Applies to interworking units concerned with operating in the Open Systems Interconnection (OSI) environment. Provides a combination of OSI base standards that collectively supply a network-relay function for the connectionless-mode Network Service. Defines the RA53.1121 profile, which applies to interworking units operating between Token Ring LAN subnetworks and PSDNs using virtual calls over a digital data circuit/CSDN leased line permanent access.