Simple Object Access Protocol (SOAP) is an XML-based protocol that lets you activate an application, or even an individual object or method within an application, across the Internet.

SOAP was developed by Microsoft, DevelopMentor, and Userland Software and has been proposed as a standard interface to the IETF(Internet Engineering Task Force).

SOAP is a way for a program running in one kind of operating system to communicate with a progam in the same or another kind of an operating system by using the World Wide Web's Hypertext Transfer Protocol (HTTP) and its Extensible Markup Language (XML) as the mechanisms for information exchange.

In SOAP there are several different types of messaging patterns, but by far the most common is the Remote Procedure Call (RPC) pattern, in which one network node (the client) sends a request message to another node (the server), and the server immediately sends a response message to the client.

A major design goal for SOAP is simplicity and extensibility.

A SOAP message always appears within an envelope.

The envelope can have a header, just like an HTML document would, but this is not required.

The message must have a body.The message content appears within the body.

RPC(Remote Procedure Call) is a protocol that allows a computer program running on one computer to cause a subroutine on another computer to be executed without the programmer explicitly coding the details for this interaction.

RPC is a powerful technique for constructing distributed, client-server based applications.
It is a client/server infrastructure that increases the interoperability, portability, and flexibility of an application by allowing the application to be distributed over multiple heterogeneous platforms.

Remote Procedure Call increases the flexibility of an architecture by allowing a client component of an application to employ a function call to access a server on a remote system. It allows the remote component to be accessed without knowledge of the network address or any other lower-level information. Most RPCs use a synchronous, request-reply ("call/wait") protocol which involves blocking of the client until the server fulfills its request.