Kwong, Kin-Wah
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Publication Always Acyclic Distributed Path Computation(2008-05-20) Guérin, Roch A; Ray, Saikat; Kwong, Kin-Wah (Eric); Sofia, RuteDistributed routing algorithms may give rise to transient loops during path recomputation, which can pose significant stability problems in high-speed networks. We present a new algorithm, Distributed Path Computation with Intermediate Variables (DIV), which can be combined with any distributed routing algorithm to guarantee that the directed graph induced by the routing decisions remains acyclic at all times. The key contribution of DIV, besides its ability to operate with any routing algorithm, is an update mechanism using simple message exchanges between neighboring nodes that guarantees loop-freedom at all times. DIV provably outperforms existing loop-prevention algorithms in several key metrics such as frequency of synchronous updates and the ability to maintain paths during transitions. Simulation results quantifying these gains in the context of shortest path routing are presented. In addition, DIV's universal applicability is illustrated by studying its use with a routing that operates according to a non-shortest path objective. Specifically, the routing seeks robustness against failures by maximizing the number of next-hops available at each node for each destination.Publication On the Feasibility and Efficacy of Protection Routing in IP Networks(2009-12-10) Kwong, Kin-Wah (Eric); Guérin, Roch A; Gao, Lixin; 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.Publication Quantifying Content Consistency Improvements Through Opportunistic Contacts(2009-08-12) Kwong, Kin-Wah; Guérin, Roch A; Chaintreau, AugustinThe sharing and dissemination of online content is one of the main purposes of social network applications, and the amount of content accessed through them, in particular through portable devices such as smartphones and PDAs, is expected to increase. Consumption of online content, however, does not require a continuous online presence. Content can be downloaded, consumed, modified, and uploaded at different times. An opportunity to improve a user's access to up-to-date information from its own social network is to take advantages of opportunistic contacts between mobile devices, \ie without waiting for connectivity to the network infrastructure. In other words, users of a social network application may receive more fresh content with no extra infrastructure deployment, simply by communicating with mobile devices of other users, in a delay-tolerant manner. Assessing the magnitude of this improvement is, however, challenging. For example, the frequency and patterns of such contacts are partly a function of the social connectivity of users, and so will be the availability of relevant information to share and more importantly the willingness to share that information. All these influence in non-trivial ways the gains that can be realized through opportunistic contacts. The paper's main contribution is in providing a quantitative handle through which these gains can be estimated, while accounting for the above factors.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 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 Always Acyclic Distributed Path Computation(2009-10-01) Ray, Saikat; Guérin, Roch A; Kwong, Kin Wah (Eric); Sofia, RuteDistributed routing algorithms may give rise to transient loops during path recomputation, which can pose significant stability problems in high-speed networks. We present a new algorithm, Distributed Path Computation with Intermediate Variables (DIV), which can be combined with any distributed routing algorithm to guarantee that the directed graph induced by the routing decisions remains acyclic at all times. The key contribution of DIV, besides its ability to operate with any routing algorithm, is an update mechanism using simple message exchanges between neighboring nodes that guarantees loop-freedom at all times. DIV provably outperforms existing loop-prevention algorithms in several key metrics such as frequency of synchronous updates and the ability to maintain paths during transitions. Simulation results quantifying these gains in the context of shortest path routing are presented. In addition, DIV’s universal applicability is illustrated by studying its use with a routing that operates according to a non-shortest path objective. Specifically, the routing seeks robustness against failures by maximizing the number of next-hops available at each node for each destination.Publication Improving Service Differentiation in IP Networks through Dual Topology Routing(2007-10-23) Kwong, Kin-Wah (Eric); Guérin, Roch A; Shaikh, Anees; Tao, ShuThe convergence on IP of a wide variety of traffic types has strengthened the need for service differentiation. Service differentiation relies on two equally important components: (i) resource allocation, i.e., what resources does a given service class have access to; and (ii) contention resolution, i.e., how is access to shared resources arbitrated between services classes. The latter has been well studied with numerous mechanisms, e.g., scheduling and buffer management, supporting it in modern routers. In contrast, relatively few studies exist on the former, and in particular on the impact of routing that determines the resources a given service class is assigned to. This is the focus of the paper, which seeks to investigate how routing influences a network’s ability to efficiently support different service classes. Of particular interest is the extent to which the ability to route service classes separately is beneficial. This question is explored for a base configuration involving two classes with either similar or entirely different service objectives (cost functions). The paper’s contributions are in demonstrating and quantifying the benefits that the added flexibility of different (dual) routing affords, and in developing an efficient heuristic for computing jointly optimal routing solutions. The former can motivate the deployment of newly standardized multi-topology routing (MTR) functionality. The latter is a key enabler for the effective use of such capability.Publication Controlling the Growth of Internet Routing Tables Through Market Mechanisms(2010-01-01) Kwong, Kin-Wah; Guerin, RochThe growth of core Internet routing tables has been such that it is now viewed as an impediment to the continued expansion of the Internet. The main culprit is multi-homing that stems from sites' desire for greater reliability and diversity in connectivity. These locally rational decisions have a global impact on the Internet, and there is currently no mechanism to effectively control them. A number of technical solutions are being pursued, but this paper explores the use of a "market mechanism." It formulates a model that accounts for sites' incentives and the impact their connectivity choices have on the size of routing tables, and introduces a pricing scheme that seeks to better reapportion the resulting costs. The model is solved for two configurations that capture different deployment realizations and stages. They demonstrate the scheme's effectiveness in controlling the growth of Internet routing tables, while improving the welfare of sites and Internet Service Providers.