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Wireless Networking Handbook
(Publisher: Macmillan Computer Publishing)
Author(s): Jim Geier
ISBN: 156205631x
Publication Date: 09/01/96

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Hughes Network Systems Inc.’s DirecPC

Another option for satellite networking is Hughes Network Systems Inc.’s DirecPC, a PC-based satellite interface that enables users to access the Internet, capture broadcasts, and write them directly to the hard drive at speeds up to 2 Mbps. DirecPC services are based on VSAT (Very Small Aperture Satellite Terminal) facilities, and an access kit for PCs includes a 24-inch VSAT dish connected by cable to an ISA-bus card. The kit also includes Windows-based software.

DirecPC has several subscriber services as follows:

  DirecPC Digital Package Delivery. Distributes large files simultaneously to many locations. You can send the files on demand or pre-scheduled. To send data, the information provider transmits the information to the DirecPC Network Operation Center, which broadcasts the data via a 12 Mbps Ku-band satellite to one or more recipients.
  DirecPC Access Service. A basic monthly subscription that provides the user access to a wide range of information services, such as online news, sports, financial information, and software ordering.
  DirecPC Multimedia. A service enabling you to schedule the broadcast of desktop video, audio, or regularly transmitted information. This service uses DES encryption for security.
  DirecPC Turbo Internet. A high speed, low cost Internet connection that uses DirecPC technology to receive data packets from the Internet.

The DirecPC 16-bit ISA adapter card enables a PC to receive high speed satellite data via the DirecPC’s Network Operations Center. The adapter card provides DirecPC signal reception and DES encryption to prevent unauthorized access.

The 24-inch dish antenna can withstand severe weather, and you can mount it in a number of areas—sloped roof, vertical wall, ground pole, or exterior pipes. When installing DirecPC, allow about an hour to assemble and mount the antenna, install the ISA adapter card, and adjust the antenna to pick up the correct satellite signal.

ACT Network’s SkyFrame

ACT Network’s SkyFrame combines satellite modem and radio frequency (RF) terminal, multiplexer, and frame relay technology. Refer to Chapter 8, “Designing a Wireless Network,” for a discussion on frame relay. SkyFrame makes frame relay services available to sites where it is not physically or economically feasible to use terrestrial-based frame relay. SkyFrame consists of a base unit that houses modulators, demodulators, voice/fax cards, LAN cards, and high-speed data cards. The modulator card includes a frame relay switch and a modulator that concentrates all packets received from the access ports and transmits the data. The demodulator receives the satellite signal and filters the received packets according to their addresses.

Comsat Mobile Communication’s Planet 1

Many other companies are working on satellite solutions that support user needs for remote access to the Internet and corporate networks. Comsat Mobile Communications, for example, is working on a personal satellite communications system that will offer (in 1997) personal voice and data communications on a “seamless” global basis. Comsat calls this system Planet 1, and it will use a portable notebook-sized terminal. The system will incorporate functions such as global roaming, fax and voice-mail notification, paging, e-mail, and Internet access.

Planet 1 will provide secure communication channels via the Inmarsat-3 satellites. The transponders on the satellite will use spot beam technology that concentrates greater power onto the Earth’s surface. This improves spectrum efficiency because the system provides frequency reuse and should minimize per-minute usage charges.

Meteor Burst Communications

Occasionally at night, you can see the burning trail of a meteor as it enters the Earth’s atmosphere. Actually, billions of tiny microscopic meteors enter the atmosphere every day. As these meteors penetrate the ionosphere, they leave a trail of ionized gas. Meteor burst communications direct a radio wave, modulated with a data signal, at this ionized gas (see fig. 4.9). The radio signal reflects off the gas and is directed back to Earth in the form of a footprint that covers a large area of the Earth’s surface, enabling long distance operation.


Figure 4.9  A meteor burst communications system.

A meteor burst communications system is advantageous because it can reach into remote areas where there is no packet radio or cellular network coverage. In addition, the implementation of a meteor burst system will generally cost less than leasing satellite service. These benefits make meteor burst systems well-suited for remote telemetry, water management, environmental monitoring, pipeline regulation, and oceanographic observation.

To use a meteor burst system, you must purchase and implement the equipment yourself. Meteor Communications Corporation (MCC) sells the MCC-520B Meteor Burst Master Station and the MCC-550C Remote Data Terminal that support data rates up to 8 Kbps over a range of 1,000 miles. These devices operate in the 40–50 MHz frequency range.

The Master Station is the main component in a meteor burst communications system. It controls the routing of messages and data from hundreds of Remote Data Terminals throughout the system. A Remote Data Terminal collects data from analog and digital sensor inputs and is designed for unattended and automatic operation. When the Remote Data Terminals receive a beam from a Master Station, they are able to send data containing information obtained from their sensors. Because of low power consumption, the Remote Data Terminals can operate unattended for a year or more.


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