RFC 1057 (rfc1057) - Page 2 of 25

RPC: Remote Procedure Call Protocol specification: Version 2

RFC 1057            Remote Procedure Call, Version 2           June 1988


   particular hardware entity (host) or software entity (process or
   program) could operate in both roles at different times.  For
   example, a program that supplies remote execution service could also
   be a client of a network file service.  On the other hand, it may
   simplify software to separate client and server functionality into
   separate libraries or programs.

3. THE RPC MODEL

   The Sun 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 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 Sun 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



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