Roman Chertov

Aerospace Corporation, Los Ángeles, California, United States

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Publications (22)1.56 Total impact

  • Daniel M. Havey · Roman Chertov · Kevin C. Almeroth
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    ABSTRACT: Streaming video over the Internet to wireless mobile devices has seen a tremendous increase in popularity amongst users. Recent improvements in infrastructure have made the delivery of video over wireless a reality. However, user demand for high definition video streams promises to quickly devour the bandwidth provided by these improvements. There has been extensive work to solve these problems. However, recent advancements at the application and transport layers have made possible the development of new methods that can improve throughput in existing HTTP/TCP infrastructure. In this paper we present a novel client driven application layer rate adaptation mechanism. Our solution can achieve significant throughput increases as compared to a standard rate adaptive HTTP/TCP video stream operating over a wireless link. In addition it operates with standard HTTP/TCP video servers and requires no in-network modifications or kernel changes at the client. We demonstrate the performance improvements of our proposed system through both emulation and deployment on a wireless mesh network in South Africa.
    No preview · Conference Paper · Jan 2012
  • Roman Chertov · Sonia Fahmy

    No preview · Article · Feb 2011 · ACM Transactions on Modeling and Computer Simulation
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    Roman Chertov
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    ABSTRACT: Most popular simulation and emulation tools use high-level models of forwarding behavior in switches and routers, and give little guidance on setting model parameters such as buffer sizes. Thus, a myriad of papers report results that are highly sensitive to the forwarding model or buffer size used. Incorrect conclusions are often drawn from these results about transport or application protocol performance, service provisioning, or vulnerability to attacks. In this paper, we argue that measurement-based models for routers and other forwarding devices are necessary. We devise such a model and validate it with measurements from three types of Cisco routers and one Juniper router, under varying traffic conditions. The structure of our model is device-independent, but the model uses device-specific parameters. The compactness of the parameters and simplicity of the model make it versatile for high-fidelity simulations that preserve simulation scalability. We construct a profiler to infer the parameters within a few hours. Our results indicate that our model approximates different types of routers significantly better than the default ns-2 simulator models. The results also indicate that queue characteristics vary dramatically among the devices we measure, and that backplane contention can be a factor.
    Preview · Article · Jan 2011
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    R. Chertov · K. Almeroth
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    ABSTRACT: Once, satellites were considered an important option for creating global Internet access. However, for a period of time, satellites were supplanted by other ground-based technologies. More recently, satellites have been proposed as an integral component in highly dynamic challenged environments where large numbers of mobile devices connect through satellite-based terminals. Routing within groups of mobile devices is performed by one of the myriad of wireless routing protocols, but over the space/ground link, BGP is the protocol of choice. In this work, we conduct a high fidelity experimental study of link intermittency on the space/ground link and its effect on BGP peering sessions between ground and satellite routers. Our results show that a routing architecture that does not correctly adapt to the particular characteristics of satellite links performs very poorly. By contrast, a correctly tuned routing architecture can survive prolonged outages intermixed with short periods of link connectivity.
    Preview · Conference Paper · Jul 2010
  • R. Chertov · K. Almeroth
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    ABSTRACT: Over the last several years there has been an ever increasing trend in using emulated testbeds for network experimentation. Emulated testbeds offer a reproducible and highly controlled experimental environment; however, due to the physical proximity of the nodes to each other in the data centre, the available links have very low propagation delays and unrealistic bandwidth. In this work, we conduct a qualitative comparison of three link shaping approaches. We focus on evaluating approaches as opposed to individual link shaping tools. Our goal in this work is to ascertain which approach yields the fewest emulation artefacts. Our results indicate that a transparent link shaping node significantly outperforms the other two methods.
    No preview · Article · Jul 2010 · International Journal of Communication Networks and Distributed Systems
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    Roman Chertov · Daniel Havey · Kevin Almeroth
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    ABSTRACT: Satellite systems are ideal for distributing the same content to a large number of users, as well as providing broadband connectivity in remote areas or backup in case of terrestrial network failures. Unlike terrestrial networks, satellite networks face a unique set of challenges, such as signal fading and interference from multiple transmitters combined with long propagation delays. A well known challenge is that these unique characteristics can have an adverse impact on various protocols, making it necessary to study protocol behavior in satellite networks. The challenge of our research, and the focus of this paper, is to develop an architecture for a high-fidelity and scalable emulation testbed tailored for mobile satellite communications research. The testbed is designed to provide multi-beam, multi-satellite, TDMA, and mobility functionality. Our validation studies demonstrate that the testbed is capable of achieving delay, loss, and jitter that can be associated with a mobile satellite link.
    Preview · Conference Paper · Apr 2010
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    D. Havey · R. Chertov · K. Almeroth
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    ABSTRACT: A wired testbed's usefulness for wireless research hinges on its ability to faithfully reproduce the wireless medium. One of the key properties of a wireless medium is its broadcast nature. Wireless broadcast behavior is used in applications such as cell phone and satellite networks to disseminate the same data to multiple users as well as perform time synchronization. In this paper, we investigate two methods that can be used to ascertain if a given wireless emulator is modeling the broadcast property correctly. Our results indicate that the better of the two proposed methods offers micro-second precision.
    Preview · Conference Paper · Jul 2009
  • Daniel Havey · Roman Chertov · Kevin Almeroth
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    ABSTRACT: Multiuser information-theoretic analysis of achievable communication rate regions over networks traditionally assumes that individual sources of information are independent. However, fully exploiting network-wide synergies requires an understanding of ...
    No preview · Conference Paper · Jun 2009
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    Roman Chertov
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    ABSTRACT: In this report, we have focused on three link shaping methods:hidden delay bridge, router rate limiting, and pause frames. The focus of the study was to determine which method produced the specified delay and bandwidth limit. In addition, the study also took into consideration variance of inter-packet gaps (jitter). To obtain the results, we have created a variety of constant UDP flows and compared the performance of the link shaping methods with each other. The results revealed that the delay bridge using the click modular router is superior to the other two methods.
    Preview · Article · Jan 2009
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    D. Havey · E. Barlas · R. Chertov · K. Almeroth · E. Belding
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    ABSTRACT: Because of the near ubiquitous communication available to network nodes beneath a satellites footprint, satellite network technology has enjoyed a recent and substantial increase in interest from academia, government, and commercial sectors. However, the benefit resulting from being beneath the satellite footprint comes at the cost of a substantial propogation delay, as well as other challenging network characteristics. To study networking over satellites, researchers need a network simulation tool that is capable of modeling existing and proposed satellite networks. This paper addresses the network modeling problem by adding an open source satellite mobility model (SatMob) suitable for Low/Medium Earth Orbit (LEO/MEO) satellites to Qualnet network simulation tool. We perform a basic set of experiments commonly found in network research by using an existing mobility model and SatMob. Our results indicate that our model yields an appreciable improvement over an existing Qualnet approach.
    Full-text · Conference Paper · Dec 2008
  • Roman Chertov · Sonia Fahmy · Ness B. Shroff

    No preview · Article · Dec 2008 · ACM Transactions on Modeling and Computer Simulation
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    Roman Chertov · Sonia Fahmy · Ness B. Shroff
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    ABSTRACT: Several popular simulation and emulation environments fail to account for realistic packet forwarding behaviors of commercial switches and routers. Such simulation or emulation inaccuracies can lead to dramatic and qualitative impacts on the results. In this paper, we present a measurement-based model for routers and other forwarding devices, which we use to simulate two different Cisco routers under varying traffic conditions. The structure of our model is device-independent, but requires device-specific parameters. We construct a profiling tool and use it to derive router parameter tables within a few hours. Our preliminary results indicate that our model can approximate the Cisco routers. The compactness of the parameter tables and simplicity of the model makes it possible to use it for high-fidelity simulations while preserving simulation scalability.
    Preview · Conference Paper · Apr 2008
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    Roman Chertov · Sonia Fahmy · Ness B. Shroff
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    ABSTRACT: In this paper, we investigate the dierences between simulation and emulation when conducting denial of service (DoS) attack experiments. As a case study, we consider low-rate TCP-targeted DoS attacks. We design constructs and tools for emulation testbeds to achieve a level of con- trol comparable to simulation tools. Through a careful sensitivity analysis, we expose diculties in obtaining meaningful measurements from the DETER, Emulab, and WAIL testbeds with de- fault system settings. We nd dramatic dierences between simulation and emulation results for DoS experiments. Our results also reveal that software routers such as Click provide a exible experimental platform, but require understanding and manipulation of the underlying network device drivers. Our experiments with commercial Cisco routers demonstrate that they are highly susceptible to the TCP-targeted attacks when ingress/egress IP lters are used.
    Preview · Article · Jan 2008
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    ABSTRACT: While the DETER testbed provides a safe environment and basic tools for security experimentation, researchers face a significant challenge in assembling the testbed pieces and tools into realistic and complete experimental scenarios. In this paper, we describe our work on developing a set of sampled and comprehensive benchmark scenarios, and a workbench for experiments involving denial-of-service (DoS) attacks. The benchmark scenarios are developed by sampling features of attacks, legitimate traffic and topologies from the real Internet. We have also developed a measure of DoS impact on network services to evaluate the severity of an attack and the effectiveness of a proposed defense. The benchmarks are integrated with the testbed via the experimenter's workbench - a collection of traffic generation tools, topology and defense library, experiment control scripts and a graphical user interface. Benchmark scenarios provide inputs to the workbench, bypassing the user's selection of topology and traffic settings, and leaving her only with the task of selecting a defense, its configuration and deployment points. Jointly, the benchmarks and the experimenter's workbench provide an easy, point-and-click environment for DoS experimentation and defense testing.
    Full-text · Conference Paper · Jun 2007
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    Roman Chertov · Sonia Fahmy · Ness B. Shroff
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    ABSTRACT: Simulation, emulation, and wide-area testbeds exhibit different strengths and weaknesses with respect to fidelity, scalability, and manageability. Fidelity is a key concern since simulation or emulation inaccuracies can lead to a dramatic and qualitative impact on the results. For example, high-bandwidth denial of service attack floods of the same rates have very different impact on the different platforms, even if the experimental scenario is supposedly identical. This is because many popular simulation and emulation environments fail to account for realistic commercial router behaviors, and incorrect results have been reported based on experiments conducted in these environments. In this paper, we describe the architecture of a black-box router profiling tool which integrates the popular ns-2 simulator with the Click modular router and a modified network driver. We use this profiler to collect measurements on a Cisco router. Our preliminary results demonstrate that routers and other forwarding devices cannot be modeled as simple output port queues, even if correct rate limits are observed. We discuss our future work plans for using our data to create high-fidelity network simulation/emulation models that are not computationally prohibitive.
    Preview · Conference Paper · Jun 2007
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    Roman Chertov · Sonia Fahmy · Ness B. Shroff
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    ABSTRACT: In this paper, we investigate the applicability of simulation and emulation for denial of service (DoS) attack experimentation. As a case study, we consider low-rate TCP-targeted DoS attacks. We design constructs and tools for emulation testbeds to achieve a level of control comparable to simulation tools. Through a careful sensitivity analysis, we expose difficulties in obtaining meaningful measurements from the DETER and Emulab testbeds with default system settings, and find dramatic differences between simulation and emulation results for DoS experiments. Our results also reveal that software routers such as Click provide a flexible experimental platform, but require understanding and manipulation of the underlying network device drivers. We compare simulation and testbed results to a simple analytical model for predicting the average size of the congestion window of a TCP flow under a low-rate TCP-targeted attack, as a function of the DoS attack frequency. We find that the analytical model and ns-2 simulations closely match in typical scenarios. Our results also illustrate that TCP-targeted attacks can be effective even when the attack frequency is not tuned to the retransmission timeout. The router type, router buffer size, attack pulse length, attack packet size, and attacker location have a significant impact on the effectiveness and stealthiness of the attack
    Preview · Conference Paper · Jan 2006
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    Roman Chertov · Sonia Fahmy
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    ABSTRACT: Distributed virtual environments such as massive multi-player games require multiple servers to balance computational load. This paper investigates the architecture of a unified environment where the virtual online world is not partitioned according to rigid boundaries, but according to an adaptive paradigm. Since it is difficult to develop an optimal load balancing algorithm for a unified environment, we propose an optimistic scheme that quickly converges. The cost of frequent migrations is reduced by following a push/push data exchange model. We analyze the computational time costs of such a system and give simulation results to gauge its performance. The simulation results confirm that our load balancing scheme is efficient and can support large numbers of clients.
    Preview · Conference Paper · Jan 2006
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    Roman Chertov · Sonia Fahmy · Ness B. Shroff
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    ABSTRACT: I. INTRODUCTION Experimentation with security attacks introduces additional requirements compared to traditional networking and distributed system experiments. High capacity attack flows can push sys- tems beyond their expected operational regions, and expose un- expected behaviors. Many popular simulation and emulation environments fail to account for such behaviors, and incorrect results have been reported based on experiments conducted in these environments. In addition, simulation and emulation en- vironments sometimes introduce artifacts, altering the experi- mental outcome and its interpretation. Finally, identification of systems settings that significantly impact experimental results is crucial for creating repeatable experiments. In this paper, we present the results of a careful sensi- tivity analysis we have conducted, which exposes difficulties in obtaining meaningful measurements from three emulation testbeds: DETER at http://www.isi.deterlab.net/, Emulab at http://www.emulab.net/, and Wisconsin Advanced Internet Lab- oratory (WAIL) at http://www.schooner.wail.wisc.edu with de- fault system settings. We compare these results to ns-2 sim- ulation results, and find dramatic differences between simula- tion and emulation results for Denial of Service (DoS) attack experiments. We select low-rate TCP-targeted DoS attacks as a case study, since these attacks have generated significant in- terest in the research community in the past few years. To validate our comparisons, we use a simple analytical model of TCP performance degradation, in the presence of a special case of TCP-targeted DoS attacks (those not causing timeouts), as a lower bound. Our results reveal that software routers such as Click provide a flexible experimental platform, but require understanding and manipulation of the underlying network de- vice drivers. We also discuss our future work plans for creating higher fidelity network simulation and emulation models that are not computationally prohibitive. The remainder of this paper is organized as follows. Section II summarizes related work. Section III describes the simple an- alytical model we have developed. Section IV explains the ex- perimental setup that we use. Section V summarizes our results and the problems in achieving high fidelity DoS simulation and emulation. Finally, Section VI concludes the paper.
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    Daniel Havey · Roman Chertov · Kevin Almeroth
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    ABSTRACT: Wireless network topologies have developed in a considerably different manner than the original vision of the ad-hoc network. Rather than a number of nodes with similar capabilities moving about in randomly in an open field, today's wireless topologies are both hierarchical and heterogeneous. They consist of nodes with very different capabilities and contain both infrastructured and non infrastructured components. With detailed knowledge of network topology, mobility, traffic patterns, and routing characteristics it is possible for a node to make better routing decisions that will enhance performance, and provide improved characteristics.
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