JPH0251309B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an audible signal identification method for an audible signal provided in a digital code format in a time division digital switch.

Time division digital switching equipment is becoming the most popular switching equipment due to rapid advances in digital communication technology and LSI technology. Furthermore, due to its affinity for digital signals, its scope of application is expanding not only to telephones but also to data terminals and data processing devices. Particularly from the point of view of streamlining business communications, the emergence of an integrated voice/data switch that accommodates both telephone and data equipment and exchanges them all together is essential.

There are various ways to implement such an integrated voice/data switch. For example, it is conceivable to provide advanced functions to the exchange itself using a packet switching method, but it is also possible to achieve this by interconnecting devices with equivalent functions using a circuit switching method. This is because, in this method, the exchange itself becomes extremely simple, and the restrictions on connections with terminals and the like are relaxed.

There are several possible circuit switching methods. The big issue here is how to deal with the differences in terminal types. Particularly problematic is the difference in line control signals between the terminal and the exchange, such as line setting, disconnection, and transmission of selection signals. On the other hand, the method of using different line control signals for each terminal has the disadvantage that the control program for the exchange becomes complicated, and it is necessary to register the type of terminal, which causes inconvenience when changing. On the other hand, if an interface circuit is provided at the input section from the terminal to the exchange, and this interface circuit unifies the line control signals so that all terminals look exactly the same from the control section of the exchange, the above-mentioned method can be achieved. It has no problems and is extremely advantageous. Furthermore, since telephones are considered to be the most common terminal in business communications, a method of unifying the line control signals of each terminal into the line control signal of the telephone is promising.

In other words, in the above-mentioned interface circuit, call origination and call termination signals (STX,
(ETX, etc.) into off-hook and on-hook signals, and converts selection signals from character dials, etc., into dial pulses or push button signals. On the other hand, the exchange sends audible signals (such as dial tone, busy tone, ringback tone, etc.) to notify the call progress status, such as ready to receive dialing, busy, ringing, etc. The interface circuit converts these signals into ACK, NACK, Ready,
It must be converted to a signal such as Wait. Therefore, the interface circuit requires an audible signal identification circuit.

However, since these audible signals have conventionally been used to prompt humans to perform actions and to determine the progress of a call, it can be said that there are almost no examples of circuits that allow machines to recognize these audible signals. However, by analogy with the function of specific frequency identification from audio signals as well, if an audible signal identification circuit is constructed in the style of a push button signal receiver (PBR), it will be as shown in FIG. 1. Note that these audible signals are, in principle, signals expressed in the form of the sum of sine waves of two frequencies.

In FIG. 1, the received digital code (a standard 8-bit PCM code) applied to the input terminal 10 is a compressed nonlinear code, so it is converted into a linear code by the decompression circuit 11.
It is added to the low-pass filter 12 and the high-pass filter 13. Both of these filters are digital filters, and the cutoff frequency is determined depending on the two frequencies contained in the audible signal to be discriminated. For example, in the case of a dial tone consisting of two frequencies, 350 Hz and 440 Hz, it is easy to set the boundary at 395 Hz, which is the intermediate frequency between the two, and pass the frequency components below that to the band filter 14, and the frequency components above that to the band filter 14. Add to 15. The filters 14 and 15 are narrow band filters whose center frequencies are two frequencies included in the audible signal to be identified, and are also constructed from digital filters. The dial mentioned earlier
In the tone example, the filter 14 has a center frequency
350Hz, filter 15 is a 440Hz band filter. In this way, desired frequency components are extracted by the filter and added to the detection circuits 16 and 17 to measure the level of each frequency component. The determination circuit 18 determines the presence or absence of an audible signal from the measured level and outputs the result to the output terminal 19.

When there are several types of audible signals, a set of a low-pass filter, a high-pass filter, and a band filter, a detection circuit, and a determination circuit are provided for each type to identify the presence or absence of each audible signal. Examples of audible signals other than dial tone include ringback tone: 440Hz and 480Hz.
Hz, busy tone: 480Hz and 620Hz, etc.

In the conventional audible signal detection circuit as described above, the frequency components are 350Hz and 440Hz in the above example.
There are four types: Hz, 480Hz, and 620Hz, but the combined frequencies and frequency differences are different, and the smallest frequency difference is 40Hz, which is quite small. Therefore, the cut-off frequencies of the low-pass filter 12 and the high-pass filter 13 are different, and a high-order filter is required to deal with small frequency differences. This increases the number of filters and the complexity of the individual filters.

Also, as in the case of PBR, such an audible signal identification circuit prevents malfunctions in response to audio signals,
Furthermore, in order to quickly and accurately detect a desired audible signal, various characteristic standards must be set and the order, coefficients, etc. of the filter must be optimally designed to meet these standards. A further problem is that the standards for the audible signals themselves, such as dial tones and busy tones, are not as unified and standardized as push button signals (PB signals). In other words, it is necessary to optimally design a filter that satisfies the characteristic standards as described above for various audible signals each time, which is complicated and inefficient, and increases the cost due to the increased amount of work required for design. It also leads to Furthermore, it is not desirable to include such a complicated circuit in each interface circuit provided for each terminal. Therefore, the method of unifying line control signals using an interface circuit also has little feasibility.

Although the above explanation assumes a digital filter, it is of course also possible to convert a digital code into an analog signal by a decoding circuit and construct an audible signal identification circuit using an analog filter. be. However, even in that case, the design of the filter will be more complicated and difficult than in the digital case.

The present invention aims to eliminate such drawbacks in the prior art and to provide an extremely simple and highly accurate audible signal identification method by slightly reducing the quality of the audible signal.

That is, according to the present invention, in the audible signal identification method in a time-division digital switch, the audible signal generating circuit assigns a unique bit pattern that is different for each audible signal to the least significant bit of each code of a digital code series representing the audible signal. insert and output,
The audible signal receiving circuit constantly monitors the least significant bit of the received digital code, and detects the audible signal by observing whether the bit sequence of the least significant bit matches a bit pattern specific to each of the audible signals. An audible signal identification method is obtained which is characterized by identifying the presence or absence and type of an audible signal.

The present invention will be described in detail below with reference to the drawings.
FIG. 2 is a diagram showing an embodiment of the present invention. In FIG. 2, the audible signal generation circuit 20 has a read-only memory (read Only Memory (hereinafter abbreviated as ROM) 21. By reading this ROM by an n-ary counter 23 incremented by a sampling clock applied to an input terminal 22, the code sequence is repeatedly obtained, which is further processed by a parallel-to-serial converter 24. It is converted into a serial signal and supplied to the communication path 25 of the exchange. Call path 2
5 exchanges this signal and distributes it to subscribers in need. An interface circuit (subscriber circuit) 27 for the telephone subscriber 26 converts this signal into an analog format audible signal using a serial/parallel conversion circuit 28 and a PCM decoding circuit 29, and allows the telephone subscriber 26 to hear this audible signal. That will happen.

Now, in the audible signal generation circuit 20, ROM2
1 stores a PCM code of 8 bits/code, of which the least significant bit is not supplied to the parallel/serial conversion circuit, but instead is supplied with the output of the pattern generator 30. Pattern generator 30 is also operated by the sampling clock applied to input terminal 22 and outputs a fixed pattern one bit per sampling clock. For example, an 8-bit fixed pattern 01010101 is repeatedly output bit by bit.

The audible signal generation circuit 31 is the audible signal generation circuit 20
Although this is a circuit for generating an audible signal different from the one shown in FIG. However, the pattern generator 35 generates a fixed pattern different from that of the pattern generator 30, for example, 00110011.

In this way, an audible signal generation circuit is provided for each required audible signal, and a PCM representing each audible signal is provided.
The least significant bits of the code repeat a unique bit pattern that varies with each audio signal.
However, each bit pattern must not be indistinguishable from other bit patterns when it occurs repeatedly. That is,
Each bit pattern must be chosen such that when it is cyclically shifted by any number of bits, it will not match any other bit pattern. In the above explanation, the generation circuits for each audible signal are spatially separate for convenience of explanation, but by using time-division multiplexing of the circuits, a large portion of the circuits can be made common, and multiple circuits can be generated as a whole. It is extremely easy to obtain an audible signal generation circuit that generates several audible signals.

For the audible signal generated in this way, the interface circuit 37 for the data terminal 36 converts the PCM code received from the communication path 25 into a parallel signal by the serial/parallel conversion circuit 38, and converts the least significant bit of the signal into a parallel signal. Each audible signal is monitored by detection circuits 39, 40, and the presence or absence of an audible signal is identified by whether it matches the bit pattern specific to each audible signal previously described. for example,
If the pattern 01010101 is repeated, it is determined that the first audible signal is being received, and 00110011 is received.
If this pattern is repeated, it is determined that the second audible signal is being received. If the received PCM code corresponds to an audio signal, the bit pattern of the least significant bit can be considered to be approximately random, and the bit pattern unique to each of the above audio signals is continuously repeated for a predetermined period of time. It can be said that it is rarely repeated faithfully. Furthermore, although data signals are not as random as audio signals, if they are observed over a fairly long period of time, it is unlikely that they will be mistakenly recognized as an audible signal.

When the interface circuit 37 identifies the audible signal in this way, the interface circuit 37 selects the content as Ready or Wait.
Data terminal 3 converts it into a signal suitable for the data terminal.
Send to 6. Note that in FIG. 2, the portion that performs this conversion is omitted.

On the other hand, the audible signal is directly converted into an analog waveform by a decoding circuit 29 and supplied to the telephone subscriber 26. Therefore, the portion of the fixed pattern inserted into the least significant bit that differs from the original code becomes noise, degrading the characteristics of the audible signal. The quality is essentially the same as that of a 7-bit PCM code, but the audible signal level is usually within a good S/N level range most suitable for encoding, so the S/N is about 32 to 33 dB. can be obtained sufficiently. Therefore, auditory deterioration is hardly perceptible.

In the above description, the communication path 25 has been described as a serial communication path, but the present invention is equally applicable even if the communication path 25 is a parallel communication path. In that case, the effect is even greater because a parallel-to-serial conversion circuit and a serial-to-parallel conversion circuit are not required.

FIG. 3 shows the pattern generator 3 in FIG.
0 and 35 are diagrams showing specific examples of circuit configurations. However, since the pattern generator itself is an existing technology and many examples already exist, only a very simple example is shown in FIG. First, FIG. 3A shows an example in which a 3-bit octal counter is used as a pattern generator. A counter 42 counts up by a sampling clock applied to an input terminal 41, and 8-bit fixed patterns of 01010101, 00110011, and 00001111 are repeatedly output to output terminals 43, 44, and 45, respectively.
Each of these bit patterns is a combination that will not match any other bit pattern even if it is cyclically shifted by an arbitrary number of bits. By inserting each of these outputs into the least significant bit of each audible signal, the audible signal generating circuit shown in FIG. 2 can be constructed. Figure 3A shows another example of a pattern generator.
An octal counter 4 counts the 8-bit pattern set in the pattern setting circuit 46 by the sampling clock applied to the input terminal 47.
The selection circuit 49 sequentially selects and outputs one bit at a time according to the output of the bit. With this circuit, unlike method A, any bit pattern can be generated; however, as mentioned above, each bit pattern is different from other bit patterns even if it is shifted cyclically. It is necessary to choose combinations that do not match.

The pattern detection circuit is also an existing technology, but the fourth
An example is shown in the figure. In FIG. 4, the input terminal 50
The least significant bit of the received PCM code is input to
The sampling signal applied to the input terminal 51
input to the shift register 52 by the clock;
After that, they will be shifted sequentially. The shift register 52 is an 8-bit shift register, and its output is
It is supplied to the ROM 53 as an address. ROM5
Reference numeral 3 denotes a memory that stores as data which of the bit patterns of the least significant bits unique to each audible signal correspond to the 8 bits of the input address. For example, 3 of 01010101, 00110011, 00001111
ROM for identifying different bit patterns
The memory contents of 53 are shown in FIG. However, FIG. 5 shows the contents of the first half of addresses 0 to 255. In FIG. 5, the first bit #1 of the data stores "1" when the address corresponds to the bit pattern of 01010101, and "0" otherwise.
Similarly, when the second bit #2 corresponds to 00110011, "1" is stored when the third bit #3 corresponds to 00001111. Therefore the address
00001111, and the addresses 00011110, 00111100, which are cyclically rotated one bit at a time.
... has 001 as data, address 00110011,
01100110,... has data 010, address
Data 100 is stored in 01010101 and 10101010.
Further, data 000 is stored in addresses other than this (portions indicated by dotted lines in the address column in FIG. 5).

Therefore, each output of the ROM 53 corresponds to the presence or absence of a particular audible signal bit pattern.
Counters 54 and 55 output the presence or absence of each audible signal to output terminals 56 and 57 by counting sampling clocks based on their outputs. That is, when the output of the ROM 53 is 1, the counters 54 and 55 count up according to the sampling clock, and output "1" to the output terminal 56 or 57 when a predetermined number is reached. Thereafter, while the output of the ROM 53 is "1", counting up is stopped and the same state is maintained. on the other hand
When the output of the ROM 53 becomes 0, the counter 54 or 55 is reset to 0, and the output also becomes 0. That is, this circuit is a circuit that determines that an audible signal has been received when a unique bit pattern appears in the audible signal consecutively a predetermined number of times. The inversion gate 58 is provided to prevent the change point of the read address of the ROM 53 and the timing of the count-up of the counters 54 and 55 from overlapping.

In the above description, an example in which an 8-bit unique bit pattern is used is shown as an example, but this is not intended to limit the scope of the present invention in any way.
It is also possible to use a so-called self-synchronizing code as the unique bit pattern.

In addition, the unique pattern of the least significant bit itself is stored in the ROM (21 and 32 in Figure 2) in the audible signal generation circuit.
Another possible method is to store the data as data. However, in this case, since the number of data stored in the ROM for each audible signal is different, the fixed pattern is not necessarily accommodated in the data series stored in the ROM. Therefore, some refinement is necessary. FIG. 6 shows an example.
In Figure 6, the lowest bit of each data is
A fixed pattern 0111 is embedded, but due to the number of data, the fixed pattern cannot fit in the last part of the data series. Therefore, this part is all set to 0. On the other hand, the audible signal receiving circuit counts the number of consecutive 1's in the sequence of the least significant bit of the code. It may be determined that an audible signal has been received. In Figure 6, MSB is the most significant bit,
LSB is the least significant bit, X is “0” or “1”
represents arbitrary data.

As can be seen from the above description, the audible signal identification system according to the present invention has an extremely simple configuration for both the audible signal generation circuit and the audible signal reception circuit. First of all, there is no need for an expansion circuit for the digital filter or a decoding circuit for the analog filter. Further, complicated functions such as filters and circuits themselves are not required, and there is no need to perform optimal design of filter orders and coefficients. Also, even if the audible signal itself changes, the pattern generator and pattern detection circuit can remain the same. On the other hand, sufficient discrimination characteristics can be obtained by lengthening the pattern monitoring time.

Therefore, according to the present invention, an audible signal identification method with excellent characteristics can be obtained with a very simple configuration without using complex functions and circuits such as filters, and its effects are extremely large. .

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an audible signal identification circuit according to the prior art, FIG. 2 is a block diagram showing an embodiment of the present invention, and FIGS. 3A and 3B are circuit examples of the pattern generator in FIG. FIG. 4 is a block diagram showing an example of the pattern detection circuit in FIG. 2, FIG. 5 is a diagram showing an example of the memory contents in FIG. 4, and FIG. FIG. 7 is a diagram showing an example of the contents of a memory in another embodiment of the invention. In the figure, 11 is an expansion circuit, 12, 13, 1
4, 15 are filter circuits, 23, 33 are counters, 21, 32 are ROMs, 24, 34 are parallel-to-serial conversion circuits, 28, 38 are serial-to-parallel conversion circuits, 30, 3
5 is a pattern generator, 39 and 40 are pattern detection circuits, 29 is a decoding circuit, 42 and 48 are counters,
49 is a selection circuit, 52 is a shift register, and 53 is a selection circuit.
ROMs 54 and 55 are counters.

Claims (1)

[Claims] 1. An audible signal identification method in a time division digital exchange, in an audible signal generation circuit,
A unique bit pattern that differs for each audible signal is inserted into the least significant bit of each code of a digital code series representing an audible signal and output, and the audible signal receiving circuit always uses the least significant bit of the received digital code. The presence or absence of an audible signal and the type of the audible signal are identified by monitoring and observing whether the bit sequence of the least significant bit matches a bit pattern specific to each of the audible signals. Signal identification method.