Prakash
Nair, RA
December 2001
etwork
connectivity issues daunt school districts around the country. Schools
need affordable, expandable computer networks that are resistant to obsolescence.
But should these networks employ wireless technology, stick to venerable
hard-wired solutions, or combine both?
A wide area network (WAN) is a communications network utilizing devices
such as telephone lines, satellite dishes, antennas, and microwaves to
span a larger geographic area than can be covered by a local area network
(LAN). Typically, a WAN consists of two or more LANs. A metropolitan area
network, or MAN, is a term sometimes used to describe a system that falls
somewhere between a WAN and LAN and combines some of the features of both.
If cost were no issue, schools would build their WANs using fiber optic
cable, which is capable of transmitting data at a billion or more bits
per second (1 Gb/s). Fiber cable provides the fastest, most reliable,
and secure way to transmit computer data. But it is often an expensive
approach.
To connect their buildings when the Internet was in its infancy, school
districts used basic telephone lines costing about $30 per building per
month and offering modest speeds of up to 56 kb/s. Communications between
buildings were usually limited to electronic text transmissions of administrative
data, not graphics. The relatively low-speed connection was not a major
issue, and the connection between computers in limited areas, such as
offices and computer labs, was generally provided by LANs.
As demand for network access grew following the rapid deployment of educational
technologies and Internet access in classrooms, so too did the need for
higher capacity and transmission speed, known as bandwidth. Consequently,
schools installed services such as ISDN (Integrated Services Digital Network)
at 128 kb/s and T1 leased lines at 1.5 Mb/s. These have been expensive
options, with a T1 line, for example, costing upwards of $300 per month
per building and as much as $2,000 per month for service to remote locations.
And, because these lines had to be shared by many users with an attendant
reduction in speed for each additional person using the system, speeds
at the desktop could be anything but impressive.
Today, with computers in nearly every classroom, Internet access for every
computer, and computer labs placing more demands on network resources
than ever before, inter-building connectivity has become a hot issue,
with schools scrambling for all the bandwidth they can get. But when examining
such expensive options as T3 lines that offer speeds of up to 45 Mb/s
and dedicated fiber connections costing thousands of dollars per month
to lease, many school districts have been seriously viewing the wireless
option. Its numerous advantages include high bandwidth, zero ongoing connection
costs, reasonable periodic maintenance costs, no trenching, no line leasing,
and no need to obtain easements to traverse public rights-of-way.
Wireless WANs are hardly new. They have been utilized since the mid 1980s
when microwave transmissions were beamed about by complex and powerful
transmitting units that required Federal Communications Commission (FCC)
licenses and radios and antennas costing $40,000 to $50,000. Today, wireless
systems can deliver up to 100 Mb/s speeds at 40 miles' distance, and speeds
are increasing.
Wireless systems gained a foothold for widespread use with the adoption
of a standard, IEEE 802.11, in 1997 by the Institute of Electrical and
Electronics Engineers that established clear guidelines that helped wireless
vendors begin to produce standardized, interoperable products. IEEE 802.11
established 1 Mb/s and 2 Mb/s wireless data transmission rates, but these
speeds were inadequate for most business requirements, and wireless LAN
and WAN systems were slow to be adopted.
The 1997 technology also was hampered by high costs, with wireless network
adapters typically costing $400—twice what they cost in 2001. The earlier
products also provided little security, permitting nearly anyone to tap
into a private wireless network.
Recognizing the critical need for faster data transmission and improved
security, IEEE ratified what it called the 802.11b high rate standard,
which permits transmissions at 5.5 and 11 Mb/s. The revised standard fostered
explosive growth in wireless LANs in the business community and, more
recently, in schools because it promised wireless transmission speeds
rivaling the wired Ethernet. In practice, however, IEEE 802.11b only permitted
a data transmission rate of about 7 Mb/s— still impressive, but insufficient
to transfer data from, for instance, a digital video disk or a video file.
IEEE has recently approved the 802.11g standard, which permits transmission
rates of 54 Mb/s and makes wireless wide area networks more viable than
ever. This standard is backwardly compatible with the existing 802.11b
standard, and it will usher in many new products that harness the increased
speed.
For schools, the primary advantage of IEEE 802.11b and subsequent standards
is fast communication between buildings with no recurring costs other
than periodic maintenance expenses. That means installation costs can
be amortized within a year or two in most cases by eliminating fees to
telephone companies.
Wireless installations enjoy another advantage over cable in that they
represent a one-time capital cost that can benefit a school district for
many years. This scenario is far more likely to attract grant money than
the situation where a school is making recurring payments to a service
provider—typically the telephone company—for leased lines.
A major limitation of wireless WANs is that they require a clear line
of sight between the transmitters and receivers that provide the communications
link between buildings. While installations exist where signals can traverse
short distances through such obstructions as heavy foliage, in general
wireless transmitters and receivers must be located so that no obstructions
exist between them.
What does this mean for a school district that has several buildings but
none offering obstruction-free signal paths? The problem is not insurmountable.
Moderate obstructions often can be overcome by using transmitting towers.
In some cases, school districts have employed existing structures, such
as light poles, to surmount problematic transmission conditions caused
by obstructions between buildings.
If other cost-effective, high speed wireless products operating on the
licensed 5 GHz frequency band become available, schools will be able to
transmit data more securely over their wireless WANs. Experts are debating
the value of the 5 GHz products for building-to-building connectivity.
Of note are concerns over licensing issues and the shorter transmission
distances possible on this frequency compared to the two lower frequencies—900
MHz and 2.4 GHz—presently authorized by the FCC for unlicensed microwave
transmission. Most wireless WANs operate on the 2.4 GHz band.
While unlicensed use frees a school district from the red tape of government
approvals, it also opens up the possibility of interference caused by
others using the same, free, unlicensed frequency. To solve this problem,
wireless equipment manufacturers such as Lucent Tech-nologies, Cisco Systems,
Inc., 3Com Corp., and Symbol Technologies, Inc. rely on the IEEE 802.11
family of standards, which include communications protocols that let users
on a particular wireless system communicate freely while blocking unauthorized
users. This eliminates most interference problems.
But there is still the security issue to consider. Present wireless WAN
security technology offers two levels of encryption: 40 bit and 128 bit.
Typically, 40-bit encryption should be sufficient to prevent unauthorized
entry. For greater security, experts recommend 128-bit encryption.
Encrypting signals that traverse the wireless link itself is just one
of several layers of security that a school should provide for its computer
networks. Other appropriate security methods such as password authentication,
firewalls, and virtual private network solutions can greatly reduce security
risks for users and for LAN-based resources networked over a wireless
WAN.
Wireless systems sometimes can be considered more reliable than leased
lines because all the wireless equipment belongs to the owner and remains
on the owner's property. Leased lines may experience problems caused by
power failures or other interruptions, including unscheduled repairs and
maintenance by utility companies. Microwave transmissions can travel up
to 25 miles without significant signal degradation and can withstand most
weather conditions, including wind, rain, and snow, although they are
susceptible to heavy fog. But severe wind might dislodge an antenna, and
caked ice and snow can degrade signals. Antennas must also be protected
by lightning arrestors to avoid severe damage and consequent loss of service.
Though areas that experience severe weather may be unsuitable for wireless
connectivity, weather is generally not a significant factor. An installation
at the Bronx Zoo in New York City survived the relatively harsh winter
of 2000 without fault. Arizona's Vail School District connects 15 buildings
wirelessly, and the district's technology director Billy Martin said the
system withstands the Southwest's infamous desert storms without a problem.
School districts with multiple buildings within a few miles of each other
but located outside of dense urban environments are good candidates for
wireless WANs. Unless special arrangements are made with local utilities
or other institutions to provide connectivity via fiber, no other system
delivers the high bandwidth connectivity between buildings that wireless
offers.
Other factors to consider beyond building proximity are terrain and visual
obstructions. Wireless works best when terrain is relatively flat. Hills
and valleys may destroy clear lines of sight between buildings. Such was
the case at Saugus Union School District in Santa Clarita, California,
which considered and rejected a wireless solution, despite the recurring
fees it had to pay Pacific Bell. In the words of James Klein, the school
district's director of information services, "We would have preferred
to avoid recurring costs altogether by using wireless links for the wide
area network; however, this solution would have required clear line of
sight between the radios, which was not possible in the canyon where our
school district is located."
Wireless WAN solutions can work in concert with wired network backbones.
These hybrid solutions may take many forms and provide satisfactory performance,
giving schools the benefits of a wired network backbone and the flexibility
of wireless connectivity. For example, a school district may choose a
wireless system to connect buildings up to 25 miles apart that have a
clear line of sight and use leased or fiber lines to connect buildings
that don't.
The thousands of mobile classrooms and temporary buildings in this country
offer a strong case for wireless building-to-building connectivity. Many
of these facilities lack network capability, and school districts are
loath to spend money to install network cabling in such temporary structures.
Moreover, burying cable between structures and main buildings is often
too impractical or too costly.
This was the case with the Wake County school system in North Carolina's
Research Triangle Park region, which decided to wirelessly connect its
mobile classrooms to its district network. "Our first initiative was to
provide connectivity to our mobile classrooms, which number about 525
here," said Vass Johnson, director of networking. "We already have a fiber
network throughout the district, but every year the facilities department
must relocate a host of mobile units to meet changing needs at many of
the schools. We were constantly reinstalling the fiber connections to
keep the desktops and laptops in these classrooms connected with the campus
LAN. With wireless, there's no need because the mobile classrooms are
always connected. We save a lot of money by not having to make these adjustments
every year."
Making a final determination about wireless requires a site survey of
all buildings involved. If line-of-sight issues arise, a relay station
or antenna can provide a third point for a line of sight between two buildings
with a blocked signal path. Surveys also can determine likely antenna
placement locations and they can provide installation cost estimates.
A school district in North Plainfield, New Jersey, illustrates how a school
system with six school buildings and one administrative building can first
consider and then make the actual transition to a wireless WAN. The seven
buildings had been connected to their district network (centered in the
high school) by leased ISDN lines operating at 128 kb/s. Director of technology
Ron Fisher realized that the proximity of these buildings to each other
(within a 1.5-mile radius) made them good candidates for wireless connectivity.
Accordingly, the school district authorized a site survey of all seven
buildings.
During the survey, workers installed one omni-directional antenna about
20 feet above the high school's roof and attempted to make contact with
directional antennas located at each of the six satellite locations. Initially,
they established 11 Mb/s connections with four buildings. The line of
sight to the East End school, located in a valley, however, was blocked,
and the high school's antenna could establish a maximum connection of
only 5.5 Mb/s with the district administrative office because of its distance
from the high school and its relatively low profile.
Nevertheless, the school's technical consultants recommended that the
high school remain the central point for communications with the other
buildings, since the line-of-sight problem could likely be solved by placing
the antenna on a chimney on the high school. Failing this option, the
project could be implemented in two phases. Phase one would connect the
first five buildings and phase two would connect the Somerset and East
End schools once renovation work was completed at Somer-set school. At
that time, a relay antenna located at Somerset would be used to establish
a line-of-sight connection with East End and the high school, thereby
providing a bridge to the two buildings having obstructions between them.
The hardware required to install a wireless
WAN is simple. It consists of access points, which provide access for
all users to the wireless network, antennas with mounting hardware and
lightning arrestors, rooftop antenna towers of varying heights as needed,
cabling required to connect antennas to the LAN, and access to standard
electrical outlets for each access point.
In each building, the wireless network terminates at an access point that
connects to a local hub or switch and serves as a bridge to the wired
LAN. Access points must be located as close as possible to the building
antenna (less than 25 feet is preferred to avoid loss of bandwidth) and
must be protected from the elements.
Installation costs per location will vary depending upon the height of
antenna towers and the extent of cabling required. In general, materials,
equipment, and installation costs will likely range from $4,000 to $10,000
per building. Where towers are needed, add $2,000 to $10,000 per tower.
These one-time costs permit buildings to be connected at up to 54 Mb/s.
Compare this to the telephone company's charge of $3,500 per year for
a 1.5 Mb/s T1 connection. While good wireless WAN installations rarely
require continuous adjustment and maintenance, it is advisable to set
aside about 15 percent of the initial installation cost for annual maintenance.
The promise of connected schools remains just a promise unless school
districts find ways to efficiently bring to all students and staff the
electronic resources available on the district-wide network and Internet.
It is incumbent upon each school district to evaluate the feasibility
of wireless networks as part of its overall plan to implement educational
technology within its schools.
LAN. Local area network. A communications network of computers or
other electronic equipment in a local area such as a school or office.
MAN. Metropolitan area network. A communications network designed
for a city or town that is larger than a local area network but smaller
than a wide area network.
WAN. Wide area network. A communications network utilizing devices
such as telephone lines, satellite dishes, antennas, and microwaves to
span a larger geographic area than can be covered by a local area network.
_________________
kb/s. Kilobits (one thousand bits) per second.
Mb/s. Megabits (one million bits) per second; one thousand times
faster than a kb/s.
Gb/s. Gigabits (one billion bits) per second; one million times
faster than a kb/s.
_________________
Access point. An antenna that transmits and receives signals over
the airwaves and thereby serves as the interface between the wired network
and wireless LAN adapters (see definition for wireless network adapters)
installed in laptop computers or other wireless devices.
Backbone. The principal or main transmission line in a network
that carries data gathered from smaller wires or cables that interconnect
with it.
Bandwidth. The amount of data that can pass along a communications
channel in a given time period.
Bit. A unit of information that has the value 0 or 1; short for
binary digit.
Byte. A unit of information comprising eight bits, generally used
to signify a letter of the alphabet.
Encryption. Use of code to obscure communications. The numbers,
such as 128- or 40-bit encryption, refer to the size of the key used to
encrypt the message. Encryption with a 128-bit key would require 309,485,009,821,345,068,724,781,056
times more computer power to decipher than encryption with a 40-bit key.
Ethernet. A popular apparatus for enabling communications between
two or more computers over a communications cable. Ethernet supports data
transfer rates of 10 Mb/s. Fast Ethernet, a newer version, supports transfer
rates of 100 Mb/s. Evolving 10 Gigabit Ethernet systems support transfer
rates of 10,000 Mb/s. Faster systems are being developed.
Fiber optic cable. A thin strand of very pure glass covered in
plastic developed to supercede the use of copper cable for transmitting
great quantities of information encoded as pulses of laser light.
Firewall. A security plan intended to prevent unauthorized users
from accessing a computer network.
Hard-wired. To connect (computer components, for example) by electrical
wires or cables.
IEEE. Institute of Electrical and Electronic Engineers, an international
standards organization.
Interoperability. The harmonious working together of different
types of computer hardware and software.
Virtual private network. A private network that uses the Internet
to connect remote sites or users and that utilizes advanced security techniques
to create secure communications.
Wireless network. The extension of a LAN or WAN without wires so
that devices equipped with wireless network adapters can communicate with
the wired network via the airwaves (also see access point)
Wireless network adapters. Electronic circuit boards that install
in a variety of computers, from desktops to handhelds, and are intended,
in wireless networks, to give users of laptop computers, notebook computers,
and handheld devices the ability to move freely within a campus or building
environment while maintaining uninterrupted connection to a network and
the Internet.
The URLs herein were accurate on the date of publication. For the most
current URL, try searching by author or title on the NCEF website search
page located at http://www.edfacilities.org/search/
Buchanan, Larry. 1999. "The Evolution of a Wide Area Network." Multimedia
Schools 6, no. 1 (January/ February). http://pqasb.pqarchiver.com/infotoday/37778770.html?did=37778770&FMT=ABS&FMTS=FT:TG:PAGE&date=Jan%2FFeb+1999&author=Larry+Buchanan&pub=MultiMedia+Schools&desc=The+evolution+of+a+wide+area+network
Klein, James. 1998. "How We Got Wired. One District Builds a Network Infrastructure
from Scratch." American School Board Journal. 185, no. 9: A19A21.
Electronic School supplement. http://www.electronicschool.com/199809/0998f2.html
Lamont, Bradley H. 1996. "A Guide to Networking a K12 School District."
Master's thesis, University of Illinois, Champaign-Urbana, Illinois.
Liu, Bob. 2001. "TI's 802.11g Specifications Taken Out of Running." Internet
News (May 16). http://www.internetnews.com/bus-news/article.php/9_767571
Rysavy, Peter. 1997. "Wide Area Wireless Computing." Network Computing
(September). http://www.networkcomputing.com/netdesign/wireless1.html
Trivedi, Anand. 2001. "Wireless Local Area Network—IEEE 802.11." Fairleigh
Dickinson University. http://web.archive.org/web/20011012115656/http://alpha.fdu.edu/~anandt/index.cfm
Whatis.com. 2000. "Wireless and Mobile Computing—802.11" (September).
http://whatis.techtarget.com/definition/0,289893,sid9_gci341007,00.html
See the NCEF resource lists on Technology Integration and Wired and Wireless
Networks at http://www.edfacilities.org/rl/
The author thanks Mike Hoernecke, Edward H. Brzezowski, P.E., Ron Fisher,
North Plainfield Schools, New Jersey, and Larry Buchanan, Poudre School
District, Fort Collins, Colorado, for their help with the preparation
of this publication.
Gerald D. Bailey, Eric P. Flack, Walter Horowitz, Glenn Meeks, Chuck Philips,
Mike Vitiello, Terry Whitney
This publication was produced by the National Clearinghouse for Educational
Facilities (NCEF), an affiliate clearinghouse of the Educational Resources
Information Center (ERIC) of the U.S. Department of Education.