Calypso is totally compliant with Java Card Operating System and Global Platform mechanisms for the downloading of applications.
Calypso as a software application (see Calypso Applet) can be downloaded in a customer media (card or more generally portable object such as SIM card for mobile phones, EMV credit cards, USB keys, etc.) with absolutely no modification in the Javacard operating system or Global Platform mechanisms. It is an absolute condition to ensure full interoperability: in an open system, the customer media issuance and the downloading of the Applet are realized by different entities: the only way to succeed is that both strictly respect the standards.
In the scope of the proposed solutions on the market, it is a real trick for the operators or transport authorities, because many, in fact, require some modifications in the operating system or of the Global Platform: consequently interoperability is impossible.
The following figure demonstrates this absolute respect of all standards by Calypso.