Unplugged Facilities

People who spend a lot of time in a school building don't want to see miles of technology wires everywhere — behind desktops, hanging from the ceiling, snaking across the floor.

But how can a technologically connected school facility avoid it? It should look into the feasibility of wireless networking. Three basic technologies are used for wireless networking:

  • Wireless laser

    This essentially is a point-to-point technology used to connect two locations where a physical connection may be difficult. A low-power laser beam is used to carry large amounts of information.

  • Infrared wireless

    This technology is limited to short-range, line-of-sight applications such as in a classroom.

  • Radio frequency (RF) wireless

    Wireless networking using radio frequency operates in the industrial, scientific and medical (ISM) frequency band of the radio spectrum. In this spectrum, various users co-exist by following certain guidelines. Therefore, the availability of the radio spectrum is not guaranteed. (It should be noted that microwave ovens also operate in this spectrum.) The main advantage of RF wireless networking is that the signal can travel through most building materials. However, the range that the signal covers is much greater in open spaces. Inside a building, the radio signal can be attenuated by building material, furniture, electric wiring and people.

Standard fare

The wireless networking technology is based on industry standards developed by the Institute of Electrical and Electronics Engineers (IEEE). A quick overview of some wireless standards:

  • IEEE Standard 802.11a: Standard for wireless networking in the 5 gigahertz (GHz) frequency range, with data throughput of 54 megabits per second (MBPS).

  • IEEE Standard 802.11b: Standard for wireless networking in the 2.4 GHz frequency range, with data throughput of 11 MBPS.

  • IEEE Standard 802.11g: Standard for wireless networking in the 2.4 GHz frequency range, with data throughput of 54 MBPS.

At present, most wireless networking products are consumer products. The equipment operates based on IEEE 802.11b, IEEE 802.11a or IEEE 802.11g standard. The stated data throughput (data rate) for 802.11b technology is 11 MBPS, while the throughput for 802.11a and 802.11g is 54 MBPS. The actual throughput for any of these technologies is about half or less because of various system overhead needs and the interference that may be encountered. Such systems now are available for less than $100. Many portable computers have built-in wireless technology.

The range (coverage) and the throughput of a wireless networking system are important considerations. The RF environment inside a building is complicated; therefore, it is not easy to determine the range of the wireless equipment accurately. The range can vary based on the building construction, the furniture (such as metal filing cabinets) and the people in the area.

Thus, designing wireless system coverage can be hit-and-miss. The range is large in open air. The figure at right shows the range of 802.11b wireless technology inside a building. The distance is about 300 feet (100 meters), where the throughput will be about 11 MBPS.

The figure on p. 371 shows the range of 802.11a (high-speed) wireless technology equipment. The range of 802.11a (high speed) wireless technology equipment is less because of the use of higher radio frequency; the signal attenuation in the building is higher. Therefore, the 54 MBPS data rate is for about 60 feet (20 meters); the data rate at 150 feet (50 meters) is less than 11 MBPS. The range for 802.11g technology is similar to that of 802.11b. However, both of these technologies operate in the crowded 2.4 GHz ISM frequency band.

Don't cut the cord

An obvious question: Why not use wireless networking everywhere and eliminate wires? The answer is not simple and must be developed after careful consideration of several facts. The wired networks at this time are operated at 10 MBPS or 100 MBPS. Most new cabling installations in the last two years have been done using cables that will support 1,000 MBPS. It is true that most people are not using 1,000 MBPS to the desktop at this time. However, the capability is there (remember, networks in 1983 used 100 KBPS!). The cabling infrastructure is a long-term (20-plus years) investment.

The data-networking technology used almost without exception is an Ethernet. This is a “contention-based” technology, meaning that the computers connected to a network all can transmit with no regard to what the other computers are doing. Therefore, the information packets often collide and must be re-sent. This technology is known as Carrier Sense Multiple Access Collision Detection (CSMA/CD). Therefore, if the number of computers on a network is small, there are fewer collisions/retransmissions — the network throughput is higher. As the number of computers increases, the throughput decreases in an indeterminate manner. According to IEEE literature under average usage conditions, with five computers, the actual throughput may be one-sixth of the available capacity (bandwidth); with 15 computers, the throughput will drop to one-twentieth of the bandwidth. These are simple estimates, as it is not possible to accurately estimate the throughput of an Ethernet network.

In a wired network, each computer has a dedicated 10, 100 or 1,000 MBPS channel to the network resources. In a wireless network, a number of users share the same channel. This channel is 11 or 54 MBPS. So, if 15 users are using this channel and there is no radio interference, the best case (per IEEE) is about 700 KBPS data rate per user (depending on what the users are doing). The last part of the previous statement is important. If users need to read e-mail and access mostly text-based resources, then the available data throughput will not be a problem. Many more such users can be added to the network. However, if the users are working with high-quality multimedia or data for scientific visualization, then the system would be slow to the point of being non-functional. Therefore, wireless networks must be used with clear understanding based on the application and the need for mobility. For some applications, wired connections must be used. An optimum network is a careful mix of wired and wireless technologies.

The security of wireless networks is another critical issue. The basic wireless networking standard has weak security built into it and can be cracked easily. Various industry groups are working on this issue. The networking standard recently has been enhanced to include tighter security. The fact that a wireless system is installed in a building and that no one can “see it” from outside does not matter. The radio signals are transmitted in all directions, so it is easy to snoop on the network from a nearby public area.

Final considerations

Finally, before embarking upon a large-scale wireless project, consider the following:

  • Evaluate the use pattern of the network in various areas. Which applications will be used? Many instructors now are using real-time multimedia information from the Internet. Internet connections to most schools are now at higher speeds, and this speed is increasing.

  • For users that do not create large network traffic, wireless technology may be appropriate.

  • For users requiring larger bandwidth or a high degree of security, wired connections should be used.

  • The fact that one access point and one computer work well in an area does not mean the entire network is working as effectively. When a large number of wireless devices are used in a small area, interference is a definite possibility.

  • Always keep wireless network users on a separate virtual local area network (VLAN). This improves security to a certain degree.

  • The placement of wireless access points must be done with caution. These should be situated away from sources of electromagnetic interference (EMI), such as electric panels, light fixtures and microwaves.

Other wireless networking technologies in various stages of development:

  • Ultra Broad Band (UWB): a large radio spectrum is used to send very low power signal with data rates of about 1,000 MBPS.

  • Various cellular telephone technologies in combination with “smart antennae” and “ad hoc” networking promise data rates of 100 MBPS or more.

So what does the future of wireless technologies look like? The technical hurdles are being conquered every day. Non-technical issues such as the implementation, the business model and the regulatory environment still need to be perfected.

A “no wires” network is nice, but one problem is that laptop computers need electricity. The batteries typically will last two hours.

However, tremendous advances are occurring in battery technology. Soon, polymer batteries will be available. These will be cheaper and lighter, and have higher power density. Small fuel-cell systems are also in the works. These systems may use a small vial of methanol to power a laptop for 10 hours. The use of ultra capacitors is another technology, in which the laptop case will be a large capacitor that will store a large amount of charge and will be used instead of a battery.

Ahmed, PE, is an engineering principal with Burt Hill Kosar Rittelmann Associates, Butler, Pa.

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