Abstract:
The present invention discloses a method for controlling a physical bandwidth of a ring-based network by employing a ring application of a data link layer that operates in a physical layer. The method includes the steps of a) requesting each of a plurality of node apparatuses included in the ring-based network to confirm whether the bandwidth can be changed, b) instructing each node of the apparatuses to prepare for the bandwidth change upon receiving a confirmation that the bandwidth can be changed, c) reporting that the preparation for the bandwidth change is completed, and d) changing the bandwidth by using a bandwidth changing function of the ring application upon receiving the report of the completion of the preparation for the bandwidth change.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention generally relates to a bandwidth controlling method and a node apparatus station for a ring-based network.  
         [0003]     2. Description of the Related Art  
         [0004]      FIG. 1  shows an exemplary configuration of a ring-based network in which RPR (Resilient Packet Ring) is applied over a SONET (Synchronous Optical Network). In  FIG. 1 , by providing SONET path in two directions between each of the adjacently disposed node apparatuses (RPR stations)  1 A- 1 D, all of the the node apparatuses  1 A- 1 D can be connected by a pair of bidirectional SONET paths of equal bandwidth. An RPR ring is provided over this SONET path.  
         [0005]     A technology for managing/controlling the bandwidth and flow of an RPR network is disclosed in Japanese Laid-Open Patent Application NO. 2004-289799.  
         [0006]     With these kinds of ring-based networks, there is a demand to increase/decrease the physical bandwidth without having to affect the traffic (paths being in use). Nevertheless, such ring-based networks have the following disadvantages.  
         [0007]     First, in a case of changing the ring bandwidth of the RPR network (RPR over SONET) from an upper level NMS (Network Management System), it is necessary for the SONET path to be removed in order to reset the bandwidth. This causes a state of signal disconnection for a maximum period of approximately 30 minutes (although this may vary depending on the number of nodes in the network).  
         [0008]     Second, although the changing of a SONET path between a pair of adjacent nodes (i.e. changing of a single span) may be performed in a short period of time, the RPR requires the bandwidth for all spans in the ring network to be changed simultaneously since any inconsistency in bandwidth among the spans may cause an abnormality in the performance of the RPR. Therefore, the bandwidth of the ring cannot be changed with an RPR application.  
         [0009]     Furthermore, in a case where a failure occurs in the SONET path, an RPR protection function switches the RPR regardless of whether the error has little influence with respect to a bandwidth guarantee service. This leads to a problem of inefficient use of bandwidth.  
       SUMMARY OF THE INVENTION  
       [0010]     It is a general object of the present invention to provide a bandwidth controlling method and a node apparatus station for a ring-based network that substantially obviates one or more of the problems caused by the limitations and disadvantages of the related art.  
         [0011]     Features and advantages of the present invention will be set forth in the description which follows, and in part will become apparent from the description and the accompanying drawings, or may be learned by practice of the invention according to the teachings provided in the description. Objects as well as other features and advantages of the present invention will be realized and attained by a bandwidth controlling method and a node apparatus station for a ring-based network particularly pointed out in the specification in such full, clear, concise, and exact terms as to enable a person having ordinary skill in the art to practice the invention.  
         [0012]     To achieve these and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, the invention provides a method for controlling a physical bandwidth of a ring-based network by employing a ring application of a data link layer that operates in a physical layer, the method including the steps of: a) requesting each of a plurality of node apparatuses included in the ring-based network to confirm whether the bandwidth can be changed; b) instructing each node of the apparatuses to prepare for the bandwidth change upon receiving a confirmation that the bandwidth can be changed; c) reporting that the preparation for the bandwidth change is completed; and d) changing the bandwidth by using a bandwidth changing function of the ring application upon receiving the report of the completion of the preparation for the bandwidth change.  
         [0013]     In the method for controlling a physical bandwidth of a ring-based network by employing a ring application of a data link layer that operates in a physical layer according to an embodiment of the present invention, the request of step a) may be executed in accordance with a command from a network management system connected to the ring-based network, wherein the completion of the bandwidth change in step d) may be reported to the network management system.  
         [0014]     In the method for controlling a physical bandwidth of a ring-based network by employing a ring application of a data link layer that operates in a physical layer according to an embodiment of the present invention, the bandwidth change may include an increase of the bandwidth, wherein the bandwidth can be increased if the bandwidth requested to be increased is less than the bandwidth that is unused in the ring-based network, wherein the bandwidth cannot be increased if the bandwidth requested to be increased is greater than the bandwidth that is unused in the ring-based network.  
         [0015]     In the method for controlling a physical bandwidth of a ring-based network by employing a ring application of a data link layer that operates in a physical layer according to an embodiment of the present invention, the bandwidth change may include a decrease of the bandwidth, wherein the bandwidth can be decreased if it is determined that predetermined bandwidth will be available after the bandwidth is decreased, wherein the bandwidth cannot be decreased if it is determined that the predetermined bandwidth will be unavailable after the bandwidth is decreased.  
         [0016]     In the method for controlling a physical bandwidth of a ring-based network by employing a ring application of a data link layer that operates in a physical layer according to an embodiment of the present invention, the request of step a) may be executed when a failure is detected in the ring-based network.  
         [0017]     In the method for controlling a physical bandwidth of a ring-based network by employing a ring application of a data link layer that operates in a physical layer according to an embodiment of the present invention, an RPR switching function may be activated in a case where the bandwidth cannot be decreased when the failure is detected in the ring-based network.  
         [0018]     In the method for controlling a physical bandwidth of a ring-based network by employing a ring application of a data link layer that operates in a physical layer according to an embodiment of the present invention, the request of step a) may be executed when a recovery of a failure is detected in the ring-based network.  
         [0019]     In the method for controlling a physical bandwidth of a ring-based network by employing a ring application of a data link layer that operates in a physical layer according to an embodiment of the present invention, the physical bandwidth of the ring-based network may include at least one of a SONET bandwidth and a SDH bandwidth.  
         [0020]     In the method for controlling a physical bandwidth of a ring-based network by employing a ring application of a data link layer that operates in a physical layer according to an embodiment of the present invention, the bandwidth changing function of the ring application may include an RPR function, wherein the control information may include an RPR control frame.  
         [0021]     Furthermore, the present invention provides a node apparatus used for controlling a physical bandwidth of a ring-based network by employing a ring application of a data link layer that operates in a physical layer, the node apparatus including: a requesting part for requesting another node apparatus included in the ring-based network to confirm whether the bandwidth can be changed; an instructing part for instructing the other node apparatus to prepare for the bandwidth change upon receiving a confirmation that the bandwidth can be changed; a reporting part for reporting that the preparation for the bandwidth change is completed; and a changing part for changing the bandwidth by using a bandwidth changing function of the ring application upon receiving the report of the completion of the preparation for the bandwidth change.  
         [0022]     Other objects and further features of the present invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0023]      FIG. 1  is a schematic view showing an exemplary configuration of a ring-based network;  
         [0024]      FIG. 2  is a schematic view showing an exemplary configuration of a node apparatus according to an embodiment of the present invention;  
         [0025]      FIG. 3  is a schematic view showing an exemplary format of a control frame;  
         [0026]      FIG. 4  is a schematic view showing an exemplary format of a control data unit inside a control frame;  
         [0027]      FIG. 5  is a schematic view showing an exemplary format of user data inside a control data unit;  
         [0028]      FIG. 6  is a schematic view for describing an exemplary case of increasing the bandwidth of a ring network;  
         [0029]      FIG. 7  is a schematic view for describing an exemplary case of decreasing the bandwidth of a ring network;  
         [0030]      FIG. 8  is a schematic view for describing an exemplary case of decreasing the bandwidth of a ring network when there is a failure in a path of the network (Part 1);  
         [0031]      FIG. 9  is a schematic view for describing an exemplary case of decreasing the bandwidth of a ring network when there is a failure in a path of the network (Part 2);  
         [0032]      FIG. 10  is a schematic view for describing an exemplary process of increasing/decreasing the bandwidth of a ring network (Part 1);  
         [0033]      FIG. 11  is a schematic view for describing an exemplary process of increasing/decreasing the bandwidth of a ring network (Part 2);  
         [0034]      FIG. 12  is a flowchart for describing an exemplary process of determining whether to decrease the bandwidth of a ring network;  
         [0035]      FIG. 13  is a schematic view for describing an exemplary process of decreasing the bandwidth of a ring network when there is a failure in a path of the network; and  
         [0036]      FIG. 14  is a schematic view for describing an exemplary process of restoring the bandwidth of a ring network when recovering from a failure in a path of the network. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0037]     In the following, embodiments of the present invention will be described with reference to the accompanying drawings.  
         [0038]      FIG. 2  shows an exemplary configuration of a node apparatus  1  according to the first embodiment of the present invention. In  FIG. 1 , the node apparatus  1  includes an NMS information sending section  11 , an RPR processing section  12 , a VCG (Virtual Concatenation Group) controlling section  13 , and a VCG generating/detecting section  14  (which includes an EOS mapping/demapping part  15  and a VCG generation/detection processing part  16 ).  
         [0039]     The NMS information sending section  11  has a function of sending bandwidth increase/decrease information to the RPR processing section upon receiving a command to increase/decrease the bandwidth (bandwidth increase/decrease command) from an upper level NMS, and a function of sending an answer to the NMS upon receiving a bandwidth increase/decrease result and a VCG status from the RPR processing section  12 .  
         [0040]     In a case where the RPR processing section  12  receives the bandwidth increase/decrease information from the NMS information sending section  11  (i.e. in a case where the node apparatus  1  is the master station), the RPR processing section  12  has a function of conducting a predetermined process for increasing/decreasing the bandwidth and sending a bandwidth increase/decrease result and a VCG status to the NMS information sending section  11 .  
         [0041]     Furthermore, the RPR processing section  12  also has a function of generating a control frame and sending the control frame to the VCG generating/detecting section  14  as well as receiving a control frame of another node apparatus from the VCG generating/detecting section  14 . Furthermore, the RPR processing section  12  also has a function of sending the received bandwidth increase/decrease information (VCG control information) to the VCG controlling section  13  and determining whether to increase/decrease the bandwidth according to a VCG status obtained from the VCG controlling section.  
         [0042]     The VCG controlling section  13  has a function of controlling the increase/decrease of bandwidths in the VCG generating/detecting section  14  in accordance with the bandwidth increase/decrease information from the RPR processing section  12 , and obtaining a VCG status from the VCG generating/detecting section  14 .  
         [0043]     The EOS mapping/demapping part  15  in the VCG generating/detecting section  14  has a function of mapping/demapping various parameters (e.g. EOS (End Of Sequence) serving to designate the path which is to be a member of the VCG) to the overhead information. The VCG generation/detection processing part  16  in the VCG generating/detecting section  14  has a function of sending/receiving control frames, sending/receiving VCG frames, and detecting/reporting VCG status.  
         [0044]      FIG. 3  shows an exemplary format of a control frame generated by the RPR processing section  12  (defined in IEEE 802.17) according to an embodiment of the present invention. The control frame includes items, such as, TTL (Time To Live), Base Control, DA (Destination Address), SA (Source Address), TTL Base, Extended Control, HEC (Header Error Check), Control Type, Control Version, Control Data Unit, and FCS. The values allotted to the Control Type are listed in the table shown in  FIG. 3 . In this example of the present invention, the control type of “OA16: CT 13 OAM 13 ORG: OAM organization specific frame” is used.  
         [0045]      FIG. 4  shows an exemplary format of a control data unit inside a control frame according to an embodiment of the present invention. In this example of the present invention, “User Data” is used.  
         [0046]      FIG. 5  shows an exemplary format of user data inside a control data unit according to an embodiment of the present invention. The exemplary format includes a Frame ID, a Frame Type, and the Number of Channels. The values listed in the table of  FIG. 5  are allotted as the frame type according to an embodiment of the present invention.  
         [0047]      FIG. 6  shows an exemplary case of increasing the bandwidth of the ring network.  FIG. 7  shows an exemplary case of decreasing the bandwidth of the ring network.  FIGS. 8 and 9  show exemplary cases of decreasing the bandwidth of a ring network when there is a failure in a path of the network.  FIG. 8  shows an exemplary case of decreasing the bandwidth of the path and  FIG. 9  shows an exemplary case of separating a portion of a path.  
         [0048]      FIGS. 10-11  show an exemplary process of increasing/decreasing the bandwidth of a ring network according to an embodiment of the present invention.  FIG. 12  shows an exemplary process of determining whether to decrease the bandwidth of a ring network.  FIG. 13  shows an exemplary process of decreasing the bandwidth of a ring network when there is a failure in a path of the network.  FIG. 14  shows an exemplary process of restoring the bandwidth of a ring network when recovering from a failure in a path of the network.  
         [0049]     With reference with the aforementioned drawings, the process and operation according to an embodiment of the present invention are described below.  
         [0000]     [Process of Increasing Bandwidth] 
         [0050]     An example of increasing the ring bandwidth from “STSxx−nV” to “STSxx−(n+m) V” is described with reference to  FIG. 6 . It is to be noted that “STS1−nV” is a name of a SONET path, and “n” is the number of paths included in the VCG. Furthermore, although only one ring (a ring for one direction) is illustrated in  FIG. 6 , both the one ring and another ring (a ring for the other direction) are to have their bandwidths increased.  
         [0051]     In  FIG. 10 , when the NMS sends a bandwidth increase command to the node apparatus  1 A (Step S 11 ), the node apparatus  1 A transmits (broadcasts) a “bandwidth increase request” and “number of channels” to all of the node apparatuses on the ring by using the control frame (Step S 12 ). That is, as shown in  FIG. 2 , when the NMS information sending section  11  in the node apparatus  1  receives a bandwidth increase command from the NMS, the RPR processing section  12  generates a control frame and sends the control frame to the VCG generating/detecting section  14 . Then, after the VCG generating/detecting section  14  conducts a SONET mapping process, the VCG generating/detecting section  14  sends the control frame to the ring.  
         [0052]     Returning to  FIG. 10 , each of the other node apparatuses  1 B- 1 D, having received the information including the “bandwidth increase request” and the “number of channels” from the node apparatus  1 A, determines whether it is possible to increase the bandwidth of the node apparatus itself (each node apparatus except for node apparatus  1 A). If the other node apparatus  1 B- 1 D determines that the bandwidth increase is possible, the other node apparatus  1 B- 1 D transmits (unicasts) an affirmative response “OK” to the node apparatus  1 A by using the control frame, and if the other node apparatus  1 B- 1 D determines that the bandwidth increase is impossible, the other node apparatus  1 B- 1 D transmits (unicasts) a negative response “NG” to the node apparatus  1 A by using the control frame (Step S 13 ). That is, as shown in  FIG. 2 , the RPR processing section  12 , upon receiving the control frame from the VCG generating/detection section  14 , determines whether the bandwidth increase is possible by referring to the number of IDLE paths inside the VCG status information obtained from the VCG controlling section  13 . In determining whether the bandwidth increase is possible, the RPR processing section  12  compares the “number of channels” requested to be increased and the number of IDLE paths of the node apparatus itself. In a case where the “number of IDLE paths” and the “number of channels requested to be increased” satisfy a relation where “number of IDLE paths” ≧ “number of channels requested to be increased”, the increase of bandwidth is determined to be possible. In a case where the “number of IDLE paths” and the “number of channels requested to be increased” satisfy a relation where “number of IDLE paths” ≦“number of channels requested to be increased”, the increase of bandwidth is determined to be impossible. The status of the path (number of IDLE paths) is constantly monitored by the VCG generating/detecting section  14 , and the status is sent from the VCG controlling section  13  to the RPR processing section  12 , to thereby enable determination of the increase of bandwidth.  
         [0053]     Returning to  FIG. 10 , when the node apparatus  1 A receives the “OK” reply from all of the other node apparatuses  1 B- 1 D and determines that the bandwidth increase of itself (i.e. node apparatus  1 A) is possible, the node apparatus  1 A transmits (broadcasts) an answer containing the “increase of bandwidth” and the “increased number of channels” to all of the other node apparatuses  1 B- 1 D by using the control frame (Step S 14 ). On the other hand, when the node apparatus  1 A receives the reply “NG” from at least one of the other node apparatuses  1 B- 1 D or when the node apparatus  1 A determines that the bandwidth increase of itself (node apparatus  1 A) is impossible, the node apparatus  1 A transmits an answer “DENY” to the NMS.  FIG. 11  shows an exemplary case where the increase of bandwidth is denied. In this example, the node apparatus  1 A, receiving the reply “NG” from the node apparatus  1 B, transmits the answer “DENY” to the NMS (Step S 24 ). The RPR processing section  12  shown in  FIG. 2  determines the possibility of bandwidth increase of the entire ring by processing the received information indicative of the possibility of bandwidth increase from the other node apparatuses  1 B- 1 D along with processing (determining) the possibility of bandwidth increase of itself (i.e. node apparatus  1 A). If the RPR processing section  12  determines that the bandwidth increase of the entire ring is possible, the RPR processing section  12  generates a control frame. If the RPR processing section  12  determines that the bandwidth increase of the entire ring is impossible, the answer “DENY” is transmitted from the NMS information sending section  11  to the upper level NMS.  
         [0054]     Returning to  FIG. 10 , the node apparatus  1 A and the other node apparatuses  1 B- 1 D receiving the control frame indicating “increase of bandwidth” and the “increased number of channels” each transmits a control frame indicating “READY” to its adjacent node apparatus  1 A- 1 D (Step S 15 ). Each node apparatus  1 A- 1 D, upon receiving the transmitted control frame “READY”, adds a VCG member (bandwidth increase) with respect to the node apparatus (source) of the transmitted control frame (Step S 16 ). That is, as shown in  FIG. 12 , the RPR processing section  12  reports the number of increased channels to the VCG controlling section  13 . Accordingly, the Overhead information, which is to be changed, is sent (reported) from the VCG controlling section  13  to the VCG generating/detecting section  14 . Then, in the VCG generating/detecting section  14 , the setting is changed such that “CTRL=NORM” is set to “n through (m−1)(ch)” (“CTRL=NORM” previously being set to “1 through (n−1) (ch)”) and “CTRL=EOS” is set to “n+m (ch)” (“CTRL=EOS” previously being set to “n (ch)”). It is to be noted that CTRL=xxx indicates a parameter included in the VCG, in which the values thereof include, for example, NORM (Normal), EOS (End Of Sequence), and DNU (Do Not Use). The process of changing the VCG to STSxx−(n+m) V (bandwidth increase) is completed in the corresponding node apparatus upon receiving the changed overhead information changed by the VCG generating/detecting section  14 . When the bandwidth increase is completed, the NMS information sending section  11  sends a completion report “COMPLD” to the NMS (Step S 17 ).  
         [0000]     [Process of Decreasing Bandwidth (NMS Setting] 
         [0055]     An example of decreasing the ring bandwidth from “STSxx−nV” to “STSxx−(n−m) V” is described with reference to  FIG. 6 .  
         [0056]     In  FIG. 10 , when the NMS sends a bandwidth decrease command to the node apparatus  1 A (Step S 11 ), the node apparatus  1 A transmits (broadcasts) a “bandwidth decrease request” and “number of channels” to all of the other node apparatuses  1 B- 1 D on the ring by using a control frame (Step S 12 ).  
         [0057]     Each of the other node apparatuses  1 B- 1 D, having received the information including the “bandwidth decrease request” and the “number of channels” from the node apparatus  1 A determines whether it is possible to decrease the bandwidth of the node apparatus itself (each node apparatus except for node apparatus  1 A). If the other node apparatus  1 B- 1 D determines that the bandwidth decrease is possible, the other node apparatus  1 B- 1 D. transmits (unicasts) an affirmative response “OK” to the node apparatus  1 A by using a control frame, and if the other node apparatus  1 B- 1 D determines that the bandwidth decrease is impossible, the other node apparatus  1 B-ID transmits (unicasts) a negative response “NG” to the node apparatus  1 A by using a control frame (Step S 13 ). That is, as shown in  FIG. 2 , the RPR processing section  12 , upon receiving the information including the “bandwidth decrease request” and the “number of channels”, calculates the ring bandwidth supposing that the bandwidth is decreased (supposed decreased bandwidth) and compares the calculated bandwidth to a CIR  1  (Committed Information Rate) bandwidth which is reserved as the rate of the guaranteed bandwidth.  FIG. 12  shows a flowchart of an exemplary process of determining the decrease of bandwidth. The process begins when a bandwidth decrease is triggered (Step S 101 ). Then, the total value of the CIR  1  and the value of the supposed decreased bandwidth are compared (Step S 102 ). If the relation of, for example, “(Total CIR  1  Value) ≦(90% of Supposed Decreased Bandwidth)” is satisfied, the decrease of bandwidth is accepted (Change Bandwidth) (Step S 103 ). If the relation of, for example, “(Total CIR  1  Value) &gt;(90% of Supposed Decreased Bandwidth)” is satisfied, the decrease of bandwidth is denied (RPR Protection) (Step S 104 ).  
         [0058]     Returning to  FIG. 10 , when the node apparatus  1 A receives the “OK” reply from all of the other node apparatuses  1 B- 1 D and determines that the bandwidth decrease of itself (i.e. node apparatus  1 A) is possible, the node apparatus  1 A transmits (broadcasts) an answer including the “decrease of bandwidth” and the “decreased number of channels” to all of the other node apparatuses  1 B- 1 D by using a control frame (Step S 14 ). On the other hand, when the node apparatus  1 A receives the reply “NG” from at least one of the other node apparatuses  1 B- 1 D or when the node apparatus  1 A determines that the bandwidth decrease of itself (node apparatus  1 A) is impossible, the node apparatus  1 A transmits an answer “DENY” to the NMS (Step S 24  in  FIG. 11 ).  
         [0059]     Then, the node apparatus  1 A and the other node apparatuses  1 B- 1 D receiving the control frame indicating “decrease of bandwidth” and the “decreased number of channels” each transmits a control frame indicating “READY” to its adjacent node apparatus  1 A- 1 D (Step S 15 ). Each node apparatus  1 A- 1 D, upon receiving the transmitted control frame “READY”, removes a VCG member (bandwidth decrease) with respect to the node apparatus (source) of the transmitted control frame (Step S 16 ). That is, as shown in  FIG. 2 , the RPR processing section  12  reports the number of decreased channels to the VCG controlling section  13 . Accordingly, the Overhead information, which is to be changed, is sent (reported) from the VCG controlling section  13  to the VCG generating/detecting section  14 . Then, in the VCG generating/detecting section  14 , the setting is changed such that “CTRL=NORM” is set to “1 through (n−m−1) (ch)” (“CTRL=NORM” previously being set to “1 through (n−1) (ch)”), “CTRL=IDLE” is set to “n through (n−m+1) (ch)”, and “CTRL=EOS” is set to “n−m (ch)” (“CTRL=EOS” previously being set to “n (ch)”). The process of changing the VCG to STSxx−(n−m) V (bandwidth decrease) is completed in the corresponding node apparatus upon receiving the changed overhead information changed by the VCG generating/detecting section  14 . When the bandwidth decrease is completed, the NMS information sending section  11  sends a completion report “COMPLD” to the NMS (Step S 17 ).  
         [0000]     [Exemplary Process of Bandwidth Decrease (In a case of a partial failure)] 
         [0060]     An example of removing a channel with a defective path (path failure) from the STSxx−nV and decreasing the bandwidth to STSxx−(n−m) V (“m” indicates the number of defective paths) is described with reference to  FIG. 8 .  
         [0061]     In  FIG. 13 , when a failure in a path (failure in the SONET layer) is detected (Step S 31 ), the node apparatus  1 A transmits (broadcasts) a “failure” and “number of channels” to all of the other node apparatuses  1 B- 1 D (Step S 32 ). That is, as shown in  FIG. 2 , when the VCG generating/detecting section  14  detects a failure in the path, the VCG controlling section  13  dispatches an interruption report to the RPR processing section  12 . The RPR processing section  12 , upon receiving the interruption report, generates a control frame for reporting the failure and the number of channel(s).  
         [0062]     Returning to  FIG. 13 , each of the other node apparatuses  1 B- 1 D, having received the information including the “failure” and the “number of channels” from the node apparatus  1 A, determines whether it is possible to decrease the bandwidth of the node apparatus itself (each node apparatus except for node apparatus  1 A). If the other node apparatus  1 B- 1 D determines that the bandwidth decrease is possible, the other node apparatus  1 B- 1 D transmits (unicasts) an affirmative response “OK” to the node apparatus  1 A by using the control frame, and if the other node apparatus  1 B- 1 D determines that the bandwidth decrease is impossible, the other node apparatus  1 B- 1 D transmits (unicasts) a negative response “NG” to the node apparatus  1 A by using a control frame (Step S 33 ).  
         [0063]     When the node apparatus  1 A receives the “OK” reply from all of the other node apparatuses  1 B- 1 D, determines that the bandwidth decrease of itself (i.e. node apparatus  1 A) is possible, and confirms that the bandwidth decrease during failure is set to “YES”, the node apparatus  1 A transmits (broadcasts) an answer including the “decrease of bandwidth” and the “decreased number of channels” to all of the other node apparatuses  1 B- 1 D by using a control frame (Step S 34 ). On the other hand, when the node apparatus  1 A receives the reply “NG” from at least one of the other node apparatuses  1 B- 1 D or when the node apparatus  1 A determines that the bandwidth decrease of itself (node apparatus  1 A) is impossible, or when the node apparatus  1 A confirms that the bandwidth decrease during failure is set to “NO”, the node apparatus  1 A refrains from decreasing the bandwidth and activates an RPR switching function.  
         [0064]     Then, the node apparatus  1 A and the other node apparatuses  1 B- 1 D receiving the control frame indicating “decrease of bandwidth” each transmits a control frame indicating “READY” to its adjacent node apparatus  1 A- 1 D (Step S 35 ). Each node apparatus  1 A- 1 D, upon receiving the transmitted control frame “READY”, removes a VCG member (bandwidth decrease) with respect to the node apparatus (source) of the transmitted control frame (Step S 36 ). That is, as shown in  FIG. 2 , the RPR processing section  12  reports the number of decreased channels to the VCG controlling section  13 . Accordingly, the Overhead information, which is to be changed, is sent (reported) from the VCG controlling section  13  to the VCG generating/detecting section  14 . Then, in the VCG generating/detecting section  14 , “CTRL=DNU (Do Not Use)” is set to the failure detected channel. The VCG generating/detecting section  14 , which also generates other paths besides the path between the node apparatus  1 A and the node apparatus  1 B, changes the settings (“CTRL=EOS” previously being set to “n (ch) ”) such that “CTRL=DNU” is set to “n to (n−m+1)” (number of fail paths) and “CTRL=EOS” is set to “n−m (ch)”.  
         [0065]     Then, in the VCG generating/detecting section  14 , a state where “CTRL=NORM” is set to “1−(n−1) (ch)” and “CTRL=EOS” is set to “n (ch)” is changed to a state where “CTRL=NORM” is set to “n−(m− 1 ) (ch)” and “CTRL=EOS” is set to “n+m (ch)”. The process of changing the VCG to STSxx−(n−m) V (bandwidth decrease) is completed in the corresponding node apparatus upon receiving the changed overhead information changed by the VCG generating/detecting section  14 .  
         [0000]     [Exemplary Process of Bandwidth Restoration] 
         [0066]     An example of a case where the node apparatus  1 A detects the restoration (recovery) of the failure of the node apparatus  1 B is described with reference to  FIG. 14 .  
         [0067]     In  FIG. 14 , when the node apparatus  1 A detects the restoration of a path failure (Step S 41 ) the node apparatus  1 A transmits (broadcasts) “CLEAR” information and “number of channels” to all of the other node apparatuses  1 B- 1 D by using a control frame (Step S 42 ). That is, when the VCG generating/detecting section  14  detects a restoration (recovery) of a failure in a path, the VCG controlling section  13  dispatches an interruption report to the RPR processing section  12 . The RPR processing section  12 , upon receiving the interruption report, generates a control frame for reporting the “CLEAR” information and the “number of channels”.  
         [0068]     Returning to  FIG. 14 , each of the other node apparatuses  1 B- 1 D, having received the information including “CLEAR” and the “number of channels” from the node apparatus  1 A, determines whether it is possible to restore its corresponding path that was disconnected (separated) during failure. If the other node apparatus  1 B- 1 D determines that the restoration is possible, the other node apparatus  1 B- 1 D transmits (unicasts) an affirmative response “OK” to the node apparatus  1 A by using a control frame, and if the other node apparatus  1 B- 1 D determines that the restoration is impossible, the other node apparatus  1 B- 1 D transmits (unicasts) a negative response “NG” to the node apparatus  1 A by using a control frame (Step S 43 ). That is, the VCG controlling section  13  determines whether the disconnected (separated) path is in an “CTRL=DNU” state and whether there is any path that is in an “CTRL=DNU” state at the reception side.  
         [0069]     Returning to  FIG. 14 , when the node apparatus  1 A receives the “OK” reply from all of the other node apparatuses  1 B- 1 D and determines that the restoration of the disconnected (separated) path is possible, the node apparatus  1 A transmits (broadcasts) an answer information the “increase of bandwidth” and the “increased number of channels” to all of the other node apparatuses  1 B- 1 D by using a control frame (Step S 44 ). On the other hand, when the node apparatus  1 A receives the reply “NG” from at least one of the other node apparatuses  1 B- 1 D or when the node apparatus  1 A determines that the restoration of its&#39; corresponding path (path corresponding to node apparatus  1 A is impossible, the node apparatus  1 A refrains from restoring the bandwidth.  
         [0070]     Then, the node apparatus  1 A and the other node apparatuses  1 B- 1 D receiving the control frame indicating “increase of bandwidth” each transmits a control frame indicating “READY” to its adjacent node apparatus  1 A- 1 D (Step S 45 ). Each node apparatus  1 A- 1 D, upon receiving the transmitted control frame “READY”, restores a VCG member (bandwidth restoration) with respect to the node apparatus (source) of the transmitted control frame (Step S 46 ). That is, as shown in  FIG. 2 , the RPR processing section  12  reports the number of restored channels to the VCG controlling section  13 . Accordingly, the Overhead information, which is to be changed, is sent (reported) from the VCG controlling section  13  to the VCG generating/detecting section  14 . Then, the VCG generating/detecting section  14  changes the settings of the restored channel (previously set as “CTRL=DNU”) to “CTRL=NORM” or “CTRL=EOS”. The process of changing the VCG to STSxx−nV (bandwidth restoration) is completed in the corresponding node apparatus upon receiving the changed overhead information changed by the VCG generating/detecting section  14 .  
         [0071]     Further, the present invention is not limited to these embodiments, but variations and modifications may be made without departing from the scope of the present invention.  
         [0072]     The present application is based on Japanese Priority Application No. 2005-282096 filed on Sep. 28, 2005, with the Japanese Patent Office, the entire contents of which are hereby incorporated by reference.