Roaming protocols: OCPI, OICP, OCHP and eMIP

An open parking lot with several electric vhicle chargers

Roaming allows drivers to charge electric vehicles at public charge stations via the network of their mobility service provider (EMSP).

To facilitate roaming, EMSPs enter into agreements with charge point operators (CPOs) and implement a communication system based on open protocols.

Protocols are a set of rules that standardise communication between networks and software platforms. Roaming protocols support a range of functionalities, most importantly authorisation. CPOs and EMSPs can also use protocols to exchange charge point and tariff information as well as offer advanced features like app-based start and stop of charging sessions.

In the European EV market, four main roaming protocols are currently in use: OCPI, OICP, OCHP, and eMIP.


The Open Charge Point Interface protocol (OCPI) was developed by eViolin, an association of Dutch charge point operators and mobility service providers, in collaboration with ElaadNL, a group of major Dutch grid operators. OCPI is currently managed and maintained by the EVRoaming Foundation.

The OCPI protocol supports a wide range of use cases, such as:

  • Providing charge point information
  • Authorising charge sessions
  • Sharing tariff information
  • Enable app-based charging

OCPI supports both peer-to-peer (P2P) and roaming hub connections. In P2P roaming, CPOs and EMSPs have direct bilateral connections via which they exchange data. Meanwhile, in hub-based roaming, a charge point operator or mobility service provider can access many roaming partners via a single, standardised connection.

OCPI is the only protocol with a smart charging module, allowing drivers to choose whether they want to charge as cheaply or as fast as possible or optimise for the use of green energy.

While the module is not widely used yet, at GreenFlux we expect this to change as smart charging becomes increasingly important to stabilise the grid, and further smart charging use cases are built out.

Currently, OCPI is the most widely used roaming protocol in Europe thanks to its broad feature range and highly open approach to development.


The Open Intercharge Protocol (OICP) was developed by Hubject, a group of German automotive and energy companies, in 2012. Along with OICP, Hubject also offers an ad-hoc payment solution and a contractual framework for EV roaming.

The OICP protocol supports a range of use cases, such as:

  • Roaming via the Hubject hub
  • Ad-hoc payments
  • Authorisations
  • Real-time exchange of charge point information
  • Billing and reservations

Along with OCPI, OICP is one of the two roaming protocols that facilitates the exchange of signed meter data. Signed meter data confirms the amount of electricity provided to an EV during charging, and thereby helps charge point operators conform to German calibration law requirements (Eichrecht). This is invaluable to companies operating in the German market.

OICP connects hundreds of companies across Europe and is widely used in the DACH market.

Table 1: Comparison of roaming protocols

Hub roaming
P2P roaming
Providing charge point information
Charge point search module
Authorising charge sessions
Remote start and stop
Providing session information
Ad-hoc payments
Smart charging support
Calibration law (Eichrecht) support
Platform monitoring


The Open Clearing House Protocol (OCHP) was developed by SmartLab Innovationsgesellschaft GmbH and ElaadNL, and is managed by the roaming hub

OCHP facilitates hub-based roaming with features like:

  • Authorisation
  • Billing
  • Providing charge point and sessions information
  • Remote start-and stop

The extension OCHP-Direct allows CPOs and EMSPs to make use of the same functionality via a peer-to-peer connection.

OCHP relies mainly on asynchronous, as opposed to real-time, communication. For example, it creates so-called ‘white lists’ of users, instead of authenticating them in real-time based information from the EMSP. This means that even if the roaming hub were to ever go down, charge sessions would still work, as a single point of failure is avoided.


The eMobility Interoperation Protocol (eMIP) is designed and managed by GIREVE, an integrated platform founded by EDF, Renault, CNR, and Caisse des Dépôts. It is most widely used in France.

EMIP supports both roaming via the GIREVE platform and peer-to-peer connections, with functionalities including:

Providing charge point and session information

  • Authorisation
  • Billing
  • Platform monitoring

eMIP lets CPOs and EMSPs add any sort of data messages or identification methods, thus allowing new features to be implemented quickly, without the need for repeat protocol version updates.

Also, eMIP is the only protocol that supports a charge point search module, which allows EMSPs to retrieve a list of charge points located in a given geographic area and fulfilling a set of charging criteria (e.g. connector type).

woman charging her car

GreenFlux has developed a similar capability that allows EMSP customers to retrieve charge point information via our whitelabel ChargeAssist App and Charge Assist API.

GreenFlux roaming offering

GreenFlux supports the OCPI and OICP protocols to provide the best experience for charge point operators and mobility service providers. As e-clearing and Gireve both support OCPI, this means the GreenFlux platform supports all major roaming hubs without needing to support all protocols.

With our roaming-as-a-service packages, GreenFlux not only creates and maintains the technical connections required for roaming but also negotiates contracts and provides a settlement service to help manage this complex roaming ecosystem. This means new EMSP customers can instantly access a network of more than 200,000 charge stations, while new CPO clients can connect to nearly every charge card in Europe and beyond with the click of a button.