Buffer control device, communication node and switching device

Abstract

Buffer control device (19, 21, 23, 25) comprising: an input unit (25) that accepts input of a message containing an ID and data; a buffer unit (33) in which multiple messages are stored; a Same ID Determination Unit (31) that determines whether the same ID as the ID contained in the message accepted by the input unit is contained in the messages stored in the buffer unit; an overwrite unit (29) which overwrites at least data in one of the messages containing the same ID as the ID contained in the message accepted by the input unit with the data contained in the message accepted by the input unit when the same ID is present; a storage unit (29) that stores the message received from the input unit in the buffer unit if the same ID is not present; and an output unit (35) that extracts from the buffer unit the oldest message from the messages stored by the storage unit and outputs the oldest message that was extracted.

Description

TECHNICAL FIELD

[0001] The present invention relates to a buffer control device, a communication node and a switching device. STATE OF THE ART

[0002] A communication device includes a buffer for temporarily storing a message to be sent or a received message. A FIFO buffer can be used as the buffer of the communication device. According to another option, an individual buffer can be provided for each ID contained in a message (see JP 2000 - 244 548 A).

[0003] WO 2013 / 144 962 A1 discloses a security system for protecting an electronic vehicle system by selectively intervening in the communication path to prevent malicious messages from reaching ECUs, particularly safety-critical ECUs. The security system includes a filter that prevents illegal messages sent by a system or device communicating via a vehicle communication bus from reaching their destination. The filter can, at its own discretion and according to preconfigured rules, send messages unchanged, block messages, modify the content of the messages, request authentication, or limit the delivery rate of such messages by buffering the messages and sending them only at preconfigured intervals.

[0004] WO 2015 / 048 058 A1 discloses a real-time frame authentication protocol for vehicle networks. A frame identifier is anonymized for unauthorized entities, but remains identifiable for authorized entities. Anonymous identifiers are generated per frame and embedded in each data frame transmitted by a sending ECU. Receiving ECUs use the anonymous identifiers to filter incoming data frames before verifying data integrity. Invalid data frames are filtered without performing additional runtime calculations. SUMMARY OF THE INVENTION

[0005] A large number of messages containing the same ID may be transmitted due to a communication device failure, a DoS attack, etc. The present inventors have found that the following problems arise in such a case. When a FIFO buffer is used, a large number of messages containing the same ID are stored in the buffer, and a message containing a different ID is lost from the buffer. In the method of providing an individual buffer for each ID, a large storage area is required for the buffers provided according to the respective IDs.

[0006] In view of the above difficulties, it is an object of the present invention to provide a buffer control device, a communication node and a switching device.

[0007] According to one aspect of the present invention, a buffer control device includes: an input unit that accepts an input of a message containing an ID and data; a buffer unit in which a plurality of messages are stored; a same-ID determination unit that determines whether the same ID as the ID contained in the message accepted by the input unit is present in the messages stored in the buffer unit; an overwrite unit that overwrites at least data in one of the messages containing the same ID as the ID contained in the message accepted by the input unit with data contained in the message accepted by the input unit if the same ID is present; a storage unit that re-stores the message accepted by the input unit in the buffer unit if the same ID is not present;and an output unit that extracts from the buffer unit an oldest message from the messages stored by the storage unit and outputs the oldest message extracted;

[0008] According to the buffer control device described above, when a message having the same ID as the ID included in the message accepted by the input unit is present in the messages stored in the buffer unit, at least data of the message stored in the buffer unit is overwritten with the data included in the message having the same ID and accepted by the input unit.

[0009] With the buffer control device having the above-described configuration, even when a large number of input messages containing the same ID are input to the input unit, the large number of messages containing the same ID are not individually stored in the buffer unit. Thus, the buffer control device is capable of limiting the loss of a stored message containing a different ID from the large number of input messages from the buffer unit.

[0010] With the buffer control device having the above-described configuration, the buffer control device can update data included in the message stored in the buffer unit with the latest data. Furthermore, with the buffer control device having the above-described configuration, there is no need to provide a buffer unit individually for each ID. Thus, a memory area used as a buffer unit can be reduced.

[0011] According to another aspect of the present invention, a buffer control device includes: an input unit that accepts an input of a message containing an ID and data; a buffer unit in which a plurality of messages are stored; a same-ID determination unit that determines whether the same ID as the ID included in the message accepted by the input unit is present in the messages stored in the buffer unit; an overwritable ID determination unit that determines whether the ID included in the message accepted by the input unit is an ID provisionally set to be overwritable;an overwriting unit that overwrites at least data in one of the messages containing the same ID as the ID contained in the message accepted by the input unit with the data contained in the message accepted by the input unit when the same ID exists and the ID contained in the message accepted by the input unit is determined to be a rewritable ID; a storage unit that re-stores the message accepted by the input unit in the buffer unit when the same ID does not exist or when the ID contained in the message accepted by the input unit is not a rewritable ID; and an output unit that extracts, from the buffer unit, an oldest message from the messages stored by the storage unit and outputs the oldest message that was extracted.

[0012] According to the other buffer control device described above, when a message having the same ID as the ID included in the message accepted by the input unit is included in the messages stored in the buffer unit, and the ID included in the message is a rewritable ID, at least data of the message stored in the buffer unit is overwritten with the data included in the message having the same ID and accepted by the input unit.

[0013] With the buffer control device having the different configuration described above, even if a large number of input messages containing the same ID are input to the input unit and the input IDs are rewritable IDs, the large number of messages containing the same ID are not individually stored in the buffer unit. Thus, the buffer control device is capable of limiting the loss of a stored message containing a different ID from the large number of input messages from the buffer unit.

[0014] With the buffer control device having the above-described different configuration, the buffer control device can update data included in the message stored in the buffer unit to the latest data. Furthermore, with the buffer control device having the above-described different configuration, there is no need to individually provide a buffer unit for each ID. Thus, a memory area used as a buffer unit can be reduced.

[0015] With the buffer control device having the above-described different configuration, when a message having the same ID as the ID included in the message accepted by the input unit is present in the messages stored in the buffer unit, but the ID included in the message is not a rewriteable ID, data of the message stored in the buffer unit is not overwritten with the data included in the message having the same ID and accepted by the input unit. In this case, the message accepted by the input unit is stored in the buffer unit. Thus, when the accepted message includes a non-rewriteable ID, the buffer control device can store a plurality of messages having the same ID in the buffer unit. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a diagram showing a configuration of a communication system; Fig. 2 is a block diagram showing a configuration of a reception buffer control device; Fig. 3 is a flowchart showing processing performed by the reception buffer control device; Fig. 4A is a diagram showing a buffer unit and an input message before data is overwritten; Fig. Figure 4B is a diagram showing the buffer unit after the data has been overwritten; Fig. 5A is a diagram showing the buffer unit before the input message is stored; Fig. 5B is a diagram showing the buffer unit after the input message has been stored; Fig. 6 is a block diagram showing a configuration of a reception buffer control device; and Fig. 7 is a flowchart showing processing performed by the reception buffer control device. DESCRIPTION OF REFERENCE SYMBOLS 1 communication system 3, 5 Communication group 7 Switching device 9 Multiplex communication line 11 ECU 13 Application 15 Switching control unit 17 Main characteristic curve field 19 Receive buffer control device 21 Transmission buffer control device 23 Receive buffer control device 25 Transmission buffer control device 27 Input unit 29 Storage control unit 31 search unit 33 Buffer unit 35 Output unit 37 Overwrite permission information table EMBODIMENTS FOR CARRYING OUT THE INVENTION

[0016] Embodiments of the present invention will now be described with reference to the drawings. (First Embodiment) 1. Configuration of Communication System 1

[0017] The following describes the configuration of communication system 1 according to Fig. 1. The communication system 1 is an on-vehicle communication system installed in a vehicle. The communication system 1 is also a multiplex communication system. The communication system 1 includes a plurality of communication groups 3 and 5 and a switching device 7. Each of the communication groups 3 and 5 includes a plurality of ECUs 11 connected to a multiplex communication line 9. Each ECU 11 corresponds to a communication node.

[0018] The communication system 1 sends and receives a message according to a predetermined protocol. The message contains at least an ID and data. The ID indicates a type of data contained in the message.

[0019] The ECU 11 includes an application 13 that has a message generation function. The ECU 11 sends a message generated by its own application 13 to another ECU 11. The ECU 11 also receives a message sent from another ECU 11 and forwards the received message to its own application 13. The application 13 performs predetermined processing using the forwarded message.

[0020] The relay device 7 is connected to both communication groups 3 and 5. In the case where a message sending ECU 11 and a receiving ECU 11 belong to different communication groups, the relay device 7 relays the message. The relay device 7 includes a relay control unit 15 and a routing map 17. The relay control unit 15 performs processing related to relaying a message. IDs included in messages are stored in the routing map 17 in correspondence with destinations of the respective messages.

[0021] Upon receiving a message from a communication group, the switching control unit 15 reads an ID included in the message and determines a receiver ECU 11 that is the destination of the message by referring to the routing map 17. Then, the switching control unit 15 sends the message to a communication group to which the receiver ECU 11 belongs.

[0022] The ECU 11 also includes a reception buffer control device 19 and a transmission buffer control device 21. The reception buffer control device 19 temporarily stores a message received from another ECU 11, and the transmission buffer control device 21 temporarily stores a message to be transmitted to another ECU 11.

[0023] The switching device 7 also includes a receive buffer control device 23 and a transmit buffer control device 25 for each communication group. The receive buffer control device 23 temporarily stores a message received from the connected communication group and later outputs the stored message to the switching control unit 15. The transmit buffer control device 25 temporarily stores a message input from the switching control unit 15 and later outputs the stored message to the connected communication group. 2. Configuration of the receive buffer control device 19

[0024] The following describes the configuration of the reception buffer control device 19 according to Fig. 2. The transmit buffer control device 21, the receive buffer control device 23, and the transmit buffer control device 25 are configured in the same manner as the receive buffer control device 19.

[0025] The reception buffer control device 19 includes a communication IC that interfaces with the multiplexed communication line 9 and a microcomputer for control purposes. The reception buffer control device 19 has functions associated with an input unit 27, a memory control unit 29, an ID search unit 31, a buffer unit 33, and an output unit 35. The functions of the respective units are described below.

[0026] The functions of the respective units are realized using an internal CPU of the microcomputer by executing a program temporarily stored in an internal ROM of the microcomputer. The buffer unit 33 is arranged in an internal RAM or an internal register of the microcomputer. An internal non-volatile memory of the microcomputer other than the ROM, or a non-volatile memory or RAM arranged outside the microcomputer in the ECU 11, can be used instead of the internal ROM or RAM.

[0027] The ID search unit 31 corresponds to a same ID determination unit, and the storage control unit 29 corresponds to a rewriting unit and a storage unit. 3. Processing performed by the reception buffer control device 19

[0028] In the following, the processing performed by the reception buffer control device 19 is described in accordance with Fig. 3, Fig. 4A, Fig. 4B, Fig. 5A and Fig. 5B. The following describes processing executed by the reception buffer control device 19 included in an ECU 11 (hereinafter referred to as the dedicated ECU 11). Any ECU 11 other than the dedicated ECU 11 will also be referred to as the other ECU 11 in the following description.

[0029] In S1 of the Fig. 3, the input unit 27 accepts a message input. Hereinafter, the message input to the input unit 27 is referred to as an input message. The input message is sent from another ECU 11 to the own ECU 11, which serves as a receiver.

[0030] In S2, the input unit 27 transmits an ID included in the input message (hereinafter referred to as input message ID) to the ID search unit 31. The input unit 27 also transmits the input message ID and data included in the input message (hereinafter referred to as input message data) to the storage control unit 29.

[0031] In S3, the ID search unit 31 searches for the same ID as the input message ID transmitted in S2 in messages stored in the buffer unit 33 (hereinafter referred to as stored messages).

[0032] In S4, the ID search unit 31 determines, based on the search result in S3, whether the same ID as the input message ID is present in the stored messages. If the presence of the same ID as the input message ID is determined in the stored messages, the process proceeds to S5. If the absence of such an ID is determined, the process proceeds to S8.

[0033] In S5, the ID search unit 31 transmits first information indicating the following contents (1a) to (1c) to the memory control unit 29: (1a) the input message ID (1b) the presence of the same ID as the input message ID in the stored messages; and (1c) a storage location of the stored message containing the same ID as the input message ID (hereinafter referred to as stored message containing the same ID) in the buffer unit 33.

[0034] In S6, the storage control unit 29 identifies the storage location of the stored message containing the same ID using information indicating the content (1c). Then, the storage control unit 29 overwrites data in the stored message containing the same ID with the input message data.

[0035] An example of the above processing will be explained in more detail using a case described in Fig. 4A and Fig. 4B. In the case shown in Fig. As shown in Fig. 4A, stored messages M1, M2, ... Mi, ..., Mn are stored in the buffer unit 33. Here, n is a natural number, and i is any natural number equal to or greater than 1 and equal to or less than n. The messages M1 to Mn are stored in the buffer unit 33 in the order of M1, M2, M3, ..., Mn (hereinafter, the order is referred to as storage order). The storage order is an order in which input messages are stored by the processing in S9 described below. The buffer unit 33 maintains the storage order.

[0036] In the case of Fig. As shown in Figure 4A, the same ID as the input message ID is present in the stored message Mi. In Fig. 4A, EM denotes the input message and EM-ID denotes the input message ID. In the case described in Fig. As shown in Figure 4A, the input message ID is “333”.

[0037] That is, the stored message Mi is the stored message that contains the same ID as the input message. In such a case, the result of the determination in S4 is positive, and the data in the stored message Mi is overwritten with the input message data in S6, as described in Fig. 4B is shown.

[0038] Even if the data is overwritten as described above, the number of stored messages does not change. The storage order of the stored messages M1, M2, ... Mi, ..., Mn does not change. Even if the data in the stored message Mi is overwritten as described above, the stored message Mi remains, for example, at the i-th position in the storage order.

[0039] According to Fig. 3, the output unit 35 in S7 extracts an oldest stored message recorded at a first position in the storage order and transmits the extracted message to the application 13 of the own ECU 11. The extracted message is deleted from the buffer unit 33.

[0040] If the result of the determination in S4 is negative, the process proceeds to S8, where the ID search unit 31 transmits second information indicating the following contents (2a) and (2b) to the memory control unit 29: (2a) the input message ID; and (2b) the absence of the same ID as the input message ID in the stored messages.

[0041] In S9, the storage control unit 29 stores the input message in the buffer unit 33. The input message is newly stored in S9 at a position that follows all existing stored messages in the storage order. By storing the input message, the number of stored messages is increased by one.

[0042] The above processing will now be illustrated by a case described in Fig. 5A and Fig. 5B. In the case shown in Fig. As shown in Figure 5A, the stored messages M1, M2, ..., M1, ..., Mn are stored in the buffer unit 33. Here, n is a natural number, and i is any natural number equal to or greater than 1 and equal to or less than n. The storage order is M1, M2, M3, ..., Mn.

[0043] In the case of Fig. As shown in Figure 5A, the same ID as the input message ID is not present in the stored messages M1 to Mn. In Fig. 5A, EM denotes the input message and EM-ID denotes the input message ID. In the case described in Fig. As shown in Figure 5A, the input message ID is “123”.

[0044] Here, the result of the determination in S4 is negative, and the input message is newly stored in the buffer unit 33 in S9, as shown in Fig. 5B. The input message is newly stored at a position following all existing stored messages M1, M2, ..., Mi, ..., Mn in the storage order, more precisely, at the (n+1)-th position in the case of Fig. 5B.

[0045] The transmit buffer control device 21, the receive buffer control device 23, and the transmit buffer control device 25 perform their processing in the same manner as the receive buffer control device 17, except for the following differences. That is, in the transmit buffer control device 21, the input unit 27 accepts an input of a message generated by the application 13 in its own ECU 11. In the transmit buffer control device 21, the output unit 35 outputs a message extracted by the buffer unit 33 to another ECU 11.

[0046] In the receive buffer control device 23, the input unit 27 accepts an input of a message from the communication group connected to the receive buffer control device 23. In the receive buffer control device 23, the output unit 35 outputs a message extracted from the buffer unit 33 to the switching control unit 15.

[0047] In the transmission buffer control device 25, the input unit 27 accepts an input of a message from the switching control unit 15. In the transmission buffer control device 25, the output unit 35 outputs a message extracted by the buffer unit 33 to the communication group connected to the transmission buffer control device 25. 4. Effects achieved by the reception buffer control device 19

[0048] The following effects are achieved by the receive buffer control device 19 of the present embodiment. The same effects are also achieved by the transmit buffer control device 21, the receive buffer control device 23, and the transmit buffer control device 25.

[0049] (1A) When there is a stored message containing the same ID, the reception buffer control device 19 does not store the inputted message in the buffer unit 33 by the processing in S9. Thus, the number of stored messages does not increase.

[0050] Even if a large number of input messages containing the same ID are input to the input unit 27 due to, for example, a communication device failure or a DoS attack, the number of stored messages containing the same ID does not increase. Therefore, even if a large number of input messages containing the same ID are input to the input unit 27, the reception buffer control device 19 is able to limit the problem of a stored message containing a different ID being lost.

[0051] (1B) If a stored message containing the same ID exists, the reception buffer control device 19 overwrites a data portion of the stored message containing the same ID with the input message data. Thus, the data in the stored message containing the same ID can be updated to the latest data.

[0052] (1C) The reception buffer control device 19 does not need to include an individual buffer unit for each ID. Thus, a memory area used as a buffer unit can be reduced. (Second Embodiment) 1. Difference from the configuration of the first embodiment

[0053] The second embodiment and the first embodiment have the same basic configuration. Therefore, the difference will be mainly described, omitting a description of the common configuration. The same reference numerals as in the first embodiment are used for equivalent configurations, and reference is made to the previous description.

[0054] A reception buffer control device 19 has the Fig. 6. A transmit buffer control device 21, a receive buffer control device 23, and a transmit buffer control device 25 are configured in the same manner as the receive buffer control device 19 of the first embodiment.

[0055] The reception buffer control device 19 includes a rewrite permission information table 37 in addition to an input unit 27, a memory control unit 29, an ID search unit 31, a buffer unit 33, and an output unit 35.

[0056] The overwrite permission information table 37 contains information indicating whether a given ID is an overwrite ID or a non-overwrite ID. A specific example of the overwrite permission information table 37 is a table in which all IDs are recorded, and each ID is recorded as an overwrite ID or a non-overwrite ID.

[0057] Another specific example of the overwrite permission information table 37 is a table in which only overwriteable IDs are recorded among all IDs. In such a case, if an ID in question is recorded in the overwrite permission information table 37, it is determined that the ID in question is an overwriteable ID. If the ID in question is not recorded in the overwrite permission information table 37, it is determined that the ID in question is a non-overwriteable ID.

[0058] Another specific example of the overwrite permission information table 37 is a table in which only non-overwriteable IDs are recorded among all IDs. In such a case, if an ID in question is not recorded in the overwrite permission information table 37, it is determined that the ID in question is an overwriteable ID. If the ID in question is recorded in the overwrite permission information table 37, it is determined that the ID in question is a non-overwriteable ID.

[0059] Another specific example of the overwrite permission information table 37 is a table in which a piece of ID information is registered in advance instead of an ID itself, and only the IDs belonging to an ID group that matches the registered information are recorded. In such a case, if an ID in question belongs to the ID group recorded in the overwrite and non-overwrite table 37, it is determined that the ID in question is an overwriteable ID. If the ID in question does not belong to the recorded ID group, it is determined that the ID in question is a non-overwriteable ID.

[0060] Another specific example of the overwrite permission information table 37 is a table in which a piece of ID information is registered in advance instead of an ID itself, and only the IDs belonging to an ID group that matches the registered information are not recorded. In such a case, if an ID in question does not belong to the ID group recorded in the overwrite-and-nonwrite table 37, it is determined that the ID in question is an overwriteable ID. If the ID in question belongs to the recorded ID group, it is determined that the ID in question is a nonwriteable ID.

[0061] The ID search unit 31 corresponds to a same-ID determination unit. The ID search unit 31 and the overwrite permission information table 37 correspond to an overwritable ID determination unit. The storage control unit 29 corresponds to an overwrite unit and a storage unit. 2. Processing performed by the reception buffer control device 19

[0062] In the following, the processing performed by the reception buffer control device 19 is described in accordance with Fig. 7. The processing in S11 and S12 of the Fig. 7 is the same as the processing in S1 and S2 in the above first embodiment.

[0063] In S13, the ID search unit 31 compares an input message ID transmitted in S12 with a content of the overwrite permission information table 37.

[0064] In S14, the ID search unit 31 determines whether the input message ID is a rewritable ID based on the comparison result in S13. If the input message ID is a rewritable ID, the process proceeds to S15. If the input message ID is not a rewritable ID, the process proceeds to S20.

[0065] S15 to S21 are respectively the same as S3 to S9 in the above first embodiment.

[0066] The transmission buffer control device 21, the reception buffer control device 23 and the transmission buffer control device 25 perform their processing in the same manner as the reception buffer control device 19. 3. Effects achieved by the reception buffer control device 19

[0067] The receive buffer control device 19 of the present embodiment achieves the following effects in addition to the above-described effect (1C) of the above first embodiment. The transmit buffer control device 21, the receive buffer control device 23, and the transmit buffer control device 25 also achieve the same effects.

[0068] (2A) When a stored message containing the same ID exists and the input message ID is a rewritable ID in a simple FIFO buffer configuration, the reception buffer control device 19 does not store the input message in the buffer unit 33 by the processing in S21. Thus, the number of stored messages does not increase.

[0069] Even if a large number of input messages containing the same ID are input to the input unit 27 due to, for example, a communication device failure or a DoS attack, the number of stored messages containing the ID in question does not increase. Therefore, even if a large number of input messages containing the same ID are input to the input unit 27, the reception buffer control device 19 is able to limit the problem of a stored message containing a different ID being lost.

[0070] (2B) If a stored message containing the same ID exists and the input message ID is a rewriteable ID in a simple FIFO buffer configuration, the receive buffer controller 19 overwrites a data portion of the stored message containing the same ID with the input message data. Thus, the data in the stored message containing the same ID can be updated to the latest data.

[0071] (2C) Even if there is a stored message containing the same ID, if the input message ID is not a rewritable ID, the reception buffer control device 19 does not overwrite the data by the processing in S18, and instead stores the input message in the buffer unit 33 by the processing in S21.

[0072] Accordingly, multiple messages containing the same ID may be stored in the buffer unit 33 if the ID is not an overwritable ID. (Other embodiments)

[0073] While the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments and can be modified in various ways. (1) The structure of a message can be configured or specified as needed. For example, the message can contain another section in addition to an ID and data. (2) The data area to be overwritten in S6 or S18 can be set or specified as needed. For example, a section (e.g., an ID) in the stored message that is not the data section can be overwritten. Alternatively, the stored message can be completely overwritten with the input message. (3) The processing in S7 or S19 may be performed at a time different from the message input time. For example, the processing in S7 or S19 may be performed every predetermined period. (4) The reception buffer control device 19 and the transmission buffer control device 21 may be arranged at another communication node (for example, a host computer, a terminal device, a communication device, a switching device, etc.) instead of the ECU 11. (5) The communication system 1 may be a communication system provided for a subject other than a vehicle (e.g., infrastructure, house, office, etc.). (6) The contents (1b) and (1c), which form the first information, can be combined into one data part. (7) The first information need not include the content (1a). The second information need not include the content (2a). Even in such a case, the storage control unit 29 is capable of performing predetermined processing using an ID obtained from the input unit 27. (8) Functions performed by the receive buffer control device 19, the transmit buffer control device 21, the receive buffer control device 23, and the transmit buffer control device 25 may be implemented by hardware as single or multiple ICs or the like, either in whole or in part. (9) Functions of a single component in the above embodiments may be assigned to multiple components, or functions of multiple components may be assigned to a single component. Part of the configurations of the above embodiments may be omitted. At least part of the configurations of the above embodiments may be added to or replaced by the configuration of another embodiment. All modifications within the technical idea in the appended claims are included in the embodiments of the present invention. (10) Apart from the reception buffer control device 19, the transmission buffer control device 21, the reception buffer control device 23 and the transmission buffer control device 25 (hereinafter collectively referred to as buffer control device) described above, the present invention can be realized in various ways, including a system including the buffer control device as a component, a program that causes a computer to serve as the buffer control device, a medium on which the program is recorded, a message storage method and so on.

Claims

[1] Buffer control device (19, 21, 23, 25) comprising: an input unit (25) that accepts an input of a message containing an ID and data; a buffer unit (33) in which a plurality of messages are stored; a same-ID determining unit (31) that determines whether the same ID as the ID included in the message accepted by the input unit is included in the messages stored in the buffer unit; an overwriting unit (29) that overwrites at least data in one of the messages containing the same ID as the ID contained in the message accepted by the input unit with the data contained in the message accepted by the input unit when the same ID is present; a storage unit (29) that stores the message accepted by the input unit in the buffer unit if the same ID is not present; and an output unit (35) that extracts from the buffer unit an oldest message from the messages stored by the storage unit and outputs the oldest message that has been extracted. [2] Buffer control device (19, 21, 23, 25) comprising: an input unit (25) that accepts an input of a message containing an ID and data; a buffer unit (33) in which a plurality of messages are stored; a same-ID determination unit (319) that determines whether the same ID as the ID contained in the message accepted by the input unit is present in the messages stored in the buffer unit; a rewritable ID determining unit (31, 37) that determines whether the ID included in the message accepted by the input unit is a rewritable ID provisionally set; an overwriting unit (29) that overwrites at least data in one of the messages containing the same ID as the ID contained in the message accepted by the input unit with the data contained in the message accepted by the input unit when the same ID is present and the ID contained in the message accepted by the input unit is determined as the overwritable ID; a storage unit (29) that re-stores the message accepted by the input unit in the buffer unit if the same ID is not present or if the ID included in the message accepted by the input unit is not an overwritable ID; and an output unit (35) that extracts from the buffer unit an oldest message from the messages stored by the storage unit and outputs the oldest message that has been extracted. [3] Communication node (11) comprising: the buffer control device according to claim 1 or 2, wherein the communication node temporarily stores a transmission message or a reception message using the buffer control device. [4] Communication node according to claim 3, wherein the communication node is included in a communication system (1) of a vehicle. [5] Switching device (7) comprising: the buffer control device according to claim 1 or 2, wherein the switching device temporarily stores a message to be switched using the buffer control device. [6] Switching device according to claim 5, wherein the switching device is included in a communication system (1) of a vehicle.

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