Designing Enforceable Network Contracts
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Internet connectivity depends on contractual agreements between cooperating entities, such as administrative domains (AD), where an agreement over a certain level of service is made. Contracts (e.g., SLAs) for providing certain levels of service must be enforceable, and ADs must have an incentive to meet their contractual obligations. Previous work has designed mechanisms for both pricing and network accountability, but no existing work examines contract structures with respect to different accountability frameworks, and how together they may affect an AD’s incentives to fulfill contracts. We study how different contract structures—in particular, path-based versus pairwise contracts—affect ADs’ incentives to establish contracts (which, in turn, can affect overall connectivity) and, once contracts are established, to forward traffic according accordingly. This paper presents several contributions. First, we derive sufficient conditions for path-based contract systems and accountability frameworks for entities to have an incentive to forward traffic according to their contracts, provided that all parties involved are rational. Second, we show that for path-based contracts at equilibrium where nodes are encouraged to fulfill their contracts, only a constant amount of monitoring is required for every participant to make a positive profit; this is not the case for pairwise contracts. Third, we show how systems that rely on pairwise contracts are prone to depeering in presence of sufficient supply and demand due to coarse granularity, a contractual failure that systems which rely on path-based contracts are immune to. We propose modifications to pairwise contracts that could prevent such failures. Finally, we present situations of depeering that may be unpreventable due to maliciously behaving parties for both pairwise and path-based contract structures. For such scenarios, we show that while path-based contracts allow the sender of traffic to get reimbursed, this is not guaranteed in pairwise contract systems.