JP2009147722A - On-vehicle relay connection unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a state where there is no data to be transmitted from occurring, when relaying a message received from a communication line of a reception source to a communication line of a transmission destination of which the transmission rate is higher than that of the communication line of the reception source, by a relay connection unit using a cut-through method. <P>SOLUTION: The present invention relates to an on-vehicle relay connection unit 10 for relaying a message (m) received from an electronic control unit connected to a first communication line 31A to an electronic unit connected to a second communication line 31B of which the transmission rate is higher than that of the first communication line 31A using the cut-through method, including a relay processing section in which, the message is received from the first communication line, a relay start waiting time is calculated at a point of time when a control field has been received, the relay start waiting time being [the reception time required for completing the reception of the remaining bits in the message]-[the transmission time required for transmitting all the bits in the message to the second communication line], and relay of the message to the second communication line is started in timing delayed just by the relay start waiting time. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an in-vehicle relay connection unit, and more particularly, when the transmission speed of a communication line connected to the relay connection unit is different and the transmission speed on the transmission side is faster than the transmission speed on the reception side, the entire message is displayed. It is intended to enable reliable and efficient transmission.

  Conventionally, an electronic control unit (Electronic Control Unit: ECU) that controls a vehicle-mounted device is connected by a communication line, the communication lines are connected to each other via a relay connection unit (gateway device), and the ECUs belong to different communication lines. An in-vehicle communication system that relays messages transmitted and received between the relay connection units is employed.

When the relay connection unit receives a message from the ECU connected to the communication line, the relay connection unit relays the message to another communication line that is a relay transmission destination of the message.
Specifically, the relay connection unit includes a routing map that describes the correspondence between the message identifier of the received message and the communication line connected to the transmission destination ECU for relay transmission. The relay connection unit receives the message, reads the message identifier, refers to the routing map, determines the destination communication line corresponding to the message identifier, and transmits the message to the identified destination communication line. .

As a relay processing method of the relay connection unit, for example, a cut-through method is known as described in JP-A-9-162917 (Patent Document 1).
In the cut-through method, as shown in FIG. 7, when the relay connection unit receives a message from the communication line (reception source bus) and receives up to the arbitration field (ID) in which the message identifier is written in the message ta. In this method, a routing destination communication line (transmission destination bus) corresponding to the message identifier is identified with reference to the routing map, and transmission to the communication line is started. Since transmission to the communication line is started without receiving the message to the end, transmission starts after message reception is started, compared to the store and forward method which starts transmission after receiving the message to the end. The time until this is shortened, and the relay processing can be speeded up.

However, when the relay connection unit is performing message relay processing by the cut-through method, for example, as shown in FIG. 8, the relay connection unit has received from the communication line (bus) of the reception source at a transmission rate of 250 kpbs. When sending a message to the destination communication line (bus) at a transmission rate of 500 kbps, the message receiving speed is slower than the sending speed, so the data of the message to be sent cannot be received, There is a problem that there is a state where there is no data to be transmitted.
When there is a state where there is no data to be transmitted in this way, the relay connection unit interrupts the relay process as an error, and an error occurs on the bus, which becomes a problem.

Japanese Patent Laid-Open No. 9-162917

  The present invention has been made in view of the above problems, and a message received from a communication line on the reception side by the relay connection unit is cut to a transmission line on the transmission side that is faster than the communication line on the reception side. It is an object to prevent the occurrence of a state where there is no data to be transmitted when relaying, and to transmit a message efficiently.

In order to solve the above-mentioned problem, the present invention provides an electronic control unit connected to a second CAN communication line having a transmission speed higher than that of the first CAN communication line for a message received from the electronic control unit connected to the first CAN communication line. It is an in-vehicle relay connection unit that relays by the cut-through method.
The relay connection unit is
A transceiver connected to the first CAN communication line and the second CAN communication line;
A relay processing unit connected to the transmission / reception unit;
The relay processing unit
When reception of the control field of the message received from the first CAN communication line is completed, the reception time TA required to complete reception of the remaining number of bits of the message and the total number of bits of the message The transmission time TB required for transmission to the 2CAN communication line is obtained, the transmission time TB is subtracted from the reception time TA to calculate the transmission waiting time TC (TC = TA−TB), and the transmission waiting time TC is correct. Is set to perform relay processing for starting relaying of the message to the second CAN communication line after elapse of the transmission waiting time from completion of reception of the control field of the message. We provide in-vehicle relay connection units.

In this way, by starting the transmission of the message after the completion of the reception of the control field by the transmission waiting time (TC), the second CAN communication is performed when the reception of the message received from the first CAN communication line is completed. This can be surely faster than when the transmission of the message to be transmitted to the line is completed.
In other words, when the relay connection unit completes the message reception from the first CAN communication line, the message relay start timing is delayed so that the message transmission to the second CAN communication line is not completed.
For this reason, when the relay connection unit relays the message received from the first CAN communication line to the second CAN communication line having a higher transmission speed than the first CAN communication line by the cut-through method, there is no data to be transmitted. It can be prevented from occurring.

When the transmission waiting time TC becomes negative or zero, the relay of the message is started to the second CAN communication line immediately after the reception of the control field of the message is completed.
In such a case, even when the relay start timing of the message to the second CAN communication line is not delayed, a state where there is no data to be transmitted does not occur when the message is relayed by the cut-through method.

  Specifically, from the data length of the data field stored in the control field and the transmission speed ratio between the second CAN communication line and the first CAN communication line, (data field data length−total number of bits of message / transmission) The transmission waiting bit number which is a speed ratio) is obtained, and the elapsed time of the transmission waiting bit number at the transmission speed of the first CAN communication line is set as the transmission waiting time.

A message conforming to the CAN protocol includes an arbitration field, a control field, and a data field following the control field, and the data length of the data field is stored in the control field.
When receiving the control field of the message, the relay processing unit of the relay connection unit reads the data length of the data field. The relay processing unit obtains a transmission rate ratio between the second CAN communication line and the first CAN communication line from the transmission rates of the first CAN communication line and the second CAN communication line in advance.
Further, the relay processing unit calculates the total number of bits of the message from the number of bits of the arbitration field and the control field defined by the CAN protocol and the data length of the data field read from the control field.

The relay processing unit calculates (data field data length−total number of message bits / transmission speed ratio) from the data length of the data field, the total number of bits of the message, and the transmission speed ratio obtained as described above, and a transmission waiting bit. Seeking the number. After the reception of the control field is completed, the message received from the first CAN communication line is counted for the number of transmission waiting bits, and then relaying of the message to the second CAN communication line is started.
That is, message relaying is started after a transmission waiting time that is the elapsed time of the number of transmission waiting bits at the transmission speed of the first CAN communication line.

As described above, the transmission waiting bit number is obtained from the data length of the data field read from the control field, the total number of message bits that can be calculated from the data length, and the transmission rate ratio. For this reason, the number of bits waiting for transmission can be calculated in advance from the data length and the transmission rate ratio and stored in the relay connection unit as a table.
That is, when the reception of the control field is completed, the relay processing unit reads the data length from the control field, obtains a transmission rate ratio from the transmission rates of the second CAN communication line and the first CAN communication line, and calculates the data length. The number of bits waiting for transmission can be read from the transmission rate ratio with reference to the table.

The relay processing unit calculates a reception time required to complete reception of the remaining number of bits of the message and a transmission time required to transmit the total number of bits of the message to the second CAN communication line. Then, the transmission waiting time may be obtained by subtracting the transmission time from the reception time.
Specifically, (data field data length / first CAN communication line transmission speed) is calculated from the data length of the data field, the total number of bits of the message, and the transmission speed of each communication line, and the rest of the message is calculated. The reception time required to complete reception of the number of bits. Further, (total number of bits of message / transmission speed of second CAN communication line) is calculated, and the total number of bits of the message is set as a transmission time required for transmitting to the second CAN communication line. Further, a transmission waiting time obtained by subtracting the transmission time from the reception time is obtained, and relaying of the message is started after the transmission waiting time from completion of reception of the control field.

The transmission speed of the first CAN communication line or the second CAN communication line is 125 kbps, 250 kbps, 500 kbps, 1 Mbps, and the transmission speed ratio is one of 2, 4, and 8.
Generally, transmission rates used in the CAN protocol are 125 kbps, 250 kbps, 500 kbps, and 1 Mbps. The relay processing unit of the relay connection unit obtains the transmission rate ratio from the transmission rates of the first CAN communication line and the second CAN communication line.

  As described above, according to the relay connection unit of the present invention, the relay connection unit receives from the first CAN communication line by starting relaying the message after the transmission waiting time from the time when reception of the control field is completed. When a message is relayed to the second CAN communication line, which has a higher transmission speed than the first CAN communication line, by a cut-through method, it is possible to prevent a situation where there is no data to be transmitted.

Embodiments of the present invention will be described with reference to the drawings.
1 to 4 show a first embodiment of the present invention.
The in-vehicle relay connection unit 10 of the present invention is interposed between communication lines 31 to which an electronic control unit (ECU) 30 is connected, and relays a message m transmitted / received between the ECUs 30 belonging to different communication lines 31. .
In the present embodiment, the relay connection unit 10 is interposed between the first communication line 31A and the second communication line 31B, and the ECU 30A is connected to the first communication line 31A and the ECU 30B is connected to the second communication line 31B for communication. A system 20 is configured. The communication protocol is CAN (Controller Area Network). The transmission speed of the first communication line 31A is set to be slower than that of the second communication line 31B, and the relay connection unit 10 sends the message m transmitted by the ECU 30A connected to the first communication line 31A to that of the first communication line 31A. It relays to ECU30B connected to the 2nd communication line 31B with a high transmission speed.

The relay connection unit 10 includes a relay processing unit 11, transmission / reception units 12A and 12B, and a storage unit 13.
The relay processing unit 11 is connected to the transmission / reception units 12A and 12B and to the storage unit 13. When the relay processing unit 11 receives the message m from the ECU 30A connected to the first communication line 31A, the relay processing unit 11 receives an identifier from the arbitration field 42 of the message m. (ID) is being read out. Further, the second communication line 31B, which is a relay transmission destination of the message m, is determined from the ID using a routing map, and the message m is relayed to the communication line.
At this time, the relay is performed by a cut-through method.

Further, when the transmission speed of the second communication line 31B that is the transmission destination of the message m is higher than that of the first communication line 31A that is the reception source of the message m, the relay processing unit 11 sets the transmission waiting bit number X described later. After the reception of the control field 43 of the message m read from the storage unit 13 and received from the first communication line 31A is completed, the number of bits of the message on the first communication line 31A is counted by the number X of transmission waiting bits, 2 Transmission of the message m to the communication line 31B is started.
That is, the transmission of the message m to the second communication line 31B is started after the transmission waiting time TC when the transmission waiting bit number X has elapsed at the transmission speed of the first communication line 31A.

The storage unit 13 stores a table T in which the number X of transmission waiting bits is described. In the table T, the transmission rate ratio R, that is, (the transmission rate of the second communication line 31B / the transmission rate of the first communication line 31A) and the number X of transmission waiting bits with respect to the data length of the data field 44 of the message m are shown. Are listed. Details of the table T will be described later.
In addition, the storage unit 13 stores a routing map for relay processing of the relay processing unit 11.

  The transmission / reception unit 12A is connected to the first communication line 31A, and the transmission / reception unit 12B is connected to the second communication line 31B. The transmission / reception unit 12 transmits / receives the message m via the first communication line 31A and the second communication line 31B.

  For example, the relay processing unit 11 of the relay connection unit 10 is configured by a CPU, the transmission / reception unit 12 is configured by a CAN controller, and the storage unit 13 is configured by ROM or RAM, a nonvolatile memory, or the like.

Next, the format of the message m transmitted / received by the relay connection unit 10 will be described. As shown in FIG. 2, the frame of the message m includes a start-of-frame (SOF) field 41 indicating the start of the message frame, an arbitration field 42 storing a message identifier (ID), and a data field 44 from the upper bits. A control field 43 storing a data length (DLC) and a data field 44 indicating the contents (data) of a message m to be transmitted / received are provided.
The message m conforms to the CAN protocol and has a standard format. Therefore, the arbitration field 42 is defined as 12 bits, the control field 43 is defined as 6 bits, and the SOF field 41 is defined as 1 bit, and the data length of the data field 44 is different for each message m. The control field 43 stores the data length of the data field 44 in units of bytes.

Next, the transmission waiting bit number X will be described.
As shown in FIG. 3, the number X of transmission waiting bits means that the relay connection unit 10 receives the message m from the first communication line 31 </ b> A, and the message to the second communication line 31 </ b> B from the time t <b> 1 when the reception of the control field 43 is completed. The relay processing unit 11 counts the number of bits waiting for transmission X by counting the number of bits of the message received from the first communication line 31A.
For example, when the transmission waiting bit number X is 10 bits, the relay processing unit 11 counts 10 bits of messages received from the first communication line 31A from the time t1 when the reception of the control field 43 is completed as shown in FIG. After that, the relay of the message m is started on the second communication line 31B.
The time during which the transmission waiting bit number X elapses at the transmission speed of the first communication line 31A is defined as a transmission waiting time TC.

A method of obtaining the transmission waiting bit number X will be described.
At the completion of reception of the control field 43 of the message m from the first communication line 31A, the relay connection unit 10 has completed reception of the arbitration field 42 and the control field 43, and continuously receives the data field 44. .
The relay processing unit 11 starts the second communication line from the time t1 when the reception of the control field 43 is completed, when the transmission waiting bit number X has elapsed at the transmission speed of the first communication line 31A, that is, after the transmission waiting time TC has elapsed. The transmission of the message m is started at 31B.

At this time, when the relay connection unit 10 completes the reception of the message m from the first communication line 31A, the transmission waiting bit number X is set so that the transmission of the message m to the second communication line 31B is not completed. ing. That is, the transmission waiting bit number X is set so that the reception time t2 of the message m received from the first communication line 31A is earlier than the transmission time t3 of the message m transmitted to the second communication line 31B. Yes.
Therefore, (the time TA necessary for receiving the data field 44) should be smaller than (the transmission time TC + the time TB necessary for transmitting the total number of bits of the message m to the second communication line 31B). .

The time TA required to receive the data field 44 is obtained by the number of bits of the data field 44 / the transmission speed of the first communication line 31A. Note that the data length of the data field 44 represents the number of bits of the data field 44.
The transmission waiting time TC is obtained by the number of transmission waiting bits X / the transmission speed of the first communication line 31A, considering the transmission speed of the first communication line 31A as a reference.
The time TB required to transmit the total number of bits of the message m to the second communication line 31B is obtained by the total number of bits of the message m / the transmission rate of the second communication line 31B.
From the above, when the number X of transmission waiting bits is obtained, it becomes (the number of bits of the data field 44−the total number of bits of the message m / the transmission rate ratio R). Here, the transmission rate ratio R is the transmission rate of the second communication line 31B / the transmission rate of the first communication line 31A.

Specifically, the data length (number of bits) of the data field 44 is read from the control field 43. Since the data length is expressed in bytes and one byte is 8 bits, when the read value is n, the data length (number of bits) of the data field 44 is 8 × n bits.
The total number of bits of the message m is the sum of the number of bits in the SOF field 41, the arbitration (ID) field 42, the control (DLC) field 43, and the data field 44. As described above, since the arbitration field 42 is defined as 12 bits, the control field 43 is defined as 6 bits, and the SOF is defined as 1 bit, the total is 19 bits, and the data length of the data field 44 is 8 × n bits. Therefore, the total number of bits of the message m is (19 + 8 × n) bits.

  Further, the transmission speed of the first communication line 31A and the second communication line 31B is any one of 125 kbps, 250 kbps, 500 kbps, and 1 Mbps, and the first communication line 31A is slower than the second communication line 31B. The transmission rate ratio R is any one of 2, 4, and 8.

In addition, consider stuff bits. In the communication system based on the CAN protocol, the ECU 30 and the relay connection unit 10 cannot receive the same value bit continuously for 6 bits or more. A stuff bit is inserted. Therefore, the maximum number of bits in the data field 44 is 8 × n × 6/5. 6/5 is referred to as a bit stuff rate S.
Note that stuff bits are also inserted into the arbitration field 42 and the control field 43. However, when the total number of bits of the message m becomes long, the total number of bits of the message m transmitted to the second communication line 31B increases, and the message m is transmitted to the second communication line 31B of the relay connection unit 10. When completed, t3 is further delayed. In the present invention, the completion time t2 of the message m received from the first communication line 31A is set to be earlier than the time t3 of the transmission completion of the message m transmitted to the second communication line 31B. When the total number of bits becomes long, the calculation of the transmission waiting bit number X is not affected. Therefore, in the present embodiment, only stuff bits inserted in the data field 44 are considered.

Accordingly, the number X of transmission waiting bits is (the number of bits in the data field 44−the total number of bits of the message m / the transmission rate ratio R), and is represented by the equation (1).
The relay connection unit 10 starts relaying the message m to the second communication line 31B after counting the message m received from the first communication line 31A for the number X of transmission waiting bits from the time t1 when reception of the control field 43 is completed. To do.
If the transmission wait bit number X is “0” or a negative value according to the expression (1), the transmission wait bit number X is regarded as “0”, and immediately after t1 when reception of the control field 43 is completed. The relay of the message m is started to the 2nd communication line 31B.
(Equation 1)
X = (8 * n * S)-(19 + 8 * n * S) / R (Formula 1)

From Equation 1, the transmission wait bit number X is a function of the transmission rate ratio R and the number of bits in the data field 44. As described above, the transmission rate ratio R has a value of 2, 4, or 8, and the data length of the data field 44 is represented by 8 × n bits, that is, n bytes. In the CAN message m, the data field 44 takes a value from 0 to 8 bytes.
Therefore, when the transmission waiting bit number X is calculated from the transmission rate ratio R and the number of bytes of the data length of the data field 44, the table T shown in FIG. For example, when the transmission speed of the first communication line 31A is 250 kbps, the transmission speed of the second communication line 31B is 500 kbps, and the number of bytes n of the data field 44 is 4 bytes, the transmission speed ratio R is 500/250 = 2. The waiting bit number X is 10 bits from FIG. Therefore, the relay connection unit 10 receives the message m from the first communication line 31A, and receives the message m received from the first communication line 31A from the time t1 when the reception of the control field 43 is completed, as shown in FIG. After counting the number of bits, that is, after 10 bits have elapsed at the transmission rate of 250 kbps (transmission waiting time TC) of the first communication line 31A, the relay of the message m is started on the second communication line 31B.
The table T is calculated in advance and stored in the storage unit 13.

Next, the operation of the relay connection unit 10 will be described.
The relay connection unit 10 receives the message m from the first communication line 31A. When the arbitration field 42 of the message m is received, the relay processing unit 11 reads the ID of the message m and refers to the routing map in the storage unit 13 to determine the relay transmission destination communication line. Here, the second communication line 31B is the transmission destination.
Next, the transmission speed ratio R is obtained from the transmission speed of the first communication line 31A as the reception source and the transmission speed of the second communication line 31B as the transmission destination. The transmission rate ratio R may be stored in advance, or the transmission rate of each communication line may be stored and calculated every time the message m is received.

Next, when the control field 43 of the message m is received, the number of bytes that is the data length of the data field 44 is read from the control field 43.
Further, the relay processing unit 11 refers to the table T in the storage unit 13 and reads the number X of transmission waiting bits from the number of bytes in the data field 44 and the transmission rate ratio R.
Next, the relay processing unit 11 counts the message m received from the first communication line 31A from the time when the reception of the control field 43 is completed, and then relays the message m to the second communication line 31B. To start.

  According to the present invention, the relay connection unit 10 receives the message m from the first communication line 31A by starting the relay of the message m with a delay by the transmission waiting time TC from the time when the reception of the control field 43 is completed. At the time t2 when the process is completed, the transmission of the message m to the second communication line 31B is not completed. For this reason, the relay connection unit 10 should transmit the message m received from the first communication line 31A when relaying the message m to the second communication line 31B having a higher transmission speed than the first communication line 31A by the cut-through method. It is possible to prevent a state where there is no data.

Instead of storing the table T in the storage unit 13, the transmission waiting bit number X may be obtained by calculating each time the message m is received from the number of bytes in the data field 44 and the transmission rate ratio R.
Further, in the present embodiment, the message on the first communication line 31A is counted for the number X of transmission waiting bits, and relaying of the message m is started on the second communication line 31B after the elapsed time TC of the number of transmission waiting bits X. The elapsed time TC of the number X of transmission waiting bits may be calculated based on the transmission speed of the second communication line 31B. In this case, the elapsed time TC is obtained by TC = 8 × n × S × Ta1bit− (19 + 8 × n × S) × Tb1bit. However, Ta1bit is a time for transmitting 1 bit at the transmission speed of the first communication line 31A, and Tb1bit is a time for transmitting 1 bit at the transmission speed of the second communication line 31B.

  Further, the storage unit 13 does not have the table T, and every time the relay processing unit 11 receives the message m, the time TA required to receive the data field 44 and the total number of bits of the message m are set to the second communication line 31B. The transmission waiting time TC is obtained from the time TB required for transmission to the transmission field, and the transmission waiting time TC corresponding to the number X of transmission waiting bits at the transmission speed of the first communication line 31A has elapsed since the reception of the control field 43 is completed. After that, the relay of the message m may be started on the second communication line 31B.

FIG. 5 shows a second embodiment of the present invention.
The extended format is used as the format of the message m transmitted / received by the relay connection unit 10, which is different from the first embodiment.
As shown in FIG. 5, the extended format of the message m is defined as 32 bits for the arbitration field 42, 6 bits for the control field 43, and 1 bit for the SOF field.
The total number of bits of the message m is the sum of the number of bits of the SOF field 41, the arbitration field 42, the control field 43, and the data field 44. The data length of the data field 44 is 8 × n bits, and the total number of bits of the message m is (39 + 8 × n) bits.

Therefore, the transmission waiting bit number X is represented by (number of bits of the data field 44−total number of bits of the message m / transmission rate ratio R) = (8 × n × S) − (39 + 8 × n × S) / R. The relay connection unit 10 transfers the second communication line 31B to the second communication line 31B after a transmission waiting time TC from the time t1 when the reception of the control field 43 is completed, which is the time when the transmission waiting bit number X elapses at the transmission speed of the first communication line 31A. Start relaying message m.
In the case of the extended format, when the transmission waiting bit number X is calculated from the transmission rate ratio R and the number of bytes in the data field 44, a table T shown in FIG.

As described above, even when the message m is in the extended format, the transmission waiting time TC is obtained, and relaying of the message m is started after being delayed by the transmission waiting time TC from the time when reception of the control field 43 is completed. As a result, when the message m received from the first communication line 31A is relayed to the second communication line 31B having a higher transmission speed than the first communication line 31A by the cut-through method, there is a state where there is no data to be transmitted. Can be prevented.
In addition, since another structure and an effect are the same as that of 1st Embodiment, the same code | symbol is attached | subjected and description is abbreviate | omitted.

It is a block diagram of the communication system which connected the relay connection unit which is this invention. It is explanatory drawing of the format of a message. It is explanatory drawing of a transmission waiting time. It is the figure which showed the number of transmission waiting bits with respect to the transmission rate ratio and the data length of a data field. It is explanatory drawing of the format of the message of 2nd Embodiment. It is the figure which showed the number of transmission waiting bits with respect to the transmission rate ratio and the data length of a data field. It is explanatory drawing of a cut-through system. It is a figure which shows the state with no data which should be transmitted.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Relay connection unit 11 Relay processing part 12 Transmission / reception part 13 Storage part 30 Electronic control unit (ECU)
31A 1st communication line 31B 2nd communication line 42 Arbitration field 43 Control field X Transmission waiting bit number TC Transmission waiting time T Table R Transmission rate ratio m Message

Claims (4)

In-vehicle relay that relays a message received from the electronic control unit connected to the first CAN communication line to the electronic control unit connected to the second CAN communication line having a higher transmission speed than the first CAN communication line by a cut-through method. A connection unit,
The relay connection unit is
A transmission / reception unit connected to the first CAN communication line and the second CAN communication line;
A relay processing unit connected to the transmission / reception unit;
The relay processing unit
When reception of the control field of the message received from the first CAN communication line is completed, the reception time TA required to complete reception of the remaining number of bits of the message and the total number of bits of the message The transmission time TB required for transmission to the 2CAN communication line is obtained, the transmission time TB is subtracted from the reception time TA to calculate the transmission waiting time TC (TC = TA−TB), and the transmission waiting time TC is correct. Is set to perform relay processing for starting relaying of the message to the second CAN communication line after elapse of the transmission waiting time from completion of reception of the control field of the message. In-vehicle relay connection unit.   2. The in-vehicle relay connection according to claim 1, wherein when the transmission waiting time TC is a negative or zero value, the relay of the message is started to the second CAN communication line immediately after the reception of the control field of the message is completed. unit.   Transmission waiting bit based on the data length of the data field stored in the control field and the transmission rate ratio between the second CAN communication line and the first CAN communication line (data length of the data field−total number of bits of message / transmission rate ratio) The in-vehicle relay connection unit according to claim 1 or 2, wherein the transmission waiting time is defined as an elapsed time of the number of bits waiting for transmission at the transmission speed of the first CAN communication line.   4. The transmission speed of the first CAN communication line or the second CAN communication line is 125 kbps, 250 kbps, 500 kbps, 1 Mbps, and the transmission speed ratio is 2, 4, or 8. 4. The in-vehicle relay connection unit according to claim 1.

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