The Internet was designed as a packet-switched network in the 1960's and 1970's, with the explicit intent of sacrificing quality-of-service guarantees for an individual application in order to optimize channel usage and provide optimal median service for all applications. This approach was successful, since the application mix of the Internet heretofore has been dominated by applications with low quality-of-service needs: primarily bulk data transfer and low-bandwidth text- based interactive applications. As the Internet absorbs other networks and applications with strong quality-of-service requirements (television, voice over IP) , this tradeoff changes. We are faced with the problem of introducing the quality- of-service guarantees of circuit-switching into packet-switched networks. Fundamental change to the lower layers of the Internet stack have proven infeasible; even strongly-motivated, well-designed modifications which made transition a first-class design consideration have had difficult introductions. ATM and IPv6 are two recent examples. One effective transition strategy for new networking techniques has been the use of overlays. In this paper, we introduce the concept of a service overlay network, to offer circuit-switched behavior on legacy IP networks, and establish the requirements on the underlying IP network to make this strategy effective.

To improve the performance of VPN connections we investigate how the bandwidth of multiple access links can be aggregated with inverse multiplexing to create a single, higher capacity logical communication link. But achieving the maximum possible aggregated TCP throughput becomes extremely challenging if the underlying links either use different technologies (e.g., DSL, cable modem) or suffer different or time-varying communication characteristics (e.g., available bandwidth, packet loss rate). To maximize VPN throughput we have constructed a system that combines two distinct innovations. First, we continuously measure the communication characteristics of the underlying component links in our aggregate and dynamically assign packets to each link in proportion to its available capacity. Second, we modify TCP congestion control across the inverse-multiplexed access hop to avoid rate decreases normally initiated by the delayed acknowledgments often triggered when using legacy TCP on multiple heterogeneous paths. We describe the systempsilas implementation, the test environment we built on Emulab, and show that when access links form the communication bottleneck in the end-to-end connection we can significantly increase VPN performance over conventional approaches.

Denial-of-service (DoS) research community lacks accurate metrics to evaluate an attack's impact on network services, its severity and the effectiveness of a potential defense. We propose several DoS impact metrics that measure the quality of service experienced by end users during an attack, and compare these measurements to application-specific thresholds. Our metrics are ideal for testbed experimentation, since necessary traffic parameters are extracted from packet traces gathered during an experiment.

This paper presents Sharp, a framework for secure distributed resource management in an Internet-scale computing infrastructure. The cornerstone of Sharp is a construct to represent cryptographically protected resource claims ---promises or rights to control resources for designated time intervals---together with secure mechanisms to subdivide and delegate claims across a network of resource managers. These mechanisms enable flexible resource peering : sites may trade their resources with peering partners or contribute them to a federation according to local policies. A separation of claims into tickets and leases allows coordinated resource management across the system while preserving site autonomy and local control over resources. Sharp also introduces mechanisms for controlled, accountable oversubscription of resource claims as a fundamental tool for dependable, efficient resource management. We present experimental results from a Sharp prototype for PlanetLab, and illustrate its use with a decentralized barter economy for global PlanetLab resources. The results demonstrate the power and practicality of the architecture, and the effectiveness of oversubscription for protecting resource availability in the presence of failures.

This paper describes an operating system (OS) interface for active routers. This interface allows code loaded into active routers to access the router's memory, communication, and computational resources on behalf of different packet flows. In addition to motivating and describing the interface, the paper also reports our experiences implementing the interface in three different OS environments: Scout, the OSKit, and the esokernel.