Bridging the Future

In the engineering arena today, no one would be shocked to hear that electrical system designers regularly face access and space challenges. But the gauntlet is significantly more daunting for initiates of the engineering and construction world's newest kid on the block—telecommunication. In this particular arena, the major challenges involve supporting customers' present and future need...

By Steven C. Brohammer, RCDD and Timothy D. Ruiz, Electrical Project Engineer, Telecommunications Department, William Tao & Associates, Inc., St Louis July 1, 2002

In the engineering arena today, no one would be shocked to hear that electrical system designers regularly face access and space challenges. But the gauntlet is significantly more daunting for initiates of the engineering and construction world’s newest kid on the block—telecommunication.

In this particular arena, the major challenges involve supporting customers’ present and future needs; delivering fast network connectivity; controlling capital expenditures; and eliminating long-term contract commitments that seemingly “rob” precious funds out of monthly operating budgets.

This last point is especially true regarding campus environments and operations involving remote buildings scattered throughout an area, as monthly costs associated with dedicated leased telephone lines add up quickly.

A need for speed

No one faces such budgetary issues more than schools, as can be illustrated by the case of Drummond Elementary School, a part of the Pattonville School District in the metropolitan St. Louis area. This new school needed a telecommunication infrastructure and platform that could advance the application of this technology as it relates to education, communication and facility support.

Here is where Drummond Elementary departs from the conventional and ventures into territory worthy of its vision of a school employing 21st-century learning techniques. Instead of traditional wiring, the school employs wireless technology. Specifically, a fast-Ethernet bridge incorporates microwave technology that provides voice/data connectivity building-to-building. Before delving into the details of how the technology works, it’s useful to explore the reasons as to why the decision proved most logical.

The Pattonville School District requires high-speed data and voice connections to support their present-day operations and future 24/7 operations. To establish the basis upon which a good solution could be achieved, two inventories were collected. The first established minimum system requirements by examining and understanding the district’s present-day operations and systems equipment. Next, ultimate system requirements were established based on the district’s future expectations. This second inventory was more difficult to establish and document since it dealt with an abstract vision. Determining the ultimate system requirements also involved considering budget constraints as planners contemplated how to incorporate and support the opportunities that could potentially result from technological advancements (see “District Telecom Operations at a Glance,” p. 32).


After analyzing the situation and determining the school’s requirements, communication connection options were studied. Several options were available, but many were impractical considering bandwidth requirements, project duration and economics.

  • Public switched telephone network (PSTN). One of the most widely available technologies, PSTN accesses information through copper wires installed by the local exchange carrier. Unfortunately, telephone modems offer only a 56K transfer rate—too slow for the present and future requirements of graphics, video/sound streaming and other broadband-hungry processes. Clearly, the PSTN was never designed to handle continuous, full-duplex, high-speed data traffic, let alone high-end graphics and full-motion video.

  • Voice-and-data over cable systems. Supplied through the local cable TV providers, this choice offers the potential to provide relatively high-speed access at affordable rates. However, cable service is not suitable in most environments because speeds generally depend on system loading. Cable modem bandwidths are limited and must be shared by all users on-line at any one time. A WAN composed of modems connected via PSTN or cable modems is the least-desirable data networking option.

  • Leased services. A variety of leased services are available utilizing existing copper infrastructures. This includes ISDN, T1 and DSL. ISDN, for instance, offers user speeds of 64 or 128 kbps, and costs approximately $200 per month. On the other hand, T1, operating at 1.544 MB, full duplex—the transmission of data in two directions simultaneously—is readily available, but the cost of a single dedicated T1 connection averages more than $300 per month. To maintain the minimum system requirements, and to achieve the ultimate system requirements, two T1 connections—one for data and one for voice—would be required.

DSL services offer voice and data, but only at speeds up to 8 Mbps. However, DSL and any system dependent upon twisted-pair copper wiring will be limited in distance—typically up to 15,000 ft. from the concentrator. In addition, the performance of DSL is directly influenced by distance: the further from the concentrator, the slower the performance.

In considering such a technology for the new school’s location, it was discovered that, factoring distance, service was only available at a speed slightly faster than the district’s existing T1 connection. Furthermore, DSL service is asymmetrical, meaning that upstream data rates are substantially slower than download speeds.

  • Fiber. Consideration was given to the installation of privately owned fiber. But owning fiber translated into trenching or boring through established and densely populated urban area with an estimated cost of $1.0 to $1.5 million per mile. Getting through tedious permit applications and right-of-way issues would also be required. Obtaining these right-of-ways would not permit completion before the start of the August 2002 school year.

Bridge over troubled water

These possibilities were eliminated, leading the design team to a technology option with no wire at all—a high-capacity, point-to-point, wireless fast-Ethernet bridge. This installation would literally link the new school and the district central office, connecting LANs to the WAN and points of data aggregation to the Internet backbone.

The fixed wireless bridge, incorporating microwave technology that provides voice/data connections from building to building, offered the following benefits:

  • Very high throughput. The bridge chosen operated at 45 Mbps full duplex with a 93 Mbps aggregate throughput. This rate is equaled only by fiber.

  • No trenching or boring required to lay wires. No physical connections were required, no right-of-ways needed to be secured, no permits were required and, last but not least, no off-campus construction contracts had to be administered outside the building construction contract.

  • Cost of equipment and installation will be recouped in less than 30 months. While the wireless installation comes with higher initial cost, the absence of any long-term contracts or monthly expenses resulted in significant cost savings and reasonable payback. In addition, this was an investment into a district-owned infrastructure funded as a capital expenditure in lieu of becoming another liability, taxing the annual operating budget and funding private industry infrastructures.

  • Unregulated frequency operating at 5.3 GHz does not require FCC licensing. While there are many microwave regulations, the 5.3-GHz communication legally operates over unregulated, unlicensed frequencies eliminating governmental red tape and costly registration delays.

  • Great range. Although most installations operate over a range of 5 to 10 mi., wireless bridge connections have an effective line-of-sight range of up to 40 mi., depending on factors that include equipment and configuration. The district’s installation operates over a range of one mile, resulting in nearly impervious signal quality.

  • Interference free. The system is compatible with the most sensitive of environments—an especially important consideration as the new school is less than a mile from St. Louis’ Lambert International Airport.

  • Carrier-class reliability of 99.999% availability. Carrier-class reliability is deemed necessary, because data, as well as voice communication, travel over the system. Reliability and uptime are the utmost concerns. With carrier-class reliability, the bridge meets or exceeds traditional telecommunication wire-line standards, guaranteeing 99.999% availability, or about five minutes of network downtime annually.

No questions asked?

By no means did the district or the firm dive into the situation headfirst. Wireless bridge connections are relatively new to educational venues in this area, and the technology poses several key questions which needed to be resolved.

In doing due diligence, a number of end users were surveyed nationwide. A Tsunami system by Western Multiplex emerged as the clear favorite, as it was highly recommended for its reliability, throughput, security and licensing requirements.

Furthermore, specific questions were developed to see how the device would meet the school’s needs.

The first of these questions addressed the impact of weather on microwave transmission. Rain, fog and snow, according to surveyed users and the manufacturer, have negligible impact on system performance for wireless systems operating below 11 GHz. This was especially good news because the specific model—the 100 Base T/F—operates at 5.3 GHz. The bridge can therefore reliably span distances of up to 5 mi., even in adverse conditions with minimal signal degradation. Weather, however, can have an impact on the system’s antennas. Accumulating snow and ice can change the performance of the antenna. However, simply installing a cover, called a radome , can mitigate these problems. In areas where extreme-freezing conditions may exist, the radomes can be heated.

The second question centered on radiation emissions. The Ethernet bridges adhere to all applicable Federal Communications Commission rules pertaining to radio frequency emissions.

The third question focused on security. There is the misconception that the signal transmitted by wireless bridges can be intercepted and data stolen. In reality, the technology is more reliable and secure than wireless LAN products based on IEEE 802.11. Features such as data encoding and password protection minimize the possibility of a security breach. Additionally, the bridge supports third-party enhanced security products.

Too easy to believe

Implementing the system was relatively simple. The first step required an on-site survey to identify antenna locations for each structure. Note that line-of-site is required between the antennae. In this case, line-of-sight could be established at 8 ft. above the roof. After collecting this information, the vendor developed a system design that calculated link budgets and availability for various capacities, frequency, network management and antenna options.

A pair of bridges was selected to meet system requirements. Each unit featured fast Ethernet connections and one RJ-45 and Type-SC fiber connection, plus a wayside T1 channel for a sideband connection that allowed the district to extend PBX connectivity between buildings. This also allowed the district to maintain its telephone switch and district-wide intercom system.

A special feature of the device is its capability to allow end-to-end communications through orderwire handsets. Separate from the voice/data link, these handsets provide dedicated bridge-to-bridge communication for better tuning, maintenance and troubleshooting.

The antenna system itself consisted of two Gabriel Electronics, 5-GHz Spread Spectrum Directional Flat Panel Antennas. While it was determined that a 12-in. square flat panel was all that was required, a 24-in. antenna was installed, as it amounted to a minimal up-charge, yet provided greater reliability. A tone is generated from the bridge to assist in aiming the antennae to achieve maximum signal strength. Radomes were added to provide environmental protection. The bridge and antenna were connected with a 5/8-in. foam dielectric coaxial transmission line.

Additionally, it was important to make sure the antenna, mast and transmission cable were protected against lightning strikes. A National Lightning Protection Prevectron 4 early streamer emission system was installed at both locations. The transmission cable was also protected with in-line spark-gap-type lightning suppressors.

The remainder of the job involved antenna mounting, bridge installation, and power and signal cabling. Because the antenna and bridge were roughly 1,000 ft. from the district’s central office computer head-end room—to accommodate the line-of-sight requirements to the new school—fiber was used to connect the bridge to the Ethernet switch. On the other hand, at the new school, the antenna and bridge were located relatively close to the Ethernet switch, allowing the use of copper UTP.

Smart solution

In sum, fixed wireless telecommunication systems have made significant advances compared to physical cable connections when considering connection speed, capacity, physical access and cost: It is close to the speed and capacity of fiber-optic networks, and has significant advantages in being able to span distances of up to 40 mi. without cable. This, of course, results in major cost savings, as well as an almost negligible time of deployment.

Furthermore, fixed wireless solutions can be implemented quickly and do not suffer from the limitations, fees and delays associated with private provider solutions. With fixed wireless, the building owner can economically offer the bandwidth their end users demand and need, plus they provide the link necessary to support present-day and future building communication, as well as energy management and IT operations.

Considering all these factors, from capacity and price to ease-of-installation, wireless emerges as one of the best choices for networking LANs and other critical-connection applications.

District Telecom Operations at a Glance

The following breaks down Pattonville School District’s existing telecom operations and its needs in considering a new system for Drummond School:

Existing operations and functions

Because of its ability to quickly communicate complex information, educators are currently using presentation software containing sophisticated graphics and multimedia features. Multimedia, in general, is growing throughout the district.

Internet traffic has increased exponentially. Teachers and students routinely use web browsers and web-based communication, creating considerable traffic, taxing present broadband capabilities.

Existing systems and equipment

All computers are networked within each building at each site. A wide-area network (WAN) connects all sites, allowing all departments, teachers and students—regardless of physical location—to share information in real-time.

High-speed voice connections—utilizing a centralized telephone and intercom switch—provide immediate access between teachers and departments.

Minimum system requirements

The district’s communications are reaching its maximum capacity with the T1 connections from the local telephone providers. Utilizing the present mode of communication to connect the new school to the district would burden the existing system.

While the district’s construction budget could afford an upgraded connection for the new school, it did not allow for upgrades to the existing connections. Nevertheless, district officials wanted to establish a new means of communication when funding becomes available.

Maintaining the existing connectivity between buildings while introducing the high-speed connection to the new elementary school was imperative. The new school also needed to be able to communicate with the WAN—forward and backward communication and connectivity.

Ultimate system requirements

The increased use of e-mail, especially those with large attachments is clogging their present small-pipe connection. A single Internet connection originating in the district’s central office is shared between schools, thereby mandating a need for faster and larger connections.

Support is growing for video conferencing and distance learning. These “virtual classrooms” allow more students to participate while minimizing inefficiencies.

The capability to remotely access a facility security or video surveillance system is increasingly being considered due to recent events involving fatal activities on public properties. Administrators and emergency-response teams need the ability to view areas throughout the facility from a remote location, and also be able to review historic digital video recordings. This can be accomplished by a high-speed DSL modem connection or by simply utilizing the Internet.

Utilizing the Internet to report school closings, display event calendars, provide tutoring, support alumni activities and any other database, files, graphics or information is quickly becoming a necessity.

In the future, administrators and facility managers want the ability to access secured school files, turn on/off security systems and remotely adjust mechanical systems by using notebook computers connected to a remote telephone outlet.