CH620560A5 - Arrangement for monitoring tones in an exchange operated using pulse code modulation - Google Patents

Description

The present invention relates to an arrangement for the control of tones in an office operated in pulse code modulation which generates different tones in digital form from a single low frequency and a level-5 the signal, each tone from a sequence of identical cycles of a specific first duration, which cycles each contain a transmission phase of a specific second duration and an interruption phase of a specific third duration, the transmission phase consisting of a repeated transmission of N coded samples whose envelope curve is a sine line of the signal of the single low frequency mentioned and wherein the interruption phase consists of the transmission of coded samples of the analog value zero.

15 A specific number of tones must be generated in a central office to inform the subscriber of the status of the call. So e.g. a calling subscriber receives a dial tone from the office a few moments after lifting his handset, informing him that the office is ready to receive his or her choice. The calling party can also receive a busy tone from the office indicating that the called subscriber line is busy.

In order to increase operational security in the office, it is advisable to check the tones generated there by connecting an arrangement for checking these tones to the tone generation.

From the article by J.M. Kasson: «System self test, administration and maintenance in the ROLM CBX (Computerized 3o Branche Exchange, computer-controlled branch office of the ROLM Corporation), I.E.E.E. National Télécommunication Conference, 2nd-3rd Dec 1975.1. Bd., New York, a control device in a digital subscriber office for permanent testing of various functions in an unprotected Ï5 state is already known. In particular, the test procedure for the DTMF (Double Tone Multi Frequency, tone key selection) signaling equipment using a so-called tone generator of the subscriber office is described in the article mentioned. This tone generator sends out a specific number that is received 4o by a DTMF register of the office. The correct reception of this digit is checked in analog form. Such testing uses equipment that is already available in the office and is intended for making connections. In this way, however, no tones specific to the subscriber can be checked, since they do not have to be recognized by the office itself, so that this does not contain any tone receivers. In addition, a PCM office generates tones in digital form; It is therefore extremely advantageous to control these tones in digital form.

The purpose of the present invention is therefore to provide an arrangement for checking tones intended for the participants, which arrangement functions on a purely digital basis. The individual features of the arrangement according to the invention can be found in the characterizing part of claim 1.

An embodiment of the invention will now be explained in more detail with reference to the drawing. Show it:

1 and 2 two examples of tones,

3 shows a sine curve of the sound signal,

4 shows a block diagram of the arrangement according to the invention,

Fig. 5 is a flowchart which enables control of the tones shown in Figs. 1 and 2, and Fig. 6 shows another example of a tone.

b5 Fig. 1 shows a tone which is to be received by the subscriber. This tone consists of a sequence of

3rd

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identical cycles of duration Tcy. Each cycle contains a transmission phase of duration Te and an interruption phase of duration Tc. A low frequency signal of frequency Fv (period Tv) and level V is transmitted during each transmission phase. A signal of zero amplitude is transmitted during the interruption phase.

The other tones have the same frequency Fv and the same level V, but different transmission times Te and interruption times Tc, so that there are different speeds. The dial tone can be formed by the continuous transmission of a signal of frequency Fv and level V (see Fig. 2). The various tones are generated in analog form in a room switching office. In a PCM switching office, they can advantageously be produced • directly in the form of coded samples.

A PCM central office processes encoded samples of low frequency analog signals received by the subscribers. Each of the samples of the call occupies a specific time channel in a repetition period or a frame T. This period T corresponds to the sampling period of the analog signals. For example, the frame T can have 256 time channels. In order to improve the transmission quality, the samples are not linearly coded, the coding characteristic curve being approximately a logarithmic curve at. The codes contain b bits, the first bit indicating the character of the sample. The coding is symmetrical, which means that the codes of two opposite values are identical, with the exception of the character bits.

Fig. 3 shows a sine curve of the analog audio signal of the frequency Fv with the corresponding coded samples generated in the PCM switching office. The sine curve contains ^ coded samples in time segments T. The period Tv st is chosen such that it forms a multiple of T. The sine wave / sampling times are again chosen so that the samples of only a quarter of the sine curve are kept. Points A and B with a zero amplitude form sampling values.

For example, the following numerical values can be used:

Fv = 444.44 Hz

Tv = 2.25 ms

T = 125 ns

N = 18 samples b = 8 bits

V = 345 mV

Since the coding is symmetrical, points A and B from FIG. 3 corresponding to a null value will either have the code 00000000 or 10000000. In order to be able to distinguish these points, one of them should have the code i 0000000 and the other one the code 00000000.

The control function of the arrangement according to the invention is carried out in three main steps:

- detection of the transmission phase;

- detection of the interruption phase;

- Control of the appearance's appearance over several tone cycles.

If the sound is formed by a continuous transmission of a signal of frequency Fv, the control includes only one step:

- Detection of the sound signal for a given time TO.

FIG. 4 shows a block diagram of the arrangement for checking tones in a PCM switching office. The arrangement contains a first comparator Cl, which on the one hand detects the death of b bits of the sound signal to be checked and on the other hand a fixed code of b bits which represents a zero amplitude, i.e. receives the code OOOOOOOO ^. The received codes are designated with RCVD and the zero amplitude code with VF0. This first comparator is used in particular for the detection of the interruption phase. A second comparator C2 receives on the one hand the codes RCVD and on the other hand a fixed introduction code VFI consisting of b bits. The code VFI corresponds to one of the samples forming the tone and should only be present individually in a period Tv. In the case of the codes shown in FIG. 3, it will consequently be the code 10000000 (point A). The function of this second comparator will be described later. A third comparator C3 receives both the codes RCVD and the b-bit codes, which are supplied by a read-only memory ME with N lines. Each line contains a sample i5 of the tone signal transmitted by the exchange; the various Abja values are grouped in the same order as that of the audio signal transmitted. The first line of the memory ME contains the introduction code VFI. The memory ME is addressed by a counter K, which is switched on by clock pulses H1 with a period T. The comparator C3 is used for the detection of the transmission phase. The pulses H1 are supplied by a clock generator CL.

The clock generator CL also generates pulses H2 with a period T2 (where T2 is a multiple of T, e.g. 4 ms), which switch two time counters TKR and TKL through a frequency divider D. This divider provides the counter TKR with pulses H3 with a period T3 (where T3 is a multiple of T2, e.g. 32 ms) and the counter TKL with pulses H4 with a period T4 (where T4 is a multiple of T2, e.g. 192 ms).

The counter TKR is used to confirm the detection of the transmission and interruption phase. Using a decoder DTKR, it supplies a signal STe of logic level "1" at the end of time Te, which corresponds to the transmission time, and a signal STc with logic level "1" at the * * end of time Te, which corresponds to the interruption time. Depending on the value of the transmission and interruption time and the position of the control pulses H3 of the counter TKR, the transition to the level “1” of the signals STe and STc must not exactly at the end of the times Te and Tc, but before or 4 1 after these times. The decoder DTKR will consequently supply a signal STe = 1 or a signal STc = 1 for two successive codes which are present at the output of the counter TKR, the codes mentioned corresponding to the times which form the frames for the times Te and Tc. The "arrangement according to the invention must control different tones with different transmission and interruption times, so that the decoder DTKR also supplies further signals", such as STe 'and STc', which correspond to different times. There is also a signal STO of level "1" •!> Delivered at the end of the time TO, which signal corresponds to the reception of a continuous tone (eg a dial tone)

The counter TKL is also used as a time limiter to stop the tone control operation at the end of a time T1 if a tone cycle (transmission and interruption phase) was not recognized up to that time. It supplies a signal STI of level 1 at the end of time Tl via a decoder DTKL.

A counter TPRS which registers the duration of the tone cycles is advanced by one step each time a tone cycle is recognized. It delivers a signal STp of level 1 via a decoder DTPRS if it has been advanced by p steps corresponding to the recognition of p tone cycles.

The output signals from the comparators C1, C2 and C3 and from the decoders DTKR, DTKL and DTPRS are -> fed to a sequential logic circuit US which sequentially arranges the various tone control operations. This circuit receives a code ASP which indicates the key to be controlled. The circuit works due to a certain

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Number of phases S W and is controlled by clock pulses H5 of the period T It is set by a pulse GO in the start phase, this pulse being received when work is requested. The GO pulse also resets the TKR, TKL and TPRS counters. The counter TKR is also reset by a pulse CHSW, which the sequential logic circuit supplies with each phase change. In addition to the pulse GO, the counter TKL is also reset by the presence of a pulse PSW4, which is supplied by the sequential logic circuit when a tone cycle has been detected.

The three main steps for controlling a tone that have already been mentioned will now be explained in more detail:

Detection of a transmission phase

Each received code RCVD is compared in the comparator C3 with the codes MEC read from the read-only memory ME and cyclically addressed by the counter K. However, in order to synchronize the received codes RCVD with the read codes MEC beforehand, the addressing of the memory ME is initiated by resetting the counter K by a pulse INIT generated in the circuit US when RCVD = VFI (the comparison is made by the comparator C2 carried out). The transmission phase is recognized when the codes RCVD are identical to the codes MEC (the comparison is carried out by C3) during a time period Te, this time period being determined by the presence of a signal Ste = 1 at the output of the decoder DTKR. The counter TKR must have been reset beforehand by a pulse CHSW, which pulse was delivered by the unit US: at the time the memory ME started to be read out.

Detection of the interruption phase

Each received code RCVD is compared in the comparator C1 with the code VFO representing a zero amplitude sample. The interruption phase is recognized when the codes RCVD are identical to the code VFO for a time period Tc which is determined by the presence of a signal Stc = 1 at the output of the decoder DTKR. The counter TKR has already been reset by the pulse CHSW present at the beginning of the sub-phase detection step.

Control of persistence

At the end of each recognized tone cycle, the counter.TPRS is advanced by one step by means of the pulse PSW4 supplied by the sequential logic circuit. The tone is recognized when the mentioned counter has been advanced by p steps, i.e. when p tone cycles have been detected. The decoder DTPRS then supplies a signal STp = 1 to the sequential logic circuit.

As already mentioned, checking an uninterrupted tone only takes one step:

Detection of the sound signal during a time period TO 5 The received codes RCVD should be identical to the codes MEC from the memory ME during a time period TO, which is defined by the presence of a signal STO = 1 at the output of the decoder DTKR

FIG. 5 shows a flow chart which enables the control of an io cyclic tone according to FIG. 1 and a continuous tone according to FIG. 2. The sequential logic circuit is designed as a function of this flow chart. There are six operating phases SWO to SW5:

SWO = start i5 S W1 = synchronization of the sample values MEC with the night sample values RCVD;

SW2 = detection of a transmission phase;

71- ~ SW3 = detection of an interruption phase; SW4 = continuous;

20 SW5 = result

The read-only memory in phase SWO is set by the GO pulse. The other phases follow one after the other according to the flow diagram. The pulse INIT is emitted during the transition from phase S W1 to phase S W2 25. The CHSW pulse is emitted at every phase transition. The pulse PSW4 is delivered during phase SW4.

The sequence logic circuit 'US delivers three results using a code RES:

30th

Sound detected Sound not recognized

This is the result when the sequential logic circuit is in a phase other than SWO and STI = 1. This means that non-zero codes RCVD have been received but do not match the tone codes.

No sound

40 This is the result if the sequential logic circuit is still in the phase SWO and STI = 1 This means that only zero codes were received and consequently the tones were probably not transmitted.

The previous description concerned an arrangement which recognizes continuous tones (FIG. 2) and cyclical tones, in which - "each cycle has a transmission and an interruption phase (FIG. 1). However, it can also recognize more complex tones, e.g. For example, two different transmissions w phases Tel and Te2 and two different break phases Tel and Tc2 per cycle (see Fig. 6). The subsequent logic circuit must then be designed differently.

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Claims (5)

620560 PATENT CLAIMS L Tone control arrangement in a pulse code modulated office which generates various tones in digital form from a signal having a single low frequency (Fv) and a level "l <V), each tone being a sequence of identical cycles of a specific first duration (Tcy), which cycles each contain a transmission phase of a specific second duration (Te) and an interruption phase of a specific third duration (Tc), the transmission phase consisting of a repeated transmission of N coded samples, the envelope curve of which Sine line of the signal of the aforementioned single low frequency (Fv) is, and the interruption phase consists of the transmission of coded samples of the analog value zero, characterized by first means (K, ME, C3, C2, TKR) for recognizing the transmitted samples, one after the other, during the second period (Te), by second means (Cl) for recognizing coded A samples, the value of which is zero during the third duration (Tc), by third means (TPRS) for controlling the persistence of the phenomenon over a number p consecutive cycles, and finally by fourth means (TKL), which stop the control operation if at the end of a certain limited period of time, a cycle was not recognized. 2. Arrangement according to claim 1, characterized in that the first means contain the following elements: a read-only memory (ME) with N lines, which is addressed by a cyclic counter (K) with the same period as that of the samples to be recognized, wherein the N lines of the memory contain N consecutive samples, the envelope of which is the sinusoidal sound signal; a first comparator (C3) which on the one hand receives the samples (RCVD) to be recognized and on the other hand the samples (MEC) read from the read-only memory; a synchronization circuit with a second comparator (C2), which on the one hand receives the samples to be recognized and on the other hand a fixed introduction sample (VFI), which was selected from the N samples and is only present individually in a sine curve, the second comparator receiving the sets the cyclic counter (K) so that the latter addresses that line of the read-only memory which contains the introductory sample; and a time counter (TKR), which is advanced by clock pulses (H3) and a signal (STe) of logic level "1" at the end of the second period. (Te) returns the period of time that begins at the moment the cyclic counter is set 3. Arrangement according to claim 2, characterized in that the second means contain a third comparator (Cl) which on the one hand receives the sample values to be recognized (RCVD) and on the other hand a fixed zero amplitude sample value (VFO), and that the time counter (TKR) at the end of the third duration (Tc), which begins at the moment of the detection phase of the zero amplitude sample, supplies a second signal (STc) of the logic level “1”. 4. Arrangement according to claim 1, characterized in that the third means contain a counter registering the duration of the tone cycles (TPRS), which is incremented by one step when a tone cycle is detected. 5. Arrangement according to claim 1, characterized in that the fourth means contain a time counter (TKL), which is switched on by clock pulses (H4) and at the end of the specific, limited period of time which begins at the beginning of the detection of a sound cycle, a signal ( STI) of logical level «1».