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Showing papers by "Sonia Fahmy published in 2005"


Proceedings ArticleDOI
12 Dec 2005
TL;DR: This paper designs and implements a system, iHEED, in which node clustering is integrated with multi-hop routing for TinyOS, and results indicate that the network lifetime is prolonged by a factor of 2 to 4, and successful transmissions are almost doubled.
Abstract: Several sensor network applications, such as environmental monitoring, require data aggregation to an observer. For this purpose, a data aggregation tree, rooted at the observer, is constructed in the network. Node clustering can be employed to further balance load among sensor nodes and prolong the network lifetime. In this paper, we design and implement a system, iHEED, in which node clustering is integrated with multi-hop routing for TinyOS. We consider simple data aggregation operators, such as AVG or MAX. We use a simple energy consumption model to keep track of the battery consumption of cluster heads and regular nodes. We perform experiments on a sensor network testbed to quantify the advantages of integrating hierarchical routing with data aggregation. Our results indicate that the network lifetime is prolonged by a factor of 2 to 4, and successful transmissions are almost doubled. Clustering plays a dominant role in delaying the first node death, while aggregation plays a dominant role in delaying the last node death

86 citations


Journal ArticleDOI
TL;DR: The heuristic TAG uses the overlap among routes from the source to group members to construct an efficient overlay network in a distributed, low-overhead manner, and is effective in reducing delays and duplicate packets.

52 citations


Journal ArticleDOI
TL;DR: This work proposes REED (Robust Energy-Efficient Distributed clustering), a k-fault-tolerant clustered network, and proves that REED asymptotically achieves k-connectivity if certain conditions on node density are met.
Abstract: Node clustering in sensor networks increases scalability, robustness, and energy-efficiency. In hostile environments, unexpected failures or attacks on cluster heads (through which communication takes place) may partition the network or degrade application performance. We propose REED (Robust Energy-Efficient Distributed clustering), for clustering sensors deployed in hostile environments in an interleaved manner with low complexity. Our primary objective is to construct a k-fault-tolerant (i.e., k-connected) clustered network, where k is a constant determined by the application. Fault tolerance is achieved by selecting k independent sets of cluster heads (i.e., cluster head overlays) on top of the physical network, so that each node can quickly switch to other cluster heads in case of failures. The independent cluster head overlays also give multiple vertex-disjoint routing paths for load balancing and security. Network lifetime is prolonged by selecting cluster heads with high residual energy and low co...

47 citations


Journal ArticleDOI
TL;DR: It is found that coordinated congestion management techniques are more fair when integrated with FlowMate, and the results demonstrate that clustering of medium to long-lived flows is accurate, even with bursty background traffic.
Abstract: We design and implement an efficient on-line approach, FlowMate, for clustering flows (connections) emanating from a busy server, according to shared bottlenecks. Clusters can be periodically input to load balancing, congestion coordination, aggregation, admission control, or pricing modules. FlowMate uses in-band (passive) end-to-end delay measurements to infer shared bottlenecks. Delay information is piggybacked on feedback from the receivers, or, if impossible, TCP or application round-trip time estimates are used. We simulate FlowMate and examine the effects of network load, traffic burstiness, network buffer sizes, and packet drop policies on clustering correctness, evaluated via a novel accuracy metric. We find that coordinated congestion management techniques are more fair when integrated with Flow-Mate. We also implement FlowMate in the Linux kernel v2.4.17 and evaluate its performance on the Emulab testbed, using both synthetic and tcplib-generated traffic. Our results demonstrate that clustering of medium to long-lived flows is accurate, even with bursty background traffic. Finally, we validate our results on the Internet Planetlab testbed.

31 citations


Proceedings ArticleDOI
31 Oct 2005
TL;DR: Synergy is designed, a utility-based overlay internetworking architecture that fosters overlay cooperation and promotes fair peering relationships to achieve synergism, and results from Internet experiments with cooperative forwarding overlays indicate that the Synergy prototype improves delay, throughput, and loss performance, while maintaining the autonomy and heterogeneity of individual overlay networks.
Abstract: A multitude of overlay network designs for resilient routing, multicasting, quality of service, content distribution, storage, and object location have been recently proposed. Overlay networks offer several attractive features, including ease of deployment, flexibility, adaptivity, and an infrastructure for collaboration among hosts. In this paper, we explore cooperation among co-existing, possibly heterogeneous, overlay networks. We design Synergy, a utility-based overlay internetworking architecture that fosters overlay cooperation. Our architecture promotes fair peering relationships to achieve synergism. Results from Internet experiments with cooperative forwarding overlays indicate that our Synergy prototype improves delay, throughput, and loss performance, while maintaining the autonomy and heterogeneity of individual overlay networks.

31 citations


Proceedings ArticleDOI
13 Oct 2005
TL;DR: A new distributed power control protocol is formulated, Load-Aware Power Control (LAPC), that heuristically considers low end-to-end latency when selecting power levels.
Abstract: We investigate the impact of power control on latency in wireless ad-hoc networks. If transmission power is increased, interference increases, thus reducing network capacity. A node sending/relaying delay-sensitive real-time application traffic can, however, use a higher power level to reduce latency, if it considers information about load and channel contention at its neighboring nodes. Based on this observation, we formulate a new distributed power control protocol, Load-Aware Power Control (LAPC), that heuristically considers low end-to-end latency when selecting power levels. We study the performance of LAPC via simulations, varying the network density, node dispersion patterns, and traffic load. Our simulation results demonstrate that LAPC achieves an average end-to-end latency improvement of 54\% over the case when nodes are transmitting at the highest power possible, and an average end-to-end latency improvement of 33\% over the case when nodes are transmitting using the lowest power possible, for uniformly dispersed nodes in a lightly loaded network.

27 citations


Journal ArticleDOI
TL;DR: Simulation results indicate that this design increases application‐level throughput of data applications such as large FTP transfers; achieves low packet delays and response times for Telnet and WWW traffic; and detects bandwidth theft attacks and service violations.
Abstract: Increased performance, fairness, and security remain important goals for service providers. In this work, we design an integrated distributed monitoring, traffic conditioning, and flow control system for higher performance and security of network domains. Edge routers monitor (using tomography techniques) a network domain to detect quality of service (QoS) violations--possibly caused by underprovisioning--as well as bandwidth theft attacks. To bound the monitoring overhead, a router only verifies service level agreement (SLA) parameters such as delay, loss, and throughput when anomalies are detected. The marking component of the edge router uses TCP flow characteristics to protect 'fragile' flows. Edge routers may also regulate unresponsive flows, and may propagate congestion information to upstream domains. Simulation results indicate that this design increases application-level throughput of data applications such as large FTP transfers; achieves low packet delays and response times for Telnet and WWW traffic; and detects bandwidth theft attacks and service violations.

17 citations


Proceedings ArticleDOI
12 Dec 2005
TL;DR: This paper proposes a clustering- based time synchronization framework for multi-hop sensor net- works that exploits the tradeoff between rapid convergence (and consequently energy-efficiency) and perceived accuracy, and formulate a density model for analyzing inter- regional synchronization.
Abstract: Time synchronization is essential for several ad-hoc network protocols and applications, such as TDMA scheduling and data aggregation. In this paper, we propose a clustering- based time synchronization framework for multi-hop sensor net- works. We assume that relative node synchronization is sufficient, i.e., consensus on one time value is not required. Our goal is to divide the network into connected synchronization regions (nodes within 2-hops) and perform inter-regional synchronization in O(LLSync) × Niter time, where O(LLSync) denotes the complexity of the underlying low-level synchronization technique (used for single hop synchronization), and Niter denotes the number of iterations where the low-level synchronization protocol is invoked. We propose two novel fully-distributed protocols, SYNC-IN and SYNC-NET, for regional and network synchro- nization, respectively, and prove that Niter is O(1) for both protocols. We exploit the tradeoff between rapid convergence (and consequently energy-efficiency) and perceived accuracy. Our framework does not require any special node capabilities (e.g., being GPS-enabled), or the presence of reference nodes in the network. Our framework is also independent of the particular clustering, inter-cluster routing, and low-level synchronization protocols. We formulate a density model for analyzing inter- regional synchronization, and evaluate our protocols via extensive simulations.

9 citations


Proceedings ArticleDOI
Yan Wu1, Sonia Fahmy1
03 Oct 2005
TL;DR: An important feature of the proposed credit-based distributed protocol is its backward compatibility, which allows legacy IEEE 802.11 stations to coexist with stations adopting the new MAC protocol.
Abstract: Fair bandwidth allocation is critical in wireless communication networks, since the wireless channel is often shared by a number of stations in the same neighborhood. With fair scheduling, bandwidth can be shared by competing flows in proportion to their assigned weights. In this paper, we propose a credit-based distributed protocol for fair allocation of bandwidth in IEEE 802.11 wireless LANs. Our protocol is derived from the distributed coordination function in the IEEE 802.11 medium access control (MAC) protocol. Analytical and simulation results demonstrate that the protocol achieves the desired bandwidth allocations. An important feature of our protocol is its backward compatibility, which allows legacy IEEE 802.11 stations to coexist with stations adopting the new MAC protocol.

4 citations


01 Jan 2005
TL;DR: This work designs distributed protocols for topology management and network synchronization for heavily-loaded sensor networks serving applications that can exploit data aggregation, and considers applications and protocols that require node synchronization, and design a framework for time synchronization in multi-hop hierarchical networks that is based on relative synchronization.
Abstract: Networked embedded systems provide a versatile computing platform for supporting applications, such as environmental monitoring or military field surveillance. These networks are typically deployed in harsh environments and left unattended, which makes it impossible to re-charge their node batteries. Motivated by the large scale of sensor deployment, the high cost of wireless communications, the limited capabilities of sensor nodes, and the hostility of the encompassing environment, we design distributed protocols for topology management and network synchronization. We investigate problems that are specific to heavily-loaded sensor networks serving applications that can exploit data aggregation. We address applications that are either source-driven (in which sensors periodically send their reports to an observer), or query-driven (in which a subset of sensors respond to an observer's query). We construct a hierarchical (clustered) network in which a subset of nodes are elected as super-nodes (or cluster heads). These heads constitute the routing infrastructure and aggregate data from their neighboring non-head nodes. The super-node functionality is rotated among network nodes to achieve load balancing and prolong the lifetime of every individual sensor. For sensors deployed in harsh environments, we propose a methodology for improving the connectivity of the hierarchical network and providing opportunities for multi-path routing. In addition, we consider applications and protocols that require node synchronization, and design a framework for time synchronization in multi-hop hierarchical networks that is based on relative synchronization.

1 citations