Note on Interprocess Communication in a Resource Sharing Computer Network
RFC 61

Document Type RFC - Unknown (July 1970; No errata)
Obsoleted by RFC 62
Last updated 2013-03-02
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Network Working Group                                        Dave Walden
Request for Comments: 61                         Bolt Beranek and Newman
                                                           July 17, 1970

                  A Note on Interprocess Communication
                in a Resource Sharing Computer Network

   The attached note is a draft of a study I am still working on.  It
   may be of general interest to network participants.

Walden                                                          [Page 1]
RFC 61      Interprocess Communication in a Computer Network   July 1970

                        Interprocess Communication
                                   in a
                     Resource Sharing Computer Network


   "A resource sharing computer network is defined to be a set of
   autonomous, independent computer systems, interconnected so as to
   permit each computer system to utilize all of the resources of each
   other computer system.  That is, a program running in one computer
   system should be able to call on the resources of the other computer
   systems much as it would normally call a subroutine."  This
   definition of a network and the desirability of such a network is
   expounded upon by Roberts and Wessler in [1].

   The actual act of resource sharing can be performed in two ways: in a
   pairwise ad hoc manner between all pairs of computer systems in the
   network or according to a systematic network wide standard.  This
   paper develops one possible network wide system for resource sharing.

   I believe it is natural to think of resources as being associated
   with processes [2] and therefore view the fundamental problem of
   resource sharing to be the problem of interprocess communication.  I
   also share with Carr, Crocker, and Cerf [3] the view that
   interprocess communication over a network is a subcase of general
   interprocess communication in a multiprogrammed environment.

   These views pervade this study and have led to a two part study.
   First, a model for a time-sharing system having capabilities
   particularly suitable for enabling interprocess communication is
   constructed.  Next, it is shown that these capabilities can be easily
   used in a generalized manner which permits interprocess communication
   between processes distributed over a computer network.

   This note contains ideas based on many sources.  Particularly
   influential were -- 1) an early sketch of a Host protocol for the
   ARPA Network [1][3][4] by W. Crowther of Bolt Beranek and Newman Inc.
   (BBN) and S. Crocker of UCLA; 2) Ackerman and Plummer's paper on the
   MIT PDP-1 time sharing system [5]; and 3) discussion with R. Kahn of
   BBN about Host protocol, message control, and 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 this system.

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

Walden                                                          [Page 2]
RFC 61      Interprocess Communication in a Computer Network   July 1970


   This section describes a model time-sharing system which I think is
   particularly suitable for performing interprocess communication.  The
   basic structure of this model time-sharing system is not original

   The model time-sharing system has two pieces: the monitor and the
   processes.  The monitor performs several functions, including
   switching control from process to process as appropriate (e.g., when
   a process has used "enough" time or when an interrupt occurs),
   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, etc.

   The processes perform most of the functions normally thought of as
   being supervisor functions in a time-sharing system (system
   processes) as well as the normal user functions (user processes).  A
   typical system process is the disc handler or the file system.  For
   efficiency reasons it may be useful to think of system processes as
   being locked in core.

   A process can call on the monitor to perform several functions: start
   another, equal, autonomous process (i.e., load a program or find a
   copy of a program somewhere that can be shared, start it, and pass it
   some initial parameters); halt the running process; put the current
   process to sleep pending a specified event; send a message to a
   specified process; become available to receive a message from a
   specified process; become available to receive a message from any
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