Abstract:
An optical transmission equipment having a switchover control function of optical transmission lines enables to reduce a required space in a common equipment supervision and control portion. The optical transmission equipment includes a pair of a work interface unit and a protection interface unit each accommodating an optical transmission line, and an add drop multiplexing unit for selecting an optical signal output from either of the interface unit pair. Each interface unit includes a switchover controller, and each of the interface unit pair is mutually connected via a communication path so as to share status information among the switchover controllers. Upon a failure in the work interface unit side of the interface unit pair, the failure is reported to the protection interface unit side prepared as an object for switchover, to send a switchover request from the protection interface unit side to the add drop multiplexing unit.

Description:
FIELD OF THE INVENTION 
     The present invention relates to optical transmission equipment having switch control of optical transmission lines. 
     BACKGROUND OF THE INVENTION 
     In optical transmission equipment, transmission lines are redundantly configured to improve availability. Examples of such a redundant configuration are shown in  FIGS. 1 to 3 . 
       FIG. 1  shows an exemplary configuration of optical transmission equipment incorporating switch control of an optical transmission line to switch over between a work line and a protection line constituted on a 1:1 configuration basis. The optical transmission equipment accommodates a plurality of optical transmission lines  1 ,  2  . . . n in an add drop multiplexing unit (hereinafter referred to as ADM unit)  10  via corresponding interface units IF 1 , IF 2  . . . IFn. 
     Each interface unit IF 1 , IF 2  . . . IFn is provided with a pair of interface units IF 1 - 1  and IF 1 - 2  so as to accommodate a pair of transmission lines constituting a work line (W) and a protection line (P). 
     The optical transmission equipment further includes an equipment supervision and control portion  20 . This equipment supervision and control portion  20  has a switchover controller  21 . An alarm signal (APS) is transmitted and received to/from other optical transmission equipment through interface units IF 1 , IF 2  . . . IFn. Equipment supervision and control portion  20  receives a switchover trigger signal SWTRG when either a line failure is detected by interface units IF 1 , IF 2  . . . IFn or a hardware failure is detected in the transmission and reception portion of interface unit IF. 
     Meanwhile, in ADM unit  10 , switchover units  11 - 1  to  11 -n (which are selectors for selectively switching over from a work line to a protection line related to a certain interface unit) are provided corresponding to a plurality of optical transmission lines  1 ,  2  . . . n for switching work and protection lines. 
     Each switchover unit  11 - 1  to  11 -n switches interface units corresponding to a work line and a protection line according to a switchover command SWCMD which is generated by switchover controller  21  based on a switchover trigger signal SWTRG from interface unit IF 1 , IF 2  . . . IFn. 
     In  FIG. 2 , there is shown a configuration example of optical transmission equipment having built-in switchover control of work/protection optical transmission lines being provided on a 1:N basis. In this configuration example, one transmission line among a plurality (n+1) of optical transmission lines is reserved for a protection line. This protection line is switched over to work state when a failure occurs on a work line. 
     For this purpose, ADM unit  10  provides one switchover unit  11  (in this example, a selector to switch from a failed work interface to a protection interface), to switch the interface units corresponding to the work/protection transmission lines in response to a switchover command SWCMD sent from switchover controller  21 . 
       FIG. 3  shows a conventional BLSR (bi-directional line switched ring) switchover configuration being allocated on a ring transmission line. Switchover controller  21  in equipment supervision and control portion  20  controls switchover unit pairs (here, circuits for either bridging or switching)  11 - 1 ,  11 - 2  . . .  11 -n in ADM unit  10  corresponding to each plurality of transmission lines based on a switchover trigger signal SWTRG from interface units IF 1 , IF 2  . . . IFn. 
     In such a conventional configuration of a redundant control system, it is essential to provide switchover controller  21  as a control unit separately provided from switchover units  11 ,  11 - 1  . . .  11 -n in ADM unit  10 . Therefore, it is required to prepare a space for switchover controller  21 . 
     Also, when the number of the aforementioned switchover unit pair  11 - 1  to  11 -n becomes larger, a control unit  21  must be divided into separate units from the viewpoint of performance, which further requires additional space. 
     Therefore, it is to be assumed to provide control unit  21  independently of the switchover unit corresponding to each transmission line. However, in such a configuration, normal switchover to the protection side cannot be guaranteed on occurrence of a failure in an independent control unit itself. In addition, it is necessary to evaluate a status of the protection side prior to the switchover. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide optical transmission equipment having a switchover control function of optical transmission lines which enables to reduce a required space in a common equipment supervision and control portion, to derive switchover performance to the full extent and to implement a large scale system. 
     In order to attain the above-mentioned object, as a first embodiment of the present invention, optical transmission equipment includes a pair of a work interface unit and a protection interface unit each accommodating an optical transmission line, and an add drop multiplexing unit for selecting an optical signal being output from either of the interface unit pair to output. Each interface unit of the interface unit pair has a switchover controller, and each of the interface unit pair is mutually connected via a communication path so as to share status information among the switchover controllers. On occurrence of a failure in the work interface unit side of the interface unit pair, the failure is reported via the communication path to the protection interface unit side prepared as an object for switchover, to send a switchover request from the protection interface unit side to the add drop multiplexing unit. 
     As a second embodiment of the present invention to attain the aforementioned object, in the first embodiment of the optical transmission equipment, the add drop multiplexing unit is constituted by a selector by which an output from either the work interface unit or the protection interface unit is made effective. 
     As a third embodiment of the present invention to attain the aforementioned object, in the second embodiment of the optical transmission equipment, the add drop multiplexing unit comprises a priority circuit for assigning priority to an output from the work interface unit side of the interface unit pair. When switchover requests are sent from both the work and protection interface unit pair, a switchover request sent from the work interface unit to which the priority is assigned is made effective. 
     As a fourth embodiment of the present invention, optical transmission equipment includes (n+1) interface units each accommodating each of (n+1) optical transmission lines, and an add drop multiplexing unit for selecting optical signals being output from n work interface units among (n+1) interface units to output. Each interface unit of the (n+1) interface units comprises a switchover controller, and the (n+1) interface units are mutually connected via a communication path so as to share status information among the switchover controllers. On occurrence of a failure in a work interface unit among the (n+1) interface units, the failure is reported via the communication path to one protection interface unit prepared as an object for switchover, to send a switchover request from the protection interface unit to the add drop multiplexing unit. 
     As a fifth embodiment of the present invention to attain the aforementioned object, in the fourth embodiment of the optical transmission equipment, the add drop multiplexing unit is a selector for making an output of one protection interface unit being prepared as an object for switchover effective in place of an output of the failed work interface unit. 
     As a sixth embodiment of the present invention to attain the aforementioned object, in the fifth embodiment of the optical transmission equipment, the add drop multiplexing unit comprises a priority circuit for assigning the lowest priority to an output of one protection interface unit among (n+1) interface units and successively assigning higher priority to outputs of the other n work interface units, so as to make a switchover to an output of the protection interface unit effective in order of priority assigned in the priority circuit. 
     As a seventh embodiment of the present invention to attain the aforementioned object, optical transmission equipment includes a pair of interface units each accommodating a ring-shaped optical transmission line, and an add drop multiplexing unit having a switchover unit corresponding to the interface unit pair for either looping back an optical signal being output from one interface unit of the interface unit pair to the other interface unit, or bridging the optical signal to the other interface unit. Each interface unit of the interface unit pair has a switchover controller, and each of the interface unit pair is mutually connected via a communication path so as to share status information among the switchover controller. On occurrence of a failure in one interface unit side of the interface unit pair, the failure is reported via the communication path to the other interface unit side prepared as an object for switchover, to send a switchover request for either looping back to the other interface unit or bridging from the protection interface unit side to the add drop multiplexing unit. 
     Further scopes and features of the present invention will become more apparent by the following description of the embodiments with the accompanied drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a configuration example of optical transmission equipment in which switchover control is adopted to switch a work line and a protection line on a 1:1 basis. 
         FIG. 2  shows a configuration example of optical transmission equipment in which switchover control is adopted to switch a work line and a protection line on a 1:N basis. 
         FIG. 3  shows a conventional BLSR switchover configuration disposed in a ring-shaped transmission line. 
         FIG. 4  shows an embodiment of the present invention corresponding to the 1:1 redundant configuration shown in  FIG. 1 . 
         FIG. 5  shows an embodiment of the present invention corresponding to a 1:N redundant configuration shown in  FIG. 2 . 
         FIG. 6  shows an embodiment of the present invention corresponding to a BLSR configuration shown in  FIG. 3 . 
         FIG. 7  shows a block diagram illustrating a detailed configuration according to the present invention shown in  FIGS. 4 to 6 . 
         FIG. 8  shows a schematic diagram of the detailed configuration shown in  FIG. 7 . 
         FIG. 9  shows an operation flowchart in the configuration shown in  FIG. 7  ( FIG. 8 ). 
         FIG. 10  shows a diagram illustrating a control signal configuration to incorporate the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The preferred embodiment of the present invention is described hereinafter referring to the charts and drawings. 
       FIG. 4  shows an embodiment example according to the present invention corresponding to the 1:1 redundant configuration shown in  FIG. 1 . In  FIG. 4 , for the sake of easy understanding, there is shown a configuration of only one pair of transmission lines  1 - 1 ,  1 - 2  respectively acting as a work line and a protection line. 
     Switchover controllers  21 - 1 ,  21 - 2  are incorporated in respective interface unit pair IF 1 - 1 , IF 1 - 2  corresponding to transmission line pair  1 - 1 ,  1 - 2 . Information is interchanged between these switchover controllers  21 - 1 ,  21 - 2  so as to share the information. 
     In an ADM unit  10 , a switchover unit  11  is provided corresponding to one pair of transmission lines  1 - 1 ,  1 - 2 . This switchover unit  11  switches the outputs of interface units IF 1 - 1 , IF 1 - 2  based on a switchover command (SWCMD) issued from switchover controllers  21 - 1 ,  21 - 2 , thus performing a line switchover between the work line and the protection line. 
     Here, according to the standard specification, the time required for line switchover must be no more than 50 milliseconds (msec). In the configuration shown in  FIG. 1 , the object of switchover in each switchover unit  11  is fixed to one pair of work and protection lines. It is therefore always possible to make a switchover within 50 msec of the specified standard switchover time. Also, in case a plurality of lines are accommodated in a unit, the number of lines is small compared to the number of lines concentrated in a system. When switchover becomes not possible because of a failed switchover controller, the number of lines to which switchover is impeded can be reduced. 
       FIG. 5  is an embodiment of the present invention corresponding to the 1:N configuration shown in  FIG. 2 . In this  FIG. 5 , switchover controller  21  is built in corresponding to each of the (1+n) interface units IF 1  to IF(1+n). 
     Also in this configuration, mutual information exchange is carried out so as to share information between each interface unit IF 1  to IF(n+1). In such a configuration shown in  FIG. 5 , it is possible to switch interface output between a work line and a protection line with in a switchover time of 50 msec as specified in the standard. The reason is that the switchover performed by switchover unit  11  is always fixed against 1:N pairs or the number of lines per interface is small. 
       FIG. 6  shows an embodiment of the present invention corresponding to a BLSR (bi-directional line switched ring) configuration shown in  FIG. 3 . For the sake of easy understanding, only a configuration corresponding to a work/protection pair of duplicated transmission lines  1 - 1 ,  1 - 2  is shown in  FIG. 6 . In each interface unit pair IF 1 - 1 , IF 1 - 2  respectively corresponding to the pair of duplicated transmission lines  1 - 1 ,  1 - 2 , switchover controllers  21 - 1 ,  21 - 2  are built in, to communicate so as to share information therebetween. 
     ADM unit  10  provides a switchover unit  11  so as to correspond to a pair of duplicated transmission lines  1 - 1 ,  1 - 2 . Based on a switchover command (SWCMD) from switchover controllers  21 - 1 ,  21 - 2  in interface units IF 1 - 1 , IF 1 - 2 , switchover unit  11  switches one failed transmission line among the duplicated transmission lines  1 - 1 ,  1 - 2  so as to loop signals back to the other transmission line. Thus continuity of communication is maintained. 
     In such a BLSR configuration, it is possible to switch interface output within a specified standard switchover time 50 msec because a BLSR pair of the duplicated transmission lines  1 - 1 ,  1 - 2  to be controlled is always fixed or the number of lines per unit is small. 
       FIG. 7  shows a block diagram of a detailed configuration of transmission equipment to implement an embodiment of the present invention shown in  FIGS. 4 to 6 . In this figure, for the sake of simplification, only ADM unit  10 , a pair of interface units IF 1  and interface unit IF 2  are shown, as other configurations are identical. Interface units IF 1 , IF 2  includes a main signal processor  30  and a switchover controller  21 . 
     Main signal processor  30  includes a signal transmission/reception circuit  301 , a frame/line error detection circuit  302 , an overhead add drop multiplexing circuit  303  and a pointer control circuit  304 . 
     In frame/line error detection circuit  302 , a signal failure SF and a signal quality deterioration SD caused by a line error is detected to output. Overhead add drop multiplexing circuit  303  detects an APS condition from K 1 /K 2  byte in a signal overhead part to output. 
     Switchover controller  21  includes a CPU  210  for performing status control and a serial signal interface  211  for signal transmission and reception between an interface unit pair IF 1 , IF 2 . Further, the work/protection switchover operation according to the present invention is performed by firmware  212  to control CPU  210 . 
     Meanwhile, ADM unit  10  includes a switchover unit (signal selector/bridge/switchover circuit)  11 , a route selection circuit  12  and a priority circuit  13 . 
     In such a configuration, an operation is illustrated hereafter. For the sake of easy understanding, a detailed configuration shown in  FIG. 7  is schematically shown in  FIG. 8 . In this  FIG. 8 , identical reference numbers to the numbers shown in  FIG. 7  are assigned to the blocks corresponding to the functions shown in  FIG. 7 .  FIG. 9  shows an operation flow of the circuit shown in  FIG. 7  ( FIG. 8 ). Further,  FIG. 10  is a diagram illustrating a control signal frame structure to implement the present invention. Hereafter a switchover operation of the present invention is illustrated referring to the aforementioned diagrams. 
     Referring to  FIG. 9 , the 1:1 redundant configuration is assumed in the following explanation. 
     In a normal state, a pair of interface units IF 1 , IF 2  mutually informs each other of the normal condition through serial signal interface circuit  211  (procedures P 1 , P 2 ). 
     Here, an exemplary signal format for use in the mutual information exchange between the interface units as well as in a switchover command to be issued to ADM unit  10  is constituted as shown in  FIG. 10 . As frame signal (a), there are provided frame synchronization signal I, frame number II, data III consisting of, for example, 24 bits, and parity bit IV. 
     In this procedure, when a signal failure SF and signal quality deterioration SD caused by a line error are detected and output (A 1 ) in frame/line error detection circuit  302  of one interface unit IF 1 , APS (automatic protection switching) protocol is updated in CPU  210  to inform the other interface unit IF 2  of the signal failure (SF) notification through serial signal interface circuit  211  (procedure P 3 ). 
     This signal failure (SF) notification (b) is performed by data III constituted in the aforementioned frame signal (a), as shown in  FIG. 10(   b ). Namely, in the configuration of data III shown in  FIG. 10(   b ), SD denotes signal quality deterioration, EQT denotes a equipment failure, THR denotes a signal path/non-path notification to be dedicatedly used for BLSR, RCVK 1  denotes a status report from the equipment located on the opposite side, and RCVK 2  denotes a response signal against a signal K 1  transmitted from the own equipment indicating a switchover state of the equipment on the opposite side. Here, the above-stated THR in signal format (b) becomes effective in case of BLSR. 
     The other interface unit IF 2  updates APS according to a signal failure notification from interface unit IF 1  (procedure P 3 ), to shift the status from the protection side to the work side (procedure P 4 ). 
     At this time, interface unit IF 2  reports to interface unit IF 1  that interface unit IF 2  stays in normal condition (procedure P 5 ). Moreover, interface unit IF 2  transmits to ADM unit  10  a request for switching over from interface unit IF 1  to interface unit IF 2  (procedure P 6 ). 
     The switchover request is constituted by frame signal data III having a format shown in  FIG. 10(   c ). In the signal format shown in  FIG. 10(   c ), SEL 0  and SEL 1  are switchover commands for use in either 1:1 or 1:N redundant configuration. Either SEL 0  or SEL 1  is defined effective and the corresponding interface unit is selected in ADM unit  10 . In addition, BR 0 , BR 1 , SW 0  and SW 1  in the signal format shown in  FIG. 10(   c ) are flags for use in the BLSR configuration shown in  FIG. 6 . 
     Referring back to  FIG. 9 , on receiving the report of normal condition from interface unit IF 2  (procedure P 5 ), interface unit IF 1  disables a command line including a buffer amplifier  213  so as not to issue a switchover request from the own interface unit IF 1 . 
     Accordingly, based on the switchover request having the signal format shown in  FIG. 10(   c ) issued by interface unit IF 2  (procedure P 6 ), switchover unit  11  in ADM unit  10  is controlled so that an output from interface unit IF 2  becomes effective (A 2 ). 
     Here, it is assumed in  FIG. 9  that an equipment failure occurs in interface unit IF 2  having been acting as a work side (A 3 ) after the aforementioned switchover is completed (A 2 ). In  FIG. 7 , the equipment failure is detected by both an equipment failure detector  305  provided in main signal processor  30  and an equipment failure detector  214  provided in switchover controller  21 . 
     At this time, interface unit IF 2  updates APS to shift the status to the protection side (procedure P 7 ) and sends the equipment failure notification to interface unit IF 1  via equipment supervision and control portion  20  (procedure P 8 ). When the switchover interface unit controller in interface unit IF 2  becomes faulty, interface unit IF 2  cannot shift the own state. However, it is possible to achieve the switchover by sending an equipment failure notification from interface unit IF 2  to interface unit IF 1  prepared for switchover. 
     Based on this notification, interface unit IF 1  updates APS to shift the state to the work side (procedure P 9 ), and requests ADM unit  10  to switch over from interface unit IF 2  to interface unit IF 1  (procedure P 10 ). 
     In response to this notification, by setting high priority in priority circuit  13  of ADM unit  10  against the switchover request from interface unit IF 1 , switchover unit  11  is controlled so that the effective output side is to be switched over from interface unit IF 2  to interface unit IF 1 , irrespective of the switchover request issued from interface unit IF 2 . 
     Further, in  FIG. 9 , when equipment failure of interface unit IF 2  is restored (A 4 ), interface unit IF 2  updates APS to shift the state to the work side (procedure P 11 ), and reports normal condition information to interface unit IF 1  (procedure P 12 ). 
     When interface unit IF 1  receives this normal condition information from interface unit IF 2 , interface unit IF 1  updates APS to shift the state to the protection side (procedure P 13 ). At this time, because the normal condition information is received from interface unit IF 2 , no switchover request is issued from interface unit IF 1 . 
     Meanwhile, in interface unit IF 1 , because the state of signal failure (SF) occurrence remains unchanged, SF notification (procedure P 3 ) is sent to interface unit IF 2  (procedure P 14 ). Accordingly, a switchover request which requests to switch over to interface unit IF 2  is sent from interface unit IF 1  to ADM unit  10  (procedure P 15 ). 
     Thus, the switchover from interface unit IF 1  to interface unit IF 2  is performed (A 5 ). 
     Although the above-mentioned description illustrates a switchover operation in the 1:1 redundant configuration, the basic configuration is identical in 1:N redundant configuration excluding a part of the operation resulting from a plurality of work interface units. 
     More specifically, it is required to share information in the entire interface units IF 1  to IFn. For this reason, it is necessary that switchover controller  21  sends information to all interface units but itself successively after storing the entire information, not only bridging information to switchover controller  21  in the interface unit located on the opposite side. 
     In addition, in priority circuit  13  of ADM unit  10 , the priority is set successively to the plurality of interface units so that the interface unit on the protection side is allocated to the lowest priority. With this method, the same switchover operation can be performed in the same way as shown in  FIG. 9 . 
     Furthermore, in the BLSR configuration, the same switchover control as the aforementioned 1:1 redundant configuration is carried out except for protection by either signal bridging control or signal loop-back control. 
     As can be understood from the above description of the embodiment according to the accompanied drawings, according to the present invention, it becomes unnecessary to provide a concentrated switchover controller, which brings about guaranteeing switchover and performance without occupying too much common space. 
     The foregoing description of the embodiments is not intended to limit the invention to the particular details of the examples illustrated. Any suitable modification and equivalents may be resorted to the scope of the invention. All features and advantages of the invention which fall within the scope of the invention are covered by the appended claims.