What is a CSMS?

A Charging Station Management System (CSMS) is the backend that communicates with and controls EV chargers. In OCPP terminology, this is called the Central System.

Core Responsibilities

Function	Description
Connection Management	Accept and maintain WebSocket connections from chargers
Authorization	Validate RFID tokens and decide whether charging can start
Transaction Tracking	Record start/stop events, meter readings, and session data
Remote Control	Send commands to chargers (start/stop, reset, configuration)
Smart Charging	Set power limits and schedules to manage load
Firmware & Diagnostics	Push updates and retrieve logs from chargers

System Architecture

Communication Model

OCPP uses a request/response pattern over WebSocket:

• Charger-initiated: The charger sends a request, CSMS responds

  • BootNotification - charger coming online
  • StartTransaction - charging session beginning
  • StatusNotification - state changes

• CSMS-initiated: The CSMS sends a request, charger responds

  • RemoteStartTransaction - command to start charging
  • SetChargingProfile - apply power limits
  • Reset - reboot the charger

Each message has a unique ID. The responder echoes this ID in the response.

Key Design Considerations

Reliability

• Chargers queue messages when offline
• CSMS must handle out-of-order delivery
• Transaction data is idempotent (same transactionId = same session)

Scalability

• Each charger maintains one persistent WebSocket
• Connection count = charger count
• Message volume scales with transaction frequency

Security

• TLS for transport encryption
• Optional: client certificates for charger authentication
• Authorization tokens validated per transaction

OCPP Versions

Version	Transport	Notes
1.6-J	WebSocket + JSON	Most widely deployed
1.6-S	SOAP	Legacy, less common
2.0.1	WebSocket + JSON	Newer features, growing adoption

GridLink implements OCPP 1.6-J. See the OCPP 1.6 Specification for protocol details.