The present invention relates to a ring network system and a protection method therefor. More particularly, the invention relates to a ring network system which performs a path connection by a transoceanic function and a protection method therefor.
Generally, a ring network system is constructed by connecting a plurality of node elements (hereinafter referred to as NEs) by work lines and standby lines for protecting the work lines. And, a logical path is achieved by those physical work lines and standby lines.
Now, reference is made to a ring network system having eight NEs N1-N8, as shown in FIG. 8. In this ring network system, to send frame data from NE N1 to NE N3, the frame data is sent sequentially through NE N8, NE N7, NE N6, NE N5, NE N4, and NE N3. In FIG. 8, a thick solid line shows a route R8 used in this case.
Further, in FIG. 8, to NE N1, input work lines W1 and W4, output work lines W2 and W3, input standby lines S1 and S4, output standby lines S2 and S3, and tributary lines T1 and T2 are connected, respectively. And, in the shown construction, a frame is sent from NE N1 to NE N3. In addition, NE N3 has tributary lines T3 and T4.
In brief, in the route R8 in FIG. 8, the tributary line T1 of NE N1 is an ADD line, while the tributary line T4 of NE N3 is a DROP Line.
Each NE has functions such as shown in FIG. 9. Referring to FIG. 9, each NE comprises a terminating circuit 4i for terminating control signals called overhead (OH) or section overhead (SOH), an OH adding circuit 7i for adding new OH to a multiplexed signal, a line fault detecting circuit 80 for detecting a line fault, a cross-connect unit 3, a CPU 10 for controlling them, and a memory unit 200. On the other hand, the line fault detecting circuit 80 is provided in a photoreceiver circuit, not shown.
The CPU 10 performs the switching control of the cross-connect unit 3 by referencing a table stored in the memory unit 200. Namely, if no fault occurs, it carries out the switching control of cross-connect unit 3 according to the normal path information 200a stored in the memory unit 200. This allows the switching control of the cross-connect unit 3 to realize all routes between the NE per se and the other NEs in addition to the above described route R8.
On the other hand, if a fault occurs at any position in a ring network, a protection process is performed by referencing path information 200b for West Span, path information 200c for East Span, path information 200d for West Ring, path information 200e for East Ring, and path information 200f for through. For instance, if a fault A7 occurs between NE N6 and NE N7, as shown in FIG. 10, the above described route R8 cannot be realized, because the frame cannot pass through that portion. Thus, a route R10, shown by a solid line in FIG. 10, is achieved instead of the route R8.
To realize this route R10, the switching control of the cross-connect unit is performed as follows. First, when a frame is added from NE N1, NE N8 becomes through. Then, at NE N7, the East Ring for connecting the working line to the standby line is performed. This makes the route R10 to turn back at NE N7. After the turning back, NE N8, NE N1, NE N2, NE N3, NE N4, and NE N5 become through.
And, at NE N6, the West Ring for returning from the standby line to the original working line is performed. This allows the route R10 to turn back at NE N6. After the turning back, NE N5 and NE N4 again become through. Finally, the frame is dropped from NE N3. The above protection process allows each NE to continue the sending and receiving of frame data even if a fault occurs in part of the ring network.
The above described protection process ensues that each NE can continue the sending and receiving of frame data. However, there is a disadvantage that the route R10 shown by a solid line in FIG. 10 forms a long bypass.
As a function for solving this disadvantage, there is a transoceanic function. This function is to achieve the shortest path without going toward the position of the fault A7, as shown in FIG. 11. Namely, it is to realize a route R11 from NE N1 to NE N3, passing only NE N2, without passing through a long path like the route R10 shown in FIG. 10.
That is, when NE N1 to NE N8, which are a plurality of (16 at maximum) of multiplexers, form a ring network in FIG. 10, the signals of work lines W1 to W4 are remedied by turning back them using the standby lines S1 to S4 at NE N6 and NE N7 on both sides of the fault A7 in the conventional ring protection , as shown in FIG. 10. On the other hand, for the transoceanic function, the signals are salvaged by making a direct connection from NE N1, the signal input point, to NE N3, the output point, with the shortest distance, without making a bypass, as shown in FIG. 11.
As a specific switching process, in the conventional ring protection, through-switch is uniquely performed in which only the NE at the fault end performs a ring switch to turn back the work lines to the standby lines, with the other NEs releasing the standby lines for remedying the work lines and connecting the stand by lines on both sides. Namely, S1 is connected to S3, and S2 is connected to S4.
On the other hand, the transoceanic function requires a process in which, also at the NEs other than the NE at the faulty end, it is determined whether the fault has an effect on the ADD/DROP path of the local NE, and switching is performed if there is a path requiring a remedy. For this, an unconventional process is needed to always check the fault position, and apply a remedy according to the correlation between the fault position and the path. As a result, there is a disadvantage that the process becomes complex and the path switching time becomes longer.
The present invention was made to solve the above described disadvantages of the background art, and its object is to provide a ring network system in which the protection process has a shorter path switching time, a protection method therefor.
The ring network system according to the present invention is a ring network system in which, when a fault occurs, a path connection is performed by the transoceanic function for realizing the shortest path that does not go toward the fault position,
wherein each node comprises a cross-connect portion for switching the connections between paths to realize a ring network;
a table having previously stored therein the correspondences between the fault occurring positions and the path switching information for connecting the local node and all the other nodes by the path connection by the transoceanic function, if a fault occurs at the positions; and
a referencing portion for referencing said table in response to the occurrence of a fault to extract the path switching information corresponding to the fault occurring position,
whereby the switching control of the cross-connect portion is performed according to the path switching information extracted as a result of the referencing by the referencing portion.
The protection method for a ring network system according to the present invention is a protection method in which, when a fault occurs in a ring network, a protection process by the transoceanic function is performed for realizing the shortest path that does not go toward the fault position, the method comprising:
a referencing step for referencing a table having previously stored therein the correspondences between the fault occurring positions in the ring network and the path switching information for connecting the local node and all the other nodes by the path connection by the transoceanic function if a fault occurs at the positions, thereby to extract the path switching information corresponding to the fault occurring position; and
a step for performing the switching control of the cross-connect portion according to the path switching information extracted as a result of the referencing by the referencing step.
The recording medium having recorded thereon a program for executing a protection process according to the present invention is a recording medium having recorded thereon a program for causing a computer to execute the protection process in a ring network, the program comprising:
a referencing step for referencing a table having previously stored therein the correspondences between the fault occurring positions in the ring network and a path switching information for connecting the local node and all the other nodes by the path connection by the transoceanic function if a fault occurs at the positions, in response to the occurrence of a fault, thereby to extract the path switching information corresponding to the fault occurring position; and
a step for performing the switching control of the cross-connect portion according to the path switching information extracted as a result of the referencing by the referencing step.
To summarize, the present invention can freely perform the cross-connect connection and multiplexing of a low-speed signal called pass, and it is applied in a system in which ADD/DROP multiplexers for inputting/outputting signals on a high-speed transmission path, called a line, are making up a ring network. And, to realize the transoceanic function, the path information corresponding to fault positions are previously increased. The path information is generated at the system start-up time or when the pass setting information is updated. When a fault occurs, the path information is referenced to select appropriate path information corresponding to the position at which the fault has occurred.