TCP/IP Services includes a standard C sockets API and a standard
    Open Network Computing Remote Procedure Call (ONC RPC) API.

    The standard C socket API provides UNIX-style access to the TCP
    and UDP transports and to the IP network layer.

    The ONC RPC library provides a method of creating communicating
    programs without the need to program the details of the transport
    protocol being used. The ONC RPC library is divided into calls
    frequently used by client programs, calls used to access the
    Portmapper utility, and calls frequently used by server programs.
    The ONC RPC library also includes XDR routines which provide
    the ability to transport data over the network in a standard
    fashion.