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Research Abstracts - 2006
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Overlay Networks: Peter Pan or Viable Networks of Future

D.D. Clark, P. Faratin, S.J. Bauer, W. Lehr & R. Sami


The goal of this project is to better understand the architectural, industrial organization and regulatory impacts of new class of networks called Overlay Networks. Example of overlay networks we consider in this project include routing overlays (e.g. RON, SureRoute), Content Distribution Networks (both propriety systems such as Akamai, as well as P2P systems) and security overlays (e.g. Onion routing, Freenet). Abstractly, an overlay network is a set of servers deployed across the Internet that a) provide some sort of infrastructure to one (or possibly several) applications, b) in some way take responsibility for the forwarding and handling of application data in ways that are different from or in competition with what is part of the basic Internet, and c) are operated in an organized and coherent way by third parties (which may include collections of end-users) to provide a well-understood service that is infrastructure-like.

The evolution of overlays is not that dissimilar to the evolution of the Internet itself. The Internet started out as a government-funded research network running on top of the Public Switched Telecommunications Network (PSTN). It was a data application, mostly unregulated, that was supported on top of the public-utility regulated telephone networks. The Internet was an "overlay" that complemented the underlying basic infrastructure of the PSTN by adding new functionality (packet-switched data network) to support the special needs of the research community (peer-to-peer computer communications). Most of the incremental investment in routers, servers, and access devices (PCs) was undertaken by new types of providers (Internet Service Providers or ISPs) and by end-users (Customer Premise Equipment or CPE) to complement the PSTN basic infrastructure already in place.

With the commercialization of the Internet in the 1980s and its emergence as a mass market platform for broadband communications in the 1990s, the Internet has evolved into the principal platform for our global public communications infrastructure. Increasingly, IP packet transport is providing the basic transport medium for telephony and other multimedia applications (voice, video, and data). What was an "overlay" application has itself now become basic infrastructure. Over time, the traditional PSTN providers have come to play a larger role in managing the infrastructure and investment required to support the Internet. Deregulation, market growth, and innovation have resulted in a more complex and interdependent Internet infrastructure ecosystem. The success of the Internet owes much to the interoperability and connectivity supported by ubiquitous adoption of the IP protocols and adherence to the "end-to-end" (e2e) design principles that have governed Internet architecture for so long.

However, the Internet's success has also posed significant problems. With growth has come heterogeneous services (not everyone needs or wants the same capabilities); new needs and requirements (support for real-time services or enhanced security); and complexity and size issues (arising from the sheer magnitude of today's Internet measured in terms of traffic and connectivity). To meet these challenges, the Internet needs to continue to evolve. In a process that looks at times like history repeating itself, the Internet is now spawning its own collection of "overlay" networks. There are many types and examples of overlays that arise to meet a range of purposes and needs. The emergence of these overlays raises interesting questions for the future of Internet architecture and the role of the Internet as a common platform for global communications. For example, are these "overlays" precursors to the future architecture of the Internet? Or, are they nasty barnacles on the Internet that threaten the e2e connectivity and interoperability that have proven to be such a key aspect of the Internet's value? What are the implications of overlays for industry structure and for the regulation of our public communications infrastructure? Will such networks will remain mainly an ingenious engineering artifact, failing to "grow up", or are they viable applications in light of technical, economic and regulatory forces.

Open questions include understanding what constitutes an overlay, the motivations for their deployment and use, and the potential conflicts and tensions that may arise among stakeholders. The goal of this project is to frame such a discussion and provide further thought on the implications of overlays for Internet architecture, industry structure/business strategy, and public policy. Our initial analysis demonstrates that the policy questions raised by overlays are multifaceted and diverse [1].


[1] D. D. Clark, W. Lehr, S. Bauer, P. Faratin. R. Sami, J. Wroclawski. The Growth of Internet Overlay Networks: Implications for Architecture, Industry Structure and Policy. In The Proceedings of the 34th Telecommunications Policy Research Conference (TPRC 05), Arlington, VA, USA, 2005.


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