Search

Abstract: Valiant load balancing (VLB) network has been proposed as a capacity-efficient solution to handle highly dynamic traffic in future backbone networks. In this paper, we study the availability of VLB networks that are overlaid over an optical infrastructure. The main challenges in such a context arise from the unique routing and protection scheme that goes beyond the definition of conventional connection-level service availability as well as the logical link failure correlation that prohibits the use of traditional analytical methods. We propose a network-level availability model to compute the probability that a VLB network is congestion-free under all traffic patterns. Numerical results show that with a proper truncation level, our calculation on availability can be accelerated significantly by generating tight lower and upper bounds. Our main finding is that physical link sharing in a two-layer setting degrades the network availability drastically by several orders of magnitude due to the full mesh requirement for VLB networks, and may remove the capacity efficiency advantage of VLB networks. [Copyright &y& Elsevier]

Abstract: Even with protection, user traffic flows can be disrupted due to network failures that are beyond the protection capability. One of the quantitative metrics to measure the service quality in such a context is “availability”. We study analytical models that compute availability of upper-layer flows in two-layer networks with dedicated path protection at either the upper or the lower layer. Our investigations reveal that existing analytical models significantly overestimate availability requirements on lower-layer links, and exaggerate upper-layer flow unavailability by treating correlated upper-layer failures as being independent. In contrast, our proposed model takes into account such correlations by tracing upper-layer failures to lower-layer root causes, thus greatly relaxing unnecessary high-availability requirements on lower-layer links without compromising the availability of upper-layer flows. In our simulation examples, using the existing models, up to 66.6% and 89.2% of the total flows are overestimated on their unavailability under dedicated path protection at the upper and the lower layer, respectively. Moreover, the average unavailability redundancy built into these flows is about 30% and 15% for protection at the upper and the lower layer, respectively. Furthermore, we compare flow availability under the two protection schemes, and show that given the same initial unprotected network states, protection at the lower layer enjoys lower average flow unavailability than protection at the upper layer. [Copyright &y& Elsevier]