Communication control device and communication control method

This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2012-160036, filed on Jul. 18, 2012, the entire contents of which are incorporated herein by reference.

The embodiment discussed herein is related to a communication control device and a communication control method.

Conventionally, in optical transport networks (OTN) using optical fibers as transmission media, a ring network in which a plurality of nodes are connected in a ring shape has become common. This topology of a network can be expanded by interconnecting rings; however, on the occurrence of a node or line failure, to curb the influence of the failure, 8-shaped expansion by connection of single nodes is not usually performed. Usually, for example, in view of the ring protection recommendation G.873.2 defined by International Telecommunication Union-Telecommunication standardization sector (ITU-T), an expansion method which is highly redundant with respect to failure is adopted. Examples of the method include a shared link that connects rings is formed using two nodes and an interconnection link that further improves the redundancy using four nodes arranged in a rectangle shape.

[Patent document 1] Japanese Laid-open Patent Publication No. 11-331227

[Patent document 2] Japanese Laid-open Patent Publication No. 2002-009802

Out of the above-mentioned two types of expansion methods (links), especially, the latter interconnection link is standardized, for example, in ITU-T G.842, and is capable of expansion of a ring network while achieving Bi-directional Line Switched Ring (BLSR)-based protection. However, this method has a problem that nodes other than connection nodes also have to create a table for path line or control traffic to an adjacent ring. This problem can be addressed by, for example, in four connection nodes, by adopting a configuration that links directly connecting diagonally opposite nodes are formed (a so-called “X-shaped configuration”); however, in the above-mentioned ITU-T G.842, a new issue arises. That is, when a network adopts the configuration, there is an increase in the number of branches of a selector or the number of nodes in the network, or the nodes have to include several types of selectors. As a result, the state management of a connecting part (connection nodes or links between nodes) between rings becomes complicated.

According to an aspect of the embodiments, a communication control device that is included in a connecting part of a plurality of rings in a ring network includes: a detecting unit that detects failure in the connecting part; a receiving unit that receives data transmitted from another communication control device on a ring to which the communication control device belongs; a setting unit that determines, when the failure has been detected by the detecting unit, whether to pass the data or return the data in reverse direction from the communication control device depending on a destination to transfer the data received by the receiving unit, and sets a transmission path of the data based on a result of the determination; and a transfer unit that transfers the data in accordance with the transmission path set by the setting unit.

The object and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the claims.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are not restrictive of the invention.

FIG. 1 is a diagram illustrating the topology of rings in a ring network;

FIG. 2 is a diagram illustrating a virtual link formed between connection nodes;

FIG. 3A is a diagram for explaining a method of setting a link redundant path between a master and a slave;

FIG. 3B is a sequence diagram for explaining the operations of connection nodes in the setting of the link redundant path between the master and the slave;

FIG. 4 is a diagram illustrating a redundant path set when a connection node has received traffic;

FIG. 5 is a diagram for explaining how a redundant path is provided in the event of a node failure;

FIG. 6 is a diagram for explaining how a redundant path is provided in the event of a link failure;

FIG. 7 is a block diagram illustrating a configuration of the connection node;

FIG. 8A is a diagram illustrating an example of data stored in a switching table when traffic has been input from a connection node N 6 to a connection node N 4 ;

FIG. 8B is a diagram illustrating paths set when the traffic has been input from the connection node N 6 to the connection node N 4 ;

FIG. 9A is a diagram illustrating an example of data stored in a switching table on the occurrence of failure in a connection node N 3 ;

FIG. 9B is a diagram illustrating paths set on the occurrence of the failure in the connection node N 3 and an example of data stored in a switching table of the connection node N 3 ;

FIG. 10 is a state transition diagram based on switching tables of the connection node;

FIG. 11 is a flowchart for explaining the operation of the connection node;

FIG. 12 is a diagram illustrating the topology of rings in a ring network according to a variation 1 ;

FIG. 13 is a block diagram illustrating a configuration of a connection node according to the variation 1 ;

FIG. 14 is a diagram illustrating the topology of rings in a ring network according to a variation 2 ;

FIG. 15 is a block diagram illustrating a configuration of a connection node according to the variation 2 ;

FIG. 16A is a diagram illustrating the topology of a network according to a variation 3 ;

FIG. 16B is a diagram illustrating the topology of the network according to the variation 3 capable of making a connecting part redundant; and

FIG. 17 is a block diagram illustrating a configuration of a connection node according to the variation 3 .

Preferred embodiments will be explained with reference to accompanying drawings.

Incidentally, the communication control device and communication control method according to the present invention are not limited to the embodiment described below.

First, a network assumed in the present embodiment is illustrated in FIG. 1 . FIG. 1 is a diagram illustrating the topology of rings R 1 and R 2 in a ring network RN. As illustrated in FIG. 1 , the ring network RN has two rings R 1 and R 2 . The ring R 1 includes connection nodes N 1 and N 2 and a node N 5 on a line thereof; the ring R 2 includes connection nodes N 3 and N 4 and a node N 6 on a line thereof. In a connecting part between the rings R 1 and R 2 , the connection nodes N 1 to N 4 are connected via links L 1 to L 6 . Especially, the link L 5 connecting between the diagonally opposite connection nodes N 1 and N 4 and the link L 6 connecting between the diagonally opposite connection nodes N 2 and N 3 cross obliquely in an X-shaped configuration, thereby making the connecting part redundant. By adopting the above-described configuration, the ring network RN achieves the BLSR traffic (a path of an ODU (Optical Data Unit)) transmission without affecting an adjacent node or a link of an adjacent ring.

Subsequently, FIG. 2 is a diagram illustrating a virtual link V 1 formed between the connection nodes N 3 and N 4 . In the ring network RN, a traffic band leading from the connection nodes N 3 and N 4 to the ring R 1 can be estimated to be all traffic bands available to the connection nodes N 3 and N 4 . Therefore, as illustrated in FIG. 2 , the virtual link V 1 is provided as shared protection in a band obtained by subtracting a traffic band closed within the ring R 2 from the traffic band. The virtual link V 1 is formed within the link L 4 between the connection nodes N 3 and N 4 set by the BLSR method, so the virtual link V 1 does not affect the ring protection. Incidentally, there is described the connection nodes N 3 and N 4 as an example; also, in redundancy between the connection nodes N 1 and N 2 , a virtual link can be formed.

FIG. 3A is a diagram for explaining a method of setting a link redundant path between a master and a slave. In FIG. 3A , circled “M” indicates that the connection node is a master node in relation with a linked connection node. Likewise, circled “S” indicates that the connection node is a slave node in relation with a linked connection node. Whether each of the connection nodes N 1 to N 4 is a master node or not is relatively determined from relations with the other linked connection nodes, and can be arbitrarily changed according to a network environment and the traffic state. For example, the connection node N 1 is a master node in relation with the connection node N 3 ; however, the connection node N 1 is a slave node in relation with the connection node N 4 . Furthermore, the connection node N 4 is a master node in relation with the connection node N 1 ; however, the connection node N 4 is a slave node in relation with the connection node N 2 .

In FIG. 3A , let's assume that a failure has occurred, for example, in the link L 2 between the connection nodes N 2 and N 4 . In this case, as a path for the connection node N 2 to perform traffic transmission to the connection node N 4 , there are at least two paths: a path passing through the connection node N 1 (N 2 -N 1 -N 4 ) and a path passing through the connection node N 3 (N 2 -N 3 -N 4 ). In the present embodiment, as described above, the connection node N 2 is set to a master in relation between the connection nodes N 2 and N 4 . Accordingly, the former path passing through the connection node N 1 on the side of the connection node N 2 (the other connection node N 1 on the ring R 1 to which the connection node N 2 belongs) is selected. Therefore, the connection node N 2 exchanges information requested for the setting of a redundant path with the connection nodes N 1 and N 4 . Furthermore, the connection nodes N 2 , N 1 , and N 4 each create a table requested for the execution of traffic transmission using the set redundant path. Incidentally, the setting of a link redundant path can be the setting by signaling on the link or the setting via an NMS (Network Management System).

FIG. 3B is a sequence diagram for explaining the operations of the connection nodes N 2 , N 1 , and N 4 in the setting of a link redundant path between the master and the slave. At S 1 , a message transmitting/receiving unit 11 of the connection node N 2 notifies the connection nodes N 1 and N 4 of an occupied band by using a TS (Tributary Slot) defined in ITU-T G.709. When having received the notification, respective message transmitting/receiving units 11 of the connection nodes N 1 and N 4 reply a TS for the receiving-side setting (S 2 ). At S 3 , in a manner similar to S 2 , the message transmitting/receiving unit 11 of the connection node N 2 replies a TS for the transmitting-side setting. Then, when having received the reply, the message transmitting/receiving units 11 of the connection nodes N 1 and N 4 reply ACK (acknowledgment) (S 4 ). Accordingly, a link redundant path P 10 passing through the connection node N 1 is established between the connection nodes N 2 and N 4 . Incidentally, there is described the link L 2 between the connection nodes N 2 and N 4 as an example; also, with respect to the link L 3 between the connection nodes N 1 and N 3 , a link redundant path can be set by the same method.

As described above, a communication control system 1 is capable of the variable master/slave settings of the connection nodes N 1 to N 4 , thereby avoiding heavy concentration of traffics to a certain connection node. As a result, uneven distribution of the load in the system can be avoided.

Subsequently, the redundant setting method is further explained on the assumption that all the links L 1 to L 6 of the connecting part have the same band. FIG. 4 is a diagram illustrating a redundant path set when the connection node N 4 has received traffic. Here, the connection node N 4 is a master node with respect to the connection node N 2 , and is a slave node with respect to the connection node N 1 . As illustrated in FIG. 4 , on the occurrence of failure in the connection node N 4 , a path P 11 is set up between the connection nodes N 2 and N 3 . Furthermore, on the occurrence of failure in the link L 2 , a path P 12 passing through the connection node N 3 on the side of the connection node N 4 which is a master node is set up. Moreover, on the occurrence of failure in the link L 5 , a path P 13 passing through the connection nodes N 4 -N 2 -N 1 or a path P 14 passing through the connection nodes N 4 -N 3 -N 1 is set up. At this time, in accordance with the above-described BLSR processing, the link L 4 between the connection nodes N 3 and N 4 provides a half of the band for protection of the ring R 2 . On the other hand, the link L 4 provides the other half of the band for a redundant path passing through the connection nodes N 4 -N 3 -N 2 and a redundant path passing through the connection nodes N 3 -N 4 -N 1 . Namely, the link L 4 becomes a shared link shared by the ring R 2 and the connection nodes N 1 to N 4 .

FIG. 5 is a diagram for explaining how a redundant path is provided in the event of a node failure. As illustrated in FIG. 5 , when the connection nodes N 1 to N 3 and the on-ring node N 6 have detected a failure in the connection node N 4 (T 1 ), a failure notification message is transmitted/received between the adjacent connection nodes N 3 and N 6 on the same ring R 2 as the connection node N 4 (T 2 ). This enables return communication between the connection nodes N 3 and N 6 . The failure notification message is, for example, an APS (Automatic Protection Switching) message of an OTN ring defined in ITU-T G.873.2. Upon detection of a node failure in the connection node N 4 or receipt of a failure notification message, the connection node N 3 provides redundancy of the connecting part between the rings R 1 and R 2 . Incidentally, the chronological order of the failure detection at T 1 and the message receiving at T 2 can be shuffled in a random order.

At T 3 , the connection node N 1 sets a protection path on the side of the connection node N 1 out of protection paths between the connection nodes N 1 and N 3 , and the connection node N 2 sets a protection path on the side of the connection node N 2 out of protection paths between the connection nodes N 2 and N 3 . Likewise, the connection node N 3 sets a protection path on the side of the connection node N 3 out of the protection paths between the connection nodes N 1 and N 3 and a protection path on the side of the connection node N 3 out of the protection paths between the connection nodes N 2 and N 3 . Furthermore, the BLSR processing is also executed in the connection nodes N 3 and N 6 (T 4 ), so, for example, in the connection node N 3 , traffic control of transferring a signal addressed to the connection node N 4 to a connection node N 7 becomes possible. Likewise, also in the connection node N 6 , bidirectional traffic control of transferring a signal addressed to the connection node N 4 in which the failure has occurred to a connection node N 8 becomes possible. Incidentally, the chronological order of the path setting at T 3 and the BLSR processing at T 4 can be shuffled in a random order.

As a result of the above-described control, paths P 21 , P 22 , and P 23 are changed to new redundant paths P 21 ′, P 22 ′, and P 23 ′. Namely, the communication control system 1 makes control of switching paths between the connection node N 4 in which the failure has occurred and the connection nodes N 2 and N 1 to paths between the connection node N 3 and the connection nodes N 2 and N 1 by the path setting means illustrated in FIG. 4 . Additionally, as the ring protection operation, the connection node N 3 processes traffics towards L 2 and L 5 input through the protection paths on the ring R 2 , and transfers the traffics to the connection nodes N 2 and N 1 , respectively. As described above, when the surrounding nodes N 1 to N 3 and N 6 have detected a failure in the connection node N 4 which potentially spreads to the ring R 1 , a redundant path is provided to the connecting part including the connection node N 4 based on a result of the detection.

FIG. 6 is a diagram for explaining how a redundant path is provided in the event of a link failure. As illustrated in FIG. 6 , when the connection node N 2 has detected a failure in the link L 2 between the connection nodes N 2 and N 4 (T 11 ), the connection node N 4 notifies the connection node N 3 on the same ring R 2 as the master-side connection node N 4 of the failure in the link L 2 (T 12 ). Incidentally, in the event of a link failure, unlike a node failure, the return control is not performed, so there is no APS message transmitted/received.

At T 13 , the connection node N 2 sets a protection path on the side of the connection node N 2 out of protection paths between the connection nodes N 2 and N 3 , and the connection node N 4 sets a protection path on the side of the connection node N 4 out of protection paths between the connection nodes N 4 and N 3 . Likewise, the connection node N 3 sets a protection path on the side of the connection node N 3 out of the protection paths between the connection nodes N 3 and N 2 and a protection path on the side of the connection node N 3 out of the protection paths between the connection nodes N 3 and N 4 .

As a result of the above-described control, a traffic path between the connection nodes N 4 and N 2 is changed to a redundant path passing through the connection nodes N 4 -N 3 -N 2 . At this time, the connection node N 2 only has to perform the normal operation based on a result of the detection of the link 2 failure. As described above, when the surrounding node N 2 has detected a failure in the connection node N 4 which potentially spreads to the ring R 1 , a redundant path is provided to the connecting part including the connection node N 4 based on a result of the detection.

FIG. 7 is a block diagram illustrating a configuration of the connection node N 4 . As illustrated in FIG. 7 , the connection node N 4 includes the message transmitting/receiving unit 11 , a switching table 12 , a port-state management unit 13 , optical-signal processing units 14 a to 14 h , failure detecting units 15 a to 15 c , signal processing units 16 a to 16 h , an APS processing unit 17 , and an ODU switch 18 . These components are connected so as to input/output a signal or data unidirectionally or bi-directionally. The connection node N 4 is connected to another node 30 via a node setting device 20 for controlling the switching table 12 . The node setting device 20 is, for example, an NMS (Network Management System).

The message transmitting/receiving unit 11 transmits/receives a signaling message with the other connection nodes N 1 to N 3 as illustrated in FIG. 3B . Although details of the switching table 12 will be described later, information referenced in the switching is stored in the switching table 12 . The port-state management unit 13 manages states of ports for connecting to the other connection nodes N 1 to N 3 . The optical-signal processing units 14 a to 14 h perform processes for the end of an optical signal, an OUT (Optical Transport Unit), and a HO (High Order) ODU at the ports for connecting to the other connection nodes N 1 to N 3 .

The failure detecting units 15 a to 15 c are provided at each of links to which the connection node N 4 is connected, and detects a signal for notification of failure in another node or a link from the optical signal and inserts the signal into the optical signal. The signal processing units 16 a to 16 h perform a separation process of extracting a LO (Lower Order) ODU from an optical signal input from the corresponding optical-signal processing units 14 a to 14 h , and multiplex the input LO ODU and output the multiplexed LO ODU to the subsequent optical-signal processing units 14 a to 14 h . The APS processing unit 17 performs an APS (Automatic Protection Switching) process of the ring R 2 on the connection nodes N 3 and N 6 , and outputs a result of the process to the port-state management unit 13 . The ODU switch 18 performs the exchange control of the LO ODU.

The configuration of the connection node N 4 is exemplarily explained above; the other connection nodes N 1 , N 2 , and N 3 have the same configuration as the connection node N 4 described above. Therefore, common components are denoted by the same reference numerals, and illustration and detailed description of the components are omitted.

FIG. 8A is a diagram illustrating an example of data stored in a switching table 12 a when traffic has been input from the connection node N 6 to the connection node N 4 . FIG. 8B is a diagram illustrating paths Xi, Yi, and Zi set when the traffic has been input from the connection node N 6 to the connection node N 4 . Incidentally, i is an integer (a natural number) of 1 or larger, and n is an integer meeting n>2i. As illustrated in FIG. 8A , the switching table 12 a has updatably stored therein LO ODU type, ODU path name, and destination to transfer in switching with respect to each PSI (Payload Structure Identifier)/TS. The ODU switch 18 determines which of the connection nodes N 1 to N 3 an ODU with a corresponding path as a transmission path is to be transferred by reference to the switching table 12 a . Respective destinations to transfer in switching in case of failure and in normal time are set separately; especially, in case of failure, destinations to transfer depending on locations of failure are individually set, so it is possible to achieve the highly-flexible switching depending on a network state.

For example, in PSI/TS “1” on the first line of the switching table 12 a , “ODUk X1 ” is defined as an LO ODU type, so a corresponding path is a “path X 1 ”. With reference to FIG. 8B , a LO ODU with the “path X 1 (Xi in FIG. 8 B)” as a transmission path is transferred to the connection node N 3 in normal time, so “N 3 ” is stored as a destination to transfer in “(1) normal time” in the switching table 12 a . Also in case of “(2) failure on ring”, “N 3 ” is set as a destination to transfer in switching. However, in case of failure in the connection node N 3 , the ODU switch 18 does not switch to the connection node N 3 , so a destination to transfer a LO ODU is set to “N 6 ”, thereby enabling BLSR processing between the connection nodes N 4 and N 7 . Furthermore, the “path X 1 ” does not include the link L 2 ; therefore, even in the event of a failure in the link L 2 , the “path X 1 ” is not affected by the failure. Thus, “N 3 ” is set as a destination to transfer in case of “(4) link L 2 failure”.

Incidentally, a normally-used slot number in PSI/TS is n/2, slots (n/2)+1 onward are applied to failure on the ring R 2 . However, the connection node N 3 adjacent to the connection node N 4 processes a LO ODU to be transferred to the connection nodes N 1 and N 2 without performing the BLSR processing by reference to a switching table held therein.

FIG. 9A is a diagram illustrating an example of data stored in a switching table 12 b on the occurrence of failure in the connection node N 3 . FIG. 9B is a diagram illustrating paths set on the occurrence of failure in the connection node N 3 and an example of data stored in a switching table 12 c of the connection node N 3 . As illustrated in FIG. 9A , when a node failure has occurred in the connection node N 3 , path setting to PSI/TS (n/2)+1 onward is performed, so the switching table 12 c defined in the connection node N 3 is referenced. As a result, a LO ODU on a path Vi that the connection node N 3 has received is transferred to the connection node N 1 or the connection node N 7 , and a LO ODU on a path Wi that the connection node N 3 has received is transferred to the connection node N 2 or the connection node N 7 . Furthermore, for example, a LO ODU addressed to the connection node N 4 that has been transmitted from a node N 9 normally passes through the node N 7 and the connection node N 3 ; however, in the event of a failure in the connection node N 3 , BLSR processing is performed. Therefore, the LO ODU addressed to the connection node N 4 is returned before the connection node N 3 (the connection node N 7 ) and gets to the connection node N 4 through the nodes N 9 , N 8 , and N 6 .

Subsequently, the transition of a mode determined by the port-state management unit 13 of the connection node N 4 is explained. FIG. 10 is a state transition diagram based on the switching tables 12 a to 12 c of the connection node N 4 . As illustrated in FIG. 10 , the connection node N 4 has three modes M 2 to M 4 according to types of failure

in addition to a “normal mode M 1 ” on the non-occurrence of failure. Namely, on the occurrence of failure on the ring R 2 , the connection node N 4 is set into the “ring protection mode M 2 ”; on the occurrence of failure in the connection link L 2 or L 4 , the connection node N 4 is set into the “ring connection protection mode M 3 ”. Furthermore, on the occurrence of failure in any of the other nodes N 1 to N 3 , the connection node N 4 is set into the “connection link protection mode M 4 ”.

These four modes M 1 to M 4 can be bi-directionally transited on the occurrence of failure or the recovery from the failure; however, the modes M 1 to M 4 do not always have to be transitable to all the other modes. For example, the normal mode M 1 can be transited to the modes M 2 to M 4 (U 1 to U 6 ); however, the ring protection mode M 2 is not directly transited to the connection link protection mode M 4 . Likewise, the connection link protection mode M 4 is not directly transited to the ring connection protection mode M 3 . Furthermore, the modes M 1 to M 4 are not always set exclusively; the connection node N 4 can be set into several modes simultaneously. For example, as illustrated in FIG. 10 , the connection node N 4 can adopt a state where the different modes M 2 and M 4 coexist in one node (a state of a two-way mode M 5 ). Likewise, the connection node N 4 can adopt a state of a two-way mode M 6 where the different modes M 3 and M 4 coexist in one node. Incidentally, the connection nodes N 1 and N 2 illustrated in FIG. 6 operate in the “ring connection protection mode M 3 ” which is a destination to transit on the occurrence of failure in the connection links L 1 to L 3 .

Subsequently, the operation of the connection node N 4 is explained. FIG. 11 is a flowchart for explaining the operation of the connection node N 4 .

When the failure detecting unit 15 b of the connection node N 4 being in the normal mode M 1 has detected a failure in the connection link L 4 (S 11 ), the port-state management unit 13 determines whether the current mode is the ring connection protection mode M 3 (S 12 ). As a result of the determination, when the connection node N 4 is not in the ring connection protection mode M 3 (NO at S 12 ), the port-state management unit 13 determines whether the failure detected at S 11 is a failure in a master port (S 13 ). As a result of the determination, when a location of the failure is the master port (YES at S 13 ), the message transmitting/receiving unit 11 transmits a message instructing to activate the switching table 12 c to an adjacent connection node (for example, the connection node N 3 ) (S 14 ).

At S 15 , the port-state management unit 13 of the connection node N 4 checks whether there are any other connection links. As a result of the check, when there is a connection link other than the connection link L 4 (for example, the links L 2 and L 5 ) in the connection node N 4 (YES at S 15 ), the port-state management unit 13 changes the port mode of the connection link from master to slave. Furthermore, the port-state management unit 13 performs signaling to use the connection link as a part of a redundant path (S 16 ). Then, the connection node N 4 returns to the normal mode M 1 .

Incidentally, when the connection node N 4 is in the ring connection protection mode M 3 at S 12 (YES at S 12 ) or when a location of the failure is a slave port at S 13 (NO at S 13 ), the port-state management unit 13 switches the connection port of the connection node N 4 from the slave to the master (S 17 ). After that, the connection node N 4 returns to the normal mode M 1 . Furthermore, at S 15 , when there is no other connection link (NO at S 15 ), a connection link vanishes from the connection node N 4 due to the occurrence of the failure in the connection node N 4 . Therefore, also in this case, the connection node N 4 returns to the normal mode M 1 .

Through a sequence of the steps described above, the communication control system 1 can place a master node in the both rings R 1 and R 2 . Therefore, even on the occurrence of failure in the ring network RN, the communication control system 1 can prevent traffic from being unevenly distributed in the ring R 2 , one of the two rings R 1 and R 2 composing the network.

Variation 1

Subsequently, a variation 1 is explained. The communication control system 1 according to the above embodiment can adopt the variation as described below. FIG. 12 is a diagram illustrating the topology of a ring R 1 and a plurality of rings R 2 , R 3 , and R 4 in a ring network RN according to the variation 1 . FIG. 13 is a block diagram illustrating a configuration of the connection node N 4 according to the variation 1 . The ring network RN and the connection node N 4 in the variation 1 include the same components as the ring network RN and the connection node N 4 in the above embodiment. Therefore, in the variation 1 , components in common with those in the above embodiment are denoted by reference numerals having the same last number as in the embodiment, and detailed description of the components is omitted. The variation 1 differs from the above embodiment in the number of rings.

Namely, in the above embodiment, the ring network RN is formed by connection of single rings; however, in the variation 1 , the plurality of rings R 2 , R 3 , and R 4 are formed as illustrated in FIG. 12 . To respond to this, as illustrated in FIG. 13 , the connection node N 4 includes three sets of switching tables 22 , optical-signal processing units 24 a and 24 g , APS processing units 27 , and ODU switches 28 to correspond to the number of rings. In the variation 1 , the maximum value of bands of the connection rings R 1 to R 4 is max{Σ (a band between the connection nodes N 1 and N 2 ), (a band between the connection nodes N 3 and N 4 )}. The communication control system 1 according to the variation 1 can respond to an increase in the number of rings only by increasing the number of ports; however, the connection nodes N 1 and N 2 need to have the function of multiplexing and separating respective bands of the rings R 2 , R 3 , and R 4 . Incidentally, in the variation 1 , one of the two rings is a plurality of rings; alternatively, both of the rings can be the plurality of rings. Furthermore, the number of rings formed is not limited to three, and can be two or four or more.

Variation 2

The communication control system 1 according to the above embodiment can further adopt a variation as described below. FIG. 14 is a diagram illustrating the topology of a ring R 1 and the plurality of rings R 5 , R 6 , and R 7 in a ring network RN according to a variation 2 . As illustrated in FIG. 14 , the topology of the ring network RN according to the variation 2 is about the same as the ring network RN according to the above-described variation 1 , but differs in the number of links between the connection nodes N 3 and N 4 . Namely, in the variation 1 , the connection nodes N 3 and N 4 are connected by three links L 4 , L 7 , and L 8 ; however, in the variation 2 , there is adopted a configuration that the connection nodes N 3 and N 4 are multiplexed and connected by one link. FIG. 15 is a block diagram illustrating a configuration of the connection node N 4 according to the variation 2 . Components of the connection node N 4 according to the variation 2 are the same as in the variation 1 , so detailed description of the components is omitted; however, as illustrated in FIG. 15 , the connection node N 4 includes one each of the switching table 22 , the optical-signal processing unit 24 g , and the ODU switch 28 , and multiplexes the APS transmission in the rings R 5 to R 7 .

Variation 3

The communication control system 1 according to the above embodiment can be applied to not only a ring network but also the other network topologies. FIG. 16A is a diagram illustrating the topology of a network N according to a variation 3 . As illustrated in FIG. 16A , in the network N according to the variation 3 , dual-homing is achieved by setting paths between nodes N 12 a to N 12 c and nodes N 13 a to N 13 c via the connection nodes N 1 to N 4 . In this topology, an NNI (Network Network Interface) is provided between the connection nodes N 1 , N 2 and the connection nodes N 3 , N 4 . FIG. 16B is a diagram illustrating the topology of the network N according to the variation 3 capable of making a connecting part redundant. As illustrated in FIG. 16B , for example, on the occurrence of failure in links L 7 , L 9 , and L 10 between the nodes N 12 a to N 12 c and the connection node N 1 , links L 8 , L 11 , and L 12 are provided alternatively; however, there are no effects on links L 13 , L 15 , and L 16 between the connection node N 3 and the nodes N 13 a to N 13 c . Therefore, the provision of redundancy to the operation inside a network N−1 is completed. FIG. 17 is a block diagram illustrating a configuration of the connection node N 4 according to the variation 3 . Components of the connection node N 4 according to the variation 3 are the same as in the variation 2 , so detailed description of the components is omitted; however, as illustrated in FIG. 17 , the connection node N 4 includes one each of the switching table 22 , the optical-signal processing unit 24 g , and the ODU switch 28 , and multiplexes the APS transmission in links L 2 and L 3 .

As described above, the connection node N 3 according to the present embodiment is included in the connecting part of the rings R 1 and R 2 in the ring network RN. The connection node N 3 includes the failure detecting unit 15 a , the optical-signal processing units 14 d , 14 f , and 14 h , the ODU switch 18 , and the optical-signal processing units 14 c , 14 e , and 14 g . The failure detecting unit 15 a detects failure in the above-mentioned connecting part (for example, the connection node N 4 in FIG. 5 and the link L 2 in FIG. 6 ). The optical-signal processing units 14 d , 14 f , and 14 h receive data (an ODU) transmitted from the other node N 6 on the ring R 2 to which the connection node N 3 belongs. When the failure has been detected by the failure detecting unit 15 a , the ODU switch 18 determines whether to pass the data toward the other connection nodes N 1 and N 2 on the different ring R 1 from the ring R 2 or return the data in the reverse direction from the connection node N 3 (BLSR processing) depending on a destination to transfer the data received by the optical-signal processing units 14 d , 14 f , and 14 h . For example, when a destination to transfer is within the different ring R 1 from the ring to which the connection node N 3 belongs, the connection node N 3 passes the data and transfers the data to the opposite ring R 2 . On the other hand, when a destination to transfer is within the same ring R 2 as the connection node N 3 , the connection node N 3 transfers the data in the reverse direction (the direction from which the data was transmitted, the direction of the node N 7 in FIG. 5 ) at the connection node N 3 , thereby preventing the data from being transmitted to the failure part. Furthermore, the ODU switch 18 sets a transmission path of the data based on a result of the determination. The optical-signal processing units 14 c , 14 e , and 14 g transfer the data in accordance with the transmission path set by the ODU switch 18 .

Namely, the communication control system 1 achieves the protection by connecting a plurality of ring networks RN to which the BLSR method is applied by four connection nodes. The four connection nodes are arranged, for example, in a rectangle shape, and the adjacent nodes are directly linked together. Furthermore, diagonally opposite connection nodes are directly connected so that linked links cross obliquely (in an X-shaped configuration). Specifically, with respect to traffic transmitted on the ring, the connection node N 3 performs: (1) traffic setting and switching for transmission to another ring, (2) provision of a connection link, and (3) provision of redundant traffic based on a communication state. Consequently, even on the occurrence of failure on the ring including failure in the connection node N 3 , the connection node N 3 can provide redundancy and maintain the protection function without destroying the BLSR-based framework. In addition, highly-reliable network expansion becomes possible.

In other words, even on the occurrence of failure in one of the rings composing the ring network RN or failure in the connecting part between the rings, the communication control system 1 can provide the protection function using a redundant path without affecting the operation of the other ring. Furthermore, the communication control system 1 can delete a large number of management items (for example, a ring map) in the connection nodes or a line connection table created with respect to each of the connection nodes. This enables reduction of the memory capacity, reduction of the processing load associated with the management, and the fast communication control.

In the connection node N 3 , the failure detecting unit 15 a can be configured to detect failure in the link L 2 connecting the rings R 1 and R 2 out of the connecting part. Furthermore, when a failure in the link L 2 has been detected by the failure detecting unit 15 a , the ODU switch 18 can set, as a transmission path of the data, a path making the link L 2 redundant through the ring R 1 on the side of the connection node N 2 set to a master out of a plurality of connection nodes N 2 and N 4 connected by the link L 2 . This prevents transfer data from being excessively provided to either one of the connection nodes N 2 and N 4 placed at both ends of the link L 2 . As a result, uneven distribution of the load between the connection nodes N 2 and N 4 can be avoided.

Furthermore, in the connection node N 3 , the connecting part can include the links L 5 and L 6 that connect the connection nodes N 3 and N 4 on the same ring R 2 as the connection node N 3 and the connection nodes N 1 and N 2 on the different ring R 1 from the ring R 2 in the shape of reciprocally-crossed diagonal lines (in a so-called X-shaped configuration). This makes the connecting part between the rings R 1 and R 2 redundant. Therefore, the communication control system 1 composing the ring network RN can achieve the higher protection function for data transfer across the rings R 1 and R 2 in a simple configuration. As a result, it is possible to improve the reliability of the system and distribute the load among the links L 2 , L 3 , L 5 , and L 6 in the connecting part.

Moreover, the connection node N 3 can further include the switching table 12 that updatably stores therein identification information of the data (for example, a LO ODU type), a transmission path of the data, and a destination to transfer the data with respect to each location of failure ((2) to (4) illustrated in FIG. 8A ) in an associated manner. Furthermore, the ODU switch 18 can set a transmission path of the data so that a destination to transfer the data is a transfer destination corresponding to a location of the failure by reference to the switching table 12 . Accordingly, the connection node N 3 can easily and rapidly set a path including the optimum transfer destination for protection by redundancy as a new transmission path depending on the location of failure. Consequently, it is possible to achieve the more adaptive, highly-flexible data transfer control (switching) with high accuracy.

Incidentally, in the above embodiment, on the assumption of application to an OTN, there is described a data unit subject to the traffic control as a LO ODU. However, the data unit is not limited to this. For example, a frame, a packet, and a cell of an ATM (Asynchronous Transfer Mode) can be set as the data unit depending on a type of network. Furthermore, the topology of the network is not limited to the ring, and can be a mesh network, a star network, a bus network, a tree network, and a network that the above-mentioned topologies are combined.

Components of the connection nodes N 1 to N 4 do not always have to be physically configured as illustrated in the drawings. Namely, the specific forms of division and integration of the units are not limited to those illustrated in the drawings, and all or some of the units can be configured to be functionally or physically divided or integrated in arbitrary units depending on respective loads and use conditions, etc. For example, the optical-signal processing units 14 a to 14 h for performing a HO (High Order) process and the signal processing units 16 a to 16 h for performing a LO (Low Order) process or the ODU switch 18 and the switching table 12 can be integrated into one unit. On the contrary, the optical-signal processing units 14 a to 14 h can be divided into a part that performs a process relating to an OTU (Optical Transport Unit) and a part that performs a process relating to an ODU (Optical Data Unit). Furthermore, a memory storing therein the switching table 12 , etc. can be an external device of the connection nodes N 1 to N 4 , and the external memory can be connected to the connection nodes N 1 to N 4 via a network or a cable.

According to an aspect of a communication control device discussed in the present application, it is possible to achieve a ring network that has a protection function and is easy to manage a connecting part between rings in a simple configuration.

All examples and conditional language provided herein are intended for pedagogical purposes of aiding the reader in understanding the invention and the concepts contributed by the inventor to further the art, and are not to be construed as limitations to such specifically recited examples and conditions, nor does the organization of such examples in the specification relate to a showing of the superiority and inferiority of the invention. Although one or more embodiments of the present invention have been described in detail, it should be understood that the various changes, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention.