Forum OpenACS Q&A: Response to Suggest where or how to research OpenACS vs. other Web systems

Entity that initiates XML-RPC request.

Server is the entity that waits for XML-RPC requests initated by clients and responds to them.

Exactly the same as HTTP server and HTTP client. And yes, XML-RPC has exactly the same limitations as HTTP. XML-RPC is HTTP with different syntax (or rather it's a syntax and semantics for the payload of an HTTP request).