| abstract | - Since 1995, when commercial backbone networks permanently replaced NSFNET, commercial Internet backbone providers have generally interconnected with each other through voluntary, market-negotiated agreements. There are no general, industry-specific regulations that govern backbone interconnection in the United States. Instead, commercial backbone operators independently make decisions about interconnection by weighing the benefits and costs on a case-by-case basis. Typically, backbones connect to each other under one of two types of arrangements. In a "peering" arrangement, backbones of similar size engage in a barter arrangement in which backbone A carries traffic for backbone B in exchange for backbone B carrying a similar amount of traffic for backbone A. In this arrangement, exchanged traffic generally is destined only for the other backbone’s end users. In a "transit" arrangement, a smaller backbone pays a larger backbone to carry its customers' traffic to all end users on the Internet. To date, market forces have encouraged interconnection among backbones and between backbones and last-mile ISPs. Today, these backbones make up the core or "middle" of the Internet. Generally, individual backbone networks are made up of a multiplicity of redundant, high-speed, high-capacity, long-haul, fiber-optic transmission lines that join at hubs or points of interconnection across the globe. Transmission over the backbone is generally reliable even when one component fails because there are multiple different routes of transmission from one computer to another. A backbone's customers include ISPs providing connectivity to end users, providers of content and applications that wish to connect their computer servers directly to a backbone, and specialized companies that lease space on shared or dedicated computer servers to smaller content and applications providers.
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