JP2011193261A - Communication system, switching hub, and router - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent generation of a useless data stream, while suppressing power consumption in a switching hub. <P>SOLUTION: The switching hub 50 determines whether the packet is an IGMP packet, based on only a header of a packet received from the downstream side. When the packet is the IGMP packet, the switching hub executes the processing for notifying a router 60 of a port identifier of a port which receives the packet, and the processing for opening and closing a downstream side port according to instructions from the router 60. Alternatively, when notification of the port identifier is received, the router 60 is made to determine whether a packet relayed by a notification source of the port identifier is IGMP Join by referring to a payload part of the packet, and to execute processing for instructing opening and closing of the port to the switching hub at the notification source according to its determination results. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a data relay technique, and more particularly to a multicast data relay technique.

  As an example of a relay device used for constructing a communication system, a router and a switching hub can be cited. A router is a relay device that connects from the first layer (physical layer) to the third layer (network layer) of the OSI reference model. Data is exchanged with other routers via an IP (Internet Protocol) network such as the Internet. It plays the role of sending and receiving. On the other hand, the switching hub is a relay device for connecting from the first layer to the second layer (data link layer), and a communication terminal (for example, a personal computer) located at the end of data communication is used as a communication network. Take the role of containing. Here, the connection of the nth layer means performing data transfer control according to the communication protocol of the nth layer.

  For example, the header portion of a frame that is a data block of the second layer includes a MAC (Media Access Control) address that is a hardware address of a transmission device and a transmission destination communication device (relay device or communication terminal) of the frame. It is written as a transmission source address and a transmission destination address of the frame, and a packet which is a data block of the third layer is written in the payload portion. In the header portion of the packet, an IP address, which is a communication address for identifying the transmission source and transmission destination in the third layer, is written as the transmission source address and transmission destination address of the packet. In the router or switching hub, transfer control of the data block is performed based on the destination address written in the header part of the received data block. The data block transfer control performed by the router and the switching hub will be described below with reference to FIG.

  FIG. 8 is a diagram illustrating an example of a communication system including a router and a switching hub. In the communication system illustrated in FIG. 8, data is transmitted from the transmission device 10 to the reception devices 40-k (k = 1 to 4). Although detailed illustration is omitted in FIG. 8, between the router 20 and the transmission device 10, an IP network to which the router 20 is connected and other routers that connect the IP network and the transmission device 10. Exists. A switching hub 30 is connected to the router 20, and communication terminals (receiving devices 40-1 to 40-4) that receive data transmitted from the transmitting device 10 are connected to the switching hub 30.

  When the router 20 in FIG. 8 receives a frame containing a packet transmitted from the transmission device 10 to the reception device 40-1 (a frame in which the packet is written in the payload portion), the router 20 displays the header portion of the packet. If the destination IP address is an IP address assigned to a communication terminal under its control, the frame is transferred to the switching hub 30. On the other hand, when the packet included in the received frame is not transmitted to the subordinate communication terminal, the router 20 transfers the frame to another router according to the stored contents of the routing table. To do.

  The switching hub 30 in FIG. 8 has a plurality of ports connected to other communication devices (routers, other switching hubs, communication terminals), and each of the ports is associated with each of the plurality of ports. It stores the MAC address of the communication device to be connected. When the switching hub 30 receives a frame via any of the ports, the switching hub 30 refers to the transmission destination MAC address written in the header part of the frame, and sends the frame to the port corresponding to the transmission destination MAC address. Is output. In the following, among a plurality of ports of a switching hub, a port connected to the router (or a port connected to the router via another switching hub) is referred to as an “upstream port”, and others (In FIG. 8, the port to which the receiving device 40-k is connected) is referred to as a “downstream port”.

  In this way, the switching hub performs frame transfer control based on the MAC address associated with each port and the transmission destination MAC address of the received frame. For this reason, when a frame containing an IP multicast packet is received from the upstream side, a wasteful data stream is generated on the downstream side of the switching hub. The reason is as follows. IP multicast is a mode in which a packet is not sent to a specific communication terminal, but is sent to a group of communication terminals (multicast group) that has declared reception of the packet. In IP multicast, the packet destination address is the IP address assigned to the multicast group. Similarly, as a transmission destination MAC address of a frame including an IP multicast packet, a multicast MAC address generated from an IP address of a multicast group is used instead of a MAC address of a specific communication terminal.

  Since the multicast MAC address is generated from the IP address of the multicast group, it does not match any of the MAC addresses associated with each port of the switching hub. As described above, when a frame having a destination MAC address that does not match any of the MAC addresses associated with each port is received, the switching hub sends the frame to all downstream ports (flooding). ) Is executed. For example, in the communication system illustrated in FIG. 8, even when the transmission device 10 transmits a packet to a certain multicast group and only the reception device 40-1 participates in the multicast group, the switching hub 30. Since the flooding is performed, the frame including the packet addressed to the multicast group is transferred to the receiving apparatuses 40-2 to 40-4. Since the receiving apparatuses 40-2 to 40-4 do not participate in the multicast group, the transfer of the frame to them is nothing but a useless data stream. This is the reason why a useless data stream is generated downstream of the switching hub when a frame containing an IP multicast packet is received.

  Various techniques for avoiding the occurrence of such problems have been proposed, and one example is IGMP (Internet Group Management Protocol) snooping. Here, IGMP is one of communication protocols for realizing multicast communication, and is a communication protocol for notifying a router to join a multicast group from a communication terminal. When a router is notified of participation in a multicast group from a subordinate communication terminal in accordance with IGMP, the router stores information indicating that there is a communication terminal participating in the multicast group under its own device (hereinafter, participation management process). In addition, a packet that is sent to the multicast group from the upstream side is called “join / leave management process” together with the process of deleting the information in response to the notice of leaving from the multicast group. The transfer to the downstream side is started. Snooping means “peek”, and a switching hub equipped with an IGMP snooping function refers to the payload part of the packet contained in the frame received by the downstream port, and the packet is sent to the multicast group. Is a packet (IGMP Join) for notifying the router of participation, an identifier indicating the multicast group (for example, multicast MAC address: hereinafter referred to as multicast group identifier) is stored in association with the port. If the destination MAC address of the frame transferred from the upstream side matches the multicast group identifier, the frame is sent only to the downstream port associated with the multicast group identifier, and the other downstream side The frame is not sent to the port. This avoids the generation of useless data streams. Patent Document 1 is cited as a prior art document related to a switching hub having an IGMP snooping function.

JP 2007-288544 A

By the way, in recent years, it has become a big issue to suppress the power consumption of electronic devices to the minimum value according to the function due to the heightened awareness of environmental problems. In some cases, laws and regulations are imposed. Such a trend is no exception for communication devices such as switching hubs (see Article 21 Specified Equipment of Law Enforcement Ordinance on Rational Use of Energy). As described above, it is necessary to implement the IGMP snooping function in the switching hub to prevent useless data streams from being generated. However, when the IGMP snooping function is implemented, it is higher than when the function is not implemented. Processing power is required, and power consumption naturally increases.
The present invention has been made in view of the above problems, and an object of the present invention is to provide a technique that makes it possible to prevent generation of useless data streams while suppressing power consumption in a switching hub.

  In order to solve the above problems, the present invention comprises (A) a plurality of downstream ports to which downstream communication devices are connected and upstream ports to be connected to upstream communication devices. 1 or a plurality of switching hubs that perform transfer control of the received frame based on a transmission destination address of the frame, and a router located upstream of the one or the plurality of switching hubs, and (B) the 1 or Each of the plurality of switching hubs has, for each of the plurality of downstream ports, a packet included in a frame received by the downstream port transmitted according to a predetermined communication protocol for realizing multicast communication Is determined by referring to the header part of the packet and transmitted according to the communication protocol. If it is determined, a first process for notifying the router of a port identifier indicating the downstream port and a second process for opening and closing the downstream port in accordance with an instruction from the router are executed. C) When the router is notified of the port identifier from any of the one or a plurality of switching hubs, the packet relayed to the router by the switching hub that is the notification source indicates that the router has joined the multicast group. If it is determined whether it is for notification according to the protocol with reference to the payload part of the packet, and if it is determined for notification of participation in the multicast group, the port identifier Only the downstream port indicated by the port identifier is assigned to the multicast group that is the notification source of the multicast group. To provide a communication system, characterized by instructing to open to.

  In the conventional switching hub having the IGMP snooping function, the process of determining whether or not the IGMP Join is performed with reference to the payload portion of the packet is performed. However, in the switching hub included in the communication system, Refers to the header of the packet. The processing that refers to the header portion of the packet has a lower processing load than the processing that refers to the payload portion of the packet. For this reason, the switching hub included in the communication system is sufficient to have a lower processing capability than the conventional switching hub having the IGMP function, and the power consumption can be suppressed. Note that a process for determining whether the packet is IGMP Join with reference to the payload portion of the packet is performed by the router, and the router instructs the switching hub to open and close the downstream port according to the determination result. In the switching hub, since the downstream port is opened and closed in accordance with an instruction from the router, no useless data stream is generated on the downstream side of the switching hub.

  In order to solve the above-mentioned problem, the present invention provides (A) a frame between a router via one or more other switching hubs, or between a router without any other switching hub. A plurality of downstream ports for transmitting / receiving frames to / from a downstream communication device, and control of transfer of frames received via each port. In the switching hub performed based on the destination address, (B) predetermined communication for realizing, for each of the plurality of downstream ports, a packet included in a frame received via the downstream port to realize multicast communication Whether the packet is transmitted according to the protocol is determined by referring to the header of the packet, and the communication protocol is used. And (C) a port that opens and closes the downstream port in accordance with an instruction from the router when it is determined that the received port identifier is transmitted to the router. An opening / closing control means is provided. In another aspect of the present invention, it is conceivable to provide a program that causes a computer to function as the notification means and the port opening / closing control means.

  In order to solve the above problems, the present invention (A) forwards a packet received via one or more switching hubs to another router, while transferring a packet received from the other router to the above 1 or In a router that forwards to a destination via a plurality of switching hubs, (B) a packet transmitted according to a predetermined communication protocol is received from any one of the one or more switching hubs to realize multicast communication. In order to notify the router of participation in the multicast group according to the communication protocol when the notification indicating that the port identifier indicating the port that received the packet is notified is received. Refer to the payload part of the packet to determine whether it was sent or not. And (C) if it is determined by the determination means that it is for notifying participation in the multicast group, the port identifier is notified to the switching hub that has notified the port identifier. And a port opening / closing instruction means for instructing to open only the port indicated by the multicast group to the multicast group. In another aspect of the present invention, it is conceivable to provide a program that causes a computer to function as the determination unit and the port opening / closing instruction unit.

It is a figure which shows the structural example of 1 A of communication systems of 1st Embodiment of this invention. It is a block diagram which shows the structural example of the switching hub 50 contained in the communication system 1A. It is a flowchart which shows the flow of the IGMP packet determination process which the switching engine part 520 of the switching hub 50 performs. It is a block diagram which shows the structural example of the router 60 contained in the communication system 1A. It is a flowchart which shows the flow of the switching hub control process which the routing engine part 620 of the router 60 performs. It is a figure which shows the communication systems 1B and 1C of 2nd Embodiment of this invention. It is a figure for demonstrating the notification aspect of the port identifier of a modification (1). It is a figure for demonstrating the function of a router and a switching hub.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(A: 1st Embodiment)
(A-1: Configuration)
FIG. 1 is a diagram illustrating a configuration example of a communication system 1A according to the first embodiment of the present invention. In FIG. 1, the same components as those in FIG. 8 are denoted by the same reference numerals. As is clear from a comparison between FIG. 1 and FIG. 8, this communication system 1 </ b> A shows that a router 60 is provided instead of the router 20 and a switching hub 50 is provided instead of the switching hub 30 in FIG. 8. Different from the communication system shown. In this communication system 1A, even if any one of the reception devices 40-k (k = 1 to 4) receives a packet transmitted from the transmission device 10 addressed to a certain multicast group, By causing the switching hub 50 to perform processing that clearly shows the characteristics of this embodiment and to cooperate with each other, the downstream side of the switching hub 50 (that is, between the switching hub 50 and another receiving device 40-k). This prevents unnecessary data streams from being generated. Hereinafter, the switching hub 50 and the router 60 that clearly show the features of the present embodiment will be mainly described.

  FIG. 2 is a block diagram showing the configuration of the switching hub 50. As shown in FIG. 2, the switching hub 50 includes a communication interface (hereinafter, “I / F”) unit 510, a switching engine unit 520, a storage unit 530, and a control unit 540. The control unit 540 is, for example, a CPU (Central Processing Unit), and centrally controls the operation of each unit according to firmware stored in the storage unit 530. Processing executed by the control unit 540 according to this firmware will be described in detail later.

  The communication I / F unit 510 is an interface that exchanges frames with other communication devices, and each of the plurality of ports to which the other communication devices are connected (ports 512U and 512D-1 to 512D in FIG. 2). -4 five ports). In the present embodiment, frames are exchanged with the connection destination communication device via each of the plurality of ports. Port 512U in FIG. 2 is an upstream port connected to the router 60, and ports 512D-k (k = 1 to 4) are downstream ports connected to the receiving devices 40-k. A port identifier for uniquely identifying each port is assigned in advance to each of the plurality of ports. In the present embodiment, port number “0” is assigned to port 512U, and port number “k” is assigned to port 512D-k (k = 1 to 4), and these port numbers serve as port identifiers. Fulfill.

  The switching engine unit 520 is, for example, an ASIC. The switching engine unit 520 refers to the content stored in the frame transfer control table stored in the storage unit 530, and based on the transmission destination MAC address of the frame received via each port of the communication I / F unit 510. The above-described frame transfer control is performed. In addition, when the frame is received via the downstream port, the switching engine unit 520 of the present embodiment executes the IGMP packet determination process shown in FIG. 3 prior to the transfer control of the frame. Although details will be clarified in the operation example, this IGMP packet determination processing is performed when the frame received via the downstream port includes an IGMP packet (whether or not it is IGMP Join). This is a process of notifying the router 60 of the port identifier of the port that has received the frame. In the present embodiment, a dedicated frame (hereinafter referred to as a port identifier notification frame) is used for notifying the router 60 of the port identifier. In the header portion of the port identifier notification frame, type information indicating that the frame is a port identifier notification frame in addition to the MAC addresses of the transmission source (that is, the switching hub 50) and the transmission destination (router 60) of the frame. Is written. Also, the port identifier of the downstream port that received the frame containing the IGMP packet is written in the payload portion of the port identifier notification frame.

  Although detailed illustration is omitted in FIG. 2, the storage unit 530 includes, for example, a volatile memory such as a RAM (Random Access Memory) and a nonvolatile memory such as an EPROM (Erasable Programmable ROM). The firmware is stored in a nonvolatile memory, and the frame transfer control table is stored in the volatile memory. The volatile memory is used by the control unit 540 as a work memory when executing the firmware, and also serves as a buffer for temporarily storing frames during the frame transfer control described above.

  In the frame transfer control table of FIG. 2, the MAC address of the communication device connected to the port is registered in association with the port identifier of each port. A well-known method may be employed for registering the MAC address and port identifier in the frame transfer control table. Also, in this frame transfer control table, when the communication device to which each port is connected participates in the multicast group, the multicast group identifier of the multicast group is registered in association with the port identifier of the port. . When the frame received from the communication I / F unit 510 is addressed to the multicast group, the switching engine unit 520 registers the port identifier registered in the frame transfer control table in association with the multicast group identifier of the multicast group. This frame is output only from the port indicated by the above, thereby avoiding the generation of useless data streams.

Registering a multicast group identifier in the frame forwarding control table in association with the port identifier in this way is to allow a frame addressed to the multicast group to pass through the port indicated by the port identifier. To open the port. " Conversely, deleting a set of port identifiers and multicast group identifiers registered in association with each other in the frame forwarding control table, or not performing such registration, “blocks the port against the multicast group. It is said. Although details will be described later, the port opening / closing control process for opening (or closing) the port for the multicast group is executed by the control unit 540 in response to an instruction from the router 60. A newly defined dedicated frame (port opening / closing instruction frame) is also used for the port opening / closing instruction from the router 60.
The above is the configuration of the switching hub 50.

  Next, the configuration of the router 60 will be described with reference to FIG. FIG. 4 is a block diagram showing the configuration of the router 60. As illustrated in FIG. 4, the router 60 includes a communication I / F unit 610, a routing engine unit 620, and a storage unit 630. The communication I / F unit 610 has a plurality of ports (two ports 612U and 612D in FIG. 4) similarly to the communication I / F unit 510 of FIG. A port 612U in FIG. 4 is an upstream port connected to an IP network (not shown), and a port 612D is a downstream port connected to the switching hub 50. Note that the communication I / F unit 610 of the present embodiment has only one downstream port, but may of course have a plurality of downstream ports.

  The routing engine unit 620 includes a CPU and a RAM (both not shown in FIG. 4). In accordance with the firmware (program) stored in the storage unit 630, the CPU writes a packet written in a routing table stored in the storage unit 630 and a payload portion of a frame delivered from the communication I / F unit 610. Packet transfer control based on the destination IP address and participation / leaving management processing for the multicast group. The packet transfer control processing is omitted because it is not particularly different from that performed by a general router. In this embodiment, the routing engine unit 620 is configured by a CPU and a RAM, but may be configured by an ASIC.

In addition, prior to the packet transfer control process and the multicast group participation / leaving management process, the CPU of the routing engine unit 620 of this embodiment executes the switching hub control process shown in FIG. 5 according to the firmware. Although details will be described later, in this switching hub control process, it is first determined whether or not the frame delivered from the communication I / F unit 610 is a port identifier notification frame, and further, transmission of the port identifier notification frame is performed. It is determined whether or not a packet included in another frame received from the original (that is, the switching hub 50) is for notifying participation in the multicast group (or departure from the multicast group). . When all of these requirements are satisfied, the routing engine unit 620 returns the port opening / closing instruction frame described above to the transmission source of the port identifier notification frame. That is, the routing engine unit 620 that operates according to the firmware returns a determination unit that performs each determination, and a port that instructs the opening and closing of the downstream port by returning a port opening / closing instruction frame to the transmission source of the port identifier notification frame. It functions as an opening / closing instruction means. In the header portion of the port opening / closing instruction frame, type information indicating that the frame is a port opening / closing instruction frame is written together with the MAC addresses of the transmission source (that is, the router 60) and the transmission destination (that is, the switching hub 50). It is. In the payload part of the port opening / closing instruction frame, a multicast group identifier indicating a multicast group notified of participation (or leaving) by the IGMP packet, and a port of a port to be opened (or blocked) from the multicast group An identifier (that is, a port identifier notified by the port identifier notification frame) and an indicator that indicates whether to open or close the port are written.
The above is the configuration of the router 60.

(A-2: Operation)
Next, operations performed by the switching hub 50 and the router 60 will be described by taking as an example a case where the receiving device 40-1 receives data multicast from the transmitting device 10 in the communication system 1A shown in FIG.

  When the user of the receiving device 40-1 desires to receive data multicast from the transmitting device 10, first, the user performs an operation for instructing participation in the multicast group to the receiving device 40-1. When such an operation is performed, the control unit (not shown) of the reception device 40-1 generates an IGMP packet (that is, IGMP Join) for notifying participation in the multicast group. The IGMP packet generated in this way is written in the payload portion of the frame that is the data block of the second layer in the receiving device 40-1 and is transmitted to the router 60. In the header portion of this frame, the MAC address of the receiving device 40-1 is written as the source MAC address, and the MAC address of the router 60 is written as the destination MAC address.

  The frame transmitted from the receiving device 40-1 in this way is input to the switching engine unit 520 via the port (in this operation example, the port 512D-1) connecting the receiving device 40-1 in the switching hub 50. Is done. As described above, when the frame is received via the downstream port, the switching engine unit 520 executes the IGMP packet determination process shown in FIG. 3, and then performs frame transfer control based on the destination. When a frame is received via the upstream port, the switching engine unit 520 performs frame transfer control based on the destination without performing IGMP packet discrimination processing. In the present operation example, the switching hub 50 receives the frame via the port 512D-1 which is the downstream port, and therefore the IGMP packet determination process of FIG. 3 is executed prior to the frame transfer control.

  FIG. 3 is a flowchart showing a flow of IGMP packet determination processing executed by the switching engine unit 520 of the switching hub 50. As shown in FIG. 3, the switching engine unit 520 refers to the header portion of the packet written in the payload portion of the frame received via the downstream port, and determines whether or not the packet is an IGMP packet. (Step SA100). Specifically, the switching engine unit 520 reads the header portion of the packet written in the payload portion of the received frame, and determines whether or not the protocol type described in the header portion indicates IGMP. judge. If the protocol identifier indicates IGMP, the determination result in step SA100 is “Yes”, and if it indicates another protocol, the determination result in step SA100 is “No”. Then, the switching engine unit 520 generates a port identifier notification frame for notifying the port identifier of the downstream port that has received the IGMP packet only when the determination result of step SA100 is “Yes”, to the router 60. Transmit (step SA110).

  As described above, the IGMP packet (specifically, IGMP Join) is written in the payload portion of the frame transmitted from the receiving device 40-1 to the switching hub 50 in this operation example. Accordingly, the determination result in step SA100 is “Yes”, and the port identifier notification frame in which the port identifier of the port that received the frame (port identifier of the port 512D-1) is written in the payload portion is transmitted from the switching hub 50 to the router 60. Sent to. Separately from the port identifier notification frame, a frame (a frame including an IGMP packet) received from the reception device 40-1 is also transferred to the router 60.

  FIG. 5 is a flowchart showing the flow of the switching hub control process executed by the routing engine unit 620 of the router 60. As shown in FIG. 5, when the routing engine unit 620 receives a frame via the downstream port (port 612D), it first writes in the header part of the frame whether or not the frame is a port identifier notification frame. The determination is made with reference to the type information (step SB100). Then, the routing engine unit 620 executes the processes after step SB110 only when the determination result of step SB100 is “Yes”. In this operation example, since the port identifier notification frame is first transmitted from the switching hub 50, the determination result in step SB100 is “Yes”, and the processing after step SB110 is executed.

  The process of step SB110 determines whether or not another frame received from the transmission source of the port identifier notification frame includes an IGMP packet notifying participation in the multicast group (or leaving the multicast group). It is processing to do. Here, the determination as to whether or not a packet included in another frame received from the transmission source of the port identifier notification frame is an IGMP packet notifying participation in the multicast group (or leaving the multicast group) Similar to the case of the conventional IGMP snooping, it may be performed by referring to the payload portion of the packet included in the frame.

  If the determination result in step SB110 is “Yes”, the routing engine unit 620 generates a port opening / closing instruction frame for instructing opening / closing of the downstream port according to the contents of the IGMP packet, and It transmits to the transmission source of the port identifier notification frame (step SB120). For example, when the packet included in another frame received from the transmission source of the port identifier notification frame is an IGMP packet (IGMP Join) for notifying participation in the multicast group, the routing engine unit 620 Then, a port open / close instruction frame for instructing to open only the port indicated by the port identifier notified in the port identifier notification frame to the multicast group is generated and transmitted. On the other hand, in the case of an IGMP packet for notifying the departure from the multicast group, the routing engine unit 620 sets the port indicated by the port identifier notified in the port identifier notification frame to the multicast notified of the departure. A port open / close instruction frame for instructing the group to be blocked is generated and transmitted.

  In this operation example, since the packet transmitted from the receiving device 40-1 via the switching hub 50 is IGMP Join, the determination result in Step SB110 is “Yes”, and the processing in Step SB120 is executed. That is, in this operation example, it is instructed to release only the port having the port number “1” to the multicast group notified of participation by the IGMP Join (in other words, to block other downstream ports). A port open / close instruction frame to that effect is transmitted from the router 60 to the switching hub 50.

When receiving the port opening / closing instruction frame via the communication I / F unit 510 and the switching engine unit 520, the control unit 540 of the switching hub 50 opens / closes the downstream port (that is, the frame transfer control table) according to the contents of the frame. Update the stored contents). As a result, among the four ports on the downstream side of the switching hub 50, only the port with the port number “1” (that is, the port 512D-1) is opened to the multicast group, and the other downstream ports are blocked. The For this reason, even if transmission of the packet addressed to the multicast group is started from the transmission device 10 and the packet is transferred from the router 60 to the switching hub 50, the packet is received by the reception devices 40-2, 40-3, and 40-. 4 is not transferred, and no useless data stream is generated.
The above is the operation of this embodiment.

  In the conventional switching hub having the IGMP snooping function, the process of determining whether or not the IGMP Join is performed with reference to the payload portion of the packet is performed. In the switching hub 50 of the present embodiment, the packet is determined. The router 60 performs processing for determining whether the packet is IGMP Join by referring to the payload portion of the packet. The processing that refers to the header portion of the packet has a lower processing load than the processing that refers to the payload portion of the packet. Therefore, the switching hub 50 has a processing capability lower than that of a switching hub having an IGMP snooping function. The power consumption can be suppressed. In addition, as described above, no wasteful data stream is generated downstream of the switching hub 50 in the present embodiment. As described above, according to the present embodiment, it is possible to prevent a useless data stream from being generated downstream of the switching hub while suppressing power consumption in the switching hub.

(B: Second embodiment)
In the communication system 1A of the first embodiment described above, only one switching hub is connected to the router 60, but a mode in which a plurality of switching hubs are connected downstream of the router 60 is also conceivable. This embodiment differs from the first embodiment described above in that a plurality of switching hubs are connected downstream of the router 60.

  Here, as a specific example of a mode in which a plurality of switching hubs are connected downstream of the router 60, the following two modes can be considered. First, as in the communication system 1B shown in FIG. 6A, a plurality of switching hubs (four switching hubs 50A, 50B, 50C, and 50D in FIG. 6A) are directly connected to the router. (In other words, each switching hub is connected to the router without any other switching hub). In FIG. 6A, illustration of a communication device upstream of the router 60 (for example, the transmission device 10 in FIG. 1) is omitted (the same applies to FIG. 6B). And the 2nd mode includes what is connected to a router via one or more other switching hubs to a plurality of switching hubs like communication system 1C shown in Drawing 6B. This is a mode. For example, in FIG. 6B, the switching hub 50B is connected to the router 60 via one other switching hub (switching hub 50A), and the switching hub 50C includes a plurality of other switching hubs ( That is, it is connected to the router 60 via the switching hubs 50B and 50A).

  6A and 6B, each of the switching hubs 50A to 50D is caused to execute the IGMP packet determination process and the port opening / closing control process of FIG. 3 and is shown in FIG. By causing the router 60 to execute the switching hub control process, it is possible to avoid generation of useless data streams. In the connection mode shown in FIG. 6B, the switching hub to which another switching hub is connected on the downstream side does not perform the IGMP packet discrimination process and the port open / close control process, and has an IGMP snooping function. Even if the switching hub is not a switching hub (that is, a switching hub that does not perform filtering of multicast packets), the switching hub can transfer the port identifier notification frame and the port opening / closing instruction frame, and the downstream switching hub. However, if the IGMP packet discrimination process and the port opening / closing control process of FIG. 3 can be executed, no useless data stream is generated downstream of the downstream switching hub.

  For example, in the aspect shown in FIG. 6B, it is assumed that the switching hub 50A does not perform the IGMP packet discrimination process and the port opening / closing control process and does not have an IGMP snooping function. The switching hubs 50B to 50D are all capable of executing the IGMP packet determination process and the port opening / closing control process. In this case, when only the receiving device 40B connected to the switching hub 50B transmits IGMP Join, the switching hub 50B notifies the router 60 of the port identifier of the port to which the receiving device 40B is connected. In response to the instruction, only the port is released to the multicast group. Since the switching hubs 50C and 50D do not transmit IGMP Joins from the receiving devices connected to them, the router 60 does not perform the IGMP packet discrimination process and instructs the router 60 to open a port for the multicast group. It will never be done. In other words, the ports on the downstream side of the switching hubs 50C and 50D remain blocked from the multicast group.

  When transmission of a packet addressed to the multicast group is started in such a situation, since the switching of the multicast packet is not performed in the switching hub 50A, the frame including the packet is transferred to the switching hubs 50B and 50D. The However, since the downstream port for the multicast group is not opened in the switching hub 50D, the frame is not transferred to the downstream side of the switching hub 50D. On the other hand, in the switching hub 50B, since only the port to which the receiving device 40B is connected is opened to the multicast group, the frame is transferred only through this port, and the switching hub 50B transfers to the switching hub 50C. The frame is not transferred. Thus, even if the most upstream switching hub 50A does not perform multicast packet filtering, no useless data stream is generated downstream of the downstream switching hubs 50B, 50C, and 50D.

  In this way, even when a plurality of switching hubs are connected downstream of the router, a wasteful data stream can be generated while reducing the processing load of each switching hub as compared with the case where IGMP snooping is performed only by the switching hub. Occurrence can be prevented. For this reason, compared with the case where IGMP snooping is performed by each switching hub, the processing capability of each switching hub can be suppressed low, and it becomes possible to suppress the power consumption.

(C: deformation)
Although the first and second embodiments of the present invention have been described above, it is needless to say that these embodiments may be modified as follows.
(1) In the above-described embodiment, the port identifier of the downstream port that received the frame containing the IGMP packet is notified to the router 60 by transmitting the port identifier notification frame, but a predetermined area ( For example, the notification to the router 60 may be realized by adding and transferring the port identifier and the MAC address of the switching hub that notifies the port identifier to an option field. Here, in addition to the port identifier, the MAC address of the notification source of the port identifier is additionally written in order to transmit the notification source to the router 60. If the communication system includes a switching hub connected to the router via one or more other switching hubs, the upstream switching hub is closer to the top of the predetermined area. What is necessary is just to make it add a port identifier and a MAC address hierarchically, such as adding a port identifier and a MAC address. For example, when the switching hub 50B of FIG. 6B transfers the frame F1 including the IGMP packet, the port identifier of the port that received the frame and the MAC address of the notification source of the port identifier (that is, switching) The frame F2 (see FIG. 7) in which the header of the MAC address of the hub 50B is added is transmitted to the switching hub 50A, and the switching hub 50A sends the port identifier of the port that received the frame and the notification source of the port identifier. The router 60 may transmit the frame F3 (see FIG. 7) in which the MAC address (that is, the MAC address of the switching hub 50A) is added to the header portion.

(2) In the above-described embodiment, the switching hub 50 that has received the frame containing the IGMP packet is notified to the router 60 of the port identifier of the downstream port that has received the frame. However, in addition to the port identifier, the source communication address (MAC address or IP address) of the IGMP packet may be notified. According to such an aspect, even if each of the receiving devices 40-k (k = 1 to 4) participates in a plurality of multicast groups each having a different multicast address, each receiving device 40-k Each multicast join is associated with the port identifier of the downstream port of the switching hub that has received the frame including the IGMP Join based on the source address of the IGMP Join and the communication address notified together with the port identifier, and each multicast It becomes possible to appropriately open and close the port for the group.

(3) In the above-described embodiment, the packet included in the frame relayed by the switching hub that is the transmission source of the port identifier notification frame is for notifying participation in or leaving from the multicast group. Whether or not there is a router 60 is determined, and a port opening / closing instruction frame corresponding to the determination result is transmitted to the router 60. However, depending on the version of IGMP, an IGMP packet for notifying the departure from the multicast group may not be defined. For this reason, of course, only the packet for notifying the participation in the multicast group may be set as the determination target in step SB110. As described above, when only the packet for notifying the participation in the multicast group is set as the determination target in step SB110, the port is set to the multicast group when a certain time has elapsed since the reception of the packet. The router 60 may be caused to execute timer processing such as transmitting a port open / close instruction frame instructing blocking.

(4) In the above-described embodiment, the IGMP packet discrimination process in the switching hub 50 is executed by the ASIC (switching engine unit 520), and the port opening / closing control process is executed by the control unit 540 according to the firmware. That is, in the above-described embodiment, the IGMP packet determination process is realized by hardware, and the port opening / closing control process is realized by software. However, both may be realized by software (or hardware), IGMP packet discrimination processing may be realized by software, and port opening / closing control processing may be realized by hardware. Similarly, of course, the switching hub control process in the router 60 may be realized by hardware.

  Further, in an aspect in which the IGMP packet discrimination process and the port opening / closing control process are realized by software (that is, by the firmware of the switching hub), the computer-readable recording medium such as a CD-ROM (Compact Disk-Read Only Memory) is used. The firmware may be written and distributed, or the firmware may be distributed by downloading via a telecommunication line such as the Internet. This is because, by rewriting the firmware of the existing switching hub with the firmware thus distributed, the same function as the switching hub 50 can be given to the existing switching hub. Similarly, the firmware that implements the switching hub control process may be distributed by writing in a computer-readable recording medium, or may be distributed by downloading via an electric communication line such as the Internet. This is because, by rewriting the firmware of the existing router with the firmware distributed in this way, the same function as the router 60 can be given to the existing router. Note that the firmware (that is, the program for causing the control unit 540 to execute the port opening / closing control processing) stored in the storage unit 530 of the switching hub 50 in the above embodiment is also written and distributed on a computer-readable recording medium. It may also be distributed by downloading via a telecommunication line.

  1A, 1B, 1C ... communication system, 10 ... transmission device, 20,60 ... router, 30,50 ... switching hub, 40-k (k = 1-4) ... reception device, 510,610 ... communication I / F unit 512U, 512D-k (k = 1 to 4), 612U, 612D ... port, 520 ... switching engine unit, 620 ... routing engine unit, 530, 630 ... storage unit, 540 ... control unit.

Claims (3)

(A) a plurality of downstream ports to which downstream communication devices are respectively connected and upstream ports connected to upstream communication devices, and transfer control of frames received via each port is performed. One or more switching hubs based on a destination address, and a router located upstream of the one or more switching hubs,
(B) For each of the one or more switching hubs, a predetermined communication protocol for realizing, for each of the plurality of downstream ports, a packet included in a frame received by the downstream port to realize multicast communication Port identifier indicating the downstream port when it is determined whether the packet is transmitted according to the communication protocol, and when it is determined that the packet is transmitted according to the communication protocol. And a second process for opening and closing the downstream port in accordance with an instruction from the router,
(C) When the router is notified of the port identifier from any of the one or a plurality of switching hubs, the packet relayed to the router by the switching hub that is the notification source will participate in the multicast group. If it is determined whether it is for notification according to the communication protocol with reference to the payload part of the packet, and if it is determined for notification of participation in the multicast group, the port A communication system characterized by instructing a switching hub that is an identifier notification source to release only the downstream port indicated by the port identifier to the multicast group. (A) An upstream port for transmitting / receiving a frame to / from a router via one or more other switching hubs or from / to a router without going through another switching hub and a downstream side In a switching hub that includes a plurality of downstream ports for transmitting and receiving a frame to and from the communication device, and performs transfer control of a frame received via each port based on a transmission destination address of the frame,
(B) For each of the plurality of downstream ports, is the packet included in the frame received via the downstream port transmitted according to a predetermined communication protocol for realizing multicast communication? A notification means for notifying the router of a port identifier indicating the downstream port when it is determined whether the packet is transmitted according to the communication protocol. ,
(C) Port switching control means for opening and closing a downstream port according to an instruction from the router. (A) In a router that forwards a packet received via one or more switching hubs to another router, while forwarding a packet received from the other router to its destination via the one or more switching hubs ,
(B) A notification indicating that a packet transmitted in accordance with a predetermined communication protocol for realizing multicast communication is received from any of the one or a plurality of switching hubs, and the port that has received the packet is Whether or not the packet is transmitted for notifying the router according to the communication protocol whether or not the packet is transmitted when the notification indicating the port identifier is received. Determining means for determining with reference to a section;
(C) If the determination means determines that the notification is for notifying participation in the multicast group, only the port indicated by the port identifier is assigned to the switching hub that has notified the port identifier. And a port opening / closing instruction means for instructing the multicast group to be opened.

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