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Network Working Group                                          R. WatsonRequest for Comments: 592                                            SRINIC 20391                                                  November 1973Some Thoughts on System Design to Facilitate Resource SharingINTRODUCTION   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      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   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.Watson                                                          [Page 5]