Abstract:
A T-S-T 3-staged structure switching network control system in a digital switching system which avoids an entire switching system malfunction even a failure occurred in a space switch module, and guarantees a connection within a time switch module is realized for providing the switching system capable of improving its reliability. In each time switch module including a first stage time switch and a third stage time switch with their control processor, a selecting circuit is provided in front of an input of the third time switch for selectively connecting a junctor highway which is connected to an output of a second stage space switch in a space switch module or a highway which is connected to an input of the first stage time switch to the input of said third time switch. The control processor in each time switch module controls the selecting circuit to connect the highway to the input of the third stage time switch in the case that the space switch module is a faulty condition.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a time-division switch control system of a digital switching system, and more specifically, to a switch control system for a T-S-T (time switch-space switch-time switch) 3-staged structure switching network controlled by a plurality of control processors (a multi-processor type digital switching system.) 
     2. Description of the Related Art 
     In the digital switching system, data to be switched is flowed into the switching network in the form of series of time slots through an incoming highway, and necessary switching operation for each time slot is performed and output from the switching network through an outgoing highway. 
     FIG. 5 is a block diagram illustrating the principle of time slot switching by a T-S-T 3-staged structure switching network which can provides a large capacity switching network. The incoming highway from a line circuit  310 - 31 N is coupled to a first stage time switch  110 - 11 N, and junctor highways HW 10 -HW 1 N from each of first stage time switches  110 - 11 N are coupled to a second stage space switch  200 . Each of junctor highways HW 20 -HW 2 N from the second stage space switch  200  are coupled to each of third stage time switches  120 - 12 N respectively. The outgoing highway from a third stage time switch  120 - 12 N is coupled to a line circuit  320 - 32 N. Each line circuit is coupled to a subscriber terminal  1 -N, or  10 - 1 N. 
     Under these configurations, the principle of switching is like this; the time switch exchanges data in a certain time slot number to a different time slot number, and the space switch exchanges data in a certain time slot number of a certain junctor highway number to a same time slot number of a different junctor highway number. 
     For more detail, operation performed by the T-S-T 3-staged structure switching network will be explained with reference to FIG.  5 . 
     It is assumed that a communication path is to be established between a subscriber terminal  1  connected to the line circuit  310  and a subscriber terminal  1 L connected to the line circuit  32 L. 
     In the digital switching system, a time slot number of the originating subscriber (subscriber terminal  1 ) on the incoming highway is known as the originating subscriber accommodated position which has informed by a peripheral unit of the digital switching system at the time of call origination request by the subscriber terminal  1 , and the time slot number on the incoming highway is assumed as No. k. And also, a time slot number of the terminating subscriber (subscriber terminal  1 L) on the outgoing highway and the junctor highway number corresponding to the outgoing highway are known as the result of analysis of the dialled number by the subscriber terminal  1 , and the time slot number on the outgoing highway is assumed as No.  1  and the corresponding junctor highway number is assumed as No. HW 2 L. Therefore, switching is to be performed by exchanging data in the time slot number k on the incoming highway corresponding to the junctor highway HW 10  to the time slot number  2  on the outgoing highway corresponding to junctor highway HW 2 L. 
     The digital switching system searches a time slot number which is idle state on both junctor highways HW 10  and HW 2 L, and it is assumed that time slot number  2  is available for both junctor highways and the time slot number  2  is reserved for communication path establishment. 
     After that, the digital switching system instructs the first stage time switch  110  to exchange data in the time slot number k on the incoming highway from the subscriber terminal  1  to the time slot number  2  on the junctor highway HW 10 , instructs the second stage space switch  200  to exchange data in the time slot number  2  from the junctor highway HW 10  to the junctor highway HW 2 L, and also instructs the third stage time switch  12 L to exchange data in the time slot number  2  on the junctor highway HW 2 L to the time slot number  1  on the outgoing highway to the subscriber terminal  1 L. 
     The T-S-T 3-staged structure switching network of a conventional multi-processor type digital switching system employs such a configuration, as shown in FIG. 6, that the first stage time switch  110  and the third stage time switch  120  are equipped in a one time switch module  100  together with a control processor  130  for controlling those time switches, and a plurality of time switch modules  100 - 10 N are provided depending on number of subscriber terminals  1 -N,  10 - 1 N and junction circuits (not shown) to/from other switching systems which are accommodated in this digital switching system, and also a plurality of second stage space switches  210 - 21 N are equipped in a space switch module  200  together with a control processor  230  for controlling those space switches. That is, a plurality of control processors  130 - 13 N,  230  are installed in a distributed manner in each time switch module  100 - 10 N or a space switch module  200  respectively. 
     Each first stage time switch  110 - 11 N is connected to all of second stage space switches  210 - 21 N by a respective junctor highway HW 10 -HW 1 N, and each second space switch  210 - 21 N is connected each third stage time switch  120 - 12 N respectively by a junctor highway HW 20 -HW 2 N. Control processors  130 - 13 N,  230  are connected each other by a processor bus  400 . 
     A communication path establishment from a subscriber terminal  1  accommodated in the line circuit  310  connected to the time switch module  100  to a subscriber terminal  1 N accommodated in the line circuit  32 N connected to the time switch module  10 N will now be considered. 
     In this communication path establishment, such a connection is required from the first stage time switch  110  via the junctor highway HW 10 , the second stage space switch  21 N, and the junctor highway HW 2 N to the third stage time switch  12 N. First, the control processor  130  makes an inquiry about an idle time slot number available on both junctor highways HW 10  and HW 2 N to the control processor  230  in the space switch module  200 . The control processor  230  searches an idle time slot available on both junctor highways HW 10  and HW 1 N, and then selects one of available time slot number. The control processor  230 , which has found an idle time slot, reserves this idle time slot and notifies this information to the control processor  130 . The control processor  130  instructs the time switch  110  to perform a time slot exchange operation from an incoming time slot to the time slot which has been informed by the control processor  230 , also, the control processor  130  instructs the control processor  230  and the control processor  13 N to perform path establishment in the space switch  21 N and in the time switch  12 N respectively. In the space switch  21 N, the time slot which has been reserved on the junctor highway HW 10  is switched to the same time slot on the junctor highway HW 2 N, and also, in the time switch  12 N, a time slot exchange operation from the time slot on the junctor highway HW 2 N, informed by the control processor  130 , to the time slot on the outgoing highway corresponding to the subscriber terminal  1 N is performed. 
     As a result, the switching operation of the communication path from the subscriber terminal  1  to the subscriber terminal  1 N has been completed. 
     In Japanese Patent Application Laid-Open No. sho. 63-50293, similar T-S-T structure switching network model of combining time switches and a space switch is described. In this publication, a configuration of a distributed switching network system which is constituted by coupling a plurality of switch modules, each switch module includes time switches and space switch, is proposed for improving independent characteristics of the control processor in respective switch modules, and it is proposed that highway from other switch module is connected to the space switch via the additional time switch. That is, the proposed configuration, which is a T-(T-S)-T structure switching network, can eliminate common management of busy/idle information on junctor highways to/from each space switch, and can perform switching operation by using own busy/idle information. It means that the control processor in each switch module can operate more independently, and can realize more independent distributed control system. 
     However, there is a problem, in the above-described conventional T-S-T structure switching network, that all of the connections within the switching network cannot be performed in the case that any one of the second stage space switches or the control processor in the space switch module fails, even when the time switch module including the first stage time switch and the third stage time switch is operated under normal condition. This is because that the means for connecting between the first stage time switch and the third stage time switch is interrupted. 
     SUMMARY OF THE INVENTION 
     The present invention has been made to solve the above-described problem, and therefore, has an object to provide a T-S-T 3-staged structure switching network control system in a digital switching system, capable of improving reliability of the switching system. The present invention realizes a T-S-T 3-staged structure switching network control system which avoids an entire switching system malfunction even when a failure occurred in a space switch module, and guarantees a connection within a time switch module. 
     To achieve the above-described object, a control system of a 3-staged time-division switch, according to the present invention, is constituted by a space switch module including a plurality of second stage space switches and a plurality of time switch modules, each including a first stage time switch connected to an input of one of the second stage space switches by a junctor highway and a third stage time switch connected to an output of the second stage space switch by another junctor highway, for forming a T-S-T (time switch-space switch-time switch) 3-staged structure switching network, and a control means is provided in each time switch module for connecting a highway which is connected to an input of the first stage time switch, instead of the junctor highway from the output of the second stage space switch, to the input of the third time switch for constituting a one-staged time switch switching network when it is detected that the space switch module is a faulty condition. 
     The control means also connects the highway to the input of the third time switch for constituting a one-staged time switch switching network when it is detected that a junctor highway coupling between the first stage time switch and the second stage space switch is a faulty condition. 
     The control means selectively connects the junctor highway from the output of the second stage space switch or the highway coupled with the input of the first stage time switch to the input of the third time switch in accordance with a state of the space switch module and a state of the junctor highway between the first time switch and the second space switch, and it constitutes a one-staged time switch switching network by connecting the highway to the input of the third stage time switch when either of the space switch module or the junctor highway between the first time switch and the second space switch is a faulty condition. 
     The control means is constituted by a selecting circuit provided in front of the input of the third time switch for selectively connecting the junctor highway from the output of the second stage space switch or the highway coupled with the input of the first stage time switch to the input of the third time switch, and a control processor for controlling the selecting circuit to connect the highway to the input of the third stage time switch when either of the space switch module or the junctor highway between the first time switch and the second space switch is a faulty condition. 
     A supervisory circuit for supervising a state of the junctor highway coupling between the first stage time switch and the second stage space switch is also provided in the space switch module, and a control processor in the space switch module detects a state of the junctor highway through the supervisory circuit. The control processor in the space switch module distributes information about the state of the junctor highway through a processor bus which is connected to all control processors in the time switch modules. Therefore, the control processor in the time switch module controls the selecting circuit to connect the highway to the input of the third stage time switch when a faulty condition of the junctor highway is informed. 
     The control processors in each time switch module maintains the T-S-T 3-staged structure switching network unless otherwise the junctor highway under faulty condition is connected to own time switch module. 
     A supervisory circuit for supervising a state of the junctor highway between the selecting circuit and the second stage space switch is also provided in each time switch module. The control processor in the time switch module controls the selecting circuit to connect the highway coupled with the input of the first stage time switch to the input of the third stage time switch for intra time switch module calls when a faulty condition of the junctor highway is found, and distributes this faulty information to other control processors in other time switch modules through the processor bus. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram illustrating a configuration of a first embodiment of the present invention. 
     FIG. 2 is a block diagram illustrating a configuration of a second embodiment of the present invention. 
     FIG. 3 is a flow chart explaining an operation of the first embodiment of the present invention. 
     FIG. 4 is a flow chart explaining an operation of the second embodiment of the present invention. 
     FIG. 5 is a block diagram illustrating the principle of time slot switching by a T-S-T 3-staged structure switching network. 
     FIG. 6 is a block diagram illustrating a configuration of the conventional T-S-T 3-staged structure switching network. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1 is a block diagram illustrating a configuration of a first embodiment of the present invention. 
     The incoming highway from a line circuit  310 - 31 N is coupled to a first stage time switch  110 - 11 N and also coupled to a selecting circuit  140 - 14 N which will be described later, and junctor highways HW 10 -HW 1 N from each of first stage time switches  110 - 11 N are coupled to a second stage space switch  200 . Each of junctor highways HW 20 -HW 2 N from the second stage space switch  200  are coupled to each of selecting circuits  140 - 14 N respectively. An output of the selecting circuit  140 - 14 N is coupled to the third stage time switch  120 - 12 N. The outgoing highway from a third stage time switch  120 - 12 N is coupled to a line circuit  320 - 32 N. Each line circuit is coupled to a subscriber terminal  1 -N, or  10 - 1 N. That is, the selecting circuit  140 - 14 N inputs data flow on the highway from the line circuit  310 - 31 N and data flow on the junctor highway HW 20 -HW 2 N from the space switch  210 - 21 N, and selects one of data flows and outputs to the third stage time switch  120 - 12 N under control of a control processor  130 - 13 N in the same time switch module  100 - 10 N. Control processors  130 - 13 N,  230  are connected each other by a processor bus  400 . 
     When the T-S-T 3-staged structure switching network is a normal condition, the selecting circuit  140 - 14 N selects data flow on the junctor highway HW 20 -HW 2 N as the input of the third stage time switch  120 - 12 N. However, when there is a failure in the space switch module  200 , the selecting circuit  140 - 14 N selects data flow on the highway from the line circuit  310 - 31 N as the input of the third stage time switch  120 - 12 N. This means that the switching network operates as a T one-staged switching network instead of a T-S-T 3-staged switching network when a failure happens in the space switch module  200 . Calls among the same time switch module (e.g. a call between the subscriber terminals  1  and  10  in the time switch module  100 ) is relieved even a failure occurred in the space switch module, and this arrangement can improve the reliability of the switching system. 
     More detail operation of the present invention will be described with reference to the flow chart shown in FIG. 3 together with a block diagram shown in FIG.  1 . 
     It is assumed that the subscriber terminal  1  accommodated in the line circuit  310  connected to the time switch module  100  originates a call. 
     In this case, the control processor  130  detects the call origination from the subscriber terminal  1  and performs necessary control operation for the call, such as an analysis of dialled number for discriminating destination of the call (step  301 ). After the destination has been discriminated, the control processor  130  confirms if the space switch module is a normal state (step  302 ). 
     When it is confirmed that the space switch module is a normal state (step  302 : no), a normal path connection operation is performed (step  305 ) in the same manner as described for FIG.  6 . 
     That is, if the destination of this call is the subscriber terminal  1 N, the following operation will be performed to connect subscriber terminals  1  and  1 N. 
     The control processor  130  makes an inquiry about an idle time slot number available on both junctor highways HW 10  and HW 2 N to the control processor  230 . The control processor  230  searches an idle time slot available on both junctor highways HW 10  and HW 1 N, and then selects one of available time slot number and notifies this information to the control processor  130 . The control processor  130  instructs the time switch  110  to perform a time slot exchange operation from an incoming time slot to the time slot which has been informed by the control processor  230 , also, the control processor  130  instructs the control processor  230  and the control processor  13 N to perform path establishment in the space switch  21 N and in the time switch  12 N respectively. In the space switch  21 N, the time slot which has been reserved on the junctor highway HW 10  is switched to the same time slot on the junctor highway HW 2 N, and also, in the time switch  12 N, a time slot exchange operation from the time slot on the junctor highway HW 2 N which is connected to the time switch  12 N via the selecting circuit  14 N, informed by the control processor  130 , to the time slot on the outgoing highway corresponding to the subscriber terminal  1 N is performed. 
     However, when it is confirmed that the space switch module is a malfunction state (step  302 : yes), the destination of the call is confirmed whether the destination of the call is within the same time switch module or not (step  303 ). If the destination is in the other time switch module (step  303 : no), it means that no path is available due to space switch module failure, and the call process is interrupted and the call is rejected (step  306 ) as the result. 
     If the destination is in the same time switch module, assuming that it is the subscriber terminal  10 , (step  303 : yes), it means that communication path is still available via the third stage time switch  120 , and the call process by the control processor  130  is proceeded by connecting incoming highway from the line circuit  310  to the input of the time switch  120  via the selecting circuit  140 . 
     As the control processor  130  has both of time slot number information of the subscriber terminals  1  and  10 , the control processor  130  instructs the time switch  120  to exchange a time slot on the incoming highway from the line circuit  310  to a time slot on the outgoing highway to the line circuit  320 . Then, the communication path between subscriber terminals  1  and  10  has been completed. 
     As a consequence, each of the time switch modules  100 - 10 N is solely operated as the T 1 -staged switch, so that the connections between the subscriber terminals accommodated in the same time switch module are guaranteed even if the space switch module becomes failure. 
     In the case that the failure in the space switch module  200  has been recovered, the control processors  130 - 13 N of the time switch modules  100 - 10 N, and also the control processor  230  of the space switch module  200  mutually perform the matching operations in order that the switching network again constitute the T-S-T 3-staged structure. At this time, each control processor  130 - 13 N controls the corresponding selecting circuit  140 - 14 N so as to connect the junctor highway HW 20 -HW 2 N from the space switch module  200  instead of the incoming highway from the line circuit  310 - 32 N, so that the normal switching network structure is restored. 
     FIG. 2 is a block diagram showing a configuration of a second embodiment of the present invention. The same reference numerals shown in FIG. 1 will be employed as those for indicating the same, or similar functional elements in FIG.  2 . 
     Referring now to FIG. 2, in addition to the abovedescribed first embodiment indicated in FIG. 1, in accordance with this embodiment, there are provided incoming junctor highway supervisory circuits  240 - 24 N and outgoing junctor highway supervisory circuits  150 - 15 N. These supervisory circuits supervises respectively a state of each of junctor highways HW 10 -HW 1 N which are incoming junctor highways for the space switch module  200 , and junctor highways HW 20 -HW 2 N which are outgoing junctor highways for the spaces switch module  200 . 
     Each of control processors  130 - 13 n periodically receives result of supervision by the corresponding supervisory circuit  150 - 15 N, and the control processor  230  periodically receives result of supervision by each of supervisory circuits  240 - 24 N. If none of supervisory result has been received within a predetermined time, or a fault state has been reported by a supervisory circuit, it is detected as a fault state of the corresponding junctor highway. Also, the control processors  130 - 13 n and the control processor  230  mutually confirm through the processor bus  400  as to whether or not each of the control processors are operated under normal conditions. 
     When a fault state is detected in any of supervisory circuits  240 - 24 N by the control processor  230 , this fault state is reported to all control processors  130 - 13 N through the processor bus  400 . Then, if a failure was detected in the supervisory circuit  240 , it means that the junctor highway HW 10  cannot be used for path establishment, the control processor  130  in the time switch module  100  which is corresponding to the fault junctor highway HW 10  instructs the selection circuit  140  to select incoming highway from the line circuit  310  instead of the junctor highway HW 20  from the space switch module  200  for relieving internal communication within the same time switch module. In this case, however, control processors in the time switch modules other than the control processor  130  do not perform any special operations, and maintains a T-S-T 3-staged switching network configuration because a failure of the junctor highway HW 10  does not affect to any of time switch modules other than the time switch module  100 . 
     When a fault state is detected in any of supervisory circuits  150 - 15 N by the corresponding control processor  130 - 13 N, this fault state is reported to control processors in other time switch modules through the processor bus  400 . Then, if a failure was detected in the supervisory circuit  150 , it means that the junctor highway HW 20  cannot be used for path establishment, the control processor  130  in the time switch module  100  which is corresponding to the fault junctor highway HW 20  instructs the selection circuit  140  to select incoming highway from the line circuit  310  instead of the junctor highway HW 20  from the space switch module  200  only for internal communication within the same time switch module. That is, as the fault junctor highway HW 20  does not affect to an operation for communication path establishment from a subscriber terminal in the time switch module  100  to a subscriber terminal in other time switch module, the control processor  130  performs normal operation by using a T-S-T 3-staged switching network configuration, but the fault junctor highway HW 20  affects to a call within the same module, the control processor  130  performs a switching operation for such a call using a T one-stage switching network configuration. 
     In this case, control processor in the time switch module other than the control processor  130  performs the control operation that it rejects a call requiring communication path establishment for which the time switch module  100  is involved, but it performs normal control operation using a T-S-T 3-staged switching network as far as the call does not involve the time switch module  100 . 
     FIG. 4 summarizes the foregoing operations. 
     Also, in such a case that a failure happens to occur in the control processor  230 , since the control processors  130 - 13 N cannot mutually confirm the normal characteristics thereof, each control processor  130 - 13 N can discriminates that the failure occurs in the control processor  230 . Similarly, in this case, the respective control processors  130 - 13 N control the selecting circuits  140 - 14 N in the own time switch module, so that each of these selecting circuits may be operated as a T one-staged switching network. 
     When the failure is recovered, the recovery information is obtained, and then control processors perform the ordinary T-S-T 3-staged switching network structure operation. 
     In the above-described embodiment, the T one-staged switching network configuration is used for relieving internal communication in the same time switch module. Alternatively, even in such a system that the T-T 2-staged switching network configuration which connects the junctor highway from the first stage time switch to the selecting circuit may be achieved. 
     As previously explained, in accordance with the present invention, even when the failure happens to occur in the space switch module in the T-S-T 3-staged structure switching network, the internal communication within the same time switch module can be made in unit of the T one-staged switching network. 
     Although the present invention has been fully described by way of the preferred embodiments thereof with reference to the accompanying drawings, various changes and modifications will be apparent to those having skill in this field. Therefore, unless these changes and modifications otherwise depart from the scope of the present invention, they should be construed as included therein.