Anatomy of a charging session

A charging session runs through several steps, from identifying the driver to settling the payment. This page walks through each one and the protocol that carries it.

1. The driver identifies themselves

The driver presents a token: an RFID card tapped on the reader, a button in an app, an auto-charge trigger, or Plug & Charge where the car itself identifies over ISO 15118. Either way the charging station now has a token and a request to start.

2. Authorisation

The charging station asks its management system whether this token may charge, over OCPP (an Authorize request, or the identifier carried on the transaction start). Two cases:

• On-network. The token belongs to the operator's own drivers, so the CPMS decides directly.
• Roaming. The token belongs to another provider, so the CPO asks that eMSP in real time and gets a yes or no in a few hundred milliseconds. This usually runs over OCPI (a token authorization), though other roaming protocols exist too.

Only after a yes does energy flow.

3. The session runs

A transaction opens on the charging station and the meter starts. The charging station streams meter values (energy, sometimes power and other readings) to the management system throughout, over OCPP. The applicable tariff is tracked against those readings so the running cost is always current, not estimated afterwards. During a roaming session the CPO can also publish a live Session object to the eMSP over OCPI so the driver's app can show progress.

4. The session ends

The driver stops the charge or unplugs, the transaction closes, and the charging station reports the final energy delivered and duration.

5. The billable record (CDR)

The session is turned into a Charge Detail Record (CDR): the authoritative, final record of what was delivered and what it cost. For a roaming session the CPO sends the CDR to the eMSP over OCPI. A CDR is immutable once sent; a correction is issued as a separate credit CDR rather than an edit. The CDR, not the live session, is what money is based on.

6. Settlement

Finally the money moves. Across roaming, the CPO and eMSP settle with each other on the exchanged CDRs. The eMSP bills the driver according to the price it set, which need not match what it paid the CPO. A platform in the middle reconciles all of this: what the driver paid, what the operator earns, and what clears between parties.

When a session does not count

Not every transaction becomes a clean, billable CDR. Sessions can be excluded or flagged for reasons such as a failed or unauthorised start, a simulated or test session, a duplicate, fraud checks, or data-integrity problems. Reconciliation has to account for these so the books balance, which is why a real platform tracks exclusion reasons explicitly rather than assuming every plug-in is a sale.