Stop 04 of 09 · A session in messages

Which messages make up one session?

About 7 min · 3 questions ·

Tuesday
The situation

A driver taps a card at connector 1. Twenty-eight minutes later the car leaves with 60 kWh more.

In the backend, the session is a short list of messages, each with a timestamp.

The questionWhich messages tell the story of one session?

One session, two versionsThe same story in different messages
OCPP 1.6One message per event.
  1. Authorizeis this card allowed?
  2. StartTransactionfirst meter value
  3. MeterValuesduring charging
  4. StopTransactionlast meter value
OCPP 2.0.1One message type for the whole transaction.
  1. Authorizeis this token allowed?
  2. TransactionEventStarted
  3. TransactionEventUpdated
  4. TransactionEventEnded

Message names as used in the Open Charge Alliance white papers. OCPP 2.0.1 unified all transaction-related messages.

Six conditions before the start

For a charger with a certified meter, the Open Charge Alliance describes six requirements for a session to start under 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.

How a session ends

The session ends when one of the start conditions is withdrawn: the cable is unplugged, the card is tapped again, a stop button is pressed, or the backend stops it remotely. The charger stops the energy, reads the last meter value and sends it with the end of the transaction.

From these messages, the backend builds the record of the session that later becomes the , see EV charging fundamentals, stop 05.

Check your understanding

3 questions. Answer all of them to complete this stop. Each answer explains itself.

01Question 1 of 3

In OCPP 1.6, which message carries the last meter reading of a session?

02Question 2 of 3

What changed for transactions in OCPP 2.0.1?

03Question 3 of 3

Which event can end a session?

Further in other paths

  1. OCPI and roaming · Stop 04How does a token reach the charger?Cached token lists or real-time authorisation: the four whitelist types of OCPI, and what each one means when the driver taps the card.
  2. OCPI and roaming · Stop 06How does a CDR settle a session?The charge detail record from session end to invoice: push or pull, signed meter data, and why a CDR is never deleted, only credited.
  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: 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.
  3. 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.
  4. 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.
  5. 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.
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