Fault recovery system of a ring network

Details Fault recovery system of a ring network Fault recovery system of a ring network

1996-04-25

2001-10-02

Le, Dieu-Minh T. (Department: 2785)

Error detection/correction and fault detection/recovery

Pulse or data error handling

Transmission facility testing

C714S716000, C714S004110

Reissue Patent

active

RE037401

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a fault recovery system of a ring network, and more particularly to a fault recovery system of a ring network based on a synchronous transport module (STM) transmission system called a new synchronization system.
Ring networks based on the synchronous transport module (STM) transmission system such as a synchronous digital hierarchy (SDH) or synchronous optical network (SONET) the standardization of which has been developed in the CCITT or United States T1 Committee, are expected to be applied to subscriber systems (Urban Networks) in the future. The STM transmission system is applied to a high speed and broad band system of more than 155.52 Mbps. When a ring network, based on such a STM transmission system which is a high speed and broad band optical transmission system, is constructed, the ability to survive a fault in the network is important and should be considered from the beginning of the construction of the system, since a network fault can have a great influence on the transfer of information in a modern information society.
2. Description of the Related Art
As a conventionally proposed network fault recovery system, there are recovery systems employing a loopback used in a local area network (LAN) and so forth. These conventional recovery systems, however, are networks based on packet communication through predetermined protocols, and therefore, there are problems in that it takes a long processing time of several seconds to recover from a fault because the fault must be recovered by the use of the above-mentioned predetermined protocols. Since the recovery time in a new synchronization system should be shorter than, for example, 50 msec, a recovery method which uses these protocols cannot be employed in a new synchronization system.
On the other hand, for point to point communication, the standard usage of automatic protection scheme (APS) bytes (K
1
and K
2
bytes in an STM frame) for a switching control between a working line and a protection line has been recommended by the CCITT or the United States T1 Committee. For application to a ring network, however, standard usage has not been proposed.
A fault recovery system applied to a ring network is disclosed in Japanese Patent Publication 1-45782, published on Oct. 4, 1989. This fault recovery system, however, is not applied to the STM transmission system. Further, in this document, if multiple faults occur in the working line and the protection line, the positions of the faults cannot be determined.
SUMMARY OF THE INVENTION
Accordingly, the present invention has an object to provide, based on the synchronous transport module (STM) transmission system, a system for rapidly and efficiently recovering a ring network even when multiple faults occurs.
There is provided, according to the present invention, a centralized control type ring network based on a synchronous transport module transmission system, with a fault recovery system for recovering a fault in the ring network. The ring network provides 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,

to
each other through the optical fiber transmission lines and a supervision node, connected through the optical fiber transmission lines to the drop/insert nodes.
Each of the drop/insert nodes
has:

has
an input fault detecting unit for detecting an input fault on the working line or the protection line. A fault data writing unit is also provided within each drop/insert node for writing, when the input fault is detected by the input fault detecting unit, fault data into a predetermined user byte within an overhead of a frame flowing through both the working line and the protection line. A user byte passing unit is also provided with each drop/insert node for passing the user byte as is, when an input fault is not detected by the input fault detecting unit, through the node.
The supervision node has a fault data detecting unit for detecting the fault data in the user byte transmitted from the node which has detected the input fault through the downstream sides of the working line and the protection line of the node which has detected the input fault. A fault position determining unit is also provided within the supervision node for determining, based on the fault data detected by the fault data detecting unit, a node which has detected the input fault. A writing unit is also provided within the supervision node for writing, into the user bytes, loopback requests for requesting nodes located immediately downstream and upstream of the fault position and closest to the supervision node, to execute loopback operations. Finally, a sending unit for sending the loopback requests through the working line and the protection line to the nodes located immediately downstream and upstream of the fault position and closest to the supervision node. Based on this construction, the nodes located immediately downstream and upstream of the fault position and closest to the supervision node execute loopback operations to recover from the fault.
According to another aspect of the present invention, there is provided a distributed control type ring network based on a synchronous transport module transmission system, with a fault recovery system for recovering a fault in the ring network. The distributed control type ring network provides 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 is also provided connected to each other through the optical fiber transmission lines.
Each of the drop/insert nodes has an input fault detecting unit for detecting an input fault on the working line or the protection line. Each drop/insert node also has fault data and loopback request writing unit for writing, when the input fault is detected by the input fault detecting unit, fault data and a loopback request into a predetermined user byte within an overhead of a frame flowing through both the working line and the protection line. A loopback executing unit is also provided within each drop/insert node for executing, based on the fault data detected by the fault data detecting unit, a loopback when the node is located immediately upstream of the input fault and adjacent to a node which has not detected an input fault. The node executing the loopback returns, in response to the loopback request, a loopback response by the use of the predetermined user byte to the node which has detected the input fault.
Based on this construction, as in the construction described in the previous aspect of the invention, the nodes located immediately upstream of the fault position and adjacent to a node which has not detected an input fault execute loopback operations to recover from the fault.
Although the invention described herein can be provided in many different forms of varying detail, without departing from the basic concept and spirit of the invention, preferred details of the above aspects of the prevent invention are described below.
It is preferable that the synchronous transport module transmission system is a system according to the recommendation of CCITT G.707, 708, and 709.
It is preferable that the fault data includes a node identification number for identifying the node which has detected the input fault.
It is preferable that the fault data includes fault line information indicating whether the input fault has occurred on the working line or on the protection line.
It is preferable that the fault data includes fault reporting information.
It is preferable that the loopback requests are formed by rewriting the fault data to include a node identification number of a node at which the loopback should be executed, and to include loopback request information.
It is preferable that the loopback requests are formed by using another byte within the overhead of the frame, other than the predetermin

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