Which OCPP messages make up a charging session?

In OCPP 1.6: Authorize, StartTransaction, MeterValues and StopTransaction. In 2.0.1, the transaction messages are events of one type, TransactionEvent.

Explained in

OCPP in depth · Stop 04Which messages make up one session?Authorise, start, meter values, stop: one charging session as a sequence of OCPP messages, in version 1.6 and in 2.0.1.

For a charger with a certified meter, the Open Charge Alliance describes six requirements for a session to start under OCPP 1.6: the driver is allowed to charge, the cable is plugged in on both ends, and, inside the charger, the meter has been set up with the session, its time verified, a tariff configured where needed and the charging point's ID stored. Only then does the charger take the first reading and send the start of the transaction.

From “Six conditions before the start”, stop 04

Terms

  1. OCPPOpen Charge Point Protocol: the open protocol between a charger and its operator's backend.
  1. Is a CSMS the same as a CPMS?Yes, both name the operator's backend. OCPP 1.6 calls it the Central System, OCPP 2.0.1 and 2.1 the charging station management system (CSMS); CPMS is another name used in the industry.
  2. What is the difference between OCPP 1.6 and 2.0.1?OCPP 2.0.1 is not backward compatible with 1.6: transactions became configurable and unified, and the device model was added. OCPP 2.1 builds on 2.0.1 and keeps it compatible.
  3. How does a charger connect to the backend?The charger opens a WebSocket to its backend, announces itself and then checks in at a set interval. Commands from the backend travel over the same connection.
  4. How secure is OCPP?OCPP has three security profiles. Profile 2 adds TLS and a backend certificate, profile 3 certificates on both sides; profile 1 is not recommended for the field.
  1. Open Charge Alliance: Signed Meter Values (Eichrecht paper), version 1.0, February 2025. https://openchargealliance.org/wp-content/uploads/2025/05/signed_meter_values-v10-1.pdf. Checked 09 Oct 2026. Licence: CC BY-ND 4.0.
  2. Open Charge Alliance: Signed Meter Values (Eichrecht paper), version 1.0, February 2025. https://openchargealliance.org/wp-content/uploads/2025/05/signed_meter_values-v10-1.pdf. Checked 09 Oct 2026. Licence: CC BY-ND 4.0.