BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to restoration strategies in ATM transmission systems, and in particular to a permanent virtual circuit (PVC) management method and system in an ATM switch for restoring data transmission when a fault occurs on a transmission line between ATM switches. 
     2. Description of the Related Art 
     Asynchronous Transfer Mode (ATM) communications are becoming widely used to allow various kinds of data of different bit rates to be transferred at high speeds, which is expected to realize the Broadband Integrated Services Digital Network (B-ISDN). In an ATM switched network composed of a plurality of ATM switches, a permanent virtual circuit (PVC) is established to provide a point-to-point connection through a plurality of ATM switches. Since PVC is a static connection, however, when a failure occurs on a transmission line between ATM switches, ATM cell transmission becomes impossible. 
     To avoid such a breakdown of communications, there has been proposed an ATM switch having a restoration function in Japanese Patent Unexamined Publication No. 9-247153. This conventional ATM switch is provided with a VPI/VCI conversion table storing a set of VPI and VCI for working path and another set of VPI and VCI for protecting path for each cell. When a failure is detected on a working line, the call on the working line is switched to an alternative line without call interruption. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a PVC management method and system which can achieve rapid fault recovery when a fault occurs on a transmission line between ATM switches. 
     Another object of the present invention is to provide a method and system which can achieve automatic fault recovery with simplified procedures. 
     According to an aspect of the present invention, in a system for managing a permanent virtual circuit (PVC) including a plurality of ATM switches in an ATM network including a network management system, each of the ATM switches includes a pair of an incoming header translator and an outgoing header translator, which are provided for each line; and a PVC controller controlling the incoming header translator and the outgoing header translator to provide a working PVC and a protection PVC which are associated with different transmission lines, wherein the working PVC and the protection PVC are selectable under control of the network management system. 
     The PVC controller may control the incoming header translator and the outgoing header translator such that the working PVC is set up and the protection PVC stands ready to be set up, wherein, when a failure occurs on a transmission line associated with the working PVC, the protection PVC is set up to ensure cell communication in place of the working PVC. When the transmission line associated with the working PVC has been restored, the working PVC is set up to ensure cell communication in place of the protection PVC. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram showing the functional configuration of an ATM switch according to an embodiment of the present invention; 
     FIG. 2 is a schematic diagram showing an example of the setting operation of a PVC management controller according to the embodiment of the present invention; and 
     FIG. 3 is a block diagram showing a route switching operation of the embodiment when a failure occurs on a transmission line. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     As shown in FIG. 1, a system according to the present invention and the operation thereof will be described hereinafter, taking as an example the case of two ATM switches  10  and  20  which are managed by a network management system (NMS)  30 . And it is further assumed that the ATM switches  10  and  20  are connected to each other through transmission lines  40  and  50  that may be composed of an optical fiber. 
     The ATM switch  10  includes a PVC management controller  101  which manages a pair of header translator incoming (HTI) and header translator outgoing (HTO) provided for each of the lines set therein. The HTI performs a conversion of the header of an incoming cell to an internal channel header according to PVC information set by the PVC management controlling  101 . The HTO performs a conversion of the internal channel header to a header of an outgoing cell according to PVC information set by the PVC management controller  101 . 
     In this example, HTO 11  and HTI 11  are provide with PVC information for a line  102  connected to a transmission line  60 . HTO 12  and HTI 12  are provided with PVC information for a line  103  connected to the transmission line  40 . HTO 13  and HTI 13  are provided with PVC information for a line  104  connected to the transmission line  50 . 
     Similarly, the ATM switch  20  includes a PVC management controller  201  which manages a pair of HTI and HTO provided for each of the lines set therein. The HTI performs a conversion of the header of an incoming cell to an internal channel header according to PVC information set by the PVC management controller  201 . The HTO performs a conversion of the internal channel header to a header of an outgoing cell according to PVC information set by the PVC management controller  201 . 
     In this example, HTO 21  and HTI 21  are provided with PVC information for a line  202  connected to a transmission line  70 . HTO 22  and HTI 22  are provided with PVC information for a line  203  connected to the transmission line  40 . HTO 23  and HTI 23  are provided with PVC information for a line  204  connected to the transmission line  50 . 
     The respective lines  103  and  203  terminate the transmission line  40  at the ends thereof and the respective lines  104  and  204  terminate the transmission line  50  at the ends thereof. The line  102  terminates the end of the transmission line  60  and the line  202  terminates the end of the transmission line  70 . 
     The PVC management controllers  101  and  201  perform the PVC setup and the working/protection-PVC switching depending on instructions received from the network management system NMS  30 . More specifically, the PVC management controller  101  performs the setup of working PVC by sending a working-PVC setup request to each of relevant HTIs and HTOs and saving the set working-PVC information. Similarly, the PVC management controller  101  performs the setup of protection PVC by sending a protection-PVC setup request to each of relevant HTIs and HTOs and saving the set protection-PVC information. Further, the PVC management controller  101  performs the switching between the working PVC and the protection PVC by sending a PVC switch request to each of relevant HTIs and HTOs. Therefore, as will be described later, the PVC management controller  101  can interconnect one line and another line to set up a bi-directional PVC according to the control of the NMS  30 . 
     Similarly, the PVC management controller  201  performs the setup of working PVC by sending a working-PVC setup request to each of relevant HTIs and HTOs and saving the set working-PVC information. The PVC management controller  201  performs the setup of protection PVC by sending a protection-PVC setting request to each of relevant HTIS and HTOs and saving the set protection-PVC information. Further, the PVC management controller  201  performs the switching between the working PVC and the protection PVC by sending a PVC switch request to each of relevant HTIs and HTOs. Therefore, as will be described later, the PVC management controller  201  can interconnect one line and another line to set up a bi-directional PVC according to the control of the NMS  30 . 
     WORKING PVC SETUP 
     A working-PVC setup request is supplied from the NMS  30  to both the PVC management controllers  101  and  201 . When receiving the working-PVC setup request, the PVC management controller  101  perform the working-PVC setup operation to form a bi-directional working PVC consisting of working PVC  105 . 1  from HTI 11  to HTO 12  and working PVC  105 . 2  from HTI 12  to HTO 11 . Similarly, the PVC management controller  201  perform the working-PVC setup to form a bi-directional working PVC consisting of working PVC  205 . 1  from HTI 21  to HTO 22  and working PVC  205 . 2  from HTI 22  to HTO 21 . The details will be described hereinafter referring to FIGS. 1 and 2. 
     Referring to FIG. 2, to set up the working PVC  105 . 1  and  105 . 2 , the PVC management controller  101  requests the working-PVC setup of the HTI 11 , HTO 11 , HTO 12 , and HTI 12  as shown by reference numerals  301 ,  302 ,  303 , and  304 , respectively. At this time, the PVC management controller  101  saves working-PVC information HTI W  and HTO W  for the HTI 11  and HTO 11  in a working-PVC administration table for the line  102  and further saves working-PVC information HTO W  and HTI W  for the HTI 12  and HTO 12  in a working-PVC administration table for the line  103 . 
     Similarly, to set up the working PVC  205 . 1  and  205 . 2 , the PVC management controller  201  requests the working-PVC setup of the HTI 21 , HTO 21 , HTO 22 , and HTI 22 . At this time, the PVC management controller  201  saves working-PVC information HTI 11  and HTO 11  for the HTI 21  and HTO 21  in a working-PVC administration table for the line  202  and further saves working-PVC information HTO W  and HTI W  for the HTI 22  and HTO 22  in a working-PVC administration table for the line  203 . 
     In this manner, a shown in FIG. 1, the bi-directional working PVC  105 . 1  and  105 . 2  is set up between the lines  102  and  103  in the ATM switch  10 . The bi-directional working PVC  205 . 1  and  205 . 2  is set up between the lines  202  and  203  in the ATM switch  20 . As a result, incoming calls from the line  102  flows out the line  202  through HTI 11 , the working PVC  105 . 1 , HTO 12 , the line  103 , the transmission line  40 , the line  203 , HTI 22 , the working PVC  205 . 2 , and HTO 21 . Incoming cells from the line  202  flows out the line  102  through HTI 21 , the working PVC  205 . 1 , HTO 22 , the line  203 , the transmission line  40 , the line  103 , HTI 12 , the working PVC  105 . 2 , and HTO 21 . Therefore, ATM services are realized using the working bi-directional PVC. 
     PROTECTION PVC PROVISION 
     An operator instructs the NMS  30  to provision an alternative route of the working PVC  105 . 1  and  105 . 2  and the working PVC  205 . 1  and  205 . 2 . According to the protection PVC provision instruction, the NMS  30  selects the transmission line  50  to be used for an alternative route. Then the NMS  30  transmits a protection-PVC provision request for protection PVC  106 . 1  and  106 . 2  to the PVC management controller  101  of the ATM switch  10  and also transmits a protection-PVC provision request for protection PVC  206 . 1  and  206 . 2  to the PVC management controller  201  of the ATM switch  20 . 
     When receiving the protection-PVC provision request for protection PVC  106 . 1  and  106 . 2 , the PVC management controller  101  perform the protection-PVC provision operation to make the provision of the one-directional protection PVC  106 . 1  from HTI 12  to HTO 13  and the one-directional protection PVC  106 . 2  from HTI 13  to HTO 11 . 
     More specifically, as shown in FIG. 2, to set up the one-directional protection PVC  106 . 1 , the PVC management controller  101  requests the protection-PVC setup of the HTO 13  as shown by reference numeral  305 . At this time, the PVC management controller  101  saves the protection-PVC information HTO P  for the HTO 13  in a protection-PVC administration table for the line  104 . However, the PVC management controller  101  does not request the protection-PVC setup of the HTI 12  at this time. Since the working-PVC information has been set on the HTI 12 , if the protection-PVC setup of the HTI 12  is performed, then the setting of the HTI 12  would be updated, resulting in invalid working PVC  105 . 2 . Therefore, the protection PVC  106 . 1  is unavailable at this provision stage. 
     On the other hand, to set up the one-directional protection PVC  106 . 2 , the PVC management controller  101  request the protection-PVC setup of the HTI 13  as shown by reference numeral  306 . At this time, the PVC management controller  101  saves the protection-PVC information HTI P  for the HTI 13  in the protection-PVC administration table for the line  104 . Since the working-PVC information has been set on the HTO 11 , it can be also used in the protection PVC  106 . 2 . Therefore, the PVC management controller  101  does not request the protection-PVC setup of the HTO 11 . 
     Similarly, in the ATM switch  20 , to set up the one-directional protection PVC  206 . 1 , the PVC management controller  201  requests the protection-PVC setup of the HTO 23 . At this time, The PVC management controller  201  saves the protection-PVC information HTO P  for the HTO 23  in a protection-PVC administration table for the line  204 . However, the PVC management controller  201  does not request the protection-PVC setup of the HTI 22  at this time. Since the working-PVC information has been set on the HTI 22 , if the protection-PVC setup of the HTI 22  is performed, then the setting of the HTI 22  would be updated, resulting in invalid working PVC  205 . 2 . Therefore, the protection PVC  206 . 1  is unavailable PVC  206 . 1  is unavailable at this provision stage. 
     On the other hand, to set up the one-directional protection PVC  206 . 2 , the PVC management controller  201  request the protection-PVC setup of the HTI 23 . At this time, the PVC management controller  201  saves the protection-PVC information HTI P  for the HTI 23  in the protection-PVC administration table for the line  204 . Since the working-PVC information has been set on the HTO 21 , it can be also used in the protection PVC  206 . 2 . Therefore, the PVC management controller  201  does not request the protection-PVC setup of the HTO 21 . 
     In this manner, as shown in FIG. 1, the one-directional protection PVC  106 . 1  stands ready to be set up from the line  103  to the line  104  and the one-directional protection PVC  106 . 2  is set up from the line  104  to the line  102  in the ATM switch  10 . Similarly, in the ATM switch  20 , the one-directional protection PVC  206 . 1  stands ready to be set up from the line  203  to the line  204  and the one-directional protection PVC  206 . 2  is set up from the line  204  to the line  202 . 
     SWITCHING FROM WORKING TO PROTECTION PVC 
     As shown in FIG. 3, it is assumed that a failure occurs on the transmission line  40  and is detected by both the ATM switches  10  and  20 . When detecting the failure, the ATM switches  10  and  20  each transmit line failure alarm signals to the NMS  30 . 
     When receiving the line failure alarm signals from both the ATM switches  10  and  20 , the NMS  30  transmits PVS switching request signals to both the ATM switches  10  and  20 . Alternatively, the operator may instruct the NMS  30  to transmit the PVC switching request signals to both the ATM switches  10  and  20 . 
     When receiving the PVC switching request signal from the NMS  30 , the PVC management controller  101  sends a loopback request to the line  103  to make the outgoing cells from the HTO 12  go back to the HTI 12  without transmitting them to the transmission line  40 . At the same time, the PVC management controller  101  requests the protection-PVC setup of the HTI 12  using the protection-PVC information HTI P  for the HTI 12  which has been saved in the protection-PVC administration table for the line  103 . The protection-PVC information HTI P  is overwritten onto the HTI 12  as shown by reference numeral  401  in FIG. 2, which causes the protection PVC  106 . 1  to be set up from the HTI 12  to the HTO 13 . 
     Similarly, in the ATM switch  20 , when receiving the PVC switching request signal from the NMS  30 , the PVC management controller  201  sends a loopback request to the line  203  to make the outgoing cells from the HTO 22  go back to the HTI 22  without transmitting them to the transmission line  40 . At the same time, the PVC management controller  201  requests the protection-PVC setup of the HTI 22  using the protection-PVC information HTI P  for the HTI 22  which has been saved in the protection-PVC administration table for the line  203 . The protection-PVC information HTI P  is over-written onto the HTI 22 , which causes the protection PVC  206 . 1  to be set up from the HTI 22  to the HTO 23 . 
     In this state, as shown in FIG. 3, incoming cells from the line  102  flows out the line  202  through the protection route formed by the HTI 11 , the working PVC  105 . 1 , the HTO 12 , the loopback line  103 , the HTI 12 , the protection PVC  106 . 1 , the HTO 13 , the line  104 , the transmission line  50 , the line  204 , the HTI 23 , the protection PVC  206 . 2 , and the HTO 21 . 
     Conversely, incoming cells from the line  202  flows out the line  102  through the protection route formed by the HTI 21 , the working PVC  205 . 1 , the HTO 22 , the loopback line  203 , the HTI 22 , the protection PVC  206 . 1 , the HTO 23 , the line  204 , the transmission line  50 , the line  104 , the HTI 13 , the protection PVC  106 . 2 , and the HTO 11 . 
     SWITCHING BACK TO WORKING PVC 
     In the case where normal operations are restored on the transmission line  40 , the ATM switches  10  and  20  each transmit line restoration alarm signals to the NMS  30 . When receiving the line restoration alarm signals from both the ATM switches  10  and  20 , the NMS  30  transmits PVC switching request signals to both the ATM switches  10  and  20 . Alternatively, the operator may instruct the NMS  30  to transmit the PVC switching request signals to both the ATM switches  10  and  20 . 
     When receiving the PVC switching request signal from the NMS  30 , the PVC management controller  101  sends a loopback-release request to the line  103  to make the outgoing cells from the HTO 12  go to the transmission line  40 . At the same time, the PVC management controller  101  requests the working-PVC setup of the HTI 12  using the working-PVC information HTI P  for the HTI 12  which as been saved in the working-PVC administration table for the line  103 . The working-PVC information HTI W  is over-written onto the HTI 22  as shown by the reference numeral  304  in FIG. 2, which causes the working PVC  105 . 2  from the HTI 12  to the HTO 11  to be restored. 
     Similarly, in the ATM switch  20 , when receiving the PVC switching request signal from the NMS  30 , the PVC management controller  201  sends a loopback-release request to the line  203  to make the outgoing cells from the HTO 22  go to the transmission line  40 . At the same time, the PVC management controller  201  requests the working-PVC setup of the HTI 22  using the working-PVC information HTI W  for the HTI 22  which has been saved in the working-PVC administration table for the line  203 . The working-PVC information HTI W  is over-written onto the HTI 22 , which causes the working PVC  205 . 2  from the HTI 22  to the HTO 21  to be restored. 
     In this manner, as shown in FIG. 1, the bi-directional working PVC  105 . 1  and  105 . 2  and the bi-directional working PVC  205 . 1  and  205 . 2  are restored. Therefore, incoming cells from the line  102  flows out the line  202  through HTI 11 , the working PVC  105 . 1 , HTO 12 , the line  103 , the transmission line  40 , the line  203 , HTI 22 , the working PVC  205 . 2 , and HTO 21 . Incoming cells from the line  202  flows out the line  102  through HTI 21 , the working PVC  205 . 1 , HTO 22 , the line  203 , the transmission line  40 , the line  103 , HTI 12 , the working PVC  105 . 2 , and HTO 21 .
A PVC management system in each of ATM switches is disclosed. Each of the ATM switches includes a pair of an incoming header translator and an outgoing header translator, which are provided for each line. The incoming header translator and the outgoing header translator are controlled to provide a working PVC and a protection PVC which are associated with different transmission lines, wherein the working PVC and the protection PVC are selectable under control of a network management system.