and thus must adapt to external conditions; all layers must make cost-based decisions about what mode of operation to use in response to performance feedback. This paper focuses on the generic interface between adjacent layers (client and server) in a multi-level hierarchy. The Adaptive Research Contracts (ARC) framework uses a bottom-up approach in which the server exposes a range of quality/cost modes to the client above. This allows the client to trade off various algorithms generating different workloads for multiple resources. A case study shows that control can be distributed effectively over multiple layers with ARC; global cost-effective solutions can be obtained with exchanging a small fraction of all possible control settings.

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This dissertation describes VServ, a service oering dynamic and resource-assured VPNs that can be acquired and modi ed on demand. In VServ, a VPN is both a subset of physical resources, such as bandwidth and label space, together with the means to perform ne-grained management of those resources. This network programmability, combined with QoS guarantees, enables the multiservice network|a single universal network that can support all types of service and thus be ecient, cost-eective and exible