Abstract:
A stored program controlled switching system is comprised of a first set of detachably mounted nonvolatile semiconductor memory devices such as memory cards for respectively storing data of different types including a control program, a second set of detachably mounted nonvolatile semiconductor memory devices for respectively storing the data of different types. A first controller is provided for operating the first set of memory devices in a working mode and the second set of memory devices in a standby mode, copying data from the memory devices of the working mode into a main memory and further into the memory devices of the standby mode, and performing a switchover between the operating modes when trouble occurs in the first set of memory devices. A second controller operates the switching system according to the data stored in the main memory.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a stored program controlled switching system. 
     2. Description of the Related Art 
     Current stored program controlled switching systems employ a hard disk system as a huge memory device for storing a vast amount of data such as control program, subscriber information, tariff information and information concerning maintenance, operations and administration. In order to meet new services and features and cope with software imperfections, system file data are updated by downloading data from a storage device such as digital recording tape and magnetic optical disks. For maintenance purposes, the data stored in the hard disk system are routinely duplicated onto a backup system including digital recording tape and magnetic optical disks. Because of the enormous volume of data and the speed limitations imposed on the hard disk system, it takes a long time, typically several tens of minutes, to complete an updating or a duplicating routine. Much longer time (typically several hours) is necessary to duplicate data onto a newly installed standby storage system. 
     In order to minimize the routine work time, Japanese Patent Publication No. 9-135465 discloses a system in which an extra memory system is provided for exclusively storing updating information, which is compared with working data. If a mismatch is detected, the corresponding portion of the working data is replaced with the updating data. Another technique disclosed in Japanese Patent Publication No. 1-309493 also relates to a stored program controlled switching system in which a card reader is provided and memory cards are used as an external storage means to store program and system data. Data stored in each memory card is read by the card reader and downloaded onto the random access memory of the switching system. A further technique is disclosed in Japanese Patent No. 2630263 in which all system are duplicated by a pair of identical subsystems including the switching network, the central processor and the hard disk system. In the duplicated hard disk systems, identical data are stored and constantly checked against each other and one of the systems is used as a working system and the other is in a standby mode. If the working system fails, a mismatch will be detected and a flag is set up, and the system is switched over from the working to the standby hard disk system. When the failed system is restored and duplicated with the current working system, the mismatched portion of data is copied from the current working hard disk system into the restored hard disk system so that same data are stored in both hard disk systems. 
     However, the prior art techniques still require the use of digital recording tape or magnetic optical disks as an external storage system, which contributes to the system size. Additionally, since a number of different types of data are stored, it takes time during a fault finding and recovery process to identify such data types and locate the troubled portion. Furthermore, it is often necessary to replace a failed hard disk drive. In such instances, a new hard disk drive may be shipped over long distances. During shipment, the hard disks are subjected to unfavorable transport conditions which may cause damages. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to provide a stored program controlled switching system that allows efficient trouble shooting and efficient maintenance routine. 
     Another object of the present invention is to provide a stored program controlled switching system that reduces the system size by eliminating the need to provide bulky recording systems. 
     Still another object of the present invention is to provide a stored program controlled switching system that reduces shipment cost at low probability of damage which would otherwise occur during shipment of memory devices. 
     According to the present invention, there is provided a stored program controlled switching system comprising a first set of detachably mounted nonvolatile semiconductor memory devices for respectively storing data of different types including a control program, a second set of detachably mounted nonvolatile semiconductor memory devices for respectively storing the data of different types, and a main memory. A first controller is provided for operating the first set of memory devices in a working mode and operating the second set of memory devices in a standby mode, copying data from the memory devices of the working mode into the main memory and into the memory devices of the standby mode, and performing a switchover between the operating modes when trouble occurs in the first set of memory devices. A second controller operates the switching system according to the data stored in the main memory. 
    
    
     BRIEF DESCRIPTION OF THE DRAWIGNS 
     The present invention will be described in detail further with reference to the following drawings, in which: 
     FIG. 1 is a front view of storage units of the present invention; 
     FIG. 2 is a cross-sectional view taken along the lines  2 — 2  of FIG. 1; 
     FIG. 3 is a block diagram of a stored program controlled switching system of the present invention; 
     FIG. 4 is a flowchart of the operation of a system controller during system startup time; 
     FIG. 5 is a flowchart of the operation of a memory card controller during the system startup time; and 
     FIG. 6 is a flowchart of the operation of the system controller during normal operation of the switching system; 
     FIG. 7 is a flowchart of the operation of the memory card controller during normal operation of the switching system; and 
     FIG. 8 is a flowchart of the system controller during the normal operation of the switching system. 
    
    
     DETAILED DESCRIPTION 
     In FIGS. 1 and 2, there is shown a pair of storage units of the present invention for use in a stored program controlled switching system. Each of the storage units  11 A and  11 B is formed with an array of vertically extending slots  12  through which nonvolatile semiconductor memory cards  14  are inserted. At the innermost end of the slots  12  is provided a female connector  13  that is adapted to engage with connector pins  15  of the memory cards  14 . 
     As shown in FIG. 3, the stored program controlled switching system is comprised of a number of trunk interfaces  20  and a number of subscriber interfaces  21 . Control signals from these interfaces are supplied to a system controller  23  through a system bus  24 . Although not shown in the drawings, the traffic signals from other switching systems and subscribers to these interfaces are supplied to a switch fabric which is also controlled by the system controller  23 . A maintenance interface  22  is also connected to the system bus  24  for applying a maintenance test signal to the switching system. Also connected to the system bus  24  are a main memory  25  and a memory card controller  26 . Female connectors  13  of both working and standby storage units are connected to the memory card controller  26 . 
     In the working unit  11 A, the memory cards store data of different types. For example, switching control program, switching office database, tariff database, and trouble records are stored respectively in the memory cards  14   1    14   2    14   3  and  14   4 . System controller  23  accesses the memory card controller  26  to cause it to perform a read operation on the memory cards of the working unit  11 A according to a control program stored in the main memory  25 . Initially, the system controller  23  accesses the memory card controller  26  to copy the data stored in each memory card of the working unit lla onto a specified area of the main memory  25 . In addition, under control of the memory card controller  26 , data stored in the memory cards of the working unit  11 A are duplicated by copying into corresponding memory cards of the standby unit  11 B by synchronizing both units to each other. The contents of all memory cards of the working unit are checked against those of the standby unit so that when a change occurs in one memory card of the working unit, it is copied into the corresponding memory card of the standby unit. 
     When trouble occurs in the switching system, the system controller  23  directs the memory card controller  26  to perform a switchover from the working storage unit  11 A to the standby storage unit  11 B and alerts the maintenance personnel. In response to the alarm signal, the maintenance personnel withdraws all the memory cards of the suspected storage unit from their slots  12  and analyzes the contents of each memory card according to the type of its stored data in an attempt to locate the trouble. Data are stored in the memory cards  14  in such a format that personal computers are able to access. Data analysis of stored data can be efficiently performed and significant time saving can be achieved. 
     The operation of the system controller  23  during system startup proceeds according to a program stored in its read-only memory as illustrated in the flowchart of FIG.  4 . At decision step  40 , the system controller  23  monitors the maintenance interface  22  to detect a startup command signal. If a startup command signal is detected, flow proceeds to step  41  to send a copy command signal to the memory card controller  26  to direct it to read the system control program from the memory card  14   1  of the working unit  11 A and copies the read program into a specified location of the main memory  23 , and proceeds to decision step  42  to check to see if an end-of-copy message is received from the memory card controller  26 . If the decision at step  42  is affirmative, the system controller repeats steps  41  and  42  until the stored data of all memory cards of the working unit  11 A are copied into the main memory  25  (step  43 ). At step  44 , the system controller  23  references a mapping table created by the memory card controller  26  and reads an address that is mapped to the storage location of the system control program in the main memory  25 . System controller  23  reads the system control program and initializes the trunk interfaces  20  and the subscriber interfaces  2  (step  45 ) and proceeds to the end of the routine. 
     The operation of memory card controller  26  during the startup routine proceeds according to the flowchart of FIG.  5 . At decision step  50 , the memory card controller determines whether a copy command signal is received from the system controller  23 . In response to a copy command signal, the memory card controller  26  proceeds from step  50  to step  51  to test a memory card of the working unit  11 A to see if it is properly inserted into its own slot. If the test indicates that the memory card is not properly inserted, flow proceeds to step  56  to switchover to the standby storage unit  11 B and generates an alarm (step  57 ) and returns to the starting point of the startup routine. Otherwise, the memory card controller proceeds to step  52  to read data from the memory card and copies it in a storage location of the main memory  25  and sends an end-of-copy message to the system controller  23  (step  53 ). Steps  50  to  53  are repeatedly performed until all memory cards are read and copied into the main memory  25  (step  54 ). At step  55 , the memory card controller  26  creates a mapping table for mapping addresses of the main memory  25  to corresponding data of the memory cards and sends this address mapping table to the system controller  23 . 
     During normal operation of the switching system, the system controller  23  executes a routine illustrated in FIG.  6 . System controller  23  monitors the output of maintenance interface  22  to detect a system database read command (step  60 ) or a system database update command (step  61 ). If the decision at step  60  is affirmative, the controller  23  reads the system database from the storage location of main memory  25  specified by the address mapping table supplied from the memory card controller  26  (step  62 ) and sends the read data to the maintenance center, not shown, through the maintenance interface  22 . If a database update command signal is received (step  61 ), the system controller proceeds to step  64  to receive update data from the maintenance interface  22  and replace the corresponding data in the main memory  25  with the update data (step  65 ). At step  66 , the system controller sends an update command signal to the memory card controller  26  and waits for an end-of-update message from the memory card controller (step  67 ). 
     During the normal operation, the memory card controller  26  executes the routine shown in FIG.  7 . Memory card controller  26  starts the routine by monitoring the central processor  23  (step  70 ) and the working storage unit  11 A (step  71 ). If an update command signal generated at step  66  by the system controller  23  is detected at step  70 , the memory card controller  26  reads subscriber data from the main memory (step  72 ) and updates a pair of corresponding memory cards of both working and standby units  11 A and  11 B, which are synchronized to each other, with the read subscriber data (step  73 ). An end-of-update message is then returned to the system controller (step  74 ). If trouble occurs in a memory card of the working unit  11 A, the memory card controller  26  proceeds from step  71  to step  75  to send a trouble report to the system controller  23  and waits for a stop sync command signal from the system controller (step  76 ). In response to a stop sync command signal, the memory card controller  26  stops synchronization between the working and standby storage units  11 A and  11 B (step  77 ) and switchovers the system to the standby unit  11 B (step  78 ). When the system controller  23  receives the trouble report (step  80 ) as shown in FIG. 8, it sends a stop sync command signal to the memory card controller  26 . 
     It will be seen from the foregoing that when trouble occurs in the working storage unit  11 A, the memory cards can be withdrawn individually from their slots and can be checked according to the data types. This facilitates trouble shooting and maintenance routine. Furthermore, the present invention is advantageous over the prior art hard disk system because of reduced inventory that will be required for holding replacement parts. In addition, the memory cards are in the format that allows personal computers to perform read/write operation, data analysis can be significantly improved in efficiency. Since the same recording medium is used for both working and standby storage units, efficient backup and maintenance operations can be achieved.