Network Working Group                                          R. Watson
Request for Comments: 592                                            SRI
NIC 20391                                                  November 1973

     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.

   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)

      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.

   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.

   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.