OpenTP1's remote system can be an OpenTP1 system or an XDM (XDM/DF/TP) system. When OSI TP communication is used, a transaction started at the local system's OpenTP1 can be extended to the remote system even if the remote system is not an OpenTP1 system.

APIs with the XATMI interface are used for client/server communication under OSI TP. For details about the XATMI interface, see 3.2.4 Communication via RPCs that use the XATMI interface.