RPC uses the client-server model. The program requesting is a client and a server provides the program. RPC works as a synchronous operation and the requesting program is suspended until the client receives an answer from the server with the remote procedure answer.

Using threads we can simultanously do multiple calls from client to server doing different requests.

There are different options about for legacy modernization - each of them with advantages and disadvatanges.

• When program statements that use RPC framework are compiled into an executable program, a stub is included in the compiled code that acts as the representative of the remote procedure code. When the program is run and the procedure call is issued, the stub receives the request and forwards it to a client runtime program in the local computer.
• Middleware is computer software that provides services to software applications beyond those available from the operating system.
• It connects two or more software applications enabling communications and procedures among them. The term is most commonly used for software that enables communication and management of data in distributed applications

Several different technologies support remote procedure calls - Java RMI - DCOM - CORBA - Web Services - .NET Remoting