Guérin, Roch A
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Publication Improving Performance Through Channel Diversity in the Presence of Bursty Losses(2005-08-29) Guérin, Roch A; Sarkar, Saswati; Guérin, Roch A; Sarkar, SaswatiAs more applications migrate to IP networks, ensuring a consistent level of service is increasingly important. One option is for the network to offer service guarantees. Another is to leverage the path diversity that the Internet intrinsically offers. Our focus is on understanding if and when one can indeed take advantage of multiple disjoint paths to improve performance. We consider an environment where loss patterns are bursty and where coding is used to provide robustness against packet losses. We assume that only long-term loss statistics are known about each path, and we seek to identify the best strategy for sending packets over the available paths. Our contributions are two-fold. First we demonstrate that even with minimal knowledge of channel characteristics and using simple transmission policies, path diversity can help significantly improve performance. Second, we derive an efficient method for identifying optimal policies, and more importantly characterize when having access to multiple paths can be of benefit.Publication Public Review - A Cooperative Uplink Power Control Scheme for Elastic Data Services in Wireless CDMA Systems(2006-07-01) Guérin, Roch A; Guérin, Roch AThis is a paper that is actually an excellent illustration of how CCR differs from more traditional publications, and also one for which I am glad to have the opportunity to write a public review that hopefully can shed some light on the reasons behind its acceptance. Don’t get me wrong, this is not a paper that I regret seeing in CCR, but this is paper that most likely would not have been accepted in most other publications, including conferences and workshops, at least not in its first submission. The focus of the paper is on resource management on the uplink of a CDMA wireless system, and in particular the combination of an admission control algorithm and a cooperative power control algorithm that maximize a utility function across admitted mobiles while taking QoS requirements into account. The topic is arguably important given the growing presence of CDMA wireless systems and the emergence of new standards such EVDO-1X Rev. A, which offer a range of new options allowing the use of "independent" transmission policies by mobile devices rather than always subjecting them to tight control from the base station. Understanding, if, when, and how such flexibility can be beneficial or harmful is an interesting and timely research area.Publication Distributed Uplink Scheduling in CDMA Networks(2007-05-14) Subbaraman, Ramesh; Guérin, Roch A; Subbaraman, Ramesh; 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 Supporting Excess Real-Time Traffic With Active Drop Queue(2006-10-01) Guérin, Roch A; Guérin, Roch A; Gupta, PranavReal-time applications often stand to benefit from service guarantees, and in particular delay guarantees. However, most mechanisms that provide delay guarantees also hard-limit the amount of traffic the application can generate, i.e., to enforce to a traffic contract. This can be a significant constraint and interfere with the operation of many real-time applications. Our purpose in this paper is to propose and investigate solutions that overcome this limitation. We have four major goals: 1) guarantee a delay bound to a contracted amount of real-time traffic; 2)transmit with the same delay bound as many excess real-time packets as possible; 3) enforce a given link sharing ratio between excess real-time traffic and other service classes, e.g., best-effort; and 4) preserve the ordering of real-time packets, if required. Our approach is based on a combination of buffer management and scheduling mechanisms for both guaranteeing delay bounds, while allowing the transmission of excess traffic. We evaluate the "cost" of our scheme by measuring the processing overhead of an actual implementation, and we investigate its performance by means of simulations using video traffic traces.Publication Balancing Performance, Robustness and Flexibility in Routing Systems(2010-01-01) Kwong, Kin-Wah; Guérin, Roch; 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 On the Feasibility and Efficacy of Protection Routing in IP Networks(2011-02-25) Kwong, Kin Wah (Eric); Guérin, Roch A; 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.Publication Making IGP Routing Robust to Link Failures(2005-05-02) Guérin, Roch A; 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 Real-Time Monitoring of Video Quality in IP Networks(2005-06-13) Tao, Shu; Guérin, Roch A; Guérin, Roch AThis paper investigates the problem of assessing the quality of video transmitted over IP networks. Our goal is to develop a methodology that is both reasonably accurate and simple enough to support the large-scale deployments that the increasing use of video over IP are likely to demand. For that purpose, we focus on developing an approach that is capable of mapping network statistics, e.g., packet losses, available from simple measurements, to the quality of video sequences reconstructed by receivers. A first step in that direction is a loss-distortion model that accounts for the impact of network losses on video quality, as a function of application-specific parameters such as the video codec and loss recovery technique, coded bit rate, packetization, video characteristics, etc. The model, although accurate, is poorly suited to large-scale, on-line monitoring, because of its dependency on many parameters that are difficult to estimate in real-time. As a result, we introduce a "relative quality" metric that bypasses this problem by measuring video quality against a quality benchmark that the network is expected to provide. The approach offers a lightweight video quality monitoring solution that is suitable for large-scale deployments. We assess its feasibility and accuracy through extensive simulations and experiments.Publication Does Over-Provisioning Become More or Less Efficient as Networks Grow Larger?(2005-11-06) Guérin, Roch A; Guérin, Roch AIP networks have seen tremendous growth in not only their size and speed, but also in the volume of traffic they carry. Over-provisioning is commonly used to protect network performance against traffic variations, be they caused by failures or transient surges. This paper investigates the influence that increasing network size has on the efficacy of over-provisioning in absorbing a certain range of traffic variations and preserving performance guarantees. For that purpose, we develop a general model that accounts for network topology, base offered traffic, and traffic variations, and allows us to explore how their combination behaves as the network and the traffic it carries grow. The model's generality enables us to investigate several representative scenarios and to identify critical thresholds in the relation between network and traffic growth, which delineate regions where a given amount of over-provisioning provides increasingly better protection against traffic variations. The results offer insight into how to grow IP networks in order to enhance their robustness.Publication A Simple FIFO-Based Scheme for Differentiated Loss Guarantees(2006-07-22) Huang, Yaqing; Guérin, Roch A; Huang, Yaqing; Guérin, Roch AToday’s Internet carries traffic from a broad range of applications with different requirements. This has stressed its original, one-class, best-effort model, and has been a major driver of the many efforts aimed at introducing QoS. These efforts have, however, been met with only limited success, in part because the complexity they add is often at odds with the scalability requirements of the Internet. This has motivated many investigations for solutions that offer a better trade-off between service differentiation and complexity. This paper shares similar goals and proposes a simple scheme, Bounded Random Drop (BRD), that supports multiple service classes and is implemented using a single FIFO queue and a basic random dropping mechanism. BRD focuses on loss differentiation, as although losses and delay are both important, the steady rise of Internet link speeds is progressively limiting the impact of delay differentiation. It offers strong loss differentiation capabilities, and does not require traffic profiles or admission controls. BRD guarantees each class losses that, when feasible, are no worse than a specified bound, while enforcing differentiation only when required to meet those bounds. The performance of BRD is investigated for a broad range of traffic mixes and shown to consistently achieve its design goals.