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Traditional Internet protocol (IP) networks are built with very limited-capacity planning and design optimization, and can only provide best-effort service without performance guarantees. To meet customer expectations, however, IP networks must be designed for predictable performance; in particular, network service providers must be able to offer bandwidth guarantees for virtual private network (VPN) customers. Lucent Technologies' PacketStar IP switch supports novel traffic scheduling and buffer management capabilities - including per-flow queuing with weighted fair queuing (WFQ) and longest-queue drop (LQD) - that provide minimum bandwidth guarantees for VPNs while achieving a very high level of resource utilization. Legacy routers, on the other hand, do not support adequate flow isolation. Their first-in-first-out (FIFO) scheduling, even when combined with random early detection (RED) buffer management, results in little control over bandwidth sharing among VPNs, and throughput is dictated mainly by the dynamic properties of transport control protocol (TCP). In this paper, we present algorithms for IP network design and capacity optimization that serve as a foundation for determining the economic benefits of providing quality of service (QoS) differentiation on a network-wide basis using advanced, next-generation routers such as the Lucent PacketStar IP switch. The algorithms yield strategies for optimal placement of such routers in an embedded network of legacy routers. We illustrate and validate our design proposals with several case studies, including one based on a large-scale carrier-class network. |
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