JP2012248914A - Transfer device, communication method, and communication program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent unnecessary transfer of a multicast frame.SOLUTION: A transfer device includes a plurality of ports, a transfer part, a load factor measurement part, a confirmation part and a control part, and receives a multicast frame through a first port. The transfer part selects a second port to which a terminal receiving the multicast frame is connected from the plurality of ports, and transfers the multicast frame to the second port. The load factor measurement part measures a load factor which is the ratio of a load of processing having been performed at the second port per unit time to a processable load at the second port per unit time. The confirmation part confirms a multicast group in which the terminal connected through the second port joins, when the load factor exceeds a threshold. The control part performs control so that a multicast frame addressed to a multicast group in which the terminal connected through the second port does not join is not transferred from the second port.

Description

The present invention relates to a communication method, a transfer device used for communication, and a communication program.

  A router device in the network uses a protocol such as Internet Group Management Protocol (IGMP) to determine whether to transfer data that has been multicast transmitted to a subnet connected to the router device. For example, when a membership message (IGMP Membership) is received, the router device recognizes that it is connected to a terminal that has joined the multicast group identified by the membership message, and starts forwarding multicast packets. When IGMPv2 (IGMP version 2) or IGMPv3 (IGMP version 3) is used, a terminal that leaves the multicast group transmits a Leave message to the router device to which the terminal is connected. The router device checks whether there is a terminal that continues to participate in the multicast group identified by the Leave message among the terminals connected through the port that has received the Leave message. When there is a terminal that continues to participate, the router device continues to transfer the multicast packet. However, when there is no terminal that continues to participate, the router device ends the transfer of the multicast packet.

  By the way, a switch may be used to connect the router device and the terminal. Therefore, IGMP snooping may be used to control the transfer of frames including multicast packets at the switch. In this case, the switch determines whether to transfer a frame including a multicast packet to each port of the switch by acquiring information included in a message used in IGMP such as a membership message or a Leave message.

  A system that performs multicast congestion control is known as a technique related to multicast transmission. In this system, a router that detects congestion transmits a congestion notification to each connected terminal. The terminal that has received the congestion notification suppresses a request to start forwarding a multicast packet until notified from the router device that the congestion has been resolved.

JP 2007-174489 A

  As described in the background art, a switch that supports IGMP snooping recognizes a port that forwards a multicast packet by using a membership message or a Leave message, but the switch may fail to confirm the message. If confirmation of the Leave message fails, the switch may continue to forward frames that contain unused multicast packets. As described above, if the frame including the multicast packet that is not used by the terminal is continuously transferred, the network bandwidth is compressed with useless data, which may cause data drop.

  In the background art, a system using IPv4 (Internet Protocol version 4) has been described as an example, but a similar problem may occur even in a system using IPv6 (Internet Protocol version 6).

  An object of the present invention is to prevent useless transfer of multicast frames.

  A transfer device according to an embodiment includes a plurality of ports including a first port, a transfer unit, a load factor measurement unit, a confirmation unit, and a control unit. The transfer device receives the multicast frame via the first port. The transfer unit selects, from the plurality of ports, a second port connected to a terminal that receives the multicast frame, and transfers the multicast frame to the second port. The load factor measuring unit measures a load factor that is a ratio of a load of processing performed in the unit time in the second port to a load that can be processed in the unit time in the second port. When the load factor exceeds a threshold, the confirmation unit confirms a multicast group in which a terminal connected via the second port is participating. The control unit prevents the transfer unit from selecting the second port as a transfer destination for a multicast frame addressed to a multicast group to which a terminal connected via the second port does not participate. Control.

  Useless transfer of multicast frames is prevented.

It is a figure which shows the example of a structure of the transfer apparatus concerning 1st Embodiment. It is a figure which shows the example of a MAC address table. It is a figure which shows the example of the table which the load factor measurement part has memorize | stored. It is a figure which shows the example of a connection of the transfer apparatus to a router apparatus and a terminal. It is a figure which shows the structural example of the message used by IGMP. It is a figure explaining the example of transmission / reception of the multicast frame via a transfer apparatus. It is a flowchart explaining the example of operation | movement of a transfer apparatus. It is a figure which shows the example of a structure of the transfer apparatus which concerns on 2nd Embodiment. It is a figure which shows the example of an address table. It is a table which shows the example of the information which the calculation setting part determined. It is a figure which shows the example of a specific query message. It is a flowchart explaining the example of operation | movement of the transfer apparatus concerning 2nd Embodiment. It is a table which shows the example of the information which a check part holds. It is a figure which shows the example of a structure of the transfer apparatus which concerns on 3rd Embodiment. It is a table which shows the example of the information which a circuit load factor measurement part hold | maintains. It is a flowchart explaining the example of operation | movement of a transfer apparatus. It is a figure which shows the example of a structure of the transfer apparatus which concerns on 4th Embodiment. It is a figure which shows the example of a structure of a membership message, and the example of an MRT table. It is a flowchart explaining the example of the change method of response time.

<First Embodiment>
FIG. 1 shows an example of the configuration of a transfer apparatus 10 according to the first embodiment. The transfer device 10 includes a plurality of ports (ports P1 to Pn) in addition to the Media Access Control (MAC) address table 11, the load factor measuring unit 12, and the switch unit 20. In the example of FIG. 1, two ports P1 and Pn are shown in the figure for easy understanding of the drawing, but the transfer device 10 can include any number of ports. The switch unit 20 includes a transfer unit 21, a confirmation unit 22, and a control unit 23.

  As shown in FIG. 2 (a), the MAC address table 11 includes a port number provided in the transfer apparatus 10 and a multicast used in a multicast group in which terminals connected to the port are participating. The MAC address is associated and stored. The MAC address table 11 can also store address information obtained from a unicast-transmitted frame as appropriate. The transfer unit 21 determines the output destination port of the frame received via the ports P1 to Pn by referring to the MAC address table 11. Thereafter, the transfer unit 21 transfers the frame toward the destination by outputting the frame to the determined port. Further, when receiving the control message from the port connected to the terminal, the transfer unit 21 appropriately transfers the control message to the port (router port) connected to the router device.

  The load factor measuring unit 12 monitors the amount of data input to the port provided in the transfer device 10 and measures the load factor. Here, the ratio of the maximum amount of data that a port can process during a unit time to the amount of data that the port is processing during the unit time is defined as the “load factor” of the port. Further, the load factor can be the usage rate of the communication band for each port. As shown in FIG. 3, the load factor measuring unit 12 can store the load factor obtained for each port in association with the port number. The load factor measurement unit 12 notifies the confirmation unit 22 of the load factor in association with the port number. Note that the load factor measuring unit 12 does not measure the load factor for the router port.

  The confirmation unit 22 compares the value of the load factor notified from the load factor measurement unit 12 with a threshold value stored in advance. When the load factor exceeds the threshold value, the confirmation unit 22 confirms the multicast group in which the terminals connected via the port having the load factor larger than the threshold value are participating. For example, the confirmation unit 22 transmits an inquiry message inquiring about a participating multicast group to a terminal connected to a port having a load factor greater than a threshold value. Here, an arbitrary format can be used for the inquiry message. For example, the inquiry message can be an IGMP general query message. In addition, the threshold used by the confirmation unit 22 can be set to any value that does not hinder communication via the transfer device 10. For example, the threshold value may be set to an upper limit value of a load factor that is less likely to cause communication interruption even if a terminal connected to a certain port joins a new multicast group.

  When receiving a response message in response to the inquiry message from the terminal, the confirmation unit 22 identifies the multicast group in which the terminal that transmitted the response message participates based on the response message. As described later, an IGMP membership report or the like is used for the response message. The confirmation unit 22 notifies the control unit 23 of the multicast group in which the terminal connected to the port is associated with the port number of the confirmed port. Further, when the confirmation unit 22 obtains a message requesting participation in the multicast group transmitted from a terminal connected to the transfer apparatus 10, the confirmation unit 22 registers the multicast address specified by the message in the MAC address table 11. Further, the confirmation unit 22 identifies the type of IGMP message input from each port and identifies the router port. The confirmation unit 22 notifies the specified router port to the load factor measurement unit 12 and the transfer unit 21.

  The control unit 23 controls the multicast frame addressed to the multicast group to which the connected terminal does not participate according to the result notified from the confirmation unit 22 so as not to be transferred. For example, from the MAC address table 11, the control unit 23 stores information on the multicast group that has not been notified from the confirmation unit 22 among the multicast groups recorded in the MAC address table 11 in association with the port whose participation status has been confirmed. delete. Since the transfer unit 21 determines the transfer destination of the multicast frame with reference to the MAC address table 11, when the MAC address table 11 is changed by the process of the control unit 23, the transfer unit 21 does not use the multicast frame. Will not be transferred.

  FIG. 4 shows a connection example of the router device 1 and the transfer device 10 to the terminal. In the example of FIG. 4, it is assumed that the transfer device 10 includes five ports P1 to P5. Furthermore, the ports P1 to P4 are connected to the terminals A to D, and the port P5 is connected to the router device 1. Hereinafter, an example of the operation of the transfer device 10 will be described by taking the case where the transfer device 10 is connected as shown in FIG. 4 as an example.

  FIG. 5A shows a configuration example of a control frame used in the IGMP protocol such as a membership message. The control frame includes a MAC header, an IP header, and an IGMP message. The IGMP message includes a type, a response time (Max Response Time), a checksum, and a group address. The type is used to specify whether the message is a query message, a membership message, or a Leave message. The response time is the time from the time when the query message or inquiry message is transmitted to the time when the response message for the message can be accepted. Therefore, the terminal that transmits the response message transmits the response message so that the response message reaches the transfer device 10 or the like before the response time elapses from the transmission time of the inquiry message. The group address is used to specify a multicast group that is required to join or leave. As will be described later, in the case of a general query message, the group address is set to 0. In the following description, it is assumed that a control frame as shown in FIG.

  FIG. 6 is a diagram for explaining an example of transmission / reception of a multicast frame via the transfer apparatus 10. Referring to FIG. 6A, an example of an operation performed when terminal A in FIG. 4 participates in multicast group α or β and receives a multicast frame from router device 1 via transfer device 10. explain. Here, before the procedure shown in FIG. 6A is started, the confirmation unit 22 recognizes that the router port is the port P5 and notifies the transfer unit 21 and the load factor measurement unit 12 of the fact. Shall. Although not shown in FIG. 6A, in the following description, it is assumed that the terminal D is participating in the multicast group α while the operation shown in FIG. 6A is being performed. In addition, the following description is an example, for example, order may be changed, for example, procedure (5)-(7) is performed before procedure (8) and (9).

  (1) The terminal A transmits a membership message to the router device 1 in order to participate in the multicast group α. Here, it is assumed that the multicast IP address of the multicast group α is 224.0.0.5. Therefore, it is assumed that the terminal A has transmitted the membership message shown in FIG.

  (2) The transfer device 10 receives the membership message transmitted from the terminal A to the router device 1 from the port P1. The received membership message is input to the confirmation unit 22 from the port P1. The confirmation unit 22 recognizes that the membership message has been received from the type value included in the input message.

  Next, the confirmation unit 22 acquires a group address and maps the obtained multicast IP address to the multicast MAC address. The confirmation unit 22 generates the multicast MAC address by continuing the lower 23 bits of the multicast IP address to the lower side of the bit string defined for the upper 25 bits of the multicast MAC address. When the upper 24 bits of the multicast MAC address are expressed in hexadecimal by 4 bits, 01-00-5e is obtained. The upper 25th bit of the multicast MAC address is 0. Therefore, the confirmation unit 22 calculates that the multicast MAC address is 01-00-5e-00-00-05 for the multicast group α. The confirmation unit 22 records the obtained multicast MAC address in association with the port P1. An example of the MAC address table 11 updated by the confirmation unit 22 is shown in FIG. As described above, since the terminal D connected to the port P4 has already joined the multicast group α, 01-00-5e-00-00-05 is associated with both the ports P1 and P4. Yes.

  Further, the confirmation unit 22 outputs the received membership message to the transfer unit 21 in association with the MAC address of the multicast group that participates by the membership message. The transfer unit 21 confirms whether or not the frame addressed to the multicast group whose participation is notified by the membership message is being relayed. For example, the transfer unit 21 confirms whether a frame of the multicast group α is already transferred from any port before receiving the membership message notifying that the port P1 joins the multicast group α. Here, since the terminal D has already participated in the multicast group α in which the terminal A has joined, as shown in FIG. 2A, the transfer apparatus 10 has already sent a frame addressed to the multicast group α to the port P4. Transferring to a connected terminal. Therefore, the transfer unit 21 determines that the multicast frame can be transferred without notifying the router device 1 of participation by the membership message, and does not transfer the membership message to the router device 1.

(3) The router device 1 transfers the frame addressed to the multicast group α to the transfer device 10. Here, it is assumed that the destination address of the multicast frame addressed to the multicast group α is specified as follows.
Destination IP address: 224.0.0.5
Destination MAC address: 01-00-5e-00-00-05

(4) The transfer unit 21 of the transfer device 10 receives a multicast frame addressed to the multicast group α from the port P5. The transfer unit 21 searches the MAC address table 11 for the destination MAC address of the received frame. When the MAC address table 11 of FIG. 2A is used, the ports P1 and P4 are associated with the destination MAC address. The transfer unit 21 outputs the received frame to the ports P1 and P4 (time T1). Terminal A receives the multicast frame output to port P1. Similarly, terminal D receives the multicast frame output to port P4.

  FIG. 6B shows an example of the time change of the load factor obtained by the calculation of the load factor measuring unit 12 for the port P1. At time T1, data addressed to the multicast group α is transferred from the port P1, but it is assumed that the load factor of the port P1 does not exceed the threshold Th as shown in FIG. 6B.

  (5) Thereafter, it is assumed that the terminal A has left the multicast group α. The terminal A transmits a Leave message to the router device 1 in order to notify the departure from the multicast group α.

  (6) It is assumed that the transfer device 10 receives the Leave message transmitted from the terminal A via the port P1, but fails to snooping the Leave message. In this case, the transfer device 10 does not change the MAC address table 11. Accordingly, the port P1 is still recorded in the MAC address table 11 as a target for transferring a multicast frame addressed to the multicast group α. Further, the transfer unit 21 transfers the Leave message to the router device 1.

  (7) The router device 1 receives the Leave message via the transfer device 10. In order to check whether there is a terminal participating in the multicast group α, the router device 1 sends a specific query message specifying the multicast group α as a group address to a terminal (not shown) connected to the router device 1 Transmit to the transfer device 10. As described above, since the terminal D participates in the multicast group α, the terminal D sends a message indicating that it is participating in the multicast group α to the router device 1 via the ports P4 and P5 of the transfer device 10. Send. By analyzing the message sent from the transfer device 10, the router device 1 continues to transfer the frame addressed to the multicast group α to the transfer device 10.

  (8) It is assumed that the terminal A next joins the multicast group β. The terminal A transmits a membership message to the router device 1 in order to participate in the multicast group β. Here, it is assumed that the multicast IP address of the multicast group β is 224.0.0.10.

  (9) The transfer apparatus 10 receives the membership message transmitted from the terminal A from the port P1. The confirmation unit 22 obtains a multicast MAC address based on the group address 224.0.0.10 in the message by the same process as the process described in the procedure (2). The obtained address is 01-00-5e-00-00-10. Therefore, the confirmation unit 22 records the obtained address in the MAC address table 11 in association with the port P1. The MAC address table 11 after recording is as shown in FIG.

  Furthermore, the membership message for requesting participation in the multicast group β is output to the transfer unit 21 in association with the MAC address of the multicast group β. Then, the transfer unit 21 refers to the MAC address table 11 to check whether the frame of the multicast group β has already been transferred from any port. Here, since the transfer destination of the frame addressed to the multicast group β is not recorded in the MAC address table 11, the transfer apparatus 10 determines that the frame addressed to the multicast group β is not transferred. Therefore, the transfer unit 21 transfers the membership message to the router device 1.

  (10) When the router device 1 receives the membership message transmitted from the terminal A, the router device 1 recognizes that the transfer of the frame addressed to the multicast group β is requested from the device connected to the transfer device 10. Therefore, the router device 1 transfers both the frame addressed to the multicast group α and the frame addressed to the multicast group β to the transfer device 10. Here, the destination MAC address of the multicast frame addressed to the multicast group β is 01-00-5e-00-00-10.

  (11) The transfer unit 21 of the transfer device 10 receives frames addressed to the multicast groups α and β from the router device 1 via the port P5. The transfer unit 21 determines the frame transfer destination with reference to the MAC address table 11 (FIG. 2B). Since the MAC addresses of both the multicast groups α and β are associated with the port P1, the transfer unit 21 transfers the frame addressed to the multicast group α and the frame addressed to the multicast group β to the port P1 (time T2). ). On the other hand, since the multicast MAC address of the multicast group α is associated with the port P4, the frame addressed to the multicast group α is also transferred to the port P4.

  At time T2, since both the frame addressed to the multicast group α and the frame addressed to the multicast group β are transferred from the port P1, the load factor of the port P1 exceeds the threshold Th as shown in FIG. 6B. It shall be. For example, assume that the load factor of each port is as shown in FIG.

  (12) Terminal A receives the multicast frame output to port P1. However, since the terminal A has already left the multicast group α, the frame addressed to the multicast group α is discarded.

  (13) The load factor measuring unit 12 notifies the confirmation unit 22 that the load factor of the port P1 exceeds the threshold value. Therefore, the confirmation unit 22 confirms the participation status in order to cancel the transfer of frames that are not used by the terminal connected to the port P1 among the multicast frames transferred to the port P1. The confirmation unit 22 transmits an inquiry message to all the terminals connected to the port P1. Here, the inquiry message is assumed to be a general query message. An example of a general query message is shown in FIG. In the general query message, by designating the group address to 0.0.0.0, it is confirmed whether there is a terminal receiving a frame addressed to a multicast group to which an arbitrary multicast IP address is allocated.

  (14) The terminal A that has received the general query message transmits a membership message notifying that it is participating in the multicast group β to the transfer apparatus 10. In this membership message, the group address is the IP address of the multicast group β. On the other hand, since the terminal A has already left the multicast group α, the membership message is not transmitted for the multicast group α.

  (15) It is assumed that the transfer device 10 receives the membership message of the multicast group β from the port P1 within the response time, but has not received the membership message of the multicast group α. The confirmation unit 22 notifies the control unit 23 of the multicast MAC address of the multicast group from which the port number and the membership message are obtained. The control unit 23 deletes the MAC address that has not been notified from the MAC address table 11. Here, the MAC address 01-00-5e-00-00-10 of the multicast group β is notified from the confirmation unit 22 in association with the port P1, but the address 01-00-5e-00-00 of the multicast group α is notified. -5 is not notified. The transfer unit 21 compares the MAC address associated with the port P1 in the MAC address table 11 in FIG. 2B and the MAC address notified from the confirmation unit 22. Then, since 01-00-5e-00-00-5 corresponding to the multicast group α is not notified from the confirmation unit 22, the control unit 23 deletes the address from the list of MAC addresses to be transferred to the port P1. . That is, the control unit 23 changes the MAC address table 11 from FIG. 2B to FIG.

  (16) The router device 1 transfers both the frame addressed to the multicast group α and the frame addressed to the multicast group β to the transfer device 10.

  (17) The transfer unit 21 of the transfer device 10 receives frames addressed to the multicast groups α and β from the router device 1 via the port P5. The transfer unit 21 determines a frame transfer destination with reference to the MAC address table 11 shown in FIG. Since the MAC address of the multicast group β is associated with the port P1, the transfer unit 21 transfers the frame addressed to the multicast group β to the port P1, but does not transfer the frame addressed to the multicast group α (time T3). ). Since the frame addressed to the multicast group α is not transferred to the port P1, it is assumed that the load factor of the port P1 falls below the threshold value. On the other hand, since the multicast MAC address of the multicast group α is associated with the port P4, the frame addressed to the multicast group α is transferred to the port P4.

(18) The router device 1 periodically transmits a query message to check whether the multicast group is maintained.
FIG. 7 is a flowchart for explaining an example of the operation of the transfer apparatus 10. FIG. 7 shows the processing procedure for the port Pm, but it is assumed that the same processing is performed for the other ports. The load factor measuring unit 12 monitors the output of the port Pm and measures the bandwidth load factor (step S1). Next, the load factor measuring unit 12 compares the load factor with a threshold value (step S2). In the example of FIG. 7, the threshold is 50%. The processes in steps S1 and S2 are repeated until the bandwidth load factor exceeds the threshold value. When the bandwidth load factor of the port Pm exceeds the threshold value, the confirmation unit 22 transmits an inquiry message from the port Pm (step S3). The confirmation unit 22 determines whether a membership message (response message) has been received from the terminal via the port Pm within the response time (step S4). If the membership message cannot be received within the response time, the confirmation unit 22 transmits the inquiry message from the port Pm again (No in step S4, step S5). The confirmation unit 22 determines whether a membership message has been received from the terminal via the port Pm within the response time from the transmission time of the inquiry message transmitted the second time (step S6). If it is determined in step S4 or S6 that the response message has been received from the terminal within the response time, the transfer apparatus 10 continues to transmit the frame addressed to the multicast group whose identifier is included in the response message (step S7). . On the other hand, when the response message is not received from the terminal within the response time in response to the inquiry message, the transfer device 10 stops transmission of the frame addressed to the multicast group (step S8). After the process of step S7 or S8 is completed, the processes after step S1 are repeated.

  As described above, according to the present embodiment, unnecessary multicast transmission of frames is performed in order to confirm multicast groups in which terminals connected to ports with a high load factor participate and to cancel the transmission of unused multicast frames. Is prevented. In addition, this embodiment has an advantage that useless frame transfer can be found quickly. As shown in the procedure (18) of FIG. 6A, the router device 1 also periodically checks whether the multicast group to which the router device 1 forwards the frame is maintained using the query message. The frequency of confirmation by the router device 1 is low. Specifically, transmission of the query message from the router device 1 is often performed once every 60 seconds to 125 seconds. Therefore, it takes time to find uselessness of multicast frame transfer by the query message transmitted by the router device 1. On the other hand, according to the present embodiment, without waiting for the transmission of the query message by the router device 1, the transfer device 10 confirms whether there is a useless frame transfer for each port according to the load factor of the port, and cancels the useless transfer. Is done. Accordingly, communication failure due to network capacity pressure can be prevented in advance.

  Furthermore, even if the query message transmission interval from the router device 1 is shortened, the query message and the membership message responding to the query message are frequently exchanged in the network, which may cause a load on the network. . On the other hand, in the case of the present embodiment, since the state of participation of the terminal in the multicast group is confirmed for the port having a high load factor, the burden on the network can be reduced.

  In addition, even if the query message from the router device 1 is used, the switch device cannot find useless frame transfer, and it may be preferable to use a network using the transfer device 10. For example, it is assumed that the switching device (L2 switch) misses the Leave message of the multicast group α for the port P1, but the terminal connected via the port P4 continues to participate in the multicast group α. In addition, it is assumed that terminals participating in the multicast group α are not connected to the port P1. In this case, since the membership message specifying the multicast group α reaches the router device 1 via the port P4, the router device 1 continues the frame related to the multicast group α. Further, even if the switching device snooping the membership message transferred to the router device 1 via the port P4, it cannot recognize that it is useless to transfer the frame addressed to the multicast group α to the port P1. On the other hand, when the transfer device 10 according to the present embodiment is used, the switch unit 20 confirms whether the transfer of the multicast frame is useless for each port. For this reason, the forwarding device 10 can prevent wasteful forwarding of multicast frames for each port even if processing of the Leave message fails.

  The transfer apparatus 10 is particularly useful when the terminal frequently receives stream data having a large capacity such as video data. For example, it is assumed that video data captured by a plurality of cameras is switched and received every few seconds for the purpose of monitoring or the like. In terminal A connected to port P1, it is assumed that received data is switched in the order of camera C1, camera C2, camera C3, and camera C4 in about 5 seconds. When the camera video is multicast, terminal A repeats joining and leaving the multicast group among the groups that distribute the four types of video from cameras C1 to C4. If the switch connected to the terminal A fails to acquire the Leave message, video data that is not used by the terminal A continues to be transferred to the terminal A wastefully. In the case of video data, since the capacity is large, it is easy to press the capacity of the network and easily cause communication failure. Therefore, the transfer device 10 can prevent useless transfer and communication failure by checking the participation status of a multicast group of a terminal connected to a port with a high load factor.

<Second Embodiment>
FIG. 8 shows an example of the configuration of the transfer apparatus 30 according to the second embodiment. The transfer device 30 according to the second embodiment checks the participation status in order from the multicast group with the earliest time at which the transfer is started. The transfer device 30 includes an address table 31, a calculation setting unit 32, a timer 33, a switch unit 40, ports P1 to Pn, and a load factor measurement unit 12. The switch unit 40 includes a transfer unit 41, a confirmation unit 42, and a control unit 23. The operations of the load factor measuring unit 12 and the control unit 23 are the same as those in the first embodiment.

  An example of the address table 31 is shown in FIG. The address table 31 records the MAC address of the transfer destination of the transfer unit 41 for each port number. The address table 31 records, for each multicast MAC address, the multicast IP address used for address mapping. Further, the address table 31 also stores the time when the address is recorded in the address table 31 for each multicast MAC address. For example, in the address table 31 shown in FIG. 9, the multicast MAC address associated with the port P4 is 01-00-5e-00-00-05, and the corresponding multicast IP address is 224.0.0.5. It is recorded that there is. In addition, the fact that the transfer of the multicast frame addressed to 01-00-5e-00-00-05 to the port P4 is registered at the time T9 is also recorded in the address table 31.

  The calculation setting unit 32 determines a port for confirming the participation status based on the load factor information calculated by the load factor measuring unit 12. Further, the calculation setting unit 32 calculates a set value of the timer 33. In the following description, the set value of the timer 33 for each port may be referred to as an “interval control value”. As will be described later, when the timer 33 set to the interval control value expires, the confirmation unit 42 confirms the participation status.

  When there are a plurality of ports whose participation status is to be confirmed, the calculation setting unit 32 determines the order in which the participation status is confirmed by obtaining an interval control value. The calculation setting unit 32 can calculate the interval control value by an arbitrary calculation method in which the interval control value becomes smaller as the port with the higher load factor is checked so that the participation status is checked in order from the port with the higher load factor. it can. For example, for each port whose load factor exceeds a threshold value, a multiple of the numbers assigned in descending order of load factor can be set as the set value. In this case, for example, if the load factors are ports P1 = 70%, P2 = 80%, and P3 = 90%, the order of the load factors is P3 = 1, P2 = 2, and P1 = 3. When the calculation setting unit 32 sets 5 times the order as the set value, the timer values set in the respective ports are P3 = 5, P2 = 10, and P1 = 15. Moreover, the calculation setting part 32 can also make a setting value the divisor of (100-load factor). FIG. 10 is a table showing an example of information determined by the calculation setting unit 32. In the example of FIG. 10, it is assumed that the ports other than the port P3 among the ports P1 to P4 are not targets for confirming the participation state because of low load factors. The operation of the load factor measuring unit 12 may be modified so that the load factor is measured at regular time intervals. In this case, the calculation setting unit 32 sets the interval for measuring the load factor with the timer 33. Can be set.

  The transfer unit 41 uses the address table 31 to determine an output destination port for frames received via the ports P1 to Pn. Moreover, the transfer unit 41 transfers the received control message to the router device as appropriate.

  When the timer 33 is notified that the interval control value has passed for a certain port, the confirmation unit 42 transmits an inquiry message to that port. Here, the inquiry message transmitted by the confirmation unit 42 is a specific query message, and the participation status is confirmed with priority given to the multicast group whose participation status is early among the multicast groups whose participation status is to be confirmed. For example, it is assumed that when the address table 31 is as shown in FIG. 9, it is confirmed from the timer 33 that the interval control value has elapsed for the port P3. The confirmation unit 42 confirms the time when the transfer is started and the multicast IP address for each multicast group that is being transferred to the port P3. Then, the confirmation unit 42 has the earliest frame addressed to 01-00-5e-00-00-05 (224.0.0.5) among the four addressed multicast groups transferred to the port P3. It recognizes that it has started at time T4. Therefore, the confirmation unit 42 uses the specific query message shown in FIG. 11 and the terminals that are participating in the multicast group whose multicast IP address is 224.0.0.5 among the terminals connected to the port P3. Check if there is. Thereafter, the confirmation unit 42 transmits a specific query message for each of the multicast groups in which the frame is transferred to the port P3 in order of the time when the transfer is started. The confirmation unit 42 confirms whether there is a participating terminal for each multicast group, using a response message in response to the specific query message. Note that a membership message is used for the response message, as in the first embodiment. The confirmation unit 42 notifies the control unit 23 of the obtained result.

  FIG. 12 is a flowchart for explaining an example of the operation of the transfer apparatus 30 in the second embodiment. FIG. 12 shows the processing procedure for the port Pm, but the same processing is performed for the other ports. FIG. 12 shows an example of the operation of the transfer device 30. For example, the threshold used in step S13, the calculation method in step S15, and the like may be changed. In addition, the timer 33 may be modified so that the set value of the timer 33 is not changed after the timer 33 starts counting down. In this case, steps S16 to S19 are omitted, and the processing after step S20 is performed after step S15.

  The load factor measuring unit 12 monitors the output of the port Pm (step S11). When the timer set in the time interval for measuring the load factor expires, the load factor measuring unit 12 measures the load factor (step S12). The load factor measuring unit 12 compares the load factor with a threshold value (step S13). Here, the threshold is assumed to be 50%. If it is determined in step S13 that the bandwidth load factor does not exceed the threshold value, the calculation setting unit 32 clears the interval control value and sets it to be out of processing (Yes in step S13, step S14). On the other hand, when the band load factor exceeds the threshold value, the calculation setting unit 32 obtains an interval control value (step S15). Here, it is assumed that the interval control value is a value obtained by subtracting one-tenth of the bandwidth load factor from 10 and truncating after the decimal point. The calculation setting unit 32 outputs the obtained interval control value to the confirmation unit 42 in association with the port number (Pm).

  The confirmation unit 42 confirms whether the timer 33 has already started counting down the interval control value for the port (port Pm) identified by the notified port number Pm (step S16). If the timer 33 has not counted down the interval control value for the port Pm, the confirmation unit 42 sets the interval control value in the timer 33 and causes the timer 33 to start counting down (step S17). On the other hand, when the timer 33 is counting down the interval control value for the port Pm, the confirmation unit 42 confirms which of the remaining time of the timer 33 and the interval control value is larger (step S18). If the remaining time of the timer 33 is less than or equal to the interval control value, the confirmation unit 42 continues the countdown of the timer 33 without changing the value of the timer 33 (Yes in step S18). On the other hand, when the remaining time of the timer 33 is longer than the interval control value, the confirmation unit 42 continues the countdown of the timer 33 after changing the value of the timer 33 to the interval control value (No in step S18, step S19). The confirmation unit 42 confirms the address table 31 in parallel and identifies the multicast group that is transferring the frame via the port Pm (step S20).

  When the timer 33 expires, the confirmation unit 42 transmits a specific query message for confirming the participation status for each of the multicast groups recognized in step S20 from the port Pm (step S21). At this time, it is assumed that the confirmation unit 42 transmits the specific query message in order from the multicast group whose transfer is started earlier. The confirmation unit 42 confirms whether a response message is received from the terminal connected to the port Pm within the response time (step S22). If the membership message cannot be received within the response time, the confirmation unit 42 transmits the specific query message from the port Pm again (No in step S22, step S23). The confirmation unit 42 determines whether a membership message has been received from the terminal via the port Pm within the response time from the transmission time of the specific query message transmitted the second time (step S24). When the membership message is received from the terminal within the response time with respect to the specific query message transmitted in step S22 or S24, the transfer device 30 continues to transmit the frame addressed to the multicast group (step S26). On the other hand, when the membership message cannot be received from the terminal within the response time in response to the specific query message, the transfer device 30 stops transmitting the frame addressed to the multicast group (step S25). After the processing of step S25 or S26 is completed, the confirmation unit 42 ends the control of the port Pm and sets the query interval control value for the port Pm to infinity (step S27).

  In the above description, the timer 33 is installed separately from the confirmation unit 42, but the timer 33 may be included in the confirmation unit 42. In this case, the confirmation unit 42 holds information as shown in FIG. 13 and manages the set value (interval control value) of the timer and the remaining time of the timer for each port. When the remaining time of the timer becomes 0, a specific query message is transmitted for each multicast group to which the address held in the multicast group column is assigned.

  Since the transfer device 30 confirms the participation status in order from the multicast group with the earliest transfer start time, the transfer device 30 is effectively useless in a system that is likely to have failed the processing of the Leave message for the multicast group with a long transfer period. It becomes easy to prevent transfer. As an example of such a system, there is a system that is considered to have failed to process a Leave message when video data captured by a plurality of cameras is switched every few seconds and the transfer continues for several tens of seconds. Can be mentioned.

  Furthermore, since the calculation setting unit 32 sets the interval control value to a smaller value for a port with a higher load factor, the participation state is confirmed earlier for a port with a higher load factor. When the load factor is high, there is a high possibility that useless transfer of frames due to failure of processing of the Leave message is performed. Therefore, in the transfer device 30, since the frequency of confirmation of the participation state increases as the port that has a high possibility of useless transfer of frames, useless transfer of frames can be efficiently prevented.

<Third Embodiment>
FIG. 14 shows an example of the configuration of a transfer apparatus according to the second embodiment. In the third embodiment, the transfer device 50 that can adjust the frequency of confirming the participation state for each port in consideration of loads due to operations of the load factor measuring unit 12, the calculation setting unit 32, the switch unit 40, and the like. Will be described. The transfer device 50 includes a circuit load factor measuring unit 51, a load factor measuring unit 12, an address table 31, a calculation setting unit 32, a timer 33, a switch unit 40, and ports P1 to Pn. The operations of the load factor measuring unit 12, the address table 31, the calculation setting unit 32, the timer 33, and the switch unit 40 are the same as those in the second embodiment.

  The circuit load factor measuring unit 51 measures the load of the central processing unit (CPU) that operates as the load factor measuring unit 12, the calculation setting unit 32, and the switch unit 40. In the following description, the amount of processing performed during the unit time by the CPU operating as the load factor measuring unit 12, the calculation setting unit 32, and the switch unit 40 and the amount of processing that the CPU can perform during the unit time are described. The ratio with the maximum value is described as “CPU load factor”. The circuit load factor measuring unit 51 can measure the CPU load factor and store the obtained result as a table as shown in FIG. The circuit load factor measuring unit 51 outputs the calculated result to the calculation setting unit 32.

  The calculation setting unit 32 uses the value input from the circuit load factor measurement unit 51 to calculate a time interval (calculation time) for measuring the load factor. The load factor measuring unit 12 measures the load factor every time the calculation time elapses. The calculation setting unit 32 sets the calculation time so that the calculation time increases as the CPU load factor increases. For example, the calculation setting unit 32 can set the value obtained by dividing the CPU load factor (%) by 10 as the calculation time. Furthermore, when there is a possibility that the calculation time is too short and the load on the load factor measuring unit 12 is increased, the calculation setting unit 32 can also set a lower limit value of the calculation time. For example, the calculation setting unit 32 can set the calculation time with 1 second as the shortest time.

  FIG. 16 is a flowchart for explaining an example of the operation of the transfer device 50. FIG. 16 shows the processing procedure for the port Pm, but the same processing is performed for the other ports. FIG. 16 shows an example of the operation of the transfer apparatus 50. For example, the threshold value may be changed according to the implementation. The load factor measuring unit 12 monitors the output of the port Pm. Further, the circuit load factor measuring unit 51 measures the CPU load factor (step S31). The calculation setting unit 32 sets the calculation time in the timer 33 based on the value of the CPU load factor. When notified from the timer 33 that the computation time has elapsed, the load factor measuring unit 12 measures the load factor (step S32). The load factor measuring unit 12 determines whether the difference between the load factor and the CPU load factor exceeds a threshold value (50%) (step S33). If it is determined in step S33 that the difference between the load factor and the CPU load factor does not exceed the threshold value (50%), the calculation setting unit 32 clears the interval control value and sets the port Pm to be out of processing. (Yes in step S33, step S34). On the other hand, when the difference between the load factor and the CPU load factor exceeds the threshold, the calculation setting unit 32 obtains an interval control value (step S35). Here, it is assumed that the interval control value is calculated in the same manner as in step S15 described with reference to FIG. The calculation setting unit 32 outputs the obtained interval control value to the confirmation unit 42 in association with the port number (Pm). The processing of steps S36 to S47 is the same as that of steps S16 to S27 described with reference to FIG.

  In this embodiment, since the interval at which the load factor is measured is changed according to the size of the CPU load factor, when the CPU mounted on the transfer apparatus 10 is large, the participation status in the multicast group is performed. The interval that appears is longer. Therefore, the processing load caused by the confirmation of the participation status in the multicast group is adjusted to such an extent that the processing load on the transfer apparatus 10 is not increased.

<Fourth Embodiment>
FIG. 17 shows an example of the configuration of the transfer device 60 according to the fourth embodiment. The transfer device 60 can change the response time in the inquiry message according to factors such as network congestion. In the following description, a case where the inquiry message is a specific query message will be described, but the response time may be adjusted even when the inquiry message is a general query message as in the first embodiment.

  The transfer device 60 includes a switch unit 70, a Max Response Time (MRT) table 75, a load factor measuring unit 12, an address table 31, an arithmetic setting unit 32, a timer 33, a circuit load factor measuring unit 51, and ports P1 to Pn. The switch unit 70 includes a transfer unit 41, a confirmation unit 42, a control unit 23, a round trip time measurement unit 71, and a response time setting unit 72. The operations of the load factor measurement unit 12, the calculation setting unit 32, the timer 33, the transfer unit 41, the confirmation unit 42, the control unit 23, and the circuit load factor measurement unit 51 are the same as those in the second or third embodiment. The address table 31 is the same as in the second and third embodiments.

  The round-trip time measuring unit 71 acquires the source IP address included in the IP header of the response message (membership message) received by the confirmation unit 42. FIGS. 18A and 18B show examples of membership message configurations. FIG. 18A shows a membership message used in IGMPv2, and FIG. 18B shows a membership message used in IGMPv3. Note that the membership message used in IGMPv3 is transmitted to a multicast router compatible with IPMPv3. Regardless of which protocol is used, as shown in FIGS. 18A and 18B, the source IP address is included in the membership message. The round trip time measuring unit 71 records the acquired address in the MRT table 75 in association with the port number of the port from which the response message is acquired. FIG. 18C shows an example of the MRT table 75.

  The round trip time measuring unit 71 transmits the first measurement frame toward the IP address acquired from the response message. Here, the first measurement frame can be an echo request frame used in a program such as Packet INternetGroper (ping). The round trip time measurement unit 71 calculates the time from the time when the first measurement frame is transmitted to the time when the second measurement frame (response frame) responding to the first measurement frame is received from the destination terminal. Round trip time. The round trip time measuring unit 71 also records the round trip time in the MRT table 75.

  Here, as in the case of the port P3, when the round trip time measuring unit 71 acquires a plurality of IP addresses by receiving a plurality of response messages, the round trip time measuring unit 71 sets the first address for each of the acquired addresses. Send a measurement frame. When the response time differs depending on the destination of the first measurement frame, the round trip time measurement unit 71 compares the round trip time observed for each port and records the longest round trip time in the MRT table 75.

  The response time setting unit 72 refers to the round trip time of the MRT table 75 and determines the response time. For example, the response time setting unit 72 can set the response time to a value equal to or greater than the round trip time by a method according to the implementation, such as a value obtained by rounding up the round trip time in units of 100 ms. In this case, since the maximum value of the round trip time is 120 ms at the port P3, the response time setting unit 72 sets the response time to 200 ms. Similarly, since the round trip time is 50 ms at the port P4, the response time setting unit 72 sets the response time to 100 ms. The response time setting unit 72 notifies the confirmation unit 42 of the determined response time and requests to set the response time of the inquiry message. Note that the MRT table 75 is periodically initialized (refreshed) because there is a possibility that a terminal to which a registered IP address is assigned may leave the multicast group. The frequency of initialization is arbitrarily set, such as once a day, depending on the implementation. The timer 33 can also measure the interval at which refresh is performed. The transfer device 60 may include a refresh timer (not shown) in addition to the timer 33, and may be modified so that the refresh timer counts down the time interval at which refresh is performed.

  FIG. 19 is a flowchart illustrating an example of a response time changing method. The round trip time measuring unit 71 acquires the source IP address of the membership message and registers it in the MRT table 75 (steps S51 and S52). The round trip time measuring unit 71 transmits the first measurement frame to the transmission source IP address registered in the MRT table 75, and responds to the first measurement frame from the transmission time of the first measurement frame. The time until the reception time of the measurement frame is measured (step S53). The round trip time measurement unit 71 compares the round trip time obtained in step S53 with the maximum round trip time recorded in the MRT table 75 (step S54). If the round trip time obtained in step S53 is less than or equal to the maximum round trip time, the processes in steps S51 to S54 are repeated (No in step S54). On the other hand, when the round trip time obtained in step S53 exceeds the round trip time maximum value, the round trip time measurement unit 71 updates the round trip time maximum value (step S55). The response time setting unit 72 rounds up the round-trip time maximum value in units of 100 ms to obtain a response time (step S56). The response time setting unit 72 notifies the confirmation unit 42 of the set response time as appropriate. The response time setting unit 72 confirms whether the refresh timer used for initializing the MRT table 75 is up (step S57). Steps S51 to S57 are repeated until the refresh timer expires. On the other hand, when the refresh timer expires, the response time setting unit 72 initializes the MRT table 75 (step S58). Thereafter, the operations after step S51 are repeated.

  In this manner, the transfer device 60 can change the response time in the inquiry message according to factors such as network congestion. For this reason, since the response time is too short, the possibility that the round trip time measurement unit 71 fails to receive the membership message from the terminals participating in the multicast group can be reduced. For this reason, since the membership message is not received at a port where there is a terminal participating in the multicast group, the possibility that the transfer of the multicast frame is stopped can be reduced.

The embodiment is not limited to the above, and can be variously modified. Some examples are described below.
In the first to fourth embodiments described above, the system using IPv4 has been described as an example. However, the transfer apparatus 10 can also be used in a system using IPv6. It is assumed that the transfer apparatus 10 applied to a system using IPv6 supports Multicast Listener Discovery Protocol (MLD) snooping. In this case, a multicast listener query is used as the inquiry message. A multicast listener report is used for the response message.

  Also in the transfer apparatus 10 described in the first embodiment, by including the calculation setting unit 32 and the timer 33, when there are a plurality of ports for which the participation status is to be confirmed, the participation status according to the magnitude of the load factor Can be modified to determine the order of confirmation. Further, the transfer device 10 described in the first embodiment may be modified to include the circuit load factor measurement unit 51 so as to determine the frequency of confirming the participation status according to the load of the CPU. it can.

  In the fourth embodiment, the case where the source IP address in the membership message is recorded for each port in the MRT table 75 and the response time is obtained has been described. However, the transfer device 60 uses all the response times obtained from a certain port. Can adapt to any port. In this case, the MRT table 75 does not record the data for each port, but records the data for the port selected as the target for obtaining the response time.

The following additional notes are further disclosed with respect to the embodiments including the first to fourth embodiments described above.
(Appendix 1)
A plurality of ports including a first port for receiving a multicast frame;
A transfer unit that selects a second port connected to a terminal that receives the multicast frame from the plurality of ports, and transfers the multicast frame to the second port;
A load factor measuring unit that measures a load factor that is a ratio of a load of processing performed in the unit time in the second port to a load that can be processed in the unit time in the second port;
When the load factor exceeds a threshold value, a confirmation unit for confirming a multicast group in which a terminal connected via the second port participates;
A control unit that controls the transfer unit not to select the second port as a transfer destination for a multicast frame addressed to a multicast group to which a terminal connected via the second port does not participate A transfer device comprising:
(Appendix 2)
After the multicast frame transmitted by the router device connected via the first port is received from the first port and the multicast frame is transmitted from the second port, the router device Before confirming whether it is connected to the terminal receiving the multicast frame, the confirmation unit confirms the multicast group to which the terminal connected through the second port is participating. The transfer apparatus according to appendix 1, wherein:
(Appendix 3)
An identifier table storing a group identifier for identifying a multicast group of a destination of a multicast frame transmitted from the second port;
The confirmation unit
Sending an inquiry message for inquiring a group identifier for identifying a participating multicast group to a terminal connected via the second port;
Confirming the multicast group in which the terminal connected via the second port is participating by confirming the group identifier included in the response message in response to the inquiry message;
The control unit deletes a group identifier of a multicast group not included in the response message from the identifier table,
The forwarding unit forwards the multicast frame addressed to the multicast group identified by the group identifier recorded in the identifier table updated by the control unit to the second port. The transfer device described in 1.
(Appendix 4)
The control unit stores a response time for receiving a response message from a terminal that has received the inquiry message,
The control unit extracts, from the group identifier stored in the identifier table, a group identifier that is not included in the response message received until the response time elapses after the inquiry message is transmitted,
The transfer apparatus according to appendix 3, wherein the control unit deletes the extracted group identifier from the identifier table.
(Appendix 5)
A first measurement frame is transmitted to a terminal to which a source address of the response message is assigned, a second measurement frame is received in response to the first measurement frame, and the first measurement frame is received. A round trip time measuring unit for obtaining a round trip time from the time at which the second measurement frame is received to the time at which the second measurement frame is received;
The transfer apparatus according to appendix 4, further comprising: a response time setting unit that sets the response time to a length equal to or longer than the round trip time.
(Appendix 6)
A third port connected to a terminal that receives the multicast frame received via the first port;
The load factor measuring unit obtains a first load factor from the processing of the second port and a second load factor from the processing of the third port;
When both of the first and second load factors exceed the threshold, the confirmation unit assigns a port having a large value between the first load factor and the second load factor to the control unit. Determining the target port that is the target of the control by sending the inquiry message to the terminal connected to the target port,
The control unit controls the transfer unit not to select the target port as a transfer destination for a frame addressed to the multicast group identified by the group identifier not included in the response message. The transfer device according to any one of appendices 3 to 5.
(Appendix 7)
The ratio of the amount of processing performed during the unit time in the circuit operating as the load factor measuring unit, the confirmation unit, and the control unit to the amount of processing that the circuit can perform during the unit time. A circuit load measuring unit for obtaining a circuit load to be represented;
Any one of Supplementary notes 1 to 8, further comprising: an operation setting unit that sets a lower frequency of processing performed by the load factor measurement unit, the confirmation unit, and the control unit as the circuit load increases. The transfer device according to item 1.
(Appendix 8)
Selecting a transfer destination of a multicast frame received from the first port of the transfer device from a plurality of ports included in the transfer device;
Measuring a load factor that is a ratio of a load of processing performed at the second port to the load that can be processed at the selected second port per unit time;
When the load factor exceeds a threshold, confirm a multicast group in which terminals connected via the second port are participating,
A process for performing control so that the second port is not selected as a transfer destination is performed for a multicast frame addressed to a multicast group in which a terminal connected via the second port does not participate. Communication method.
(Appendix 9)
Selecting a transfer destination of a multicast frame received from the first port of the transfer device from a plurality of ports included in the transfer device;
Measuring a load factor that is a ratio of a load of processing performed at the second port to the load that can be processed at the selected second port per unit time;
When the load factor exceeds a threshold, confirm a multicast group in which terminals connected via the second port are participating,
Causes a computer to perform processing for controlling the second port not to be selected as a forwarding destination for a multicast frame addressed to a multicast group to which a terminal connected via the second port does not participate A communication program characterized by the above.

DESCRIPTION OF SYMBOLS 1 Router apparatus 10, 30, 50, 60 Transfer apparatus 11 MAC address table 12 Load factor measurement part 20, 40, 70 Switch part 21, 41 Transfer part 22, 42 Confirmation part 23 Control part 31 Address table 32 Calculation setting part 33 Timer 51 Circuit Load Factor Measurement Unit 71 Round Trip Time Measurement Unit 72 Response Time Setting Unit

Claims (8)

A plurality of ports including a first port for receiving a multicast frame;
A transfer unit that selects a second port connected to a terminal that receives the multicast frame from the plurality of ports, and transfers the multicast frame to the second port;
A load factor measuring unit that measures a load factor that is a ratio of a load of processing performed in the unit time in the second port to a load that can be processed in the unit time in the second port;
When the load factor exceeds a threshold value, a confirmation unit for confirming a multicast group in which a terminal connected via the second port participates;
A control unit that controls the transfer unit not to select the second port as a transfer destination for a multicast frame addressed to a multicast group to which a terminal connected via the second port does not participate A transfer device comprising: After the multicast frame transmitted by the router device connected via the first port is received from the first port and the multicast frame is transmitted from the second port, the router device Before confirming whether it is connected to the terminal receiving the multicast frame, the confirmation unit confirms the multicast group to which the terminal connected through the second port is participating. The transfer apparatus according to claim 1. An identifier table storing a group identifier for identifying a multicast group of a destination of a multicast frame transmitted from the second port;
The confirmation unit
Sending an inquiry message for inquiring a group identifier for identifying a participating multicast group to a terminal connected via the second port;
Confirming the multicast group in which the terminal connected via the second port is participating by confirming the group identifier included in the response message in response to the inquiry message;
The control unit deletes a group identifier of a multicast group not included in the response message from the identifier table,
The forwarding unit forwards a multicast frame addressed to a multicast group identified by a group identifier recorded in the identifier table updated by the control unit to the second port. 2. The transfer device according to 2. The control unit stores a response time for receiving a response message from a terminal that has received the inquiry message,
The control unit extracts, from the group identifier stored in the identifier table, a group identifier that is not included in the response message received until the response time elapses after the inquiry message is transmitted,
The transfer apparatus according to claim 3, wherein the control unit deletes the extracted group identifier from the identifier table. A first measurement frame is transmitted to a terminal to which a source address of the response message is assigned, a second measurement frame is received in response to the first measurement frame, and the first measurement frame is received. A round trip time measuring unit for obtaining a round trip time from the time at which the second measurement frame is received to the time at which the second measurement frame is received;
The transfer apparatus according to claim 4, further comprising: a response time setting unit that sets the response time to a length equal to or longer than the round-trip time. A third port connected to a terminal that receives the multicast frame received via the first port;
The load factor measuring unit obtains a first load factor from the processing of the second port and a second load factor from the processing of the third port;
When both of the first and second load factors exceed the threshold, the confirmation unit assigns a port having a large value between the first load factor and the second load factor to the control unit. Determining the target port that is the target of the control by sending the inquiry message to the terminal connected to the target port,
The control unit controls the transfer unit not to select the target port as a transfer destination for a frame addressed to the multicast group identified by the group identifier not included in the response message. The transfer device according to any one of claims 3 to 5. Selecting a transfer destination of a multicast frame received from the first port of the transfer device from a plurality of ports included in the transfer device;
Measuring a load factor that is a ratio of a load of processing performed in the unit time in the second port to a load that can be processed in unit time in the selected second port;
When the load factor exceeds a threshold, confirm a multicast group in which terminals connected via the second port are participating,
A process for performing control so that the second port is not selected as a transfer destination is performed for a multicast frame addressed to a multicast group in which a terminal connected via the second port does not participate. Communication method. Selecting a transfer destination of a multicast frame received from the first port of the transfer device from a plurality of ports included in the transfer device;
Measuring a load factor that is a ratio of a load of processing performed in the unit time in the second port to a load that can be processed in unit time in the selected second port;
When the load factor exceeds a threshold, confirm a multicast group in which terminals connected via the second port are participating,
Causes a computer to perform processing for controlling the second port not to be selected as a forwarding destination for a multicast frame addressed to a multicast group to which a terminal connected via the second port does not participate A communication program characterized by the above.

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