RFC 62 (rfc62) - Page 2 of 20

Systems for Interprocess Communication in a Resource Sharing Computer Network

RFC 62                  IPC for Resource Sharing          3 August 1970


   permit communication between remote processes.  The second part of
   the study presents such a generalization.  The application of this
   generalized system to the ARPA Computer Network [9] is also
   discussed.

   The ideas enlarged upon in this paper came from many sources.
   Particularly influential were -- 1) an early sketch of a Host
   protocol for the ARPA Network by S. Crocker of UCLA and W. Crowther
   of Bolt Beranek and Newman Inc. (BBN); 2) Ackerman and Plummer's
   paper on the MIT PDP-1 time-sharing system [1]; and 3) discussions
   with W. Crowther and R. Kahn of BBN about Host protocol, flow
   control, and message routing for the ARPA Network.  Hopefully, there
   are also some original ideas in this note.  I alone am responsible
   for the collection of all of these ideas into the system described
   herein, and I am therefore responsible for any inconsistencies or
   bugs in the system.

   It must be emphasized that this paper does not represent an official
   BBN position on Host protocol for the ARPA Computer Network.


2.  A System for Interprocess Communication within a Time-Sharing System

   This section describes a set of operations enabling interprocess
   communication within a time-sharing system.  Following the notation
   of [10], I call this interprocess communication facility an IPC.  As
   an aid to the presentation of this IPC, a model for a time-sharing
   system is described; this model is then used to illustrate the use of
   the interprocess communication operations.

   The model time-sharing has two pieces: the monitor and the processes.
   The monitor performs such functions as switching control from one
   process to another process when a process has used "enough" time,
   fielding hardware interrupts, managing core and the swapping medium,
   controlling the passing of control from one process to another (i.e.,
   protection mechanisms), creating processes,caring for sleeping
   processes, and providing to the processes a set of machine extending
   operations (often called Supervisor or Monitor Calls).  The processes
   perform the normal user functions (user processes) as well as the
   functions usually thought of as being supervisor functions in a
   time-sharing system (systems processes) but not performed by the
   monitor in the current model.  A typical system process is the disc
   handler or the file system.  System processes is the disc handler or
   the file system.  System processes are probably allowed to execute in
   supervisor mode, and they actually execute I/O instructions and
   perform other privileged operations that user processes are not
   allowed to perform.  In all other ways, user and system processes are
   identical.  For reasons of efficiency, it may be useful to think of



Walden