rfc1709.txt

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                                                applications.

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     Table 1:  Network Adapters and Software for Typical Computers






ISN Working Group                                              [Page 10]

RFC 1709            K-12 Internetworking Guidelines        November 1994


1.2  Premise wiring

   A major component of the implementation will be installation of
   cabling to connect individual computers or clusters of computers to
   the LAN.  The recommended topology is a "star" where each computer is
   wired directly to a "hub site" within the building as shown in
   Figures 1 & 2.  A cluster of computers, typically found in a teaching
   lab or library, may be interconnected within the room where they are
   installed, and the cluster connected to the hub site with a single
   cable as shown in Figures 3 & 4.

   The recommended premise wiring is "unshielded twisted pair" (UTP)
   wire that meets the Electronic Industries Association (EIA) category
   5 standards for high speed data communication service.  (See
   EIA/TIA-568 "Commercial Building Telecommunications Wiring
   Standard.")  While 2 pair cable may be adequate for most purposes,
   industry standards recommend installation of 4 pair cable.  The
   difference in cost is minimal so we recommend installation of the
   latter.  One end of each cable terminates in a category 5 RJ-45 jack
   (A standard RJ45 jack can be used for ethernet or lower speeds if
   initial cost is amajor factor.  Such jacks can be replaced with
   category 5 versions later as needed.) located near the computer.  The
   other end terminates on a standard "110 distribution block" (In older
   sites, M66 distribution blocks may already be installed.  These can
   be used for the time being but will not support newer higher speed
   technologies.) at the hub site utility closet.  A labeling scheme
   must be chosen and strictly adhered to so that cables can be
   identified at both ends later, as needed.

        [Figure 1:  Individual ethernet connection to the network]

             [Figure 2:  LocalTalk connection to the network]

   In most cases, the hub site utility closet will be shared with
   telephone services.  It is essential that a separate wall area be set
   aside within the closet for data service interconnections. Typically
   there will be a "field" of interconnect blocks for termination of all
   premise wires, another field for termination of trunk cables (used
   for low speed data terminals), and a third field for hub equipment
   ports.  Interconnections between premise wiring blocks and hub or
   trunk blocks are installed as needed in order to provide the
   appropriate service to each location where communication service is
   required.

       [Figure 3:  A cluster of computers connected to the network]

        [Figure 4:  A Macintosh cluster connection to the network]




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RFC 1709            K-12 Internetworking Guidelines        November 1994


   Installation of wiring in a building typically is performed by a
   qualified data wiring contractor.  This is a critical aspect of the
   program and must be planned and installed professionally with both
   current and future requirements in mind.  (See "Virtual Schoolhouse -
   A Report to the Legislature on Distribution Infrastructures for
   Advanced Technologies in the Construction of New Schools, K through
   12" (Department of General Services, State of California, February,
   1993) for example conduit and utility closet plans.)  To be prepared
   for future distribution of video signals, school network planners
   should consider installation of RG-59 coaxial cable to those
   locations where video may be required at the same time that the UTP
   premise wiring is being installed.  The coaxial cable would terminate
   on a wall plate mounted "F" connector in the classroom, and would be
   left unterminated in the utility closet.  Future technologies may
   support video signals over other media so the installation of RG-59
   cable should be limited to near term potential requirements.

   It will be cost effective to install premise wiring to as many
   locations as might ever serve a computer.  This will include
   administrative offices as well as classrooms, laboratories as well as
   libraries.  In high density locations such as offices, consideration
   should be given to installation of two UTP cables to each outlet
   location in order to provide the potential for several computers or
   workstations.  Terminating both cables on the same wall plate will
   add little to the overall wiring project costs and will add greatly
   to the flexibility of the system.  Premise wiring that is not to be
   used initially will not be connected to any electronics in the hub
   site.

   Hub sites should be utility closets or other protected, non-occupied
   areas.  Hub sites can be created by construction of small closets or
   cabinets in low use areas.  A hub site must be located within 300
   feet of any connection.  Typically, multiple hub sites are required
   in large or multi-story buildings.

1.3  Network Distribution System

   All hub sites within a school must be interconnected to complete the
   school LAN.  The design of this network distribution system will
   depend greatly on the physical layout of the school buildings.  We
   assume that ethernet technology will be used since higher speed
   technology is still quite expensive.

                 [Figure 5:  A complete small school LAN]

   If all hub sites are within 300 cable feet of a central location,
   then 10-base-T wiring can be used from a central hub to connect each
   hub site, as shown in Figure 5.  If longer distances are required,



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RFC 1709            K-12 Internetworking Guidelines        November 1994


   either thin-net or standard thick ethernet can be used.  Fiber optic
   cable can be used if distance requires it and funding permits.  (If
   fiber optic cable is installed, consideration should be given to
   including both multimode fiber for current and future data
   requirements and single mode fiber for video and future very high
   speed data systems.) Specific design of the "backbone" network
   distribution system will depend on the layout of the buildings to be
   served.

   With proper design as many as 250 computers can be connected to a
   single ethernet segment.  Most often the practical maximum number
   will be much lower than this due to the amount of data sent onto the
   network by each computer.  For planning purposes, one can assume
   100-125 computers per segment.  Beyond that size the network must be
   subdivided using "subnetworks".  Design of a such a system is not
   difficult, but is beyond the scope of this document.

   The network distribution system cabling should include unshielded
   multi-pair trunk cabling as well as ethernet trunk cabling.  The
   multi-pair trunk cable will be needed to connect terminals or older
   computers emulating terminals to a central "network access server"
   (NAS).  A typical NAS can serve from 8 to 128 such connections.  It
   is most cost effective to provide one per LAN, if needed.  The NAS
   connects directly to the ethernet LAN.

1.4  Local Network Server

   It is highly recommended that each school install a "network server"
   to support local storage of commonly used information, software,
   electronic mail, and other functions that may require high speed
   communication to the users computer.  Since the connection to the
   outside network will be much slower than the school LAN, it will be
   most efficient to access information locally.  In particular,
   software that is to be shared among the schools computers must be
   stored locally since it would be very tedious to transfer it across
   the slower external link.  The network server will be connected
   directly to the ethernet network.

   The location of the server should be chosen carefully to ensure its
   protection from abuse and environmental damage.  Traditionally the
   school library is the focus of information gathering and storage
   activities and many school libraries have clusters of computers or
   terminals already installed.  The library would be a very logical
   place to locate the network server computer.  The Network Router (see
   below) might also be located there if a suitable utility space is not
   available.





ISN Working Group                                              [Page 13]

RFC 1709            K-12 Internetworking Guidelines        November 1994


   The network server will be a small but powerful computer with a large
   amount of disk storage capacity, typically 1-4 gigabytes.  It will
   run software capable of supporting access by a large number of users
   simultaneously.  It could also support dial-in access from teachers
   or students homes using standard inexpensive modems.  (Access control
   with user authentication is essential if dial-in service is to be
   provided.)  If more than a few modems are to be installed, a NAS
   might prove more cost effective.  If dial-in access is to be provided
   to more than a few school sites within a district, a single central
   modem pool maintainted at the district offices will be the most cost
   effective.

1.5  External Connection

   A single communication circuit will connect the school LAN to the
   local school district offices.  In the school, there will be a
   Network Router attached between the LAN and this circuit.  On the LAN
   side, the connection will be a typical ethernet cable.  On the
   external side, the connection will depend on the type of
   communication circuit used, as discussed in step 2 below.

Step 2: Interconnection of Schools with District Offices

   All schools within a district should be connected individually to the
   network router at the school district offices.  This "star topology"
   will be much easier to manage and the capacity of each schools
   connection can be increased appropriately as needs change.

   Several standard communication circuit services may be used to effect
   this connection.  The least expensive for situations where only
   limited use is needed will be dial-up using high speed modems.
   However, this type of connection is not recommended for serious usage
   due to its very limited capacity.  Also, since most schools receive
   telephone service under business tariffs, usage will be measured and
   the cost will be dependent on how long the connection is maintained.
   This will be true in general for other "switched services" as well
   such as "switched-56" and ISDN.  Dedicated (permanently installed)
   communications circuits are strongly recommended since they will
   allow unattended access to and from the school network at all hours.
   This will be particularly important if information files are to be
   down-loaded during the night to local network servers or teachers and
   students are to access the schools information resources from home.

   Table 2 shows the most common options for dedicated circuit services.
   Costs are indicated in relative terms since they vary greatly by
   location and as tariffs are modified.  The exact costs must be
   determined by contacting local communications service providers.
   Total cost must take into account the equipment needed at each



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RFC 1709            K-12 Internetworking Guidelines        November 1994


   location as well.

Type of Circuit         Data Rate                       Relative cost
________________________________________________________________________

Voice grade leased      20 kilobits per sec             modest*
telephone line           (Kb/s)

ADN-56                  56 Kb/s                         high

ISDN, where              64 or 128 Kb/s                 modest**
available

Low power radio         64 to 256 Kb/s                  high startup
                                                        cost

Frame Relay             56 Kb/s to 1.5 Mb/s             modest to high

DS1                     1.5 megabits per sec            very high
________________________________________________________________________

* Measured service charges must be taken into account.
** At this time, most ISDN tarriffs include message unit charges
   which can make theuse of ISDN prohibitively expensive for
   full-time connectivity.

          Table 2: External Connection Communications Options

   Frame Relay communication services are becoming available in many
   areas.  Frame Relay is a shared, packet based data transport service.
   A school site would contract for Frame Relay service as part of a
   larger service group that includes the school district office and may
   include the Internet service provider.  All members of that group
   would share the communications capacity.  The advantage of this
   service is that only one end of the circuit needs to be ordered (each