Sonia Fahmy

HEED: a hybrid, energy-efficient, distributed clustering approach for ad hoc sensor networks

Topology control in a sensor network balances load on sensor nodes and increases network scalability and lifetime. Clustering sensor nodes is an effective topology control approach. We propose a novel distributed clustering approach for long-lived ad hoc sensor networks. Our proposed approach does not make any assumptions about the presence of infrastructure or about node capabilities, other than the availability of multiple power levels in sensor nodes. We present a protocol, HEED (Hybrid Energy-Efficient Distributed clustering), that periodically selects cluster heads according to a hybrid of the node residual energy and a secondary parameter, such as node proximity to its neighbors or node degree. HEED terminates in O(1) iterations, incurs low message overhead, and achieves fairly uniform cluster head distribution across the network. We prove that, with appropriate bounds on node density and intracluster and intercluster transmission ranges, HEED can asymptotically almost surely guarantee connectivity of clustered networks. Simulation results demonstrate that our proposed approach is effective in prolonging the network lifetime and supporting scalable data aggregation.

Distributed clustering in ad-hoc sensor networks: a hybrid, energy-efficient approach

Prolonged network lifetime, scalability, and load balancing are important requirements for many ad-hoc sensor network applications. Clustering sensor nodes is an effective technique for achieving these goals. In this work, we propose a new energy-efficient approach for clustering nodes in ad-hoc sensor networks. Based on this approach, we present a protocol, HEED (hybrid energy-efficient distributed clustering), that periodically selects cluster heads according to a hybrid of their residual energy and a secondary parameter, such as node proximity to its neighbors or node degree. HEED does not make any assumptions about the distribution or density of nodes, or about node capabilities, e.g., location-awareness. The clustering process terminates in O(1) iterations, and does not depend on the network topology or size. The protocol incurs low overhead in terms of processing cycles and messages exchanged. It also achieves fairly uniform cluster head distribution across the network. A careful selection of the secondary clustering parameter can balance load among cluster heads. Our simulation results demonstrate that HEED outperforms weight-based clustering protocols in terms of several cluster characteristics. We also apply our approach to a simple application to demonstrate its effectiveness in prolonging the network lifetime and supporting data aggregation.

Topology-aware overlay networks for group communication

We propose an application level multicast approach, Topology Aware Grouping (TAG), which exploits underlying network topology information to build efficient overlay networks among multicast group members. TAG uses information about path overlap among members to construct a tree that reduces the overlay relative delay penalty, and reduces the number of duplicate copies of a packet on the same link. We study the properties of TAG, and model and experiment with its economies of scale factor to quantify its benefits compared to unicast and IP multicast. We also compare the TAG approach with the ESM approach in a variety of simulation configurations including a number of real Internet topologies and generated topologies. Our results indicate the effectiveness of the algorithm in reducing delays and duplicate packets, with reasonable algorithm time and space complexities.

On the Construction of a Maximum-Lifetime Data Gathering Tree in Sensor Networks: NP-Completeness and Approximation Algorithm

Energy efficiency is critical for wireless sensor networks. The data gathering process must be carefully designed to conserve energy and extend the network lifetime. For applications where each sensor continuously monitors the environment and periodically reports to a base station, a tree-based topology is often used to collect data from sensor nodes. In this work, we study the construction of a data gathering tree to maximize the network lifetime, which is defined as the time until the first node depletes its energy. The problem is shown to be NP-complete. We design an algorithm which starts from an arbitrary tree and iteratively reduces the load on bottleneck nodes (nodes likely to soon deplete their energy due to high degree or low remaining energy). We show that the algorithm terminates in polynomial time and is provably near optimal.

Editorial: Wired/wireless internet communications

Mobile communications technologies have reached a significant penetration today and the development of technologies and applications is still emerging. The Internet has become the major core network around which several wireless access networks are inter-connected. These access networks are not just single wireless links, but are becoming diverse and complex. For example, sensors are connected via sensor networks, cars connect via mobile ad hoc networks, and users in areas without GSM/UMTS coverage might only be reached via satellites. Moreover, the requirements to mobile communications are increasing. Security is a major concern in such networks and small wireless/mobile devices need to save as much power as possible to ensure long lifetimes. The 4th International Conference on Wired/Wireless Internet Communications (WWIC 2006) took place at University of Bern (Switzerland) from May 10 to 12, 2006. WWIC 2006 addressed relevant research issues such wireless networks, UMTS and OFDM, mobile ad hoc networks, power saving and sensor networks, voice and video over wireless networks, mobility, transport protocol issues as well as signalling, charging, and security. The goal of the conference was to present high-quality results in the field. The international conference program committee selected 29 papers out of 142 submissions for conference presentation. Finally, five papers from the ones presented at the conference have been selected for this special issue. The selected papers have been improved based on the conference reviews and extended in order to present latest research results in more detail. The paper on ‘‘Simulating Mobile Ad Hoc Networks in City Scenarios’’ from Illya Stepanov and Kurt Rothermel argues that it is very important to use more realistic models for user mobility and wireless transmission as well as real applications. The authors developed a more realistic mobility and wireless transmission model for the city of Stuttgart and showed that simulation results differ significantly compared to models that are typically used for the evaluation of mobile ad hoc networks. The work is based on integrating new models into ns-2 and using the emulation facility of ns-2.

Constraint-based routing in the internet: Basic principles and recent research

Novel routing paradigms based on policies, quality of service (QoS) requirements, and packet content have been proposed for the Internet over the last decade. Constraint-based routing algorithms select a routing path satisfying constraints that are either administrative-oriented (policy routing) or service-oriented (QoS routing). The routes, in addition to satisfying constraints, are selected to reduce costs, balance network load, or increase security. In this article, we discuss several constraint-based routing approaches and explain their requirements, complexity, and recent research proposals. In addition, we illustrate how these approaches can be integrated with Internet label switching and QoS architectures. We also discuss examples of application-level routing techniques used in todays Internet.

Analysis of vulnerabilities in Internet firewalls

Firewalls protect a trusted network from an untrusted network by filtering traffic according to a specified security policy. A diverse set of firewalls is being used today. As it is infeasible to examine and test each firewall for all possible potential problems, a taxonomy is needed to understand firewall vulnerabilities in the context of firewall operations. This paper describes a novel methodology for analyzing vulnerabilities in Internet firewalls. A firewall vulnerability is defined as an error made during firewall design, implementation, or configuration, that can be exploited to attack the trusted network that the firewall is supposed to protect. We examine firewall internals, and cross-reference each firewall operation with causes and effects of weaknesses in that operation, analyzing twenty reported problems with available firewalls. The result of our analysis is a set of matrices that illustrate the distribution of firewall vulnerability causes and effects over firewall operations. These matrices are useful in avoiding and detecting unforeseen problems during both firewall implementation and firewall testing. Two case studies of Firewall-1 and Raptor illustrate our methodology.

Source behavior for ATM ABR traffic management: an explanation

The available bit rate (ABR) service has been developed to support data applications over asynchronous transfer mode (ATM) networks. The network continuously monitors its traffic and provides feedback to the source end systems. This article explains the rules that the sources have to follow to achieve a fair and efficient allocation of network resources.

A Survey of Application Layer Techniques for Adaptive Streaming of Multimedia

Though the integrated services model and resource reservation protocol (RSVP) provide support for quality of service, in the current Internet only best-effort traffic is widely supported. New high-speed technologies such as ATM (asynchronous transfer mode), gigabit Ethernet, fast Ethernet, and frame relay, have spurred higher user expectations. These technologies are expected to support real-time applications such as video-on-demand, Internet telephony, distance education and video-broadcasting. Towards this end, networking methods such as service classes and quality of service models are being developed. Todays Internet is a heterogeneous networking environment. In such an environment, resources available to multimedia applications vary. To adapt to the changes in network conditions, both networking techniques and application layer techniques have been proposed. In this paper, we focus on the application level techniques, including methods based on compression algorithm features, layered encoding, rate shaping, adaptive error control, and bandwidth smoothing. We also discuss operating system methods to support adaptive multimedia. Throughout the paper, we discuss how feedback from lower networking layers can be used by these application-level adaptation schemes to deliver the highest quality content.

Analyzing video services in Web 2.0: a global perspective

Serving multimedia content over the Internet with negligible delay remains a challenge. With the advent of Web 2.0, numerous video sharing sites using different storage and content delivery models have become popular. Yet, little is known about these models from a global perspective. Such an understanding is important for designing systems which can efficiently serve video content to users all over the world. In this paper, we analyze and compare the underlying distribution frameworks of three video sharing services - YouTube, Dailymotion and Metacafe - based on traces collected from measurements over a period of 23 days. We investigate the variation in service delay with the users geographical location and with video characteristics such as age and popularity. We leverage multiple vantage points distributed around the globe to validate our observations. Our results represent some of the first measurements directed towards analyzing these recently popular services.