RPC Data Flow
The flow of data from caller to callee and back again is illustrated in Figure 1. The calling program executes as a client process and the RPC runs on a remote server. All data movement between the client and the network and between the server and the network pass through XDR filter routines. In principle, any type of network transport can be used, but our discussion of implementation specifics centers on ONC RPC, which typically uses either Transmission Control Protocol routed by Internet Protocol (the familiar TCP/IP) or User Datagram Protocol also routed by Internet Protocol (the possibly not so familiar UDP/IP). Similarly, any type of data representation could be used, but our discussion focuses on XDR since it is the method used by ONC RPC.
Figure 1. RPC Data Flow