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March 1997: Volume 12, Number 4


Satellite Systems - Everywhere You Are!

By Joan Burek

magine your 'consolidated applications' wide area network (WAN) -- serving voice, data and video applications -- providing consistent connectivity from your rural and urban sites to a centralized host location -- everything, everywhere at one consistent, national price. That, in a nutshell, defines satellite services.  Figure 1: Satellite Antennas

Satellite's virtues -- communications applications versatility, geographical indifference, bandwidth-on-demand and cost containment -- have made this communications alternative globally popular. Whether it's the Philippine telephone system, a major Canadian retailer data backbone, or a national distance learning consortium, satellite systems have provided the economical means to reach above and beyond the classic telephone pole.  Figure 2: Satellite Antennas

Within Canada, satellite systems usually employ a hierarchical (hub and spoke) structure, where many remote satellite antennas are trained to ONE centrally-located master earth station. Few corporations can support the cost of their own master earth station and thus, satellite systems providers offer shared 'hub' services, where many corporations 'share' master hub facilities and infrastructure. In this scenario, the master hub facilities are managed, maintained and controlled by the satellite system provider. In Canada, the two main contenders, a.k.a. satellite systems providers, are Cancom (Canadian Satellite Communications Inc.) and Telesat.

The components necessary for end-to-end satellite connectivity are:

Satellite systems come in many flavours, but the two most familiar to the Canadian environment are intelligent and clear channel systems. Similar in concept to X.25 and Frame Relay networks, intelligent systems possess an integrated 'access device', which provides localized 'protocol-sensitivity' to minimize the amount of supervisory (a.k.a. non-data) transfer over the satellite link. Clear channel systems provide, well, a clear channel, similar in concept to leased line/T1 facilities offered by current carriers.  Figure 3: Satellite Antennas

Intelligent Satellite Systems

Commonly referred to as VSAT(1) or Very Small Aperture Terminal systems, intelligent satellite systems provide 'protocol-spoofing' similar to the access device technologies found in national X.25 networks and Frame Relay Access Devices (FRADs). Their 'intelligence' comes from an integral access device which minimizes protocol overhead by adopting host computer-like attributes at the remote site.

VSAT systems excel in versatility, providing connectivity options that serve broadcast data, voice (radio) and video, and two-way data and voice. Ideal for two-way data, VSAT systems offer high cost economies, particularly within your 'hard-to-reach' locations. Satellite bandwidth, of course, is allocated dependent upon communications connectivity need.

Clear Channel Satellite Systems

Clear channel systems provide bulk bandwidth for any and all of your higher bandwidth applications. The satellite system's indoor unit usually provides a single, high speed termination which is connected to an external multiplexer. The multiplexer serves as the connection point between your connecting devices and the indoor unit.

There's a lot more to satellite systems then what is mentioned in this article. New advances within the satellite forum include Iridium (global voice/data communications), LEO (Low Earth Orbit) satellites, Internet-specific satellite systems, and so on. Future articles will explore these new advances and 'space ... the final frontier'. However, for more information on VSAT, clear channel, and any of the topics mentioned above, please contact: Joan Burek T < G


(1) In the beginning, VSAT, or Very Small Aperature Terminal referred to the antena, or dish size usually under 2.4 meters, regardless of inherent intelligence. Over time, however, the term "VSAT" was used to represent intelligent satellite systems that utilized the smaller dish sizes.