An Engineering Perspective on the Layered and End-to-End Approaches Christopher S. Yoo University of Pennsylvania Law School May 6, 2010

Goals Clear up some misconceptions in the legal literature Examine the limitations of examining end points or layers in isolation Highlight some of the complexities of network behavior May 6, 2010 Yoo - Innovations in Internet Architecture 2

Belied by the hourglass model  Lots of innovation in the core  Especially in wireless networks Sparked debate among engineers  RFC 1958 vs. RFCs 3439, 3724  Blumenthal & Clark (2001) Inconsistent with the original e2e paper – Yoo (2004) The End-to-End Argument as “Dumb Pipes” May 6, 2010 Yoo - Innovations in Internet Architecture 3 Network Transport Applications Physical Data Link

Layers as Presented in the Legal Literature Tend to present as four layers: content, application, network, physical Tend to map onto the end-to-end argument By compressing transport and network layers, ignores key differences  Transport layer runs only on the edge; network layer also runs in the core  Many key protocols violate the layers principle: UDP, FTP, H.323 (VoIP) May 6, 2010 Yoo - Innovations in Internet Architecture 4

Interactions Among Layers Discussion of AIMD and RED in tutorial shows how layers interact with one another  Multiple sessions (application layer) affects queuing fairness (data link layer)  Lack of ACKs (transport layer) affects congestion management May 6, 2010 Yoo - Innovations in Internet Architecture 5

Advantages of Core Based Solutions Scale economies Aggregation of information  Congestion is the interaction of flows; individual hosts do not have information about other hosts  Some security risks require seeing behavior of multiple hosts (spam, botnets) Trust  Third party intermediaries may be more trustworthy than the host – Blumenthal & Clark (2007) May 6, 2010 Yoo - Innovations in Internet Architecture 6

The Localization of Information Application layer does not have enough information Individual autonomous systems may have only localized information  Routing  Downstream congestion Internet may be analyzed as a problem of distributed optimization with incomplete information  Architectural goal is to encourage local optimization decisions that promote global optimization May 6, 2010 Yoo - Innovations in Internet Architecture 7

Design Hierarchies and Innovation Innovation in the presence of network economic effects requires horizontal coordination It is even more difficult in the context of design hierarchies (interdependent technological processes)  Promotes innovation and competition consistent with the hierarchy  Retards innovation inconsistent with the hierarchy Sets technological agenda and institutions Requires vertical as well as horizontal coordination May 6, 2010 Yoo - Innovations in Internet Architecture 8

May 6, 2010 Yoo - Innovations in Internet Architecture 9 How End-to-End and Layers Can Obscure Analysis: Web Error Redirect DNS-based Three possibilities: networks, search engine, browser End-to-end: not appropriate for network provider Real issue in WER: advertising revenue Antitrust: focus on product market Antitrust: focus on geographic market (national)  Search engines have national footprint  Last-mile providers limited to 30% of the country

Conclusion Legal literature does not frame layers and end-to- end in a manner consistent with engineering Layering and end-to-end promote certain kinds of innovation at the expense of others Complex interactions as traffic scales are one of the defining characteristics of network behavior Localization of information makes interactions even more unpredictable May 6, 2010 Yoo - Innovations in Internet Architecture 10