ISO 18443:2016 Practice defines extensions to the SLE API in terms of:
a) the RCF-specific functionality provided by API components;
b) the RCF-specific interfaces provided by API components; and
c) the externally visible behavior associated with the RCF interfaces exported by the components.
It does not specify:
a) individual implementations or products;
b) the internal design of the components; and
c) the technology used for communications.
ISO 18443:2016 defines only interfaces and behavior that must be provided by implementations supporting the Return Channel Frames service in addition to the specification in reference .