Digital Termination Systems Handle Varying Volumes of Digital Traffic.
DTS alternatives to the local loop have captured the attention and interest of companies because they provide an obviously valuable alternative to telephone company tie trunks, off premise extensions, and other private-network links. With DTS, planning for or maintaining an existing network is less time consuming. DTS also answers an emerging need for companies to have media diversity intheir telecommunications strategy.
As companies develop their own private local-area networks, they have often found a problem in obtaining adequate, high-quality trunking between facilities. Most telephone company facilities were designed for analog transmission. Analog trunks and private lines are notorious for their inconsistency of signal levels, noise and crosstalk. For companies interested in transmitting data with a requirement for ultra-low bit error rates (BER), the need for an alternative is obvious.
On April 17, 1981, the FCC allocated 130-MHz spectrum in the 10.55 to 10.68 GHz band to digital termination systems. The commission defined DTS as a two-way point-to-multipoint microwave radio facility made up of local collection and distribution stations, each providing two-way transmission links to multiple outlying stations located at user premises. DTS promised to provide business users with a data transmission capacity necessary for large computer operations, rapid facsimile, videotex and videoconferencing.
DTS Facilities Licensed throughout the Country
That promise has been met across the country as the FCC has issued operating licenses for DTS facilities in city after city. In New York City, a large congested urban system ideally suited for DTS services, Local Area Telecommunications (Locate) Corporation is one such licensee. Locate uses local-distribution radio (LDR) in serving the specialized communications needs of the resellers as well as the financial and banking community's and large corporation population.
While a DTS carrier that serves the needs of the local-distribution market, Locate also brings its customers to other common carriers for their intercity needs. The point-to-multipoint and specialized point-to-point links required by individual users in the heavily congested metropolitan areas of the United States demand equipment and configurations that maximize the number of subscribers that can be served in a given area.
In serving its users in New York City and other locations, Locate operates a point-to-multipoint local distribution radio using NEC equipment. This 10.5 GHz FCC-approved radio was selected because it offers a proven range of benefits to both common carrier and end user.
LDR System Suited to Locate Demands
The local-distribution radio (LDR) system is suited to the application Locate demands. Besides providing maximum use of the available spectrum, it offers an advanced frequency reuse plan that uses all six carriers and a quadrant sector configuration to keep similar frequency allocation patterns six local-node rows apart. This amount of separation together with the LDR's low C/N requirement allows close positioning of local nodes in limited metropolitan areas.
Two types of DTS network are in operation to serve 30 or more Standard Metropolitan Statistical Areas. A carrier could implement and extended DTS network with 5 MHz of bandwidth. Limited DTS networks like Locate, with 2.5 MHz of bandwidth, ard intended to serve networks handling up to 30 SMSAs.
The Securities Industries Automation Corporation (SIAC) is one such Locate customer. A division of the New York Stock Exchange, SIAC performs vital information processing, recording and data-reduction services for the members of the New York Stock Exchange. Locate serves SIAC by providing a radio link between in NYSE and SIAC's main data processing center. This DTS link handles only a portion of SIAC's communications volume, but is nevertheless vital in that it serves as a much-needed alternative to the hard-wired interconnections between the facilities. Like many other organizations that cannot tolerate an extended loss of communications, SIAC considers media diversity an integral element of total communications strategy.
Evaluating User Benefits of DTS Installations
DTS installations, using second-generation equipment are being put online every day. Together with the accumulated experience of DTS installations overseas, a considerable data base exists on which to evaluate user benefits of DTS. These benefits could be summarized as follows:
* DTS offers quality links that are very close to being error-free by all normal standards, DTS exceeds telco's analog transmission standard of 10.sup.-5 BER by several orders of magnitude.
* Reliability of the radio equipment is excellent. The reliability of each path length is a function of the radio path supported. Path lengths with good reliability (less than two minutes of system outage per month) will range from approximately two miles in the heavy rain regions of the South to over 10 miles in the arid areas of the country.
* DTS has the capability to break the bottleneck of business data communications within the first mile-last mile.
* Installation is quick and simple. The DTS subscriber unit, not much larger than an office typewriter, can be placed virtually anywhere in the office. The electronics package may be housed directly behind the dish. The RF package is installed easily on a two-inch pipe mount. The dish may be installed behind a window.
* The transportability of DTS equipment makes it practical to operate temporary installations and emergency services.
DTS Gear Installed by Locate Easy to Expand
The DTS equipment installed by Locate is easy to expand as needs emerge and change. The basic configuration consists of subscriber equipment located on the telecommunications user's premises, and the central-site equipment located at the common carrier's facilities.
The central station or local-node station transmits digital traffic continuously toward its associated subscriber locations within a sector. The signal is a composite bit stream comprised of 26 data channels with 64 kilobits per data port, frame bits and bit-error monitoring (parity) bits.
The signal, which is time division multiplexed (TDM) into a continuous stream, carries information addressed to specific subscriber sites. The transmission is broadcast on one of several available frequencies.
Locate is well-positioned to grow with the expansion of DTS technology across the country. In addition to a growing client base in the New York City area where it began in 1982, Locate has been granted construction permits and/or is operational in several other cities such as Atlanta, Boston, Chicago, Detroit, Minneapolis, St. Louis, Philadelphia, San Francisco, Stanford, Newark, Dallas, Houston, and Pittsburgh.
T1 Facilities Also Provided by Locate
In its analysis of corporate communications needs, Locate also decided to provide T1 facilities as part of its service offering. With the emergence of 32K voice circuits, this offering has become a very cost-effective alternative. With its pure 1.544 Mb/s (not formatted), Locate's T1 offering displays a bandwidth capable of transmitting voice, data, video and facsimile in numerous combination for a myriad of applications.
Business and telecommunications managers have the opportunity to reap great benefits from DTS and the new technologies in office automation, computers and communications technology. The public telephone system is in the midst of change, and private users are now limited only by their imaginations in building systems that meet their individual needs. DTS is one of the important tools in the mix of resources that now possible great opportunities for savings and benefits.
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|Date:||Oct 1, 1985|
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