Typically ECU sends out Network Management (NM) messages at regular intervals. As more ECUs are added, the bus load due to NM messages increases, potentially leading to congestion.
Let’s explore the Bus Load Reduction Mechanism in CAN NM with an example involving three ECUs: ECU A, ECU B, and ECU C. The mechanism reduces the bus load by allowing only two nodes to transmit NM messages.
How It Works: Example with ECU A, ECU B, and ECU C
To see this in action, let’s consider a scenario with ECU A, ECU B, and ECU C on a CAN network.
Repeat Message State
Each ECU would transmit an NM PDU based on a standard timing parameter called Cycle Time (a fixed interval across all ECUs in the network).
Normal Operation State
Alternating Transmissions
- Suppose ECU A and ECU B have the shortest Reduced Times in the network. The Bus Load Reduction Mechanism uses this fact to allow ECU A and ECU B to take turns transmitting NM PDUs.
- ECU C does not transmit its NM.
Adjusting for Node Changes
- If ECU A stops transmitting it NM – for instance, then ECU C, which has the next shortest Reduced Time, steps in and alternates with ECU B.
- This adjustment means that as each ECU finishes its task or goes into a sleep, other ECUs with the next smallest Reduced Time take over, ensuring minimal NM traffic.
Single ECU Communication
- If only ECU B needs to stay active, it continues sending one NM PDU per Cycle Time.
Summary
The Bus Load Reduction Mechanism in CAN NM smartly manages the network traffic by reducing unnecessary NM messages.
Reference
| Details | Link |
| Specification of CAN Network Management (Chapter 7.8) | https://www.autosar.org/fileadmin/standards/R21-11/CP/AUTOSAR_SWS_CANNetworkManagement.pdf |
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