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Digital Microwave Voice and Data Link Gives Ebasco Access to SBS Services.

There's a new digital microwave voice and 56-kb/s data link between Ebasco Services and Satellite Business Systems (SBS) in downtown New York City. The installation demonstrates a new and promising approach to customer access to interexchange common carriers in a crowded urban environment.

Using a Harris Farinon DM18 microwave terminal and two-foot parabolic antenna mounted inside its 77th floor World Trade Center office, Ebasco transmits and receives at an angle through a narrow glass window facing the SBS rooftop antenna six-tenths of a mile away at Number One State Street Plaza.

The digital path presently is equipped with three T1 channels and more are planned. It gives Ebasco direct high-speed data and voice access, through the nationwide SBS Network, to PBXs and computers in regional offices for exchange and processing of administrative, computer-aided design (CAD) and scheduling data. We found that putting the antenna inside the office and shooting through a window was substantially less expensive than an outdoor installation.

Ebasco Services, a subsidiary of Enserch Corporation, is a worldwide engineering, consulting and construction firm with offices in 15 US cities and 10 foreign countries.

SBS, a major interexchange common carrier, provides a family of SBS Skyline long-distance services to commercial and residential clients. The SBS Network includes four satellites, earth stations and switching centers in major cities, and extensive terrestrial facilities throughout the United States.

This new and, we believe, broadly applicable solution to metropolitan and inter-urban telecommunications was evoked by the problems of operating in downtown. Manhattan--one of the world's most crowded communications environments--and by Ebasco's constant need for responsive, reliable and flexible interstate high-speed data service.

Ebasco is diversifying and expanding its market base in response to new opportunities and to the slowdown in the nuclear power industry, in which it has been a major contractor.

We had experienced bottleneck problems before in communications between our World Trade Center main offices and groups in Lyndhurst, New Jersey, over eight miles away. We had 17 voice circuits and three 9.6-kb/s data circuits leased from the local Bell operating company, but at any given time several of those under-the-river lines were out of service, and the voice-grade data circuits were particularly vulnerable. A factor in the telephone company's problems was that these lines ran through some of the oldest cable plant in New York, under the streets of lower Manhattan, where cable ducts are frequently flooded.

Further, four-wire trunks were not readily available. It was impractical to provide the New Jersey offices with tandem service through our New York switch and corporate network to regional offices because of the marginal quality of the available two-wire lines. Ebasco Services staff in New York could use the network while our New Jersey staff was forced to use WATS.

In addition to the problems of quality, there was a lack of flexibility. It was necessary to anticipate circuit demands by three to six months. It took that long to obtain them. Because of our market expansion, we sought more rapid response.

We could understand the problems the local telephone companies had in response to our orders. The private-line situation has been a nightmare ever since the AT&T divestiture. But, the facts were that for our specific needs we could not obtain the reliability, flexibility and economy we sought.

The solution to that New York-New Jersey problem was based on previous experience with using 18-GHz microwave to extend PBX service from one Lyndhurst office to remote peripheral equipment in offices in another building 800 yards away. At that time, Ebasco had purchased four Harris Farinon DM18-1A-6 digital microwave terminals and associated M1-2 multiplexer. Two were installed and two were intended for backup on the same path. The reliability of the first system proved so high we decided to use dial backup rather than install a fully redundant system. This made the second two terminals available for the across-the-river path to the World Trade Center.

First Attempt at Transmitting through a Window

It was there that Ebasco first tried transmitting through an office window rather than taking on the expense of renting an outdoor antenna site on the roof, drilling holes in intervening concrete floors, running cables and contending with the numerous fire and construction codes involved.

The Port Authority of New York and New Jersey, landlord in the World Trade Center, was concerned about possible radiation hazards and interference from the indoor terminal and antenna, even though the rated power output of the microwave terminal is less than one-quarter watt. They adopted the latest American National Standards Institute radiation-level minimum standard, divided it by 10, and presented it as the criterion to be met.

Ebasco developed a mathematical model that showed emission would be substantially lower, then had an independent consultant make field tests that verified the model. Finally, we had certified health physicists from Ebasco's Envirosphere subsidiary conduct a second test. The model was again confirmed. The only measurable radiation was found in the area directly in front of the antenna, and the level was only a small fraction of the Port Authority standard. Elsewhere, no radiation could be detected at all. The Port Authority was satisfied.

With that digital path established, the leased analog circuits were replaced with digital voice and data circuits. It was turned up for service in January, 1984. In the following year, outages from all causes including rain interference totaled less than 15 minutes,a dn bit-error rate has averaged around 1X10.sup.-12.

Based on that successful experience, Ebasco began talking with SBS about a direct digital-microwave access to the SBS Network, eliminating the need for analqg leased-telephone lines. And, there was the added potential of high-speed data service to its regional offices and major clients.

The SBS response was enthusiastic. Robert McGuire, regional manager, and George Reither, communications systems manager, saw the potential, not only for Ebasco, but also for other SBS clients in New York and elsewhere. It would be a clean digital interface between Ebasco's facilities and the SBS Network. Voice circuits could enter SBS' DMS-250 digital switch directly via T1 ports with no intervening multiplexers.

Office-Window Antenna Question Settled

The office-window antenna question at the World Trade Center had been settled. In fact, the Port Authority was by now using the radiation standards developed with Ebasco for other World Trade Center tenants who were considering the same approach. The Ebasco antenna again transmits and receives at an angle through an eighteen-inch window, but because of the deep setback of the glass pane, the effective transmission aperture is about one foot wide.

Ebasco's antenna at SBS is mounted on a rooftop load frame that supports SBS' Ku-band earth station. Some adjustment of antennas was required to eliminate diffraction, a problem associated with this urban high-rise environment. Ebasco moved its indoor antenna to an adjacent window, and SBS moved its outdoor antenna a few feet laterally on the load frame.

To save time and installation costs, the microwave radio, M1-2 multiplexer, power supply and gel-cell backup batteries were preassembled, tested and packaged in a single cabinet prior to installation at SBS. Placement of this equipment in a mechanical room directly below the load frame afforded convenient access and required less than one day.

The interface provides Ebasco's New York and New Jersey offices with tie lines, through the SBS Network, equivalent to Band-6 WATS and Canadian calling.

The next step in exploiting the new Ebasco-SBS interface was extending access between Ebasco's New York headquarters and a shared computer facility in Houston. The first phase was to make the IBM mainframe in Houston, primarily used for financial operations, directly accessible via a 56-kb/s circuit and IBM controller to appropriate terminals in New York through the SBS network.

A major consideration in using the satellite relay is the six-month to one-year delay typical in obtaining leased digital-data service circuits. Ebasco's market growth and diversification, both depending upon flexibility of communications, make these delays unacceptable. In the case of Houston, though, the "last mile" still makes use of leased digital-data system lines. Fortunately, both the SBS earth station and the Houston office are in the same central office, and Southwestern Bell was able to respond promptly with digital service.

Second Phase of High-Speed Data Plan

The second phase of the New York-Houston high-speed data plan will make the New York office's Burroughs 7700 mainframe--primarily set up for engineering, critical-path scheduling and other project-control calculations--directly accessible to Houston staff through compatible terminals there.

The objective is to balance computer workload with capacity through shared access regardless of location, letting each mainframe do what it is best suited for.

A microwave link to connect the Houston office with SBS has already been designed, and we are also considering terrestrial T1 service from Southwestern Bell. Either could be implemented quickly if circuit requirements increase.

With the New York-Lyndhurst-Houston link established, the next logical step will be to use it for computer-aided design (CAD), a major support service to Ebasco's clients.

The first CAD application will be realized this month when the New York and Lyndhurst CAD mainframes (actually Digital Equipment Corporation superminis) are consolidated in New York. This will allow for better load-sharing between the computers and will make more-effective use of available systems people and expensive support facilities. The Lyndhurst CAD workstations, printers and plotters will remain in place, linked to the New York computers by digital microwave circuits.

The next step may be to extend the load-sharing concept by linking CAD systems in New York with those in regional offices. Finally, we hope to have a "quick response" capability to place full-blown CAD workstations at project sites and client locations. High-speed data communications will make this a practical reality by providing CAD operators with the same low turnaround time they now enjoy with co-located systems.

It's possible that at Atlanta and other regional engineering and management centers, Ebasco will ultimately use digital microwave for access to the SBS network. We could find out that where we now have one T1 channel we could use more a month from now. With this approach, we can add circuits at short notice by equipping more channels instead of calling upon hard-pressed telephone companies to work miracles.

With this new level of direct digital access to long-haul communications, and with the enthusiastic cooperation of SBS, Ebasco now has the desired flexibility and reliability that we sought, and can offer a new level of service to our cleints.

Ebasco now operates a total of four digital microwave systems, three at 18 GHz and one at 23 GHz. Besides achieving our goals of high-speed data capability, flexibility and responsiveness, we also found there were two other welcome benefits:

First, we saved a great deal of money. The 116 digital voice and data circuits now on the systems would cost $223,800 per year on a private-line basis.

Effects of Rainfall on System

The second benefit stemmed from a problem we had in the initial design of the systems. There was no convenient way to predict the effects of rainfall on the microwave system, or to evaluate various design objectives and alternatives. Manufacturers publish charts and tables, but these were too general for the degree of refinement we required, and they also proved very cumbersome to use.

The solution was to develop our own software for modeling and design of urban microwave systems. With it we can quickly design a system to any required performance objective, using any of 28 regional rain climates and any type of microwave equipment.

The software proved to be so successful that it is now being used by two microwave radio equipment manufacturers.

Ebasco has already designed and built conventional telecommunication facilities for its clients. With the experience gained in installing and operating digital microwave and both voice-grade and high-speed data equipment in metropolitan areas such as New York City, Ebasco Services has added this specialty to its engineering consulting services. Professional services range from feasibility studies through equipment specification, system design, turnkey projects, testing and acceptance to training.
COPYRIGHT 1985 Nelson Publishing
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1985 Gale, Cengage Learning. All rights reserved.

Article Details
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Author:Cooper, W.
Publication:Communications News
Date:Oct 1, 1985
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