4 number of binary signals delivered
This invention relates to a method for transmitting a signal in HDBn code combined with an auxiliary binary signal on a digital transmission medium.
The auxiliary signal has a lower bit-rate than the bit-rate of the HDBn code signal. More particularly, the invention concerns such a method specially adapted to the monitoring of pairs of repeaters in a bidirectional digital transmission line between a monitoring end equipment and a monitored end equipment.
The majority of known repeater monitoring systems involve a frequency combination of the information signal whose in-line code is an HDBn code, and of one or more binary remote locate signals which modulate a low-frequency subcarrier with a frequency decidedly lower than that of the information signal.
The end equipments and repeaters in these systems comprise, associated with each of two channels of the line, separating and combining filters for the low-frequency remote locate auxiliary signals transmitted from the monitoring equipment or low-frequency auxiliary signals representative of repeater error rates and transmitted from the repeaters with the respective information signal toward the monitoring equipment.
The filters consists of transformers and shock coils which have the drawback of being heavy and cumbersome. Additionally, the use of such filters prevents high ratios between the information signal bit-rate and the auxiliary signal bit-rate.
4 number of binary signals delivered results in restricting any remote monitoring of 4 number of binary signals delivered bit-rate digital information signals using low-frequency 4 number of binary signals delivered signals; this 4 number of binary signals delivered is becoming much more common-place in digital transmission trunks between multistage multiplexers-demultiplexers.
Another object of this invention is to do away with the need for a carrier frequency in order to transmit the auxiliary signals. A further object of this invention is to obviate any detrimental spectral congestion of the base band that the auxiliary signals might cause.
Transmission of the auxiliary signal simultaneously with the HDBn code information signal is thus carried out by a modification of predetermined element sequences of the HDBn code signal, i.
By comparison with the combining filters and modulators in the known monitoring systems, an encoder for obtaining the encoded sequences and a decoder for decoding the encoded sequences can be integrated and thus offer much reduced costs and dimensions.
Furthermore, no limit on the ratio between the bit-rate of auxiliary binary signals and the bit-rate of the HDBn code information signal is required. The method in accordance with the invention is applied in particular to the remote monitoring of bidirectional pairs of repeaters included in a digital transmission line between a monitoring end equipment and a monitored end equipment.
An auxiliary remote locate signal is transmitted from the monitoring equipment to the monitored equipment for interrogating remote locate means associated with the repeater pairs. An auxiliary response signal responsive to the remote locate signal is transmitted from the remote locate means in the pair of repeaters toward the monitoring equipment.
The auxiliary signal bits having the predetermined binary state modify one or more predetermined sequences included in the respective HDBn code information signals delivered from the end equipments.
Further advantages of the present invention will be more clearly apparent from the following more particular description of preferred embodiments of this invention in reference to the corresponding accompanying drawings in which:. A reminder is first of all given of the features regarding a high-density binary code HDBn as referred to for example in an article by T.
In the HDBn code, n is a predetermined integral number indicating the maximum number of successive zeros that may be contained in the bipolar signal. The mark V is a bipolar mark which violates the bipolarity, i. The bipolar mark B obeys the alternation in polarity: By way of an example, the first three lines in FIG.
The fourth and fifth lines in FIG. According to the invention, predetermined sequences of the digital information signal in HDBn code to be transmitted are modified when an auxiliary binary signal has a predetermined binary state. The auxiliary binary signal is transmitted over a same transmission medium as that of the information signal in HDBn code in a digital transmission system.
The auxiliary binary signal has a binary rate much below that of the information signal such that during the elementary period of a binary element in the auxiliary signal, a statistically high number of predetermined sequences destined for modification in the information signal are transmitted.
Rephrasing this, one of the binary states in the auxiliary signal is recognized when several predetermined sequences of the HDBn code are present during the elementary period and are modified such that they cannot be normally present 4 number of binary signals delivered the information signal, in the absence of any auxiliary signal.
The following convention is adopted. The "zero" state binary elements of the auxiliary signal do not modify the information signal and the predetermined "one" state binary elements of the auxiliary signal modify one or more of the four predetermined sequences in the HDBn code signal.
Table II below summarizes the various modifications possible which can be applied 4 number of binary signals delivered the four different predetermined HDBn code sequences. By way of an example, it is assumed that the bipolar code for the PCM information signal is the HDB3 code and that two predetermined sequences are to be modified. The two predetermined sequences can be a and d as illustrated in the sixth line of FIG.
For both these cases, 4 number of binary signals delivered is only one permutation. In an information signal of this nature, the statistical time interval which separates two usable bipolarity violations, i. This high number makes it possible to avoid any error in decoding the auxiliary signal. A decoder embodying the invention enables a binary element "1" in the auxiliary signal, for example, when the decoder has recognized a number of modified sequences lying between and over the elementary period of 5 ms.
To obviate any mistake at the receiver end, when restoring the auxiliary signal, each binary word of the auxiliary signal is successively repeated in the transmission end, P times for instance, in order to form an auxiliary sequence. P is an integral number greater than two and in practice equal to ten or so. The encoding and decoding operations are based on the fact that to detect a sequence such as d or d 0the sequence converted into binary code for the same polarity as the marks it contains, corresponds to a sequence of zeros after conversion into binary code for an opposite polarity.
The encoding and decoding operations are performed using shift registers. With reference to FIG. The output of the flips-flops - to - in the second register 11 - are connected to inputs of a NOR gate In the encoder 1, an AND gate 14 has two inputs that are connected to the outputs of the gates 12 and 13, and a third input which receives the auxiliary binary signal. The converter 17 performs the inverse operation to that performed by the input converter The decoder 2 depicted in FIG.
The outputs of the flips-flops - to - in the other register 21 - are connected to the inputs of a NOR gate In the decoder 2, an AND gate 24 has two inputs connected to the outputs of the gates 22 and The "1" state of the auxiliary signal is enabled later when a number of successive "1" bits at the output of the gate 24 lies between and for 5 ms as already stated.
A "1" bit is detected in the auxiliary signal by means of an auxiliary signal restoring circuit such as circuit 28 illustrated in FIG. The circuit 28 comprises a counter and a unretriggerable monostable flip-flop Clock input H in counter and the input of flip-flop are connected to output of AND gate Flip-flop output delivers a 5 ms pulse to a counting input of the counter in response 4 number of binary signals delivered a "1" bit of its input whatever the later state on its input during the following 5 milliseconds.
The counter counts the sequences d 0 for 5 ms following in practice the positive going edge of a "1" bit in the auxiliary signal. At the end of the 5 ms, an output bus 4 number of binary signals delivered the counter 28 delivers the count of detected sequences d 0i.
Inputs of an AND gate are connected to the outputs of the comparators and When the number of sequences d 0 lies between andthe output from AND gate provides a "1" bit which through a monostable flip-flop is converted into a "1" bit of the auxiliary signal having an elementary period of 5 ms.
Until such time as input of gate 24 is no longer in the "0" 4 number of binary signals delivered, the information signal received at the input of the decoder goes unmodified. In response to a "1" bit on output of gate 24, i. Using the structures for the encoder 1 and the decoder 2 described hereinafter, those skilled in the art can design encoders and 4 number of binary signals delivered for other predetermined sequences such as a, b, c to be modified into any HDBn code.
Between the two end equipments 3 and 4, a first information digital signal is transmitted in a forward direction, from the equipment 3 to the equipment 4 via forward repeaters 5 1 to 5 Mand a second information digital signal is transmitted in a backward direction from the equipment 4 to the equipment 3 via backward repeaters 6 M to 6 1.
The transmission medium in both the forward and backward directions includes, for example, a coaxial cable 50, 60, although it may be a radio link or an optical fiber line.
The remote monitoring of the bidirectional pairs of repeaters 5 1 -6 1 to 5 M -6 M consists essentially of the transmission of an auxiliary signal called as a remote locate signal from the monitoring equipment 3 in the forward channel 4 number of binary signals delivered and the transmission of an auxiliary signal called as a performance signal from each pair of repeaters 5 1 -6 1 to 5 M -6 M toward the monitoring equipment 3 via the backward line The monitoring equipment 3 includes several encoders analogous to that 1 of FIG.
In practice, the performance signal supplied by each pair of repeaters 5 1 -6 1 to 5 M -6 M indicates the error rate detected in the forward and backward information digital signals in response to the interrogation by the detected remote locate signal.
The remote monitoring operation is performed step-by-step. For the monitoring equipment 3 to acquire the error rates from all the repeaters in the line, including those contained in the equipments 3 and 4, a remote monitoring and acquisition cycle is longer than the forward and backward transmission path of an auxiliary signal binary element in the transmission line The acquisition cycle of error rates in the forward and backward repeaters of all the pairs can be analogous to that described in U.
Referring to this patent, the control pulse transmitted in the forward direction and modulating a low frequence signal is replaced by an auxiliary remote locate sequence according to the invention.
The supervisory bit pattern which indicates the error rates in both repeaters of each pair with respect to predetermined error-rate ranges and which modulates the low frequency signal, is replaced by two auxiliary response sequences according to the invention.
The 4 number of binary signals delivered and modulators equipping the repeaters disclosed in U. For instance, the latter three performance words indicate that each repeater has, during the previous remote locating and acquisition cycle, detected a certain number of errors in the respective digital signal that is less than 2 3 -1, lying 4 number of binary signals delivered 2 3 -1 and 2 9 -1, or greater than 2 9 A further method for remote monitoring repeaters is now described in reference to FIG.
This method enables to locate each pair of repeaters individually without remotely locating all the repeaters in the digital transmission line. Each pair of repeaters 5 m -6 m is associated with a remote locate circuit 7 m.
On the side of monitoring equipment 3, the circuit 7 m comprises two detectors 70 and 71 including decoders analogous to that 2 is FIG. Detectors 70 and 71 respectively decode and enable an auxiliary remote locate signal and an auxiliary so-called remote locate end signal transmitted in the forward channel from the monitoring end equipment 3. 4 number of binary signals delivered remote locate signal is composed of sequences each having P successive auxiliary binary words such as "10".
The remote locate end signal is composed of a sequence having Q successive auxiliary binary words such as "11". Two counters 72 and 73 count P recurring words "10" and the recurring words "11" respectively. The counter 73 is automatically reset to zero RS when its count has reached Q, and simultaneously controls the zero-reset in the counter The count in the counter 72 is blocked at P after P detected words 4 number of binary signals delivered have been counted.
Provisions are made in the forward channel 50 upstream of the input of the forward repeater 5 for a circuit with two parallel paths that are selected by a two-position switch 74 controlled by an output of the counter One 75 of the parallel paths is a short channel section.
The other path comprises a decoder 76 in series, analogous to that 2 in FIG. The decoder 76 decodes the modified predetermined sequences, such as a 0d 0 in accordance with 4 number of binary signals delivered invention, into normal sequences such as a, d of the information digital signal.
The decoder 76 does not comprise an auxiliary signal restoring circuit such as 28, preferably. The remote 4 number of binary signals delivered circuit 7 m comprises two error detecting and counting circuits 51 and 61 which respectively detect and count the errors in the information digital signals in the forward and backward channels through the repeaters 5 m and 6 m.
A coder 77 receives the error rates from the circuits 51 and 61 and codes them into binary words when the count of the counter 72 is equal to P, i. An error-rate 4 number of binary signals delivered order is delivered from the counter 72 in a link toward the circuits 51 and The coding can be analogous to that described in the above U. Two error binary words representative of the two error rates are delivered by the coder 77 and transmitted in series along a lead to an encoder The encoder 78, analogous to that 2 in FIG.
The auxiliary response signal is composed of a sequence of two binary words which are respectively identical to the two error binary words. Under normal operating conditions, namely in the absence of any remote locating operation and so long as the count in the counter 72 differs from P, the path 75 is opened by the switch 74 and the information signal in 4 number of binary signals delivered code flows through the decoder When it comes to remote-locating the pair of repeaters 5 m -6 mwhere the integral number m lies between 1 and M, the monitoring equipment 3 transmits m identical auxiliary remote locate sequences each having P recurring words "10" into the forward channel In the first remote locate circuit 7 1 associated with the pair of repeaters 5 1 and 4 number of binary signals delivered 1the detector 70 detects first of all the first sequence of "10" words which blocks the corresponding counter 72 on P.
The output from the counter 72 turns on the "1" state and controls the corresponding switch 74 such that the switch connects the forward 4 number of binary signals delivered 50 to the respective path 75 short-circuiting the respective decoder As a result, prior to this switching operation, the predetermined encoded sequences such as d 0 in the first P words "10" replaced by corresponding HDB3 code sequences such as d in the decoder 76 which delivers the unmodified normal information signal in code HDB3 to the following repeaters 5 2 to 5 M ; the first P auxiliary words "10" thus have no effect in the other remote locate circuits 7 2 to 7 M.
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