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A remote procedure call (RPC) is a protocol that allows a computer program running on one host to cause code to be executed on another host without the programmer needing to explicitly code for this. When the code in question is written using object-oriented principles, RPC is sometimes referred to as remote invocation or remote method invocation.
RPC is an easy and popular paradigm for implementing the client-server model of distributed computing. An RPC is initiated by the caller (client) sending a request message to a remote system (the server) to execute a certain procedure using arguments supplied. A result message is returned to the caller. There are many variations and subtleties in various implementations, resulting in a variety of different (incompatible) RPC protocols.
In order to allow servers to be accessed by differing clients, a number of standardized RPC systems have been created. Most of these use an interface description language (IDL) to allow various platforms to call the RPC. Examples of such systems include Sun RPC (sometimes called ONC RPC), the Distributed Computing Environment (DCE), Microsoft's DCOM (and ActiveX), which is based in part on DCE, and CORBA.
Recently a number of vendors have started using XML as the IDL, and HTTP as the network protocol. The advantage of this system, known as web services, is simplicity and standardization, the IDL is a text file that is widely understood, and HTTP is built into almost all modern operating systems. An example of such an RPC system is SOAP, developed in turn from XML-RPC.
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