ISO 18438:2013 is one of a family of documents specifying the SOIS-compliant services to be provided by onboard subnetworks.

ISO 18438:2013 defines services and service interfaces provided by the SOIS Subnetwork Test Service. Its scope is to specify the service only and not to specify methods of providing the service over a variety of onboard data links.

ISO 18438:2013 conforms to the principles set out in the Spacecraft Onboard Interface Services Green Book and is intended to be applied together with it. The protocols which provide this service are to be documented for individual links, and this may be in the purview of individual missions, agencies, or CCSDS, depending on future circumstance.