A user's guide for the evaluation of micro earth station networks.
While interactive transaction networks are becoming an increasingly important business asset, changes in telephone tariffs resulting from the AT&T divestiture have sent many companies looking for a better price/performance solution than that provided by terrestrial common carriers. Many companies needing to transfer large amounts of data from point to point--minicomputer to mainframe communications, for example--have already turned to satellite networks. These systems support high-speed batch transmission and free companies from dependence on the telephone company.
Not until recently, however, have transaction-oriented businesses, such as banks, retail stores and insurance companies, had access to similar satellite networking capabilities. The development of micro earth stations (four-foot-diameter rooftop dishes that send and receive satellite signals) has made satellite networks a viable, cost-effective communications solution for companies involved in interactive/two-way inquiry and response applications. Low-cost micro earth stations are particularly well suited for applications in which hundreds to thousands of geographically dispersed computer terminals must access a central data base.
Instead of voice-grade leased telephone lines and modems, a digital satellite-based network is configured with a micro earth station at each transaction site. Data inquiries are sent from the earth station to a satellite transponder, where they are relayed to a master earth station or "hub." The hub is connected to a central computer via telephone lines or high-speed connection. Data that is retrieved from the corporate data base returns to the earth station along the reverse path.
If you are involved in a transaction-oriented business, a micro earth station based satellite network not only will be a strategic business tool, but also can give you a significant competitive edge. It can free you from both long-distance and local telephone carriers and enable you to reduce communications costs on multipoint leased lines by up to 40 percent on a location-by-location basis, fix communications costs for five years or more, significantly reduce data errors (satellite network bit-error rates typically are one percent of rates normally encountered on leased lines), substantially increase network availability, and simply and easily expand network services (with a satellite network, your company is not dependent on telephone carriers for expanded services, maintenance or configuration changes).
First, analyze your data communications needs. A variety of different systems are marketed with widely ranging price/performance attributes.
Start by identifying network goals. Why are you designing or redesigning the network? To cut terrestrial line costs? To cut operating expenses by centralizing network management? To improve reliability and availability of network services?
Typically, satellite communications networks are categorized into three tiers:
* High-end systems, which support host-to-host file transfers with data transmission rates up to 40 million bits per second. Earth station terminals are priced at approximately $200,000 and up. Dish size is typically 4.5 to 10 meters.
* Mid-size systems, which support batch file transfer, transaction processing and optional single-channel voice with data rates up to 56,000 bits per second. Earth station equipment is priced from $15,000 and up. The size of the dish is typically 1.8 meters.
* Low-end systems, which support terminal-to-mainframe transactions with bit rates up to 19.2 kb/s. Earth station equipment is priced from $6,000 to $15,000. Dish size is typically 1.2 to 1.4 meters.
The cost of a micro earth station communication network is closely related to the characteristics and quantity of data to be transferred. Generally speaking, the higher the speed requirement, the more expensive the system. For example, a company that needs to send large amounts of data from point to point such as mainframe-to-mainframe communications, will require a higher data transfer rate than a regional insurance office that needs occasional brief inquiry and response-related access to the corporate data base. Similarly, companies that also want to send voice and video on their satellite network will require higher speeds and a more-complicated architecture.
What's the Right Speed for a Transaction Network?
What's the right speed for a transaction-oriented satellite network? There are actually two components to the speed question: the inbound data rate from the operator terminal and the outbound data rate to the terminal. In a transaction environment, most inbound data is limited to human typing speeds; for example, an airline reservationist keying in ticket information. Consequently, most of today's on-line transaction networks involve relatively low inbound data rates.
Outbound data rates from the host computer are typically higher because, generally speaking, data can be read faster from the screen than it can be entered. In a data-base retrieval system, for example, a 9600-b/s line is often used, enabling a full screen of text to be transmitted in about two seconds.
While a variety of satellite systems tout data transfer rates in excess of 9600 b/s, many transaction-oriented businesses would be well served with a 9600-b/s system specifically designed for interactive transaction processing. Not only would it be optimized for the application, but also the price of such a network would be substantially less than that of a higher-speed system.
Speed is not the only issue in determining how well a satellite network will work in your data application. You must understand the flow of data in your network. You need to consider such variables as typical inquiry and response size, protocol used, average response time of your current network, and required level of availability.
A small-aperture global satellite network must be configured as a "star" network, where data is transmitted from a large dish located at the network's hub to small dishes located throughout the country. These small dishes cannot communicate with one another directly, but must transmit to and from the hub. This network topology complements the architecture of many database access applications where a host computer conducts transactions with terminals throughout the network.
Voice applications, on the other hand, are based on a "mesh" architecture, whereby each part of the network should be able to communicate directly with any other point in the network. A typical desk phone, for example, could dial up any other phone that is connected to the public network. As a result, mesh architecture, which is more complicated and expensive to employ, is not well suited to transaction-oriented applications where terminals only need access to a central data base.
Should the Network Be on C-Band or Ku-Band?
Commercial satellites operate at one of two frequency bands, the C-band (4 to 6 GHz) or the Ku-band (12 to 14 GHz). C-band has traditionally been the preferred choice for satellite communications, because of its inherently superior propagation characteristics that make it impervious to rain and other atmospheric disturbances. This is because C-band employs lower frequencies, which have a longer wavelength than Ku-band. Earth station electronics are also more mature for C-band micro earth stations and therefore less expensive.
Until recently, however, C-band has required the use of larger antennas than Ku-band to transmit signals to a single satellite separated only two degrees from its neighbors on the same frequencies. The broader focus of a dish antenna at C-band is due to the larger wavelength-to-diameter ratio. Another consideration in the use of C-band has been the potential for interference from terrestrial microwave stations.
To take advantage of the superior transmission characteristics of C-band and its reduced hardware costs and operating expenses, my company has pioneered the commercial use of a technology called "spread spectrum." Previously used in radio astronomy and military applications, where high interference and jamming are commonplace, spread spectrum solves the local interference problem and enables the use of four-foot dishes for two-way communications on C-band. Spread spectrum is a data encoding technique that enables data packets to be reconstructed, even if there is considerable interference during transmission. As a result of this technology, manufacturers can now provide small C-band micro earth station networks with guaranteed data reliability.
By using Ku-band, manufacturers are able to get a micro earth station antenna to focus on a single satellite in orbit. However, Ku-band wavelengths are small enough to resonate with, and be absorbed by, moisture in the atmosphere. Without significantly enhanced power, this type of system is often non-operational on rainy days.
To overcome the atmospheric problem, many Ku-band designers increase their system's power levels in an effort t "burn through" the atmosphere. Not only does this require more-expensive equipment, but satellite costs and system complexity also rise.
It is likely that both C-band and Ku-band frequencies will continue to be used for micro earth station applications. The use of spread-spectrum technology on C-band, however, has resulted in cost-competitive small dish antennas (two to four-feet in diameter) that are not affected by atmospheric moisture or terrestrial microwave interference.
Customers have a variety of options in obtaining, installing and maintaining a satellite system. The system may be purchased outright, with the buyer retaining end-to-end responsibility over the network; systems or services can be purchased from third-party vendors and pieced together by the buyer; or a turnkey vendor can be employed for a complete solution.
The components and costs of a small-aperture satellite network typically include:
* A micro earth station, which consists of a small-aperture antenna connected via a coaxial cable to a controller, typically a typewriter-sized electronics package that in turn connects to a terminal by means of one or more built-in ports.
Micro earth stations can be purchased or leased. Our company offers a rental program that enables customers to obtain both micro earth stations and other network services for a single fixed monthly charge for 36 months. For $290-a-month per location, customers receive one transmit/receive earth station, continuous network operation, earth station licensing and onsite maintenance.
* Satellite transponder capacity, whereby a unit on the satellite receives a signal, converts it to the appropriate frequency and relays the signal back to earth. Satellite capacity available from many suppliers and can be purchased or leased.
Most of these services are sold on the basis of month-to-month leases with no long-term cost control and no long-term availability guarantee. While this may be suitable for applications in the television and entertainment fields, for a fixed-pointed small-dish network you'll want a long-term commitment on price and availability from your satellite vendor.
* Network facility and management, which includes a master earth station, a large hub antenna and packet-switching electronics connected to your central computer via leased lines or a satellite link. It provides centralized access for remote sites. Often, master earth stations are shared by multiple users.
Sharing a Master Earth Station Will Cut Network Costs
Since a master earth station is a relatively expensive facility, you should have the option to own your own or to share one with other users to keep costs in line. In the latter case, the master earth station would be owned and operated by the same common carrier that supplies the small-aperture earth stations and satellite capacity. This approach has the further advantage that the carrier can also supply the software and personnel required for network management.
Network management includes performance verification testing, fault detection and isolation, failure repair and service restoral, and such customer services as new service requests, change orders, trouble ticketing, dispatching of field personnel, and status reporting and verification.
* Nationwide installation and maintenance, of which field support must be considered an integral part of your network to ensure the high level of availability your on-line applications require. Installation costs vary from location to location and from one installation company to another. In addition to the antenna, installation involves getting site authority, preparing the site, running the cable and installing the controller.
Because most transaction networks are essential to business operations, a responsive and dependable service organization must be ready to support your network. As in other systems maintenance, knowledgeable people and professional organizational controls must be in place to support reliable operations.
To be better assured of receiving the improved performance and cost savings that satellite transaction networks promise, you'll need to thoroughly qualify your network supplier. Many companies offer to integrate a variety of different vendors' equipment and services into one cohesive network. Other companies offer to take end-to-end responsibility for your network's successful operation, providing fully compatible micro earth stations, satellite transponder capacity, network management and nationwide service.
Before Deciding, Here Are Questions to Ask a Vendor
You'll want to choose the solution that provides the best opportunity for long-term cost control, availability and technical support. Before you make your decision, ask the vendor the following questions:
* Are you micro earth stations specifically designed for my network?
* How many earth stations have you installed?
* How many years of experience do you have in manufacturing small earth stations?
* Do you manage your own network or do you rely on other suppliers' services and equipment?
* Do you offer guarantees on network availability, reliability and data transit time?
* Do you have references from companies similar to my company?
* Do you provide long-term service contracts?
* Can you provide sufficient satellite capacity to operate my network over the long term?
* Do you own satellite transponders and provide long-term service contracts for them?
* Do you have a nationwide factory-trained field service force?
* Do you support a range of standard protocols and offer customization services to meet specific requirements?
For transaction-oriented companies, small-dhs networks can offer both price and performance advantages over existing leased telephone lines. By analyzing your data communications needs, you may be able to free your company from dependence on the telephone company and increase the capabilities and performance of your data communications network.
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|Date:||Mar 1, 1986|
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