What does an OCPP message look like?

In OCPP 1.6 over JSON, a message is a short array: 2 for a call with an action name and payload, 3 for the result with the same id, 4 for an error. The deep dive reads a whole session of them.

Explained in

OCPP in depth · Deep diveOne session as raw OCPP messagesThe session of stops 04 and 05 as the backend logged it: every OCPP 1.6 message between charger and backend, in the JSON that travels over the WebSocket, read line by line.

Four habits make a log readable:

From “How to read a line”, stop 10

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 the common industry term.
  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.