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  • 1. Aberer, Karl
    et al.
    Onana Alima, Luc
    RISE, Swedish ICT, SICS.
    Ghodsi, Ali
    RISE, Swedish ICT, SICS.
    Girdzijauskas, Sarunas
    RISE, Swedish ICT, SICS, Computer Systems Laboratory.
    Hauswirth, Manfred
    Haridi, Seif
    RISE, Swedish ICT, SICS, Computer Systems Laboratory.
    The essence of P2P: A reference architecture for overlay networks2005Conference paper (Refereed)
    Abstract [en]

    The success of the P2P idea has created a huge diversity of approaches, among which overlay networks, for example, Gnutella, Kazaa, Chord, Pastry, Tapestry, P-Grid, or DKS, have received specific attention from both developers and researchers. A wide variety of algorithms, data structures, and architectures have been proposed. The terminologies and abstractions used, however, have become quite inconsistent since the P2P paradigm has attracted people from many different communities, e.g., networking, databases, distributed systems, graph theory, complexity theory, biology, etc. In this paper we propose a reference model for overlay networks which is capable of modeling different approaches in this domain in a generic manner. It is intended to allow researchers and users to assess the properties of concrete systems, to establish a common vocabulary for scientific discussion, to facilitate the qualitative comparison of the systems, and to serve as the basis for defining a standardized API to make overlay networks interoperable.

  • 2.
    Ali, Khayri Mohammed
    et al.
    RISE - Research Institutes of Sweden, ICT, SICS.
    Haridi, Seif
    RISE, Swedish ICT, SICS, Computer Systems Laboratory.
    Global garbage collection for distributed heap storage systems1987Report (Other academic)
    Abstract [en]

    We present a garbage-collection algorithm, suitable for loosely-coupled multiprocessor systems, in which the processing elements (PE's) share only the communication medium. The algorithm is global, i.e. it involves all the PE's in the system. It allows space compaction, and it uses a system-wide marking phase to mark all accessible objects where a combination of parallel breadth-first/depth-first strategies is used for tracing the object-graphs according to a decentralized credit mechanism that regulates the number of garbage collection messages in the system. The credit mechanism is crucial for determining the space requirement of the garbage-collection messages. Also a variation of the above algorithm is presented for systems with high locality of reference. It allows each PE to perform first its local garbage collection and only invokes the global garbage collection when the freed space by the local collector is insufficient.

  • 3.
    Alima, Luc Onana
    et al.
    RISE - Research Institutes of Sweden, ICT, SICS.
    Ghodsi, Ali
    RISE - Research Institutes of Sweden, ICT, SICS.
    Haridi, Seif
    RISE - Research Institutes of Sweden, ICT, SICS.
    A Framework for Structured Peer-to-Peer Overlay Networks2004Report (Other academic)
    Abstract [en]

    Structured peer-to-peer overlay networks have recently emerged as good candidate infrastructure for building novel large-scale and robust Internet applications in which participating peers share computing resources as equals. In the past three year, various structured peer-to-peer overlay networks have been proposed, and probably more are to come. We present a framework for understanding, analyzing and designing structured peer-to-peer overlay networks. The main objective of the paper is to provide practical guidelines for the design of structured overlay networks by identifying a fundamental element in the construction of overlay networks: the embedding of k-ary trees. Then, a number of effective techniques for maintaining these overlay networks are discussed. The proposed framework has been effective in the development of the DKS system.

  • 4. Alima, Luc Onana
    et al.
    Haridi, Seif
    RISE, Swedish ICT, SICS, Computer Systems Laboratory.
    Van Roy, Peter
    NetProber: a component for enhancing efficiency of overlay networks in P2P systems2002Conference paper (Refereed)
  • 5. Almgren, Jonas
    et al.
    Andersson, Stefan
    Carlsson, Mats
    RISE, Swedish ICT, SICS, Computer Systems Laboratory.
    Flood, Lena
    Haridi, Seif
    RISE, Swedish ICT, SICS, Computer Systems Laboratory.
    Frisk, Claes
    Nilsson, Hans
    Sundberg, Jan
    SICStus Prolog library manual, version 2.1 #81993Report (Other academic)
    Abstract [en]

    This Manual corresponds to SICStus Prolog release 2.1. #8 The Prolog library comprises a number of packages which are thought to be useful in a number of applications. Note that the predicates in the Prolog library are built-in predicates. One has to explicity load each package to get access to its predicates. To load a library package Package, you will normally enter a query. I ?- use_module(library(Package)). Library packages may be compiled and consulted as well as loaded.

  • 6. Appleby, Karen
    et al.
    Carlsson, Mats
    RISE, Swedish ICT, SICS, Computer Systems Laboratory.
    Haridi, Seif
    RISE, Swedish ICT, SICS, Computer Systems Laboratory.
    Sahlin, Dan
    RISE, Swedish ICT, SICS.
    Garbage Collection for Prolog Based on WAM (Revised version)1986Report (Other academic)
    Abstract [en]

    Warren Abstract Machine (WAM) has become a generally accepted standard Prolog implementation technique. Garbage collection is an important aspect in the implementation of any Prolog system. We first present a synopsis of the WAM and then show marking and compaction algorithms that take advantage of WAM's unique use of the data areas. Marking and compaction are performed on both the heap and the trail. The marking and compaction algorithms use pointer reversal techniques, which obviate the need for extra stack space. However, two bits for every pointer on the heap are reserved for the garbage collection algorithm. The algorithm can work on segments of the heap, which may lead to a significant reduction of the total garbage collection time. The time of the algorithms are linear in the size of the areas.

  • 7.
    Arad, Cosmin
    et al.
    RISE, Swedish ICT, SICS, Computer Systems Laboratory.
    Haridi, Seif
    RISE, Swedish ICT, SICS, Computer Systems Laboratory.
    Kompics: a message-passing component model for building distributed systems2010Report (Other academic)
    Abstract [en]

    The Kompics component model and programming framework was designedto simplify the development of increasingly complex distributed systems. Systems built with Kompics leverage multi-core machines out of the box and they can be dynamically reconfigured to support hot software upgrades. A simulation framework enables deterministic debugging and reproducible performance evaluation of unmodified Kompics distributed systems. We describe the component model and show how to program and compose event-based distributed systems. We present the architectural patterns and abstractions that Kompics facilitates and we highlight a case study of a complex distributed middleware that we have built with Kompics. We show how our approach enables systematic development and evaluation of large-scale and dynamic distributed systems.

  • 8.
    Arad, Cosmin
    et al.
    RISE - Research Institutes of Sweden, ICT, SICS.
    Kafray, Ozair
    Ghodsi, Ali
    RISE - Research Institutes of Sweden, ICT, SICS.
    Haridi, Seif
    RISE, Swedish ICT, SICS, Computer Systems Laboratory.
    GODS: Global Observatory for Distributed Systems2007Report (Other academic)
    Abstract [en]

    We propose GODS, an ecosystem for the evaluation and study of world-wide distributed and dynamic systems under a realistic emulated network environment. GODS allows the evaluation of a system's actual implementation in reproducible experiments, collecting global knowledge about the system state. Furthermore, GODS addresses the problems of debugging distributed algorithms, performance tuning, measuring bandwidth consumption, regression testing, and benchmarking similar systems, thus offering a complete evaluation environment for distributed applications. Our framework uses ModelNet for the network emulation and enhances that by (1) adding dynamism by varying link properties, partitioning the network and emulating churn, (2) offering global knowledge about the observed system by gathering statistics and events and (3) enabling the user to easily deploy, manage and monitor complex, large-scale distributed systems.

  • 9.
    Arad, Cosmin
    et al.
    RISE, Swedish ICT, SICS. Computer Systems Laboratory.
    Shafaat, Tallat M.
    RISE, Swedish ICT, SICS. Computer Systems Laboratory.
    Haridi, Seif
    RISE, Swedish ICT, SICS. Computer Systems Laboratory.
    Brief Announcement: Atomic Consistency and Partition Tolerance in Scalable Key-Value Stores2012Conference paper (Refereed)
  • 10.
    Arad, Cosmin
    et al.
    RISE, Swedish ICT, SICS. Computer Systems Laboratory.
    Shafaat, Tallat M.
    RISE, Swedish ICT, SICS. Computer Systems Laboratory.
    Haridi, Seif
    RISE, Swedish ICT, SICS. Computer Systems Laboratory.
    CATS: linearizability and partition tolerance in scalable and self-organizing key-value stores2012Report (Other academic)
    Abstract [en]

    Distributed key-value stores provide scalable, fault-tolerant, and self-organizing storage services, but fall short of guaranteeing linearizable consistency in partially synchronous, lossy, partitionable, and dynamic networks, when data is distributed and replicated automatically by the principle of consistent hashing. This paper introduces consistent quorums as a solution for achieving atomic consistency. We present the design and implementation of CATS, a distributed key-value store which uses consistent quorums to guarantee linearizability and partition tolerance in such adverse and dynamic network conditions. CATS is scalable, elastic, and self-organizing; key properties for modern cloud storage middleware. Our system shows that consistency can be achieved with practical performance and modest throughput overhead (5%) for read-intensive workloads.

  • 11.
    Brand, Per
    et al.
    RISE, Swedish ICT, SICS.
    Franzén, Nils
    Klintskog, Erik
    RISE, Swedish ICT, SICS.
    Haridi, Seif
    RISE, Swedish ICT, SICS, Computer Systems Laboratory.
    A platform for constructing virtual spaces1998Conference paper (Refereed)
    Abstract [en]

    Virtual spaces (worlds) applications are among the most complex of distributed applications. They are both distributed and open. Minimizing network latency, fault-tolerance, persistence, resource control, and security are also important aspects. Designing and implementing virtual spaces is currently difficult in that the already not insignificant complexities of program functionality, distribution, openness, and efficiency are interwound and cannot be tackled separately. We present a distributed programming language, distributed-Oz, that greatly reduces the complexity of distributed programming by clearly separating the different aspects of distributed programming. The design and implementation of distributed-Oz is ongoing work, but considerable progress has been made. The current prototype demonstrates network transparency, that computations behave the same way regardless of how the computation is partitioned between different sites. This is the basis for realizing clean separation of the functionality aspect from other aspects. Network awareness allows the programmer to predict and control network communication patterns. The current system gives the programmer the means to tackle separately the aspects of openness, efficiency (minimizing latency), distribution, and functionality. We have extended distributed-Oz with a tool for graphics in a distributed setting. This extends the idea of network transparency and network awareness to graphics. From the programmers point of view graphics programming for a multi-user application is virtually the same as programming for a single-user application. The differences are necessary extensions for achieving network and site awareness, such as visualization control (deciding which users should see what). Finally we consider virtual space applications, and propose a number of abstractions for use by developers of virtual spaces, relating them to the properties of distributed-Oz upon which they are based.

  • 12.
    Dowling, Jim
    et al.
    RISE, Swedish ICT, SICS, Computer Systems Laboratory.
    Haridi, Seif
    RISE, Swedish ICT, SICS, Computer Systems Laboratory.
    Decentralized Reinforcement Learning for the Online Optimization of Distributed Systems2008In: Reinforcement Learning: Theory and Applications, Vienna, Austria: I-Tech Education and Publishing (Advanced Robotic Systems Journal) , 2008, , p. 25p. 143-166Chapter in book (Refereed)
  • 13.
    Dowling, Jim
    et al.
    RISE - Research Institutes of Sweden, ICT, SICS.
    Sacha, Jan
    Haridi, Seif
    RISE, Swedish ICT, SICS, Computer Systems Laboratory.
    Improving ICE Service Selection in a P2P System using the Gradient Topology2007Conference paper (Refereed)
  • 14.
    Drejhammar, Frej
    et al.
    RISE, Swedish ICT, SICS, Computer Systems Laboratory.
    Haridi, Seif
    RISE, Swedish ICT, SICS, Computer Systems Laboratory.
    Efficient simulation of view synchrony2012Report (Other academic)
    Abstract [en]

    This report presents an algorithm for efficiently simulating view synchrony, including failure-atomic total-order multicast in a discrete-time event simulator. In this report we show how a view synchrony implementation tailored to a simulated environment removes the need for third party middleware and detailed network simulation, thus reducing the complexity of a test environment. An additional advantage is that simulated view synchrony can generate all timing behaviours allowed by the model instead of just those exhibited by a particular view synchrony implementation.

  • 15.
    Drejhammar, Frej
    et al.
    RISE, Swedish ICT, SICS, Computer Systems Laboratory.
    Haridi, Seif
    RISE, Swedish ICT, SICS, Computer Systems Laboratory.
    Brand, Per
    RISE, Swedish ICT, SICS, Computer Systems Laboratory.
    Schulte, Christian
    Flow Java: declarative concurrency for Java.2003In: Proceedings of the Nineteenth International Conference on Logic Programming, 2003, 1Conference paper (Refereed)
    Abstract [en]

    Logic variables pioneered by (concurrent) logic and concurrent constraint programming are powerful mechanisms for automatically synchronizing concurrent computations. They support a declarative model of concurrency that avoids explicitly suspending and resuming computations. This paper presents Flow Java which conservatively extends Java with single assignment variables and futures as variants of logic variables. The extension is conservative with respect to object-orientation, types, parameter passing, and concurrency in Java. Futures support secure concurrent abstractions and are essential for seamless integration of single assignment variables into Java. We show how Flow Java supports the construction of simple and concise concurrent programming abstractions. We present how to moderately extend compilation and the runtime architecture of an existing Java implementation for Flow Java. Evaluation using standard Java benchmarks shows that in most cases the overhead is between 10% and 40%. For some pathological cases the runtime increases by up to 75%.

  • 16.
    El-Ansary, Sameh
    et al.
    RISE - Research Institutes of Sweden, ICT, SICS.
    Alima, Luc Onana
    Brand, Per
    RISE - Research Institutes of Sweden, ICT, SICS.
    Haridi, Seif
    A Framework for Peer-To-Peer Lookup Services based on k-ary search2002Report (Other academic)
    Abstract [en]

    Locating entities in peer-to-peer environments is a fundamentaloperation. Recent studies show that the concept of distributed hash table can be used to design scalable lookup schemes with good performance (i.e. small routing table and lookup length). In this paper, we propose a simple framework for deriving decentralized lookup algorithms. The proposed framework is simple in that it is based on the well-known concept of k-ary search. To demonstrate the applicability of our framework, we show how it can be used to instantiate Chord. When deriving a generalized Chord from our framework, we obtain better performance in terms of the routing table size (38% smaller than the generalization suggested by the Chord authors).

  • 17. El-Ansary, Sameh
    et al.
    Aurell, Erik
    Brand, Per
    RISE, Swedish ICT, SICS, Computer Systems Laboratory.
    Haridi, Seif
    RISE, Swedish ICT, SICS, Computer Systems Laboratory.
    Experience with a physics-style approach for the study of self properties in structured overlay networks2004Conference paper (Refereed)
  • 18.
    El-Ansary, Sameh
    et al.
    RISE, Swedish ICT, SICS. DSL.
    Aurell, Erik
    RISE, Swedish ICT, SICS. DSL.
    Haridi, Seif
    RISE, Swedish ICT, SICS. DSL.
    Physics-inspired Performace Evaluation of a Structured Peer-to-Peer Overlay Network2005Conference paper (Refereed)
    Abstract [en]

    In the majority of structured peer-to-peer overlay networks a graph with a desirable topology is constructed. In most cases, the graph is maintained by a periodic activity performed by each node in the graph to preserve the desirable structure in face of the continuous change of the set of nodes. The interaction of the autonomous periodic activities of the nodes renders the performance analysis of such systems complex and simulation of scales of interest can be prohibitive. Physicists, however, are accustomed to dealing with scale by characterizing a system using intensive variables, i.e. variables that are size independent. The approach has proved its usefulness when applied to satisfiability theory. This work is the first attempt to apply it in the area of distributed systems. The contribution of this paper is two-fold. First, we describe a methodology to be used for analyzing the performance of large scale distributed systems. Second, we show how we applied the methodology to find an intensive variable that describe the characteristic behavior of the Chord overlay network, namely, the ratio of the magnitude of perturbation of the network (joins/failures) to the magnitude of periodic stabilization of the network.

  • 19.
    El-Ansary, Sameh
    et al.
    RISE, Swedish ICT, SICS.
    Brand, Per
    RISE, Swedish ICT, SICS.
    Haridi, Seif
    RISE, Swedish ICT, SICS, Computer Systems Laboratory.
    Efficient broadcast in structured P2P networks2003Conference paper (Refereed)
    Abstract [en]

    In this position paper, we present an efficient algorithm for performing a broadcast operation with minimal cost in structured DHT-based P2P networks. In a system of N nodes, a broadcast message originating at an arbitrary node reaches all other nodes after exactly N-1 messages. We emphasize the perception of a class of DHT systems as a form of distributed k-ary search and we take advantage of that perception in constructing a spanning tree that is utilized for efficient broadcasting. We consider broadcasting as a basic service that adds to existing DHTs the ability to search using arbitrary queries as well as dissiminate/collect global information.

  • 20.
    El-Ansary, Sameh
    et al.
    RISE, Swedish ICT, SICS. DSL.
    Haridi, Seif
    RISE, Swedish ICT, SICS. DSL.
    An Overview of Structured Overlay Networks2005In: Theoretical and Algorithmic Aspects of Sensor, Ad Hoc Wireless and Peer-to-Peer Networks, CRC Press , 2005, 1Chapter in book (Refereed)
  • 21.
    El-Ansary, Sameh
    et al.
    RISE - Research Institutes of Sweden, ICT, SICS.
    Krishnamurthy, Supriya
    RISE - Research Institutes of Sweden, ICT, SICS.
    Aurell, Erik
    RISE - Research Institutes of Sweden, ICT, SICS.
    Haridi, Seif
    RISE - Research Institutes of Sweden, ICT, SICS.
    An Analytical Study of Consistency and Performance of DHTs under Churn2004Report (Other academic)
    Abstract [en]

    In this paper, we present a complete analytical study of dynamic membership (aka churn) in structured peer-to-peer networks. We use a master-equation-based approach, which is used traditionally in non-equilibrium statistical mechanics to describe steady-state or transient phenomena. We demonstrate that this methodology is infact also well suited to describing structured overlay networks by an application to the Chord system. For any rate of churn and stabilization rates, and any system size, we accurately account for the functional form of: the distribution of inter-node distances, the probability of network disconnection, the fraction of failed or incorrect successor and finger pointers and show how we can use these quantities to predict both the performance and consistency of lookups under churn. Additionally, we also discuss how churn may actually be of different 'types' and the implications this will have for structured overlays in general. All theoretical predictions match simulation results to a high extent. The analysis includes details that are applicable to a generic structured overlay deploying a ring as well as Chord-specific details that can act as guidelines for analyzing other systems.

  • 22. Ghodsi, Ali
    et al.
    Alima, Luc Onana
    RISE - Research Institutes of Sweden, ICT, SICS.
    Haridi, Seif
    RISE - Research Institutes of Sweden, ICT, SICS.
    A Symmetric Replication Scheme for Increased Security and Performance in Structured Overlay Networks2004Report (Other academic)
    Abstract [en]

    Existing structured peer-to-peer systems heavily rely on replication as a means to provide fault-tolerance. Many systems use the so-called successor- list scheme for replication. We argue that this scheme has grave limitations. First, these systems are vulnerable to, what we call, Mendacity attacks, where a malicious peer can lie about other peers to gain full control over all replicas of an item. Second, the successor-list scheme prevents the peers from doing concurrent-requests to replicas of an item. We present, and provide full algorithmic specification for, a generic replication scheme called symmetric replication. The scheme is applicable to all existing structured peer-to-peer systems. In contrast to the successor-list scheme, our scheme makes replicas independent of each other, preventing Mendacity attacks while enabling concurrent requests. Concurrent requests can be used for increasing the security by using voting or consensus algorithms to ensure the correctness of replicas. Moreover, concurrent requests can be used for load-balancing of requests, and to add locality awareness. Finally, to maintain the replication factor, the successor-list scheme uses a complex algorithm that involves all peers replicating a departing peer. In contrast, our symmetric replication scheme only involves two peers to restore the replication factor and thus avoids such complex algorithms.

  • 23.
    Ghodsi, Ali
    et al.
    KTH.
    El-Ansary, Sameh
    RISE - Research Institutes of Sweden, ICT, SICS.
    Krishnamurthy, Supriya
    RISE - Research Institutes of Sweden, ICT, SICS.
    Haridi, Seif
    KTH.
    A Self-stabilizing Network Size Estimation Gossip Algorithm for Peer-to-Peer Systems2005Report (Other academic)
    Abstract [en]

    We present a self-stabilizing network size estimation gossip algorithm which determines the number of nodes in a structured peer-to-peer system. The algorithm can handle joins, leaves, and failures and is applicable to most structured peer-to-peer systems providing a distributed hash table abstraction. Furthermore, the algorithm is self-stabilizing with respect to the local estimates of any node, which might be arbitrary at any given time. Once state corruption ceases, the algorithm eventually adjusts all estimates to the correct value even in presence of joins and leaves. The algorithm only assumes that the system is weakly fair, and does hence not require the nodes to make the same number of exchanges, to be correct.

  • 24.
    Ghodsi, Ali
    et al.
    RISE, Swedish ICT, SICS, Computer Systems Laboratory.
    Haridi, Seif
    RISE, Swedish ICT, SICS, Computer Systems Laboratory.
    Atomic Ring Maintenance for Distributed Hash Tables2007Report (Other academic)
    Abstract [en]

    This paper provides algorithms to maintain a ring-structure for structured peer-to-peer systems. The algorithms guarantee consistent lookup results in the presence of joins and leaves, regardless of at which node the lookup is initiated. Every join and leave event appears as if it happened atomically, thus guaranteeing that lookup results will be the same as if no joins or leaves took place. The ring maintenance algorithms guarantee that no routing failures occur as nodes are joining and leaving. We also show that lookup consistency is impossible to provide given failure detector, and show how the algorithms can be extended to handle failures. The correctness of all the provided algorithms is proven. Previous approaches to this problem either assume a fault-free environment, or have no proof of correctness.

  • 25.
    Ghodsi, Ali
    et al.
    RISE, Swedish ICT, SICS, Computer Systems Laboratory.
    Haridi, Seif
    RISE, Swedish ICT, SICS, Computer Systems Laboratory.
    ForestCast: a central solution to heuristically constructing trees2007Report (Other academic)
    Abstract [en]

    We present Forestcast which is a flexible and centralized solution to building a forest of trees, which are used to stream live media. A number of heuristic strategies are described to handle joins. Leaves are handled through rejoins. To enable fail-overs, we describe a scheme where the server gives each peer a backup parent such that it is guaranteed that the failure of any peer can be handled. We also describe how the scheme can be efficiently coupled with multiple stripes to allow for better bandwidth utilization. Finally, it is shown how the centralized solution can be decentralized. The provided scheme has three main advantages. i) It is difficult for peers to hack ForestCast as all decisions are taken by the central server. A peer just follows the server's orders about where it should download its stream. It is also possible to use a PKI scheme, where a peer can verify whether it should give its stream to another peer. ii) As the server has complete information about the state of all trees, it can optimize the number and shape of trees based on any metric, e.g. total latency, bandwidth utilization, robustness against failures etc. iii) The client software, running on the peers, contains little intelligence. Hence, it will be simple and can therefore be adapted for various OS and environments. Furthermore, most updates will be to the server infrastructure. A decentralized solution would need software updates to be applied to all peers.

  • 26.
    Ghodsi, Ali
    et al.
    RISE, Swedish ICT, SICS, Computer Systems Laboratory.
    Haridi, Seif
    RISE, Swedish ICT, SICS, Computer Systems Laboratory.
    Weatherspoon, Hakim
    Exploiting the Synergy Between Gossiping and Structured Overlays2007In: ACM SIGOPS Operating Systems Review, Vol. 41, p. 61-66Article in journal (Refereed)
    Abstract [en]

    In this position paper we argue for exploiting the synergy between gossip-based algorithms and structured overlay networks (SON). These two strands of research have both aimed at building fault-tolerant, dynamic, self-managing, and large-scale distributed systems. Despite the common goals, the two areas have, however, been relatively isolated. We focus on three problem domains where there is an untapped potential of using gossiping combined with SONs. We argue for applying gossip-based membership for ring-based SONs---such as Chord and Bamboo---to make them handle partition mergers and loopy networks. We argue that small world SONs---such as Accordion and Mercury---are specifically well-suited for gossip-based membership management. The benefits would be better graph-theoretic properties. Finally, we argue that gossip-based algorithms could use the overlay constructed by SONs. For example, many unreliable broadcast algorithms for SONs could be augmented with anti-entropy protocols. Similarly, gossip-based aggregation could be used in SONs for network size estimation and load-balancing purposes.

  • 27.
    Ghodsi, Ali
    et al.
    RISE, Swedish ICT, SICS. DSL.
    Onana Alima, Luc
    RISE, Swedish ICT, SICS. DSL.
    El-Ansary, Sameh
    RISE, Swedish ICT, SICS. DSL.
    Brand, Per
    RISE, Swedish ICT, SICS. DSL.
    Haridi, Seif
    RISE, Swedish ICT, SICS. DSL.
    Self-Correcting Broadcast in Distributed Hash Tables2003Conference paper (Refereed)
    Abstract [en]

    We present two broadcast algorithms that can be used on top of distributed hash tables (DHTs) to perform group communication and arbitrary queries. Unlike other P2P group communication mechanisms, which either embed extra information in the DHTs or use random overlay networks, our algorithms take advantage of the structured DHT overlay networks without maintaining additional information. The proposed algorithms do not send any redundant messages. Furthermore the two algorithms ensure 100% coverage of the nodes in the system even when routing information is outdated as a result of dynamism in the network. The first algorithm performs some correction of outdated routing table entries with a low cost of correction traffic. The second algorithm exploits the nature of the broadcasts to extensively update erroneous routing information at the cost of higher correction traffic. The algorithms are validated and evaluated in our stochastic distributed-algorithms simulator.

  • 28.
    Ghodsi, Ali
    et al.
    RISE, Swedish ICT, SICS. DSL.
    Onana Alima, Luc
    RISE, Swedish ICT, SICS. DSL.
    Haridi, Seif
    RISE, Swedish ICT, SICS. DSL.
    Low-Bandwidth Topology Maintenance for Robustness in Structured Overlay Networks2005Conference paper (Refereed)
    Abstract [en]

    Structured peer-to-peer systems have emerged as infrastructures for resource sharing in large-scale, distributed, and dynamic environments. One challenge in these systems is to efficiently maintain routing information in the presence of nodes joining, leaving, and failing. Many systems use costly periodic stabilization protocols to ensure that the routing information is up-to-date. In this paper, we present a novel technique called correction-on-change, which identifies and notifies all nodes that have outdated routing information as a result of a node joining, leaving, or failing. Effective failure handling is simplified as the detection of a failure triggers a correction-on-change which updates all the nodes that have a pointer to the failed node. The resulting system has increased robustness as nodes with stale routing information are immediately updated. We proof the correctness of the algorithms and evaluate its performance by means of simulation. Experimental results show that for the same amount of maintenance bandwidth correction-on-change makes the system by far more robust when compared to periodic stabilization. Moreover, compared to adaptive stabilization which adjusts its frequency to the dynamism in the system, correction-on-change gives the same performance but with considerably less maintenance bandwidth. As correction-on-change immediately updates incorrect routing entries the average lookup length is maintained close to the theoretical average in the presence of high dynamism. We show how the technique can be applied to our DKS system as well as the Chord system.

  • 29.
    Ghodsi, Ali
    et al.
    RISE, Swedish ICT, SICS. DSL.
    Onana Alima, Luc
    RISE, Swedish ICT, SICS. DSL.
    Haridi, Seif
    RISE, Swedish ICT, SICS. DSL.
    Symmetric Replication for Structured Peer-to-Peer Systems2005Conference paper (Refereed)
    Abstract [en]

    Structured peer-to-peer systems rely on replication as a basic means to provide fault-tolerance in presence of high churn. Most select replicas using either multiple hash functions, successor-lists, or leaf-sets. We show that all three alternatives have limitations. We present and provide full algorithmic speci¯cation for a generic replication scheme called symmetric replication which only needs O(1) message for every join and leave operation to maintain any replication degree. The scheme is applicable to all existing structured peer-to-peer systems, and can be implemented on-top of any DHT. The scheme has been implemented in our DKS system, and is used to do load-balancing, end-to-end fault-tolerance, and to increase the security by using distributed voting. We outline an extension to the scheme, implemented in DKS, which adds routing proximity to reduce latencies. The scheme is particularly suitable for use with erasure codes, as it can be used to fetch a random subset of the replicas for decoding.

  • 30. Gkogkas, Alexandros
    et al.
    Roverso, Roberto
    Haridi, Seif
    RISE, Swedish ICT, SICS. Computer Systems Laboratory.
    Accurate and Efficient Simulation of Bandwidth Dynamics for Peer-To-Peer Overlay Networks2011Conference paper (Refereed)
    Abstract [en]

    When evaluating Peer-to-Peer content distribution systems by means of simulation, it is of vital importance to correctly mimic the bandwidth dynamics behavior of the underlying network. In this paper, we propose a scalable and accurate flow-level network simulation model based on an evolution of the classical progressive filling algorithm which implements the max-min fairness idea. We build on top of the current state of art by applying an optimization to reduce the cost of each bandwidth allocation/deallocation operation on a node-based directed network model. Unlike other works, our evaluation of the chosen approach focuses both on efficiency and on accuracy. Our experiments show that, in terms of scalability, our bandwidth allocation algorithm outperforms existing directed models when simulating large-scale structured overlay networks. Whereas, in terms of accuracy we show that allocation dynamics of the proposed solution follow those of the NS-2 packet-level simulator by a small and nearly constant offset for the same scenarios. To the best of our knowledge, this is the first time that an accuracy study has been conducted on an improvement of the classical progressive filling algorithm.

  • 31.
    Hagersten, Erik
    et al.
    RISE - Research Institutes of Sweden, ICT, SICS.
    Haridi, Seif
    RISE, Swedish ICT, SICS, Computer Systems Laboratory.
    The cache coherence protocol of the data diffusion machine1989Report (Other academic)
    Abstract [en]

    The Data Diffusion Machine (DDM) is a scalable shared memory multiprocessor in which the location of a datum in the machine is completely decoupled from its address. A data access "snooping" protocol provides an automatic duplication and migration of the data to wherever needed. The protocol also handles data coherence and replacement. The hardware organization consists of a hierarchy of buses and data controllers linking an arbitrary number of processors each having a large set-associative memory. Each data controller has a set-associative directory containing status bits for data under its control. The rest of the system appears to one processor like shared memory system, which makes the DDM a general architecture. The DDM is scalable in that there may be any number of levels in the hierarchy. The logical topmost bus (or any other bus) can be implemented by an unlimited number of physical buses removing an anticipated bottleneck.

  • 32. Hagersten, Erik
    et al.
    Haridi, Seif
    RISE, Swedish ICT, SICS, Computer Systems Laboratory.
    Warren, David H.D.
    The cache-coherence protocol of the data diffusion machine1990Conference paper (Refereed)
  • 33. Hagersten, Erik
    et al.
    Landin, Anders
    Haridi, Seif
    RISE, Swedish ICT, SICS.
    Ddm: a cache-only memory architecture1992In: IEEE Computer, Vol. 25, no 9, p. 44-54Article in journal (Refereed)
  • 34. Hagersten, Erik
    et al.
    Landin, Anders
    Haridi, Seif
    RISE, Swedish ICT, SICS, Computer Systems Laboratory.
    Multiprocessor consistency and synchronization thru transient cache states1991Conference paper (Refereed)
  • 35.
    Haridi, Seif
    et al.
    RISE, Swedish ICT, SICS, Computer Systems Laboratory.
    Janson, Sverker
    RISE, Swedish ICT, SICS, Computer Systems Laboratory.
    Kernel Andorra Prolog and its computation model1990In: Logic Programming: Proceedings of the Seventh International Conference, MIT Press , 1990, 12Chapter in book (Refereed)
    Abstract [en]

    The logic programming language framework Kernel Andorra Prolog is defined by a formal computation model. In Kernel Andorra Prolog, general combinations of concurrent reactive languages and nondeterministic transformational languages may be specified. The framework is based on constraints.

  • 36.
    Haridi, Seif
    et al.
    RISE, Swedish ICT, SICS, Computer Systems Laboratory.
    Janson, Sverker
    RISE, Swedish ICT, SICS, Computer Systems Laboratory.
    Kernel Andorra Prolog and its Computational Model1990Report (Other academic)
    Abstract [en]

    The logic programming language framework Kernel Andorra Prolog is defined by a formal computation model. In Kernel Andorra Prolog, general combinations of concurrent reactive languages and nondeterministic transformational languages may be specified. The framework is based on constraints. The languages Prolog, GHC, Parlog, and Atomic Herbrand, are all executable in the Kernel Andorra Prolog computation model. There are instances of the framework in which all of these languages are embeddable.

  • 37.
    Haridi, Seif
    et al.
    RISE, Swedish ICT, SICS, Computer Systems Laboratory.
    van Roy, Peter
    Brand, Per
    RISE, Swedish ICT, SICS, Computer Systems Laboratory.
    Mehl, Michael
    Scheidhauer, Ralf
    Smolka, Gert
    Efficient logic variables for distributed computing1999In: ACM Transactions on Programming Languages and Systems, ISSN 0164-0925, E-ISSN 1558-4593, Vol. 21, no 3, p. 569-626Article in journal (Refereed)
  • 38.
    Haridi, Seif
    et al.
    RISE - Research Institutes of Sweden, ICT, SICS.
    van Roy, Peter
    Brand, Per
    RISE - Research Institutes of Sweden, ICT, SICS.
    Schulte, Christian
    Programming languages for distributed applications1998In: New generation computing, ISSN 0288-3635, E-ISSN 1882-7055, Vol. 16, no 3, p. 223-261Article in journal (Refereed)
  • 39.
    Hausman, Bogumil
    et al.
    RISE - Research Institutes of Sweden, ICT, SICS.
    Ciepielewski, Andrzej
    RISE - Research Institutes of Sweden, ICT, SICS.
    Haridi, Seif
    RISE, Swedish ICT, SICS, Computer Systems Laboratory.
    OR-parallel Prolog made efficient on shared memory multiprocessors1987Report (Other academic)
    Abstract [en]

    With the arrival of commercially available shared-memory multiprocessors, Prolog implementation efforts begin to shift from single processor architectures to the new ones. Among the main problems are efficient implementation of operations on variables and of task switching. Most of the solutions proposed so far suffer from expensive, non-constant time implementation of operations on variables. We propose a model (Versions-Vector Model) in which operations on all variables are constant time operations. The price we pay is a non-constant time of a task switch. As a remedy we propose two ways of decreasing that price. The first is promotion of variables on a task switch, from versions-vectors to the stack or heap, making subsequent task switches cheaper. The second is delayed installation of variables in versions-vectors, decreasing the cost of short branches. We believe that the increased memory consumption induced by our model can be accepted as it is traded for speed.

  • 40.
    Janson, Sverker
    et al.
    RISE, Swedish ICT, SICS, Computer Systems Laboratory.
    Haridi, Seif
    RISE, Swedish ICT, SICS, Computer Systems Laboratory.
    Programming paradigms of the Andorra Kernel Language1991Report (Other academic)
    Abstract [en]

    The Andorra Kernel Language (AKL) is introduced. It is shown how AKL provides the programming paradigms of both Prolog and GHC. This is the original goal of the design. However, it has also been possible to provide capabilities beyond that of Prolog and GHC. There are means to structure search, more powerful than plain backtracking. It is possible to encapsulate search in concurrent reactiveprocesses. It is also possible to write a multi-way merger with constant delay.In these respects AKL is quite original. Although AKL is an instance of our previously introduced Kernel Andorra Prolog framework, this exposition contains important extensions, and a considerable amount of unnecessary formal overhead has been stripped away.

  • 41. Jernberg, Jimmy
    et al.
    Vlassov, Vladimir
    Ghodsi, Ali
    RISE, Swedish ICT, SICS. DSL.
    Haridi, Seif
    DOH: A Content Delivery Peer-to-Peer Network2006Conference paper (Refereed)
    Abstract [en]

    Many SMEs and non-pro¯t organizations su®er when their Web servers become unavailable due to °ash crowd e®ects when their web site becomes popular. One of the solutions to the °ash-crowd problem is to place the web site on a scalable CDN (Content Delivery Network) that replicates the content and distributes the load in order to improve its response time. In this paper, we present our approach to building a scalable Web Hosting environment as a CDN on top of a structured peer-to-peer system of collaborative web-servers integrated to share the load and to improve the overall system performance, scalability, availability and robustness. Unlike clusterbased solutions, it can run on heterogeneous hardware, over geographically dispersed areas. To validate and evaluate our approach, we have developed a system prototype called DOH (DKS Organized Hosting) that is a CDN implemented on top of the DKS (Distributed K-nary Search) structured P2P system with DHT (Distributed Hash table) functionality [9]. The prototype is implemented in Java, using the DKS middleware, the Jetty web-server, and a modi¯ed JavaFTP server. The proposed design of CDN has been evaluated by simulation and by evaluation experiments on the prototype.

  • 42. Kavassalis, Petros
    et al.
    Stelios, Lelis
    Rafea, Mahmoud
    Haridi, Seif
    RISE, Swedish ICT, SICS, Computer Systems Laboratory.
    What makes a Web site popular?2004In: Communications of the ACM, ISSN 0001-0782, E-ISSN 1557-7317, Vol. 47, no 2, p. 50-55Article in journal (Refereed)
  • 43.
    Klintskog, Erik
    et al.
    RISE, Swedish ICT, SICS.
    El Banna, Zacharias
    Brand, Per
    RISE, Swedish ICT, SICS.
    Haridi, Seif
    RISE, Swedish ICT, SICS, Computer Systems Laboratory.
    The design and evaluation of a middleware library for distribution of language entities2003In: Advances in Computing Science: Proceedings of the 8th Asian Computing Conference (ASIAN'03), 2003, 1, , p. 17Conference paper (Refereed)
    Abstract [en]

    The paper presents a modular design of a distribution middleware that supports the wide variety of entities that exist in high level languages. Such entities are classified into mutables, immutables and transients. The design is factorized in order to allow multiple consistency protocols for the same entity type, and multiple coordination strategies for implementing the protocols that differ in their failure behavior. The design is implemented and evaluated. It shows a very competitive performance.

  • 44.
    Klintskog, Erik
    et al.
    RISE, Swedish ICT, SICS.
    El Banna, Zacharias
    RISE, Swedish ICT, SICS.
    Brand, Per
    RISE, Swedish ICT, SICS, Computer Systems Laboratory.
    Haridi, Seif
    RISE, Swedish ICT, SICS, Computer Systems Laboratory.
    The DSS, a middleware library for efficient and transparent distribution of language entities.2004In: Proceedings of the 37th Hawaii International Conference on System Sciences (HICSS-37): Software Technology Track: Distributed Object and Component-based Software Systems Minitrack, 2004, 1Conference paper (Refereed)
    Abstract [en]

    This paper describes a novel language independent model for distribution of language entities, which allows for fine-grained instrumentation of entity consistency protocols on a per-entity basis. The model is implemented as a middleware component, designed to enhance arbitrary high-level programming languages with distribution support on the language entity level. The middleware library is extendable using internal interfaces to add new protocols over three different aspects of distribution.

  • 45.
    Klintskog, Erik
    et al.
    RISE, Swedish ICT, SICS.
    El Banna, Zacharias
    Brand, Per
    RISE, Swedish ICT, SICS, Computer Systems Laboratory.
    Haridi, Seif
    RISE, Swedish ICT, SICS, Computer Systems Laboratory.
    Mesaros, Valentin
    A peer-to-peer approach to enhance middleware connectivity2003Conference paper (Refereed)
    Abstract [en]

    One of the problems of middleware for shared state is that they are designed, explicitly or implicitly, for symmetric networks. However, since the Internet is not symmetric, end-to-end process connectivity cannot be guaranteed. Our solution to this is to provide the middleware with a network abstraction layer that masks the asymmetry of the network and provides the illusion of a symmetric network. We describe the communication service of our middleware, the Distribution Subsystem~(DSS), which carefully separates connections to remote processes from the protocols that communicate over them. This separation is used to plug-in a peer-to-peer module to provide symmetric and persistent connectivity. The P2P module can provide both up-to-date addresses for mobile processes as well as route discovery to overcome asymmetric links.

  • 46.
    Klintskog, Erik
    et al.
    RISE - Research Institutes of Sweden, ICT, SICS.
    Neiderud, Anna
    Brand, Per
    RISE, Swedish ICT, SICS, Computer Systems Laboratory.
    Haridi, Seif
    RISE, Swedish ICT, SICS, Computer Systems Laboratory.
    Fractional weighted reference counting2001In: Proceedings of the 7th International Euro-Par Conference Manchester on Parallel Processing, 28-31 Aug 2001, Manchester, UK, 2001, 1Conference paper (Refereed)
    Abstract [en]

    We introduce a scheme for distributed garbage collection that is an extension of Weighted Reference Counting. This scheme represents weights as fractions. It solves the problem of limited weight, preserves the property of third-party independence, and does not induce extra messages for reference merging.

  • 47.
    Krishnamurthy, Supriya
    et al.
    RISE, Swedish ICT, SICS. DSL.
    El-Ansary, Sameh
    RISE, Swedish ICT, SICS. DSL.
    Aurell, Erik
    RISE, Swedish ICT, SICS. DSL.
    Haridi, Seif
    RISE, Swedish ICT, SICS. DSL.
    A Statistical Theory of Chord under Churn2005Conference paper (Refereed)
    Abstract [en]

    Most earlier studies of DHTs under churn have either depended on simulations as the primary investigation tool, or on establishing bounds for DHTs to function. In this paper, we present a complete analytical study of churn using a master-equation-based approach, used traditionally in non-equilibrium statistical mechanics to describe steady-state or transient phenomena. Simulations are used to verify all theoretical predictions. We demonstrate the application of our methodology to the Chord system. For any rate of churn and stabilization rates, and any system size, we accurately predict the fraction of failed or incorrect successor and finger pointers and show how we can use these quantities to predict the performance and consistency of lookups under churn. We also discuss briefly how churn may actually be of different 'types' and the implications this will have for the functioning of DHTs in general.

  • 48.
    Krishnamurthy, Supriya
    et al.
    RISE, Swedish ICT, SICS. DSL.
    El-Ansary, Sameh
    RISE, Swedish ICT, SICS. DSL.
    Aurell, Erik
    RISE, Swedish ICT, SICS. DSL.
    Haridi, Seif
    RISE, Swedish ICT, SICS. DSL.
    An Analytical Study of a Structured Overlay in the presence of Dynamic Membership2005In: Joint IEEE/ACM Transactions on NetworkingArticle in journal (Refereed)
    Abstract [en]

    In this paper, we present a complete analytical study of dynamic membership (aka churn) in structured peer-to-peer networks. We use a master-equation-based approach, which is used traditionally in non-equilibrium statistical mechanics to describe steady-state or transient phenomena. We demonstrate that this methodology is in fact also well suited to describing structured overlay networks by an application to the Chord system. For any rate of churn and stabilization rates, and any system size, we accurately account for the functional form of: the distribution of inter-node distances, the probability of network disconnection, the fraction of failed or incorrect successor and finger pointers and show how we can use these quantities to predict both the performance and consistency of lookups under churn. Additionally, we also discuss how churn may actually be of different 'types' and the implications this will have for structured overlays in general. All theoretical predictions match simulation results to a high extent. The analysis includes details that are applicable to a generic structured overlay deploying a ring as well as Chord-specific details that can act as guidelines for analyzing other systems.

  • 49.
    Krishnamurthy, Supriya
    et al.
    RISE, Swedish ICT, SICS.
    El-Ansary, Sameh
    RISE, Swedish ICT, SICS.
    Aurell, Erik
    Haridi, Seif
    RISE, Swedish ICT, SICS, Computer Systems Laboratory.
    Comparing maintenance strategies for overlays2007Report (Other academic)
    Abstract [en]

    In this paper, we present an analytical tool for understanding the performance of structured overlay networks under churn based on the master-equation approach of physics. We motivate and derive an equation for the average number of hops taken by lookups during churn, for the Chord network. We analyse this equation in detail to understand the behaviour with and without churn. We then use this understanding to predict how lookups will scale for varying peer population as well as varying the sizes of the routing tables. We also consider a change in the maintenance algorithm of the overlay, from periodic stabilisation to a reactive one which corrects fingers only when a change is detected. We generalise our earlier analysis to understand how the reactive strategy compares with the periodic one.

  • 50.
    Krishnamurthy, Supriya
    et al.
    RISE, Swedish ICT, SICS.
    El-Ansary, Sameh
    RISE, Swedish ICT, SICS, Computer Systems Laboratory.
    Aurell, Erik
    Haridi, Seif
    RISE, Swedish ICT, SICS, Computer Systems Laboratory.
    Comparing Maintenance Strategies for Overlays2008Conference paper (Refereed)
    Abstract [en]

    In this paper, we present an analytical tool for understanding the performance of structured overlay networks under churn based on the master-equation approach of physics. We motivate and derive an equation for the average number of hops taken by lookups during churn, for the Chord network. We analyse this equation in detail to understand the behaviour with and without churn. We then use this understanding to predict how lookups will scale for varying peer population as well as varying the sizes of the routing tables. We also consider a change in the maintenance algorithm of the overlay, from periodic stabilisation to a reactive one which corrects fingers only when a change is detected. We generalise our earlier analysis to understand how the reactive strategy compares with the periodic one.

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