Patent Publication Number: US-2005122957-A1

Title: Router, traffic volume control method therefor, communication system, and traffic control program recorded computer-readable recording medium

Description:
BACKGROUND OF THE INVENTION  
      (1) Field of the Invention  
      The present invention relates to a router, traffic volume control method therefor, communication system and traffic control program recorded computer-readable recording medium suitable for use in a user&#39;s site receiving, for example, L2-VPN (Layer 2-Virtual Private Network) services.  
      (2) Description of the Related Art  
      A VPN signifies a network with a higher-security function, capable of making safe communications even by way of the Internet by making mutual connections, like dedicated lines, between sites through the use of encryption technique or capsulaizing technique.  
       FIG. 11  is an illustration of a network establishing one example of a conventional L2-VPN service a network carrier provides. The network shown in  FIG. 11  includes a transit network  100  comprising bridge functions, and LANSWs (Local Area Network Switches)  121  to  124  constituting the transit network  100  are connected to routers  111  to  114  of user networks  101  to  104  forming sites, respectively.  
      As the routers  111  to  114  of the user networks  101  to  104  shown in  FIG. 11 , the L2-VPN enables connectionless access to a plurality of sites through the use of one interface. That is, an identifier indicative of a site to which a packet is addressed is not added to a packet. For example, the router  111  of the user network  101  shown in  FIG. 11  is designed to gain connectionless access to the routers  112  to  114  of the three user networks  102  to  104 .  
      In addition, accesses are made through access lines  131  to  134  between each of the routers  101  to  104  and each of the LANSWs  121  to  124  as shown in  FIG. 11  and, in general, these access lines and the transit network  100  are different in contract from each other. That is, as the bands of the transit network  100  and the aforesaid access lines  131  to  134 , selection is made from a best effort type and a band assurance type.  
      For example, a best effort type of 100 Mbps can be selected for the access lines  131  to  134  between the routers  111  to  114  and the LANSWs  121  to  124 , while a band assurance type of 100 Mbps can be selected for the transit network  100 .  
      The band assurance type assures a minimum band. That is, a traffic to be transmitted under assurance is handled as the best effort type. Incidentally, as the aforesaid transit network  100 , there are two types: a type shared by a plurality of users and a type monopolized by one user.  
      At this time, for example, if overflow occurs at an exit (for example, the access lines  131  to  134 ) of the transit network  100 , frames are abandoned in these access lines  131  to  134 . Incidentally, since the L2-VPN is made up of bridge functions, it does not have a congestion notification function to the transmission/reception side routers  111  to  114 .  
      In TCP/IP (Transmission Control Protocol/Internet Protocol) forming an upper layer relative to L 2 , there is defined a function which suppresses transmission quantity to an opposite end system (terminal accommodated in a router, or the like) by using an ICMP (Internet Control Message Protocol) message when a reception buffer reaches a full condition so that frame abandonment occurs or tends to occur.  
      However, in a case in which the traffic concentrates to the user networks  101  to  104  at one site to run above the access line rate or transit network rate at that site, there is a possibility of the occurrence of frame abandonment. In the user network  101  to  104  side units, such ad the router units  111  to  114 , connected to the L2-VPN, in a case in which frame abandonment occurs in the access lines  131  to  134  or the transit network  100  as mentioned above, difficulty is experienced in detecting this occurrence thereof.  
      That is, as shown in  FIG. 11 , in a case in which the connections among the user networks  101  to  104  in a plurality of sites are made through the use of an L2-VPN service, if the concentration of the traffic occurs in one site, the frame abandonment arises in the access lines  131  to  134  or the transit network  100 , which particularly degrades the communication quality of real-time-type applications (telephone, stream).  
      The occurrence of the frame abandonment in the access lines  131  to  134  or in the transit network  100  is unavoidable under the conventional ICMP congestion control. This is because the traffic suppression in the routers  111  to  114  is made to consistently promote the traffic suppression when a reception buffer falls into an overflow condition or its own processing bottlenecks.  
      In this connection, since most of routers are designed in consideration of a plurality of high-speed LAN supports, they usually have a function to prevent the occurrence of congestion therein even at the inflow of 100% traffic from the L2-VPN and, hence, there is a low possibility of carrying out the congestion control in the ICMP with respect to the L2-VPN.  
      Moreover, as a technique related to the invention as claimed in the application concerned, Japanese Patent Laid-Open No. 2000-349776 (which will be referred to hereinafter as patent document) discloses a technique about a route detouring method to be employed at in-switch congestion, which assures the traffic from end users by making a detour with IP protocol or hardware for distributing the load biased to an ATM (Asynchronous Transfer Mode) switch.  
      However, in a case in which the aforesaid patent document is applied to the L2-VPN network configuration shown in the aforesaid  FIG. 11  where the connection to the transit network  100  is made through the access lines  111  to  114 , difficulty is encountered in making a further detour on the access lines  131  to  134  serving as interfaces to the user networks  101  to  104 , which can develop a possibility of the occurrence of frame abandonment as well as the above-mentioned case.  
      The present invention has been developed in consideration of these problems, and it is therefore an object of the invention to provide a router, traffic volume control method therefor, communication system, and traffic control program recorded computer, capable of constructing a network which can prevent the degradation of communication efficiency in employing a virtual private network having no frame abandonment notification function and no abandonment function based on priority.  
     SUMMARY OF THE INVENTION  
      For achieving the above-mentioned purpose, a router according to the present invention, connected through a bridge unit to a transit network constituting a virtual private network, is characterized by comprising a reception traffic volume measuring unit for measuring a reception traffic volume on data received from all next hop routers forming other communication parties connected through the transit network, and a measurement result notifying unit for notifying a measurement result on the measured reception traffic volume to all the next hop routers.  
      Moreover, the router according to the present invention is characterized by comprising, in addition to the aforesaid configuration, a transmission traffic control unit for, when receiving the notification on the measurement result of the reception traffic volume in any one of the next hop routers from this next hop router, controlling a transmission traffic volume to this next hop router in accordance with the measurement result notified from this next hop router.  
      Furthermore, a router according to the present invention, connected through a bridge unit to a transit network constituting a virtual private network, is characterized by comprising an interface unit for carrying out transmission/reception of data with respect to all next hop routers forming other communication parties connected to the transit network and a relay control unit for carrying out relay control on data between the interface unit and a local interface unit made to conduct transmission/reception of data with respect to a local unit accommodated thereunder, wherein the interface unit includes a reception traffic volume measuring unit for measuring a reception traffic volume on data received from all the next hop routers through the transit network and a measurement result notifying unit for notifying a measurement result of the reception traffic volume, measured in the reception traffic volume measuring unit, to all the next hop routers, while the relay control unit includes a control data producing unit for producing control data corresponding to the measurement result to be notified by the measurement result notifying unit on the basis of the reception traffic volume measured in the reception traffic result measuring unit, with a request being made to all the next hop routers so as to control a traffic volume on transmitted data to themselves on the basis of the measurement result notified by the measurement result notifying unit.  
      Still furthermore, the router according to the present invention is characterized in that, in addition to the above-mentioned configuration, the interface unit includes a transmission traffic control unit for, when receiving a measurement result of the reception traffic volume in any one of the next hop routers from this next hop router, controlling a transmission traffic volume to this next hop router in accordance with the measurement result notified from this next hop router.  
      Yet furthermore, preferably, the interface unit includes a threshold decision unit for making a decision on magnitude relation between the reception traffic volume measured by the reception traffic volume measuring unit and a predetermined threshold, and when a result of the decision in the threshold decision unit shows that the reception traffic volume exceeds the predetermined threshold, the control data producing unit puts this fact into the control data.  
      More preferably, the measurement result notifying unit, when a result of the decision in the threshold decision unit shows that the reception traffic volume exceeds the predetermined threshold, makes a notification for a request to the next hop router for suppression of transmission data volume to the router, to which it pertains, so as to eliminate a possibility of occurrence of congestion in the virtual private network.  
      Moreover, preferably, the transmission traffic control unit controls the transmission traffic volume to the next hop router to a first suppressed traffic volume for a first period of time after the reception of the information from the next hop router and, for a second period of time after the elapse of the first period of time, carries out increase control to increase the transmission traffic volume gradually toward a second traffic volume intended.  
      Still moreover, it is also appropriate that, when carrying out the transmission traffic control, the transmission traffic control unit controls the transmission traffic volume while transmitting transmission data according to priority.  
      Yet moreover, preferably, it is also appropriate that the measurement result notifying unit notifies the measurement result according to ICMP (Internet Control Message Protocol).  
      It is also acceptable that the measurement result in the measurement result notifying unit is notified through a management server made to manage the virtual private network, or that it is notified according to a format based on an original protocol.  
      In addition, a traffic control method for a router connected through a bridge unit to a virtual private network according to the present invention is characterized by comprising a traffic volume measuring step of, when communication is made with respect to all next hop routers forming other communication parties connected through the virtual private network, measuring a reception traffic volume on data received from the next hop routers through the virtual private network, a notification step of notifying a measurement result on the measured reception traffic volume to all the next hop routers, and a transmission traffic control step of, in all the next hop routers, controlling a transmission traffic to the router in accordance with the notified measurement result.  
      Still additionally, a communication system according to the present invention, which is made to make communication between routers connected through a bridge unit to a virtual private network, is characterized in that a router, which receives data from all next hop routers forming other communication parties connected through the virtual private network, comprises a reception traffic volume measuring unit for measuring a reception traffic volume on data received from all the next hop routers and a measurement result notifying unit for notifying a measurement result on the measured reception traffic volume to all the next hop routers, and the next hop router, which receives the notification from the measurement result notifying unit, comprises a transmission traffic control unit for controlling a transmission traffic to the router in accordance with the notified measurement result.  
      Furthermore, a traffic control program recorded computer-readable recording medium according to the present invention, which is for recording a traffic control program, which makes a computer, serving as a router connected through a bridge unit to a virtual private network, carry out a traffic control function to control a traffic volume of the router, is characterized in that the traffic control program makes the computer fulfill functions as a reception traffic volume measuring unit for measuring a reception traffic volume on data received from all next hop routers, forming other communication parties connected through the virtual private network, through the virtual private network and a measurement result notifying unit for notifying a measurement result on the measured reception traffic volume to all the next hop routers.  
      Still furthermore, a traffic control program recorded computer-readable recording medium according to the present invention, which is for recording a traffic control program, which makes a computer, serving as a router connected through a bridge unit to a virtual private network, carry out a traffic control function to control a traffic volume of the router, is characterized in that the traffic control program makes the computer fulfill functions as a reception traffic volume measuring unit for measuring a reception traffic volume on data received from all next hop routers, forming other communication parties connected through the virtual private network, through the virtual private network, a measurement result notifying unit for notifying a measurement result on the measured reception traffic volume to all the next hop routers, and a transmission traffic control unit for, when receiving the notification on the measurement result of the reception traffic volume in any one of the next hop routers from the next hop router, controlling a transmission traffic to this next hop router in accordance with the measurement result notified from the next hop router.  
      As described above, according to the present invention, a router has functions as a reception traffic volume measuring unit, a measurement result notifying unit and a transmission traffic volume control unit and, hence, in a case in which, when the router connected to an edge of a user measures its own router reception volume, the measurement result shows that congestion tends to occur in an access line or in a transit network, the router notifies this fact to other routers so that the router, which has received the notification, controls a volume to be transmitted for preventing the occurrence of frame abandonment. This provides an advantage of constructing a network so as not to degrade the communication efficiency in the case of the employment of a layer-2 virtual private network which does not have a frame abandonment notification function and an abandonment function based on priority. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       FIG. 1  is an illustration of an L2-VPN network using mode according to an embodiment of the present invention.  
       FIG. 2  is a flow chart for explaining a traffic control method for a router according to an embodiment of the present invention.  
       FIG. 3  is a block diagram showing a router according to an embodiment of the present invention.  
       FIGS. 4 and 7  are block diagrams showing an essential part of a router according to an embodiment of the present invention.  
       FIG. 5 ( a ) is an illustration of a first table according to an embodiment of the present invention, and  FIG. 5 ( b ) is an illustration of a second table according to an embodiment of the present invention.  
       FIG. 6 ( a ) to  FIG. 6 ( d ) are block diagram showing a format for an ICMP message to be used as a rate control packet to be transmitted/received between routers according to an embodiment of the present invention.  
      FIGS.  8  to  10  are flowcharts for explaining an operation for traffic control in a router connected to a transit network according to an embodiment of the present invention.  
       FIG. 11  is an illustration of a network forming one example of a conventional L2-VPN service provided by a network carrier. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      (a) Description of Embodiment of the Present Invention  
      An embodiment of the present invention will be described hereinbelow with reference to the drawings.  
      (a1) Description of Network Configuration According to Embodiment of the Present Invention  
       FIG. 1  is an illustration of an L2-VPN network using mode according to an embodiment of the present invention, and a communication system  1  shown in  FIG. 1  is one example of an L2-VPN service as well as the above-described case shown in  FIG. 11  and is made up of a transit network line  10  serving as a virtual facility network comprising a bridge function and user networks  20 A to  20 D connected to the transit network line  10 .  
      That is, LANSWs  11  to  14  constituting the transit network line  10  are connected through access lines  15 A to  15 D to routers  21 A to  21 D of the user networks  20 A to  20 D serving as sites, respectively. The LANSWs  11  to  14  are for bridging a frame transmitted. That is, the LANSWs  11  to  14  make a reference to a physical address at a data link layer of the layer  2  to relay a frame.  
      Moreover, each of the routers  21 A to  21 D includes ports a 1  to d 1  for making connections to the aforesaid access lines  15 A to  15 D and ports a 2  to d 2  and a 3  to d 3  for making connections to local networks placed thereunder. This enables communications to be made through the access lines  15 A to  15 D and the transit network  10  even between terminals accommodated in the routers  21 A to  21 D different from each other.  
      That is, the routers  21 A to  21 D are connected through the L2-VPN made up of the transit network line  10  and the access lines  15 A to  15 D, and this L2-VPN enables mutual connectionless access to be made between the sites (routers  21 A to  21 D).  
      In this case, although both the transit network line  10  and access lines  15 A to  15 D organize the L2-VPN as mentioned above, they can be constructed as lines having characteristics different from each other. For example, it is possible that the access lines  15 A to  15 D are of a best effort type of 100 Mbps while the transit network line is of a band assurance type of 100 Mbps.  
      In this network configuration, as a communication system designed to make communications between the routers  21 A to  21 D connected through bridge units  11  to  14  to the transit network  10 , connections are made as shown in  FIG. 2 , thereby controlling a traffic volume in each of the routers  21 A to  21 D.  
      Although the following description will be given focusing on a case in which the router  21 A receives frame data from next hop routers (routers forming other communication parties with the router  21 A)  21 B to  21 D, this also applies to a case in which the routers  21 B to  21 D other than the router  21 A receive frame data from the next hop routers.  
      That is, as shown in  FIG. 2 , when making communication with all the next hop routers  21 B to  21 D forming opposite communication parties connected through the transit network  10  serving as a virtual private network, the router  21 A measures a reception traffic volume on frame data received from the next hop routers  21 B to  21 D through the transit network  10 , i.e., frame data inputted from the bridge unit  11  (step S 1 , traffic volume measuring step).  
      Subsequently, a measurement result on the reception traffic volume measured in the router  21 A is notified to all the aforesaid next hop routers  21 B to  21 D (step S 2 , notification step).  
      Concretely, a decision is made as to magnitude relation between the reception traffic volume measured in the router  21 A and a predetermined threshold. When the decision shows that the aforesaid reception traffic volume exceeds the predetermined threshold, information to the effect of it is inserted into a control packet and notified to all the next hop routers  21 B to  21 D. In other words, the router  21 A performs the notification on the fact that the reception traffic volume exceeds the predetermined threshold and the probability of the occurrence of frame abandonment becomes relatively high in the transit network  10  acting as the layer  2  (L 2 ) virtual facility network or in the access line  15 A.  
      When receiving the control packet from the router  21 A through the transit network  10 , each of the aforesaid next hop routers  21 B to  21 D controls the transmission traffic on data to be transmitted to this router  21 A (step S 3 , transmission traffic control step).  
      That is, each of the routers  21 B to  21 D suppresses the transmission traffic volume to the router  21 A to a predetermined volume. This suppresses the traffic concentration in the access line  15 A making connection between the bridge unit  11  and the router  21 A, thereby preventing the occurrence of a congestion state or frame abandonment.  
      (a2) Description of Configuration of Router According to Embodiment of the Present Invention  
      For example, shown in  FIG. 3 , the routers  21 A to  21 D connected to the transit network as shown in  FIG. 1  are made up of an interface unit  22 , a relay control unit  23  and a local interface unit  24 , which enables the aforesaid traffic volume control shown in  FIG. 2 .  
      Although, for convenience only, the following description will be made focusing on the configuration of the router  21 A shown in  FIG. 1 , the other routers  21 B to  21 D shown in  FIG. 1  have a similar configuration.  
      The interface unit  22  of the router  21 A is for carrying out frame transmission/reception to/from all the next hop routers  21 B to  21 D forming opposite communication parties connected to the transit network  10 , and is composed of a receiving unit  31 , a transmitting unit  32 , a reception rate check unit  33  and a transmission rate check unit  34 .  
      Moreover, the local interface unit  24  is for carrying out packet transmission/reception through the port a 2  or a 3 , shown in  FIG. 1 , with respect to a local unit such as a terminal accommodated under the router  21 A to which it pertains, and is composed of a local receiving unit  35  for packet reception and a local transmitting unit  36  for packet transmission.  
      Still moreover, the relay control unit  23  is for implementing relay control on data between the interface unit  22  and the local interface unit  24 , and is composed of a relay processing unit  37 , a routing table  38 , a rate control information processing unit  39  and a rate control table  40 .  
      Yet moreover, the receiving unit  31  and the transmitting unit  32  in the interface unit  22  are for conducting the interface between the access lines  15 A to  15 D and the router  21 A to which it pertains. That is, the receiving unit  31  is made to receive a frame from the access lines  15 A to  15 D and transfer it to the latter-stage relay processing unit  37  after the conversion into a packet, while the transmitting unit  32  is made to convert the packet from the relay processing unit  37  into a frame and transmit this frame through the access lines  15 A to  15 D.  
      In addition, the transmitting unit  32  functions as a measurement result notifying unit to notify a measurement result on a reception traffic volume, measured, to all the next hop routers in the aforesaid notification step.  
      Still additionally, the reception rate check unit  33  is for transferring, of reception packets received from the next hop routers  21 B to  21 D by the receiving unit  31 , a data packet to the relay processing unit  37  for the relay processing to a local unit and for transferring a control packet, which will be mentioned later, to the rate control information processing unit  39 .  
      Yet additionally, this reception rate check unit  33  is made to measure and check a reception traffic volume (reception rate) on a reception packet from the aforesaid receiving unit  31  in the aforesaid traffic volume measuring step, and it functions as a reception traffic volume measuring unit.  
      Concretely, it measures a reception rate of a reception packet from the receiving unit  31  and makes a decision as to whether or not the measurement result exceeds a predetermined threshold. That is, if this reception rate check unit  33  shows that the reception rate of the reception packet exceeds the predetermined threshold, a rate-over flag area of the rate control table  40 , which will be mentioned later, is set at “1” and the reception rate control is set into an active state (so-called flag-rising state).  
      In other words, the reception rate check unit  33  functions as a reception traffic volume measuring unit to measure a reception traffic volume (reception rate) on data received from all the next hop routers  21 B to  21 D through the transit network  10  and further functions as a threshold decision unit to make a decision as to magnitude relation between the reception traffic volume measured in the reception traffic volume measuring unit and a predetermined threshold.  
      Furthermore, the transmission rate check unit  34  is made to receive, from there lay control unit  23 , transmission packet data to be transmitted through the transit network  10  to the next hop routers  21 B to  21 D and measure a transmission traffic volume (transmission rate) on this transmission packet data for carrying out transmission rate suppression control or increase control according to an instruction from the rate control information processing unit  39  which will be mentioned later.  
      Concretely, the transmission rate check unit  34  is made to carry out suppression control for conducting frame transmission at a suppression rate determined for each of the reception side routers  21 B to  21 D or to implement increase control for increasing transmission rate gradually from a suppression control condition.  
      Accordingly, in the aforesaid transmission traffic control step, in cooperation with the rate control information processing unit  39  which will be mentioned later, the aforesaid transmission rate check unit  34  functions as a transmission traffic volume control unit to, when receiving a notification on a measurement result of a reception traffic volume in any one of the next hop routers from this next hop router, control a transmission traffic volume to this next hop router in accordance with the measurement result notified from this next hop router.  
      Still furthermore, the relay processing unit  37  of the relay control unit  23  is made to make a reference to a routing table  38  recording routing information for conducting routing processing on a data packet from the reception rate check unit  33  to transfer it to the transmitting unit  36 , with this data packet being transferred through the local transmitting unit  36  to the local unit which is a destination.  
      Likewise, this relay processing unit  37  makes a reference to the routing table  38  to conduct routing processing on a data packet received through the local receiving unit  35  for transferring it to the interface unit  22 , with this data packet from the local receiving unit  35  being transmitted through the transmitting unit  32  to the access line  15 A after processed in the transmission rate check unit  34  of the interface unit  22 .  
      Yet furthermore, the rate control information processing unit  39  is for, when the aforesaid reception rate check unit  33  shows that the reception traffic volume exceeds the predetermined threshold, carrying out first control information processing when the information to the effect of it is inserted into a control packet and notified to all the next hop routers  21 B to  21 D and second control information processing when a control packet is received from the next hop routers  21 B to  21 D to control a transmission traffic on data to be transmitted to the next hop routers  21 B to  21 D.  
      As a functional aspect, as shown in  FIG. 4 , the rate control information processing unit  39  is composed of a time-out processing unit  41 , a rate control packet transmission timer  42 , a rate control packet transmission processing unit  43 , processing units  44 - 1  to  44 - 3  provided to correspond to the next hop routers  21 B to  21 D, and a next hop entry processing unit  45 .  
      The aforesaid time-out processing unit  41 , rate control packet transmission timer  42  and rate control packet transmission processing unit  43  constitute a functional unit for conducting the aforesaid first control information processing, while the aforesaid time-out processing unit  41  and processing units  44 - 1  to  44 - 3  organize a functional unit for conducting the aforesaid second control information processing.  
      Moreover, the rate control data  40  is for managing control data for control information processing in the aforesaid rate control information processing unit  39 , and includes a first table  40 A for the aforesaid first control information processing, for example, shown in  FIG. 5 ( a ) and a second table  40 B for the aforesaid second control information processing, for example, shown in  FIG. 5 ( b ).  
      That is, the first table  40 A shown in  FIG. 5 ( a ) is composed of an alarm rate storing areas  40 A- 1 , a rate-over flag storing area  40 A- 2  and a rate control packet transmission timer set value storing area  40 A- 3 .  
      An alarm rate to be stored in the storing area  40 A- 1  is a reference value (threshold) to be taken for making a comparison with a reception rate of a reception packet received through a reception port al connected to the access line  15 A. That is, in the reception rate check unit  33 , the alarm rate (in this case,  80  Mbps) stored in the storing area  40 A- 1  is used as a threshold and compared in magnitude with a measured reception traffic volume so that, when the reception traffic volume exceeds the alarm rate, “1” is set in the storing area  40 A- 2 .  
      The time-out processing unit  41  of the rate control information processing unit  39  is triggered by setting “1” in the aforesaid storing area  40 A- 2  and made to output production and transmission instructions for a rate control packet to the rate control packet transmission processing unit  43  and to activate the rate control packet transmission timer  42  with a value (in this case, timer value “3”) stored in the storing area  40 A- 3  as a time-out value.  
      When receiving a rate control packet transmission instruction from the time-out processing unit  41 , the rate control packet transmission processing unit  43  produces a rate control packet and outputs it to the transmitting unit  32  of the interface unit  22 , and when receiving a time-out notification on the rate control packet transmission timer  42  from the time-out processing unit  41 , it stops the production of this rate control packet.  
      In other words, the rate control packet transmission processing unit  43  produces a rate control packet while the aforesaid rate control packet transmission timer  42  is in operation, and outputs it to the transmitting unit  32  of the interface unit  22 . Therefore, the aforesaid rate control packet transmission processing unit  43  functions as a control data producing unit to produce, as a rate control packet, control data corresponding to a measurement result to be notified through the frame transmission by the transmitting unit  32 , on the basis of a reception traffic volume measured in the reception rate check unit  33 .  
      In addition, when a result of the threshold decision in the reception rate check unit  33  shows that the reception traffic volume exceeds the predetermined threshold, the rate control packet transmission processing unit  43  serving as a control data producing unit produces a rate control packet as control data including the information to the effect of it.  
      That is, the rate control packet produced in this rate control packet transmission processing unit  43  can notify to the next hop routers  21 B to  21 D that its own (router  21 A) reception traffic volume exceeds the predetermined threshold and the probability of the occurrence of frame abandonment in the transit network  10  acting as the layer  2  (L 2 ) virtual facility network or in the access line  15 A is relatively high.  
      Still additionally, since the aforesaid control packet can be placed in a frame to be transmitted through the access line  15 A, the transmitting unit  32  can transmit the rate control packet through the transit network  10  to each of the next hop routers  21 B to  21 D. Accordingly, the rate control packet is transmitted as a measurement result of a reception traffic volume through the transmitting unit  32 , which enables a request to all the next hop routers  21 B to  21 D for control on the traffic volume on transmission data to the router  21 A, it pertains to.  
      That is, when the result of the threshold decision in the reception rate check unit  33  indicates that the reception traffic volume exceeds the threshold, the transmitting unit  32  serving as a measurement result notifying unit makes a notification to the next hop routers  21 B to  21 D as a request for the suppression of transmission data to the router  21 A, it pertains to, in order to prevent the congestion which can occur in the transit network  10  or in the access lines  15 A to  15 D.  
      In this case, as the above-mentioned rate control packet, there is employable ICMP Source Quench Message (message to be transmitted for, when a router is short of resource needed for the reception or replay of packets, suppressing the transmission from a transmission side of a frame acting as a trigger). In a case in which the access lines  15 A to  15 D are Ethernet (R), the aforesaid rate control packet is producible with formats, for example, shown in FIGS.  6 ( a ) to  6 ( d ).  
      That is, an ICMP message  70  serving as a rate control packet is composed of areas of an MAC header  71 , an IP header  72  and IP data  73  as shown in  FIG. 6 ( a ). The MAC header  71  includes a reception side physical address (MAC-DA)  71 - 1 , a transmission side physical address (MAC-SA)  71 - 2 , a type  71 - 3  and optional VLAN information  71 - 4  as shown in  FIG. 6 ( b ).  
      Moreover, as shown in  FIG. 6 ( c ), the format for the IP header  72  includes Version information  72 - 1 , IHL  72 - 2 , toS  72 - 3 , Length  72 - 4 , ID  72 - 5 , F  72 - 6 , Offset  72 - 7 , TTL  72 - 8 , Protocol  72 - 9 , Check sum  72 - 10 , IP Transmission side address (IP-SA)  72 - 11 , IP Reception side address (IP-DA)  72 - 12 , Option  72 - 13  and Padding  72 - 14 .  
      Still moreover, as shown in  FIG. 6 ( d ), the format for the IP data  73  includes Type information  73 - 1  of “Type=4”, Code information  73 - 2  of “Code=0”, Check sum  73 - 3 , unused  73 - 4  and IP Header+Message (IP Header+64 bit of original Message)  73 - 5 .  
      In a case in which a rate control packet according to the aforesaid frame format is transmitted to be broadcasted in a subnet, all “1” signifying the broadcasting is set as the aforesaid reception side physical address  71 - 1 , and a value for in-subnet broadcasting is set as the IP transmission side address  72 - 11 , and all “0” depicting the rate control packet is set in the IP header+Message  73 - 5 .  
      Yet moreover, in a case in which a rate control packet according to the aforesaid frame format is individually transmitted to the respective next hop routers, an MAC address of a next hop router is set as the aforesaid reception side physical address  71 - 1 , and an IP address of a next hop router is set as the IP transmission side address  72 - 11 , and all “0” representing a rate control packet is set in the IP Header+Message  73 - 5 .  
      Furthermore, for the above-mentioned second control information processing, each of the processing units  44 - 1  to  44 - 3  provided in corresponding relation to the aforesaid next hop routers  21 B to  21 D is functionally made up of a rate control packet reception processing unit  46 , a suppression timer  47 , a first counter  48  for counting the number of times of time-out of the suppression timer  47 , an increase timer  49  and a second counter  50  for counting the number of times of time-out of the increase timer  49 .  
      In this configuration, the rate control packet reception processing unit  46  is made to, when receiving a rate control packet from the next hop routers  21 B to  21 D through the reception rate check unit  33 , give an instruction on transmission rate control to the transmission rate check unit  34  on the basis of the timer values and count values managed in the suppression timer  47 , the first counter  48 , the increase timer  49  and the second counter  50  in a manner such that the rate control packet is used as a trigger.  
      Concretely, when receiving the rate control packet from the next hop routers  21 B to  21 D, the suppression timer  47 , the first counter  48  and the time-out processing unit  41  manage a period of time to be taken for suppressing the transmission rate from the router  21 A to the next hop routers  21 B to  21 D, while the increase timer  49 , the second counter  50  and the time-out processing unit  41  manages a period of time to be taken for increasing the suppressed transmission rate gradually.  
      The suppression timer  47  is activated when the rate control packet reception processing unit  46  receives the rate control packet from the next hop routers  21 B to  21 D and is made to measure the time of the suppression control on the transmission rate being implemented in the transmission rate check unit  34  which will be mentioned later. Moreover, the first counter  48  is for counting the number of times of time-out of the aforesaid suppression timer  47  and, when this frequency of time-out reaches a reference frequency, the aforesaid transmission rate check unit  34  shifts the transmission rate control from the suppression control to the increase control.  
      Therefore, in cooperation with the rate control information processing unit  39 , the transmission rate check unit  34  serving as a transmission traffic control unit carries out the control to set the transmission traffic volume to a next hop router (for example, router  22 C) at a first traffic volume, suppressed, (suppression rate) for a first period of time after receipt of a notification on a request for the control of the traffic on transmission data from the next hop router  22 C, and carries out the control to increase the transmission traffic volume gradually toward a second traffic volume, intended, (maximum transmission rate) for a second period of time after the elapse of the first period of time.  
      The increase timer  49  is for measuring the time of the transmission rate increase control being implemented in the transmission rate check unit  34 . Moreover, the second counter  50  is for counting the number of times of time-out of the increase timer  49 . The time-out processing unit  41  is made to conduct the time-out processing on the aforesaid rate control packet transmission timer and further to conduct the time-out processing on the suppression timer  47 , the first counter  48 , the increase timer  49  and the second counter  50 .  
      For each of the next hop routers  21 B to  21 D, the second table  40 B [see  FIG. 5 ( b )] for the second control information processing includes a maximum transmission rate storing area  40 B- 1 , a suppression rate storing area  40 B- 2 , a maximum transmittable rate storing area  40 B- 3 , a storing area  4 DB- 4  for storing a reference value of frequency of time-out of the suppression timer  47 , an area  4 DB- 5  for storing a reference value of frequency of time-out of the suppression timer  47 , a storing area  4 DB- 6  for storing a state of the increase timer  49 , and a storing area  40 B- 7  for storing an increase rate.  
      The maximum transmission rate storing area  40 B- 1  is for storing a maximum transmission rate at normal timer which is to be set for each of the next hop routers  21 B to  21 D. In this case, the maximum transmission rate to the router  21 B is set at 70 Mbps, the maximum transmission rate to the router  21 C at 40 Mbps and the maximum transmission rate to the router  21 D at 50 Mbps.  
      Moreover, the suppression rate storing area  40 B is for storing a suppression rate (maximum transmission rate at suppression control) to be set for each of the next hop routers  21 B to  21 D. In this case, each of the suppression rates to the routers  21 B to  21 D is set at 30 Mbps.  
      Still moreover, the maximum transmittable rate storing area  40 B- 3  is for storing a maximum transmittable rate to each of the routers  21 B to  21 D which is to be determined on the basis of the assurance bands of the access lines  15 A to  15 D and the transit network  10 . In this case, each of the suppression rates to the routers  21 B to  21 D is set at 100 Mbps.  
      Yet moreover, the storing area  40 B- 4  is an area in which a time-out value of the suppression timer  47  is stored for each of the routers  21 B to  21 D, while the storing area  40 B- 5  is an area in which a reference value of frequency of time-out of the suppression timer  47  is stored for each of the routers  21 B to  21 D. That is, the timer-out processing unit  41  is made to activate the suppression timer  47  at a time-out value set for each of the routers  21 B to  21 D by making a reference to the contents of this table  40 B and further to count the number of times of time-out for shifting to the increase control through the use of the first counter  48 .  
      In addition, the storing area  40 B- 6  is an area in which a time-out value of the increase timer  49  is stored for each of the routers  21 B to  21 D, while the storing area  40 B- 7  is an area in which a reference value of frequency of time-out of the increase timer  48  is stored for each of the routers  21 B to  21 D. That is, the time-out processing unit  41  is made to activate the increase timer  48  at a time-out value set for each of the routers  21 B to  21 D, which implements the increase control, by making a reference to the contents of this table  40 B and further to count the number of times of time-out in the increase timer  49  through the use of the second counter  50 .  
      Still additionally, as shown in detail in  FIG. 7 , the transmission rate check unit  34  of the interface unit  22  is composed of a next hop classifying unit  51  and transmission rate control units  52 - 1  to  52 - 3  provided for the respective next hop routers.  
      For example, in the router  20 A, the transmission rate control unit  52 - 1  is made to control the transmission rate of a data packet to the next hop router  20 B, and the transmission rate control unit  52 - 2  is made to control the transmission rate of a data packet to the next hop router  20 C, and the transmission rate control unit  52 - 3  is made to control the transmission rate of a data packet to the next hop router  20 D.  
      The next hop classifying unit  51  is made to classify data packets, transferred from the relay processing unit  37 , for each next hop router forming a reception side router, with the data packets classified for each next hop router being transferred to the transmission rate control units  52 - 1  to  52 - 3  of each corresponding next hop router.  
      Still additionally, each of the transmission rate control units  52 - 1  to  52 - 3  is made to control the transmission rate on the aforesaid data packet classified for each router and hand it over to the transmitting unit  32  and is composed of a transmission byte counter  53 , an actual transmission rate calculating unit  54 , a transmission rate maximum value holding unit  60 , a queue  61  and a transmission decision unit  62 .  
      For example, in the transmission rate control unit  52 - 1  of the router  20 A, the transmission byte counter  53  is made to count the number of transmission bytes of a data packet addressed to the router  20 B. The actual transmission rate calculating unit  54  is made to calculate an actual transmission rate on the basis of the transmission bytes counted by the transmission byte counter  53  and is composed of a current number-of-byte holding unit  55 , a previous number-of-byte holding unit  56 , a timer  57 , a time-out processing unit  58  and an actual transmission rate holding unit  59 .  
      The current number-of-byte holding unit  55  is made to add up the numbers of transmission bytes counted in the transmission byte counter  53  and hold it, and the previous number-of-byte holding unit  56  is made to store the number of transmission bytes held in the current number-of-byte holding unit  55  immediately before a time-out time managed in the timer  57 .  
      Moreover, the time-out processing unit  58  is for conducting the time-out processing every predetermined time managed in the timer  57 . Concretely, it calculates an actual transmission rate through the use of values held in the current number-of-byte holding unit  55  and the previous number-of-byte holding unit  56  every predetermined time managed in the timer  57  and writes a value, held in the current number-of-byte holding unit  55 , in the previous number-of-byte processing unit  56 .  
      Concretely, in the time-out processing unit  58 , as expressed by an equation (1), the number of transmission bytes per unit time is calculated as an actual transmission rate, and the calculation result is held in the actual transmission rate holding unit  59 .  
      In other words, the time-out processing unit  58  obtains the number of transmission bytes, counted for a predetermined time managed by the timer  57 , on the basis of the difference between the number of transmission bytes held in the current number-of-byte counter  55  and the number of bytes held in the previous number-of-byte holding unit  56  and divides the obtained number of transmission bytes by a time-out interval in the timer  57 , thereby calculating an actual transmission rate. 
 
Actual Transmission Rate={(Current Number of Bytes) −(Previous Number of Bytes)}/(Time-out Interval)   (1) 
 
      Still Moreover, the transmission rate maximum value holding unit  60  is made to hold the maximum value of the transmission rate set in the aforesaid time-out processing unit  41 . The queue  61  is made to queue the data packets counted in number of transmission bytes in the transmission byte counter  53  in accordance with priority such as a predetermined WFQ (Waited Fair Queuing) or the like.  
      In other words, in carrying out the transmission traffic control, owing to the aforesaid queue  61 , the transmission traffic volume is controllable while transmitting the transmission data according to the priority.  
      Yet moreover, the transmission decision unit  62  is made to control the transmission rate on the basis of the actual transmission rate calculated in the actual transmission rate calculating unit  54  and the transmission rate maximum value held in the transmission rate maximum value holding unit  60 . Concretely, the transmission decision unit  62  is designed to carry out the limiter control by making a decision on the right of transmission so that the aforesaid actual transmission rate does not exceed the maximum transmission rate when a data packet is derived from the queue  61  and transferred as a transmission packet to the transmitting unit  32 .  
      In the aforesaid transmission decision unit  62 , the time-out from the timer  57  or the queuing of a transmission packet from the transmission byte counter  53  is used as a trigger for making the aforesaid transmission decision.  
      The function as the reception traffic measuring unit depending on the aforesaid reception rate check unit  33 , the measurement result notifying unit depending on the cooperation among the transmitting unit  32 , the rate control information processing unit  39  and the rate control table  40 , and the function as the transmission traffic control unit depending on the cooperation among the transmission rate check unit  34 , the rate control information processing unit  39  and the rate control table  40  are realizable in a manner such that a processor carries out a program developed on a memory which is not shown. Moreover, it is also realizable in a manner such that this program is read out from a recording medium such as DVD or CD-ROM, which stores the program, and a processor carries out the program developed on a memory.  
      (a3) Description of Traffic Control Operation in the Routers  20 A to  20 D Connected to the Transit Network  10  According to First Embodiment of the Present Invention Focusing on the control in the router  20 A, a description will be given hereinbelow of, in the above-described configuration, a flow of traffic control in the routers  20 A to  20 D connected to the transit network  10  according to the embodiment of the present invention.  
      First, with reference to flow charts of  FIGS. 8 and 9 , a description will be given hereinbelow of the processing to be conducted in the router  20 A when a frame is received from the next hop routers  20 B to  20 D.  
      In the router  20 A, in a case in which a program is executed in order to fulfill the functions as the aforesaid reception rate check unit  33 , the transmission rate check unit  34 , the rate control information processing unit  39  of the relay control unit  23  and the rate control table  40 , the following five types of interruption processing will be conducted from a state in which the set values of timers, flags and others are set to initial set values (step T 1 ).  
      First, when the receiving unit  31  of the interface unit  22  receives a frame, this receiving unit  31  converts it into a packet signal and, subsequently, the reception rate check unit  33 , the rate control information processing unit  39  and the rate control table  40  cooperate with each other to conduct reception rate check processing (reception traffic measurement step, steps A 1  to A 4  shown in  FIG. 8 ) and reception packet processing (steps B 1  to B 3  shown in  FIG. 8 , B 11  to B 15  shown in  FIG. 9 ).  
      That is, the reception rate check unit  33  calculates a reception rate on a packet signal from the receiving unit  31  and makes a comparison in magnitude between the calculation result and an alarm rate value read out from the first table  40 A of the rate control table  40 . Incidentally, as mentioned above, the alarm rate value is set in the storing area  40 A- 1  [see  FIG. 5 ( a )] of the first table  40 A in corresponding relation to the port a 1  (see  FIG. 1 ) of the router  20 A.  
      In a case in which a result of the comparison between the calculated reception rate and the alarm rate shows that the reception rate exceeds the alarm rate, in the storing area  40 A- 2  of the first table  40 A, “1” is set as a rate-over flag (step A 2  through YES route of step A 1 ).  
      When the rate-over flag “1” is set in the aforesaid storing area  40 A- 2 , if the rate control packet transmission timer  42  is not in an activated condition, the time-out processing unit  41  of the rate control in formation processing unit  39  activates this rate control packet transmission timer  42 , and gives an instruction for the production of a rate control packet to the rate control packet transmission processing unit  43 .  
      Thus, upon receipt of the instruction from the time-out processing unit  41 , the rate control packet transmission processing unit  43  produces a rate control packet, and the transmitting unit  32  inserts it into a data packet forming a transmission packet framed. In other words, the rate control packet is transmitted, as a frame to be transmitted from the transmitting unit  32 , to the next hop routers  20 B to  20 D (step A 4  through YES route of step A 3 ).  
      That is, through the use of this rate control packet, with respect to frame data received by the router  21 A it pertains to, a notification to the effect that a possibility of the occurrence of frame abandonment due to congestion in the access line  15 A or the transit network  10  is made to the next hop routers  21 B to  21 D.  
      In a case in which the result of the reception rate comparison in the reception rate check unit  33  in the aforesaid step A 1  shows that the reception rate does not exceed the alarm rate, the rate-over flag in the storing area  40 A- 2  is set at “0”, and the interruption processing serving as the reception rate check processing comes to an end (NO route of step A 1 ). Moreover, if the rate control packet transmission timer  42  is already in activation in the step A 3 , since the rate control packet is already transmitted, the interruption processing serving as the reception rate check processing comes to an end (NO route of step A 3 ).  
      In addition, as the second interruption processing, on the reception packets which undergo the aforesaid reception rate check, the reception packet processing is conducted according to packet types (steps B 1  to B 3 ) That is, when, in the reception rate check unit  33 , an identification is made as the reception packet is a rate control packet [see FIGS.  6 ( a ) to  6 ( d )] from the next hop routers  20 B to  20 D, this rate control packet is handed over to the rate control packet reception processing unit  46  (see  FIG. 4 ) of the rate control information processing unit  39 , and the following rate control is implemented on a transmission packet to the rate control packet transmission side router (transmission traffic control step).  
      That is, upon receipt of a rate control packet, the rate control packet reception processing unit  46  sets the maximum transmission rate for the aforesaid rate control packet transmission side router (for example, router  20 C) at a suppression rate by making a reference to the rate control table  40 .  
      Concretely, the rate control packet reception processing unit  46  rewrites the transmission rate maximum value, which is held in the transmission rate maximum value holding unit  60  of the transmission rate control unit  52 - 2  corresponding to the router  20 C in the transmission rate check unit  34 , into a suppression rate (corresponding to the router  20 C) read out from the storing area  40 B- 2  [see  FIG. 5 ( b )] of the second table  40 B (step B 2  through YES route of step B 1 ). In this case, the transmission rate maximum value is rewritten from the maximum transmission rate of 40 Mbps into a suppression rate of 30 Mbps.  
      This prevents the congestion which can occur in the access line  15 C or the transit network  10 , thus preventing the occurrence of frame abandonment of a reception frame to be received by the router  21 C.  
      In addition, when the increase timer  49  is in activation, the rate control packet reception processing unit  46  stops the increase timer  49  and resets and activates the suppression timer  47  (the timer value is set at “0”) and further resets the count value (the number of times of time-out of the suppression timer  47 ) of the first counter  49  (the count value is set at “0”, step B 3 ).  
      In a case in which, when the aforesaid reception packet processing interruption takes place, a decision is made that the reception packet is not a rate control packet, if the aforesaid reception packet is a packet according to a routing protocol, for example, the reception rate check unit  33  conducts frame reception processing according to this routing protocol (NO route of step B 1 , step B 12  through YES route of step B 11  shown in  FIG. 9 ).  
      At this time, if information change does not arise in the next hop routers  20 B to  20 D, the interruption for the reception packet processing comes to an end (NO route of step B 13 ), and if the information change arises in the next hop routers  20 B to  20 D, the reception rate check unit  33  updates the entry information in the second table  40 B constituting the rate control table  40 .  
      That is, the reception rate check unit  33 , when receiving a packet according to the routing protocol, takes out the updated contents of the entry information of the next hop routers  20 B to  20 D from this packet and updates the set values stored in the storing areas  40 B- 1  to  40 B- 7 , which are objects of updating on the second table  40 B, and the interruption for the reception packet processing comes to an end (step B 14  through YES route of step B 13 ).  
      If the aforesaid reception packet is not a packet according to the routing protocol but is a normal data packet, the normal frame reception processing is conducted to transfer this data packet to the relay processing unit  37  (NO route of step B 1 , step B 15  through NO route of step B 11 ).  
      In other words, the contents of the rate control table  40  of the router  20 A can be updated from the next hop routers  20 B to  20 D through the packet according to the aforesaid routing protocol.  
      Following this, in the rate control information processing unit  39 , when the value of the rate control packet transmission timer  42  reaches a value (in this case, “3”) stored in the storing area  40 A- 3  of the rate control table  40 , which signifies the occurrence of time-out, interruption processing are conducted in steps C 1 , C 2  and A 4 .  
      That is, when the time-out occurs in the rate control packet transmission timer  42 , the time-out processing unit  41  makes a reference to a state of the rate-over flag in the storing area  40 A- 2  of the rate control table  40 .  
      At this time, if the rate-over flag shows “0”, the time-out processing unit  41  stops the rate control packet transmission timer  42  and the interruption processing comes to an end (step C 2  through NO route of step C 1 ). On the other hand, if the rate-over flag shows “1”, the time-out processing unit  41  again gives an instruction to the rate control packet transmission processing unit  43  for the production of a rate control packet and the transmission control, and activates the rate packet transmission timer  42  (step A 4  through YES route of step C 1 ), and the interruption processing comes to an end.  
      Subsequently, in the rate control information processing unit  39 , when the value of the suppression timer  47  activated reaches a value (in this case, “5”) stored in the storing area  40 B- 4  of the rate control table  40 , which signifies the occurrence of time-out, the interruption processing are conducted in steps D 1  to D 7 .  
      That is, when the time-out of the suppression timer  47  occurs, the time-out processing unit  41  increments the value of the first counter  48 , indicating the frequency of time-out of the suppression timer  47 , by “1” (step D 1 ) and stops the suppression timer  47  (step D 2 ).  
      Furthermore, in a case in which the value stored in the storing area  40 B- 5  of the rate control table  40  exceeds the value of the first counter  48 , i.e., if the number of times of time-out of the suppression timer  47  exceeds a set value of frequency of time-out of the suppression timer  47 , the transmission rate maximum value held in the transmission rate maximum value holding unit  60  (see  FIG. 7 ) of the transmission rate check unit  34  is set to be gradually increased from the suppression rate toward the maximum transmission rate stored in the storing area  40 B- 1  of the rate control table  40  (YES route of step D 3 ).  
      Concretely, the time-out processing unit  41  makes a decision as to whether or not a value obtained by multiplying the transmission rate maximum value held in the maximum transmission rate holding unit  60  by a value stored in the storing area  40 B- 7  of the rate control table  40  exceeds the maximum transmission rate stored in the storing area  4 DB- 1 , and if it does not exceed the stored value, updates the maximum transmission rate holding unit  60  so that the value obtained by the aforesaid multiplication is set as a new transmission rate maximum value (step D 5  through NO route of step D 4 ), and activates the increase timer  49  (step D 6 ), and the interruption processing comes to an end.  
      If a decision is made such that the value obtained by the aforesaid multiplication exceeds the maximum transmission rate stored in the storing area  40 B- 1 , the time-out processing unit  41  updates the maximum transmission rate holding unit  60  so that this maximum transmission rate is set as a new transmission rate maximum value (step D 7  through YES route of step D 4 ), and the interruption processing comes to an end.  
      If the decision in the aforesaid step D 3  shows that the number of times of time-out of the suppression timer  47  does not exceed the set value of frequency of time-out of the suppression timer  47 , the interruption processing terminates at this time.  
      Moreover, in the rate control information processing unit  39 , when the value of the increase timer  49  activated reaches a value (in this case, “5”) stored in the storing area  40 B- 6  of the rate control table  40 , because of the occurrence of time-out, as well as the above-mentioned case, the time-out processing unit  41  increases and sets the transmission rate maximum value gradually toward the maximum transmission rate (steps D 4  to D 7 ).  
      Furthermore, referring to a flow chart of  FIG. 10 , a description will be given hereinbelow of the processing to be conducted when the router  20 A transmits a frame to the next hop routers  20 B to  20 D. The transmission rate check in the transmission rate check unit  34  is conducted in unit of next hop router.  
      That is, in the router  20 A, for the transmission of a frame to the next hop routers  20 B to  20 D, when a program is executed in order to fulfill the functions as the aforesaid reception rate check unit  33 , transmission rate check unit  34 , rate control information processing unit  39  of the relay control unit  23  and rate control table  40 , the following three types of interruption processing are conducted by means of interruption from a state in which set values of timers, flags and others are set at initial set values.  
      That is, in the rate control packet transmission processing unit  43  of the rate control information processing unit  39 , when receiving an instruction on the production of a rate control packet and transmission processing from the time-out processing unit  41 , the rate control packet transmission processing unit  43  outputs a rate control packet to the transmitting unit  32  as the interruption processing. The transmitting unit  32  processes the rate control packet together with other transmission packets into the form of a frame and transmits it to the next hop routers  20 B to  20 D (notification step, step F 1 ).  
      In addition, transmission packets other than the aforesaid rate control packet are framed in the transmitting unit  32  through the processing in the transmission rate check unit  34 . For example, in the transmission decision unit  62 , a transmission data packet undergoing the routing processing in the relay processing unit  37  is derived from the queue  61  under the rate control of preventing it from exceeding a transmission rate set in the transmission rate maximum value holding unit  60  for each of the reception side next hop routers  20 B to  20 D, and is outputted to the transmitting unit  32  (step E 1 ).  
      At this time, if the entry information in the rate control table  40  is updated (see step B 14  in  FIG. 9 ), a notification on this fact is made to the transmission rate check unit  34  (steps G 1  to G 4 ).  
      That is, in a case in which an entry is added or deleted in the contents of the rate control table  40 , for example, in the case of addition or deletion of the next hop routers  20 B to  20 D forming other communication parties registered in the rate control table  40 , this entry change is notified to the transmission rate check unit  34  (step G 2  through YES route of step G 1 ).  
      Moreover, in a case in which the updating contents of the rate controltable  40  do not relate to addition or deletion of the next hop routers  20 B to  20 D forming other communication parties and in the case of a change of the maximum transmission rate stored in the storing area  40 B- 1  of the rate control table  40 , this change of the maximum transmission rate is notified to the transmission rate check unit  34  (NO route of step G 1 , step G 4  through YES route of step G 3 ).  
      As described above, according to an embodiment of the present invention, since the router is equipped with the reception rate check unit  33 , the transmission rate check unit  34 , the rate control information processing unit  39  and the rate control table  40 , the routers  21 A to  21 D themselves connected to edges of users measure their own reception quantity and, when congestion tends to occur in the access lines  15 A to  15 D or in the transit network  10 , notify this fact to the other routers  21 A to  21 D so that the router, receiving the notification, adjusts the transmission quantity to prevent the occurrence of frame abandonment. As advantages, this enables constructing a network in which the communication efficiency does not degrade in the case of the employment of a layer  2  virtual private network which does not have a frame abandonment notification function and an abandonment function based on priority.  
      In particular, even if the probability of the occurrence of frame abandonment becomes relatively high due to the association with a queuing function such as WFQ in the router, the employment of the layer  2  virtual private network becomes easy for communications handling data in a manner such that a traffic volume of data with a relatively low priority is decreased while a traffic volume on data to be set at a high priority, such as data on real-time-system applications including voice or stream and data on important service, is secured on a preferential basis.  
      In addition, when providing, to users, a router supporting the functions according to the present invention as a router for the connection to a layer  2  virtual private network, a network carrier can also provide an integrated network service employing a layer  2  virtual private network and oriented to enterprises.  
      Although in the above-described embodiment each of the routers  21 A to  21 D has the functions as the reception traffic volume measuring unit, the measurement result notifying unit and the transmission traffic volume control unit, the present invention is not limited to this. For example, if it is equipped with only the reception traffic volume measuring unit and the measurement result notifying unit, at least the suppression of the traffic volume from the other router to this router is feasible, thus suppressing the congestion or frame abandonment which can occur in the access lines of this router.  
      Moreover, although in the above-described embodiment a rate control packet is notified as a measurement result on a reception traffic volume according to ICMP, the present invention is not limited to this. For example, when a management server according to a protocol such as SNMP (Simple Network Management Protocol) is provided as a management server for managing a virtual private network, the aforesaid reception traffic volume measurement result can be notified by way of this management server. Alternatively, it is also acceptable that the aforesaid reception traffic volume measurement result is notified according to an original protocol other than the aforesaid ICMP or SNMP.  
      The present invention is not limited to the above-described embodiment, and covers all changes and modifications which do not constitute departures from the spirit and scope of the invention.  
      The disclosure of each embodiment of the present invention enables manufacturing by a person skilled in the art.  
      As described above, a router according to the present invention is useful for constructing a network in which communication efficiency does not degrade in the case of the employment of a virtual private network which does not have a frame abandonment notification function and an abandonment function based on priority and, in particular, it is suitable in the case of the employment of a layer  2  virtual facility network.