Abstract:
A method of automatically and equally distributing the ring load for an exchange system. The subscribers are grouped so that at any one time the subscribers of one group only is supplied with the ring current for ringing the telephone. If the number of the subscribers exceeds the allowable limit within the specified on time, the on time is automatically reset by use of a subtracting time to limit the ring load within a specified value.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a method of providing subscribers with ring signal service in an exchange system, and more particularly a method of automatically and equally distributing the ring signal to a plurality of subscribers with a ring signal generator of small capacity. 
     Generally, the ring signal generator 10 of an exchange system in FIG. 1 is connected to a subscriber circuit 20 to supply the ring signal to one or a plurality of telephones ST1-STm under control of a central processing unit (CPU) module 30. 
     Referring to FIG. 2 for representing an exemplified waveform of a fundamental ring signal, an interval ON represents a time duration connecting the ring signal, and a next interval OFF another time duration disconnecting the ring signal. A control signal from the CPU module 30 is decoded by a decoder 50, whereby ring service control data from the CPU module 30 are latched by addressable latch 40 to control on/off of ring relays RYl-RYn. Namely, the addressable latch 40 latches the output data of the CPU module 30 to switch the relays RYl-RYn on or off, whereby supplying of the ring signal is controlled. 
     Since a ring current should be supplied from the ring signal generator 10 to any one of the subscriber telephones ST1-STn to provide the ring service in a specified time period such as T1 to T2, T3 to T4 and so on, as shown in FIG. 3, an amount of the ring current to be supplied depends on a number of the subscriber telephones ST1-STn to be serviced. Therefore, as increases the number of the subscribers to be served, also increases the quantity of the ring current of the ring signal generator 10. This large amount of the ring current often results in waste of electric power in the exchange system. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a method of supplying an adequate ring signal to a plurality of subscriber telephones, with single ring signal generator. 
     It is another object of the present invention to provide a method of equally and adequately furnishing a ring service to a plurality of subscribers who requires a waking-up service. 
     According to one aspect of the present invention, a method of performing automatically equalized distribution of ring loads for an exchange system, particularly an electronic exchange system, comprises the steps of: 
     (a) comparing a total number of subscribers to be ring serviced with a number of basic groups multiplied by a maximum number of the subscribers in one of said groups; 
     (b) conforming an on/off time of the ring signal to the basic on/off time, by clearing a subtracting time, and also conforming a number of the ring service groups to the number of the basic groups, when the total number of the subscribers to be served is smaller than the number of the basic groups multiplied by the maximum number of the subscribers in each basic group; 
     (c) calculating the subtracting time, a dynamic on/off time, and the number of the ring service groups, when the number of the subscribers to be served is greater than the number of the basic groups multiplied by the maximum number of the subscribers in each basic groups; 
     (d) representing a state of the ring service and the group to be served onto a given subscriber port table and thereafter correcting a table of the ring service group, on the basis of results of the steps (b) as well as (c); 
     (e) checking whether it is time to interrupt ring signal or not; 
     (f) decreasing on-time of the present service data when it is the time of ring service; 
     (g) providing all the subscribers in a corresponding group with the ring signal while it is the time of ring service; and 
     (h) after the ring signal service, correcting the dynamic service data by data of a next group. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying diagrammatic drawings, in which: 
     FIG. 1 shows a schematic block diagram of a part of exchange system to be applied for the present invention; 
     FIG. 2 shows an example of a fundamental ring signal with on/off intervals; 
     FIG. 3 shows waveforms of the ring signals for furnishing the conventional ring service to each of the subscriber groups; 
     FIG. 4 shows waveforms of the ring signals for furnishing the ring service to each of the subscriber groups in accordance with the present invention; 
     FIG. 5 shows waveforms of another ring signals for furnishing the ring service to each of the subscriber groups, wherein a subtracting time is applied upon exceeding the allowable service capacity of the exchange system, in accordance with the present invention; 
     FIG. 6 shows a flow chart of registering subscribers of the ring service of the present invention; 
     FIG. 7 shows a flow chart of periodically intermitting a ring current for a periodic ring service according to the present invention; and 
     FIGS. 8A to 8E show memory map tables according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention will now be described more specifically with reference to the drawings attached only by way of example. 
     Referring to FIG. 4 showing the inventive time for furnishing the ring signal to the subscriber&#39;s telephones ST1-STn, the waveforms 4a-4c represent the intermitting time periods for switching the ring relays Ryl-Ryn on or off to supply the ring signal to the telephones ST1-STn, employing the time period for intermitting the ring signal as shown in FIG. 2. ON represents the time interval during which the ring current flows, and OFF the time interval during which the ring current does not flow. Here, one stage on/off time intervals are represented for convenience. 
     4a represents the time period for intermitting the relay Ryl of the subscriber circuit 20 for supplying the ring signal to the subscriber&#39;s telephone ST1, wherein t1-t2 represents the on-time, and t2-t4 the off-time. Namely, it begins to ring at t1, stops ringing form t2 to t4, and again rings from t4 to t5. 4b represents the time period for intermitting the relay Ry2 of the subscriber circuit 20 for supplying the ring signal to the telephone ST2, wherein it begins to ring at t2, continuing to t3, and stops ringing from t3 to t5. If n telephones ST1-STn are devided into several groups for receiving the ring service, the telephones assigned to only the first group ring during the time interval t1-t2. Of course, during the time interval t2-t3 ring the telephones assigned to only the second group. Hence, the load put on the ring signal generator circuit 10 during the time interval t1-t2 depends only on the number of the subscribers assigned to the first group, and the load during the time interval t2-t3 only on the number of the subscribers assigned to the second group. Namely, the load put on the ring signal generator circuit 10 to furnish the ring service to n subscribers is only the portion obtained by dividing the n by the number of the groups. Consequently, the capacity of the ring signal generator circuit 10 depends on the maximum number of the subscribers assigned to one group. 
     FIG., 5 which is an improvement of FIG. 4, represents another on/off intermitting time period for dynamically changing the on-time in case that the capacity of the ring signal generator circuit 10 is small. In this case, the subtracting time is introduced for dynamically reducing the on-time interval, since the ring current becomes reduced if the number n of the subscribers is greater than the product of the number of the basic groups and the number of the subscribers assigned to a group. 
     Assuming that the number of the subscribers to be served be n, the number of the subscribers to which the ring signal generator 10 may properly furnish the ring service to subscribers be m, the on-time interval be On, the off-time interval off, and the subtracting time d, the new on-time interval is On-d, and the number of the groups allowable during the time On+Off is ##EQU1## Hence, the number of the subscribers to be served is ##EQU2## The subtracting time obtained from the above formula is expressed by the following formula (2). ##EQU3## Namely, d will be the minimum integer that satifies the inequality (2). For example, assuming On=4, Off=8, and m=2, the value of d will be expressed as in the following table 1 according to the number n of the subscribers. 
     
                       TABLE 1______________________________________n    1     2      3   4    5   6    7   8    9   10 . .______________________________________                                            .d    0     0      0   0    0   0    1   1    2    2 . .______________________________________                                            . 
    
     Referring to FIG. 6, the registration of the subscribers to be served comprises the steps of: 
     comparing the total number of the subscribers to be served with the product of the number of the basic groups &#34;n BG  &#34; and the maximum number of the subscribers in one of said groups &#34;n S  &#34;; 
     conforming the on/off time of the ring signal to the basic on/off time by clearing the subtracting time (d) and the number of the ring service groups to the number of the basic groups when the number of the subscribers to be served is smaller or equal than the product of the number of the basic groups and the maximum number of the subscribers in one of the basic groups; 
     calculating the subtracting time (d), the dynamic on/off time, and the number of the ring service groups when the number of the subscribers to be served is greater than the product of the number of the basic groups and the maximum number of the subscribers in one of the basic groups; and 
     presenting the state of the ring service and the intermitting group onto the subscriber&#39;s port table together with correcting the present service data table. 
     Namely, FIG. 6 describes determination of the state of ring service whenever a new subscriber is registered, according to the new on/off time and subtracting time obtained by calculating the number of the present subscribers. In this way, the number of the groups to be served is determined to assign the new subscriber to one of the ring signal groups. 
     Referring to FIG. 7, furnishing ring signal service with subscribers comprises the steps of; 
     checking the intermitting time; 
     decreasing on-time of the present service data when it is not the intermitting time; 
     providing all the subscribers in a corresponding group with the ring signal when it is the intermitting time; and 
     correcting the present service data by the data of the a next group, after the ring signal service. 
     Namely, according to a routine of FIG. 7 for intermitting the ring current to furnish the periodic ring service, on-time is newly set to change the intermission interval at the at the moment of intermitting ring signal service, i.e., at the moment of changing signal from on to off or vice versa when there exists a subscriber to be served in the subscriber port. In this way, the subscriber&#39;s telephone begins to ring or stops ringing. 
     Referring to FIG. 8A-FIG. 8B, FIG. 8A schematizes the subscriber&#39;s port table, FIG. 8B the service group table, FIG. 8c the dynamic data table, FIG. 8D the basic data table, and FIG. 8E the present service data table. 
     Now, a preferred embodiment of the present invention will be described with reference to FIG. 4-FIG. 8E. 
     The ring relays Ryl-Ryn of the subscriber&#39;s circuit 20 are connected to the ring signal generator 10 according to the conventional subscriber&#39;s circuit in order to supply the ring current to the telephones ST1-STn by the CPU module 30. The control signal from the CPU module 30 is decoded by the decoder 50 to control the addressable latch circuit 40 to latch the ring service data from the CPU module 30, thereby switching the ring relays Ryl-Ryn on or off. 
     When the ring signal should be sent to the telephones ST1-STn, a ring message is produced by comparing the total number of the telephones to be served with the number of the telephones to be basically served in the step 61. If the number of the subscribers is smaller or equal than the number of the telephones allowed to be served, the ring service is possibly served with the basic on/off time in the basic groups in the step 62 of FIG. 6. Hence, the CPU module 30 causes the subtracting time (d) to be zero on the table of the dynamic ring signal service data table, as shown in FIG. 8c. The on/off time is the basic on/off time as shown in the basic service data table of FIG. 8D. Also, the number of the ring service groups equals to the number of the basic groups. 
     In the step 61, if the number of the subscribers is greater than the number of the telephones allowed to be served, the subtracting time (d) is calculated to satisfy the equation (2), and recorded into the table of the dynamic ring signal service data table of FIG. 8C. In this case, the on-time will be the remainder left after subtracting the subtracting time (d) from the basic on-time of the basic service data table, and the off-time the addition of the basic off-time and the subtracting time. The addition of the on-time and off-time obtained by the step 63 is divided by the new on-time so as to determine the number of the ring service groups. Subsequently to the above steps 62, 63 and 64, the state of the ring service is presented on each of the subscriber&#39;s port table in the step 65, as shown in FIG. 8A, and one of the groups having less subscribers than other groups is chosen as the service groups of the subscribers from the service group table of FIG. 8B. Additionally, the service group table is corrected to new data. 
     In the service routine of FIG. 7, it is determined whether the on-time of the present service data table FIG. 8E is zero or not, in the step 71. If it is not zero, the on-time is reduced by some count time in the step 72, and supplying ring signal to corresponding subscribers is continued. However, if it is the intermitting time, that is, if the on-time of the present service data table FIG. 8E is zero, the rings of all the subscribers assigned to the present service group are intermitted in the step 73. Thereafter the present service group of the present service data table of FIG. 8E is corrected by the next served group data. The on-time thereof is corrected by the on-time of the dynamic ring signal service data table FIG. 8c in the step 74. 
     As described above, the present invention obviates the heavy load to be put on at any one time, so that the scale of the ring signal generator is minimized, and the maximum service is secured for the users with its own capacity. Particularly, the present invention provides a method to automatically adjust the on/off time according to the amount of the ring load to equally distribute it without adding any means to the designed system.