    Network Working Group                                           NIC 5739
    Request for Comments: 96                               Richard W. Watson
    Category: Informational                                          SRI-ARC
                                                            12 February 1971

    An Interactive Network Experiment to Study Modes of Access the Network
    Information Center

    1.   Introduction

         This NWG/RFC outlines the framework for a simple interactive
    experiment to study modes of access to the Network Information Center
    (NIC). A detailed specification for the initial access conventions to
    the NIC is contained in NWG/RFC 97, NIC (5740,). The initial online
    service to be provided by the Network Information Center are oriented
    around the SRI-ARC (ARC) Online System, typewriter version - NLS(T).
    These services will involve creation, manipulation, searching, and
    distribution of symbolic material (text initially). The initial Online
    System was display oriented and considerable development has gone into
    the study of features required for a comfortable interface to the user.
    In preparation for use with the Network Information Center, a typewriter
    oriented version has been developed. Assuming good computer response and
    a typewriter terminal operating at 30 char/sec, the system provides
    powerful and comfortable to use capabilities for handling structured
    textual material.

         The question to which the experiment, to be described below,
    addresses itself is to determine how to extend these capabilities
    through the network to users at remote sites, possibly operating 10
    char/sec and higher speed terminals through fairly heavily loaded
    systems. This experiment will also provide useful information about the
    interactive characteristics of the network, and guidelines for designers
    of other interactive systems to be used with the network. We propose
    that this experiment will be conducted with the assistance and
    cooperation of one other site. We estimate that the experiment will
    require about three calendar months. In order to minimize the resources
    required for the experiment, we will collect meaningful response time
    statistics that are easy to obtain with presetly existing metering
    facilities in the SRI and cooperating site systems, and network
    performance measuring facilities. We will not conduct formal
    productivity studies with the users of the connection, but will obtain
    their subjective impressions on use of the various connection modes. The
    result will be data indicating the costs and benefits obtained using the
    types of access described below. We would expect that this information
    would be useful to sites in determining how they want to implement
    access to the NIC and other interactive sites.

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    NETWORK WORKING GROUP           RFC #96                         NIC 5739

    During the period of the experiment, other sites will want to access the
    NIC as they come up on the network. We would recommend a simple
    approach, such as described in Section 2b, initially with a possible
    change later if the experiment indicates improved response and/or human
    factors coupling can be obtained with one of the other approaches,
    NWG/RFC 97, NIC (5740,) specifies this initial access approach in
    detail.

    2.   Getting Connected to the Network

       2a.   Introduction

            There are three basic approaches to allowing remote sites to
       connect to the NIC through the network, which we can call User
       Program Telnet, NLS(T) Front End, Monitor Telnet. Each of these is
       discussed below. Each approach requires code which will run in the
       remote host.

            We assume that standard conventions for Telnet programs will be
       specified by the Network Working Group. In the companion paper
       (NWG/RFC 97), NIC (5740,)) we include recommended conventions on
       solving those problems which we are aware exists relative to initial
       NIC access, although we have tried to specify conventions useful more
       generally. The NLS(T) Front End Program would interface to the Telnet
       Program.

            We assume that no matter which approach is taken, the software
       at the ARC end use the information obtained during the connection
       process to log-in the remote terminal under a general account and
       will place the terminal user in the NIC version of NLS, which we will
       call NLS(NIC) for short. The NLS(NIC) will ask the terminal user for
       his initials. The remote user then has access to all NIC facilities.

            The initial typewriter oriented system accepts commands of the
       general form:

       <command words> <operand> <delimiter> ... <operand> <delimiter>

            The <command words> is usually two words, the first to indicate
       a general operation class, and the second to indicate a general data
       structure type to be operated on. The <operand>s specify specific
       data entities to be operated upon, or instructions to adjust NLS
       parameters.

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    NETWORK WORKING GROUP           RFC #96                         NIC 5739

            The system at ARC is full duplex and allows the user to type the
       first character of the command words and the system immediately echos
       the remaining characters as feedback and support for the user. Other
       feedback is echoed where appropriate. The question we need to answer
       is what changes in this system will be required to suit it to the
       network and remote site constraints. We now look at problems existing
       at the remote sites.

            To gain connection to the NIC we assume that the user logs into
       his local system and calls up a subsystem or cusp. This subsystem or
       system program, Telnet program will be used to access other sites as
       well. The remote terminal and its controlling software system can
       operate in three basic modes as seen by the host subsystems

          Case 1 - Character at a time half duplex

          Case 2 - Character at a time full duplex

          Case 3 - Line at a time half duplex

            Although line at a time is full duplex is a logical possibility,
       no such approach is in general use and we ignore it in the following
       discussion.

       In the discussions to follow, in Section 2b, 2c and 2d, we describe
       the modes of access which we would like to investigate
       experimentally.  We want to study user reaction with 10 char/sec, 15
       char/sec, and 30 char/sec devices.

       2b.   User Program Telnet

            Consider the above classes of terminal in turn and the ways the
       Telnet program might handle communications between them and the NIC.
       The Telnet program might allow both full and half duplex
       communication as specified by the user.

          2b1.   Case 1 - Character at a Time Full Duplex

                The simplest approach would be for the Telnet program to
          take each character received from the terminal (except a special
          character or character sequence needed to escape back to the
          terminals host system), convert the code to ASCII and transmit it
          as a message to NLS(NIC). NLS(NIC) would handle all character
          echoing and transmit echo messages back to the Telnet for actual
          transmission to the terminal in the appropriate terminal code.
          This mode of communication involves full duplex transmission user
          to user and is probably the severest test of the interactive
          characteristics of the host-network-host system.

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    NETWORK WORKING GROUP           RFC #96                         NIC 5739

                Depending on loading at the remote host, on the network, and
          at ARC, round trip delay for simple character echoing may be
          several seconds. Experience in communication between the old ARC
          940 and a heavily loaded PDP-10 at Utah showed occasional delays
          on the order of 4 or 5 seconds and longer for single character
          echoing. Human factors considerations in use of NLS(NIC) indicate
          that such delays would be frustrating to the user. A more cageful
          study of this mode of communication should give a base against
          which to measure the other modes of communication.

          2b2.   Case 2 - Character at a Time Half Duplex

             There are two subcases which we treat identically:

             i) The Telnet program sees a half duplex terminal.

             ii) The Telnet program sees a full duplex terminal, but
             provides echoing so as to make the terminal half duplex as seen
             by NIC.

             With the character at a time half duplex case the NIC program
             will operate in two modes:

             a) short mode

             b) long mode

             In short mode the user will type in the command and receive on
             his terminal only the characters echoed by his system and the
             NIC response to the command.

             In long mode. the user will receive feedback from NIC at an
             appropriate point in the command. We want to see how novice and
             experienced users feel about working in these two modes, given
             the delays in the system response.

          2b3.   Case 3 - Line at a Time Half Duplex

             From the point of ciew of the NIC this case is essentially the
             same as Case 2.  From the point of ciew of the network this
             case is a more efficient use fo the network as the messages are
             longer.  This case is also more efficient for the user host
             system as it will require fewer calls to the Telnet subsystem;
             response for Case 3 may be better than Case 2.

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    NETWORK WORKING GROUP           RFC #96                         NIC 5739

       2c.   The NLS(T) Front End

               In this mode of communication, the subsystem which handles
          communication with the NIC is to perform some of the interactive
          and other tasks now performed by NLS(T). The type of tasks to be
          performed are echoing of the characters typed and the additional
          feedback characters for the full spell out of the command words,
          parsing of the command string, error handling where appropriate,
          and the sending of a parsed string as a message to NLS(T). If it
          should turn out that this mode of communication is the one
          preferred by sites, we would expect to supply an example version
          of the Front End program written in some language to serve as a
          model for implementation. The Network Working Group may want to
          give further study to a standard language for specifying such
          programs as indicated in NWG/RFC 51, NIC (4752,).

       2d.   Monitor Telnet

               Much of the response delay in the experiments of Section 2b
          is expected to result from the fact that the Telnet described
          there is a user program. We will run the experiments of Section 2b
          with the appropriate Telnet routines resident as a part of the
          user host monitor.

              [ This RFC was put into machine readable form for entry ]
              [ into the online RFC archives by Henrik Johansson 4/97 ]

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