Loop network and method for operating the same

• US 20020194371A1
• Filed: 06/05/2002
• Published: 12/19/2002
• Est. Priority Date: 06/05/2001
• Status: Abandoned Application

• Current Assignee: NEC Corporation
• Original Assignee: NEC Corporation
• Inventors: Kadoi, Tadashige
• Application Number:
  US10/161,685
• Publication Number:
  US 20020194371A1
• Time in Patent Office: Days
• US Class Current: 709/239
• CPC Class Codes: H04L 12/42 Loop networks

Abstract

A loop network without a standby loop is provided, wherein switch devices in plural stages are connected through multiple loops. The network has at least a pair of loops each of which transfers data in the opposite directions. Under normal conditions, the respective loops transfer data separately. On the other hand, when an error occurs in either loop in a switch device, a switch device located immediate upstream of the faulty section executes loop back operation to build one end of a C-loop. Moreover, the switch device in which the error occurs in the loop also executes loop back operation after outputting data in process to build the other end of the C-loop. By this way, the C-loop circumventing the faulty point can be established. Thereby, it becomes possible to transfer data through the C-loop with a guarantee of ordering and to repair, replace and/or maintain the faulty point without any influenced on the network.

Claims

1. A loop network wherein a plurality of switch devices are connected through multiple loops, a pair of loops are connected to each of the switch devices, and the respective loops in one pair transmit data in the opposite directions, wherein:

each node transmits data to another node through a predetermined loop using a predetermined switch device; and

each switch device buffers data until the data has been successfully transferred, and retransmits the buffered data when the transfer failed;

when an O-loop is used;

each switch device takes in data addressed to a node related to the switch device, and delivers the data to the node, and transfers other data through the same loop through which the data was inputted;

when a fault occurs in a loop between adjacent two switch devices;

a switch device located immediate upstream of the faulty section switches the O-loop to a C-loop by connecting an input port on the faulty loop to an output port on the other loop in one pair, and transfers buffered data from the output port; and

after the switch device located immediate upstream of the faulty section switched the loop to the C-loop, a switch device located immediate downstream of the faulty section switches the O-loop to the C-loop by connecting an output port on the faulty loop and an input port on the other loop in one pair, and transfer data through the C-loop circumventing the faulty section;

when the C-loop is used;

a switch device wherein an input port on a loop is not connected to an output port on the other loop in one pair takes in data addressed to a node related to the switch device and inputted through a predetermined loop of a node that transmitted the data, and transfers other data from an output port on the same loop through which the data was inputted; and

the switch device wherein the input port on a loop is connected to the output port on the other loop in one pair takes in all data addressed to a node related to the switch device, and transfers other data from the output port.

9. The loop network as claimed in claim 1 wherein, when the C-loop is switched to the O-loop;

one of the two switch devices in which the input port on a loop is connected to the output port on the other loop in one pair stops data transfer, buffers inputted data, and transmits a management packet through the C-loop, and when receiving the management packet again, transfers the buffered data through the C-loop, and switches the loop to the O-loop to start data transfer through the O-loop; and

the other switch device switches the loop to the O-loop when receiving the management packet, and transfers the management packet to the one of the switch devices.

11. The loop network as claimed in claim 1 wherein, when the C-loop is switched to the O-loop:

a switch device that is to participate in the network transmits a management packet to one of the switch devices adjacent to the participating switch device;

having received the management packet, the one of the switch devices stops data transfer, buffers inputted data, switches the C-loop to the O-loop, and transfers the management packet through the O-loop, and when receiving the management packet again, transfers the buffered data through the O-loop, and start data transfer through the O-loop; and

having received the management packet, the other switch device switches the C-loop to the O-loop, transfers the management packet through the O-loop, and transfers data inputted thereafter through the O-loop.

2. A loop network wherein a plurality of switch devices are connected through multiple loops, a pair of loops are connected to each of the switch devices, and the respective loops in one pair transmit data in the opposite directions, wherein:

each node transmits data to another node through a predetermined loop using a predetermined switch device; and

each switch device buffers data until the data has been successfully transferred, and retransmits the buffered data when the transfer failed;

when an O-loop is used;

each switch device takes in data addressed to a node related to the switch device, and delivers the data to the node, and transfers other data through the same loop through which the data was inputted;

when there is a direction to build a C-loop circumventing a section between arbitrary two switch devices adjacent to each other by a network maintainer;

one of the two switch devices switches the O-loop to the C-loop by connecting an input port on a loop through which data is transferred to the other switch device and an output port on the other loop in one pair, and transfers buffered data from the output port; and

the other switch device switches the O-loop to the C-loop by connecting an input port on a loop through which data is transferred to the one of the switch devices and an output port on the other loop in one pair, and transfers data through the C-loop circumventing the section between the switch devices;

when the C-loop is used;

a switch device wherein an input port on a loop is not connected to an output port on the other loop in one pair takes in data addressed to a node related to the switch device and inputted through a predetermined loop of a node that transmitted the data, and transfers other data from an output port on the same loop through which the data was inputted; and

the switch device wherein the input port on a loop is connected to the output port on the other loop in one pair takes in all data addressed to a node related to the switch device, and transfers other data from the output port.

10. The loop network as claimed in claim 2 wherein, when the C-loop is switched to the O-loop;

one of the two switch devices in which the input port on a loop is connected to the output port on the other loop in one pair stops data transfer, buffers inputted data, and transmits a management packet through the C-loop, and when receiving the management packet again, transfers the buffered data through the C-loop, and switches the loop to the O-loop to start data transfer through the O-loop; and

the other switch device switches the loop to the O-loop when receiving the management packet, and transfers the management packet to the one of the switch devices.

12. The loop network as claimed in claim 2 wherein, when the C-loop is switched to the O-loop:

a switch device that is to participate in the network transmits a management packet to one of the switch devices adjacent to the participating switch device;

having received the management packet, the one of the switch devices stops data transfer, buffers inputted data, switches the C-loop to the O-loop, and transfers the management packet through the O-loop, and when receiving the management packet again, transfers the buffered data through the O-loop, and start data transfer through the O-loop; and

having received the management packet, the other switch device switches the C-loop to the O-loop, transfers the management packet through the O-loop, and transfers data inputted thereafter through the O-loop.

3. A loop network wherein a plurality of switch devices are connected through multiple loops, a pair of loops are connected to each of the switch devices, and the respective loops in one pair transmit data in the opposite directions, wherein:

each node transmits data to another node through a predetermined loop using a predetermined switch device; and

each switch device comprises a switch device switchover demanding means, a degradation loop transition means, a buffering data transferring means, and an ordering guarantee means;

when an O-loop is used;

the ordering guarantee means in a switch device takes in data addressed to a node related to the switch device, delivers the data to the node, and transfers other data through the same loop through which the data was inputted; and

the buffering data transferring means in a switch device buffers data until the data has been successfully transferred, and retransmits the buffered data when the transfer failed;

when a fault occurs in a loop between adjacent two switch devices, the switch device switchover demanding means in a switch device detecting the fault transmits a switchover demand for switching the O-loop to a C-loop to a switch device located immediate upstream of the faulty section;

the degradation loop transition means in the switch device that transmitted the switchover demand transfers data buffered by the buffering data transferring means through the O-loop, connects an output port on the faulty loop to an input port on the other loop in one pair to switch the O-loop to the C-loop; and

having received the switchover demand, the buffering data transferring means in the switch device located immediate upstream of the faulty section switches the O-loop to the C-loop by connecting an input port on the faulty loop to an output port on the other loop in one pair, transfers buffered data from the output port, and transfers data through the C-loop;

when the C-loop is used;

the ordering guarantee means in a switch device wherein an input port on a loop is not connected to an output port on the other loop in one pair takes in data addressed to a node related to the switch device and inputted through a predetermined loop of a node that transmitted the data, and transfers other data from an output port on the same loop through which the data was inputted; and

the ordering guarantee means in the switch device wherein the input port on a loop is connected to the output port on the other loop in one pair takes in all data addressed to a node related to the switch device, and transfers other data from the output port.

15. The loop network as claimed in claim 3, further including a normal loop transition means, wherein, when the C-loop is switched to the O-loop:

the normal loop transition means in one of the two switch devices wherein the input port on a loop is connected to the output port on the other loop in one pair stops data transfer, buffers inputted data, and transfers a management packet through the C-loop, and when receiving the management packet again, transfers the buffered data through the C-loop, and switches the loop to the O-loop to start data transfer through the O-loop; and

having received the management packet, the normal loop transition means in the other switch device switches the loop to the O-loop, and transfers the management packet through the O-loop.

17. The loop network as claimed in claim 3 further including a normal loop transition means, wherein, when a switch device participates in the network and the C-loop is switched to the O-loop:

the normal loop transition means in the participating switch device transmits a management packet to one of the switch devices adjacent to the participating switch device;

having received the management packet, the one of the switch device stops data transfer,, buffers inputted data, switches the C-loop to the O-loop, and transfers the management packet through the O-loop, and when receiving the management packet again, transfers the buffered data through the C-loop, and starts data transfer through the O-loop; and

when receiving the management packet from the one of the switch device, the other switch device switches the C-loop to the O-loop, and transfers the management packet through the O-loop.

21. The loop network as claimed in claim 3, wherein:

the data includes information about a loop in which the data is being transferred; and

the ordering guarantee means determines whether or not to take in data referring to the information.

4. A loop network wherein a plurality of switch devices are connected through multiple loops, a pair of loops are connected to each of the switch devices, and the respective loops in one pair transmit data in the opposite directions, including a switchover instructing means, wherein:

each node transmits data to another node through a predetermined loop using a predetermined switch device; and

each switch device comprises, a switch device switchover demanding means, a degradation loop transition means, a buffering data transferring means, and ordering guarantee means;

when an O-loop is used;

the ordering guarantee means in a switch device takes in data addressed to a node related to the switch device, delivers the data to the node, and transfers other data through the same loop through which the data was inputted; and

the buffering data transferring means in a switch device buffers data until the data has been successfully transferred, and retransmits the buffered data when the transfer failed;

when the switchover instructing means is directed to build a C-loop circumventing a section between arbitrary two switch devices adjacent to each other by a network maintainer;

the switchover instructing means transmits a switchover instruction to the switch device switchover demanding means in one of the switch devices;

having received the switchover instruction, the switch device switchover demanding means in the one of the switch devices transmits a switchover demand for switching the O-loop to the C-loop to the other switch device;

after the switch device switchover demanding means transmitted the switchover demand, the degradation loop transition means in the one of the switch devices to which the switchover instruction was inputted transfers data buffered by the buffering data transferring means through the O-loop, and switches the O-loop to the C-loop by connecting an input port on a loop through which data is transferred to the one of the switch devices to an output port on the other loop in one pair; and

having received the switchover demand, the buffering data transferring means of the other switch device switches the O-loop to the C-loop by connecting an input port on a loop through which data is transferred to the one of the switch devices to an output port on the other loop in one pair, transfers buffered data from the output port, and transfers data through the C-loop circumventing the section between the two switch devices;

when the C-loop is used;

the ordering guarantee means in a switch device wherein an input port on a loop is not connected to an output port on the other loop in one pair takes in data addressed to a node related to the switch device and inputted through a predetermined loop of a node that transmitted the data, and transfers other data from an output port on the same loop through which the data was inputted; and

the ordering guarantee means in the switch device wherein the input port of a loop is connected to the output port of the other loop in one pair takes in data addressed to a node related to the switch device, and transfers other data from the output port.

16. The loop network as claimed in claim 4, further including a normal loop transition means, wherein, when the C-loop is switched to the O-loop:

the normal loop transition means in one of the two switch devices wherein the input port on a loop is connected to the output port on the other loop in one pair stops data transfer, buffers inputted data, and transfers a management packet through the C-loop, and when receiving the management packet again, transfers the buffered data through the C-loop, and switches the loop to the O-loop to start data transfer through the O-loop; and

having received the management packet, the normal loop transition means in the other switch device switches the loop to the O-loop, and transfers the management packet through the O-loop.

18. The loop network as claimed in claim 4 further including a normal loop transition means, wherein, when a switch device participates in the network and the C-loop is switched to the O-loop:

the normal loop transition means in the participating switch device transmits a management packet to one of the switch devices adjacent to the participating switch device;

having received the management packet, the one of the switch device stops data transfer, buffers inputted data, switches the C-loop to the O-loop, and transfers the management packet through the O-loop, and when receiving the management packet again, transfers the buffered data through the C-loop, and starts data transfer through the O-loop; and

when receiving the management packet from the one of the switch device, the other switch device switches the C-loop to the O-loop, and transfers the management packet through the O-loop.

22. The loop network as claimed in claim 4, wherein:

the data includes information about a loop in which the data is being transferred; and

the ordering guarantee means determines whether or not to take in data referring to the information.

29. The method for operating loop network as claimed in claim 25, when switching the C-loop to the O-loop, further including the steps of:

directing one of the two switch devices in which the input port on a loop is connected to the output port on the other loop in one pair to stop data transfer, to buffer inputted data, and to transfer a management packet through the C-loop;

directing the other switch device to switch the loop to the O-loop when receiving the management packet, and to transfer the management packet to the one of the switch devices; and

directing the one of the switch devices to transfer the buffered data through the C-loop when receiving the management packet again, and to switch the loop to the O-loop to start data transfer through the O-loop.

30. The method for operating loop network as claimed in claim 26, when switching the C-loop to the O-loop, further including the steps of:

directing one of the two switch devices in which the input port on a loop is connected to the output port on the other loop in one pair to stop data transfer, to buffer inputted data, and to transfer a management packet through the C-loop;

directing the other switch device to switch the loop to the O-loop when receiving the management packet, and to transfer the management packet to the one of the switch devices; and

directing the one of the switch devices to transfer the buffered data through the C-loop when receiving the management packet again, and to switch the loop to the O-loop to start data transfer through the O-loop.

31. The method for operating a loop network as claimed in claim 27, when switching the C-loop to the O-loop, further including the steps of:

directing a switch device to participate in the network to transmit a management packet to one of the switch devices adjacent to the participating switch device;

directing the one of the switch devices to stop data transfer when receiving the management packet, to buffer inputted data, to switch the C-loop to the O-loop, and transfer the management packet through the O-loop;

directing the other switch device to switch the C-loop to the O-loop when receiving the management packet, to transfer the management packet through the O-loop, and to transfer buffered data through the O-loop; and

directing the one of the switch devices to transfer the buffered data through the C-loop when receiving the management packet again, to start data transfer, and to transfer data through the O-loop.

32. The method for operating a loop network as claimed in claim 28, when switching the C-loop to the O-loop, further including the steps of:

directing a switch device to participate in the network to transmit a management packet to one of the switch devices adjacent to the participating switch device;

directing the one of the switch devices to stop data transfer when receiving the management packet, to buffer inputted data, to switch the C-loop to the O-loop, and transfer the management packet through the O-loop;

directing the other switch device to switch the C-loop to the O-loop when receiving the management packet, to transfer the management packet through the O-loop, and to transfer buffered data through the O-loop; and

directing the one of the switch devices to transfer the buffered data through the C-loop when receiving the management packet again, to start data transfer, and to transfer data through the O-loop.

5. A loop network wherein a plurality of switch devices are connected through multiple loops, a pair of loops are connected to each of the switch devices, and the respective loops in one pair transmit data in the opposite directions, wherein:

each node transmits data to another node through a predetermined loop using a predetermined switch device; and

each switch device buffers data until the data has been successfully transferred, and retransmits the buffered data when the transfer failed;

when an O-loop is used;

each switch device takes in data addressed to a node related to the switch device, and delivers the data to the node, and transfers other data through the same loop through which the data was inputted; and

when hardware serious failure occurs;

a switch device located immediate downstream of a usable loop switches the O-loop to a C-loop by connecting an output port on the usable loop and an input port on the other loop in one pair, and transfers buffered data from the output port; and

a switch device located immediate upstream of the usable loop switches the O-loop to the C-loop by connecting an input port on the usable loop to an output port on the other loop in one pair, transfers buffered data from the output port, and transfers data through the C-loop circumventing the faulty section;

when the C-loop is used;

a switch device wherein an input port on a loop is not connected to an output port on the other loop in one pair takes in data addressed to a node related to the switch device and inputted through a predetermined loop of a node that transmitted the data, and transfers other data from an output port on the same loop through which the data was inputted; and

the switch device wherein the input port on a loop is connected to the output port on the other loop in one pair takes in all data addressed to a node related to the switch device, transfers other data from the output port, and does not transfer data addressed to a node related to the switch device that is not connected to the C-loop.

13. The loop network as claimed in claim 5 wherein, when the C-loop is switched to the O-loop:

a switch device that is to participate in the network transmits a management packet to one of the switch devices adjacent to the participating switch device;

having received the management packet, the one of the switch devices stops data transfer, buffers inputted data, switches the C-loop to the O-loop, and transfers the management packet through the O-loop, and when receiving the management packet again, transfers the buffered data through the O-loop, and start data transfer through the O-loop; and

having received the management packet, the other switch device switches the C-loop to the O-loop, transfers the management packet through the O-loop, and transfers data inputted thereafter through the O-loop.

6. A loop network wherein a plurality of switch devices are connected through multiple loops, a pair of loops are connected to each of the switch devices, and the respective loops in one pair transmit data in the opposite directions, wherein:

each node transmits data to another node through a predetermined loop using a predetermined switch device; and

each switch device buffers data until data has been successfully transferred to a switch device located immediate downstream, and retransmits the buffered data to the switch device located immediate downstream when the transfer failed;

when an O-loop is used;

each switch device takes in data addressed to a node related to the switch device, and delivers the data to the node, and transfers other data;

when an arbitrary switch device is instructed to build a C-loop circumventing the switch device by a network maintainer;

the instructed switch device directs one of the switch devices adjacent to the instructed switch device to switch the O-loop to the C-loop by connecting an input port on a loop through which data is transferred to the instructed switch device and an output port on the other loop in one pair, and to transfer buffered data from the output port; and

the instructed switch device directs the other switch device to switch the O-loop to the C-loop by connecting an input port on a loop through which data is transferred to the instructed switch device and an output port on the other loop in one pair, to transfer buffered data from the output port, and to transfer data through the C-loop circumventing the instructed switch device;

when the C-loop is used;

a switch device wherein an input port on a loop is not connected to an output port on the other loop in one pair takes in data addressed to a node related to the switch device and inputted through a predetermined loop of a node that transmitted the data, and transfers other data from an output port on the same loop through which the data was, inputted; and

the switch device wherein the input port on a loop is connected to the output port on the other loop in one pair takes in all data addressed to a node related to the switch device, transfers other data from the output port, and does not transfer data addressed to a node related to the switch device that is not connected to the C-loop.

14. The loop network as claimed in claim 6 wherein, when the C-loop is switched to the O-loop:

a switch device that is to participate in the network transmits a management packet to one of the switch devices adjacent to the participating switch device;

having received the management packet, the one of the switch devices stops data transfer, buffers inputted data, switches the C-loop to the O-loop, and transfers the management packet through the O-loop, and when receiving the management packet again, transfers the buffered data through the O-loop, and start data transfer through the O-loop; and

having received the management packet, the other switch device switches the C-loop to the O-loop, transfers the management packet through the O-loop, and transfers data inputted thereafter through the O-loop.

7. A loop network wherein a plurality of switch devices are connected through multiple loops, a pair of loops are connected to each of the switch devices, and the respective loops in one pair transmit data in the opposite directions, wherein:

each node transmits data to another node through a predetermined loop using a predetermined switch device; and

each switch device comprises a switchover notifying means, failure occurrence notifying means, a buffering data transferring means, and an ordering guarantee means;

when an O-loop is used;

the ordering guarantee means in a switch device takes in data addressed to a node related to the switch device, delivers the data to the node, and transfers other data through the same loop through which the data was inputted;

the buffering data transferring means buffers data until the data has been successfully transferred, and retransmits the buffered data when the transfer failed;

the switchover notifying means in a switch device in which hardware serious failure occurred in a loop in one pair transmits a serious failure notification for demanding a switchover from the O-loop to a C-loop to a switch device located immediate downstream of the faulty section;

after the switchover notifying means transmitted the serious failure notification, the failure occurrence notifying means in the switch device having the hardware serious failure transmits a switchover demand for switching the O-loop to the C-loop to a switch device located immediate upstream of the faulty section; and

the buffering data transferring means in the switch device having received the serious failure occurrence notification or the switchover demand switches the O-loop to the C-loop by connecting an input port on a loop through which data can be transferred to the switch device that transmitted the failure occurrence notification or the switchover demand and an output port on the other loop in one pair, and transfers buffered data from the output port;

when the C-loop is used;

the ordering guarantee means in a switch device wherein an input port on a loop is not connected to an output port on the other loop in one pair takes in data addressed to a node related to the switch device and inputted through a predetermined loop of a node that transmitted the data, and transfers other data from an output port on the same loop through which the data was inputted; and

the ordering guarantee means in the switch device wherein the input port on a loop is connected to the output port on the other loop in one pair takes in all data addressed to a node related to the switch device, transfers other data from the output port, and does not transfer data addressed to a node related to the switch device that is not connected to the C-loop.

19. The loop network as claimed in claim 7 further including a normal loop transition means, wherein, when a switch device participates in the network and the C-loop is switched to the O-loop:

the normal loop transition means in the participating switch device transmits a management packet to one of the switch devices adjacent to the participating switch device;

having received the management packet, the one of the switch device stops data transfer, buffers inputted data, switches the C-loop to the O-loop, and transfers the management packet through the O-loop, and when receiving the management packet again, transfers the buffered data through the C-loop, and starts data transfer through the O-loop; and

when receiving the management packet from the one of the switch device, the other switch device switches the C-loop to the O-loop, and transfers the management packet through the O-loop.

23. The loop network as claimed in claim 7, wherein:

the data includes information about a loop in which the data is being transferred; and

the ordering guarantee means determines whether or not to take in data referring to the information.

8. A loop network wherein a plurality of switch devices are connected through multiple loops, a pair of loops are connected to each of the switch devices, and the respective loops in one pair transmit data in the opposite directions, including a switchover instructing means, wherein:

each node transmits data to another node through a predetermined loop using a predetermined switch device; and

each switch device comprises a switchover notifying means, a failure occurrence notifying means, a buffering data transferring means, and an ordering guarantee means;

when an O-loop is used;

the ordering guarantee means in a switch device takes in data addressed to a node related to the switch device, delivers the data to the node, and transfers other data through the same loop through which the data was inputted; and

the buffering data transferring means buffers data until the data has been successfully transferred, and retransmits the buffered data when the transfer failed;

when the switchover instructing means is directed to build a C-loop circumventing a switch device specified by a network maintainer;

the switchover instructing means transmits a switchover instruction to the switchover notifying means in the specified switch device;

having received the switchover instruction, the switchover notifying means in the specified switch device transmits a first switchover demand for switching the O-loop to the C-loop to one of the switch devices adjacent to the specified switch device;

after the switchover notifying means transmitted the first switchover demand, the failure occurrence notifying means in the specified switch device transmits a second switchover demand for switching from the O-loop to the C-loop to the other switch device; and

having received the first or second switchover demand, the buffering data transferring means in each of the switch devices switches the O-loop to the C-loop by connecting an input port on a loop through which data can be transferred to the sender of the first or second switchover demand to an output port on the other loop in one pair, transfers buffered data from the output port, and transfers data inputted thereafter through the C-loop circumventing the specified switch device;

when the C-loop is used;

the ordering guarantee means in a switch device wherein an input port on a loop is not connected to an output port on the other loop takes in data addressed to a node related to the switch device and inputted through a predetermined loop of a node that transmitted the data, and transfers other data from an output port on the same loop through which the data was inputted; and

the ordering guarantee means in the switch device wherein the input port on a loop is connected to the output port on the other loop in one pair takes in all data addressed to a node related to the switch device, transfers other data from the output port, and does not transfer data addressed to a node related to the switch device that is not connected to the C-loop.

20. The loop network as claimed in claim 8 further including a normal loop transition means, wherein, when a switch device participates in the network and the C-loop is switched to the O-loop:

the normal loop transition means in the participating switch device transmits a management packet to one of the switch devices adjacent to the participating switch device;

having received the management packet, the one of the switch device stops data transfer, buffers inputted data, switches the C-loop to the O-loop, and transfers the management packet through the O-loop, and when receiving the management packet again, transfers the buffered data through the C-loop, and starts data transfer through the O-loop; and

when receiving the management packet from the one of the switch device, the other switch device switches the C-loop to the O-loop, and transfers the management packet through the O-loop.

24. The loop network as claimed in claim 8, wherein:

the data includes information about a loop in which the data is being transferred; and

the ordering guarantee means determines whether or not to take in data referring to the information.

25. A method for operating a loop network wherein a plurality of switch devices are connected through multiple loops, a pair of loops are connected to each of the switch devices, and the respective loops in one pair transmit data in the opposite directions, when a fault occurs in a loop between adjacent two switch devices, including the steps of:

directing a switch device located immediate upstream of the faulty section to switch an O-loop to a C-loop by connecting an input port on the faulty loop to an output port on the other loop in one pair, and to transfer buffered data from the output port; and

directing a switch device located immediate downstream of the faulty section to switch the O-loop to the C-loop by connecting an output port on the faulty loop to an input port on the other loop in one pair to transfer data through the C-loop;

when the C-loop is used;

directing a switch device wherein an input port on a loop is not connected to an output port on the other loop in one pair to take in data addressed to a node related to the switch device and inputted through a predetermined loop of a node that transmitted the data, and to transfer other data from an output port on the same loop through which the data was inputted; and

directing the switch device wherein the input port on a loop is connected to the output port on the other loop in one pair to take in all data addressed to a node related to the switch device, and to transfer other data from the output port.

26. A method for operating a loop network wherein a plurality of switch devices are connected through multiple loops, a pair of loops are connected to each of the switch devices, and the respective loops in one pair transmit data in the opposite directions, when there is a direction to build a C-loop circumventing a section between arbitrary two switch devices adjacent to each other by a network maintainer, including the steps of:

directing one of the two switch devices to switch an O-loop to a C-loop by connecting an input port on a loop through which data is transferred to the other switch device and an output port on the other loop in one pair, and to transfer buffered data from the output port; and

directing the other switch device to switch the O-loop to the C-loop by connecting an input port on a loop through which data is transferred to the one of the switch devices to an output port on the other loop in one pair to transfer data through the C-loop circumventing the section between the switch devices;

when the C-loop is used;

directing a switch device wherein an input port on a loop is not connected to an output port on the other loop in one pair to take in data addressed to a node related to the switch device and inputted through a predetermined loop of a node that transmitted the data, and to transfer other data from an output port on the same loop through which the data was inputted; and

directing the switch device wherein the input port on a loop is connected to the output port on the other loop in one pair to take in all data addressed to a node related to the switch device, and to transfer other data from the output port.

27. A method for operating a loop network wherein a plurality of switch devices are connected through multiple loops, a pair of loops are connected to each of the switch devices, and the respective loops in one pair transmit data in the opposite directions, including the steps of:

instructing a switch device in which hardware serious failure occurred to direct a switch device located immediate downstream of a usable loop to switch an O-loop to a C-loop by connecting an output port on the usable loop to an input port on the other loop in one pair and to transfer buffered data from the output port; and

instructing the switch device in which the hardware serious failure occurred to direct a switch device located immediate upstream of the usable loop to switch the O-loop to the C-loop by connecting an input port on the usable loop to an output port on the other loop in one pair, to transfer buffered data from the output port, and to transfer data through the C-loop circumventing the switch device having the hardware serious failure;

when the C-loop is used;

directing a switch device wherein an input port on a loop is not connected to an output port on the other loop in one pair to take in data addressed to a node related to the switch device and inputted through a predetermined loop of a node that transmitted the data, and to transfer other data from an output port on the same loop through which the data was inputted; and

directing the switch device wherein the input port on a loop is connected to the output port on the other loop in one pair to take in all data addressed to a node related to the switch device, to transfer other data from the output port, and not to transfer data addressed to a node related to the switch device that is not connected to the C-loop.

28. A method for operating a loop network wherein a plurality of switch devices are connected through multiple loops, a pair of loops are connected to each of the switch devices, and the respective loops in one pair transmit data in the opposite directions, when an arbitrary switch device is instructed to build a C-loop circumventing the switch device, including the steps of:

directing the instructed switch device to direct one of two switch devices adjacent to the instructed switch device to switch an O-loop to a C-loop by connecting an input port on a loop through which data is transferred to the instructed switch device to an output port on the other loop in one pair, and to transfer buffered data from the output port; and

directing the instructed switch device to direct the other switch device to switch the O-loop to the C-loop by connecting an input port on a loop through which data is transferred to the instructed switch device to an output port on the other loop in one pair, to transfer buffered data from the output port, and transfer data through the C-loop circumventing the instructed switch device;

when the C-loop is used;

directing a switch device wherein an input port on a loop is not connected to an output port on the other loop in one pair to take in data addressed to a node related to the switch device and inputted through a predetermined loop of a node that transmitted the data, and to transfer other data from an output port on the same loop through which the data was inputted; and

directing the switch device wherein the input port on loop is connected to the output port on the other loop in one pair to take in all data addressed to a node related to the switch device, to transfer other data from the output port, and not to transfer data addressed to a node related to the switch device that is not connected to the C-loop.