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Peering
The Unpublicized Sea Change in the Internet
Oliver Spatscheck and Jacobus Van der Merwe AT&T LabsResearch
The Internet is widely (and rightly) recognized as a key enabler of new applications and services. But its always surprising
how much a substantial fraction of the computer science community ignores some of the fundamental changes in the nature of the Internet itself. In particular, its surprising that top conferences still publish signicant numbers of papers that assume the Internet in its entirety consists of pure IP routers, organized in a strict three-tiered ISP hierarchy.
The Internets success can largely be credited to the simple yet powerful service abstraction offered by IP networks: best-effort delivery of IP packets, each of which includes a source and destination address as well as user data. This narrow waist of the Internet architecture has allowed networks to inexpensively interconnect as well as change their physical connections without changing the abstraction visible to services and applications.
Generally speaking, this abstraction is desirable, but its occasionally vitally important to understand how the network actually functions in more detail. These details especially matter if you want to optimize communication on the Internet, argue about network resiliency or security, or determine how to apply public policy to the Internet. This is also where a lack of details can inadvertently lead to incorrect conclusions.
In this article, we summarize some of the important changes the Internet has experienced, focusing primarily on changes below the IP layer. We also highlight how networks participating in the Internet actually interconnect.
Once Upon a Time
Before we start discussing current trends, lets rst review a traditional view of the Internet, a description still found in many textbooks.
The Internet is a largely unafliated and
loosely coupled set of computer networks that interconnect and interwork to realize functionality. A specic network in this collection of networks that is under the control of a single organization is called an autonomous system (AS). Physical interconnection between ASes is typically achieved by connecting the two networks using one or multiple point-to-point links. Global reachability within this collection of interconnecting networks is achieved by having each AS advertise to its neighbors the IP address ranges (or prexes) that can be reached within the AS.
An...