Which protocol enables a program on one computer to execute a program on a server computer?

• A. FTP
• B. HTTP
• C. SOAP
• D. SMTP

Answer: (C)

Remote procedure invocation is what this question targets. SOAP is designed specifically to let a client request a server to run a defined operation and return the result. It does this by sending an XML-encoded message that describes the method to call and its parameters, wrapped in a SOAP envelope, typically carried over HTTP. The server processes the request, executes the specified function, and replies with the result in another XML message. This makes SOAP well-suited for enabling one computer to cause a server to execute code on behalf of the client.

FTP is about moving files, not running server-side code. HTTP simply transfers resources and doesn’t by itself define a mechanism for invoking remote functions, though it often carries SOAP or other RPC payloads. SMTP is for email and isn’t used for remote procedure calls.