How does a charger connect to its backend?
The charger restarts. Within seconds it opens a connection to its operator's backend and announces itself: manufacturer, model, firmware.
The backend answers, sets how often the charger should check in, and the connectors report: available.
The questionWhat happens in those first seconds, and why does the charger start the conversation?
The charger opens a WebSocket connection to the backend's address, which includes its own identity. The connection then stays open in both directions.
Select each step to see what is exchanged.
Why the charger calls
In over JSON, the charger opens the connection: an HTTP request that is upgraded to a , to an address that contains the charger's own identity. That suits the real world, where chargers sit behind mobile networks and routers that would not let the backend call in. Once open, the connection carries messages in both directions, so the backend can still send commands at any time.
JSON over WebSockets came with OCPP 1.6 and cut mobile data costs considerably compared with the earlier SOAP variant.
Request and response
Every OCPP call expects a result or an error in return, tied to it by a message ID. Neither side sends a new call before its earlier calls have been answered or have timed out; how long to wait is up to the implementation, and mobile networks need longer. When the charger announces itself, it sends no other request until the backend has accepted it.
Check your understanding
3 questions. Answer all of them to complete this stop. Each answer explains itself.
Who opens the OCPP connection?
The charger opens a WebSocket to the backend; commands from the backend travel back over the same connection.
What does a charger tell the backend when it starts?
The boot announcement identifies the device; the backend accepts it and sets the interval for its sign of life.
Why is the charger's regular sign of life useful?
A missing heartbeat can be the first sign of a lost connection or a stuck charger.
- OCPP Open Charge Point Protocol: the open protocol between a charger and its operator's backend. EV charging fundamentals, stop 03 Glossary
- WebSocket A connection that the charger opens to the backend and keeps open, so messages can travel in both directions at any time. Glossary
- Open Charge Alliance: OCPP-J 1.6 specification (October 2015): connection URL, CALL, CALLRESULT and CALLERROR, synchronicity and time-outs; free download. https://openchargealliance.org/download-ocpp/. Checked 13 Oct 2026.
- Open Charge Alliance: What is new in OCPP 2.0.1? Whitepaper, version 1.0, March 2023. https://openchargealliance.org/wp-content/uploads/2024/01/new_in_ocpp_201-v10.pdf. Checked 09 Oct 2026. Licence: CC BY-ND 4.0.
- Open Charge Alliance: OCPP-J 1.6 specification (October 2015): connection URL, CALL, CALLRESULT and CALLERROR, synchronicity and time-outs; free download. https://openchargealliance.org/download-ocpp/. Checked 13 Oct 2026.
- Open Charge Alliance: OCPP 1.6 edition 2 (2017), sections 3.5 Authorization Cache, 3.16 Metering Data, 4.2 Boot Notification and 9.1 StopTransactionOnEVSideDisconnect; free download. https://openchargealliance.org/download-ocpp/. Checked 13 Oct 2026.