OCPP gets a charger talking to your CSMS. It has nothing to say about what happens when a driver on your app pulls up to a charger that belongs to a completely different network. That's a different protocol solving a different problem - the Open Charge Point Interface, or OCPI - and it's what makes EV roaming work.
OCPP vs. OCPI - two protocols, two jobs
OCPP is the connection between a charger and the CSMS that operates it - start a session, report status, send meter values. OCPI is the connection between two platforms: your CSMS and a roaming partner's CSMS (or a roaming hub sitting between many of them). Where OCPP asks “how do I talk to this charger,” OCPI asks “how do I let a driver from a different network charge here, and how do I charge on theirs.”
The two roles in a roaming relationship
- CPO (Charge Point Operator) - the party that owns and operates the physical chargers. Publishes station locations, availability and tariffs over OCPI so other networks' apps can find and use them.
- eMSP (e-Mobility Service Provider) - the party with the driver relationship, typically through a branded app. Looks up a CPO's stations over OCPI, authorizes a session on the driver's behalf, and bills the driver.
A single business is often both at once: a CPO for its own stations, and an eMSP for its own branded app, so its drivers can charge on other networks and other networks' drivers can charge on its stations - all without either side building a direct, custom integration with the other.
How a roaming session actually works
A simplified version of what happens when a driver starts a session on a partner's charger:
- The driver's app (their eMSP) shows a station published by the host network (the CPO) over OCPI.
- The driver starts a session; the eMSP sends an authorization request to the CPO over OCPI.
- The CPO authorizes it and starts the session on the physical charger, over OCPP, exactly as it would for one of its own drivers.
- Session data - energy delivered, duration, cost - flows back to the eMSP over OCPI so it can bill its driver and settle with the CPO.
Bilateral connections between every pair of networks don't scale, so most roaming today happens through a roaming hub - a single OCPI connection to the hub gives a network reach to every other network already connected to it, instead of negotiating and maintaining a separate integration per partner.
Why roaming matters for a white-label network
For an enterprise or CPO running a branded network, roaming solves a real gap: your own footprint of stations will never cover everywhere a driver wants to charge. Turning on OCPI roaming lets your branded app show and bill for charging at partner stations - your driver never has to leave your app - and lets drivers from other networks find and pay to use your stations, adding a revenue stream from hardware you've already deployed. CarChargeOS supports OCPI 2.2.1 as part of the platform, offered as part of the Operator and Enterprise tiers on the pricing page.
What to check before turning on roaming
- Settlement and reconciliation. Roaming sessions create a financial relationship between two businesses - confirm how payouts and reconciliation between CPO and eMSP are handled, not just the technical connection.
- Tariff consistency. A driver roaming onto your network sees your published tariff, not their home network's - make sure pricing is actually set up to be shown to an unfamiliar driver, not just your own.
- OCPI version compatibility. Roaming partners and hubs need to speak the same OCPI version - 2.2.1 is the current standard most active hubs support.
- Branded app experience. Confirm whether partner-network stations appear in your app the same way your own stations do, so the roaming relationship stays invisible to your driver.
Frequently asked questions
Do I need OCPI if I only operate my own stations?
Not to run your own network - OCPP alone covers connecting and operating your chargers. OCPI is specifically for extending reach beyond your own hardware, either by letting your drivers use other networks or by opening your stations to theirs.
Is OCPI the same as a roaming hub?
No - OCPI is the protocol; a roaming hub is a service that uses it to connect many networks together through one integration each, instead of every network integrating with every other network directly.
Can a driver tell they're charging on a partner network?
Not necessarily - a well-implemented roaming setup shows partner stations inside the same branded app the driver already uses, with the same start/stop/pay flow, so the roaming relationship is invisible to them.