Fault recovery system of a ring network

Abstract

A fault recovery system of a ring network based on a synchronous transport module transmission system, having a fault data writing unit for writing, when an input fault is detected by a node, fault data in a predetermined user byte in an overhead of a frame flowing through both a working line and a protection line running in opposite directions to each other. By detecting the fault data in a supervision node or a node just before the fault position, the supervision node or the node just before the fault position executes a loopback operation.

We claim:  
     
       1. A centralized control type ring network based on a synchronous transport module transmission system, having a fault recovery system for recovering a fault in said centralized control type ring network, said centralized control type ring network comprising: 
       optical fiber transmission lines including a working line and a protection line running in opposite directions to each other;  
       a plurality of drop/insert nodes connected to each other through said optical fiber transmission lines;  
       a supervision node, connected through said optical fiber transmission lines to said drop/insert nodes;  
       each of said drop/insert nodes having  
       input fault detecting means for detecting an input fault on the working line or the protection line,  
       fault data writing means for writing, when said input fault is detected by said input fault detecting means, fault data in a predetermined user byte in an overhead of a frame flowing through both of the working line and the protection line, and  
       user byte passing means for passing said user byte as is through said node, when an input fault is not detected by said input fault detecting means;  
       said supervision node having  
       fault data detecting means for detecting the fault data in said user byte transmitted from the node which has detected said input fault through the downstream sides of the working line and the protection line of said node which has detected said input fault;  
       fault position determining means for determining, based on said fault data detected by said fault data detecting means, a node which has detected said input fault;  
       writing means for writing, into said user bytes, loopback requests for requesting nodes located immediately downstream and upstream of the fault position and closest to said supervision node, to execute loopback operations; and  
       sending means for sending said loopback requests through said working line and said protection line to said nodes located downstream and upstream of the fault position, whereby said nodes located immediately downstream and upstream of the fault position and closest to said supervision node execute loopback operations to recover the fault.  
     
     
       2. A ring network as claimed in claim  1 , wherein said synchronous transport module transmission system is a system according to a recommendation of CCITT G.707, 708, and 709. 
     
     
       3. A ring network as claimed in claim  1 , wherein said fault data includes a node identification number for identifying the node which has detected the input fault. 
     
     
       4. A ring network as claimed in claim  1 , wherein said fault data includes fault line information indicating whether said input fault has occurred on said working line or on said protection line. 
     
     
       5. A ring network as claimed in claim  4 , wherein said fault data includes fault reporting information. 
     
     
       6. A ring network as claimed in claim  4 , wherein said loopback requests are formed by rewriting said fault data to include a node identification number of a node at which the loopback should be executed, and loopback request information. 
     
     
       7. A ring network as claimed in claim  1 , wherein said loopback requests are formed by using another byte other than said predetermined user byte in said overhead of said frame. 
     
     
       8. A ring network as claimed in claim  7 , wherein said other type in said overhead of said frame is the K 1  byte or the K 2  byte according to a recommendation of CCITT G.707, 708, and 709. 
     
     
       9. A ring network as claimed in claim  1 , wherein said writing means includes rewriting means for rewriting said fault data transmitted through said working line into a first loopback request and for rewriting said fault data transmitted through said protection line into a second loopback request, and said sending means through said protection line and for sending said second loopback request to said working line. 
     
     
       10. A ring network as claimed in claim  1 , wherein said ring network is a bidirectional ring network comprising a pair of clockwise and counterclockwise working lines and a pair of counterclockwise and clockwise protection lines. 
     
     
       11. A ring network as claimed in claim  10 , comprising a plurality of pairs of said working lines and a single pair of said protection lines. 
     
     
       12. A distributed control type ring network based on a synchronous transport module transmission system, having a fault recovery system, said distributed control type ring network comprising: 
       optical fiber transmission lines including a working line and a protection line running in opposite directions to each other;  
       a plurality of drop/insert nodes connected to each other through said optical fiber transmission lines,  
       each of said drop/insert nodes having  
       input fault detecting means for detecting an input fault on the working line or the protection line,  
       fault data and loopback request writing means for writing, when said input fault is detected by said input fault detecting means, fault data and a loopback request in a predetermined user byte in an overhead of a frame flowing through both the working line and the protection line, 
       loopback executing means for executing, based on said fault data detected by said fault data detecting means, a loopback when said node is located immediately upstream of said input fault and adjacent to a node which has not detected an input fault; and  
       said node executing said loopback returning, in response to said loopback request, a loopback response by the use of said predetermined user byte to said node which has detected said input fault.  
     
     
       13. A ring network as claimed in claim  12 , characterized in that said synchronous transport module transmission system is the system according to a recommendation of CCITT G.707, 708, and 709. 
     
     
       14. A ring network as claimed in claim  12 , wherein said fault data includes a node identification number for identifying the node which has detected the input fault. 
     
     
       15. A ring network as claimed in claim  14 , wherein said fault data includes fault line information indicating whether said input fault has occurred on said working line or on said protection line. 
     
     
       16. A ring network as claimed in claim  15 , wherein said fault data includes fault reporting information. 
     
     
       17. A ring network as claimed in claim  16 , wherein said loopback request is formed by rewriting said fault reporting information in said fault data. 
     
     
       18. A ring network as claimed in claim  12 , wherein said loopback request is formed by using another byte other than said predetermined user byte in said overhead of said frame. 
     
     
       19. A ring network as claimed in claim  18 , wherein said other byte in said overhead of said frame is the K 1  byte or the K 2  byte according to a recommendation of CCITT G. 707, 708 and 709. 
     
     
       20. A ring network as claimed in claim  12 , wherein said ring network is a bidirectional ring network comprising a pair of clockwise and counterclockwise working lines and a pair of counterclockwise and clockwise protection lines. 
     
     
       21. A ring network as claimed in claim  20 , comprising a plurality of pairs of said working lines and a single pair of said protection lines. 
     
     
       22. A hybrid type ring network based on a synchronous transport module transmission system, having a fault recovery system, said hybrid type ring network comprising: 
       optical fiber transmission lines including a working line and a protection line running in opposite directions to each other; and  
       a plurality of drop/insert nodes connected to each other through said optical fiber transmission lines, each of said drop/insert nodes including  
       input fault detecting means for detecting an input fault on the working line or the protection line,  
       selecting means for dropping the input signal from said protection line when the input signal from said working line is faulty, for dropping the input signal from said working line when the input signal from said protection line is faulty, and for dropping the input signal from said working line when both are normal, and passing the signal as is when the signal is not to be dropped;  
       fault data writing means for writing, when said input fault is detected by said input fault detecting means, fault data in a predetermined user byte in an overhead of a frame flowing through both of the working line and the protection line; and  
       user type passing means for passing, when an input fault is not detected by said input fault detecting means, said user byte as is through said node.  
     
     
       23. A fault recovery system of a hybrid type ring network as claimed in claim  22 , characterized in that said synchronous transport module transmission system is a system according to the  a recommendation of CCITT G. 707, 708, and 709. 
     
     
       24. A fault recovery system of a hybrid ring network as claimed in claim  22 , wherein said fault data includes a node identification number for identifying the node which has detected the input fault. 
     
     
       25. A fault recovery system of a hybrid ring network as claimed in claim  22 , wherein said fault data includes fault line information indicating whether said input fault has occurred on said working line or on said protection line. 
     
     
       26. A node for communication through a ring network having a plurality of nodes interconnected by first and second transmission lines, the first transmission line transporting a transmission signal frame including an overhead byte around the ring network in a first direction and the second transmission line transporting a transmission signal frame including an overhead byte around the ring network in a second direction opposite to the first direction, the node comprising: 
       
         detecting means for detecting a fault on an upstream side of the first transmission line; and  
       
       
         transmitting means for transmitting to a downstream side of the first transmission line, in response to the fault detected by said detecting means, a request signal for directing a received transmission signal frame from the upstream side of the first transmission line to a downstream side of the second transmission line by inserting the request signal onto the overhead byte of the transmission signal frame. 
       
     
     
       27. The node according to claim  26 , wherein said transmitting means transmits the request signal to the downstream sides of both of the first and second transmission lines. 
     
     
       28. The node according to claim  26 , wherein the first transmission line is a working line for the transmission signal frame and the second transmission line is a protection line for the transmission signal frame. 
     
     
       29. The node according to claim  26 , wherein said transmitting means transmits, via the second transmission line, the request signal addressed to an adjacent node connected thereto on the upstream side of the first transmission line on which the fault is detected. 
     
     
       30. A node for communication through a ring network having a plurality of nodes interconnected by first and second transmission lines, the first transmission line transporting a transmission signal frame including an overhead byte around the ring network in a first direction and the second transmission line transporting a transmission signal frame including an overhead byte around the ring network in a second direction opposite to the first direction, said node comprising: 
       
         a fault detector, to detect a fault on an upstream side of the first transmission line; and  
       
       
         an overhead processor to insert, in response to the fault detected by said fault detector, a request signal for directing a received transmission signal frame from the upstream side of the first transmission line to a downstream side of the second transmission line onto the overhead byte of the transmission signal frame, and to transmit the transmission signal frame to a downstream side of the first transmission line. 
       
     
     
       31. The node according to claim  30 , wherein the overhead processor transmits the transmission signal frame to the downstream side of both the first transmission line and the second transmission line. 
     
     
       32. The node according to claim  30 , wherein the first transmission line is a working line for the transmission signal frame and the second transmission line is a protection line for the transmission signal frame. 
     
     
       33. The node according to claim  30 , wherein the overhead processor inserts, onto the overhead byte, the request signal addressed to an adjacent node connected thereto via the first transmission line on the upstream side of which the fault is detected, and the second transmission line. 
     
     
       34. A node for communication through a ring network having a plurality of nodes interconnected by first and second transmission lines, the first transmission line transporting a transmission signal frame including an overhead byte around the ring network in a first direction and the second transmission line transporting a transmission signal frame including an overhead byte around the ring network in a second direction opposite to the first direction, said node comprising: 
       
         receiving means for receiving the transmission signal frame from an upstream side of the first transmission line;  
       
       
         detecting means for detecting a request signal to direct a received transmission signal frame from the upstream side of the first transmission line to the downstream side of the second transmission line, the request signal inserted onto the overhead byte of the received transmission signal frame and originated at a different node detecting a fault on the first transmission line upstream of the different node; and  
       
       
         directing means for directing, in response to the request signal detected by said detecting means, a received transmission signal frame from the upstream side of the first transmission lines to the downstream side of the second transmission line. 
       
     
     
       35. The node according to claim  34 , wherein the first transmission line is a working line for the transmission signal frame and the second transmission line is a protection line for the transmission signal frame. 
     
     
       36. A node for communication through a ring network having a plurality of nodes interconnected by first and second transmission lines, the first transmission line transporting a transmission signal frame including an overhead byte around the ring network in a first direction and the second transmission line transporting a transmission signal frame including an overhead byte around the ring network in a second direction opposite to the first direction, said node comprising: 
       
         a signal receiver to receive a transmission signal frame from an upstream side of the first transmission line;  
       
       
         an overhead processor, operatively connected to the signal receiver, to detect a request signal for directing a received transmission signal frame from the upstream side of the first transmission line to a downstream side of the second transmission line, the request signal inserted onto the overhead byte of the received transmission signal frame and originated at a different node detecting a fault on the first transmission line upstream of the different node; and  
       
       
         a route selector to direct a received signal frame from the upstream side of the first transmission line to the downstream side of the second transmission line in response to the request signal detected by said overhead processor. 
       
     
     
       37. The node according to claim  36 , wherein the first transmission line is a working line for the transmission signal frame and the second transmission line is a protection line for the transmission signal frame. 
     
     
       38. A ring network, comprising: 
       
         a first transmission line for transporting a transmission signal frame including an overhead byte around said ring network in a first direction;  
       
       
         a second transmission line for transporting a transmission signal frame including an overhead byte around said ring network in a second direction opposite to the first direction; and  
       
       
         a plurality of nodes connected by said first and second transmission lines, each node including:  
       
       
         a fault detector to detect a fault on an upstream side of said first transmission line; and  
       
       
         an overhead processor to insert, in response to the fault detected by said fault detector, a request signal for directing a transmission signal frame received from the upstream side of said first transmission line to a downstream side of said second transmission line onto the overhead byte of the transmission signal frame, and to transmit the transmission signal frame to the downstream side of said first transmission line. 
       
     
     
       39. A ring network, comprising: 
       
         a first transmission line for transporting a transmission signal frame including an overhead byte around said ring network in a first direction;  
       
       
         a second transmission line for transporting a transmission signal frame including an overhead byte around said ring network in a second direction opposite to the first direction; and  
       
       
         a plurality of nodes connected by said first and second transmission lines, each node including:  
       
       
         a signal receiver to receive a transmission signal frame from an upstream side of said first transmission line;  
       
       
         an overhead processor, operatively connected to said signal receiver, to detect a request signal for directing a transmission signal frame from the upstream side of said first transmission line to a downstream side of said second transmission line, the request signal inserted onto the overhead byte of the transmission signal frame and originated at a different node detecting a fault on the first transmission line upstream of the different node; and  
       
       
         a route selector to direct another signal frame from the upstream side of said first transmission line to the downstream side of said second transmission line in response to the detected request signal. 
       
     
     
       40. A method of recovering from a fault in a ring network having a plurality of nodes interconnected by first and second transmission lines, the first transmission line transporting a first transmission signal frame including an overhead byte around the ring network in a first direction and the second transmission line transporting a second transmission signal frame including an overhead byte around the ring network in a second direction opposite to the first direction, comprising: 
       
         detecting a fault on an upstream side of the first transmission line;  
       
       
         inserting a request signal for directing a transmission signal frame received from the upstream side of the first transmission line to a downstream side of the second transmission line onto the overhead byte of the transmission signal frame in response to detection of the fault; and  
       
       
         transmitting the transmission signal frame to the downstream side of the first transmission line. 
       
     
     
       41. The method according to claim  40 , wherein said inserting includes the step of addressing the request signal to a node located immediately upstream along the first transmission line on which the fault is detected. 
     
     
       42. The method according to claim  40 , wherein said transmitting includes transmitting the transmission signal frame to the downstream sides of both the first and the second transmission lines. 
     
     
       43. A method of recovering from a fault in a ring network having a plurality of nodes interconnected by first and second transmission lines, the first transmission line transporting a first transmission signal frame including an overhead byte around the ring network in a first direction and the second transmission line transporting a second transmission signal frame including an overhead byte around the ring network in a second direction opposite to the first direction, comprising: 
       
         detecting a fault on an upstream side of the first transmission line;  
       
       
         inserting a request signal for directing a transmission signal frame received from the upstream side of the first transmission line to a downstream side of the second transmission line onto the overhead byte of the transmission signal frame in response to detection of the fault;  
       
       
         transmitting the transmission signal frame to a downstream side of the first transmission line;  
       
       
         receiving the transmission signal frame from the upstream side of the first transmission line;  
       
       
         detecting the request signal from the overhead byte of the transmission signal frame; and  
       
       
         directing the transmission signal frame from the upstream side of the first the transmission line to the downstream side of the second transmission line in response to detection of the request signal. 
       
     
     
       44. The method according to claim  43 , wherein said inserting includes addressing the request signal to a node located immediately upstream along the first transmission line on which the fault is detected. 
     
     
       45. The method according to claim  43 , wherein said transmitting includes transmitting the transmission signal frame to the downstream side of both the first and the second transmission lines. 
     
     
       46. A method of recovering from a fault in a ring network having a plurality of nodes interconnected by first and second transmission lines, the first transmission line transporting a first transmission signal frame including an overhead byte around the ring network in a first direction and the second transmission line transporting a second transmission signal frame including an overhead byte around the ring network in a second direction opposite to the first direction, comprising: 
       
         receiving the transmission signal frame from an upstream side of the first transmission line;  
       
       
         detecting a request signal to direct a received transmission signal frame from the upstream side of the first transmission line to a downstream side of the second transmission line, the request signal inserted onto the overhead byte of the received transmission signal frame and originated at a different node detecting a fault on the first transmission line upstream of the different node; and  
       
       
         directing, in response to the request signal, the received transmission signal frame from the upstream side of the first transmission line to the downstream side of the second transmission line.