Introduction
In the industrialized world, it is an everyday experience to make a voice
call, fax transmission, or even join a videoconference—often across
many time zones.
Where communications facilities are intermittent, of poor quality, or
expensive, the most efficient way to transmit data electronically is by use of
digitally encoded messages rather than direct "real-time" voice or fax connections.
This is the essence of "off-line" or "store-and-forward" communications.
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Satellite
The cornerstone of SATELLIFE's technology is its low earth orbit (LEO) satellite.
HealthSat-2, pictured below,
is capable of store and forward full-duplex
communication at 9,600 bits per second. The satellite's unique polar orbit
allows ground stations to communicate with it from any point on Earth
everyday.
Stations close to the equator acquire the satellite four times a day.
Each acquisition—or "pass"—lasts for about 13 minutes.
At any given time, the satellite is visible
to ground stations within a diameter of 6,000 kilometers.
HealthSat-2 has one downlink and two uplink
communication channels. There can be several users requesting messages
from the satellite at any given time.
HealthSat-2 and its earlier predecessor,
HealthSat-1 (UoSAT-3), were both designed and constructed by
Surrey Satellite Technology, Limited (SSTL).
SATELLIFE has two systems of ground stations that work in conjunction with the
satellite to make communication possible. The first system is a
terminal groundstation capable of serving several users in remote
locations using a single computer. The terminal groundstation employs the
WiSP (Windows Satellite Program) software developed by SSTL. The second
system is a network ground station capable of serving several users on a
local area network in remote locations. SATELLIFE developed all the
software for its satellite gateway operations and network ground stations
using the Linux operating system.
The ground equipment needed to contact the satellite consists of a IBM-PC
compatible computer, a Terminal Node Controller (TNC), a satellite radio,
and antennas.
For the user, the HealthNet software is similar to any e-mail offline
reader/writer software. The system permits messages to be addressed
to Internet destinations, or to any other HealthNet
user. Binary files may be attached to messages or transferred by separate
file request. All routing and delivering is transparent to the user.
Through an innovative arrangement, SATELLIFE has pooled resources with
Volunteers in Technical Assistance (VITA), a deliverer of technical
information to the developing world, and Wavix, a premier oceanographic
research institution. Wavix developed WavSat, its 2-way satellite-based
communication system, in cooperation with SATELLIFE, VITA, and Surrey
Satellite Technology, LTD (SSTL). This collaboration is devoted to using
satellites for health, humanitarian, and development purposes in developing
countries.
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Telephone
Fidonet, developed in an experimenter
community similar to that of Amateur Radio,
provides an economical alternative to a fully-connected Internet.
FidoNet networks transfer electronic mail
by a series of scheduled telephone calls, or polls. Nodes stay connected
for only the period of time necessary to transfer the messages.
The evolution of HealthNet has produced a large network of FidoNet nodes, some using SATELLIFE low earth orbit satellites
and others polled directly by telephone from our Boston office
where we operate a central Internet gateway.
The network is still growing rapidly,
with much of its growth being in the "points" connected to network
nodes, rather than the nodes themselves.
This FidoNet-based service is kept affordable for HealthNets in
the developing world because the Boston office calls are billed at U.S.
rates rather than rates set by PTTs. We are beginning to
move these telecommunications expenses and other costs of operation
back to the independent HealthNets on a cost-recovery basis, thus fulfilling
our goal of creating independent, self-sustaining HealthNets.
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Internet
Since 1994, SATELLIFE has been providing
a seamless electronic mail interface between HealthNet and the
Internet. This allows HealthNet users to send and receive electronic
mail to and from users on the global Internet. SATELLIFE believes
that store-and-forward technology will continue to be a vital
tool for low-cost networking. However, direct connection technologies
are now appearing in the developing world context, and SATELLIFE
has begun positioning HealthNet to take advantage of these technologies.
All 54 countries in Africa now have Internet access via at least one Internet
Service Provider. However, continued high costs make
it difficult for professionals to become connected.
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