ISO/IEC ISP 10612 is applicable to interworking units concerned with operating in the Open Systems Interconnection (OSI) Local Area Network environment. It specifies a combination of OSI standards that collectively provide a MAC relay function. This part of ISO/IEC ISP 10612 is applicable to interworking units operating between CSMA/CD LAN Subnetworks. ISO/IEC ISP 10612-1 specifies the relay function and LAN subnetwork-independent requirements, ISO/IEC ISP 10612-2 specifies the CSMA/CD LAN subnetwork-dependent requirements, and this part of ISO/IEC ISP 10612 defines profile RD51.51.