JP2018148265A - Transmission node and circuit switching method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce data loss due to line switching in bidirectional communication between transmission nodes and shorten recovery time of bidirectional communication. In bidirectional communication between transmission nodes, each of the transmission nodes may monitor the traffic volume of a plurality of transmission lines # 611 to # 614 and a plurality of reception lines # 621 to # 624. For each of the transmission nodes, a higher switching priority may be set for a transmission line having a larger total traffic amount of the transmission line and the reception line forming the pair of bidirectional communication. Then, when each of the transmission nodes detects a failure of the work system to which the transmission lines # 611 to # 614 belong, the transmission lines # 611 to # 614 are transferred to the protection system in the order of the switching priority. You may switch. [Selection diagram] FIG. 17

Description

  The present invention relates to a transmission node and a line switching method.

  In order to improve the reliability of communication between transmission nodes, a communication line between transmission nodes may be made redundant between a work system and a protection system. For example, when a failure occurs in the work system communication, the work system traffic is switched to the protection system, and the work system communication is relieved by the protection system. Such a line switching function may be referred to as a protection function.

Japanese Patent Laying-Open No. 2015-37198

ITU-T G.8031 ITU-T Y.1731

  When switching between lines using a protection function between transmission nodes capable of bidirectional communication, switching between uplink and downlink without considering traffic volume may increase data loss. When data loss increases, network congestion may occur due to frequent retransmission control, for example.

  Further, in one-way communication, if one of the downlink and uplink pairs is switched to the other after a delay, a delay occurs in the time until the two-way communication is established (in other words, restored).

  In one aspect, one of the objects of the present invention is to reduce data loss associated with line switching in bidirectional communication between transmission nodes and shorten recovery time of bidirectional communication.

  In one aspect, the (first) transmission node is a node that performs bidirectional communication with another (second) transmission node, and may include a monitoring unit, a setting unit, and a control unit. . The monitoring unit may monitor the traffic amount of a plurality of transmission lines and a plurality of reception lines in the bidirectional communication. The setting unit may set a higher switching priority for a transmission line having a larger total traffic amount of the transmission line and the reception line forming the bidirectional communication pair. The control unit may switch the transmission lines to the protection system in the order of the switching priority when a failure of a work system to which the transmission lines belong is detected.

  In one aspect, the line switching method may monitor the traffic volume of a plurality of transmission lines and a plurality of reception lines in each of the transmission nodes in bidirectional communication between the transmission nodes. Each of the transmission nodes may set a higher switching priority for a transmission line having a larger total traffic volume of a transmission line and a reception line that form the bidirectional communication pair. Then, each of the transmission nodes may switch the transmission lines to the protection system in the order of the switching priority when a failure of a work system to which the transmission lines belong is detected.

  As one aspect, it is possible to reduce data loss associated with line switching in bidirectional communication between transmission nodes and shorten the recovery time of bidirectional communication.

It is a block diagram which shows the structural example of the communication network which concerns on one Embodiment. It is a figure which shows typically the example in which the some user line was made redundant in the two transmission nodes in which bidirectional communication is possible. FIG. 3 is a diagram schematically illustrating an example in which a user line is switched from a work system to a protection system in the example of FIG. 2. FIG. 4 is a diagram for explaining an example in which data loss may increase when switching is performed without considering traffic volume in the line switching illustrated in FIG. 3. FIG. 4 is a diagram for explaining an example when the switching order of uplink and downlink sub-logical lines forming a pair in the line switching illustrated in FIG. 3 does not match between transmission nodes. FIG. 4 is a diagram for explaining an example when the switching order of uplink and downlink sub-logical lines forming a pair in the line switching illustrated in FIG. 3 matches between transmission nodes; It is a block diagram which shows typically the example in which communication is performed between two transmission nodes using a work type | system | group line. FIG. 8 is a diagram illustrating an example of a VLAN (virtual local area network) tag and transmission traffic information for each sub logical line in the example of FIG. 7. FIG. 8 is a diagram schematically illustrating an example in which a failure occurs in a work line in the example of FIG. 7. FIG. 10 is a diagram schematically illustrating an example in which line switching from the work system to the protection system is performed in the example of FIG. 9. FIG. 10 is a diagram schematically showing that bidirectional communication is not established when the line switching to the protection system is not an uplink and downlink line pair in the example of FIG. 9. It is a flowchart for demonstrating the creation procedure of the pair management table in the transmission node which concerns on one Embodiment. It is a figure which shows an example of the pair management table (at the time of initial creation) which concerns on one Embodiment. It is a figure which shows an example of the pair management table (at the time of sub logical line registration) which concerns on one Embodiment. It is a figure which shows the example of a format of a tagged Ethernet (trademark) frame. It is a flowchart for demonstrating the traffic monitoring in the transmission node which concerns on one Embodiment, and the setting procedure of switching priority. It is a figure which shows an example of the pair management table (at the time of total traffic update) which concerns on one Embodiment. It is a figure which shows an example of the priority table which concerns on one Embodiment. It is a flowchart for demonstrating an example of the line switching procedure from the work type | system | group to a protection type | system | group in the transmission node which concerns on one Embodiment. It is a flowchart for demonstrating the modification (modification of a priority table creation process) of one Embodiment. It is a flowchart for demonstrating the traffic monitoring in the transmission node which concerns on the modification of one Embodiment, and the setting procedure of switching priority. It is a figure which shows an example of the static priority table which concerns on one Embodiment. It is a figure which shows an example of the sub logical line switching availability table which concerns on one Embodiment. (A) is a diagram illustrating an example of a priority table created when the static priority table illustrated in FIG. 22 and the sub-logical line switching availability table illustrated in FIG. 23 are considered. FIG. 10 is a diagram showing an example of a priority table created when the total traffic volume is further considered in (A). It is a flowchart for demonstrating an example of the line switchback procedure from the protection system to the work system in the transmission node which concerns on one Embodiment. It is a block diagram which shows the hardware structural example of the transmission node which concerns on one Embodiment. FIG. 27 is a block diagram illustrating a functional configuration example of a control unit illustrated in FIG. 26. It is a figure which shows the example of a format of CCM (continuity check message) -PDU (protocol data unit) frame in Ethernet OAM (operation, administration and maintenance).

  Hereinafter, embodiments will be described with reference to the drawings. However, the embodiment described below is merely an example, and there is no intention to exclude various modifications and technical applications that are not explicitly described below. Various exemplary embodiments described below may be implemented in combination as appropriate. Note that, in the drawings used in the following embodiments, portions denoted by the same reference numerals represent the same or similar portions unless otherwise specified.

  FIG. 1 is a block diagram illustrating a configuration example of a communication network according to an embodiment. The communication network 1 illustrated in FIG. 1 may be referred to as a “communication system 1” or a “transmission system 1”, and may include a plurality of transmission apparatuses 11 by way of example. An external communication device 12 such as a router may be communicably connected to any one or more of the plurality of transmission devices 11.

  The “transmission device” may be an optical transmission device or a frame transmission device. The “transmission device” is an example of an element or entity of the communication network 1 and may be expressed as “NE”. The “transmission device” may also be referred to as a “transmission node”, a “communication node”, or simply a “node”. FIG. 1 illustrates the case of the number of nodes = 6, but the number of nodes may be two or more.

  As illustrated in FIG. 1, the plurality of nodes 11 may be communicably connected to form a mesh network. Alternatively, the plurality of nodes 11 may be connected to be able to communicate in a ring shape to form a ring network. In other words, the topology of the communication network 1 is not particularly limited. For example, an optical fiber may be used for the connection (in other words, the communication path) between the nodes 11.

  By the way, in recent years, with the increase in speed and capacity of the communication network 1, the number of lines set and multiplexed per node (may be referred to as “multiplicity”) tends to increase. The “line” may be set in the node 11 in units of logical lines such as paths or channels (sometimes referred to as “user lines” or “sub logical lines”).

  For example, as schematically shown in FIG. 2, 1000 or more logical lines may be set and multiplexed per port of one node 11. The “line” may be set separately for upstream and downstream. The uplink and downlink “user lines” are examples of lines in bidirectional communication between the nodes 11.

  Also, the “user line” should be made redundant into a work system and a protection system as shown in FIG. 2, for example, by a technique called a protection function in order to improve communication reliability. There is. A user line belonging to the work system may be referred to as a “work line”, and a user line belonging to the protection system may be referred to as a “protection line”.

  For example, when the node 11 detects that a failure (for example, signal interruption) has occurred in any user line in the work system, the node 11 switches the user line in which the failure has been detected from the work system to the protection system. Is possible. As a result, it is possible to relieve the work system user line in which the failure is detected by the protection system.

  When a failure of a plurality of user lines is detected, the node 11 may switch each user line from the work system to the protection system in order, for example, in the order in which the failure is detected. Alternatively, by setting a static priority for a plurality of user lines, switching control may be performed in the order of the set priority when a failure is detected.

  FIG. 3 schematically shows an example in which bidirectional communication is possible in the protection system after the line switching from the work system to the protection system is completed. For user lines for which priority is not set in advance, switching control may be performed in the order in which line faults are detected regardless of the traffic volume.

  However, when the multiplicity of user lines increases, switching takes time, and service recovery for some users may be delayed. In addition, user lines that actually have high priority do not always use a large amount of bandwidth, and there are user lines that have a low priority but a large amount of traffic and use a large amount of bandwidth at some point. Depending on the operational status, various line usage situations are assumed.

  When a line failure occurs in such a situation, if switching control is performed without considering the amount of traffic on the user line, transmission data loss frequently occurs on a certain user line depending on the switching order. May end up. An example of transmission data is packet data, frame data, or the like.

  For example, if switching control of a user line with a larger traffic volume than other user lines is delayed and delayed, transmission data loss may occur frequently. When transmission data loss frequently occurs, network congestion may occur due to frequent retransmission control and the like.

FIG. 4 shows an example of the relationship between line switching time and traffic volume, assuming that the traffic volumes of user lines A to C, which are three sub-logical lines, are T _LA , T _LB and T _LC , respectively. .

FIG. 4 shows lines in the order of sub-logical lines A, B, and C when the magnitude relationships of traffic volumes T _LA , T _LB, and T _LC are as shown in (1) to (3) below. A case where switching is performed is illustrated.

(1) T _LA > T _LB > T _LC
(2) T _LB > T _LA > T _LC
(3) T _LC > T _LB > T _LA

  The above conditions (1) to (3) correspond to the graphs indicated by (1) to (3) in FIG. Here, in the line switching control by the protection function, a switching time that has no or minimum influence on communication is defined. For example, 50 milliseconds (ms) may be defined as the switching time from failure detection to completion of line switching.

  Since the number of sub logical lines that can be switched within the specified switching time is limited, the data loss associated with line switching can be minimized by preferentially switching and recovering the sub logical lines with a large amount of traffic. It is possible to shorten the recovery time of the entire communication service.

  Therefore, as illustrated in FIG. 4, the switching is completed within a predetermined switching time by performing the line switching in the order of the sub logical lines A, B, and C having the large traffic volume under the condition (1). In addition, data loss can be minimized.

  On the other hand, if the line switching is performed in the order of the sub logical lines C, B, and A with a small traffic volume as in the condition (3), the switching cannot be completed within a predetermined switching time, and data loss occurs. Will increase.

The condition (2) is an intermediate position between the conditions (1) and (3), and the sub logical line A having a smaller traffic amount T _LA is switched first than the sub logical line B having a larger traffic amount T _LB. It is done. Therefore, as compared with the case of condition (1), the time until line switching is completed is delayed and the data loss also increases.

  As described above, it is advantageous to perform the switching control with priority from the sub logical line having a large traffic amount. However, each of the nodes 11 monitors and detects a failure only on the transmission side (downlink) user line viewed from the own node 11 among the uplink and downlink user lines, so that the downlink user line can be switched. Stay on.

  Therefore, when both the upstream and downstream user lines are disconnected, even if only the one-way user line is switched to the protection system first, only one-way communication is possible. Communication service is not restored. Also, it is not possible to prevent an increase in network congestion due to frequent occurrence of retransmission control or the like. Such a situation can become more serious as the number of user lines set and multiplexed per port of the node 11 increases.

  In FIG. 5, when a failure is detected in both the upstream and downstream user lines # 1 to # 3 in the work system between the two nodes 11 (# 1 and # 2), the upstream and downstream bidirectional line switching is performed. An example of an image until the completion of is schematically illustrated.

  In the example of FIG. 5, the failure is detected in the order of the user lines # 1, # 2, and # 3 in the node # 1, and the failure is detected in the order of the user lines # 3, # 1, and # 2 in the node # 2. Assumes.

  In other words, the failure detection order of the user lines # 1 to # 3 does not match between the nodes # 1 and # 2. Such a situation may occur, for example, due to a time difference between internal processes of the nodes # 1 and # 2, even if failures occur simultaneously in the user lines # 1 to # 3.

  In node # 1, failures are detected in the order of user lines # 1, # 2, and # 3, so failure detection is notified to the internal redundancy control function in that order. Therefore, the redundancy control function performs line switching processing in the order of user lines # 1, # 2, and # 3. In the example of FIG. 5, it is assumed that the line switching process per user line requires about 30 ms.

  On the other hand, since the failure is detected in the order of the user lines # 3, # 1, and # 2 in the node # 2, the failure detection is notified to the internal redundancy control function in that order. Therefore, the redundancy control function performs line switching processing in the order of user lines # 3, # 1, and # 2.

  In this case, even if the user line # 1 is switched to the protection system about 30 ms after the failure detection in the node # 1, the user line # 1 is switched to the protection system in the node # 2 about 60 ms after the failure detection. . Therefore, it is about 60 ms after failure detection that bidirectional communication is restored for user line # 1.

  Similarly, even if the user line # 2 is switched to the protection system about 60 ms after the failure detection in the node # 1, the user line # 2 is switched to the protection system in the node # 2 about 90 ms after the failure detection. . Therefore, the two-way communication for user line # 2 is restored about 90 ms after the failure detection.

  As for the user line # 3, even if the node # 2 is switched to the protection system about 30 ms after the failure detection, the node # 1 is switched to the protection system about 90 ms after the failure detection. For this reason, the two-way communication is restored for the user line # 3 about 90 ms after the failure detection.

  In this way, if the failure detection order does not match between the nodes # 1 and # 2, the user line in the reverse direction is switched behind the switching of the user line in one direction. There may be a delay in recovery.

  On the other hand, the example of FIG. 6 is an image until the bidirectional line switching is completed when the failure detection order for the user lines # 1 to # 3 is the same between the nodes # 1 and # 2. Is schematically shown. In the example of FIG. 6, the failure detection order at the nodes # 1 and # 2 is the order of user line # 1 → user line # 2 → user line # 3.

  In this case, in both the nodes # 1 and # 2, the user line # 1 is switched to the protection system about 30 ms after the failure detection. Therefore, the bidirectional communication for the user line # 1 is restored about 30 ms after the failure detection.

  Similarly, for user line # 2, both nodes # 1 and # 2 enter the protection system about 60 ms after failure detection, and for user line # 3, about 90 ms after failure detection on both nodes # 1 and # 2. Can be switched. Therefore, the two-way communication is restored for the user lines # 2 and # 3 after about 60 ms and about 90 ms after the failure detection, respectively.

  As described above, if the failure detection order for the user lines # 1 to # 3 is the same between the nodes # 1 and # 2, the time required to restore the bidirectional communication of each of the user lines # 1 to # 3 is minimized. Can be. Since the time required for bidirectional communication recovery can be minimized, data loss due to line switching can also be minimized.

  In other words, even if a failure detection order for a plurality of user lines does not match between nodes # 1 and # 2 as shown in FIG. 5, the line switching order matches between nodes # 1 and # 2. By rearranging in such a manner, the recovery time of bidirectional communication can be minimized as shown in FIG.

  Therefore, data loss accompanying line switching can be minimized. Therefore, the retransmission control frequency can be reduced. As a result, the occurrence rate of network congestion due to frequent retransmission control can be reduced.

  Therefore, in this embodiment, an example in which line switching control is performed in an order based on the total (total) traffic volume of a pair of uplink and downlink user lines in bidirectional communication (which may be referred to as “priority”). Will be described.

  7 to 9 schematically show an example of line switching control according to an embodiment. In FIGS. 7 to 9, attention is focused on the first node 610 and the second node 620 corresponding to the communication partner of the first node 610. Note that the node 620 may correspond to a “first node”, and the node 610 may correspond to a “second node”.

  The nodes 610 and 620 may be regarded as corresponding to any one of the plurality of nodes 11 illustrated in FIG. Therefore, when the nodes 610 and 620 are not distinguished, they may be expressed as “node 11”.

  A bidirectional work line and a protection line may be set between the node 610 and the node 620. For example, four sub logical lines # 611 to # 614 may be set in the node 610 as an example of a plurality of sub logical lines. On the other hand, for example, four sub logical lines # 621 to # 624 may be set in the node 620 as an example of a plurality of sub logical lines.

  During normal operation, the nodes 610 and 620 can multiplex and transmit signals of four sub-logical lines to work lines.

  For example, the sub logical lines # 611 to # 614 correspond to downlink lines (in other words, “transmission lines”) for the node 610, and the sub logical lines # 621 to # 624 correspond to uplink lines for the node 610. It may be considered that it corresponds to a line (in other words, “receiving line”).

  Also, the sub logical lines # 621 to # 624 correspond to downlink lines (in other words, “transmission lines”) for the node 620, and the sub logical lines # 611 to # 614 are uplink lines for the node 620. It may be considered that it corresponds to a line (in other words, “receiving line”).

  As information that can identify the sub logical lines # 611 to # 614 and the sub logical lines # 621 to # 624 (which may be referred to as “line ID” for convenience), as a non-limiting example, a VLAN tag May be applied. “VLAN” is an abbreviation for “virtual local area network”.

  FIG. 8 shows an example of VLAN tags for the sub logical lines # 611 to # 614 and # 621 to # 624. The VLAN tags of the sub logical lines # 611 to # 614 are “A” to “D”, respectively, and the VLAN tags of the sub logical lines # 621 to # 624 are “C”, “D”, and “A”, respectively. "," B ".

  Here, it may be understood that the sub-logical lines of the same VLAN tag form a bidirectional communication pair. For example, in the node 610, the upstream sub logical line paired with the downstream sub logical line # 611 having the VLAN tag “A” is the sub logical line # 623.

  Similarly, in the node 610, the upstream sub logical lines paired with the downstream sub logical lines # 612 to # 614 whose VLAN tags are “B” to “D” are sub logical lines # 624 and # 621, respectively. , # 622.

  Further, as illustrated in FIG. 8, in the node 610, it is assumed that the transmission traffic amounts of the sub logical lines # 611 to # 614 per unit time are 30 megabytes (MB), 40 MB, 50 MB, and 10 MB, respectively. .

  On the other hand, in node 620, it is assumed that the transmission traffic amounts of sub logical lines # 621 to # 624 per unit time are 20 MB, 40 MB, 10 MB, and 20 MB, respectively.

  Note that the “unit time” may be determined by a measurement period (also referred to as an “update period”) of the transmission traffic amount in each of the nodes 610 and 620 as a non-limiting example. The update period is preferably set to the same period between the nodes 610 and 620. As will be described later, this is to prevent inconsistencies in the switching priority calculated and set by each of the nodes 610 and 620 as much as possible.

  With the above exemplary settings and conditions, the flow of the line switching procedure of the present embodiment is as shown in the following (1) to (4).

  (1) Before starting operation, information on sub-logical lines that are paired in both directions is managed in each of the nodes 610 and 620.

  (2) After the operation is started, the total traffic volume of the sub logical lines that are paired in both directions is collected and updated at each of the nodes 610 and 620 periodically, for example, and the sub logical lines belonging to the pair with the large total traffic volume The higher switching priority is calculated and set.

  (3) The calculation and setting of the switching priority may be performed autonomously by each of the nodes 610 and 620. The autonomous implementation may cause inconsistencies in the calculated and set switching priorities between the nodes 610 and 620, but this is not a big problem in terms of line switching time and data loss as a whole. The reason will be described later.

  (4) When a failure occurs in the work line (FIG. 9), the nodes 610 and 620 perform switching control of the sub logical line to the protection line in the order of the calculated and set switching priorities (FIG. 10). ).

  As illustrated in FIG. 11, bidirectional communication is not established until each of the upstream and downstream sub-logical lines that are paired with bidirectional communication is switched to the protection line.

  Further, in the above procedure (1), there is no particular limitation on the format in which the information on the pair of bidirectional sub logical lines is managed by the nodes 610 and 620, but it may be a table format by way of example. The sub logical line pair information managed as table format information may be referred to as a “pair management table” for convenience.

(Operation example)
First, the creation procedure of the pair management table in the procedure (1) will be described with reference to FIGS.

  As illustrated in FIG. 12, the node 11 may perform setting of an internal interface and a sub logical line (process 801). The “interface setting” may include, for example, setting of a port used for communication. “Sub logical line setting” may include setting of a line ID (for example, a VLAN tag).

  Further, the node 11 may set the apparatus monitoring function (process 802). The “place monitoring function” illustratively monitors and manages information such as the communication state of the sub logical line, failure detection, and performance. “Communication state monitoring” may include monitoring the amount of downlink transmission traffic.

  Further, the node 11 may perform redundant configuration setting of the work line and the protection line (process 803). “Redundant configuration setting” may include, for example, setting of logical ports and sub logical lines used by the own node 11 and the partner node 11 for the work line and the protection line, respectively.

  Note that, in the own node 11 and the partner node 11, the sub logical lines in which the same VLAN tag is set form a pair of uplink and downlink communications when viewed in units of users. The VLAN tag may be set to a signal transmitted from each node 11 to the downstream.

  Therefore, each node 11 receives the signals transmitted through the sub logical lines of the partner node 11 to acquire VLAN tag information (hereinafter sometimes referred to as “VLAN tag information”) from the received signal. be able to.

  FIG. 15 shows an IEEE 802.1Q tagged Ethernet frame as a non-limiting example of a signal transmitted from each node 11 to the downstream. “Ethernet” is a registered trademark. In the case of the frame, by referring to the 4-byte “tag” information, the VLAN tag information set in the node 11 as the communication partner can be known.

  In FIG. 15, “TPID” is an abbreviation for “tag protocol identifier” and is a field (16 bits) in which information indicating a frame with a tag according to IEEE 802.1Q is set. “PCP” is an abbreviation for “priority code point”, and is a field (3 bits) in which information indicating the priority of a frame is set.

  “CFI” is an abbreviation for “canonical format indicator”, and is a field (1 bit) in which information indicating whether or not the media access control (MAC) address is a regular format is set. In the case of Ethernet, “0” indicating that the MAC address is in a regular format is set in the CFI.

  “VID” is an abbreviation of “VLAN identifier” and is a field (12 bits) in which information indicating the VLAN to which the frame belongs is set. Therefore, it is possible to identify that the frame transmitted through the “user line” or “sub logical line” belongs to the VLAN identified by the VID.

  In other words, the node 11 forms a pair with the downstream sub logical line based on the information that can identify the upstream sub logical line set in the upstream traffic received from the other node 11 that is the communication partner. The upstream sub logical line can be identified.

  Therefore, for example, it is not necessary for the operator to individually set information on the upstream sub logical pair paired with the downstream sub logical line in the bidirectional communication for each of the nodes 11. Further, it is not necessary to transmit information on the sub logical line pair between the nodes 11 by control signal communication or the like.

  In FIG. 15, “FCS” is an abbreviation for “frame check sequence”, and is a field in which a code for detecting and correcting data errors is set.

  Returning to FIG. 12, the node 11 creates a pair management table (see, eg, FIG. 13) with an empty entry and stores it in the memory (process 804).

  Then, the node 11 may acquire the VLAN tag information of the sub logical line set in the process 801 and the VLAN tag information set in the signal received from the counterpart node 11 (process 805).

  Based on the information acquired in the process 805, the node 11 may register and manage the sub-logical lines of the same VLAN tag as a pair in the pair management table as shown in FIG. 14, for example (process 806).

  In FIG. 14, the sub logical line of the partner node 620 that forms a pair with the sub logical line # 611 in the node 610 is a sub logical line (# 623) in which the same VLAN tag “A” is set.

  Similarly, the sub logical lines of the partner nodes 620 that form a pair with the sub logical lines # 612 to # 614 are sub logical lines (# 624, # 621, # 621) in which the same VLAN tags “B” to “D” are set. # 622).

  However, the node 610 may not know information such as the number and name of the sub logical line managed by the counterpart node 620. Therefore, the node 610 may register the VLAN tag information set in the received signal in the pair management table as a number or name for pair management in the node 610.

  In other words, the information on the sub logical line of the partner node 620 registered as a pair in the pair management table is converted into other information (number or name), etc., as long as the information is uniquely distinguishable in the node 610. Or may be mapped.

  The node 620 can also create and manage a table similar to the pair management table illustrated in FIG. 14 based on the VLAN tag information set in the signal received from the counterpart node 610.

  Returning to FIG. 12, the node 11 may initialize the total traffic volume for each sub logical line registered in the pair management table to “0” as shown in FIG. 14, for example (process 807).

  Next, procedures (2) and (3) described above after the start of operation will be described with reference to FIGS. 16 and 17.

  When the operation of the communication network 1 (see FIG. 1) is started, the state shown in FIG. 7 is obtained. As illustrated in FIG. 16, the node 11 may measure the traffic volume by measuring the amount of signal transmission and reception (for example, counting the number of frames and the number of packets) in units of work system sub-logical lines (processing). 1201).

  For example, the sub logical line traffic amount of the node 610 may be measured by measuring the signal transmission amount to the partner node 620, and the traffic amount of the paired sub logical line may be measured by measuring the signal reception amount from the partner node 620. Good.

  The node 11 totals the measured traffic volume for each pair of sub logical lines, and registers the total traffic volume in the corresponding entry of the pair management table as shown in FIG. 17, for example, and updates the pair management table. Good (processing 1202).

  In the example of FIG. 17, the total traffic amount for the pair of sub logical lines # 611 and # 623 is 30 MB + 10 MB = 40 MB from the exemplary settings and conditions of FIG. The total traffic amount for the pair of sub logical lines # 612 and # 624 is 40 MB + 20 MB = 60 MB.

  The total traffic volume for the pair of sub logical lines # 613 and # 621 is 50 MB + 20 MB = 70 MB, and the total traffic volume for the pair of sub logical lines # 614 and # 622 is 10 MB + 40 MB = 50 MB.

  In response to the registration and update of the traffic volume, the node 11 may update the priority table by setting a high switching priority to the sub logical line, for example, in descending order of traffic volume, based on the pair management table (processing) 1203).

  The switching priority for each sub logical line may be stored and managed in each node 11 as information in a table format as shown in FIG. 18 (may be referred to as “priority table”). In the example of FIG. 18, the priority is higher in the order of 1 to 4.

  The priority table may be dynamically updated according to the update of the pair management table. Therefore, the “priority table” may be referred to as a “dynamic priority table”.

  Thereafter, the node 11 may check whether or not the table update cycle has arrived (processing 1204). For example, the table update period may be measured by a timer. In addition, the table update period may be set statically as a default value, for example, or may be set statically or dynamically as a value considering the network operating environment.

  The node 11 may update the pair management table by repeatedly performing the processing 1201 to the processing 1203 at a time interval of the table update cycle (YES in the processing 1204). If the table update cycle has not arrived (NO in process 1204), the node 11 may monitor the arrival of the table update cycle.

  Next, the line switching control at the time of failure occurrence in the above procedure (4) will be described with reference to FIG.

  As illustrated in FIG. 19, when the node 11 detects that a failure has occurred in the work line (process 1501), the node 11 may confirm whether or not there are a plurality of sub-logical lines to be switched (process 1502). ). For example, when a plurality of sub logical lines are subject to line switching as a work line failure is detected, information on each sub logical line subject to line switching may be held in a queue in the node 11.

  If there are a plurality of sub logical lines subject to line switching (YES in process 1502), the node 11 may sort the sub logical lines subject to line switching in order of priority according to the priority table (process 1503).

  Upon completion of sorting, the node 11 may perform switching to the protection system in order from the sub logical line with the highest priority. For example, the node 11 may output the sub logical line switching request in the order of high priority to the internal redundancy control unit 501 (described later in FIG. 27) (processing 1505).

  The redundancy control unit 501 may control the switching unit 112 (described later with reference to FIG. 26) in response to the switching request, thereby switching the sub logical line that has received the switching request to the protection system ( Process 1506).

  Thereafter, the node 11 may check whether or not there is a sub logical line waiting for line switching in the queue (processing 1507). If there is a sub-logical line waiting for line switching (YES), the processes 1505 and 1506 may be repeated until no sub-logical line exists.

  If there is no sub logical line waiting for line switching (NO in step 1507), the node 11 may end the line switching process.

  If there is one sub-logical line to be switched in the process 1502, the node 11 may determine “NO” and output a request for switching the sub-logical line to the redundancy control unit 501 (process). 1504). The subsequent processing may be the same as the processing 1506 and 1507.

  When switching to the protection system of all the sub logical lines is completed, the state shown in FIG. 10 is obtained.

  As described above, according to the present embodiment, the switching priority from the work system to the protection system of each sub logical line is set based on the total traffic volume of the sub logical lines that form a pair in the bidirectional communication between the nodes 11. Can be determined and set.

  For example, uplink and downlink sub-logical lines can be managed in pairs, and a higher recovery priority can be set for a line with a larger total traffic volume for each pair.

  Therefore, it is possible to reduce the amount of traffic (in other words, the amount of data) that can be delayed or lost due to line switching to the protection system when a failure in the work system is detected. Multiple occurrences can be prevented or suppressed.

  Since frequent retransmission control can be prevented or suppressed, the occurrence or expansion of network congestion can also be prevented or suppressed.

  In addition, since the switching priority is set for the pair of the upstream and downstream sub-logical lines, the delay time from the detection of the work system failure to the establishment of bidirectional communication between the nodes 11 in the protection system can be shortened.

  Accordingly, it is possible to quickly restore the bidirectional communication service between the nodes 11. In other words, it becomes easy to complete the restoration of bidirectional communication within a limited line switching time of 50 ms.

  Furthermore, since switching priority is set for a pair of uplink and downlink sub-logical lines, even if the traffic volume differs greatly between uplink and downlink, the switching priority that provides the above technical effects is appropriate. Set to

  Therefore, compared to the case where switching priority is set based on individual uplink and downlink traffic volumes, the amount of traffic that can be delayed or lost due to line switching is reduced, and the recovery time for bidirectional communication services is reduced. It can be expected to shorten.

  In addition, each of the nodes 11 may autonomously implement the processes of the flowcharts illustrated in FIGS. In this case, the amount of traffic managed by the pair management table in each node 11 may slightly vary due to a difference in update timing between the nodes 11. Therefore, the switching priority set in each node 11 may not completely match between the nodes 11.

  However, although it depends on the table update cycle, it is temporary even if a situation that does not completely match occurs, and the switching priority set in each node 11 does not differ greatly between the nodes 11.

  Therefore, it can be considered that the probability of occurrence of a sub-logical line whose line switching waiting time is abnormally long is extremely low. Further, since temporary incomplete matching of the switching priority set between the nodes 11 is allowed, for example, it is necessary to provide each node 11 with an interface for transmitting information on the switching priority between the nodes 11. There is no.

(Modification of priority table creation process)
As illustrated in the process 803a of FIG. 20, a static switching priority (hereinafter may be abbreviated as “static priority”) is set for each node 11 for each sub logical line. Sometimes. FIG. 20 corresponds to a modification of the flowchart illustrated in FIG. 12, and processes 801 to 807 except for the process 803a may be the same as or similar to the processes already described in FIG.

  The static priority information may be set by the operator of the node 11 before starting the network operation, for example. An example of the set static priority is shown in FIG.

  In the example of FIG. 22, static priorities are set for the two sub logical lines # 611 and # 612, and the sub logical line # 611 is set to a higher priority than the sub logical line # 612. .

  In this case, as shown in FIG. 21 in comparison with FIG. 16, for example, the priority table update process 1203a is different from the update process 1203 described in FIG. In other words, in FIG. 21, processing 1201, processing 1202, and processing 1204 may be the same as or similar to the processing described above in FIG.

  For example, in the process 1203a, the node 11 may set and update the dynamic priority table described above based on the static priority information set in the process 803a of FIG. For example, the node 11 determines the switching priority based on the total traffic amount of the upstream and downstream sub-logical lines forming a pair with respect to the sub-logical lines for which the static priority is the highest priority and the static priority is not set. The setting may be performed as described above.

  In other words, the node 11 may not include the sub-logical line for which the static priority is set as the switching priority determination, setting candidate or target (in other words, it may be excluded).

  Further, as illustrated in FIG. 23, whether or not switching to the protection system is possible for a plurality of sub logical lines # 611 to # 614 (in other words, whether switching is permitted) is shown. Information may be preset by an operator, for example.

  This information may be referred to as “switchability information” for convenience. The switchability information for each sub logical line may be held and managed in the node 11 in a table format. The switchability information for each sub logical line in the table format may be referred to as a “sub logical line switchability table” for convenience.

  Depending on the setting of “switchability information”, there may be a sub logical line (eg, # 612) in which the line switching to the protection system is set to “impossible”. An example of a state in which line switching is “impossible” is, for example, the “LOCKOUT” state described in Non-Patent Document 1 described above.

  Note that “impossible” of line switching may be equivalent to the fact that line switching is not permitted (or prohibited) or that line switching is disabled.

  The setting of “switchability information” may also be regarded as an example of the setting related to the static priority described above. Therefore, in the example of FIG. 23, the node 11 may exclude the sub logical line # 612 in which the line switching “impossible” is set, without including it as a switching priority determination or setting candidate or target.

  FIG. 24A shows an example in which, among the sub logical lines # 611 to # 614, the sub logical line # 612 is excluded from the switching priority determination and setting candidates or targets. The node 11 may determine and set the switching priority for the other sub logical lines # 611, # 613, and # 614 excluding the sub logical line # 612 based on the total traffic volume as described above.

  For example, as illustrated in FIG. 24B, the node 11 has a larger total traffic volume than the sub logical lines # 611, # 613, and # 614 based on the pair management table updated in the process 1202 of FIG. The priority table may be updated by sequentially setting higher switching priorities.

  In the example of FIGS. 24A and 24B, the priority is set in the order of 1 to 3. In the example of FIGS. 24A and 24B, the sub logical line # 612 excluded from the switching priority setting candidates is registered in the priority table, but from the switching priority setting candidates. The excluded sub logical line may be set not to be registered in the priority table.

  Furthermore, the total traffic volume for the sub logical lines excluded from the switching priority setting candidates, in other words, the sub logical lines for which the static priority is set, is the sub logical line for which the static priority is not set. Similarly, the pair management table may be used for management.

  In other words, in the processing 1201 and processing 1202 of FIG. 21, the traffic volume measurement and pairing are performed for the sub logical lines for which the static priority is set as well as the sub logical lines for which the static priority is not set. The management table may be updated.

  As a result, for example, even if a sub logical line whose static priority is released by the operator is generated, the node 11 sets the sub logical line to the total traffic volume without delay according to the release of the static priority. It can be included in the setting priority of the switching priority based on.

  Further, for example, even if the static priority setting is changed by the operator after the network operation, the node 11 can update the dynamic priority table without delay according to the static priority setting change. .

  As described above, the node 11 should set the switching priority based on one or both of the static priority information and the switchability information when creating or updating the dynamic priority table (or switching). Sub logical line candidates (to be excluded from priority setting candidates) may be determined.

  Then, the node 11 may set higher priorities for the candidate sub-logical lines for which switching priority is to be set in descending order of the total traffic volume managed in the pair management table.

  Thus, for example, the sub logical line for which static priority is set by an operator or the like is respected, and the other sub logical lines are based on the total traffic volume of the upstream and downstream sub logical lines forming a pair. The switching priority can be set. Therefore, there are a wide variety of switching priority setting variations, and the setting flexibility can be improved.

(Example of failback operation)
Next, with reference to FIG. 25, an operation example of the node 11 when the failure of the work system is recovered after switching the sub logical line to the protection system and the sub logical line is switched back to the work system will be described.

  As illustrated in FIG. 25, when the node 11 detects recovery of the work line (process 2001), the node 11 refers to the dynamic priority table and switches back to the work line in which the sub logical lines are recovered in the order of low priority. Good. For example, the node 11 may output a switchback request to the work line of the sub-logical line in order of low priority, for example, to the redundancy control unit 501 (process 2002).

  The restoration of the work line can be detected by, for example, communication of a control signal between the nodes 11. Further, information about each sub logical line to be switched back may be held in a queue in the node 11.

  The redundancy control unit 501 may perform the switchback process to the work system of the sub logical line that has received the switchback request by controlling the switching unit 112 (see FIG. 26) in response to the reception of the switchback request. (Processing 2003).

  By performing the switchback in the order of low priority, the amount of data loss can be suppressed as compared to the case of performing the switchback in the order of high priority and the case of performing the switchback without considering the priority. For example, a low-priority sub-logical line with a small total amount of uplink and downlink traffic even if a signal interruption occurs in an unstable state shortly after the work line is restored or failure recovery is erroneously detected By carrying out the switchback in order, the amount of data loss can be minimized.

  After the switch-back process, the node 11 may confirm whether or not a signal disconnection has occurred in the work line that is the switch-back destination (process 2004).

  If signal disconnection has not occurred in the work line to be switched back (NO in process 2004; normal route), the node 11 refers to the queue and further confirms whether there is a sub logical line waiting for switch back. (Processing 2005).

  If there is a sub logical line waiting for switchback (YES in process 2005), the node 11 may repeatedly perform processes 2002 to 2005 until there is no sub logical line waiting for switchback.

  If there is no sub logical line waiting for switchback (NO in process 2005), the node 11 may end the switchback process.

  In the process 2004, when a signal disconnection has occurred in the work line to be switched back (YES; abnormal route), the node 11 refers to the dynamic priority table and selects the sub logical line switched back to the work system. You may switch to the protection system in order of priority.

  For example, the node 11 may output a request to switch the sub logical line switched back to the work system to the protection system to the redundancy control unit 501 (see FIG. 27) (process 2006). The redundancy control unit 501 may control the switching unit 112 (see FIG. 26) in response to reception of the switching request, thereby performing switching processing of the sub logical line that has received the switching request to the protection system (processing 2007). ).

  As a result, even if the sub logical line is switched back to the work system after the sub logical line is switched back to the work system, the upstream and downstream total traffic volume that forms a two-way communication pair is increased in order of increasing. Since switching is performed, the amount of data loss can be minimized.

  Thereafter, the node 11 may refer to the queue to check whether there is a sub logical line waiting to be switched to the protection system (processing 2008).

  If there is a sub logical line waiting for switching in the queue (YES in process 2008), the node 11 may repeat the processes 2006 and 2007 until there is no sub logical line waiting for switching.

  If there is no sub logical line waiting for switching in the queue (NO in process 2008), the node 11 may end the switching process of the sub logical line switched back to the work system to the protection system.

(Configuration example of node 11)
Next, a configuration example of the node 11 capable of the above-described operation will be described with reference to FIGS.

  FIG. 26 is a block diagram illustrating a hardware configuration example of the node 11, and FIG. 27 is a block diagram illustrating a functional configuration example of the control unit illustrated in FIG.

  As illustrated in FIG. 26, the node 11 may include a network (NW) interface 111, a switching unit 112, and a control unit 113. The “switching unit” may be referred to as a “switching circuit”, a “protection switch”, or simply a “switch”. The “control unit” may be referred to as a “controller”.

  A plurality of NW interfaces 111 may be provided according to the number of communication paths to which the node 11 can be connected. For example, the NW interface 111 may include a port circuit 114 having a plurality of ports.

  Further, the NW interface 111 may be provided with a driver circuit (not shown) that controls the operation of the NW interface 111.

  The port circuit 114 may include a failure detection circuit 115 that detects a line failure and failure recovery. For example, the processing 1501 in FIG. 19, the processing 2001 and the processing 2004 in FIG. 25 may be performed by the failure detection circuit 115.

  Note that the line failure and the failure recovery detected by the failure detection circuit 115 may be transmitted to the control unit 113 (for example, the redundancy control unit 501 in FIG. 27) exemplarily.

  The switching unit 112 illustratively controls connections between the plurality of NW interfaces 111. By controlling the connection, switching between the work system and the protection system of the sub logical line is possible. For example, the processing 1506 in FIG. 19, the processing 2003 and the processing 2007 in FIG. 25 may be performed by the switching unit 112.

  The control unit 113 illustratively controls the overall operation as the node 11. For example, the control unit 113 may include a CPU 117 and a memory 118. The CPU 117 is an example of a processor circuit having an arithmetic processing capability.

  Instead of the CPU 117 or together with the CPU 117, another arithmetic processing unit, for example, an integrated circuit (IC) such as a microprocessing unit (MPU) or a digital signal processor (DSP) is provided in the control unit 3. May be. A processor circuit having arithmetic processing capability may be referred to as a “computer”.

  The memory 118 stores various programs and data for realizing operations and functions as the node 11. For example, the following data and information may be stored in the memory 118.

・ Sub logical line information (queue) subject to line switching
VLAN tag and transmission traffic information (Fig. 8)
Pair management table (FIGS. 13, 14, and 17)
Dynamic priority table (FIGS. 18, 24A, 24B)
Static priority table (Fig. 22)
Sub logical line switchability table (FIG. 23)

  As the memory 118, for example, a random access memory (RAM) or a read only memory (ROM) may be used. The concept of “memory” may include a storage device such as a hard disk drive (HDD) or a solid state drive (SSD). The concept of “memory” may mean a partial storage area of a storage device.

  The “program” may be referred to as “software” or “application”. The program may include a program that executes the flowcharts illustrated in FIGS. 12, 16, 19 to 21, and 25.

  Focusing on the functional configuration, the control unit 113 may include a redundancy control unit 501, a traffic monitoring unit 502, and a table processing unit 503 as illustrated in FIG.

  For example, the redundancy control unit 501 performs setting, management, and switching control of the work system and the protection system. For example, the redundancy control unit 501 can dynamically set and change the line switching order of the switching unit 112 as described above by operating in cooperation with the traffic monitoring unit 502 and the table processing unit 503. is there.

  Therefore, when a failure in a work system to which a plurality of downlink sub logical lines belong is detected, the redundancy control unit 501 transfers each downlink sub logical line to the protection system in the order of switching priority based on the total traffic volume as described above. It may be understood that this corresponds to an example of a switching control unit.

  For example, the redundancy control unit 501 may include a redundancy configuration setting management unit 511, a line switching request unit 512, and a priority table management unit 513.

  The redundant configuration setting management unit 511 illustratively sets and manages a redundant configuration (work line and protection line). For example, the processing 803 in FIG. 12, the processing 1502, the processing 1503 and the processing 1507 in FIG. 19, and the processing 2005 and the processing 2008 in FIG. 25 may be performed by the redundant configuration setting management unit 511. Note that the switching state such as manual switching by the operator may also be managed by the redundant configuration setting management unit 511.

  The line switching request unit 512 is illustratively based on the switching state in the redundant configuration setting management unit 511, the priority table managed by the priority table management unit 513, and the failure detection information in the failure detection circuit 115. In addition, a line switching request is output to the switching unit 112.

  For example, the processing 1504 and processing 1505 in FIG. 19 and the processing 2002 and processing 2006 in FIG. 25 may be performed by the line switching request unit 512.

  The priority table management unit 513 illustratively manages the above-described priority table. The managed priority table is not limited to the dynamic priority table, and may include a static priority table. For example, the processing 803a of FIG. 20 may be performed by the priority table management unit 513.

  The traffic monitoring unit 502 exemplarily monitors the traffic amount for each sub logical line transmitted / received to / from the counterpart node 11.

  For example, the traffic monitoring unit 502 may include a traffic collecting unit 521 and a traffic information holding unit 522.

  For example, the traffic collection unit 521 measures the amount of traffic transmitted from each sub logical line set in the node 11 and measures the amount of traffic received from each sub logical line set in the partner node. Execute. For example, the measurement may be performed periodically.

  The traffic information holding unit 522 exemplarily holds information on the traffic amount measured by the traffic 521. The traffic volume information to be held may be any one or more of a cumulative value or an average value in a certain period, and a measured value in a certain time interval. The traffic information holding unit 522 may be implemented in the memory 118. The process 1201 of FIG. 16 may be performed by the traffic collection unit 521 and the traffic information holding unit 522.

  The table processing unit 503 illustratively creates and updates the above-described pair management table and priority table. The table created and updated by the table processing unit 503 may include the above-described sub logical line switching availability table.

  The table processing unit 503 may be regarded as an example of a setting unit that sets a higher switching priority for a downlink sub logical line having a larger total traffic volume of sub logical lines forming a pair of bidirectional communication.

  For example, the table processing unit 502 may include a table creation unit 531, a table holding unit 532, and a table update unit 533.

  The table creation unit 531 illustratively creates the above-described pair management table and priority table. For example, the processes 804 to 807 in FIG. 12 may be performed by the table creation unit 531.

  The table holding unit 532 illustratively holds various tables created by the table creation unit 531. The table holding unit 532 may be embodied in the memory 118.

  The table updating unit 533 illustratively updates various tables held in the table holding unit 532.

  The processing 1202 to processing 1204 in FIG. 16 and the processing 1203 a in FIG. 21 may be performed by the priority table management unit 513, the table holding unit 532, and the table updating unit 533.

  It should be noted that the functions of the units 501 (511 to 512), 502 (521, 522), and 503 (531 to 533) illustrated in FIG. 27 need only be implemented in the control unit 113 of the node 11, and are not necessarily illustrated. 27 may not be classified in the manner illustrated in FIG.

  In other words, the configuration example shown in FIG. 27 is merely an example, and the control unit 113 appropriately adds, deletes, divides and divides functional blocks and integrates in an arbitrary combination. Good.

  Similarly, in the hardware configuration example illustrated in FIG. 26, as long as the functions and operations described above are possible, addition or deletion of hardware blocks, division, and integration in an arbitrary combination are appropriately performed in the node 11. May be performed.

(Modification of line ID)
In the embodiment including the above-described modification, the VLAN tag is illustrated as an example of information that can identify a pair of sub-logical lines. However, the information that can identify the pair of sub logical lines is not limited to the VLAN tag.

  For example, the MEP ID (see FIG. 28) set in the Ethernet OAM CCM-PDU frame may be applied to an embodiment including the above-described modification as another example of information that can identify a pair of sub logical lines. Good.

  “OAM” is an abbreviation for “operation, administration and maintenance”, “CCM” is an abbreviation for “continuity check message”, and “PDU” is an abbreviation for “protocol data unit”. “MEP” is an abbreviation for “MEG end point”, and “MEG” is an abbreviation for “maintenance entity group”.

  By acquiring the MEP ID, the node 11 can identify a sub logical line that is paired with the partner node 11. For example, when a redundant configuration is set for the node 11, the MEP ID (peer MEP ID) of the sub logical line paired with the MEP ID for the sub logical line of the own node 11 is set before the network operation is started, for example. Sometimes.

  The node 11 may manage the sub logical line that transmits the CCM frame that matches the peer MEP ID by using the pair management table. Since the MEP ID is set for each VLAN, it can be used as information for identifying the upstream and downstream sub-logical line pairs as with the VLAN tag.

  By using the MEP ID as information for identifying the uplink and downlink sub logical line pairs, the embodiment including the above-described modification can support the case where the CCM-PDU frame is transmitted between the nodes 11.

DESCRIPTION OF SYMBOLS 1 Communication network 11,610,620 Transmission node 12 External communication apparatus 111 Network (NW) interface 112 Switching unit 113 Control unit 114 Port circuit 115 Fault detection circuit 117 CPU
118 Memory 501 Redundancy Control Unit 502 Traffic Monitoring Unit 503 Table Processing Unit 511 Redundancy Configuration Setting Management Unit 512 Line Switch Request Unit 513 Priority Table Management Unit 521 Traffic Collection Unit 522 Traffic Information Holding Unit 531 Table Creation Unit 532 Table Holding Unit 533 Table Update department

Claims (9)

The first transmission node of the first and second transmission nodes performing bidirectional communication with each other,
In the bidirectional communication, a monitoring unit that monitors the traffic amount of a plurality of transmission lines and a plurality of reception lines;
A setting unit that sets a higher switching priority for a transmission line having a larger total traffic volume of a transmission line and a reception line that form a pair of the bidirectional communication;
When a failure in the work system to which each transmission line belongs is detected, a control unit that switches each transmission line to a protection system in the order of the switching priority;
A transmission node comprising:   The setting unit identifies the reception line paired with the transmission line based on information that can identify the reception line set in the traffic received from the second transmission node. The transmission node described in 1.   The transmission node according to claim 2, wherein the setting unit excludes a transmission line having a static switching priority set in advance from the switching priority setting candidates.   The transmission node according to claim 2, wherein the setting unit excludes a transmission line for which switching to the protection system is preset so as not to be set as the switching priority setting candidate.   The transmission node according to claim 2, wherein the information capable of identifying the reception line is information on a VLAN (virtual local area network) tag.   The transmission node according to claim 2, wherein the information capable of identifying the receiving line is a maintenance entity group end point identifier (MEP ID). The controller is
7. Each transmission line that has been switched to the protection system is switched back to the work system with a higher priority as the transmission line has a smaller total traffic volume in response to the failure recovery of the work system. The transmission node according to any one of the above. The controller is
8. The transmission node according to claim 7, wherein when a signal disconnection of a transmission line that has been switched back to the work system is detected, the transmission line is switched to the protection system. In two-way communication between transmission nodes, the amount of traffic on a plurality of transmission lines and a plurality of reception lines is monitored at each of the transmission nodes,
A higher switching priority is set in each of the transmission nodes for a transmission line having a larger total traffic volume of a transmission line and a reception line that form the bidirectional communication pair,
In each of the transmission nodes, when a work system failure to which each transmission line belongs is detected, the transmission lines are switched to the protection system in the order of the switching priority.
Line switching method.

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