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CDPD Test Areas. Cellular digital packet data is being tested by McCaw (in Las Vegas, Dallas, and Seattle), Ameritech Mobile (in Chicago), GTE Mobilnet, and AirTouch Cellular (PacTel Cellular), among others. Bell Atlantic Mobile, Inc. has announced pricing for CDPD services offered in its Baltimore/Washington DC and Pittsburgh test markets. GTE PCS and McGraw Cellular have also initiated trial services in their franchise areas.
Specialized mobile radio (SMR) services began in 1970 when the Federal Communications Commission (FCC) established frequencies in the 800900MHz range for use in land mobile communications. A typical application of SMR is a radio dispatch for service fleets and taxicabs. SMR operators are assigned licenses for exclusive use of assigned channels in a given area. SMR operators can also provide interconnection to the public network.
Racotek (Minneapolis, MN) is one provider of SMR wireless voice/data service. Racotek provides a vehicle fleet management service that is based on SMR or trunk radios. A Racoteck communications gateway facility linked to a mobile communications controller (MCC) in a customers vehicle provides a data communications link between customers (e.g., truck drivers) and their dispatch control centers. A mobile radio collocated in the vehicle with the MCC unit completes the communications link. This system allows the dispatcher to send route information, messages, or other information that cannot be sent over the radio to customers while they are in route to or from a location.
RAM Mobile Data Inc. RAM Mobile Data Inc. (New York, NY) is a joint venture between Bell South and RAM Broadcasting and provides a two-way data communications service that is based on the Mobiltex network architecture. This service is used by many companies for management of their field sales and service operations. RAM Mobile Data provides mobile data communications service in 90% of the urban business areas in the US, covering 6,000 cities and 210 metropolitan trading areas.
Access speeds of up to 9.6K bps can be supported in all areas; in select areas, it is possible to access the network at up to 19.2K bps. Common applications include E-mail and basic information access to the corporate data center for mobile travelers.
Some companies have greatly reduced their cellular telephone use by deploying the lower-cost RAM mobile network to send E-mail and messages to corporate personnel while traveling. A traveler equipped with a radio-enabled laptop or personal digital assistant (PDA) can access the nearest RAM base station. The message is then routed over a leased landline to the corporate data center. Messages can be sent to a traveler over the RAM mobile network where it is routed to the RAM local switch nearest the traveling employee. Conrail uses RAM Mobile Data to transmit train loading information to train crews advising the disposition of freight and empty freight cars. Other user companies, such as TransNet and MasterCard, use RAM Mobile Data to provide access to their central hosts so that merchants in the field can validate credit card purchases.
Ardis Mobile Services. Ardis (Lincolnshire IL) is a joint venture between IBM Corp. and Motorola and is composed of a formerly private corporate network that supported deployed field sales forces and service personnel. Ardis provides data communications services to 4,000 major metropolitan centers and 8,000 cities in the US, Puerto Rico, and the Virgin Islands. The network was originally designed by Motorola to support IBMs 18,000 deployed field service personnel. Access to the network ranges from 4.8 to 19.2K bps and can be reached from within a building or from a moving vehicle. Laptops and PDAs equipped with an Ardis/Modacom modem can be used to access company host computers to retrieve E-mail, enter orders, access diagnostic information, or obtain product information. Salespeople equipped with laptop computers can access product files to provide customers with product specifications as well as check inventories, enter orders, and print on- the-spot order confirmations.
Satellite systems are composed of a transmission device that is capable of receiving a signal from a ground station. The signal is then amplified and rebroadcast to other earth stations capable of receiving its signal. User signals neither originate nor terminate on the satellite, although the satellite does receive and act on signals from the earth that are used to control the satellite once it is in space. A satellite transmission originates at a single earth station and then passes through the satellite and ends up at one or more earth stations.
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