This International Standard is one of a family of documents specifying the SOIS-compliant services to be provided by onboard subnetworks. This International Standard 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. This International Standard 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. The scope and field of application are furthermore detailed in subclause 1.2 of the enclosed CCSDS publication.