RFC 1831 (rfc1831) - Page 3 of 18

RPC: Remote Procedure Call Protocol Specification Version 2

RFC 1831        Remote Procedure Call Protocol Version 2     August 1995


   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 process 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 caller's
   execution is resumed.

   On the server side, a process is dormant awaiting the arrival of a
   call message.  When one arrives, the server process extracts the
   procedure's parameters, computes the results, sends a reply message,
   and then awaits the next call message.

   In this model, only one of the two processes is active at any given
   time.  However, this model is only given as an example.  The ONC RPC
   protocol makes no restrictions on the concurrency model implemented,
   and others are possible.  For example, an implementation may choose
   to have RPC calls be asynchronous, so that the client may do useful
   work while waiting for the reply from the server.  Another
   possibility is to have the server create a separate task to process
   an incoming call, so that the original server can be free to receive
   other requests.

   There are a few important ways in which remote procedure calls differ
   from local procedure calls:

      1. Error handling: failures of the remote server or network must
      be handled when using remote procedure calls.

      2. Global variables and side-effects: since the server does not
      have access to the client's address space, hidden arguments cannot
      be passed as global variables or returned as side effects.

      3. Performance:  remote procedures usually operate one or more
      orders of magnitude slower than local procedure calls.

      4. Authentication: since remote procedure calls can be transported
      over unsecured networks, authentication may be necessary.
      Authentication prevents one entity from masquerading as some other
      entity.

   The conclusion is that even though there are tools to automatically
   generate client and server libraries for a given service, protocols
   must still be designed carefully.






Srinivasan                  Standards Track