JP6263926B2 - Communication device, gateway, redundant system, and communication system - Google Patents

Description

  The present invention relates to a communication device, a gateway, a redundant system, and a communication system, and can be applied to a system including a redundant system constructed using a plurality of network devices.

  Conventionally, the same device is duplicated, and one is operated as an active system and the other is operated as a standby system. When a failure occurs in the active system device, the service can be continued by switching to the standby device. Has been done.

  In VRRP (Virtual Router Redundancy Protocol) (Non-patent Document 1), a virtual MAC address and a virtual IP address are shared between an active device and a standby device, and a system switchover occurs. Since the active device takes over the address, the device connected to the redundant device can continue communication without being aware of system switching.

  As a method described in Patent Document 1, a redundancy switching method for a VRRP non-compliant device has been proposed. According to this document, in addition to a device (router) that configures redundancy, a device that is a route switching device is installed, and system switching can be performed without using VRRP by executing an ARP response.

  Specifically, in response to the ARP request from the connected device (terminal, server) to the virtual IP address of the router, the path switching device performs an ARP response with the MAC address of the active router.

  Since the terminal and the server communicate according to the MAC address acquired by the ARP response, there is no awareness of system switching. In this method, a virtual IP address is used, but a virtual MAC address is not used.

JP 2005-252315 A

RFC5798, Virtual Router Redundancy Protocol (VRRP) version 3 for IPv4 and IPv6

  However, VRRP (Non-Patent Document 1) has a problem that it cannot be used unless a redundantly configured device supports this protocol. Routers and layer 3 switches often support standards, but other network devices and servers rarely support them. Further, in the method of Patent Document 1, the cache information that associates the IP address and the MAC address stored in the opposite device (router or layer 3 switch) cannot be updated after switching, and the cache information is deleted by the timer. Until it is done, it will communicate with the device before switching, and normal communication cannot be performed.

  As a means for updating cache information, VRRP (Non-Patent Document 1) notifies a virtual MAC address and a virtual IP address after system switching. If the notification method is IPv4, the notification is performed using an ARP request message called a Gratuitous ARP request. If the notification method is IPv6, the notification is performed using a neighbor advertisement message.

  However, depending on the policy of the device that receives the notification, even if the notification is received, the cache information is not necessarily updated.

  Even if the policy is to update the cache information, in the case of a redundant device with multiple virtual MAC addresses or virtual IP addresses, a large number of notification messages will be generated, so the device that receives the notification may miss the message There is sex. In addition, message loss occurs even when the network is congested. For this reason, since the old cache information remains on the opposite device side, communication continues to the old operation system, and there is a problem that normal communication cannot be performed.

  In view of the above, there is a demand for means that can quickly update the cache information of the opposite device after system switching without supporting VRRP.

  In view of the above problems, when system switching occurs in a redundant system configured by a plurality of communication devices that perform IP communication, a network switching dedicated protocol (for example, VRRP) is not used. Therefore, a communication device, a gateway, a redundant system, and a communication system that can quickly and reliably perform switching are desired.

In the first aspect of the present invention, in a communication apparatus that constitutes one redundant system with one or a plurality of other communication apparatuses, (1) the operation state of the communication apparatus is determined as either an active system or a standby system. (2) When communicating with the gateway related to the redundant system, and when the operation state of the communication apparatus is a standby system, an IP address used for communication by the communication apparatus is assigned to the communication apparatus. Communication processing means for setting an IP address used for communication by the communication device to a shared IP address shared by the redundant system when the operation state of the communication device is active, 3) When the operation state of the operation state management means is switched from the standby system to the active system, it is a message according to the neighbor search protocol and the source IP address is changed to the shared I Those set in the address, and sends to the gateway, have a cache information updating means for updating the cache information according to the shared IP address managed by the gateway, (4) the cache information updating means, the An NDP request message or an ARP request message is used as a message in accordance with the neighbor discovery protocol. (5) After the cache information related to the shared IP address managed by the gateway is updated, the gateway receives the NDP request message or characterized in that it further have a reply message receiving means for receiving a response message corresponding to the message of the ARP request.

According to a second aspect of the present invention, (1) cache information storing cache information in which an IP address and a MAC address are associated with each other in a gateway connected to the communication device constituting a redundant system configured using a plurality of communication devices. storage means, based on the cache information stored in (2) above cache information storage unit, a communication processing means for communicating with the communication device, (3) from the communication device, as a message in accordance with a neighbor discovery protocol A cache information updating unit that updates cache information stored in the cache information storage unit based on the content of the message when an NDP request message or an ARP request message is received ; and (4) the cache information storage unit. After updating the cache information stored in the And having a response message sending means for sending a response message to the message or corresponding to the message of the ARP request.

  According to a third aspect of the present invention, there is provided a communication system including a redundant system configured using a plurality of communication devices, and a gateway connected to each of the communication devices. The present invention is applied, and (2) the gateway according to the second aspect of the present invention is applied as the gateway.

  According to the present invention, when system switching occurs in a redundant system configured by a plurality of communication devices that perform IP communication, switching on a network is performed more quickly and reliably without using a network switching dedicated protocol. Communication devices, gateways, redundant systems, and communication systems that can be used are desired.

It is the sequence diagram shown about operation | movement of the communication system which concerns on embodiment. It is the block diagram shown about the whole structure of the communication system which concerns on embodiment, and the functional structure of a router. It is the block diagram shown about the functional structure of the network device which concerns on embodiment. It is explanatory drawing shown about the structural example of the address information which the router which concerns on embodiment memorize | stores. It is explanatory drawing shown about the structural example of the cache information which the router which concerns on embodiment memorize | stores. It is explanatory drawing shown about the structural example of the address information which the network device which concerns on embodiment memorize | stores. It is the flowchart shown about operation | movement of the network apparatus which concerns on embodiment. It is the flowchart shown about operation | movement of the router which concerns on embodiment. It is explanatory drawing shown about the transition of the cache information which the router which concerns on embodiment memorize | stores.

(A) Main Embodiment Hereinafter, an embodiment of a communication device, a gateway, a redundant system, and a communication system according to the present invention will be described in detail with reference to the drawings. Below, the example which applied the communication apparatus and gateway of this invention to the network apparatus and the router is demonstrated.

(A-1) Configuration of Embodiment FIG. 2 is a block diagram showing the overall configuration of the communication system 1 of this embodiment.

  In the communication system 1, a router 10 and two network devices 20 (20-1, 20-2) are arranged.

  The network devices 20-1 and 20-2 are redundant network devices, and one network device 20 operates as an active system, and the other network device 20 operates as a standby system. Therefore, in this embodiment, the redundant system of the embodiment is configured by the network devices 20-1 and 20-2. When a failure occurs in the active network device 20, the other network device 20 becomes the active system and continues to operate. Two network devices 20-1 and 20-2 are constructed as a redundant system that provides one service (for example, an application service such as a WWW server and a cache server and a network service such as a load balancer). The contents of services provided by the network devices 20-1 and 20-2 are not limited. Each of the network devices 20-1 and 20-2 can be connected to another network via the router 10 to provide a service.

  The network devices 20-1 and 20-2 are connected to the router 10, respectively, and are configured to be able to perform IP communication with other networks (not shown) via the router 10.

  It is assumed that the router 10 and the network devices 20-1 and 20-2 are assigned unique IP addresses and MAC addresses, respectively.

  In the following, it is assumed that the MAC address of the network device 20-1 is NW1-MA and the local IP address (link local address) is NW1-LA. In the following, it is assumed that the MAC address of the network device 20-2 is NW2-MA and the local IP address (link local address) is NW2-LA.

  Hereinafter, a logical IP address (global address) shared in the redundant configuration of the network devices 20-1 and 20-2 is represented as NW-GA.

  Furthermore, in the following, the IP address on the router 10 side (next hop address and link local address viewed from the network devices 20-1 and 20-2) is indicated as R-LA, and the MAC address is indicated as R-MA.

  Next, details of the router 10 will be described with reference to FIG.

  The router 10 is a communication device that performs routing processing using IP (layer 3), and includes a network interface unit 11, a communication processing unit 12, a cache information storage unit 13, and an address information storage unit 14.

  Here, it is assumed that the network interface unit 11 is an interface that can be connected to Ethernet (registered trademark). In FIG. 2, the network interface unit 11 is illustrated as connecting to the network N and the network devices 20-1 and 20-2, but it is assumed that the network interface unit 11 is actually connected to different physical ports. Here, the network devices 20-1 and 20-2 will be described as being connected to ports of the same broadcast domain.

  The communication processing unit 12 performs processing of a packet exchanged by the network interface unit 11 (for example, processing of routing a received packet and transferring it to the next hop node). The communication processing unit 12 processes a packet using the address information registered in the cache information storage unit 13 and the address information storage unit 14. The communication processing unit 12 can also update the cache information storage unit 13 based on the contents of the packet to be exchanged.

  The address information storage unit 14 stores address information of its own device used in the communication processing unit 12.

  FIG. 4 is an explanatory diagram showing an example of contents stored in the address information storage unit 14 of the router 10 of this embodiment.

  In the address information storage unit 14, one address information (combination of MAC address and IP address) is registered for one interface (one broadcast and domain), but in FIG. 4, the network devices 20-1 and 20- Although only the address information of the interface connected to 2 is illustrated, the same setting may be performed for other interfaces.

  In FIG. 4, a combination of a MAC address R-MA and a link local address (local IP address) R-LA is registered in the router 10 as address information of an interface connected to the network devices 20-1 and 20-2. It shows about the state.

  The cache information storage unit 13 manages address information (information including a MAC address and an IP address) for each node with which the router 10 communicates.

  FIG. 5 is an explanatory diagram showing an example of contents stored in the cache information storage unit 13 of the router 10 of this embodiment.

  FIG. 5 shows address information registered in the cache information storage unit 13 when the network device 20-1 operates as an active system and the network device 20-2 operates as a standby system.

The contents of the address information storage unit 14 shown in FIG. 5, the MAC address NW1-MA network devices 20-1 indicates the state of being registered as a MAC address corresponding to the logical IP address NW-GA.

  Further, in the contents of the address information storage unit 14 shown in FIG. 5, NW1-MA is registered as the MAC address corresponding to the link local address NW1-LA of the network device 20-1, and the link local address NW2 of the network device 20-2 is registered. -NW2-MA is registered as a MAC address corresponding to LA.

  Next, the internal configuration of the network device 20 will be described with reference to FIG.

  Here, description will be made assuming that the network device 20-1 and the network device 20-2 have the same configuration.

As illustrated in FIG. 3, the network device 20 includes a network interface unit 21, a cache update control unit 22, a switching control unit 23, an address management unit 24, an address information storage unit 25, and a communication processing unit 26.

  The network interface unit 21 is an interface that can also be connected to the router 10. As the network interface unit 21, for example, various Ethernet ports can be applied.

  Here, the network interface unit 21 is configured to be directly connected to the router 10, but it may be connected via a transceiver (repeater), a layer 2 switch or the like instead of directly.

  The address management unit 24 manages IP addresses used in the network device 20 (communication processing unit 26 or the like). Specifically, the address management unit 24 manages validity / invalidity of each address stored in the address information storage unit 25. Therefore, the address management unit 24 performs management for validating or invalidating the logical IP address NW-GA.

  When the logical IP address NW-GA is valid in the address management unit 24, the network device 20 (communication processing unit 26 or the like) uses the logical IP address NW-GA as the IP address used for communication. The used packet can be transmitted and received. On the other hand, when the logical IP address NW-GA is invalid in the address management unit 24, the network device 20 (communication processing unit 26 or the like) uses the logical IP address NW-GA as the IP address used for communication. The use is prohibited, and only the local IP address (link local address) can be used.

  As described above, each address usable in the network device 20 is stored in the address information storage unit 25.

  FIG. 6 is an explanatory diagram illustrating an example of each address stored in the address information storage unit 25 of each of the network devices 20-1 and 20-2.

  FIG. 6A shows an example of the contents of the address management unit 24 of the network device 20-1. As shown in FIG. 6A, the address management unit 24 of the network device 20-1 includes a MAC address NW1-MA, a link local address NW1-LA, a logical IP address NW-GA, and a next hop address R-LA. Is set.

  FIG. 6B shows a content example of the address management unit 24 of the network device 20-2. As shown in FIG. 6B, the address management unit 24 of the network device 20-2 includes a MAC address NW2-MA, a link local address NW2-LA, a logical IP address NW-GA, and a next hop address R-LA. Is set.

  The switching control unit 23 has a function of controlling the state of the network device 20 to an active system or a standby system. The method by which the switching control unit 23 determines the operating state (active system or standby system) of the network device 20 is not limited, and systems similar to various redundant configurations can be applied. For example, the switching control unit 23 determines the state of the network device 20 based on the state of the other network device 20 configuring one redundant system, the content of a control message exchanged with the other network device 20, or the like. It may be determined.

  Further, when switching the own device from the standby system to the active system, the switching control unit 23 enables the address management unit 24 to validate the logical IP address and requests the cache update control unit 22 to update the cache information to the router 10. (Hereinafter referred to as “cache update request”). In addition, the switching control unit 23 controls the communication processing unit 12 and an application (not shown) to operate as an active system when the own apparatus is switched from the standby system to the active system.

  When switching from the active system to the standby system, the switching control unit 23 requests the address management unit 24 to invalidate (release) the logical address. Further, the switching control unit 23 controls the communication processing unit 12 and an application (not shown) to operate as a standby system when the own apparatus is switched from the active system to the standby system.

  The cache update control unit 22 notifies the router 10 of the address information (combination of the IP address and the MAC address) related to the network device 20, and the cache information of the router 10 (cache information stored in the cache information storage unit 13). A process of updating (hereinafter referred to as “cache information update process”) is performed. Specifically, the cache update control unit 22 performs cache information update processing by performing address resolution (transmitting a neighbor solicitation packet to the router 10) using an NDP request message.

  When there is a cache update request accompanying the system switching from the switching control unit 23 to the active system, the cache update control unit 22 acquires the logical IP address and the MAC address of its own device from the address management unit 24, and creates a new An NDP request message for notifying the router 10 of address information (combination of the logical IP address and the MAC address of the own device) is generated and transmitted via the network interface unit 21. Then, the cache update control unit 22 can confirm that the cache information update process has been successful by receiving the NDP response message from the router 10 via the network interface unit 21.

  At this time, the cache update control unit 22 may continuously transmit the NDP request message at regular or irregular intervals until the NDP response message is received.

(A-2) Operation | movement of embodiment Next, operation | movement of the communication system 1 of this embodiment which has the above structures is demonstrated.

  First, a single operation when system switching occurs in the network device 20 will be described with reference to the flowchart of FIG. In FIG. 7, network switching processing accompanying system switching in the network device 20 is mainly described, and description of higher-layer switching processing (for example, applications) is omitted.

  In the network device 20, when a system switching event occurs by the switching control unit 23, the switching control unit 23 first confirms the state after switching (S101). The network device 20 operates from step S102 described later when the state after switching is the active system, and operates from step S106 described later when the state after the switching is the standby system.

  When the state after switching is the active system in step S101 described above, the switching control unit 23 controls the address management unit 24 to perform control to validate the logical IP address NW-GA (S102).

  Next, the switching control unit 23 instructs the cache update control unit 22 to execute cache update processing. As a result, the cache update control unit 22 creates an NDP request message for performing cache update processing according to the state of the address management unit 24 (the state in which the logical IP address NW-GA is enabled) (S103). The data is transmitted from the interface unit 21 (S104).

  Specifically, the cache update control unit 22 generates an NDP request message in which the logical IP address NW-GA is set as the transmission source address and the request node multicast address R-MC of the router 10 is set as the destination.

  Based on the IPv6 specifications, the cache update control unit 22 can acquire the requested node multicast address R-MC of the router 10 based on the link local address R-LA of the router 10. Specifically, for example, by adding 24 bits after the link local address R-LA of the router 10 to FF02 :: 1: FF00: 0000 having a 104-bit prefix, the requested node multicast address R- of the router 10 is added. MC can be obtained.

  Thereafter, the network device 20 (cache update control unit 22) monitors the packet received by the network interface unit 21, and receives an NDP response message in response to the transmitted NDP request message (S105), the cache update processing and system switching processing Exit. As a result, the network device 20 (communication processing unit 26 or the like) operating as an active system can transmit and receive packets with the logical IP address NW-GA.

  On the other hand, if the state after switching is the standby system in step S101 described above, the network device 20 (switching control unit 23) invalidates the logical IP address NW-GA to the address management unit 24. Thus, the process accompanying the system switching is terminated. As a result, the network device 20 (communication processing unit 26 or the like) that operates as a standby system thereafter discards the packet addressed to the logical IP address NW-GA and discards the local IP address (link local address) of its own device. ) Is used to send and receive packets.

  Next, an operation when the router 10 receives an NDP request message from the network device 20 will be described with reference to FIG.

  When the router 10 (communication processing unit 12) receives the NDP request message addressed to itself (addressed to the requesting node multicast address R-MC), the cache information (record) relating to the IP address set in the NDP request message is cached. It is confirmed whether or not it is registered in the information storage unit 13 (S201). When the corresponding cache information is detected in step S201, the router 10 (communication processing unit 12) operates from step S202 described later. When the corresponding cache information cannot be detected, the router 10 (communication processing unit 12) operates from step S204 described later.

  If the corresponding cache information can be detected in step S201 described above, the router 10 (communication processing unit 12) determines the MAC address of the detected cache information and the MAC address set in the received NDP request message. Compare Then, the router 10 (communication processing unit 12) performs an update process to change the MAC address of the cache information to the MAC address set in the received NDP request message only when both MAC addresses are different. (S202, S203).

  On the other hand, when the corresponding cache information (record) cannot be detected in step S201 described above, the router 10 (communication processing unit 12) uses the combination of the IP address and the MAC address set in the received NDP request message. Update processing for additionally registering in the cache information storage unit 13 as new cache information (record) is performed (S204).

  Along with the processing in step S203 or step S204 described above, the router 10 (communication processing unit 12) generates an NDP response message (message addressed to the transmission source of the NDP request message) in response to the received NDP request message. (S205) and transmit (S206).

  Next, a specific operation example when the router 10 and the network devices 20-1 and 20-2 operate according to the above-described flowcharts will be described with reference to the sequence diagram of FIG.

  In FIG. 1, when the network device 20-1 is operating as the active system and the network device 20-2 is operating as the standby system, system switching occurs, the network device 20-1 switches to the standby system, and the network device 20- 2 shows the operation when 2 is switched to the active system. Therefore, in the initial state (state before step S301) in the sequence diagram of FIG. 1, the contents of the cache information storage unit 13 of the router 10 are the contents of FIG. In the contents of the address information storage unit 14 shown in FIG. 5 described above, the MAC address NW1-MA of the network device 20-1 is registered as the MAC address corresponding to the logical IP address NW-GA.

  Then, on the network device 20-1 side, switching to the standby system is performed, and the logical IP address NW-GA is invalidated by the processing in step S106, and the network device 20-1 is switched to a state of operating using only the link local address NW1-LA. Become. In FIG. 1, the operation on the network device 20-1 side is not shown.

  On the other hand, on the network device 20-2 side, in order to switch to the active system, the logical IP address NW-GA is activated and switched to the operating state in step S102 described above. At this time, on the network device 20-2 side, an NDP request message is generated and transmitted to the router 10 through the above-described steps S103 and S104.

  At this time, the IP field of the NDP request packet generated by the network device 20-2 (cache information storage unit 13) includes the logical IP address NW-GA as the source address and the requested node multicast address R-MC as the destination address. Is set. In the ICMP field of the NDP request packet, a link local address R-LA is set as a target address, and a MAC address NW2-MA is set as a link layer address.

  Then, in the router 10 (communication processing unit 12), the cache information related to the logical IP address NW-GA is updated based on the NDP request packet by the process in step S203 described above (S302). Specifically, the router 10 (communication processing unit 12) sets the MAC address corresponding to the logical IP address NW-GA in the cache information stored in the cache information storage unit 13 to the MAC address set in the received NDP request message. (MAC address NW2-MA set in the link layer address of the ICMP field). The contents of the updated cache information storage unit 13 at this time are the contents of FIG. In FIG. 9, the MAC address corresponding to the logical IP address NW-GA is the MAC address NW2-MA of the network device 20-2.

  Then, the router 10 (communication processing unit 12) generates an NDP response message (a message whose destination is the transmission source of the NDP request message) in response to the received NDP request message by the above-described processing of steps S205 and S206. The data is transmitted to the network device 20-2 (S303).

(A-3) Effects of Embodiment According to this embodiment, the following effects can be achieved.

  In the communication system 1, when system switching occurs in the network device 20, an NDP request message (message for performing address resolution according to the neighbor search protocol) is only transmitted to the router 10 (gateway router) that is the opposite device. Thus, the cache information of the router 10 can be quickly updated, and the network switching accompanying the system switching of the network device 20 can be performed quickly.

  Further, in the communication system 1, since it is not necessary for each device to support a dedicated protocol for configuring a redundant system such as VRRP, there is an effect of reducing the construction cost and the like of each device.

(C) Other Embodiments The present invention is not limited to the above-described embodiment, and may include modified embodiments as exemplified below.

(C-1) In the above embodiment, the configuration in which each device in the communication system 1 performs communication using an IPv6 address may be used, but communication may be performed using an IPv4 address. When each device in the communication system 1 performs communication using an IPv4 address, an NDP request message and an NDP response message are used as messages used for cache update processing between the router 10 and the network device 20, and an ARP request and an ARP reply are used. It is necessary to replace and apply.

(C-2) In the above embodiment, an example in which the network device 20 has one local IP address (link local address) has been described. However, a configuration having a plurality of IP addresses (link local addresses) may be used.

(C-3) In the above embodiment, each device in the communication system 1 assigns a link local address, but it may be replaced with a global address.

(C-4) In the above embodiment, an example in which the gateway of the present invention is applied to a router has been described. However, the gateway is applied to other gateways capable of routing processing at layer 3 or higher, such as layer 3 switches and firewalls. May be.

(C-5) When the network device 20 (cache update control unit 22) performs the cache update process in steps S103 to S105 in FIG. 7 described above, not only the cache information of the logical IP address NW-GA is updated. The NDP request message for updating the cache information related to the combination of the local IP address (link local address) of the network device 20 and the MAC address of the network device 20 may be generated and transmitted. This takes into account the case where the cache information of the local IP address of the network device 20 that has been operating as a standby system for a long time has been erased on the router 10 side (for example, the cache information that is not used for a certain period of time). Process.

  DESCRIPTION OF SYMBOLS 1 ... Communication system, 10 ... Router, 11 ... Network interface part, 12 ... Communication processing part, 13 ... Cache information storage part, 14 ... Address information storage part, 20, 20-1, 20-2 ... Network apparatus, 21 ... Network interface unit, 22 ... Cache update control unit, 23 ... Switching control unit, 24 ... Address management unit, 25 ... Address information storage unit, 26 ... Communication processing unit.

Claims (5)

In a communication device constituting one redundant system with one or more other communication devices,
An operational state management means for determining the operational state of the communication device as either the active system or the standby system;
When communicating with the gateway related to the redundant system and the operation state of the communication device is a standby system, the IP address used for communication by the communication device is set to a unique IP address unique to the communication device, and Communication processing means for setting an IP address used for communication by the communication device to a shared IP address shared by the redundant system when the operation state of the communication device is active;
When the operation state of the operation state management means is switched from the standby system to the active system, a message conforming to the neighbor search protocol and having the transmission source IP address set to the shared IP address is transmitted to the gateway. Cache information updating means for updating cache information related to the shared IP address managed by the gateway ,
The cache information update means uses an NDP request message or an ARP request message as a message according to the neighbor discovery protocol,
It further comprises response message receiving means for receiving a response message corresponding to the NDP request message or the ARP request message from the gateway after updating the cache information related to the shared IP address managed by the gateway. A communication device. The unique IP address is a link local address, the shared IP address is a global address, the message according to the neighbor search protocol is an NDP request message, and the response message receiving means is a response corresponding to the NDP request message. The communication device according to claim 1, wherein the communication device receives a message. In the gateway connected to the communication device constituting a redundant system configured using a plurality of communication devices,
Cache information storage means for storing cache information in which an IP address and a MAC address are associated with each other;
Communication processing means for communicating with the communication device based on the cache information stored in the cache information storage means;
A cache that updates the cache information stored in the cache information storage means based on the content of the message when an NDP request message or an ARP request message is received from the communication device as a message according to the neighbor discovery protocol. Information updating means;
And a response message transmission unit configured to transmit a response message corresponding to the NDP request message or the message of the ARP request after updating the cache information stored in the cache information storage unit .   A redundant system configured by using a plurality of communication devices, wherein the communication device according to claim 1 is applied as each of the communication devices. In a communication system comprising a redundant system configured using a plurality of communication devices and a gateway connected to each of the communication devices,
Applying the communication device according to claim 1 or 2 as each of the communication devices,
A communication system, wherein the gateway according to claim 3 is applied as the gateway.

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