AU749828B2

AU749828B2 - Electronic switching system for creating accurate time data and its time data creating method

Info

Publication number: AU749828B2
Application number: AU74163/98A
Authority: AU
Inventors: Yoshio Honma
Original assignee: NEC Corp
Current assignee: NEC Corp
Priority date: 1997-07-04
Filing date: 1998-07-03
Publication date: 2002-07-04
Anticipated expiration: 2018-07-03
Also published as: JPH1127769A; AU7416398A

Description

S F Ref: 426443

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT

ORIGINAL

S

Name and Address of Applicant: NEC Corporation 7-1, Shiba Minato-ku Tokyo

JAPAN

Actual Inventor(s): Address for Service: Yoshio Honma Spruson Ferguson, Patent Attorneys Level 33 St Martins Tower, 31 Market Street Sydney, New South Wales, 2000, Australia Electronic Switching System for Creating Accurate Time Data and Its Time Data Creating Method Invention Title: The following statement is a full description of this invention, including the best method of performing it known to me/us:- 5845 1 ELECTRONIC SWITCHING SYSTEM FOR CREATING ACCURATE TIME DATA AND ITS TIME DATA CREATING METHOD BACKGROUNDS OF THE INVENTION FIELD OF THE INVENTION The present invention relates to an electronic switching system provided on a public digital line for switching interconnection between terminal equipment of the public line and its time data creating method, and 10 more particularly, to an electronic switching system for creating accurate time data and its time data creating method.

DESCRIPTION OF THE RELATED ART Fig. 5 is a block diagram showing the structure of this kind of electronic switching system according to the conventional technique. The electronic switching system 120 shown in Fig. 5 comprises a trunk circuit 130, an oscillation circuit 140, a clock circuit 150, a central processing unit 160 (hereinafter, referred to as a CPU), a time division switch 170, and a subscriber circuit 131. The electronic switching system 120 is connected to a public line 110.

The public line 110 is connected to the trunk circuit 130 within the electronic circuit 120. The trunk circuit 130 is connected to the time division switch 170 and the CPU 160 for voice or data exchange.

-2- A telephone 111 used as a terminal of the electronic switching system 120 is connected to the subscriber circuit 131. The subscriber circuit 131 is connected to the time division switch 170 and the CPU 160.

The CPU 160 controls the whole operation of the electronic switching system 120. Especially, it controls a call connection in the time division switch 170, and it controls the trunk circuit 130 and the subscriber circuit 131.

The oscillation circuit 140 contains a quartz oscillator or the like, so to create and supply a clock signal CLK of a constant frequency.

"'"The clock circuit 150 activates a clock by use of the clock signal CLK supplied from the oscillation circuit 140, and creates time data required in the electronic switching system 120 to supply it. The time data is required in various service applications to be executed in the electronic switching system 120.

Therefore, the time data supplied from the clock circuit 150 is sent to the CPU 160, so to be used in various operations.

As mentioned above, since the conventional switching system activates the clock circuit by use of an oscillator included in an oscillation circuit mounted on the electronic switching system, accuracy of time data depends on the oscillation accuracy of an 3 15 20 e e• •eeo 20 :0 oo *o: oscillator. Therefore, the time data supplied from the clock circuit becomes more accurate by mounting an oscillator of higher accuracy on an oscillation circuit.

On the contrary, the accuracy of the time data becomes lower according as the accuracy of the oscillator of the oscillation circuit is lower, which may result in an error occurrence in the operations of service applications.

Generally, an electronic switching system often employs time data in various service applications such as record of communication state, date/time display on a telephone, or the like. Especially, if an error occurs in a service requiring the highest reliability of the time data, such as bill record, it becomes a serious problem. Therefore, an oscillator of high accuracy (for example, frequency stability 5x10-") is required to be mounted there in order to get accurate time data.

However, an oscillator of high accuracy is very expensive and mounting such an expensive oscillator increases the cost of the electronic switching system itself.

Accordingly, a need exists to provide an electronic switching system capable of creating time data of high accuracy upon receipt of an accurate clock signal, and the time data creating method thereof.

4 Another need exists to provide an electronic switching system capable of creating the time data of high accuracy while keeping the price of the electronic switching system itself at a low cost, and the time data creating method thereof.

SUMMARY

According to one aspect of the invention, an electronic switching system provided on a digital public line for switching interconnection between terminal equipment of the public line, comprises a single or a plurality of digital line trunk circuits connected to a digital line for processing digital signals received through the digital line into given data, so to supply the same and extracting clock 15 signal components from the digital signal, a synchronous oscillation circuit for creating and supplying a clock signal synchronized with the clock signal component of the digital signal extracted by the digital line trunk circuit, 20 a clock circuit for activating an internal clock according to the clock signal supplied from the synchronous oscillation circuit and creating time data to supply the same, a central processing unit for executing various controls and services by use of the time data supplied from the clock circuit, and g(a time division switch for switching 5 connection of the data supplied from the digital line trunk circuits according to the control of the central processing unit.

In the preferred construction, when a plurality of digital line trunk circuits are provided Sthere, each of the digital line trunk circuits supplies the clock signal extracted from the digital signal, and the synchronous oscillation circuit selects one of the clock signals supplied from the plurality of 10 digital line trunk circuits and creates a clock signal synchronized with the selected clock signal, so to supply the same.

In the preferred construction, the digital "line trunk circuit comprises a first interface means for receiving a digital signal sent through the digital line, a trunk control circuit for processing the digital signal received by the first interface means into given data and supplying the same, a second interface means for sending the data supplied from the trunk control circuit to the time division switch, a third interface means for sending the data supplied from the trunk control circuit to the central processing unit, a clock extracting circuit for extracting clock signal component from the digital signal received by the first interface means, and a fourth interface means for sending the clock signal supplied from the clock extracting circuit to the synchronous oscillation circuit.

6 In the preferred construction, the synchronous oscillation circuit comprises a phase comparing means for receiving the clock signal supplied from the digital line trunk circuit and the clock signal supplied from the synchronous oscillation circuit, so to detect the phase difference therebetween, and a voltage controlling oscillation means for supplying a clock signal synchronized with the clock signal supplied from the digital line trunk circuit according to the phase 10 difference signal detected by the phase comparing means, to the clock circuit, and feed back the same to the phase comparing means.

:°eooo In the preferred construction, the digital *"line trunk circuit comprises a first interface means for 9999 receiving a digital signal sent through the digital line, a trunk control circuit for processing the digital signal received by the first interface means into given data and supplying the same, a second interface means for sending the data supplied from the trunk control circuit to the time division switch, a third interface means for sending the data supplied from the trunk control circuit to the central processing unit, a clock extracting circuit for extracting clock signal component from the digital signal received by the first interface means and supplying the same, and a fourth interface means for sending the clock signal supplied from the clock extracting circuit to the synchronous oscillation 7 circuit, while the synchronous oscillation circuit comprises a phase comparing means for receiving the clock signal supplied from the digital line trunk circuit and the clock signal supplied from the synchronous oscillation circuit, so to detect the phase difference therebetween, and a voltage controlling oscillation means for supplying a clock signal synchronized with the clock signal supplied from the digital line trunk circuit 10 according to the phase difference signal detected by the phase comparing means, to the clock circuit, and feed back the same to the phase comparing means.

In the preferred construction, when a plurality of digital line trunk circuits are provided there, each of the digital line trunk circuits supplies the clock signal extracted from the digital signal, while synchronous oscillation circuit comprises a selecting means for selecting one of the clock signals supplied from the plurality of digital line trunk circuits, a phase comparing means for receiving the clock signal selected by the selecting means and the clock signal supplied from the synchronous oscillation circuit, so to detect the phase difference therebetween, and a voltage controlling oscillation means for supplying a clock signal synchronized with the clock signal supplied from the selecting means according to 8 the phase difference signal detected by the phase comparing means, to the clock circuit, and feeding back the same to the phase comparing means.

According to another aspect of the invention, a time data creating method for creating time data for use in various controls and services, in an electronic switching system provided on a digital public line for switching interconnection between terminal equipment of the public line, the method comprising the steps of 10 a step of extracting clock signal component 'from a digital signal received through the digital line, a step of creating a clock signal synchronized with the clock signal component extracted from the digital signal, and a step of activating a clock according to the created clock signal and creating time data.

In the preferred construction, when a plurality of digital lines are connected to the electronic switching system, in the clock signal component extracting step, the clock signal components depending on the number of the digital lines are extracted from the digital signals received by every digital line, and the clock signal creating step further includes a step of selecting one of the extracted clock signal components as that one for creating a clock signal.

9 In the preferred construction, the clock signal creating step further includes a step of receiving the clock signal extracted from the digital signal and the created clock signal, so to detect the phase difference therebetween, and a step of supplying a clock signal synchronized with the clock signal extracted from the digital signal, to the clock circuit, and feeding back the same for detecting of the phase difference.

In the preferred construction, when a plurality of digital lines are connected to the electronic switching system, in the clock signal component extracting step, "the clock signal components depending on the number of S 15 the digital lines are extracted from the digital signals received by every digital line, and the clock signal creating step further includes a step of selecting one of the extracted clock signal components as that one for creating a clock signal, a step of receiving the clock signal extracted from the digital signal and the created clock signal, so to detect the phase difference therebetween, and a step of supplying a clock signal synchronized with the clock signal extracted from the digital signal, to the clock circuit, and feeding back the same for detecting of the phase difference.

Other objects, features and advantages of the 10 present invention will become clear from the detailed description given herebelow.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be understood more fully from the detailed description given herebelow and from the accompanying drawings of the preferred embodiment of the invention, which, however, should not be taken to be limitative to the invention, but are for 10 explanation and understanding only.

In the drawings: Fig. 1 is a block diagram showing the structure of an electronic switching system according to an embodiment of the present invention; Fig. 2 is a block diagram showing the structure of a digital line trunk circuit shown in Fig.

1; Fig. 3 is a block diagram showing the structure of a synchronous oscillation circuit shown in Fig. 1; Fig. 4 is a flow chart showing the operation of creating time data according to the embodiment; Fig. 5 is a block diagram showing the structure of the conventional electronic switching system.

DESCRIPTION OF THE PREFERRED EMBODIMENT 11 The preferred embodiment of the present invention will be discussed hereinafter in detail with reference to the accompanying drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be obvious, however, to those skilled in the art that the present invention may be practiced without these specific details. In other instance, wellknown structures are not shown in detail in order to 00 0 unnecessary obscure the present invention.

Fig. 1 is a block diagram showing the structure of an electronic switching system according to an embodiment of the present invention. The electronic S" switching system 20 shown in Fig. 1 comprises digital line trunk circuits 30-1 to 30-n (n is a positive integer), a synchronous oscillation circuit 40, a clock S circuit 50, a CPU 60, and a time division switch 70. The digital line trunk circuits 30-1 to 30-n are t" respectively connected to digital lines 10-1 to The digital line trunk circuits 30-1 to 30-n are respectively connected to the switch 70, the CPU 60, and the synchronous oscillation circuit 40. Fig. 1 shows only the characteristic components of the embodiment, while the description of the other general components is omitted.

In the above components, the digital lines 1 to 10-n are public lines and supported by a 12 communication dealer using an accurate oscillator of frequency stability 5X10 or more in a clock providing device of a digital signal. For example, they correspond to such a digital line supported by the first type of communication dealer in Japanese communication business.

The digital line trunk circuits 30-1 to respectively extract clock signal components CK1 to CKn synchronized with the digital line of a network from the digital lines 10-1 to 10-n and supply the respective 0 ones to the synchronous oscillation circuit 40. The detailed structure and operation of the digital line trunk circuits 30-1 to 30-n will be described later.

The synchronous oscillation circuit 40 selects S. one of the clock signals CK1 to CKn supplied from the digital line trunk circuits 30-1 to 30-n, creates a clock signal CK synchronized with the selected clock signal, and supplies it to theclock circuit The clock circuit 50 activates the clock by oeoo use of the clock signal CK supplied from the synchronous oscillation circuit 40, creates the time data, and supplies it.

The CPU 60 controls the whole operation of the electronic switching system 20. Especially, it controls a call connection in the time division switch 70, and it controls the digital line trunk circuits 30-1 to The CPU 60 receives the time data supplied from the clock circuit 50, for use in various operations executed 13 according to the service applications.

The time division switch 70 switches the connection of call data supplied from the digital line trunk circuits 30-1 to 30-n according to the control of the CPU Fig. 2 is a block diagram showing the structure of the respective digital line trunk circuits 30-1 to 30-n (hereinafter, represented as the digital line trunk circuit 30 as shown in Fig. 2 when it is not 10 necessary to distinguish each circuit). With reference to Fig. 2, the digital line trunk circuit 30 includes a wo*line interface 31, a trunk control circuit 32, a time division switch interface 33, a CPU interface 34, a clock extracting circuit 35, and a synchronous oscillation circuit interface 36. In Fig. 2, the digital line 10 is connected to the digital line trunk circuit The line interface 31 passes the digital signal received from the digital line 10 to the trunk control circuit 32 and the clock extracting circuit The trunk control circuit 32 processes the digital signal received from the line interface 31 into given data and supplies it.

The time division switch interface 33 sends the data supplied from the trunk control circuit 32 to the time division switch The CPU interface 34 sends the data supplied 14 from the trunk control circuit 32 to the CPU The clock extracting circuit 35 extracts clock signal components from the output of the line interface 31.

The synchronous oscillation circuit interface 36 receives the clock signal components supplied from the clock extracting circuit 35, so to send them to the synchronous oscillation circuit 40 shown in Fig. 1.

Fig. 3 is a block diagram showing the 10 structure of the synchronous oscillation circuit Sshown in Fig. 1. The synchronous oscillation circuit o o shown in Fig. 3 includes a phase comparator 41, a filter 42, a voltage controlling oscillator 43, and a selector 44.

In Fig. 3, the selector 44 selects one (hereinafter, referred to as CK1) of the clock signals

*SSS

CK1 to CKn supplied from the respective synchronous oscillation circuit interfaces 36 within the respective digital line trunk circuits 30-1 to 30-n shown in Fig. 2 and passes it to the phase comparator 41.

By comparison between the phase of the clock signal CK1 selected by the selector 44 and the phase of the clock signal CK1* supplied from the voltage controlling oscillator 43, the phase comparator 41 detects the phase difference and supplies it to the filter 41.

Upon receipt of the phase difference signal 15 supplied from the phase comparator 41, the filter 41 performs waveform shaping.

The voltage controlling oscillator 43 oscillates a clock signal CK synchronized with the clock signal CK1 supplied from the selector 44 according to the phase difference signal received through the filter 42. The clock signal CK is sent to the clock circuit and one of the clock signal CK branches out as the above-mentioned clock signal CK1* so as to be fed back 10 to the phase comparator 41.

This time, the operation of synchronizing the electronic switching system of the embodiment with the clock signal CK extracted from the digital lines 10-1 to 10-n will be described below.

15 The digital signals entered into the respective digital line trunk circuits 30-1 to through the respective digital lines 10-1 to 10-n are respectively delivered to the clock extracting circuits through the line interfaces 31 in the respective digital line trunk circuits 30-1 to 30-n (Step 401). The respective clock extracting circuits 35 extract the clock signal components CK1 to CKn from the respective digital lines 10 (Step 402). The extracted clock signal components CK1 to CKn are delivered to the synchronous oscillation circuit 40 through the respective synchronous oscillation circuit interfaces 36.

In the synchronous oscillation circuit 16 some clock signal is selected from the clock signals CKI to CKn received from the digital line trunk circuits 1 to 30-n and delivered to the phase comparator 41 (Step 403). Assume that the clock signal CK1 extracted from the digital line 10-1 has been selected here. The phase comparator 41 detects the phase difference between the clock signal CK1 and the clock signal CK1* supplied from the voltage controlling oscillator 43 and returns it to the voltage controlling oscillator 43 through the filter 10 42 (Step 404). The voltage controlling oscillator 43 0000 oscillates the clock signal CK synchronized with the 0000 clock signal CK1 by use of the received phase difference (Step 405).

~Thus, the synchronous oscillation circuit supplies the clock signal CK synchronized with the digital line 10 and use of this clock signal CK r S..activates the clock circuit 50, so to create time data o. ~(Step 406).

In the above embodiment, one clock signal is selected from a plurality of clock signals extracted from a plurality of digital lines and a clock signal synchronized with the selected clock signal is created in the synchronous oscillation circuit 40 so to be supplied. However, in the synchronous oscillation circuit 40, it is also possible to create a clock signal synchronized with the clock signal which is extracted from only one digital line.

17 As set forth hereinabove, according to the electronic switching system and its time data creating method of the present invention, the clock circuit of the electronic switching system is activated by the use of a clock signal synchronized with a clock signal of a digital line, and therefore the time data of high accuracy can be used. This is why the clock circuit is activated by extracting a necessary clock signal from a digital line supported by a communication dealer using 10 an accurate oscillator of frequency stability 5x10 or .more in a clock providing device of a digital signal.

Even when a plurality of electronic switching o: systems are connected to one network, time data is created by use of a clock signal synchronized with a .ee clock signal of a digital line, in each electronic switching system, thereby making it possible to maintain |eeoc S.the difference of the time data among the electronic switching systems at a constant level. This is why all the electronic switching systems create each time data based on the identical clock signal. Namely, every clock circuit of all the electronic switching systems can be synchronized with the clock providing device of the communication dealer supporting the digital line.

Thus, the electronic switching system of the present invention can decrease errors of time data created by the clock circuit, thereby improving its accuracy at a low cost.

18 Although the invention has been illustrated and described with respect to exemplary embodiment thereof, it should be understood by those skilled in the art that the foregoing and various other changes, omissions and additions may be made therein and thereto, without departing from the spirit and scope of the present invention. Therefore, the present invention should not be understood as limited to the specific embodiment set out above but to include all possible f.

10 embodiments which can be embodies within a scope encompassed and equivalents thereof with respect to the feature set out in the appended claims.

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Claims

1. An electronic switching system provided on a digital public line for switching interconnection between terminal equipment of the public line, comprising: a single or a plurality of digital line trunk circuits connected to a digital line for processing digital signals received through the digital line into given data, so to supply the same and extracting clock 0 signal components from the digital signal; 0:* 10 a synchronous oscillation circuit for creating and supplying a clock signal synchronized with the clock signal component of the digital signal extracted by said digital line trunk circuit; a clock circuit for activating an internal clock according to the clock signal supplied from said synchronous oscillation circuit and creating time data to supply the same; a central processing unit for executing various controls and services by use of the time data supplied from said clock circuit; and a time division switch for switching connection of the data supplied from said digital line trunk circuits according to the control of said central processing unit. 20

2. An electronic switching system as set forth in Claim 1, wherein when a plurality of digital line trunk circuits are provided there, each of said digital line trunk circuits supplies the clock signal extracted from the digital signal, and said synchronous oscillation circuit selects one of the clock signals supplied from said plurality of digital line trunk circuits and creates a clock signal 10 synchronized with the selected clock signal, so to *see supply the same.

3. An electronic switching system as set forth in Claim 1, wherein said digital line trunk circuit comprising a first interface means for receiving a digital signal sent through the digital line, a trunk control circuit for processing the digital signal received by said first interface means into given data and supplying the same, a second interface means for sending the data supplied from said trunk control circuit to said time division switch, a third interface means for sending the data supplied from said trunk control circuit to said central processing unit, a clock extracting circuit for extracting 21 clock signal component from the digital signal received by said first interface means, and a fourth interface means for sending the clock signal supplied from said clock extracting circuit to said synchronous oscillation circuit.

4. An electronic switching system as set forth in Claim i, wherein said synchronous oscillation circuit comprising 5 a phase comparing means for receiving the clock signal supplied from said digital line trunk ,O55o circuit and the clock signal supplied from said synchronous oscillation circuit, so to detect the phase difference therebetween, and 0 a voltage controlling oscillation means for 00.. .supplying a clock signal synchronized with the clock signal supplied from said digital line trunk circuit according to the phase difference signal detected by said phase comparing means, to said clock circuit, and feed back the same to said phase comparing means. An electronic switching system as set forth in Claim i, wherein said digital line trunk circuit comprising a first interface means for receiving a digital signal sent through the digital line, 22 a trunk control circuit for processing the digital signal received by said first interface means into given data and supplying the same, a second interface means for sending the data supplied from said trunk control circuit to said time division switch, a third interface means for sending the data supplied from said trunk control circuit to said central processing unit, 15 a clock extracting circuit for extracting 0S*S clock signal component from the digital signal received by said first interface means and supplying the same, and a fourth interface means for sending the clock o signal supplied from said clock extracting circuit to said synchronous oscillation circuit, while said synchronous oscillation circuit comprising a phase comparing means for receiving the clock signal supplied from said digital line trunk circuit and the clock signal supplied from said synchronous oscillation circuit, so to detect the phase difference therebetween, and a voltage controlling oscillation means for supplying a clock signal synchronized with the clock signal supplied from said digital line trunk circuit according to the phase difference signal detected by 23 said phase comparing means, to said clock circuit, and feed back the same to said phase comparing means.

6. An electronic switching system as set forth in Claim i, wherein when a plurality of digital line trunk circuits are provided there, each of said digital line trunk circuits supplies the clock signal extracted from the digital signal, while said synchronous oscillation circuit comprising a selecting means for selecting one of the clock signals supplied from said plurality of digital line trunk circuits, OO9S a phase comparing means for receiving the clock signal selected by said selecting means and the clock signal supplied from said synchronous oscillation circuit, so to detect the phase difference therebetween, and a voltage controlling oscillation means for supplying a clock signal synchronized with the clock signal supplied from said selecting means according to the phase difference signal detected by said phase comparing means, to said clock circuit, and feeding back the same to said phase comparing means.

7. A time data creating method for creating 24 time data for use in various controls and services, in an electronic switching system provided on a digital public line for switching interconnection between terminal equipment of the public line, the method comprising the steps of: a step of extracting clock signal component from a digital signal received through the digital line; a step of creating a clock signal synchronized with the clock signal component extracted from the *digital signal; and step of activating a clock according to the or created clock signal and creating time data.

8. A time data creating method as set forth OS in Claim 7, wherein when a plurality of digital lines are connected to the electronic switching system, in said clock signal component extracting step, the clock signal components depending on the number of the digital lines are extracted from the digital signals received by every digital line, and said clock signal creating step further includes a step of selecting one of the extracted clock signal components as that one for creating a clock signal.

9. A time data creating method as set forth in Claim 7, wherein said clock signal creating step further includes a step of receiving the clock signal extracted from the digital signal and the created clock signal, so to detect the phase difference therebetween, and a step of supplying a clock signal synchronized with the clock signal extracted from the 10 digital signal, to said clock circuit, and feeding back OS SO the same for detecting of the phase difference. 0001 ooo S v10. A time data creating method as set forth 5055 in Claim 7, wherein when a plurality of digital lines are 5055 connected to the electronic switching system, in said clock signal component extracting step, *the clock signal components depending on the number of the digital lines are extracted from the digital signals C received by every digital line, and said clock signal creating step further includes a step of selecting one of the extracted clock signal components as that one for creating a clock signal, a step of receiving the clock signal extracted from the digital signal and the created clock signal, so to detect the phase difference therebetween, and -26- a step of supplying a clock signal synchronized with the clock signal extracted from the digital signal, to said clock circuit, and feeding back the same for detecting of the phase difference.

11. An electronic switching system substantially as herein described with reference to Figs. 1 to 4.

12. A time data creating model substantially as herein described with reference to Figs. 1 to 4. Dated 3 July, 1998 NEC Corporation Patent Attorneys for the Applicant/Nominated Person SPRUSON FERGUSON 0.. 50* S 0 °ooo S S 0 S S [N:\LIBPP]0 116:TCW