Roy Friedman

Technion - Israel Institute of Technology, H̱efa, Haifa District, Israel

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Publications (116)29.32 Total impact

  • Source
    Roy Friedman · Michel Raynal · François Taïani
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    ABSTRACT: Over the last thirty years, numerous consistency conditions for replicated data have been proposed and implemented. Popular examples of such conditions include linearizability (or atomicity), sequential consistency, causal consistency, and eventual consistency. These consistency conditions are usually defined independently from the computing entities (nodes) that manipulate the replicated data; i.e., they do not take into account how computing entities might be linked to one another, or geographically distributed. To address this lack, as a first contribution, this paper introduces the notion of proximity graph between computing nodes. If two nodes are connected in this graph, their operations must satisfy a strong consistency condition, while the operations invoked by other nodes are allowed to satisfy a weaker condition. The second contribution is the use of such a graph to provide a generic approach to the hybridization of data consistency conditions into the same system. We illustrate this approach on sequential consistency and causal consistency, and present a model in which all data operations are causally consistent, while operations by neighboring processes in the proximity graph are sequentially consistent. The third contribution of the paper is the design and the proof of a distributed algorithm based on this proximity graph, which combines sequential consistency and causal consistency (the resulting condition is called fisheye consistency). In doing so the paper not only extends the domain of consistency conditions, but provides a generic provably correct solution of direct relevance to modern georeplicated systems.
  • Roy Friedman · Anna Kaplun Shulman
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    ABSTRACT: This paper studies a density driven virtual topography based publish/subscribe service for mobile ad hoc networks. Two variants of the service are presented and evaluated by extensive simulations; the first is very communication frugal while the latter trades a higher message overhead for faster latency. Both variants are also being compared to two other representative approaches for publish/subscribe in ad hoc networks, a dissemination tree based scheme and an efficient flooding based scheme. It is shown that the density-driven approach outperforms the others in most tested scenarios.
    Ad Hoc Networks 01/2013; 11(1):522–540. DOI:10.1016/j.adhoc.2012.07.010 · 1.94 Impact Factor
  • Ziv Bar-yossef · Roy Friedman · Gabriel Kliot
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    ABSTRACT: This article presents RaWMS, a novel lightweight random membership service for ad hoc networks. The service provides each node with a partial uniformly chosen view of network nodes. Such a membership service is useful, for example, in data dissemination algorithms, lookup and discovery services, peer sampling services, and complete membership construction. The design of RaWMS is based on a novel reverse random walk (RW) sampling technique. The article includes a formal analysis of both the reverse RW sampling technique and RaWMS and verifies it through a detailed simulation study. In addition, RaWMS is compared both analytically and by simulations with a number of other known methods such as flooding and gossip-based techniques.
  • Vadim Drabkin · Roy Friedman · Gabriel Kliot · Marc Segal
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    ABSTRACT: In this paper, we propose a novel ReliAble ProbabIlistic Dissemination protocol, RAPID, for mobile wireless ad-hoc networks that tolerates message omissions, node crashes, and selfish behavior. The protocol employs a combination of probabilistic forwarding with deterministic corrective measures. The forwarding probability is set based on the observed number of nodes in each one-hop neighborhood, while the deterministic corrective measures include deterministic gossiping as well as timer based corrections of the probabilistic process. These aspects of the protocol are motivated by a theoretical analysis that is also presented in the paper, which explains why this unique protocol design is inherent to ad-hoc networks environments. Since the protocol only relies on local computations and probability, it is highly resilient to mobility and failures. The paper includes a detailed performance evaluation by simulation. We compare the performance and the overhead of RAPID with the performance of other probabilistic approaches. Our results show that RAPID achieves a significantly higher node coverage with a smaller overhead. 1
  • Source
    V. Drabkin · R. Friedman · G. Kliot · M. Segal
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    ABSTRACT: Reliable broadcast is a basic service for many collaborative applications as it provides reliable dissemination of the same information to many recipients. This paper studies three common approaches for achieving scalable reliable broadcast in ad hoc networks, namely probabilistic flooding, counter-based broadcast, and lazy gossip. The strength and weaknesses of each scheme are analyzed, and a new protocol that combines these three techniques, called RAPID, is developed. Specifically, the analysis in this paper focuses on the trade-offs between reliability (percentage of nodes that receive each message), latency, and the message overhead of the protocol. Each of these methods excel in some of these parameters, but no single method wins in all of them. This motivates the need for a combined protocol that benefits from all of these methods and allows to trade between them smoothly. Interestingly, since the RAPID protocol only relies on local computations and probability, it is highly resilient to mobility and failures and even selfish behavior. By adding authentication, it can even be made malicious tolerant. Additionally, the paper includes a detailed performance evaluation by simulation. The simulations confirm that RAPID obtains higher reliability with low latency and good communication overhead compared with each of the individual methods.
    IEEE Transactions on Dependable and Secure Computing 01/2012; 8(6-8):866 - 882. DOI:10.1109/TDSC.2010.54 · 1.14 Impact Factor
  • Roy Friedman · Alex Kogan
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    ABSTRACT: This paper investigates a novel efficient approach to utilize multiple radio interfaces for enhancing the performance of reliable multicasts from a single sender to a group of receivers. In the proposed scheme, one radio channel (and interface) is dedicated only for recovery information transmissions. We apply this concept to both ARQ and hybrid ARQ+FEC protocols, formally analyzing the number of packets each receiver needs to process in both our approach and in the common single channel approach. We also present a corresponding efficient protocol, and study its performance by simulation. Both the formal analysis and the simulations demonstrate the benefits of our scheme.
    Reliable Distributed Systems (SRDS), 2012 IEEE 31st Symposium on; 01/2012
  • Adnan Agbaria · Muhamad Hugerat · Roy Friedman
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    ABSTRACT: Data dissemination is an important service in mobile ad hoc networks (MANETs). The main objective of this paper is to present a dissemination protocol, called locBcast, which utilizes positioning information to obtain efficient dissemination trees with low-control overhead. This paper includes an extensive simulation study that compares locBast with selfP, dominantP, fooding, and a couple of probabilistic-/counter-based protocols. It is shown that locBcast behaves similar to or better than those protocols and is especially useful in the following challenging environments: the message sizes are large, the network is dense, and nodes are highly mobile.
    01/2011; 2011. DOI:10.1155/2011/680936
  • Roy Friedman · Alex Kogan · Yevgeny Krivolapov
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    ABSTRACT: This paper describes a combined power and throughput performance study of WiFi and Bluetooth usage in smartphones. The work measures the obtained throughput in various settings while employing each of these technologies, and the power consumption level associated with them. In addition, the power requirements of Bluetooth and WiFi in their respective noncommunicating modes are also compared. The study reveals several interesting phenomena and tradeoffs. In particular, the paper identifies many situations in which WiFi is superior to Bluetooth, countering previous reports. The study also identifies a couple of scenarios that are better handled by Bluetooth. The conclusions from this study suggest preferred usage patterns, as well as operative suggestions for researchers and smartphone developers. This includes a cross-layer optimization for TCP/IP that could greatly improve the throughput to power ratio whenever the transmitter is more capable than the receiver.
    INFOCOM 2011. 30th IEEE International Conference on Computer Communications, Joint Conference of the IEEE Computer and Communications Societies, 10-15 April 2011, Shanghai, China; 01/2011
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    ABSTRACT: Cornell University has developed a group communications and membership management tool, called the Ensemble system, which provides the basis for introducing guarantees such as reliability, high availability, faulttolerance, consistency, security and real-time responsiveness into applications that run on clustered parallel computers or high speed networks. Ensemble tools are flexible, extremely transparent, and achieve high performance. Our development started under Unix in 1995, but by 1996 had enlarged to include NT as a primary target. This paper reviews Ensemble and then discusses the technical issues that arose when repositioning it to fit naturally and perform well under NT. 1
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    ABSTRACT: This paper investigates proactive data dissemination and storage schemes for wireless sensor networks (WSNs) with mobile sinks. The focus is on schemes that do not impose any restrictions on the sink’s mobility pattern. The goal is to enable the sink to collect a representative view of the network’s sensed data by visiting any set of x out of n nodes, where x≪n. The question is how to obtain this while maintaining a good trade-off between the communication overhead of the scheme, the storage space requirements on the nodes, and the ratio between the number of visited nodes x and the representativeness of the gathered data. To answer this question, we propose density-based proactivE data dissEmination Protocol (DEEP), which combines a probabilistic flooding with a probabilistic storing scheme. The DEEP protocol is formally analyzed and its performance is studied under simulations using different network densities and compared with a scheme based on random walks, called RaWMS.
    Computer Communications 05/2010; 33(8-33):929-939. DOI:10.1016/j.comcom.2010.01.003 · 1.35 Impact Factor
  • Source
    Roy Friedman · Alex Kogan
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    ABSTRACT: This paper considers the problem of calculating dominating sets in bounded degree networks. In these networks, the maximal degree of any node is bounded by δ, which is usually significantly smaller than n, the total number of nodes in the system. Such networks arise in various settings of wireless and peer-to-peer communication. A trivial approach of choosing all nodes into the dominating set yields an algorithm with an approximation ratio of δ + 1. We show that any deterministic algorithm with a non-trivial approximation ratio requires Ω(log* n) rounds, meaning effectively that no local o(δ)-approximation deterministic algorithm may ever exist. On the positive side, we show two deterministic algorithms that achieve log δ and 2 log δ-approximation in O(δ3 + log* n) and O(δ2 logδ + log* n) time, respectively. These algorithms rely on coloring rather than node IDs to break symmetry.
    Proceedings of the 29th Annual ACM Symposium on Principles of Distributed Computing, PODC 2010, Zurich, Switzerland, July 25-28, 2010; 01/2010
  • Roy Friedman · Alex Kogan
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    ABSTRACT: Short-range wireless communication capabilities enable the creation of ad hoc networks between devices such as smart-phones or sensors, spanning, e.g., an entire high-school or a small university campus. This paper is motivated by the proliferation of devices equipped with multiple such capabilities, e.g., Blue-Tooth (BT) and WiFi for smart-phones, or ZigBee and WiFi for sensors. Yet, each of these interfaces has significantly different, and, to a large extent complementing, characteristics in terms of energy efficiency, transmission range, and bandwidth. Consequently, a viable ad hoc network composed of such devices must be able to utilize the combination of these capabilities in a clever way. For example, BT is an order of magnitude more power efficient than WiFi, but its transmission range is also an order of magnitude shorter. Hence, one would want to shut down as many WiFi transmitters as possible, while still ensuring overall network connectivity. Moreover, for latency and network capacity reasons, in addition to pure connectivity, a desired property of such a solution is to keep the number of BT hops traversed by each transmission below a given threshold k. This paper addresses this issue by introducing the novel k-Weighted Connected Dominating Set (kWCDS) problem and providing a formal definition for it. A distributed algorithm with a proven approximation ratio is presented, followed by a heuristic protocol. While the heuristic protocol has no formally proven approximation ratio, it behaves better than the first protocol in many practical network densities. Beyond that, a tradeoff between communication overhead and the quality of the resulting kWCDS emerges. The paper includes simulation results that explore the performance of the two protocols.
    12/2009: pages 159-173;
  • Source
    Roy Friedman · Galya Tcharny
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    ABSTRACT: Purpose – Mobile ad-hoc networks (MANET) are networks that are formed in an ad-hoc manner by collections of devices that are equipped with wireless communication capabilities, such as the popular WiFi (IEEE 802.11b) standard. As the hardware technology and networking protocols for MANETs become mature and ubiquitous, the main barrier for MANETs to become widely used is applications. Like in other areas of distributed computing, in order to expedite the development of applications, there is a need for middleware services that support these applications. Failure detection has been identified as a basic component for many reliable distributed middleware services and applications. This paper aims to investigate this issue. Design/methodology/approach – This paper presents an adaptation of a gossip-based failure detection protocol to MANETs, and an evaluation by extensive simulations of this protocol's performance in such networks. Findings – The results can be viewed as a feasibility check for implementing failure detection in MANETs, and the conclusions drawn from them can be used to motivate and improve future implementations of both a failure detection component and of applications and middleware services relying on such a component. Originality/value – This paper presents an adaptation of a gossip-based failure detection protocol to MANET environments, and presents an extensive simulation-based performance study of this protocol in MANETs with various parameters.
    International Journal of Pervasive Computing and Communications 11/2009; 5(4):476-496. DOI:10.1108/17427370911008857
  • Source
    ExtremeCom Workshop; 08/2009
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    Roy Friedman · Ari Shotland · Gwendal Simon
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    ABSTRACT: Hybrid networks are formed by a combination of access points and mobile nodes such that the mobile nodes can communicate both through the access points and using ad-hoc networking among themselves. This work deals with providing efficient routing between mobile devices in hybrid networks. Specifically, we assume the existence of a spanning tree from each access point to all mobile devices within the transitive transmission range of the access point. We utilize this spanning tree to design a family of efficient point-to-point routing protocols for communication between the mobile devices themselves. The protocols utilize the tree structure in order to avoid expensive flooding of the entire network. The paper includes a detailed simulation study of several representative communication patterns, which compares our approaches to DSR.
    Ad Hoc Networks 08/2009; DOI:10.1016/j.adhoc.2008.09.008 · 1.94 Impact Factor
  • Aline Carneiro Viana · Artur Ziviani · Roy Friedman
    IEEE Communications Letters 04/2009; 13(3):178-180. DOI:10.1109/LCOMM.2009.081990 · 1.46 Impact Factor
  • Roy Friedman · Alex Kogan
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    ABSTRACT: Modern mobile phones and laptops are equipped with multiple wireless communication interfaces, such as WiFi and Bluetooth (BT), enabling the creation of ad-hoc networks. These interfaces significantly differ from one another in their power requirements, transmission range, bandwidth, etc. For example, BT is an order of magnitude more power efficient than WiFi, but its transmission range is an order of magnitude shorter. This paper introduces a management middleware that establishes a power efficient overlay for such ad-hoc networks, in which most devices can shut down their long range power hungry wireless interface (e.g., WiFi). Yet, the resulting overlay is fully connected, and for capacity and latency needs, no message ever travels more than 2k short range (e.g., BT) hops, where k is an arbitrary parameter. The paper describes the architecture of the solution and the management protocol, as well as a detailed simulations based performance study. The simulations largely validate the ability of the management infrastructure to obtain considerable power savings while keeping the network connected and maintaining reasonable latency. The performance study covers both static and mobile networks.
    Middleware 2009, ACM/IFIP/USENIX, 10th International Middleware Conference, Urbana, IL, USA, November 30 - December 4, 2009. Proceedings; 01/2009
  • Source
    Roy Friedman · Noam Mori
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    ABSTRACT: Finding data items is one of the most basic services of any distributed system. It is particular chal- lenging in ad-hoc networks, due to their inherent decentralized nature and lack of infrastructure. A data location service (DLS) provides this capability. This paper presents 3DLS, a novel density-driven data location service. 3DLS is based on performing biased walks over a density based virtual topography. 3DLS also includes an autonomic dynamic conguration mechanism for adapting the lengths of the walks, in order to ensure good performance in varying circumstances and loads. This is without any ex- plicit knowledge of the network characteristics, such as size, mobility speed, etc. Moreover, 3DLS does not rely on geographical knowledge, its decisions are based only on local information, it does not invoke multi-hop routing, and it avoids ooding the network. The paper includes a detailed performance study of 3DLS, carried by simulations, which compares 3DLS to other known approaches. The simulations results validate the viability of 3DLS.
    Proceedings of the 10th ACM Interational Symposium on Mobile Ad Hoc Networking and Computing, MobiHoc 2009, New Orleans, LA, USA, May 18-21, 2009; 01/2009
  • Source
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    ABSTRACT: This paper investigates Wireless Sensor Networks (WSNs) with mobile sinks that collect data from sensors by following uncontrolled trajectories. In particular, the paper focuses on proactive data dissemination strategies in which the trajectory of the mobile sink is unknown to the sensors. These strategies attempt to obtain a good trade-off between the number of sensors the mobile sinks has to visit in order to collect representative data of all sensors, and the communication effort required by the sensors. All the investigated techniques also avoid the use of multi-hop routing, due to its high cost. Some of them are based on random walks whereas others are based on a combination of probabilistic forwarding and probabilistic storage. An analysis of the various methods in terms of the performance trade-off between the efficiency of the data gathering and communication overhead is also presented.
  • Roy Friedman · Alex Kogan
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    ABSTRACT: A wireless ad hoc network is composed of devices that are capable of communicating directly with their neighbors (roughly speaking, nodes that are nearby). Many such devices are battery-operated, e.g., laptops, smart-phones and PDAs. Thus, their operational life-time before the battery should be recharged or replaced is limited. Among all subsystems operating inside these devices, wireless communication is accounted for the major consumption of power [1,2]. Additionally, platforms enabled with multiple wireless communication interfaces are becoming quite common. This turns the problem of efficient power usage by the wireless communication subsystem even more acute.
    Distributed Computing, 23rd International Symposium, DISC 2009, Elche, Spain, September 23-25, 2009. Proceedings; 01/2009

Publication Stats

2k Citations
29.32 Total Impact Points

Institutions

  • 1997–2013
    • Technion - Israel Institute of Technology
      • Electrical Engineering Group
      H̱efa, Haifa District, Israel
  • 1997–2006
    • Cornell University
      • Department of Computer Science
      Ithaca, NY, United States
  • 2004
    • Université de Rennes 1
      Roazhon, Brittany, France
  • 2003
    • University of Illinois, Urbana-Champaign
      • Coordinated Science Laboratory
      Urbana, Illinois, United States