JP2006229887A - Communication equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To alleviate congestion on a transmission medium taking account of significance of transmission data. <P>SOLUTION: This communication equipment 12A is connected with other communication equipment 12B-12D via the transmission medium 11, transmits periodic frames by every predetermined period, and is provided with: a load monitoring means 15 for monitoring a communication load on the transmission medium 11; and a periodic frame control means 17 for changing transmitting periods of periodic frames according to a load state detected by the load monitoring means 15. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a communication apparatus, and in particular, intends to eliminate congestion on a bus of a frame that is multiplexed and transmitted in a vehicle-mounted LAN.

In recent years, with the advancement of information technology, the exchange of signals for controlling in-vehicle electrical components etc. has also increased rapidly in the automobile field, and in-vehicle LAN (local area network) to suppress the increase in the number of wire harnesses as transmission media A multiple communication system is being adopted.
In an in-vehicle LAN, nodes such as an ECU are connected to a common communication line to perform data communication with each other. However, since the communication line is common, access control for performing collision arbitration between data frames is performed.

There is a communication protocol called CAN (Controller Area Network) as one of in-vehicle LAN systems.
The CAN employs a multicast system, and all nodes connected on the bus receive data at the same time, and other than the corresponding nodes discard the received data. The maximum communication speed is 1 Mbps, and the access method employs a CSMA / CA (Carrier Sense Multiple Access / Collision Avoidance) method.
In the CSMA / CA system, a node that wants to transmit data confirms the presence or absence of communication on the bus, and starts data transmission if communication is not in progress. When signal collision occurs due to simultaneous transmission by a plurality of nodes, the low priority node performs an arbitration to stop transmission and request retransmission after a certain time. According to this method, although it is resistant to failures, if the communication load on the bus exceeds a certain amount, the delay time increases rapidly, so that a large load cannot be applied.

In Japanese Patent Application Laid-Open No. 2001-119416, in order to prevent the delay time from being greatly prolonged by losing transmission of low-priority data when the CAN bus is congested, the data that has lost N transmissions is data We are taking measures to increase the priority of transmission.
However, in such a system, there is no problem when the bus idle time is long, but when the bus is congested, arbitration frequently occurs and data cannot be transmitted for a long time. In other words, if the priority of a certain data is raised, it becomes impossible to transmit another data, so the congestion on the bus itself is not solved and the problem is postponed, and it can be said that the fundamental solution has not been reached.
JP 2001-119416 A

  The present invention has been made in view of the above problems, and an object thereof is to reduce congestion on a transmission medium in consideration of the importance of transmission data.

In order to solve the above-mentioned problem, the present invention is a communication device that is interconnected with another communication device via a transmission medium and transmits a periodic frame at a predetermined cycle.
Load monitoring means for monitoring a communication load on the transmission medium;
There is provided a communication apparatus comprising: a periodic frame control unit that changes a transmission period of the periodic frame in accordance with a load situation detected by the load monitoring unit.

  Comparing the importance of regular frames and event frames, event frames that are suddenly transmitted when the data content changes are more important from a real-time perspective than regular frames that are transmitted at regular intervals. You can think of it. Therefore, in the present invention, the traffic on the transmission medium can be leveled by adjusting the transmission time interval of the regular frame according to the communication load of the network.

Specifically, the periodic frame control means is preferably configured to change the transmission period of the periodic frame to be longer when the communication load becomes a predetermined threshold value or more.
That is, when the communication load on the transmission medium is equal to or greater than a predetermined threshold, it is possible to ease the transmission of the event frame by reducing the congestion on the transmission medium by increasing the transmission time interval of the regular frame. . In addition, when the communication load is less than the threshold value, the transmission period of the regular frame may be restored.
Furthermore, a plurality of threshold values may be set stepwise, and the transmission period of the regular frame may be set to be gradually increased step by step as the communication load increases.

Examples of the regular frame include analog data that changes every moment, such as vehicle speed data output from a vehicle speed sensor.
Examples of event frames include frames transmitted in response to various key operations and switch operations.

  It is preferable that frame transmission is performed in a multicast manner, and the load monitoring unit calculates a received data amount per unit time as the communication load.

In the multicast method, the communication device once receives all of the frames transmitted on the transmission medium, and continues processing when the destination address described in the frame matches the self address, while receiving if it does not match. The discarded frame is to be discarded. Therefore, the load monitoring means can easily determine the communication load (congestion degree) on the transmission medium by calculating the data amount per unit time of all frames received including the frames not addressed to itself.
In addition, when the said communication apparatus is used as the vehicle-mounted electrical equipment connected as a transmission medium with the wire harness routed in the vehicle.

  As is clear from the above description, according to the present invention, when the communication load of the network is large, the congestion on the transmission medium is reduced by increasing the transmission period of the regular frame, and the event frame can be easily transmitted. can do.

Embodiments of the present invention will be described with reference to the drawings.
1 and 2 show a multiplex transmission system mounted on a vehicle, using a wire harness (bus) wired in the vehicle as a transmission medium, a CAN (Controller Area Network) as a communication protocol, and a network topology as a bus type. It is said.
A plurality of nodes 12A to 12D serving as communication devices (vehicle electrical components) are connected to the bus 11, the access method is CSMA / CA (Carrier Sense Multiple Access / Collision Avoidance), and the maximum communication speed is 1 Mbps. Further, the CAN adopts a multicast method, and all the nodes 12A to 12D receive a frame transmitted from a certain node 12, and discard the received frame except for a node that matches the destination of transmission data.

  Each of the nodes 12A to 12D includes a node that manages transmission of a regular frame (a frame for transmitting substantially continuous data such as vehicle speed data output from a vehicle speed sensor) on the bus, and an event frame (key operation). There are mixed nodes that manage the transmission of data that occurs suddenly due to switch operations or the like to the bus.

  FIG. 2 shows a node 12A that transmits a periodic frame at a fixed period, an I / F unit 13 that becomes a communication interface with the bus 11, a reception processing unit 14 that performs reception processing of a frame received from the bus 11, and reception processing. Load monitoring means 15 for calculating the degree of congestion of the bus 11 based on the amount of data per unit time received by the unit 14, and periodic frame control for determining the transmission period of the periodic frame based on the degree of congestion calculated by the load monitoring means 15 Means 17, a transmission processing unit 18 that performs frame transmission processing, and an application unit 16 that performs functional processing of the node 12A.

The node 12A transmits a periodic frame in response to a command from the application unit 36.
The regular frame is a frame transmitted on the bus 11 at regular intervals, and includes data that occurs substantially continuously, such as vehicle speed data output from a vehicle speed sensor, for example. In the periodic frame, even if data is lost in the receiving node 12A, it can be re-received after a certain period, so there is an advantage that the reliability of data communication can be ensured.

For example, the node 12B transmits an event frame. The event frame is a frame that is suddenly transmitted onto the bus 11 as in the case where a change in the data content occurs in the processing of the application unit 36, and occurs suddenly by, for example, a key operation or a switch operation. It contains data. The event frame has an advantage that other nodes can acquire data in real time because the data can be transmitted immediately when the data content changes.
As shown in FIG. 3, the frame format of the present embodiment includes areas of a preamble, a start delimiter, a destination address, a transmission source address, a data length, data, and an FCS (Frame Check Sequence).

Next, a communication control procedure in the node 12 will be described.
Since CAN employs a multicast method, each node 12A temporarily receives all frames transmitted on the bus 11 by the reception processing unit 34 via the I / F unit 33. The load monitoring unit 35 obtains the communication load (congestion degree) on the bus 11 by calculating the data amount per unit time of the frame received by the reception processing unit 34 by the following formula 1.
[Formula 1]
Communication load = amount of received data / reception time

The load monitoring unit 35 always watches the communication load of the bus 11, and when the communication load is over a predetermined threshold and becomes congested, the load monitoring unit 35 instructs the regular frame control unit 37 to increase the transmission period of the regular frame. Change settings. Periodic frames are transmitted from the transmission processing unit 38 to the bus 11 via the I / F unit 38 in the changed time period.
When the degree of congestion obtained by the load monitoring means 35 recovers below the threshold value, the regular frame control means 37 is commanded to change the setting so that the transmission period of the regular frames is returned to the original length.
The received frame is confirmed by the application unit 16 whether the destination address matches its own address. If the destination address does not match, the frame is discarded. If the destination address matches, the application process is performed based on the information of the frame. Is made.

As described above, by increasing the transmission time interval of the regular frame when the bus 11 is congested, the traffic on the bus 11 can be reduced and the transmission delay of the event frame can be reduced. Considering the importance, the event frame is more important than the regular frame, and the congestion on the bus 11 is reduced by adjusting the transmission interval of the regular frame.
Here, if the transmission interval of a regular frame is longer than a certain time, the reliability of the data content may be impaired, but it can be said that it is negligible compared to the effect of significant transmission delay due to bus congestion. Network reliability can be increased.
In addition, when the traffic on the bus 11 detected by the load monitoring unit 35 is smaller than a predetermined threshold, control for shortening the transmission period of the regular frame may be performed.

1 is a basic configuration diagram of a communication control system according to an embodiment of the present invention. It is a block diagram which shows the node of embodiment. It is drawing which shows a frame format.

Explanation of symbols

11 Bus (Transmission medium)
12A to 12D node (communication device)
13 I / F unit 14 Reception processing unit 15 Load monitoring unit 16 Application unit 17 Periodic frame control unit 18 Transmission processing unit

Claims (3)

A communication device that is interconnected with another communication device via a transmission medium and transmits a periodic frame at a predetermined cycle,
Load monitoring means for monitoring a communication load on the transmission medium;
A communication apparatus comprising: a periodic frame control unit configured to change a transmission cycle of the periodic frame according to a load situation detected by the load monitoring unit.   The communication apparatus according to claim 1, wherein the periodic frame control unit is configured to perform a change to increase a transmission cycle of the periodic frame when a communication load becomes a predetermined threshold or more.   The communication apparatus according to claim 1, wherein frame transmission is performed in a multicast manner, and the load monitoring unit calculates a received data amount per unit time as the communication load.

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