OCPP Message Flows

Understanding the sequence of messages in OCPP is key to debugging and implementing correct logic. Here are the most common flows visualized.

1. Boot Sequence

Every time a charging station powers up or reconnects, it must identify itself.

• BootNotification: The station sends its model and vendor. The server accepts it and sets the heartbeatInterval.
• Heartbeat: The station pings the server periodically to show it's online.

2. Standard Charging Session (RFID)

The "Happy Path" for a driver swiping a card.

• Authorize: Checks if the tag is valid.
• StartTransaction: Marks the beginning of energy flow. The server MUST return a transactionId.
• StopTransaction: Ends the session. Contains the final meter value and timestamp.

3. Remote Start (Mobile App)

When a driver starts charging via an app, the flow is reversed (Server initiates).

4. Smart Charging (Load Balancing)

The server limits the power due to grid constraints.

• SetChargingProfile: Sends a schedule or limit to the station.
• ClearChargingProfile: Removes limits.

Error Handling

What happens if the network goes down?

1. Offline: The station stores messages in its internal memory.
2. Reconnect: When the connection is restored, the station sends all queued messages.
3. Order: Messages might arrive in a batch. Your server must handle StartTransaction messages that happened hours ago.