rfc1709.txt

来自「著名的RFC文档,其中有一些文档是已经翻译成中文的的.」· 文本 代码 · 共 1,371 行 · 第 1/5 页

ISN Working Group                                               [Page 5]

RFC 1709            K-12 Internetworking Guidelines        November 1994


Approach

   The implementation we suggest would use current proven and cost
   effective technology and would be expandable and upgradable to newer
   technology with minimum additional investment.  This approach
   requires careful, modular design to meet the following criteria:

   1) Any physical infrastructure development should be general and
      flexible enough to be reused as technology improves.  For
      example, a school office might have a simple terminal today
      which could be wired to a network adapter serving the school
      building.  Later a Macintosh, DOS, or Windows-based PC might
      replace the terminal, and the type of connection to the network
      would change accordingly.  However, the wiring between the
      office and the network "hub" site could remain the same if it
      is designed properly to begin with.  This is an important
      consideration since wiring typically represents 20 to 40% of
      the cost of individual network hookups;

   2) Existing computers and terminals in schools and district
      offices should be integrated as much as possible into the
      communication system.  This installed base represents a large
      investment, albeit in many cases a somewhat dated set of
      equipment.  Wholesale replacement of that base would be a
      large additional burden on funding resources.

      A consequence of the above is that the user interface and the
      services available will vary depending on the type of equipment
      used to access the network.  For example, DOS PCs, Macintosh
      computers, or Unix workstations would be connected directly to
      Local Area Networks (LANs) and would be provided with
      communications software to support a broad set of functions,
      many of which will have graphical user interfaces and will make
      use of client/server technology.  Apple-II computers, "dumb"
      terminals, or other such devices could be connected to
      intelligent network hubs that would allow access to network
      server computers or information resources, but almost certainly
      will not support the full range of functionality provided by a
      direct network connection.  In the short term, this is a
      limitation that we must accept;

   3) Network servers will be located where they can be managed and
      supported, and also provide access paths with adequate
      bandwidth.  A system of hierarchical servers should be created
      in larger school districts, with automatic transfer of common
      information from a central system to the secondary systems each
      night, or at appropriate intervals.  Local servers will allow
      each school to provide on-line information particular to its



ISN Working Group                                               [Page 6]

RFC 1709            K-12 Internetworking Guidelines        November 1994


      programs and community.  This model optimizes use of network
      bandwidth as well;

   4) School interconnect topologies (links) must be both cost
      effective and manageable.  Communication between schools,
      district offices, county offices of education, and the State
      Department of Education must be reliable and of sufficient
      capacity to support the primary applications as well as allow
      development of new applications.

      Capacity is measured both by total data traffic volume and by
      response time when information is requested over the network.
      Reliability is measured by the percentage of time that the
      network is able to transport data.  Reliability should be well
      over 99.7%.  Capacity should be such that no more than 10% of
      the communications bandwidth is used during a typical work day.
      This is intended to leave adequate capacity for good response
      time to short term communication demands.

      Many schools already have some form of communications
      infrastructure in place.  In some cases this infrastructure can
      be adapted to newer technologies; in other cases it may have to
      be replaced over time.  These issues are explored further
      following presentation of the basic model that serves as a
      guideline for future communications system development.

Implementation Model

   There is no one "blueprint" for a network that will drop into every
   school.  Each school will have particular physical constraints,
   functional needs, an existing technology base, funding constraints,
   and opportunities for collaboration with vendors and support groups
   in its area.  What is presented here is a set of general guidelines
   that can be followed in the planning of a school network
   implementation.

   The strategic decision to use Internet protocols in developing school
   networks provides the opportunity to avoid the major expense of
   building new statewide backbone infrastructures in the near term.
   Interconnection of schools, districts, county offices of education
   and the State Department of Education can be accomplished by
   acquiring Internet connection service from any of the existing
   Internet service providers in the state.  ("Connecting to the
   Internet", Susan Estrada, O'Reilly & Associates, Inc. (ISBN 1-56592-
   061-9) lists Internet service providers in California and the
   nation.)  It is critical that Internet connection service meet
   criteria for reliability and capacity but connection to any Internet
   service provider will provide communication capability to all other



ISN Working Group                                               [Page 7]

RFC 1709            K-12 Internetworking Guidelines        November 1994


   Internet subscribers within the state, the nation, and the world.

   Internet technology is designed to allow very flexible intersite
   topologies, but a hierarchical topology is the simplest to engineer.
   Generally this will mean hierarchical connection of school facilities
   to district offices, in many cases further aggregated at county
   offices, and finally a link to an Internet service provider.
   Coordination of circuit services and a single point of connection to
   an Internet service provider serves both to minimize overall costs
   and increase opportunities to make use of newer technologies.

   The basic school network implementation model is quite simple: create
   a local area network (LAN) within each school building or cluster of
   buildings, provide at least one network server for that LAN,
   interconnect that LAN with the local school district offices where a
   similar LAN should be installed and where centrally managed
   information resources should exist, and connect the district offices
   to the nearest Internet service provider, possibly through the county
   office of education.

   Primary technical support for network monitoring and problem
   resolution, and for managing network resource servers should come
   from the district or county offices initially to avoid unnecessary
   duplication at the local level.  As expertise is developed at the
   local level, more of the responsibility for daily operation and
   problem resolution can be assumed by individual schools.

   It is impossible to cover all conceivable scenarios for
   implementation of this model in specific schools.  However, it is
   possible to state general principles that should be followed in
   designing school network implementations.  The discussion below is
   organized into sections corresponding to the basic model summarized
   in the previous paragraph.  It includes a description of the general
   principles that are important to each level of the implementation.

Step 1: School Local Area Network Implementation

   A "school" is used here to mean a building or cluster of buildings
   that are managed as a unit and typically are on contiguous, district
   owned property.  Implementation of a LAN in this setting will involve
   installation of a cabling system to distribute the network throughout
   the structure(s), installation of premise wiring to support
   connections of computers and terminals to the network distribution
   system, installation of one or more network server machines in a
   central location (Other protocols, such as AppleTalk or Novells IPX,
   may be supported on a school's local area network (LAN) as needed for
   local function such as printer sharing or local resource servers.),
   and provision of a network router and telecommunications circuit or



ISN Working Group                                               [Page 8]

RFC 1709            K-12 Internetworking Guidelines        November 1994


   radio link to connect that school to the district offices.

   The most common LAN technologies in use today are ethernet and
   LocalTalk.  (IEEE 802.5 Token Ring is not recommended for new
   installations.  It is more expensive and it is not available for as
   wide a range of computers.)  Both are quite inexpensive and easy to
   install and maintain.  Ethernet is adaptable to most modern computers
   and is built-in to high performance workstations such as Sun,
   Hewlett-Packard, SGI, or Digital Equipment Corporation computers.
   LocalTalk is built-in to all Macintosh computers and is adaptable to
   DOS PC computers as well.  Ethernet is roughly 20 to 40 times faster
   than LocalTalk.  Therefore ethernet is recommended for all computer
   connections, when possible, and for the school LAN "backbone" or
   network distribution system.

1.1  Network Adapters and Software

   Individual computers will require network or communications adapters
   and appropriate software.  Table 1 gives basic recommendations for
   the computers most commonly found in schools.  Basic communications
   software is available in the public domain for many personal
   computers at no cost.  More sophisticated software is being developed
   by a number of vendors for applications such as electronic mail,
   distance learning, and multimedia database access.  For example, the
   California Technology Project is developing very easy to use software
   for Macintosh and DOS or Windows PC computers that will enable access
   to a wide variety of information resources and services.  Schools
   should look at all the available software and base choices on
   required functionality and support costs as well as acquisition
   costs.

   In locations where computers will be purchased, the choice of
   computer type should be driven by the availability of software for
   the particular application(s) to be supported.  Almost all modern
   computers can be attached to the type of network described in this
   document.















ISN Working Group                                               [Page 9]

RFC 1709            K-12 Internetworking Guidelines        November 1994


Equipment Type          Network Adapter            Communication
                                                     Software
________________________________________________________________________

Simple terminal       "Network Access Server"   Built-in to the
                      located centrally.        networkaccess server.

Apple II, Amiga,      Serial asynchronous       Serial communications
Tandy, Commodore,     port that will allow      software that emulates
older IBM PCs, etc.   connection to the         a simple terminal.
                      above.

Newer IBM PC          Ethernet adapter car      TCP/IP "TSR" software,
                      with "10-base-T" port.    for example "FTP
                      "Thin-net" port may be    Software" package.
                      used in lab clusters.     Additional software for
                                                special appl.

Older Apple           PhoneNet adapter  MacTCP  or equivalent
Macintosh computers   (external) and shared     plus "telnet" and "ftp".
                      LocalTalk to ethernet     For example, NCSA
                      router, for example the   Telnet.  Additional
                      Shiva FastPath.           software for special
                                                applications, e.g.,
                                                "electronic mail
                                                client."

Newer Apple           May use same as the       Same as the above.
Macintosh computers   above.  For higher
                      performance, use an
                      ethernet adapter card
                      with "10-base-T port.
                      "Thin-net" port may be
                      used in lab clusters.

Unix workstations     Ethernet adapter card,    Typically comes with
                      if not already built in.  the basic system.
                                                Additional software
                                                may be needed
                                                for special