ISO 18444:2016 defines extensions to the SLE API in terms of:
a) the ROCF-specific functionality provided by API components;
b) the ROCF-specific interfaces provided by API components; and
c) the externally visible behavior associated with the ROCF 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 18444:2016 defines only interfaces and behavior that must be provided by implementations supporting the Return Operational Control Fields service in addition to the specification in reference .