JP2007166532A - Communication system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a communication system for confirming the existence altogether to the communication equipment of different protocols by transmitting an existence confirmation packet once. <P>SOLUTION: The communication system comprises the communications equipment 1 and 2 which perform communications respectively by IPv6 and IPv4, a gateway device 3 connected between a network 6 and the Internet 5, and a center device 4 for transmitting the existence confirmation packet for confirming whether the communications equipment 1 and 2 exist on the basis of IPv6. The gateway device 3 is provided with an address conversion table, for which an IPv6 address and an IPv4 address are made to correspond to the communications equipment 2, and an address conversion part for referring to the address conversion table, converting the address of the existence confirmation packet from IPv6 to IPv4, transferring it to the communications equipment 2, converting the address of a response packet returned by the communications equipment 2 from IPv4 to IPv6 and transferring it to the center device 4. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a communication system, and more particularly to a communication system that performs survival confirmation for two or more communication devices having different communication rules (protocols) in a network layer.

  In recent years, IPv6 (Internet Protocol Version 6) has been spreading as a new communication protocol for the network layer. On the other hand, IPv4 (Internet Protocol Version 4), which is a communication protocol before IPv6, is still widely used as a standard technology. For this reason, for the time being, it is expected to operate in a situation where an IPv6 system and an IPv4 system, or an IPv6 compatible communication device and an IPv4 compatible communication device coexist.

Conventionally, a method of performing multicast communication between IPv6 and IPv4 by connecting an IPv6 network and an IPv4 network with a conversion device, and the conversion device mutually converts a packet address between IPv6 and IPv4 is known. (For example, refer to Patent Document 1).
Japanese Patent Laid-Open No. 2001-345845 (refer to FIG. 1 in particular) JP 2004-320260 A

  In order to check the survival status of a communication device connected to a communication network in which a plurality of communication rules are mixed, it is necessary to check the method according to each communication rule. Therefore, it takes extra time compared to the case where the communication protocol is unified. In other words, it is possible to collectively check the existence by multicast for the communication devices unified in one communication protocol. However, the survival status of a specific communication device connected to a communication network in which different communication protocols are mixed cannot be confirmed with a single survival confirmation packet by multicast.

In order to solve the above problems, the present invention is characterized in that a first communication device that communicates according to a first communication protocol in a network layer, and a second communication device that is connected to the first communication device via a first communication network. A second communication device that communicates according to a second communication protocol different from the first communication protocol in the network layer, and a second communication based on the first communication network and the first communication protocol. A gateway device connected between the network and a gateway device that mutually converts data based on the first communication protocol and data based on the second communication protocol, and connected to the second communication network Based on the first communication protocol, a first survival confirmation packet for confirming whether the first and second communication devices are alive at once is a center device. A communication system comprising a center apparatus for transmitting,
The gateway device stores, for the second communication device, an address conversion table in which an address based on the first communication protocol and an address based on the second communication protocol are stored in association with each other, and the first survival to the first communication device. A packet transfer unit that transfers a confirmation packet and transfers a first response packet returned by the first communication device to the center device, and refers to the address conversion table to set the address of the first survival confirmation packet to the first communication The protocol is converted to the second communication protocol, transferred to the second communication device, and the address of the first response packet returned by the second communication device is converted from the second communication protocol to the first communication protocol. And an address conversion unit for transfer to the center device.

  ADVANTAGE OF THE INVENTION According to this invention, the communication system which performs a survival confirmation collectively with respect to the communication apparatus from which a communication protocol differs can be provided by transmission of one survival confirmation packet.

  Embodiments of the present invention will be described below with reference to the drawings. In the description of the drawings, the same or similar parts are denoted by the same or similar reference numerals.

(First embodiment)
[Constitution]
As shown in FIG. 1, the communication system according to the first embodiment of the present invention includes a first communication device 1 (IPv6 communication device 1) that communicates according to a first communication protocol (IPv6) in a network layer, The second communication device 2 (IPv4 communication device 2) connected to the IPv6 communication device 1 via the first communication network (local area network), the IPv6 communication device 1 and the IPv4 communication device 2, and the local area network. Connected to each other, a gateway device 3 connected between the switch device 7 and the second communication network 5 (Internet 5) based on IPv6, and a center device 4 connected to the Internet 5. .

  In addition, although the local area network was mentioned as an example of the 1st communication network and the Internet 5 was mentioned as an example of the 2nd communication network 5, this invention is not limited to this.

  The IPv4 communication device 2 communicates according to a second communication protocol (IPv4) different from IPv6 in the network layer. The IPv6 communication device 1, the IPv4 communication device 2, and the switch device 7 constitute an equipment network 6. Examples of the equipment network 6 include a condominium device control system and a home network system. In the equipment network 6, two different communication protocols (IPv6 and IPv4) are mixed. A gateway device 3 is connected between the equipment network 6 and the Internet 5.

  Although not shown, a plurality of IPv6 communication devices 1 and a plurality of IPv4 communication devices 2 are connected to the switch device 7.

  The center device 4 has a role of managing the state of each device in the equipment network 6 and is a first for checking whether the IPv6 communication device 1 and the IPv4 communication device 2 are alive. The existence confirmation packet (IPv6 multicast packet) is transmitted. The center device 4 may be called a center server.

  The gateway device 3 mutually converts data based on IPv6 and data based on IPv4. Specifically, the gateway device 3 transfers the IPv6 communication device 1 as it is in the IPv6 format, that is, without changing the survival confirmation packet. On the other hand, the existence confirmation packet is transmitted to the IPv4 communication device 2 after being converted into the IPv4 format, and the response from the IPv4 communication device 2 is returned to the IPv6 format and transferred to the center device 4. Details will be described later with reference to FIG.

  When the center device 4 performs the survival check, the IPv6 communication device 1 is checked for the existence of all the IPv6 communication devices 1 that are connected together by sending only one multicast packet based on IPv6. I can do it. However, since the IPv4 communication device 2 cannot recognize the multicast packet based on IPv6 transmitted from the center device 4, the IPv4 communication device 2 cannot respond as it is. Therefore, when the survival check is performed from the center device 4, the gateway device 3 actually performs the survival check for the IPv4 communication device 2.

  With reference to FIG. 2, the detailed structure of the gateway apparatus 3 of FIG. 1 is demonstrated. The gateway device 3 transfers the first survival confirmation packet to the IPv6 communication device 1 and the address translation table 31 in which the IPv6 address and the IPv4 address are stored in association with each other for the IPv4 communication device 2. The packet transfer unit 32 that transfers the first response packet transmitted by 1 to the center device 4 and the format of the first survival confirmation packet from the IPv6 to the IPv4 by referring to the address conversion table 31 and the IPv4 communication device 2 The address conversion unit 33 converts the address of the first response packet transmitted by the IPv4 communication device 2 from IPv4 to IPv6 and forwards it to the center apparatus 4, and the packets from the connected networks 5 and 6. A packet receiver that performs reception processing and a packet that performs packet transmission processing And a door transmission unit.

  The gateway device 3 virtually sets an IPv6 address for the IPv4 communication device 2, and holds an address conversion table 31 in which the IPv6 address is associated with the IPv4 address actually provided in the IPv4 communication device 2. At the same time, the center device 4 also holds a similar address conversion table.

[Operation]
A communication procedure in the communication system of FIG. 1 will be described with reference to FIG.

  (A) First, in step S1, the center device 4 transmits a first survival confirmation packet by IPv6 multicast to the gateway device 3 via the Internet 5, and the gateway device 3 receives the packet.

  (B) In step S2, the packet transfer unit 32 in FIG. 2 transfers the first survival confirmation packet to the facility network 6 as it is. The IPv6 communication device 1 can recognize the first existence confirmation packet based on IPv6, but the IPv4 communication device 2 cannot recognize it. This is because the first survival confirmation packet based on IPv6 and the IPv4 communication device 2 have different communication rules. In step S3, the IPv6 communication device 1 that has received the first survival confirmation packet returns a first response packet including the survival information to the packet transfer unit 32.

  (C) On the other hand, simultaneously with the steps S2 to S3, in the step S4, the gateway device 3 converts the first existence confirmation packet based on IPv6 into the first existence confirmation packet based on IPv4. Specifically, the address conversion unit 33 in FIG. 2 refers to the address conversion table 31 to convert the address of the first survival confirmation packet from IPv6 to IPv4 and forwards it to the IPv4 communication device 2. Since the IPv4 communication device 2 matches the communication standard, the IPv4 communication device 2 can receive the first survival confirmation packet based on IPv4. In step S <b> 5, the IPv4 communication device 2 that has received the first survival confirmation packet returns a first response packet including the survival information to the address translation unit 33.

  More specifically, the address conversion unit 33 searches the IPv4 address of the IPv4 communication device 2 with reference to the address conversion table 31, sets the IPv4 address as the destination address, and simultaneously sets the IPv4 address as the transmission source address of the gateway device 3. An address is set, and a first survival confirmation packet based on IPv4 is transmitted to the IPv4 communication device 2. Then, the IPv4 communication device 2 returns a first response packet based on IPv4 to the first survival confirmation packet to the gateway device 3.

  (D) In step S6, the gateway device 3 converts the first response packet based on IPv4 into a first response packet based on IPv6. Specifically, the address conversion unit 33 converts the address of the first response packet received from the IPv4 communication device 2 from IPv4 to IPv6 and transfers it to the center device 4. More specifically, referring to the address conversion table 31, a virtual IPv6 address (global address) is generated from the IPv4 address, an IPv6 packet having this as a transmission source is generated, and this is transmitted from the IPv4 communication device 2. As a response to the center device 4.

  The center device 4 that has received the first response packet based on IPv6 can refer to the address translation table and know that the received first response packet is actually a response from the IPv4 communication device 2 based on IPv4. I can do it. At the same time, it can be known that the IPv4 communication device 2 is operating.

  Next, the contents of the survival confirmation packet and the response packet transmitted and received in the communication system of FIG. 1 will be described with reference to FIG.

  The first existence confirmation packet 41 by IPv6 multicast transmitted from the center apparatus 4 to the gateway apparatus 3 includes existence confirmation data, an IPv6 address of the center apparatus 4 as a transmission source address, and a multicast address A (IPv6) as a transmission destination address. have. The gateway device 3 receives this and transmits the first existence confirmation packet 42 to the IPv6 communication device 1 as it is. In response to this, the first response packet 43 from the IPv6 communication device 1 includes response data including its own survival information, the IPv6 address of the IPv6 communication device 1 as a transmission source address, and the IPv6 address of the center device 4 as a transmission destination address. have. The gateway device 3 receives this and transmits the first response packet 44 to the center device 4 as it is.

  On the other hand, the gateway device 3 rewrites the source address in the first survival confirmation packet 41 to the IPv4 address of the gateway device (GW) 3 and rewrites the destination address to the IPv4 address of the IPv4 communication device 2. Is transferred to the IPv4 communication device 2. Therefore, the first survival confirmation packet 45 based on IPv4 that the gateway apparatus 3 transmits to the IPv4 communication device 2 includes the survival confirmation data, the IPv4 address of the gateway apparatus (GW) 3 as a transmission source address, and the IPv4 as a transmission destination address. And an IPv4 address of the communication device 2. In response to this, the first response packet 46 from the IPv4 communication device 2 includes response data including its own survival information, the IPv4 address of the IPv4 communication device 2 as a transmission source address, and the IPv4 address of the gateway device 3 as a transmission destination address. have. The gateway device 3 receives this, rewrites the source address to the virtual IPv6 address of the IPv4 communication device 2, rewrites the destination address to the IPv6 address of the center device 4, and sends the first response packet 47 to the center device 4. Forward. Therefore, the first response packet 47 based on IPv6 transmitted from the gateway device 3 to the center device 4 includes the response data, the virtual IPv6 address of the IPv4 communication device 2 as a transmission source address, and the IPv6 of the center device 4 as a transmission destination address. Address.

[effect]
As described above, the center device 4 has the first communication device 1 and the second communication device 1 and 2 having different communication protocols (protocols) located in the network layer (third layer of the OSI basic reference model). A survival confirmation packet is transmitted based on the first communication protocol (IPv6). When the gateway device 3 receives the first survival confirmation packet, the packet transfer unit 32 transfers the first survival confirmation packet to the first communication device 1 as it is, and the first communication device 1 transmits the first The response packet is transferred to the center device 4 as it is. On the other hand, the address conversion unit 33 refers to the address conversion table 31 and converts the address of the first survival confirmation packet from the first communication protocol (IPv6) to the second communication protocol (IPv4) to perform the second communication. The address of the first response packet transmitted to the device 2 and transmitted by the second communication device 2 is converted from the second communication protocol (IPv4) to the first communication protocol (IPv6) and transferred to the center device 4. .

  As a result, a response packet can be received from the specific communication device 1 or 2 by transmitting the survival confirmation packet once to a system in which a plurality of communication devices 1 and 2 having different communication rules of the network layer are mixed. That is, it is possible to collectively check the existence of all communication devices in a system in which IPv6 compatible devices and IPv4 compatible devices coexist.

  When the equipment network 6 is a condominium device control system, the survival information can be managed by grouping floors or condominiums.

  An example of such a survival confirmation packet is a packet internet grouper (PING). Other than this, an original protocol to which some information is added may be used.

(Second Embodiment)
In the communication system according to the first embodiment, every time the first existence confirmation packet arrives at the gateway apparatus 3 (S1), the gateway apparatus 3 converts the first existence confirmation packet to the IPv4 communication device 2. The packet was forwarded (S4), and the first response packet was received from the IPv4 communication device 2 (S5).

  However, since the steps S4 and S5 are performed every time the S1 step (the first survival confirmation packet arrives) that occurs periodically, it is difficult to reduce the processing time.

  Therefore, in the second embodiment, the gateway device 3 sends a survival confirmation packet to the IPv4 communication device 2 in advance (the second survival confirmation packet) independently of the first survival confirmation packet from the center device 4. Confirmation packet) is transmitted, a response packet (second response packet) is received, and the survival status of the IPv4 communication device 2 is registered.

[Constitution]
The overall configuration of the communication system according to the second embodiment of the present invention is the same as that shown in FIG.

  With reference to FIG. 5, a detailed configuration of the gateway device 3 according to the second embodiment will be described. The gateway device 3 transfers the first survival confirmation packet to the IPv6 communication device 1 and the address translation table 31 in which the IPv6 address and the IPv4 address are stored in association with each other for the IPv4 communication device 2. 1 transmits the second response packet to the center device 4 and the second survival confirmation packet at regular intervals to the IPv4 communication device 2, and transmits the first response packet transmitted by 1 to the center device 4. When the survival confirmation communication unit 34 that receives the second response packet from the IPv4 communication device 2 and the first survival confirmation packet from the center device 4, the address of the second response packet is referred to by referring to the address conversion table 31. Is converted from IPv4 to IPv6 and the second response packet is transmitted to the center apparatus 4 Comprising at least a transmission unit 35.

  The survival confirmation communication unit 34 periodically transmits a second survival confirmation packet based on IPv4 to the IPv4 communication device 2 independently of the first survival confirmation packet from the center device 4 (S4). The IPv4 communication device 2 that has received the second survival confirmation packet transmits a second response packet to this (S5), and the survival confirmation communication unit 34 receives this and receives the address based on the second response packet. The survival information about the IPv4 communication device 2 registered in the conversion table 31 is registered.

  When the survival information transmission unit 35 receives the first survival confirmation packet from the center device 4 (S1), the survival information transmission unit 35 receives the second information based on IPv6 based on the survival information of the IPv4 communication device 2 registered in the survival confirmation communication unit 34. The response packet is generated and transmitted to the center device 4. Thereby, the processing time of the gateway apparatus 3 can be shortened.

  Although the existence confirmation communication unit 34 has been described to periodically transmit the second existence confirmation packet, the present invention is not limited to this. Instead of transmitting regularly at regular time intervals, it may be transmitted only when the load on the gateway device 3 is low. Alternatively, if the range of time allowed for the first survival confirmation packet from the center device 4 is specified, and the survival information of the IPv4 communication device 2 collected by the gateway device 3 is older than this time range, The gateway device 3 may collect the survival information of the IPv4 communication device 2 again. Thereby, it is possible to know the survival status of the IPv4 communication device 2 in a form almost in real time.

  The address conversion table 31 and the packet transfer unit 32 are the same as those in FIG.

[effect]
As described above, the center device 4 is the first survivor for the IPv6 communication device 1 and the IPv4 communication device 2 having different communication protocols (protocols) located in the network layer (third layer of the OSI basic reference model). A confirmation packet is transmitted based on IPv6. When the gateway device 3 receives the first existence confirmation packet, the packet transfer unit 32 transfers the first existence confirmation packet to the IPv6 communication device 1 as it is, and the first response packet transmitted by the IPv6 communication device 1 is centered. The data is transferred to the device 4 as it is. On the other hand, the survival confirmation communication unit 34 transmits a second survival confirmation packet to the IPv4 communication device 2 at regular intervals, and receives a second response packet for the second survival confirmation packet from the IPv4 communication device 2. . Then, when receiving the first survival confirmation packet, the survival information transmitting unit 35 refers to the address conversion table 31 to convert the address of the second response packet from IPv4 to IPv6, and sends the second response packet to the center device 4. Send the response packet.

  As a result, when the gateway device 3 receives the first survival confirmation packet, all communication is performed by transmitting the survival confirmation packet once to a system in which a plurality of communication devices having different network layer communication protocols are mixed. A response packet can be received from the device. That is, it is possible to collectively check the existence of all communication devices in the system.

  Further, when the first survival confirmation packet is received from the center device 4, a second response packet based on IPv6 is generated based on the survival information of the IPv4 communication device 2 registered in the survival confirmation communication unit 34. Is transmitted to the center device 4. As a result, the load on the gateway device 3 can be reduced and at the same time the processing time can be shortened.

(Other embodiments)
As described above, the present invention has been described by two embodiments. However, it should not be understood that the description and the drawings, which form a part of this disclosure, limit the present invention. From this disclosure, various alternative embodiments, examples and operational techniques will be apparent to those skilled in the art.

  When a communication device is newly added in the equipment network 6, the center device 4 can detect this. When the IPv6 communication device 1b is newly added, if the same multicast address as that of the existing IPv6 communication device 1 is assigned, a response packet can be obtained from the IPv6 communication device 1b. Therefore, the center device 4 can detect the addition of the IPv6 communication device 1b via the gateway device 3.

  However, the address conversion table 31 cannot correspond to the new IPv4 communication device 2b unless the address correspondence relationship is previously held for the new IPv4 communication device 2b. Therefore, when an IPv4 communication device 2b is newly added in the facility network 6, the addition of the device cannot be detected in the same manner as IPv6.

  Therefore, as shown in FIG. 5, the gateway device 3 confirms the source address of the packet when communication starting from the IPv4 communication device 2b side is performed, and this source address is connected to the existing connection. It is desirable to further include a survival information integrated communication unit 36 that determines that a new IPv4 communication device is connected if it is something other than the IPv4 communication device. When it is determined that a new IPv4 communication device is connected, the survival information integrated communication unit 36 updates the address conversion table 31 and notifies the center device 4 of information on the new IPv4 communication device. Thereby, when the IPv4 communication apparatus 2b is newly added in the equipment type | system | group network 6, the center apparatus 4 can detect this.

  Specifically, when a new IPv4 communication device 2b is connected in the system, since the IPv4 communication device 2b is manually set with an IP address in advance, if the IPv4 communication device 2b generates communication even once, Information on the IP address and MAC (Media Access Control) address remains in the connected L3 switch (switch device). The gateway device 3 can obtain IP and MAC address information from an L3 switch using SNMP (Simple Network Management Protocol). Thereby, it is possible to know whether or not a new IPv4 communication device 2b is connected. When a new IPv4 communication device 2 b is connected, the correspondence relationship of the IPv4 communication device 2 b is added to the address conversion table 31. The above SNMP is an example of a means for obtaining IP and MAC address information, and the present invention is not limited to this, and the IP and MAC address information may be read by other means. .

  In addition, the survival information integrated communication unit 36 determines which IPv6 communication device 1 and IPv4 communication device 2 are alive from the first response packet or the second response packet received from the IPv6 communication device 1 and the IPv4 communication device 2. Is generated and transmitted to the center apparatus 4.

  5 relates to the second embodiment, but as shown in FIG. 6, the gateway apparatus 3 according to the first embodiment may further include a survival information integrated communication unit 36. desirable.

  It is also possible to perform the following processing. That is, for the IPv4 communication device 2 connected to the local area network, a range of addresses to be assigned in advance is determined. The gateway device 3 continues to periodically transmit a survival confirmation packet to all addresses in the range, and stores the address for which the response has been received in the survival information integrated communication unit 36. At the same time, when a new address is detected, the result is also reflected in the address conversion table 31.

  When the first survival confirmation packet is received from the center device 4, a response is directly returned to the center device 4 with reference to the information held by the survival information integrated communication unit 36. As a result, it is possible to save the trouble of performing conversion / transfer and receiving / converting / forwarding a response after receiving the first survival confirmation packet, and reflect the latest connection status in the address conversion table 31.

  Thus, it should be understood that the present invention includes various embodiments and the like not described herein. Therefore, the present invention is limited only by the invention specifying matters according to the scope of claims reasonable from this disclosure.

It is a block diagram which shows the structure of the communication system concerning the 1st Embodiment of this invention. It is a block diagram which shows the structure of the gateway apparatus of FIG. It is a block diagram which shows the communication procedure in the communication system of FIG. It is a block diagram which shows the content of the survival confirmation packet and response packet which are transmitted / received in the communication system of FIG. It is a block diagram which shows the structure of the gateway apparatus concerning 2nd Embodiment. It is a block diagram which shows the structure of the gateway apparatus concerning the modification of 1st Embodiment.

Explanation of symbols

1 ... IPv6 communication device (first communication device)
2 ... IPv4 communication device (second communication device)
3 ... Gateway device 4 ... Center device 5 ... Internet (second communication network)
DESCRIPTION OF SYMBOLS 6 ... Equipment network 7 ... Switch apparatus 31 ... Address conversion table 32 ... Packet transfer part 33 ... Address conversion part 34 ... Survival confirmation communication part 35 ... Survival information transmission part 36 ... Survival information integrated communication part 41, 42 ... 1st Survival confirmation packet (IPv6)
45: First survival confirmation packet (IPv4)
43, 44, 47 ... first response packet (IPv6)
46: First response packet (IPv4)

Claims (3)

A first communication device that communicates according to a first communication protocol in the network layer;
A second communication device connected to the first communication device via a first communication network and communicating according to a second communication protocol different from the first communication protocol in the network layer;
The data based on the first communication protocol and the data based on the second communication protocol connected between the first communication network and the second communication network based on the first communication protocol are mutually exchanged. A gateway device that converts to
A first existence confirmation packet for collectively confirming whether or not the first and second communication apparatuses connected to the second communication network are alive is set in the first communication protocol. And a center device for transmitting based on,
The gateway device is
An address conversion table in which an address based on the first communication protocol and an address based on the second communication protocol are stored in association with each other for the second communication device;
A packet transfer unit for transferring the first survival confirmation packet to the first communication device and transferring a first response packet returned by the first communication device to the center device;
The address of the first survival confirmation packet is converted from the first communication protocol to the second communication protocol by referring to the address conversion table and transferred to the second communication device, and the second communication A communication system comprising: an address conversion unit that converts an address of a first response packet returned by the device from the second communication protocol to the first communication protocol and transfers the converted address to the center device. A first communication device that communicates according to a first communication protocol in the network layer;
A second communication device connected to the first communication device via a first communication network and communicating according to a second communication protocol different from the first communication protocol in the network layer;
The data based on the first communication protocol and the data based on the second communication protocol connected between the first communication network and the second communication network based on the first communication protocol are mutually exchanged. A gateway device that converts to
A first existence confirmation packet for collectively confirming whether or not the first and second communication apparatuses connected to the second communication network are alive is set in the first communication protocol. And a center device for transmitting based on,
The gateway device is
An address conversion table in which an address based on the first communication protocol and an address based on the second communication protocol are stored in association with each other for the second communication device;
A packet transfer unit that transfers the first survival confirmation packet to the first communication device and transfers a first response packet transmitted by the first communication device to the center device;
A survival confirmation communication unit that transmits a second survival confirmation packet to the second communication device at regular intervals and receives a second response packet for the second survival confirmation packet from the second communication device; ,
When the first survival confirmation packet is received, the center device converts the address of the second response packet from the second communication protocol to the first communication protocol with reference to the address conversion table. A survival information transmitting unit that transmits the second response packet to the communication system.   The gateway device, from the first response packet or the second response packet received from the first and second communication devices, a survival information packet indicating which of the first and second communication devices are alive The communication system according to claim 1, further comprising a survival information integrated communication unit that creates and transmits the information to the center device.

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