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+Network Working Group                                          R. Watson
+Request for Comments: 592                                            SRI
+NIC 20391                                                  November 1973
+
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+     Some Thoughts on System Design to Facilitate Resource Sharing
+
+INTRODUCTION
+
+   There is a growing interest in moving toward more resource sharing on
+   the ARPANET.  Some resource sharing has been taking place by having
+   systems open TELNET connections and generating user command strings.
+   I think that this is fine for experimental use, but is not the way we
+   want to operate in real usage.  What I believe network system
+   builders should do is to develop mechanisms appropriately designed
+   for computer-computer communication.
+
+SYSTEM INTERCONNECTION, AN APPROACH
+
+   The goal I would like to see us move toward is to view all systems on
+   the network as offering certain service modules, any subset of which
+   can be combined in building other systems.  Each service module would
+   have a well advertised set of primitive service capabilities that it
+   could provide.  It would have documented commands at the level of
+   present Telnet or FTP commands for gaining access to its services.
+   It would also have a defined network connection procedure.  Then any
+   system builder wanting to avail himself of these services could do so
+   and integrate them into his own user interface environment.
+
+   At the present time when a system is built, the system builders tend
+   to see it as a stand alone thing or at most something to be used
+   within a specific environment.  What I would like to see fostered is
+   the idea that any system built is not only a stand alone environment
+   but also a network service or set of services.  The builders would
+   define not only a user interface for their environment, but also a
+   set of primitives and primitive commands that can be accessed by
+   other systems around the network to get that service performed.
+
+      For example, we are redesigning the NLS Journal in light of our
+      experience and that of Network Mail as a set of protocols and
+      services.  If one looks at the processes of the NLS Journal one
+      can see a number of separate services that could be provided by
+      different network sites or combined in varying combinations by a
+      single site.  These being:
+
+         Distribution (identification of addressees and maintainance of
+         the required data bases being a related service), recording
+         (numbering and storing of items), cataloging, and retrieval.
+
+
+
+Watson                                                          [Page 1]
+
+RFC 592            System Design for Resource Sharing      November 1973
+
+
+   At the moment these services are fairly tightly interconnected in the
+   NLS Journal and what we want to do is to decouple them and define
+   their intercommunication by protocols that would allow them to be
+   distributed in different hosts on the network.  Mechanisms would also
+   be defined for the several hosts performing similar services around
+   the network to work together cooperatively.
+
+   As a further example, there are also other services that NLS could
+   probably provide such as structured file creation and manipulation;
+   information portrayal online or in hardcopy; database querying etc.
+   However, at the moment the system is not explicitly structured from
+   the point of view that outside systems could come into it anywhere
+   but at the human user interface even though internally it is quite
+   modular.  It would be straightforward for us to identify those NLS
+   services that other system builders might possibly be interested in
+   incorporating into their systems with their own user interface and
+   then to do the restructuring and primitive command definition
+   necessary.  Other groups building systems on the network could
+   perform a similar examination.
+
+   CCA, on the other hand as I understand it, has taken this point of
+   view from the beginning, namely building the Datacomputer on the
+   assumption that it is primarily a network resource and is to be used
+   by other systems.  BBN is also moving in this direction in the design
+   of Distributed TENEX.
+
+   There is nothing new in the above ideas; they come from generalizing
+   past successes we have all had with network protocol development and
+   with good software engineering practices.  It will, however, take a
+   change in the thinking of system designers, some concrete examples,
+   and ongoing dialog to make such a design philosophy the normal
+   network way of life.
+
+SOME FUNCTIONS READY FOR INTERCONNECTION
+
+   The area of dialog support may be the first area ripe to create such
+   a synthesis with the several systems in or coming into existence,
+   each solves part of the problem (with some overlap).  The dialog
+   support systems on the network known to me are:
+
+      The NLS Journal (supports recorded and cataloged dialog and linked
+      networks of documents and messages).
+
+      NLS Screen linking and splitting (supports close collaboration of
+      two or more people working together in real time in NLS)
+
+
+
+
+
+
+Watson                                                          [Page 2]
+
+RFC 592            System Design for Resource Sharing      November 1973
+
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+      The network wide linking of terminals through BBN's RSEXEC.
+
+      Tenex Sndmsg and Readmail and other mail systems support
+      nonrecorded dialog and further manipulation of received messages.
+      (Some interconnection between NLS and these facilities has been
+      established).
+
+      The communication system under design at USC-ISI to support a
+      range of message services.
+
+      The online conferencing system being built by Jim Calvin of Case,
+      John Iseli of Mitre and others supports online conferencing of
+      several members and has facilities to utilize various Tenex
+      subsystems such as TECO and NLS to support conferees.
+
+      The Hack system of CASE offers a bulletin board service.
+
+      The Forum system of IFF supports online and distributed in time
+      conferencing and other features.
+
+   Other areas possibly ripe for synthesis are 1) file and data
+   management, and information retrieval services; 2) editing and
+   hardcopy portrayal with systems like Tenex RUNOFF, SU-AI's PUB and
+   SRI-ARC's Output Processor.
+
+   If the salient service features, concepts, goals of each could be
+   defined clearly and appropriate service primitives, as per other
+   ARPANET protocols, could be defined for each, anyone wishing to
+   incorporate that service with a user interface appropriate to his
+   environment or philosophy could do so.
+
+SYSTEM INTERCONNECTION ISSUES RELATED TO THE ABOVE PROPOSAL
+
+   There are many detailed issues related to system interconnection as
+   proposed above.  A number seem worth mentioning here.
+
+
+   1) Types of Network Connections
+
+      The number and type of network connections to be opened between
+      classes of cooperating processes can probably be systematized.
+      One of the important elements of the FTP and Graphics protocol
+      efforts was to define the number and type of connections necessary
+      for these classes of transaction.  Similar classification and
+      connection definition will be required for other types of
+      processes.
+
+
+
+
+
+Watson                                                          [Page 3]
+
+RFC 592            System Design for Resource Sharing      November 1973
+
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+   2) Data Structure Translation
+
+      The whole area of translation and transfer of data structures more
+      complicated than sequential files needs vigorous thought and
+      protocol development.
+
+         Systems built around sequential files are presently dominant on
+         the ARPANET and provide a base for simple useful economical
+         tools.  I, however, do not believe that the longer run tool
+         sharing can depend on communication between sequential files,
+         but requires structured files.  Experience with NLS tree
+         structured files shows that even this level of structuring may
+         be inadequate for many uses and more sophistication may be
+         required.  A similar trend exists in work with computer
+         graphics and generalized data management systems.  Developing
+         protocols for handling structured data bases or agreement on
+         common structuring characteristics seems an important need.
+
+   3) Responsiveness
+
+      Factors influencing responsiveness to users in an environment of
+      heavy geographically separated resource sharing need determination
+      and discussion.
+
+   4) Documentation of System Interfaces
+
+      It is probably reasonably straightforward to define service
+      interfaces, but they will be useless unless their activating
+      command languages and other conventions are well documented and
+      this documentation is kept up to date.
+
+   5) Accounting
+
+      A very difficult problem once you interconnect systems at lower
+      levels is to design an appropriate network accounting and banking
+      system that will not cause undue delays in accessing distributed
+      resources.
+
+   6) Error Handling
+
+      We need to develop mechanisms for passing error signals around
+      when system environments are crossing machine boundaries.
+
+   7) Standard Parameter Formats
+
+      Data types such as strings, integers, floating point numbers,
+      arrays, pointers, etc. need to have standard representations
+      defined for passing parameters back and forth between machines.
+
+
+
+Watson                                                          [Page 4]
+
+RFC 592            System Design for Resource Sharing      November 1973
+
+
+   8) HELP at the Procedure Call Level
+
+      A HELP mechanism needs to be defined in the protocols to provide
+      information that each designer can translate to his user
+      interface.  Standards for requesting HELP information and
+      structuring HELP data bases needs agreement.
+
+ACKNOWLEDGEMENT
+
+   I wish to acknowledge the useful suggestions of Charles Irby and Jim
+   White in the thoughts above.
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+Watson                                                          [Page 5]
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