Cascading failures in critical networked infrastructures that result even from a single source of failure often lead to rapidly widespread outages as witnessed in the 2013 Northeast blackout in Northern America. The e...
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Cascading failures in critical networked infrastructures that result even from a single source of failure often lead to rapidly widespread outages as witnessed in the 2013 Northeast blackout in Northern America. The ensuing problem of containing future cascading failures by placement of protection or monitoring nodes in the network is complicated by the uncertainty of the failure source and the missing observation of how the cascading might unravel, be it the past cascading failures or the future ones. This paper examines the problem of minimizing the outage when a cascading failure from a single source occurs. A stochastic optimization problem is formulated where a limited number of protection nodes, when placed strategically in the network to mitigate systemic risk, can minimize the expected spread of cascading failure. We propose the vaccine centrality, which is a network centrality based on the partially ordered sets (poset) characteristics of the stochastic program and distributed message-passing, to design efficient approximation algorithms with provable approximation ratio guarantees. In particular, we illustrate how the vaccine centrality and the poset-constrained graphalgorithms can be designed to tradeoff between complexity and optimality, as illustrated through a series of numerical experiments. This paper points toward a general framework of network centrality as statistical inference to design rigorous graph analytics for statistical problems in networks.
Bulk data transfers, such as backups and propagation of bulky updates, account for a large portion of the inter-datacenter traffic. These bulk transfers consume massive bandwidth and further increase the operational c...
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Bulk data transfers, such as backups and propagation of bulky updates, account for a large portion of the inter-datacenter traffic. These bulk transfers consume massive bandwidth and further increase the operational cost of datacenters. The advent of store-and-forward transfer mode offers the opportunity for cloud provider companies to transfer bulk data by utilizing dynamic leftover bandwidth resources. In this paper, we study the multiple bulk data transfers scheduling problem in inter-datacenter networks with dynamic link capacities. To improve the network utilization while guaranteeing fairness among requests, we employ the max-min fairness and aim at computing the lexicographically maximized solution. Leveraging the time-expanded technique, the problem in dynamic networks is formulated as a static multi-flow model. Then, we devise an optimal algorithm to solve it simultaneously from routing assignments and bandwidth allocation. To further reduce the computational cost, we propose to select an appropriate number of disjoint paths for each request. Extensive simulations are conducted on a real datacenter topology and prove that (i) benefiting from max-min fairness, the network utilization is significantly improved while honoring each individual performance;(ii) a small number of disjoint paths per request are sufficient to obtain the near optimal allocation within practical execution time. Copyright (c) 2013 John Wiley & Sons, Ltd.
In a communication network with a source node, a multicast tree is defined as a tree rooted at the source node and all its leaves being recipients of the multicast originating at the source. The tree or bandwidth cost...
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In a communication network with a source node, a multicast tree is defined as a tree rooted at the source node and all its leaves being recipients of the multicast originating at the source. The tree or bandwidth cost is normally measured by its utilization of tree links along with the quality of service (QoS) measures such as delay constraint and end-to-end delay. however, if nodes are allowed to join or leave the multicast group at any time during the lifetime of the multicast connection, then the problem is known as dynamic multicast routing problem. In this article, we combine a greedy approach with static multicast routing using Tabu Search to find a low-cost dynamic multicast tree with desirable QoS parameters. The proposed algorithm is then compared with several static multicast routing algorithms. The simulation results show that, on a large number of events, i.e., where nodes are leaving or joining, the proposed algorithm is able to find multicast trees of lower cost and more desirable QoS properties.
At faculties preparing students in the area of computer science subjects dealing with graph theory and algorithms belong to essential parts. Students studying this field of study are also expected to have good English...
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At faculties preparing students in the area of computer science subjects dealing with graph theory and algorithms belong to essential parts. Students studying this field of study are also expected to have good English language skills. Engagement of students in the learning process and carefully prepared study materials seem to be crucial elements of a successful teaching/learning process. If students deal with a task in an interesting and enjoyable way, they can recall the explained subject matter much more easily and, even more, their engagement is supported and keeps progressing. To get students engaged in the subjects dealing with graph theory and algorithms a particular problem with a real life example or a puzzle is introduced as a prototype of the explained concept or algorithm and a suitable graph-representation of a problem is discussed. Practising and reinforcing language skills play a very important role in foreign language education. With regard to the fact that our students of computer science specialization study both graph theory and algorithms together with English language, we innovated study materials testing their skills in both subjects combining graphtheory tasks with English language tasks. Some examples using puzzles will be introduced in the paper. The aim of the paper is to introduce our approach to other pedagogues as a good inspiration for their teaching.
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