A.A. Abouzeid 2003 Publications

In coding theory, a channel coding algorithm is good if it achieves the Shannon capacity [1]. Similarly, we seek to derive a universal curve against which we can measure how good (or bad) a variable topology routing protocol (e.g. for ad-hoc networks) performs, in comparison with a theoretical minimum routing overhead, which is the amount of information needed to describe the changes in a dynamic network topology.

An analytical model of TCP (Transport Control Protocol) over an end-to-end path with random abrupt round-trip time (RTT) changes is presented. Modeling the RTT as a stochastic process, we analytically quantify and compare between the degree of degradation of the steady-state average throughput and window size due to spurious retransmissions for the different versions of TCP (Reno/NewReno versus Tahoe). The modeling methodology in this paper is used for evaluating different design alternatives for TCP for highly dynamic networks

A link model-driven approach toward transmission control protocol (TCP) performance over a wireless link is presented. TCP packet loss behavior is derived from an underlying two-state continuous time Markov model. The approach presented here is (to our knowledge) the first that simultaneously considers (1) variability of the round-trip delay due to buffer queueing; (2) independent and nonindependent (bursty) link errors; (3) TCP packet loss due to both buffer overflow and channel errors; and (4) the two modes of TCP packet loss detection (duplicate acknowledgments and timeouts). The analytical results are validated against simulations using the ns-2 simulator for a wide range of parameters; slow and fast fading links; small and large link bandwidth-delay products. For channels with memory, an empirical rule is presented for categorizing the impact of channel dynamics (fading rate) on TCP performance

This paper presents a new mathematical and simulative framework for quantifying the overhead of a broad class of reactive routing protocols, such as DSR and AODV, in wireless variable topology (ad-hoc) networks. We focus on situations where the nodes are stationary but unreliable, as is common in the case of sensor networks. We explicitly model the application-level traffic in terms of the statistical description of the number of hops between a source and a destination. The sensor network is modelled by an unreliable regular Manhattan (i.e. degree four) grid, and expressions for various components of the routing overhead are derived. Results are compared against ns-2 simulations for regular and random topologies, which corroborate the essential characteristics of the analytical results. One of the key insights that can be drawn from the mathematical results of this paper is that it is possible to design infinitely scalable reactive routing protocols for variable topology networks by judicious engineering of the traffic patterns to satisfy the conditions presented in this paper.

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This paper focuses on Bluetooth, a promising new wireless technology, developed mainly as a cable replacement. We argue that, in practice, Bluetooth devices will have different power capabilities, classifying them as either high-power or low-power nodes. We propose a deterministic, distributed algorithm that accounts for the physical properties of devices, connecting nodes into a scatternet of small diameter. The proposed protocol results in a high effective throughput and allows components to arrive and leave arbitrarily, dynamically updating the cluster formation. Performance is evaluated through extensive ns-2 simulations.

This paper focuses on Bluetooth, a promising new wireless technology, developed mainly as a cable replacement. We argue that, in practice, Bluetooth devices will have different power capabilities, classifying them as either high-power or low-power nodes. We propose a deterministic, distributed algorithm that accounts for the physical properties of devices, connecting nodes into a scatternet of small diameter. The proposed protocol results in a high effective throughput and allows components to arrive and leave arbitrarily, dynamically updating the cluster formation. Performance is evaluated through extensive ns-2 simulations.

In this paper, we define the routing overhead as the amount of information needed to describe the changes in a network topology. We derive a universal lower bound on the routing overhead in a mobile ad-hoc network. We also consider a prediction-based routing protocol that attempts to minimize the routing overhead by predicting the changes in the network topology from the previous mobility pattern of the nodes.We apply our approach to a mobile ad-hoc network that employs a dynamic clustering algorithm, and derive the optimal cluster size that minimizes the routing overhead, with and without mobility prediction. We believe that this work is a fundamental and essential step towards the rigorous modeling, design and performance comparisons of protocols for ad-hoc wireless networks by providing a universal reference performance curve against which the overhead of different routing protocols can be compared.