Professor Cruz's early work was on the analysis of information flow in communication networks. He is known for the development of a research area called "network calculus" for characterizing the flow of data through packet-switching networks, including the Internet. By analyzing the potential burstiness of traffic flows, the calculus identifies the possible delay of packets queuing up at various points in a network. Previous mathematical analyses of queuing delay were largely confined to statistical approaches that addressed only a single queue. The "traffic envelope," a key network-calculus concept, has been applied in a wider range of areas including performance-assessment of data-scheduling algorithms, in characterizations of traffic that crosses network boundaries, in connection with "Service Level Agreements" (SLAs) for billing in privately operated networks including frame-relay networks run by various telecommunication carriers, and in research aimed at better specifying quality-of-service (QoS) levels for network traffic flows.
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