Ring network for sharing protection resource by working communication paths

A communications network comprising:

• a plurality of transmission links;
• and
• a plurality of nodes for interconnecting said transmission links to form first and second working rings and first and second protection rings in a ring topology, and establishing a plurality of working paths on each of said working rings and a plurality of protection paths on each of said protection rings corresponding to said plurality of working paths,
• a first one of said working paths of said first working ring spanning across first and second nodes of said plurality of nodes for transmission of a signal in a first direction of said ring topology,
• a second one of said working paths of said second working ring spanning across the first and second nodes for transmission of a signal in a second direction of the ring topology opposite to the first direction,
• a first one of said protection paths on said first protection ring spanning across the first and second nodes for transmission of a signal in said second direction of said ring topology,
• a second one of said protection paths of said second protection ring spanning across the first and second nodes for transmission of a signal in said first direction of said ring topology,
• said first and second nodes normally using said first and second working paths, respectively, and being responsive to a failure of one of said first and second working paths for using a corresponding one of the first and second protection paths instead of the failed working path.

A communications network comprising:

• a plurality of transmission links;
• and
• a plurality of nodes for interconnecting said links to form a working ring and a protection ring in a ring topology, and establishing a plurality of working paths on said working ring and a plurality of extra traffic paths on said protection ring,
• one of said working paths spanning across first and second nodes of said plurality of nodes for transmission of a signal in a first direction of said ring topology,
• one of said extra traffic paths spanning across said first and second nodes for transmission of a low-priority signal in a second direction of said ring topology opposite to said first direction,
• said first and second nodes normally using said one working path and being responsive to a failure of said one working path for clearing said one extra traffic path to establish a first protection path and using the first protection path, clearing other extra traffic paths to establish a second protection path if said first protection path is not successfully established and using said second protection path instead of the failed working path, said first protection path having a shorter length than said second protection path.

A network node for a ring topology network, the network having first and second working rings and first and second optical protection rings in a ring topology, and a plurality of working paths on each of said working rings and a plurality of protection paths on each of said protection rings corresponding to said plurality of working paths, the network node comprising:

• a first demultiplexer for receiving a multiplex signal from one of the working paths for producing drop-off signals;
• a first multiplexer for multiplexing add-up signals onto said one working path;
• a first path switch connected between said first demultiplexer and said first multiplexer;
• a second demultiplexer for receiving a multiplex signal from one of said protection paths for producing drop-off signals;
• a second multiplexer for multiplexing add-up signals onto said one protection path;
• a second path switch connected between said second demultiplexer and said second multiplexer;
• a transmit protection switch;
• a receive protection switch;
• and
• control circuitry for monitoring said one working path and controlling said transmit protection switch so that one of said add-up signals is coupled to said first multiplexer when no failure is detected in said one working path and coupled to said second multiplexer when a failure is detected in said one working path, and controlling said receive protection switch so that one of said drop-off signals of said first multiplexer is received when no failure is detected in said one working path and one of said drop-off signals of said second multiplexer is received when said failure is detected.

A fault recovery method for a communications network, wherein the network comprises a plurality of transmission links, and a plurality of nodes for interconnecting said links to form a working ring and a protection ring in a ring topology, and establishing a plurality of working paths on said working ring and a plurality of protection paths on said protection ring corresponding to said plurality of working paths, the method comprising the steps of:

• a) establishing one of said working paths between source and destination nodes of said plurality of nodes for transmission of a signal in a first direction of said ring topology and establishing one of said protection paths between said source and destination nodes for transmission of a signal in a second direction of said ring topology opposite to said first direction;
• b) using said one working path for communication between said source and destination nodes;
• c) monitoring said working path at said destination node;
• d) transmitting a switching command message from said destination node to said source node if a failure is detected in said working path;
• and
• e) using said one protection path for communication between said source and destination nodes, instead of the failed working path, in response to said switching command message.

A fault recovery method for a communications network, wherein the network comprises a plurality of transmission links, and a plurality of nodes for interconnecting said links to form a working ring and a protection ring in a ring topology, and establishing a plurality of working paths on said working ring and a plurality of extra traffic paths on said protection ring, the method comprising the steps of:

• a) establishing one of said working paths between source and destination nodes of said plurality of nodes for transmission of a signal in a first direction of said ring topology and establishing one of said extra traffic paths between said source and destination nodes for transmission of a low-priority signal in a second direction of said ring topology opposite to said first direction,
• b) normally using said one working path between said source and destination nodes;
• c) monitoring said one working path at said destination node;
• d) clearing said one extra traffic path to establish a short-haul protection path between said source and destination nodes when a failure is detected in said one working path and using the short-haul protection path, instead of the failed working path, between said source and destination nodes;
• and
• e) clearing other extra traffic paths to establish a long-haul protection path if said short-haul protection path is not successfully established and using said long-haul protection path, instead of the failed working path, between said source and destination nodes.