Inter-domain path computation, or the ability to compute end-to-end paths across multiple domains, is the next step toward wide deployment of a distributed control plane with support for traffic engineering. A key enabler to achieve this goal is the introduction of a Path Computation Element (PCE) in each domain. There are various ways these elements can collaborate to compute an end-to-end path; of particular interest to us in this paper is cooperative path computation, a scheme where PCEs exchange path information in the context of a specific end-to-end path computation instance, often prior to signaling the path. We show that depending on the information available to each PCE, cooperation can take one of two forms, which we call model-based and ad hoc. We demonstrate that model-based cooperation is essentially a multistage decision problem, and offer a probabilistic analysis which we believe is the key to understanding the problem and developing efficient inter-domain path computation heuristics. In particular, we argue that having an estimate of the blocking probability in each domain can be helpful in determining the path computation effort needed to find an end-to-end path.
This paper contains a methodology for analyzing and designing a computer network for application to complex control systems. The focus is on the analysis and design of a local area network (LAN) for realizing the high-level control network that interconnects inputoutput controllers with devices for monitoring and analysis and with high-level controllers such as supervisory PLCs. Part of the development given in this paper can also be applied to the device-level network (fieldbus) that interconnects input-output controllers with sensors, * This work was supported in part by ERDA under Contract No. 97090. actuators, and other devices in the system being controlled. The high-level network and the device-level network form a two-layer architecture that is typical in control applications. A procedure is given for generating a network design with a hierarchical hub topology having full redundancy. Then in terms of a graph model of the network, procedures are given for studying network availability and analyzing the information flow rates through the links and internal nodes of the network
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