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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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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
      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
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      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
 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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          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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 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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/data/webs/external/dokuwiki/data/pages/rfc/rfc96.txt · Last modified: 1997/04/30 17:40 (external edit)