To Peer or Not to Peer: Modeling the Evolution of the Internet's AS-Level Topology

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Abstract
Internet connectivity at the AS level, defined in terms of pairwise logical peering relationships, is constantly evolving. This evolution is largely a response to economic, politi- cal, and technological changes that impact the way ASs conduct their business. We present a new framework for modeling this evolutionary process by identifying a set of criteria that ASs consider either in establishing a new peering relationship or in reassessing an existing relationship. The proposed framework is intended to capture key elements in the decision processes underlying the formation of these relationships. We present two decision processes that are executed by an AS, depending on its role in a given peering decision, as a customer or a peer of another AS. When acting as a peer, a key feature of the AS's corresponding decision model is its reliance on realistic inter-AS traffic demands. To reflect the enormous heterogeneity among customer or peer ASs, our decision models are flexible enough to accommodate a wide range of AS-specific objectives. We demonstrate the potential of this new framework by considering different decision models in various realistic "what if" experiment scenarios. We implement these decision models to generate and study the evolution of the resulting AS graphs over time, and compare them against observed historical evolutionary features of the Internet at the AS level. I. INTRODUCTION We present a new framework for modeling the decision process by which connectivity between Autonomous Systems (ASs) in the Internet is established. An Autonomous System is an abstraction for representing a group of networks operated by a single administrative entity. Inter-AS connectivity is defined in terms of pairwise logical peering relationships. A peering relationship between two ASs corresponds to a contractual business agreement to exchange traffic directly be- tween them. Two ASs with an established peering relationship are physically connected with each other by at least one direct router-level link. A peering relationship is typically classified as either "customer-provider" or "peer-to-peer." In the former, one AS plays the role of a customer, and the other provides the customer with transit Internet access for a fee. In the latter, two ASs see mutual benefits in interconnecting each other (e.g., obtaining direct routes to the other party's networks), and share the cost of maintaining the relationship. Our AS peering decision model attempts to capture the decision making process that an AS would go through when it enters into peering relationships with other ASs. A critical step in developing such a model is to identify and define a set of plausible decision-making criteria considered by an AS that captures the essence of peering. Unlike previous efforts to describe AS-level Internet connectivity within the generic framework of random graph models, our objective is to specify non-generic, network-centric decision criteria that are relevant to establishing inter-AS peering relationships. A similar approach was adopted for intra-domain modeling by Li et al. (1).

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