Patent Publication Number: US-2003223380-A1

Title: Ring network system

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Field of the Invention  
       [0002] The present invention relates to a ring network system, and more specifically, to a network system comprising a plurality of nodes each having a line protection function and connected together via a transmission path such as optical fibers.  
       [0003] 2. Description of the Related Art  
       [0004] A BLSR (Bidirectional Line Switched Ring) network system of the SONET (Synchronous Optical NETwork) commonly comprises a plurality of nodes connected together in ring form using optical fibers. Each node has a current interface (active interface) and a standby interface. The two adjacent nodes are connected together by connecting the current interface of one of the nodes and the current interface of the other node together by an optical fiber and connecting the standby interface of one of the nodes and the standby interface of the other node together by an optical fiber. Data transfer is normally carried out using the current interfaces and the optical fiber. However, if any fault occurs in the current transmission path, the path is automatically switched inside the corresponding node. The current transmission path is interrupted in the corresponding section and automatically switched to the standby transmission path. In this manner, this fault is avoided.  
       [0005] The details of the BLSR system is described in the document “SONET Bidirectional Line-Switched Ring Equipment Generic Criteria”, Bellcore, Generic Requirements GR-1230-CORE Issue, December, 1998).  
       [0006] In the BLSR network system, in general, the current interfaces of the adjacent nodes are connected together by the optical fiber, while the standby interfaces of the adjacent nodes are connected together by the optical fiber. This connecting operation is performed without considering whether or not signals can be communicated to the current interface of each node. Thus, disadvantageously, those sections of the current optical fiber in which signals are not communicated do not contribute to any signal transmitting operations but this optical fiber still requires laying work and maintenance operations.  
       SUMMARY OF THE INVENTION  
       [0007] It is thus an object of the present invention to provide a ring network system that enables the number of optical fibers used to be reduced without impairing a self-recovery function of the ring network system.  
       [0008] It is another object of the present invention to provide a ring network system that enables the number of optical fibers used to be minimized without impairing the self-recovery function of the ring network system.  
       [0009] Other objections of the present invention which are not specified herein will be apparent from the description below and the accompanying drawings.  
       [0010] According to the present invention, a ring network system comprising a plurality of nodes each having a current interface and a standby interface and connected together via an optical transmission path, the system comprising an automatic recovery function,  
       [0011] wherein some of the current interfaces of the plurality of nodes are not involved in signal communication, and an optical waveguide is connected to an input end and an output end of each of the current interfaces that are not involved in signal communication.  
       [0012] In the ring network system of the present invention, some of the current interfaces of the nodes are not involved in signal communication, and the optical waveguide (optical fiber) is connected to the input end and output end of each of the current interfaces that are not involved in signal communication, in such a manner that the optical fiber loops from the input end to the output end. Thus, these current interfaces do not require any fiber laying or maintenance operations. This serves to reduce the number of optical fibers used in the network system. Therefore, the number of optical fibers used can be minimized by connecting the optical fiber to each of the current interfaces that are not involved in signal communication.  
       [0013] Further, the current interfaces to each of which the optical fiber is connected in a loop-back manner are not involved in signal communication in the system. This avoids impairing the self-recovery function of the ring network system.  
       [0014] Furthermore, the optical fiber is connected to the input end and output end of each of the current interfaces that are not involved in signal communication, in such a manner that the optical fiber loops from the input end to the output end. This prevents the issuance of an unwanted warning resulting from the determination that optical signals are interrupted.  
       [0015] In a preferred example of ring network system of the present invention, the plurality of nodes are linearly connected together at least via the standby interfaces of the nodes to form a node row, and the standby interfaces of the nodes located at opposite ends of the node row are connected together by an optical waveguide.  
       [0016] In another preferred example of ring network system of the present invention, the plurality of nodes are linearly connected together via the current and standby interfaces of the nodes to form a node row, and the standby interfaces of the nodes located at opposite ends of the node row are connected together by an optical waveguide. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0017]FIG. 1 is a diagram schematically showing a configuration of a ring network system according to a first embodiment of the present invention;  
     [0018]FIG. 2 is a diagram illustrating operations of the ring network system according to the first embodiment of the present invention;  
     [0019]FIG. 3 is a diagram illustrating operations of the ring network system according to the first embodiment of the present invention;  
     [0020]FIG. 4 is a diagram illustrating how a bypass is generated when a fault occurs in both current and standby transmission lines in the ring network system according to the first embodiment of the present embodiment; and  
     [0021]FIG. 5 is a diagram schematically showing a configuration of a ring network system according to a second embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     [0022] Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings.  
     [0023]FIG. 1 is a diagram showing a ring network system according to a first embodiment of the present invention. This system comprises an automatic recovery function.  
     [0024] In FIG. 1, a ring network system  1  according to the first embodiment has three nodes  10 ,  20 , and  30  each having a line protection function.  
     [0025] The node  10  has current interfaces  11  and  12  and standby interfaces  13  and  14 . Each of the interfaces  11 ,  12 ,  13 , and  14  has an input and output ends to each of which an end of an optical fiber is connected.  
     [0026] The node  20  has current interfaces  21  and  22  and standby interfaces  23  and  24 . Each of the interfaces  21 ,  22 ,  23 , and  24  has an input and output ends to each of which an end of an optical fiber is connected.  
     [0027] The node  30  has current interfaces  31  and  32  and standby interfaces  33  and  34 . Each of the interfaces  31 ,  32 ,  33 , and  34  has an input and output ends to each of which an end of an optical fiber is connected.  
     [0028] The current interface  11  of the node  10  is not connected to any other nodes. In other words, the interface  11  is not involved in the generation of a signal path P 1  or P 2  and is unused. Thus, the opposite ends of a single optical fiber  76  are connected to the input and output ends, respectively, of the interface  11 . That is, as shown in FIG. 1, the single optical fiber  76  is connected to the input and output ends so as to loop between these ends.  
     [0029] The current interface  12  of the node  10  is connected to the current interface  21  of the adjacent node  20  by two optical fibers  71 .  
     [0030] The standby interface  13  of the node  10  is connected to the standby interface  34  of the node  30  by two optical fibers  75 . The standby interface  14  of the node  10  is connected to the standby interface  23  of the adjacent node  20  by two optical fibers  73 .  
     [0031] The current interface  22  of the node  20  is connected to the current interface  31  of the adjacent node  30  by two optical fibers  72 . The standby interface  24  of the node  20  is connected to the standby interface  33  of the node  30  by two optical fibers  74 .  
     [0032] The current interface  32  of the node  30  is not connected to any other nodes as in the case with the current interface  11  of the node  10 . In other words, the interface  32  is not involved in the generation of a signal path P 1  or P 2  and is unused. Thus, the opposite ends of a single optical fiber  77  are connected to the input and output ends, respectively, of the interface  32 . That is, as shown in FIG. 1, the single optical fiber  77  is connected to the input and output ends so as to loop between these ends.  
     [0033] Each of the nodes  10 ,  20 , and  30  has a function (line protection function) of internally switching the path to switch a signal path from current side to standby side when a fault is detected.  
     [0034] Now, with reference to FIGS.  2  to  4 , description will be given to operations of the ring network system  1  of the first embodiment configured as described above.  
     [0035] The network system in FIG. 2 is composed of the three nodes  10 ,  20 , and  30 , extracted from the system  1  in FIG. 1. In this system, it is assumed that the signal paths P 1  and P 2  are generated via the current transmission path, i.e. the current interfaces  12 ,  21 ,  22 , and  31  of the nodes  10 ,  20 , and  30  and the optical fibers  71  and  72  as shown in FIG. 2. In this condition, the standby transmission path is unused.  
     [0036] Then, it is assumed that any fault occurs in the current optical fiber  72  (or the interface  22  or  31  of the node  20  or  30 , respectively) in the section between the nodes  20  and  30  as shown in FIG. 3. Then, the nodes  20  and  30  immediately detect a fault to internally switch the path to disable the current interfaces  22  and  31 , while enabling the standby interfaces  24  and  33 . Thus, if any fault occurs, signal paths P 1 ′ and P 2 ′ are newly generated using the current interface  21  and standby interface  24  of the node  20  and the standby interface  33  of the node  30  as shown in FIG. 3. This helps protect data or packets that have been flowing through the signal paths P 1  and P 2 .  
     [0037] However, if any fault occurs in both current optical fiber  72  and standby optical fiber  74  (or the interfaces  22 ,  31 ,  24 , and  33  of the nodes  20  and  30 ) in the section between the nodes  20  and  30 , then the configuration in FIG. 3 cannot protect the data or packets that have been flowing through the signal paths P 1  and P 2 . This is because the transmission path cannot be switched, in other words, there are no paths to which the defective path is switched. However, even in this case, the system  1 , shown in FIG. 1, protects the data or packets that have been flowing through the signal paths P 1  and P 2 , in the following manner.  
     [0038] That is, if any fault occurs in both current and standby lines in the section between the nodes  20  and  30 , the nodes  20  and  30  immediately detect this fault. Then, as shown in FIG. 4, the node  20  internally connects the current interface  21  and the standby interface  23  together. Accordingly, signal paths P 1 ″ and P 2 ″ are newly generated via the current interface  12  of the node  10 , the optical fibers  73 , the standby interfaces  14  and  13  of the node  10 , the optical fibers  75 , and the standby interface  34  of the node  30 . That is, the signal paths P 1 ″ and P 2 ″ are generated as a bypass. This helps protect the data or packets that have been flowing through the signal paths P 1  and P 2 . This is the original operation of the BLSR network system.  
     [0039] In this case, clearly, the current interface  11  of the node  10  and the current interface  32  of the node  30  are not involved in the operation of the system  1 . Thus, the operation of the system  1  is not affected even if the optical fiber  76  is connected to the current interface  11  so as to loop from the interface  11  back to the interface  11 .  
     [0040] Likewise, the operation of the system  1  is not affected even if the optical fiber  77  is connected to the current interface  32  so as to loop from the interface  32  back to the interface  32 .  
     [0041] Accordingly, the number of optical fibers used can be reduced without impairing the self-recovery function of the ring network system  1 . This means that the number of optical fibers used can be minimized without impairing the self-recovery function.  
     [0042] The optical fibers  76  and  77  are connected to the current interfaces  11  and  32 , respectively, in a loop-back manner because if the optical fibers are not connected, the current interfaces  11  and  32  determine that optical signals are interrupted to issue an unwanted warning.  
     [0043] The optical fibers  76  and  77  connected to the current interfaces  11  and  32 , respectively, in a loop-back manner have arbitrary lengths. It is sufficient to connect the optical fibers in a loop-back manner.  
     [0044]FIG. 5 is a diagram showing a ring network system  1 A according to a second embodiment of the present invention. The configuration of the system  1 A according to the second embodiment is substantially the same as that of the system  1  according to the first embodiment, shown in FIG. 1, except that the number of nodes is increased to six.  
     [0045] That is, the configuration of the nodes  10 ,  20 , and  30  is the same as that in the first embodiment. Accordingly, they are denoted by the same reference numerals as those in the first embodiment. Their description is thus omitted.  
     [0046] A node  10 A has current interfaces  11 A and  12 A and standby interfaces  13 A and  14 A. Each of the interfaces  11 A,  12 A,  13 A, and  14 A has an input end and an output end to which an end of an optical fiber is connected.  
     [0047] A node  20 A has current interfaces  21 A and  22 A and standby interfaces  23 A and  24 A. Each of the interfaces  21 A,  22 A,  23 A, and  24 A has an input end and an output end to which an end of an optical fiber is connected.  
     [0048] A node  30 A has current interfaces  31 A and  32 A and standby interfaces  33 A and  34 A. Each of the interfaces  31 A,  32 A,  33 A, and  34 A has an input end and an output end to which an end of an optical fiber is connected.  
     [0049] The current interfaces  11 A and  12 A of the node  10 A are not connected to any other nodes. That is, the interfaces  11 A and  12 A are unused. No optical fibers are connected to the interface  11 A or  12 A.  
     [0050] The standby interface  13 A of the node  10 A is connected to the standby interface  34  of the node  30  by two optical fibers  78 . The standby interface  14 A of the node  10 A is connected to the standby interface  23 A of the adjacent node  20 A by two optical fibers  73 A.  
     [0051] The current interface  21 A of the node  20 A is not connected to any other nodes, as in the case with the current interface  11  of the node  10 . In other words, the interface  21 A is not involved in the generation of the signal path P 1  or P 2  and is unused. Thus, a single optical fiber  71 A is connected to the interface  21 A so as to loop from the interface  21 A back to the interface  21 A.  
     [0052] The current interface  22 A of the node  20 A is connected to the current interface  31 A of the adjacent node  30 A by two optical fibers  72 A. The standby interface  24 A of the node  20 A is connected to the standby interface  33 A of the node  30 A by two optical fibers  74 A.  
     [0053] The current interface  32 A of the node  30 A is not connected to any other nodes as in the case with the current interface  11  of the node  10  and is thus unused. A single optical fiber  77 A is connected to the interface  32 A so as to loop from the interface  32 A back to the interface  32 A.  
     [0054] The standby interface  34 A of the node  30 A is connected to the standby interface  13  of the node  10  by two optical fibers  75 .  
     [0055] In addition to the nodes  10 ,  20 , and  30 , each of the nodes  10 A,  20 A, and  30 A has the line protection function.  
     [0056] Next, the operation of ring network system  1 A of the second embodiment configured as described above is substantially the same as that of ring network system  1  of the first embodiment. The system  1 A can avoid both a possible fault between the nodes  10  and  30  and a possible fault between the nodes  20 A and  30 A.  
     [0057] In the above described first and second embodiments, three or seven nodes are connected together. However, in the present invention, the number of nodes connected together is arbitrary as long as it is two or more. Further, the connection between the nodes is not limited to the optical fibers. Other arbitrary optical waveguides may be used as long as they enable optical signals to be transmitted through themselves.  
     [0058] The present invention is preferably applied to the above described BLSR network system but is not limited to this aspect. The present invention is applicable to other similar systems with a plurality of nodes connected together in ring form.  
     [0059] As described above, according to the ring network system of the present invention, the number of optical fibers used can be reduced without impairing the self-recovery function of the ring network system. Further, the number of optical fibers used can be minimized by connecting the optical fiber to each of the current interfaces that are not involved in signal communication, in such a manner that the optical fiber loops from the current interface back to the same interface.