The act of binding a client to a service is not part of the remote procedure call specification. This important and necessary function is left up to some higher-level software. The software can use RPC itself. See rpcbind Protocol.
Implementers should think of the RPC protocol as the jump-subroutine (JSR) instruction of a network. The loader makes JSR useful, and the loader itself uses JSR to accomplish its task. Likewise, the network makes RPC useful, enabling RPC to accomplish this task.
The RPC protocol provides the fields necessary for a client to identify itself to a service and the reverse. Security and access control mechanisms can be built on top of the message authentication. Several different authentication protocols can be supported. A field in the RPC header specifies the protocol being used. You can find more information on authentication protocols in the section Record-Marking Standard.