I was reading RFC6241 about netconf, where it's said about RPC as a messaging mechanism of the protocol. However, the spec defines XML for transmitting RPC messages, so I don't quite understand why this is still called RPC? I used to think of RPC as described in ONC RPC, i.e. there should be a stub function defined (as done by rpcgen on Unix) and so on, but what NETCONF says does not strictly follow this paradigm, rather it defines a mechanism to transmit parameters over wire.
Perhaps, I misunderstand RPC as a concept. Could anybody clarify RPC in netconf for me? Thanks,
The remote procedure call concept is simply an abstraction of a request-reply mechanism in a client-server communication model. A client sends a request to a (remote) server, waits for a response and upon receiving it continues execution based on information received. That is it. This is essentially what happens when you invoke a NETCONF operation.
The specification you quoted:
The ONC RPC protocol is based on the remote procedure call model, which is similar to the local procedure call model. In the local case, the caller places arguments to a procedure in some well- specified location (such as a register window). It then transfers control to the procedure, and eventually regains control. At that point, the results of the procedure are extracted from the well- specified location, and the caller continues execution.
The remote procedure call model is similar. One thread of control logically winds through two processes: the caller's process and a server's process. The caller first sends a call message to the server process and waits (blocks) for a reply message. The call message includes the procedure's parameters, and the reply message includes the procedure's results. Once the reply message is received, the results of the procedure are extracted, and the caller's execution is resumed.
and NETCONF specification say the same thing:
The NETCONF protocol uses a remote procedure call (RPC) paradigm. A client encodes an RPC in XML [W3C.REC-xml-20001006] and sends it to a server using a secure, connection-oriented session. The server responds with a reply encoded in XML. The contents of both the request and the response are fully described in XML DTDs or XML schemas, or both, allowing both parties to recognize the syntax constraints imposed on the exchange.
NETCONF uses an RPC-based communication paradigm. A client sends a series of one or more RPC request messages, which cause the server to respond with a corresponding series of RPC reply messages.
So does the Wikipedia page on RPC:
RPC is a kind of request–response protocol. An RPC is initiated by the client, which sends a request message to a known remote server to execute a specified procedure with supplied parameters. The remote server sends a response to the client, and the application continues its process. While the server is processing the call, the client is blocked (it waits until the server has finished processing before resuming execution), unless the client sends an asynchronous request to the server, such as an XHTTP call. There are many variations and subtleties in various implementations, resulting in a variety of different (incompatible) RPC protocols.
(better late than never, right?)