WebSocket

A connection that the charger opens to the backend and keeps open, so messages can travel in both directions at any time.

Explained in

OCPP in depth · Stop 02How does a charger connect to its backend?WebSocket, boot announcement, heartbeat and status: the first seconds after a charger starts, and the connection it keeps open all day.

In OCPP over JSON, the charger opens the connection: an HTTP request that is upgraded to a WebSocket. 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.

From “Why the charger calls”, stop 02

Also in

  1. OCPP in depth · Stop 09One day of messages, fully understoodThe day in eight moments
  1. OCPPOpen Charge Point Protocol: the open protocol between a charger and its operator's backend.
  1. Open Charge Alliance: OCPP 1.6 Security Whitepaper, edition 4, February 2026. https://openchargealliance.org/ocpp-info-whitepapers/ocpp-1-6-security-whitepaper-4th-edition/. Checked 09 Oct 2026. Licence: CC BY-ND 4.0.