Remote Procedure Call (SunRPC) protocol provides access to run procedures on remote machine. RPC is used heavily in UNIX to implement many protocols, for example NFS and NIS. RPC protocol is designed to be machine, operating system, network architecture, and transport protocol independent.
NFS: Network File System Protocol Specification
NFS Version 3 Protocol Specification
Binding Protocols for ONC RPC Version 2
RPCSEC_GSS Protocol Specification
Authentication Mechanisms for ONC RPC
XDR: External Data Representation Standard
RPC: Remote Procedure Call Protocol Specification Version 2