detailed timing diagrams of the answer test protocol, interrogation signal guard window, and repeater answer guard window, respectively; and

FIG. 8 is a flow chart of the program employed at the supervisory terminal microprocessor.

A brief overview of the invention may be had from the illustration in FIG. 1 which is a simplified block diagram showing the primary and basic features of the invention. The telemonitoring terminal TT has a prescribed sequential operation and is located in the line terminal 10 prior to the first repeater 20(1) of n repeaters 20(1), 20(2), . . . , 20(n). Supervisory terminal TT interrogates the repeater 20(1) which sends the interrogation signal to the next repeater 20(2), receives and regenerates the answer from repeater 20(2) and sends the regenerated answer back to the supervisory terminal. Repeater 20(1) also checks the protocol so that it does not regenerate answers of the downstream repeaters in case of violation of the answering protocol.

As illustrated in FIG. 1, the telemonitoring terminal TT is located exclusively in the supervision terminal 10 and includes: a time based generator 21; a receiver-transmitter interface 22; an information computer or microprocessor 23; a display 24 for displaying the interrogated repeater status and its possible failure; a digital selector 25, and an interface 26 for bus data to be delivered to a maintenance center and a printer. The lines L1 and L2 represent, respectively, signal reception lines for the PCM data signal transmitted along the data transmission line. The signal line L3 represents a two-balanced or unbalanced wire line of the telemetry channel. Terminal 10 is the part of the terminal which receives and transmits PCM signals and is diagrammatically illustrated as including a receiver regenerator R0r, a transmitter R0t, a telemonitoring exchange CTS0 associated with receiver R0r and transmitter R0t, and filter 27 which is the input filter for telemetry signals TEL in the PCM channel. At the output terminal of filter 27 there is a compound data-telemetry signal PCM+TEL which is forwarded to a remote terminal (not shown) by means of successive regenerations in respective intermediate repeaters 20(1) to 20(n). The first repeater 20(1) includes a filter 28 which separates PCM signals onto line 12 (to the Rlt repeater amplifier) and the telemetry signals TEL onto line 11 (to the telemonitoring exchange CTS1). The latter is made up of the elements located in the dashed rectangle designated CTS1. A switch 41(1) is employed to check, under the control of supervisory terminal TT, the status of either the transmission regenerator R1t or the reception regenerator R1r. A local oscillator 29(1) provides basic timing signals for the circuit. Error detector 30(1) has an output signal which is applied to the counter 31(1) which is in turn connected to the status computer 32(1). The status computer 32(1) commands the answer regenerator 33(1) which causes the answer transmitter 34(1) to transmit the regenerated answer towards the supervisory terminal TT through line 35(1) and line 11. Transmitter 34(1) sends to the supervisory terminal TT not only its own answer, generated in answer regenerator 33(1), but also the answers from the downstream or subsequent regenerators 20(2) through 20(n) on lines 35(1) and line 11. In the same way, the interrogation receiver 36(1) regenerates the interrogation signal from the supervisory terminal and sends it through transmitter 37(1) to the next repeater 20(2) on line L3 in the forward direction. Finally, an automonitoring device 38(1) acts on the interrogation receiver 36(1), the answer transmitter 34(1), the answer receiver 39(1) and the interrogation transmitter 37(1). The dashed rectangle containing the telemetry exchange CTS1 illustrates an especially advantageous characteristic of the present invention whereby all of the telemonitoring elements in a repeater are part of a single integrated circuit.

By way of example, the described system is preferred for data transmission at 2 megabit per second rate. Every function (except for the passive portion of local oscillator 29) is integrated in a CMOS gate array with the lowest possible cost, energy consumption and space.

FIG. 2 is a more detailed schematic diagram of a single repeater 20(i) which is equivalent to and bears similar reference numerals and letters to regenerator 20(1) of FIG. 1. In regenerator 20(i) switch 41 is eliminated and is replaced by coupling transmitter 42(i). In addition, error detector 30(i) is disposed apart from the integrated CMOS gate array, this arrangement being preferable for 560 megabit per second data transmission.

FIG. 3 is a detailed block diagram of the supervisory terminal components wherein the same reference numerals of FIG. 1 are employed.

FIG. 5 is a timing diagram which illustrates the INTn interrogation and ANSn answer sequence between two successive repeaters 20(n) and 20(n+1), which repeaters are more simply designated by the letters A and B. Repeater A is shown to first receive the interrogation signal INTn from the supervisory terminal TT and then generate its answer ANSn which is transmitted toward the supervisory terminal. This is followed by the answer signal ANS(n+1) from repeater B which is regenerated at repeater A. Similarly, in repeater B the interrogation signal INT(n+1) is received while repeater A provides the answer ANSn to the supervisory terminal. This is followed by the answer from terminal B ANS(n+1) which is regenerated at repeater A after a delay of a fraction of a second.

FIG. 6 illustrates the time interval between an interrogation signal INTm and the following interrogation signal INT(m+1) from the supervisory terminal. During this interval all of the answers from all of the repeaters are received, indicating repeater status at the time "m". It should be noted that in the system according to the present invention, the telemonitoring terminal 10 is capable of performing the following functions:

(a) autodiagnosis;

(b) selection of the telemonitoring mode and procedure;

(c) forwarding the interrogation signal onto the telemetry channel (FIG. 5);

(d) receiving the status information transmitted on the telemetry channel (FIG. 6);

(e) storing and processing the received data at microprocessor 23;

(f) displaying the status of the line repeaters at display 24;

(g) localizing failures in the telemetry channel;

(h) allowing the interface to the printer (optional); and

(i) presenting a serial interface for data transmission towards the maintenance ccenter (optional).

Furthermore, the telemonitoring terminal TT can optionally be employed within a remote computing system.

According to one embodiment of the invention, the structure of the telemonitoring terminal TT includes a subframe (for example, a 200 mm sub-rack) which can also be permanently located within the exchange rack. As the telemonitoring system is based on a sequential interrogation and answer concept, a great advantage is obtained in that the regenerators do not need to be specialized, and in that the telemonitoring can be carried out from a single fixed station. Moreover, the telemonitoring system automatically monitors itself in the sense that it detects a failure on the telemetry line. As pointed out above, supervisory terminal TT forwards the interrogation signal INT which, if recognized by the regenerator, results in the answer ANS representing the regenerator status. The last regenerator also provides an end of chain signal.

According to a particular embodiment of the present invention, the characteristics of the various signals for a 565 megabit per second transmission rate are as follows:

The telemonitoring message includes the following typical information code:

The maximum number of regenerators that can be employed with the telemetry approach of the present invention is practically without limit; e.g., 500 regenerators are readily within the system capacity.

As illustrated in FIG. 3, the supervisory terminal TT includes the following elements: interface 22 for the telemetry signal; information microprocessor 23; display 24; interface for printer 42 and serial bus 26; and voltage supply 43. The functions performed by each of these elements are described below.

The interface 22 for the telemetry signal enables the transmission of the interrogation signal on the telemetry channel and the reception of the answer signals. The detailed schematic diagram of interface 22 is illustrated in FIG. 4. Interface 22 performs modulation 51 and demodulation 52 of the telemetry signal carrier which is generated at 24. The useful information message is provided in parallel form by the SIPO 53.

FIGS. 7(a), 7(b) and 7(c) are timing diagrams of some examples of the following functions: (a) check on answer protocol; (b) guard window for the interrogation signal; and (c) guard window for the repeater answers.

The information microprocessor 23 operates according to the flow chart illustrated in FIG. 8. When the microprocessor has been set on active status through menu guidance, it is preset for:

(1) autodiagnosis of the correct performance of the telemonitoring terminal;

(2) operating data insertion (e.g., the number of the regenerators, etc.);

(3) operation in:

(a) automatic mode--Though terminal provides as its first output or displayed segment of information the "worst" repeater status for the interrogated system along with an indication of the error rate for that repeater. The error rate is indicated with an accuracy of a decade. The operator can successively perform an examination or survey on the proper operation of the other repeaters. An examination routine may be preset with a fixed threshold (ET FIXED) for the error rate; in this case, the first repeater which exceeds the preset error rate threshold is identified at the display.

(b) manual mode--In this mode, the operator sets the monitoring operation for the system or for each repeater. The operations include detection of the error rate, detection of a predetermined error rate being exceeded, and error storage or accumulation.

(c) test mode--The telemonitoring terminal provides a special interrogation signal (two bits) which enables the terminal (e.g., the 565 megabit per second terminals) to receive an intentionally inserted error rate on the PCM signal (e.g., greater than 10.sup.-7) without any alteration of the binary information. The insertion of the error rate lasts for approximately thirty seconds. During this time, the supervisory terminal checks that the error counters at the repeaters perform the measurement correctly; otherwise, the supervisory terminal provides an indication of a malfunctioning repeater. The results of the measurement are displayed at the alphanumeric display 24. This display includes the repeater number to which the measurement relates, the measured error rate, and the accumulated errors (when the terminal is preset for this measurement).

The interface 26, 42 for the printer and serial bus is an optional feature which permits interfacing with a printer (such as the model HP 5150A) using an interface of the HP-IB type, and interfacing with a serial bus. The characteristics of this interface follow the CCITT recommendations.

It is to be understood that the preferred embodiments disclosed hereinabove are by way of example only and that the true scope of the present invention is to be measured by the appended claims.