Published on Jun 05, 2023
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.
Intelligent controls reside in the warehouse and kiosk and are required to share limited satellite bandwidth among many users and to hide the quarter-second latency of a geosynchronous satellite. The controls are a distributed algorithm, in which part runs on warehouses and part runs on kiosks. All warehouses and kiosks must cooperate and must coordinate the use of satellite resources. Multicast groups are defined to allow communication between cooperating entities (e.g., between a warehouse and multiple kiosks).
To identify which controls make sense, it is useful to look at the characteristics of Internet traffic. Three of them represent Web pages: pages that are popular for months or longer (e.g., a news service such as cnn.com); pages that are popular for a short time (e.g., hours, days, or weeks, such as those resulting from Olympic games); and pages that are accessed only a few times. One of the facts known about this traffic is that most of the requests and most of the bytes transferred in client workloads come from a small number of servers. For example, in a study of proxy or client uniform resource locator (URL) reference traces from Digital Equipment Corporation (DEC), America Online, Boston University, Virginia Tech, a gateway to South Korea, and one high school, 80% to 95% of the total accesses went to 25% of the servers.
