Network Management (NM)
Why Network Management Exists
When you park your car and walk away, should all 70+ ECUs stay powered and communicating? Obviously not — they would drain the 12V battery within hours. Network Management coordinates ECU sleep and wake-up transitions across the CAN network.
AUTOSAR NM
AUTOSAR NM uses a decentralized approach. Each node that needs the network to stay awake periodically transmits an NM message. When no NM messages are received for a timeout period, all nodes transition to sleep.
| Concept | Description |
|---|---|
| NM message | A CAN frame (typically 0x500–0x5FF range) sent by any node needing the bus active |
| NM timeout | If no NM message received for T_NM_TIMEOUT (e.g., 4000 ms), enter Prepare Bus Sleep |
| Repeat Message State | After wakeup, rapid NM messages (every 100 ms) to wake all nodes |
| Normal Operation | NM messages at slower rate (every 1000 ms) |
| Prepare Bus Sleep | No NM traffic for T_NM_TIMEOUT; preparing for sleep |
| Bus Sleep | All communication stopped; transceivers in low-power mode |
Key Concept: The NM message carries the node's source address, allowing diagnostics to identify exactly which ECUs are preventing bus sleep.
Partial Networking
Partial Networking (ISO 11898-6) allows some ECUs to sleep while others remain active. A sleeping ECU's transceiver monitors the bus for a specific wake-up pattern (WUP) without powering the MCU.
This enables features like remote start (telematics ECU stays awake, wakes only engine and body ECUs) or keyless entry (receiver ECU stays awake, wakes BCM when key fob detected).
Exercise: Filter a CANoe trace for NM messages (IDs 0x500–0x5FF). Measure the interval between messages in Normal Operation, then observe what happens when you turn the ignition off.