Maha Abdallah - Academia.edu (original) (raw)

Papers by Maha Abdallah

IEEE Transactions on Circuits and Systems for Video Technology, 2015

2011 10th IEEE/ACIS International Conference on Computer and Information Science, 2011

2013 27th International Conference on Advanced Information Networking and Applications Workshops, 2013

Despite the plethora of existing works, the efficient distribution and management of avatar state... more Despite the plethora of existing works, the efficient distribution and management of avatar states remains a highly challenging issue in P2P-based virtual environments (VEs). The present paper addresses this issue by building on our previously proposed Relaxed Triangulation (RT) overlay, designed to accommodate the dynamic nature of VEs by drastically reducing the maintenance cost inherent to the well-known Delaunay construct. Given that our RT overlay no longer supports greedy routing, we propose in this paper to complement our RT overlay with a message routing algorithm that guarantees message delivery on top of RT, thus combining in one solution the best of the two worlds. We provide simulation results to demonstrate our system performance, and also discuss its limitations.

Peer-to-Peer Networking and Applications, 2013

By randomly mapping items and nodes to a common address space, most P2P index structures based on... more By randomly mapping items and nodes to a common address space, most P2P index structures based on DHTs provide only exact match data lookups. This compromises their use in data-oriented applications where more advanced query facilities, such as range queries, are needed. We have previously proposed a P2P index structure that refines the Chord DHT by mapping data items to the Chord address space in an order-preserving way. Load balancing of skewed data is then achieved deterministically by pulling nodes to zones where too many data items reside. However, based on Chord's underlying routing infrastructure, our previous solution can no longer ensure logarithmic routing cost when the node distribution over the address space becomes highly skewed. In this paper, we push our previous study one step further and propose a simple yet efficient refinement to Chord's routing component. By offering nodes more flexibility in the choice of their neighbors, our solution ensures logarithm...

Peer-to-peer (P2P) architectures have recently become a popular design choice for building scalab... more Peer-to-peer (P2P) architectures have recently become a popular design choice for building scalable Networked Virtual Environments (NVEs). In P2P-based NVEs, system and data management is distributed among all participating users. Towards this end, a Delaunay Triangulation can be used to provide connectivity between the different NVE users depending on their positions in the virtual world. However, a Delaunay Triangulation clearly suffers from high maintenance cost as it is subject to high connection change rate due to continuous users ' movement. In this paper, we propose a new triangulation algorithm that provides network connectivity to support P2P NVEs while dramatically decreasing maintenance overhead by reducing the number of connection changes due to users' insertion and movement. Performance evaluations show that our solution drastically reduces overlay maintenance cost in highly dynamic NVEs. More importantly, and beyond its quantitative advantages, this work ques...

Abstract. Transactional standards have been promoted by OMG and X/Open to allow heterogeneous res... more Abstract. Transactional standards have been promoted by OMG and X/Open to allow heterogeneous resources to participate in an Atomic Commitment Protocol (ACP), namely the two-phase commit protocol (2PC). Although widely accepted, 2PC is a blocking protocol and it introduces a substantial time delay (two phases to commit). Several optimized protocols and non-blocking protocols have been proposed. Optimized protocols generally violate site autonomy while non-blocking protocols are inherently more costly in time and increase communication overhead. This paper proposes a new ACP that provides the non-blocking property while (1) having a lower latency than other ACPs (one phase to commit), and (2) preserving site autonomy, which makes it compatible with existing DBMSs. This protocol relies on the assumption that all participants are ruled by a rigorous concurrency control protocol. Performance analysis shows that our protocol is more efficient in terms of time delay and message complexity...

Peer-to-peer (P2P) systems provide a robust, scalable and decentralized way to share and publish ... more Peer-to-peer (P2P) systems provide a robust, scalable and decentralized way to share and publish data. Although highly efficient, current P2P index structures based on Distributed Hash Tables (DHTs) provide only exact match data lookups. This compromises their use in database applications where more advanced query facilities, such as range queries, are a key requirement. In this paper, we give a new P2P indexing structure that supports range searches over shared data while maintaining DHTs logarithmic search time. Our index structure can be seen as an extension of the Chord P2P overlay so that data items are mapped to the Chord address space in an order-preserving way, hence supporting range query executions. Load balancing of skewed data is then achieved deterministically using the underlying DHT infrastructure. Experimental evaluations show that our mechanism provides strong load balancing guarantees in systems with high data skews.

La norme actuelle dans le domaine de la validation atomique des transactions est la validation at... more La norme actuelle dans le domaine de la validation atomique des transactions est la validation atomique a deux phases (2pc). Malgre son grand succes, 2pc est inefficace en termes de latence et de cout de communication meme en l'absence de pannes, et est bloquant en cas de pannes. Cette these a pour but d'etudier et de proposer de nouvelles solutions au probleme de la validation atomique, capables de repondre aux exigences des systemes actuels en termes de haute-performance et de tolerance aux pannes. La premiere phase du 2pc est une phase de votes durant laquelle les participants a la transaction ont le droit a un abandon unilateral. Retirer le droit de veto a tous les participants reduit considerablement le cout de la validation atomique, mais introduit quelques contraintes sur la facon dont le controle de concurrence et la reprise apres pannes sont geres par les differents participants. A la lumiere de cette observation, et dans sa premiere partie, cette these comporte tro...

Databases are hosted by a growing number of lightweight intelligent devices like palmtops, cellul... more Databases are hosted by a growing number of lightweight intelligent devices like palmtops, cellular phones, car computers and even smart cards. Mobility and disconnected computing are two major issues in such environment. This paper deals with the way databases can be exploited in this context while maintaining a strong transactional coherency. More precisely, we argue that 2PC, the most well known and well-established atomic commitment protocol, is far from being adapted to this environment. We propose a new atomic commitment protocol, called Unilateral Commit for Mobile (UCM), that exhibits the following properties : it supports off-line executions and disconnection during commitment, it decreases the cost of wireless communication by reducing the message complexity and it saves resources on lightweight servers. These properties are obtained at the price of some assumptions on the way servers manage transactions. Anyway, we show that these assumptions are not constraining in the c...

ACM Transactions on Multimedia Computing, Communications, and Applications, 2017

Distributed Hash Tables provide a scalable way of indexing shared data items in P2P systems. The ... more Distributed Hash Tables provide a scalable way of indexing shared data items in P2P systems. The scalability of DHTs mainly relies on the mechanism by which the system's load is fairly balanced among all participating nodes. This is usually achieved through a uniform hash function that randomly maps data items to nodes in the DHT. While this scheme provides item-balancing guarantees, it fails in balancing the actual load of the system by (1) making the simplifying assumption that all items are equally popular, i.e., they incur the same query-load on their hosting nodes, and (2) assuming that all nodes have comparable capacities. In this paper, we address this issue by considering a more practical characterization of a system's load, and propose a load balancing mechanism that takes into account data (un)popularity and node heterogeneity. We first redefine the notion of load in terms of the number of queries per time frame. Load is then balanced by dynamically adjusting the D...

In distributed transactional systems, an Atomic Commitment Protocol (ACP) is used to ensure the a... more In distributed transactional systems, an Atomic Commitment Protocol (ACP) is used to ensure the atomicity of distributed transactions even in the presence of failures. An ACP is said to be non-blocking if it allows correct participants to decide on the transaction despite the failure of others. Several non-blocking protocols have been proposed in the literature. However, none of these protocols is able to combine high efficiency during normal processing with fault-tolerance (i.e. non-blocking). In this paper, we present a non-blocking atomic commitment protocol, noted ANB-CLL (Asynchronous Non-Blocking Coordinator Logical Log), that drastically reduces the cost of distributed transaction commitment in terms of time delay and message complexity. Performance analysis shows that the resulting protocol is more efficient than all other non-blocking protocols proposed in the literature. An important characteristic of ANB-CLL is that it can be applied to commercial transactional systems th...

The 2009 Workshop on Network and Systems Support for Games (NetGames) is the eighth in a series o... more The 2009 Workshop on Network and Systems Support for Games (NetGames) is the eighth in a series of successful events. The Workshop on Network and Systems Support for Games (NetGames) is a major annual international forum that brings together academic and industrial researchers, engineers, and practitioners in the field of networked games at large to exchange original research results, discuss ongoing research projects and initiatives, and establish new research collaborations. Since 2002, NetGames has become a well established and recognized forum for promoting exciting discussions among its participants and disseminating original ideas and research results in all areas related to online games and related technologies. The NetGames 2009 call for papers attracted 37 submissions. Each submission was carefully reviewed by at least three members of the Technical Program Committee. The reviewing process led to the acceptance of 10 papers. This made the workshop a highly selective event w...

Abstract. The current standard in governing distributed transaction termination is the so-called ... more Abstract. The current standard in governing distributed transaction termination is the so-called Two-Phase Commit protocol (2PC). The first phase of 2PC is a voting phase, where the participants in the transaction are given an ultimate right to abort that transaction. Giving up that veto right from all participants reduces the overhead of the atomic commitment protocol but also imposes some restrictions on the concurrency control and recovery protocols employed by the participants in the transaction. This paper gives, for the first time, a precise abstract specification of the Dictatorial Atomic Commitment (DAC) problem, resulting from removing veto rights from the traditional Atomic Commitment (AC) problem. We characterize transactional systems that are compatible with that specification in terms of necessary and sufficient conditions on concurrency control and recovery protocols, and discuss the practical impacts of those conditions. From this study, we capitalize on existing prot...

ACM Transactions on Multimedia Computing, Communications, and Applications