| Adding
Intelligence to Internet
|
Definition
Satellites have been used for years to provide
communication network links. Historically, the use of satellites in the Internet
can be divided into two generations. In the first generation, satellites were
simply used to provide commodity links (e.g., T1) between countries. Internet
Protocol (IP) routers were attached to the link endpoints to use the links as
single-hop alternatives to multiple terrestrial hops. Two characteristics marked
these first-generation systems: they had limited bandwidth, and they had large
latencies that were due to the propagation delay to the high orbit position of
a geosynchronous satellite.
In
the second generation of systems now appearing, intelligence is added at the satellite
link endpoints to overcome these characteristics. This intelligence is used as
the basis for a system for providing Internet access engineered using a collection
or fleet of satellites, rather than operating single satellite channels in isolation.
Examples of intelligent control of a fleet include monitoring which documents
are delivered over the system to make decisions adaptively on how to schedule
satellite time; dynamically creating multicast groups based on monitored data
to conserve satellite bandwidth; caching documents at all satellite channel endpoints;
and anticipating user demands to hide latency.
This paper examines several key questions arising in the design of a satellite-based
system:
¢ Can international Internet access using a geosynchronous satellite
be competitive with today's terrestrial networks?
¢ What elements constitute
an "intelligent control" for a satellite-based Internet link?
¢
What are the design issues that are critical to the efficient use of satellite
channels?
The paper is organized as follows. The next section, Section 2,
examines the above questions in enumerating principles for second-generation satellite
delivery systems. Section 3 presents a case study of the Internet Delivery System
(IDS), which is currently undergoing worldwide field trials. Issues
In Second-Generation Satellite Link Control Can
international Internet access using a geosynchronous satellite be competitive
with today's terrestrial networks?
The first question is whether it makes
sense today to use geosynchronous satellite links for Internet access. Alternatives
include wired terrestrial connections, low earth orbiting (LEO) satellites, and
wireless wide area network technologies (such as Local Multipoint Distribution
Service or 2.4-GHz radio links in the U.S.).
We see three reasons why geosynchronous satellites will be used for some years
to come for international Internet connections. The first reason is obvious: it
will be years before terrestrial networks are able to provide adequate bandwidth
uniformly around the world, given the explosive growth in Internet bandwidth demand
and the amount of the world that is still unwired. Geosynchronous satellites can
provide immediate relief. They can improve service to bandwidth-starved regions
of the globe where terrestrial networks are insufficient and can supplement terrestrial
networks elsewhere.
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