Guérin, Roch A
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Publication Distributed Uplink Scheduling in CDMA Networks(2007-05-14) Subbaraman, Ramesh; Sridharan, Ashwin; Guérin, Roch AEver more powerful mobile devices are handling a broader range of applications, so that giving them greater control in scheduling transmissions as a function of application needs is becoming increasingly desirable. Several standards have, therefore, proposed mechanisms aimed at giving devices more autonomy in making transmission decisions on the wireless uplink. This paper explores the impact this can have on total throughput in CDMA systems, where this control has traditionally been centralized. The investigation relies on a simple distributed policy that helps provide insight into the impact of distributed decisions on overall system efficiency, and identify guidelines on how to best mitigate it.Publication Balancing Performance, Robustness and Flexibility in Routing Systems(2010-01-01) Kwong, Kin-Wah; Guérin, Roch; Shaikh, Anees; Tao, ShuModern networks face the challenging task of handling increasingly diverse traffic that is displaying a growing intolerance to disruptions. This has given rise to many initiatives, and in this paper we focus on multiple topology routing as the primary vehicle for meeting those demands. Specifically, we seek routing solutions capable of not just accommodating different performance goals, but also preserving them in the presence of disruptions. The main challenge is computational, i.e., to identify among the enormous number of possible routing solutions the one that yields the best compromise between performance and robustness. This is where our principal contribution lies, as we expand the definition of critical links -- a key concept in improving the efficiency of routing computation -- and develop a precise methodology to efficiently converge on those solutions. Using this new methodology, we demonstrate that one can compute routing solutions that are both flexible in accommodating different performance requirements and robust in maintaining them in the presence of failures and traffic fluctuations.Publication The Impact of Reprovisioning on the Choice of Shared versus Dedicated Networks(2010-09-20) Sen, Soumya; Yamauchi, Kristin; Guerin, Roch; Hosanagar, KartikAs new network services emerge, questions about service deployment and network choices arise. Although shared networks, such as the Internet, offer many advantages, combining heterogeneous services on the same network need not be the right answer as it comes at the cost of increased complexity. Moreover, deploying new services on dedicated networks is becoming increasingly viable, thanks to virtualization technologies. In this work, we introduce an analytical framework that gives Internet Service Providers the ability to explore the trade-offs between shared and dedicated network infrastructures. The framework accounts for factors such as the presence of demand uncertainty for new services, (dis)economies of scope in deployment and operational costs, and the extent to which new technologies allow dynamic (re)provisioning of resources in response to excess demands. The main contribution is the identification and quantification of dynamic (re)provisioning as a key factor in determining the preferred network infrastructure, i.e. shared or dedicated.Publication Balancing Performance, Robustness and Flexibility in Routing Systems(2008-09-04) Kwong, Kin-Wah; Guérin, Roch A; Shaikh, Anees; Tao, ShuModern networks face the daunting task of handling increasingly diverse traffic that is displaying a growing intolerance to disruptions. This has given rise to many initiatives, and in this paper we focus on multiple topology routing as the primary vehicle for meeting those demands. Specifically, we seek routing solutions capable of not just accommodating different performance goals, but also preserving them in the presence of disruptions. The main challenge is computational, i.e., to identify among the enormous number of possible routing solutions the one that yields the best compromise between performance and robustness. This is where our principal contribution lies, as we expand the definition of critical links – a key concept in improving the efficiency of routing computation – and develop a precise methodology to efficiently converge on those solutions. Using this new methodology, we demonstrate that one can compute routing solutions that are both flexible in accommodating different performance requirements and robust in maintaining them in the presence of failures and traffic fluctuations.Publication On Evaluating Loss Performance Deviation: A Simple Tool and Its Practical Applications(2003-02-24) Xu, Ying; Guérin, Roch AThe focus of this paper is on developing and evaluating a practical methodology for determining if and when different types of traffic can be safely multiplexed within the same service class. The use of class rather than individual service guarantees offers many advantages in terms of scalability, but raises the concern that not all users within a class see the same performance. Understanding when and why a user will experience performance that differs significantly from that of other users in its class is, therefore, of importance. Our approach relies on an analytical model developed under a number of simplifying assumptions, which we test using several real traffic traces corresponding to different types of users. This testing is carried out primarily by means of simulation, to allow a comprehensive coverage of different configurations. Our findings establish that although the simplistic model does not accurately predict the absolute performance that individual users experience, it is quite successful and robust when it comes to identifying situations that can give rise to substantial performance deviations within a service class. As a result, it provides a simple and practical tool for rapidly characterizing real traffic profiles that can be safely multiplexed.Publication Making IGP Routing Robust to Link Failures(2005-05-02) Sridharan, Ashwin; Guérin, Roch AAn important requirement of a robust traffic engineering solution is insensitivity to changes, be they in the form of traffic fluctuations or changes in the network topology because of link failures. In this paper we focus on developing a fast and effective technique to compute traffic engineering solutions for OSPF/IS-IS environments that are robust to link failures in the logical topology. OSPF and IS-IS are the dominant intra-domain routing protocols where traffic engineering is primarily governed by link weights. Our focus is on computing a single set of link weights for a traffic engineering instance that performs well over all single logical link failures. Such types of failures, although usually not long lasting, of the order of tens of minutes, can occur with high enough frequency, of the order of several a day, to significantly affect network performance. The relatively short duration of such failures coupled with issues of computational complexity and convergence time due to the size of current day networks discourage adaptive reactions to such events. Consequently, it is desirable to a priori compute a routing solution that performs well in all such scenarios. Through computational evaluations we demonstrate that our technique yields link weights that perform well over all single link failures and also scales well, in terms of computational complexity, with the size of the network.Publication Achieving Near-Optimal Traffic Engineering Solutions for Current OSPF/IS-IS Networks(2003-03-30) Sridharan, Ashwin; Guérin, Roch A; Diot, ChristopheTraffic engineering is aimed at distributing traffic so as to "optimize" a given performance criterion. The ability to carry out such an optimal distribution depends on both the routing protocol and the forwarding mechanisms in use in the network. In IP networks running the OSPF or IS-IS protocols, routing is over shortest paths, and forwarding mechanisms are constrained to distributing traffic uniformly over equal cost shortest paths. These constraints often make achieving an optimal distribution of traffic impossible. In this paper, we propose and evaluate an approach, based on manipulating the set of next hops for routing prefixes, that is capable of realizing near optimal traffic distribution without any change to existing routing protocols and forwarding mechanisms. In addition, we explore the tradeoff that exists between performance and the overhead associated with the additional configuration steps that our solution requires. The paper’s contributions are in formulating and evaluating an approach to traffic engineering for existing IP networks that achieves performance levels comparable to that offered when deploying other forwarding technologies such as MPLS.Publication Light-Weight Overlay Path Selection in a Peer-to-Peer Environment(2006-04-28) Fei, Teng; Tao, Shu; Gao, Lixin; Guérin, Roch A; Zhang, Zhi-LiLarge-scale peer-to-peer systems span a wide range of Internet locations. Such diversity can be leveraged to build overlay “detours” to circumvent periods of poor performance on the default path. However, identifying which peers are “good” relay choices in support of such detours is challenging, if one is to avoid incurring an overhead that grows with the size of the peer-to-peer system. This paper proposes and investigates the Earliest Branching Rule (EBR) to perform such a selection. EBR builds on the Earliest Diverging Rule (EDR) that selects relay nodes whose AS path diverges from the default path at the earliest possible point, but calls for monitoring a much smaller number of paths. As a result, it has a much lower overhead. The paper explores the performance and overhead of EBR, and compares them to that of EDR. The results demonstrate that EBR succeeds in selecting good relay nodes with minimum control overhead. Hence, providing a practical solution for dynamically building good overlays in large peer-to-peer systems.Publication Interactions, Competition and Innovation in a Service-Oriented Internet: An Economic Model(2009-12-21) Zhang, Zhi-Li; Nabipay, Papak; Odlyzko, Andrew; Guérin, Roch AThis paper presents a new economic approach for studying competition and innovation in a complex and highly interactive system of network providers, users, and suppliers of digital goods and services (i.e., service providers). It employs Cournot and Bertrand games to model competition among service providers and network providers, respectively, and develops a novel unified model to capture the interaction and competition among these players in a “service-oriented” Internet. Incentives for service and network innovation are studied in this model.Publication On the Feasibility and Efficacy of Protection Routing in IP Networks(2011-02-25) Kwong, Kin Wah (Eric); Gao, Lixin; Guérin, Roch A; Zhang, Zhi-LiWith network components increasingly reliable, routing is playing an ever greater role in determining network reliability. This has spurred much activity in improving routing stability and reaction to failures, and rekindled interest in centralized routing solutions, at least within a single routing domain. Centralizing decisions eliminates uncertainty and many inconsistencies, and offers added flexibility in computing routes that meet different criteria. However, it also introduces new challenges; especially in reacting to failures where centralization can increase latency. This paper leverages the flexibility afforded by centralized routing to address these challenges. Specifically, we explore when and how standby backup forwarding options can be activated, while waiting for an update from the centralized server after the failure of an individual component (link or node). We provide analytical insight into the feasibility of such backups as a function of network structure, and quantify their computational complexity. We also develop an efficient heuristic reconciling protectability and performance, and demonstrate its effectiveness in a broad range of scenarios. The results should facilitate deployments of centralized routing solutions.