Patent Publication Number: US-2009219818-A1

Title: Node device, packet switch device, communication system and method of communicating packet data

Description:
This application is based upon and claims the benefit of priority from Japanese patent application No. 2008-051621, filed on Mar. 3, 2008, the disclosure of which is incorporated herein in its entirety by reference. 
     BACKGROUND 
     1. Technical Field 
     The present invention relates to a node device, a packet switch device, a communication system, and a method of communicating packet data. 
     2. Background Art 
     A resilient packet ring (RPR: ring-type packet transmission method) technique which is a ring-type network specified by IEEE 802.17 is disclosed in Japanese Laid-open patent publication NO. 2006-262169. An RPR performs data transmission by a dual-ring configuration in which two unidirectional rings are combined in the opposite directions to each other and provides a packet ring of a band sharing type. Japanese Laid-open patent publication NO. 2006-262169 discloses an inter-ring connection method and device for interconnecting a plurality of RPRS. An RPR standard specified by IEEE 802.17 defines 3 to 5 priority classes and employs a control method for dynamically changing a communication band. 
     Japanese Laid-open patent publication NO. 2007-194732 discloses a technique in which an optical network unit (ONU) and an optical line terminal (OLT) disposed between a host network and a user house side network monitor a data storage state for each priority class queue and transmit a pause frame with a priority class queue number to a user house side network and a host network. Therefore, pause/restart of traffic transmission is requested in units of priority classes. 
     Japanese Laid-open patent publication NO. H06-104917 discloses a technique in which a congestion control circuit measures a cell loss ratio for each of queues formed associated with a quality class/an output line and momentarily allocates a spare band to a queue whose loss ratio exceeds an allowable cell loss ratio which is determined in advance associated with a quality class. 
     Japanese Laid-open patent publication NO. H08-167898 discloses a technique in which packet acceleration or an upper limit value of a packet acceleration ratio is changed to a value of a transmission destination side at a point which interconnects variable speed networks which are different in packet acceleration or an upper limit value of a packet acceleration ratio when a packet is transmitted from one variable speed network to the other variable speed network. If an inter-network connection device detects congestion when a packet is transmitted from one variable speed network to the other variable speed network, the inter-network connection device inserts a congestion prediction signal into a packet which flows in a direction of a variable speed terminal device of a sender side and outputs it to the variable speed terminal device of the sender side. Therefore, the variable speed terminal device of the sender side reduces the packet transmission speed. 
     Japanese patent application publication NO. 2002-519912 discloses a system for implementing flow control in an information network such as a local area network (LAN) utilizing a Carrier Sense Multiple Access with Collision Detection (CSMA/CD) as specified by the IEEE standard 802.3. In this configuration, a control frame such as a PAUSE frame is provided to an information packet source from a downstream destination to inhibit transmission of information packets such as information frames by the information packet source to the downstream destination for a specific time period. 
     In an RPR described in Japanese Laid-open patent publication NO. 2006-262169, communication is performed by defining a Quality of Service (“QoS”) class such as band-guaranteed type, a minimum band-guaranteed type and a best effort type which is specified in IEEE 802.17. In order to add data traffic to an RPR, an RPR node device is installed at an ADD point, and packet data output from a packet switch device is output to an RPR through an RPR node. In case where communication between a packet switch device and an RPR node is specified by IEEE 802.3, flow control for data transmission between a packet switch and an RPR node is performed in units of Ethernet (registered trademark) ports. Thus, there is a problem that transmission stop or transmission start is not controlled class by class when traffics of a plurality of QoS classes of an RPR are mixed within a single port. 
     Therefore, there is a problem that a packet switch device stops data communication of a QoS class which is not congested but communicatable. Also, there is a problem that there is a case where a packet transmitted from a packet switch device is discarded in an RPR node device after it is received by the RPR node device because QoS control in a packet switch device is not succeeded to QoS control in an RPR system. 
     In Japanese Laid-open patent publication NO. H06-104917, it is necessary to prepare a spare band in advance. Also, in Japanese Laid-open patent publication NO. H08-167898 and Japanese patent application publication NO. 2002-519912, flow control cannot be performed class by class. 
     Moreover, as described, in case where communication between a packet switch device and an RPR node is specified by IEEE 802.3, a communication quality classification between a packet switch device and an RPR node is different from a communication quality classification of an RPR. In Japanese Laid-open patent publication NO. 2007-194732, however, flow control cannot be performed class by class when there are communication quality classifications which are different in standard. 
     SUMMARY 
     An exemplary object of the invention is to provide a node device, a packet switch device, a communication system, and a method of communicating packet data capable of controlling transmission stop or transmission start class by class when communication quality class classifications are different. 
     A node device according to an exemplary aspect of the invention includes; a congestion detection unit which detects an occurrence and release of congestion for each class of a second communication quality classification when packet data for each class classified by a first communication quality classification received from a port is output to a ring-type network for each class classified by the second communication quality classification which is different from the first communication quality classification; a class association table which stores association between each class of the second communication quality classification and each class of the first communication quality classification; a class conversion unit which converts a class of the second communication quality classification in which the congestion detecting unit detects an occurrence and release of congestion into an associated class of the first communication quality classification with reference to the class association table; and a notification unit which notifies a class of the first communication quality classification converted by the class conversion unit to the port as a target data for stopping read out or starting read out. 
     A packet switch device according to an exemplary aspect of the invention includes: a port which outputs packet data for each class classified by a first communication quality classification, wherein the packet switch device is connected to a ring-type network which transmits or receives packet data for each class classified by a second communication quality classification which is different from the first communication quality classification, and the port includes a class-by-class output control unit which designates, as a target data for stopping read out or starting read out, a class of the first communication quality classification obtained by converting a class of the second communication quality classification in which an occurrence or release of congestion is detected into an associated class of the first communication quality classification based on an occurrence and release of packet data congestion for each class of the second communication quality classification in the ring-type network and stops or starts an output of packet data of the class from the port. 
     A communication system according to an exemplary aspect of the invention includes: a packet switch device which outputs packet data for each class classified by a first communication quality classification; and a node device which receives the packet data output from the packet switch device and outputs the packet data to a ring-type network for each class classified by a second communication quality classification which is different from the first communication quality classification, wherein the node device includes: a congestion detection unit which detects an occurrence and release of congestion for each class of the second communication quality classification; a class association table which stores association between each class of the second communication quality classification and each class of the first communication quality classification; a class conversion unit which converts a class of the second communication quality classification in which the congestion detection unit detects an occurrence or release of congestion into an associated class of the first communication quality classification with reference to the class association table; and a notification unit which notifies a class of the first communication quality classification converted by the class conversion unit to the packet switch device as a target data for stopping read out or starting read out, and the packet switch device includes a class-by-class output control unit which is notified of the class of the target data for stopping read out or starting read out and stops or starts an output of the packet data of the class to the node device. 
     A method of communicating packet data according to an exemplary aspect of the invention, includes: receiving packet data from a port which outputs the packet data for each class classified by a first communication quality classification and outputting the packet data to a ring-type network for each class classified by a second communication quality classification which is different from the first communication quality classification; detecting an occurrence and release of congestion for each class classified by the second communication classification; converting a class of the second communication quality classification in which an occurrence and release of congestion is detected at the detecting an occurrence and release of congestion into an associated class of the first communication quality classification with reference to a class association table which stores association between each class of the second communication quality classification and each class of the first communication quality classification; and notifying a class of the first communication quality classification converted by the converting into the class to the port as a target data for stopping read out or starting read out. 
     A certain combination of the components described above and a representation of the present invention transformed between a method, a device, a system a recording medium, and a computer program are also effective as an aspect of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other objects, advantages and features of the present invention will be more apparent from the following description of certain exemplary embodiments taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a block diagram illustrating a configuration of a communication system which includes an RPR node device and a packet switch device according Lo an exemplary embodiment of the present invention; 
         FIG. 2  is a view illustrating one example of an internal configuration of a class association table; 
         FIG. 3  is a view illustrating one example of a configuration of a pause frame transmitted from a class designating pause frame transmission unit; 
         FIG. 4  is a view illustrating another example of a configuration of a pause frame transmitted from a class designating pause frame transmission unit; 
         FIG. 5  is a view illustrating one example of a configuration of a node device according to an exemplary embodiment of the present invention; 
         FIG. 6  is a view illustrating one example of a configuration of a node device according to an exemplary embodiment of the present invention; and 
         FIG. 7  is a view illustrating one example of a configuration of a communication system which includes a node device and a packet switch device according to an exemplary embodiment of the present invention. 
     
    
    
     EXEMPLARY EMBODIMENT 
     The invention will be now described herein with reference to illustrative exemplary embodiments. Those skilled in the art will recognize that many alternative exemplary embodiments can be accomplished using the advantages of the present invention and that the invention is not limited to the exemplary embodiments illustrated for explanatory purposed. 
     Hereinafter, exemplary embodiments of the present invention will be described with reference to the accompanying drawings. In the drawings, like reference numerals denote like parts, and a duplicated description will not be repeated. 
       FIG. 5  is a view illustrating one example of a configuration of a node device of the present exemplary embodiment. 
     A node device  19  includes a ring-type network port  21 . The node device  19  is connected to a ring-type network  59  through the ring-type network port  21  to configure the ring-type network  59 . The node device  19  includes a class-by-class congestion detection unit (congestion detection unit)  28 , a class association table  32 , a class conversion unit  30 , and a notification unit  33 . 
     The class-by-class congestion detection unit  28  detects an occurrence and release of congestion for each class of a second communication quality classification when packet data for each class classified by a first communication quality classification received from a different port is output to the ring-type network  59  for each class classified by the second communication quality classification which is different from the first communication quality classification. The class association table  32  stores association between each class of the second communication quality classification and each class of the first communication quality classification. The class conversion unit  30  converts a class of the second communication quality classification in which the class-by-class congestion detecting unit  28  detects an occurrence and release of congestion into an associated class of the first communication quality classification with reference to the class association table  32 . The notification unit  33  notifies a class of the first communication quality classification converted by the class conversion unit  30  to a different port as a target data for stopping read out or starting read out. 
       FIG. 6  is a view illustrating one example of a configuration of a node device of the present exemplary embodiment. 
     A packet switch device  40  includes a class-by-class congestion control port  42  which is a port that outputs packet data for each class classified by a first communication quality classification. The packet switch device  40  is connected to a ring-type network  59  which transmits or receives packet data for each class classified by a second communication quality classification which is different from the first communication quality classification through the ring-type network port  21 . The class-by-class congestion control port  42  may be connected to the ring-type network port  21  directly or indirectly through a different port. The class-by-class congestion control port  42  includes a class-by-class output control unit  43 . The class-by-class output control unit  43  designates, as a target da a for stopping read out or starting read out, a class of the first communication quality classification obtained by converting a class of the second communication quality classification in which an occurrence or release of congestion is detected into an associated class of the first communication quality classification based on an occurrence and release of packet data congestion for each class of the second communication quality classification in the ring-type network  59  and stops or starts an output of packet data of the class from a port. 
       FIG. 7  is a view illustrating one example of a configuration of a communication system which includes a node device and a packet switch device according to the present exemplary embodiment. 
     A communication system  10  includes a packet switch device  40  which outputs packet data for each class classified by a first communication quality classification, and a node device  19  which receives packet data output from the packet switch device  40  and outputs the packet data to the ring-type network  59  for each class classified by a second communication quality classification which is different from the first communication quality class classification. 
     The node device  19  has the same configuration as that shown in  FIG. 5 . A notification unit  33  notifies the packet switch device  40  of a class of the first communication quality classification converted by a class conversion unit  30  as a target data for stopping read out or starting read out. The packet switch device  40  has the same configuration as that shown in  FIG. 6 . 
     Next, a detailed exemplary embodiment will be described. 
     In the below exemplary embodiment, a case where the ring-type network  59  is a resilient packet ring and the node device  19  is an RPR node device will be exemplarily described. In the following exemplary embodiment, the RPR node device which configures the RPR includes a congestion detection function for each QoS class (class classified by the second communication quality classification) of the RPR, a conversion function between a QoS class of the RPR and a QoS class (class classified by the first communication quality classification) at a packet switch, and a notification function of a congestion state to a packet switch device. The packet switch device includes a function of receiving notification of a congestion state for each QoS class at the packet switch from the RPR node device, and a function of stopping or starting transmission of packet data to the RPR node device for each QoS class at the packet switch. Therefore, flow control can be realized for each QoS class. The exemplary embodiment will be described below in more detail with reference to the accompanying drawings. 
       FIG. 1  is a view illustrating a communication system which includes an RPR node device and a packet switch device according to the present exemplary embodiment. 
     A communication system  10  includes an RPR node device  20  and a packet switch device  40 . The RPR node device  20  includes an RPR port  22 , an RPR class-by-class output queue  24 , a class-by-class congestion control port  26 , a class-by-class congestion detection unit  28 , a class conversion unit  30 , a class association table  32 , and an input queue  36 . The class-by-class congestion control port  26  includes a class designating pause frame transmission unit  34 . The class designating pause frame transmission unit  34  corresponds to the notification units  33  shown in  FIGS. 5  arid  7 . 
     The packet switch device  40  includes a class-by-class congestion control port  42  and a packet device class-by-class output queue  50 . The class-by-class congestion control port  42  includes a pause frame determination unit  44 , a pause frame class identification unit  46  (identification unit) and a class-by-class read out unit  48 . The pause frame determination unit  44 , the pause frame class identification unit  46  and the class-by-class read out unit  48  correspond to the class-by-class output control unit  43  of  FIG. 6 . The packet switch device  40  may be realized by, for example, a bridge (Layer 2 switch) or a router (L3 switch). 
     The respective components of the RPR node device  20  and the packet switch device  40  shown in  FIG. 1  represent blocks of functional units other than configurations of hardware units. The respective components of the RPR node device  20  and the packet switch device  40  may be implemented by a combination of hardware and software based on a central processing unit (CPU) of a certain computer, a memory, a program which is loaded into a memory to implement components of the present drawing, a storage unit which stores the program such as a hard disk drive (HDD), and a network connection interface. Those of ordinary skill in the art understand that the implementation method and device may be variously modified. 
     The class-by-class congestion control port  26  of the RPR node device  20  is connected to an RPR  60  through the RPR port  22  connected through the RPR class-by-class output queue  24 . The RPR  60  may include a plurality of RPR ports which are same as the RPR port  22 . The class-by-class congestion control port  26  is also interconnected with the class-by-class congestion control port  42  of the packet switch device  40 . In the present exemplary embodiment, communication between the class-by-class congestion control port  26  and the class-by-class congestion control port  42  may be specified by IEEE 802.3. 
     The class-by-class congestion detection unit  28  monitors data traffic for each RPR class transmitted from the RPR class-by-class output queue  24 . A congestion detection threshold value for each RPR QoS class is set in each RPR class-by-class output queue  24 . Each RPR class-by-class output queue  24  detects a congestion occurrence and a congestion release of communication in the RPR  60  based on a congestion detection threshold value set for each RPR QoS class. The class-by-class congestion detection unit  28  receives a detection result for a congestion occurrence and a congestion release from each RPR class-by-class output queue  24  and detects a congestion state for each RPR QoS class. The class-by-class congestion detection unit  26  notifies the class conversion unit  30  of a change of a congestion state of an associated RPR QoS class if there is a change in congestion state for each RPR QoS class. The class conversion unit  30  refers to a class association table  32  to detect a QoS class of the packet switch device  40  associated with a RPR QoS class notified from the class-by-class congestion detection unit  28 . The class conversion unit  30  notifies the class designating pause frame transmission unit  34  of the associated QoS class of the packet switch device  40 . 
       FIG. 2  is a view illustrating one example of an internal configuration of the class association table  32 . 
     The class association table  32  stores a QoS class of the RPR and a QoS class at the packet switch in such a way that the QoS class of the RPR and the QoS class at the packet switch are associated with each other. As the QoS class of the RPR, for example, a classification specified by IEEE 802.17 may be used. As for an example, five classes A 0 , A 1 , B-CIR, B-EIR, and C, which are listed in a priority order, may be set. The classes A 0  and A 1  are full band-guaranteed type traffic, the classes B (B-CIR and B-EIR) are minimum band-guaranteed type traffic, and the class C is best effort type traffic. As for the QoS class at the packet switch, eight classes  7 ,  6 ,  5 ,  4 ,  3 ,  2 ,  1 , and  0 , which are listed in a priority order, may be set. In the class association table  32 , the association between the QoS class of the RPR and the QoS class at the packet switch may be appropriately set but may be set depending on the communication quality, for example, in such a way that QoS classes which are low in communication quality are associated with each other or QoS classes which are high in communication quality are associated with each other. Therefore, the QoS class of the RPR and the QoS class at the packet switch may automatically be associated with each other to a certain extent. 
     The class designating pause frame transmission unit  34  generates a pause frame which designates an associated QoS class of the packet switch device  40  which is notified from the class conversion unit  30  as a target data for stopping read out or starting read out. The class designating pause frame transmission unit  34  appends the generated pause frame to data packet which is input to the input queue  36  from the RPR  60  and transmits it to the class-by-class congestion control port  42 . 
       FIG. 3  is a view illustrating one example of a configuration of a pause frame transmitted by the class designating pause frame transmission unit  34 . 
     Here, a virtual local area network (VLAN) TAG identifier is inserted into a pause frame which is specified by IEEE 802.3, and the VLANTAG identifier is used as a priority identifier  82 . A pause frame  70  includes fields such as a destination address  71 , a sender address  72 , a TAG identifier  73 , a priority  74 , a canonical format indicator (CFI)  75 , a VLANTAG  76 , a TYPE  77 , a MACControl  78 , a PAUSETIME  79 , a Reserved  80 , and a frame check sequence (FCS)  81 . Of these, the TAG identifier  73 , the priority  74 , the CFI  75 , and the VLANTAG  76  configure the VLANTAG identifier. 
     The PAUSETIME  79  may instruct stop of data packet, start of transmission, and a transmission stop time. This function may use control which complies with IEEE 802.3 as it is. 
     The pause frame determination unit  44  of the packet switch device  40  separates the pause frame from data packet when data packet and the pause frame  70  are transmitted from the RPR node device  20 . The pause frame determination unit  44  transmits the separated pause frame to the pause frame class identification unit  46 . The pause frame class identification unit  46  identifies a QoS class based on the priority identifier  82  of the pause frame  70  transmitted from the pause frame determination unit  44 . The pause frame class identification unit  46  notifies the identified QoS class and an instruction designated in the PAUSETIME  79  to the class-by-class read out unit  48 . The class-by-class read out unit  48  stops read out and transmission processing of the packet device class-by-class queue  50  for a QoS class notified from the pause frame class identification unit  46 . Therefore, a transmission frame of an associated QoS class to the class-by-class congestion control port  26  is stopped. 
     Next, an operation of QoS class-by-class flow control will be described with reference to  FIGS. 1 to 3 . 
     The class-by-class congestion detection unit  28  notifies an occurrence of congestion and an RPR QoS class in which congestion occurs to the class conversion unit  30  when the class-by-class congestion detection unit  28  detects a congestion occurrence of any RPR QoS class. The class conversion unit  30  detects an associated QoS class of the packet switch device  40  with reference to the class association table  32 . For example, when the class-by-class congestion detection unit  28  detects a congestion occurrence of an RPR QoS class “A 1 ”, the class conversion unit  30  reads out the QoS class “ 5 ” at the packet switch associated with the RPRQoS class “A 1 ” with reference to the class association table  32 . The class conversion unit  30  notifies the QoS class “ 5 ” at the packet switch and a congestion occurrence to the class designating pause frame transmission unit  34 . The class designating pause frame transmission unit  34  transmits the pause frame  70  shown in  FIG. 3  to the class-by-class congestion control port  42  from the class-by-class congestion control port  26 . At this time, information which indicates the QoS class “ 5 ” at the packet switch is included in the priority  74  field. A stop instruction of data packet is included in the PAUSETIME  79 . Also, a meaningless value (for example, “0”), which is not limited to a specific value, may be included in, for example, the VLANTAG  76  of the priority identifier  82 . 
     As another example, a case where the class-by-class congestion detection unit  28  detects congestion of an RPR QoS class “A 0 ” will be described. Referring to  FIG. 2 , an RPR QoS class “A 0 ” is associated with QoS classes “ 7 ” and “ 6 ” at the packet switch. In this case, the class designating pause frame transmission unit  34  transmits to the class-by-class congestion control port  42  two pause frames: a pause frame in which information indicating the QoS class “ 7 ” at the packet switch is included in the priority  74  field; and a pause frame in which information indicating the QoS class “ 6 ” at the packet switch is included in the priority  74  field. 
     In the packet switch device  40 , the pause frame determination unit  44  receives data packet and the pause frame from the class designating pause frame transmission unit  34 . The pause frame determination unit  44  separates the received pause frame from data packet. Subsequently, the pause frame determination unit  44  transmits the separated pause frame to the pause fame class identification unit  46 . The pause frame class identification unit  46  reads out class information from the priority  74  field of the received pause frame and pause control information which represents transmission stop, transmission start or temporary transmission stop from the PAUSETIME  79  field, respectively, and notifies them to the class-by-class read out unit  48 . The class-by-class read out unit  48  performs control such as stop, start and temporary stop of data of a designated class from the packet device class-by-class output queue  50 . Therefore, class-by-class pause control is achieved. 
     Next, exemplary advantages of the communication system  10  according to the present exemplary embodiment will be described. 
     According to the communication system  10  of the present exemplary embodiment, even when packet data output to the RPR  60  and packet data output from the packet switch device  40  are different in communication quality classification, transmission of packet data can be controlled class by class, depending on a congestion state of each class. 
     According to the communication system  10  of the present exemplary embodiment, flow control according to a congestion state of an RPR QoS class can be performed with respect to data traffic on a communication path between the RPR node device  20  and the packet switch device  40 . Therefore, even when congestion occurs in traffic of a certain RPR QoS class, a phenomenon that traffic of any other QoS class is stopped between the RPR node device  20  and the packet switch device  40  can be prevented since RPR QoS control cooperated with the packet switch device can be performed. Transmission of packet data can be performed without any packet loss from the packet switch device  40  with respect to the traffic flow rate of each QoS class which dynamically changes in the RPR. 
     Also, like the RPR, in order to guarantee the classes A 0  and A 1  which are full band-guaranteed type traffic, the packet switch device  40  also needs to guarantee full band-guaranteed type traffic. Therefore, it is necessary to mount a band adjusting shaper circuit in both the packet switch device  40  and the RPR node device  20  and to limit a band at output points of both nodes. However, according to the communication system  10  of the present exemplary embodiment, transmission of packet data can be performed without any packet loss from the packet switch device  40 . Therefore, full band-guaranteed type traffic can be guaranteed by installing a shaper circuit only in the RPR node device  20  without mounting a shaper circuit at the packet switch device  40 . 
     In order to achieve a fair transmission control function or a priority transmission control function for each micro flow when the packet switch device  40  accesses the RPR through the RPR node device  20 , it is typically necessary to add a physical (virtual) queue to a class-by-class output queue of each of the packet switch device  40  and the RPR node device  20  to control transmission. However, transmission of packet data can be performed without any packet loss from the packet switch device  40 . Therefore, the RPR node device  20  can effectively utilize a function of the packet switch device  40  side, and thus a fair transmission control function or a priority transmission control function for each micro flow can be achieved by installing a physical queue only in the packet switch device  40  without mounting a physical queue in the RPR node device  20 . 
     An exemplary advantage according to the invention is that packet data transmission can be controlled class by class depending on a congestion state of each class even when communication quality classifications are different. 
     Hereinbefore, the exemplary embodiment of the present invention has been described with reference to the accompanying drawings, but it is merely an example of the present invention, and the present invention can employ various configurations other than that described above. 
     In the exemplary embodiment described above, the VLANTAG of IEEE 802.1Q is used to notify a priority, but a priority identifier for notifying a priority between the RPR node device  20  and the packet switch device  40  may be discretely defined. Since conversion between a QoS class of the RPR and a QoS class of the packet switch device is performed, traffic control of a certain flow like an IP flow and an IP priority or a MAC flow and a MAC priority can be achieved.  FIG. 4  is a view illustrating another example of a pause frame shown in  FIG. 3 . Here, a pause frame  90  can define traffic of various layers as a priority identifier  99  such as an MAC layer, an IP layer, and a transport layer (fourth layer) of an OSI7 layer used in data communication as a flow control target. As the priority identifier  99 , (1) MAC Flow DA+SA, (2) MAC CoS, (3) VLAN, (4) IP Flow DA+SA, (5) IP TOS/DSCP, (6) Mpls exp-bit, or (7) TCP/UDP DP/SP may be used. 
     Also, in the exemplary embodiment described above, the packet switch device  40  and the node device  20  are described as independent devices, but the RPR node device  20  may be configured to be mounted inside the packet switch device  40 . 
     Furthermore, in the exemplary embodiment described above, the node device  19  (RPR node device  20 ) has a configuration which includes the class conversion unit  30  and the class association table  32 , but the packet switch device  40  may have a configuration which includes the class conversion unit  30  and the class association table  32  instead. In this case, at the node device  19  side, the class-by-class congestion detection unit  28  detects a congestion occurrence and a congestion release of a class of the second communication classification, and the notification unit  33  notifies them to the class conversion unit  30  of the packet switch device  40 . The class conversion unit  30  notifies an associated class of the first communication quality classification to the class-by-class output control unit  43  with reference to the class association table  32 . Accordingly, processing which is same as described above can be performed. 
     Association of the class association table  32  may be externally changed if necessary. By externally performing association of the class association table  32  as described above, an association method of different communication quality classes becomes flexible, and thus congestion control can be more appropriately performed. 
     While the invention has been particularly shown and described with reference to exemplary embodiments thereof, the invention is not limited to these embodiments. It will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the claims.