Browsing by Author "Mihail Sichitiu, Committee Member"

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    Analysis of SIP in UMTS IP Multimedia Subsystem
    (2003-08-14) Zhu, Bei; Arne A Nilsson, Committee Chair; Mihail Sichitiu, Committee Member; Richard T Kuehn, Committee Member
    As a key member of the 3G mobile technologies identified by the ITU (international Telecommunication Union), UMTS (Universal Mobile Telecommunications System) represents an evolution in terms of services and data speeds from today's 2G mobile networks. Third Generation Partnership Project (3GPP) was formed to work on the technical specification of UMTS. A UMTS network consists of three interacting domains: Core Network (CN), UMTS Terrestrial Radio Access Network (UTRAN) and User Equipment (UE). The IP multimedia subsystem comprises all CN elements for provision of multimedia services. The Session Initiation Protocol has been chosen by the 3GPP for establishing multimedia sessions in UMTS Release 5 networks. The purpose of the research has been to analyze the SIP operation in IP Multimedia Subsystem of UMTS network from two aspects: bottleneck and delay. The bottleneck analysis was based on the investigation of the detailed call set up and release procedures. The signaling flows hit each functional entities (CSCF or HSS) along the routing chains of signaling traffic several times. Once hit, the functional entity provides some service and then forwards the traffic on. We counted the hit times of each functional entity and identified the bottlenecks in different scenarios. We concluded that which one node would be the bottleneck depends on how the traffic is distributed in the networks. We did the delay analysis firstly by describing the SIP signaling traffic with M/M/1 notation. We calculated the delay in each node and gave the waiting time distribution. Then we assumed the traffic to be M/D/1 and gave the delay in each node. The total delay in a call set up/release procedure is the summation of the delay of the nodes along the signaling path. We got that the M/M/1 analysis provides us the upper bound of the average waiting time of each node, as well as the average delay in the call set up/release procedure.
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    An Automatic, Adaptive, Ad-hoc Algorithm for Power Conservation in Sensor Networks using Switch-off
    (2004-07-29) Visweswara, Sharat; Mihail Sichitiu, Committee Member; Mladen Vouk, Committee Member; Rudra Dutta, Committee Chair
    Wireless sensor networks are set to revolutionize the way we sense and control our environment. A set of nodes equipped with sensors and capable of communicating with each other in ad-hoc fashion, they relay their data to a monitoring station. What sets them apart from other ad-hoc networks is the periodic nature of the traffic and a critical dependence on a finite source of power, the battery. The battery is a bottleneck to the lifetime of the network and careful use of the battery can increase the lifetime by orders of magnitude. The periodic nature of traffic in a sensor network can be leveraged to switch the transceiver off when not needed, as shown in existing literature. We take up one such switch-off-switch-on scheduling algorithm and show how it can be extended to be robust to dynamic conditions. We then develop an analytical model, which can be used to predict the performance of the algorithm. We also identify a better way of expressing the utility of the network and quantify the benefit accruing from using the algorithm, making it possible to compare different variations of the algorithm and different configuration parameters. The model can also be used to find ways to improve the performance of the algorithm to obtain greater power efficiency.
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    Autonomous Soaring: The Montague Cross Country Challenge.
    (2010-04-23) Edwards, Daniel; Lawrence Silverberg, Committee Chair; Charles Hall, Committee Member; Ashok Gopalarathnam, Committee Member; Mihail Sichitiu, Committee Member
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    Energy Optimization in Sensor Networks
    (2007-11-06) Chiang, Mu-Huan; Peng Ning, Committee Member; Gregory T. Byrd, Committee Chair; Mihail Sichitiu, Committee Member; Alexander G. Dean, Committee Member
    Recent advances in wireless communications and computing technology are enabling the emergence of low-cost devices that incorporate sensing, processing, and communication functionalities. A large number of these devices are deployed to create a sensor network for both monitoring and control purposes. Sensor networks are currently an active research area mainly due to the potential of their applications. However, the operation of large scale sensor networks still requires solutions to numerous technical challenges that stem primarily from the constraints imposed by simple sensor devices. Among these challenges, the power constraint is the most critical one, since it involves not only reducing the energy consumption of a single sensor but also maximizing the lifetime of an entire network. The network lifetime can be maximized only by incorporating energy awareness into every stage of sensor network design and operation, thus empowering the system with the ability to make dynamic tradeoffs among energy consumption, system performance, and operational fidelity. Optimizing the energy usage is a critical challenge for wireless sensor networks (WSNs). The requirements of energy optimization schemes are as follows. (1) Low individual energy consumption: Sensor nodes can use up their limited energy supply, carrying out computations and transmission. In typical WSNs, nodes play a dual role as both data sender and data router. Malfunctioning of some sensor nodes due to power failure can cause significant topological changes and may require rerouting of packets and network reorganization. Therefore, reducing the energy consumption of each sensor node is critical for WSNs. (2) Balanced energy usage: While minimizing the energy consumption of individual sensor nodes is important, the energy status of the entire network should also be of the same order. If certain nodes have much higher workload than others, these nodes will drain off their energy rapidly and adversely impact the overall system lifetime. The workload of sensors should be balanced in order to achieve longer system lifetime. (3) Low computation and communication overhead: The resource limitations imposed by sensor hardware call for simple protocols that require minimal processing and a small memory footprint. The extra computation and communication introduced by the energy optimization schemes must also be kept low. Otherwise, energy required to perform the optimization schemes may outweigh the benefits. This thesis concentrates on the energy optimization issues in wireless sensor networks. We study the power consumption characteristics of typical sensor platforms, and propose energy optimization schemes in network and application level. We design distributed algorithms that reduce the amount of data traffic and unnecessary overhearing waste in WSNs, and further propose load balancing mechanisms that alleviate the unbalanced energy usage and prolong the effective system lifetime. At the network level, Adaptive Aggregation Tree (AAT) is proposed to dynamically transform the routing tree, using easily-obtained overheard information, to improve the aggregation efficiency. The local adaptivity of AAT achieves significant energy reduction, compared to the shortest-path tree where aggregation occurs opportunistically. We also propose Neighborhood-Aware Density Control (NADC), which exploits the overheard information to reduce the unnecessary overhearing waste along routing paths. In NADC, nodes observe their neighborhood and adapt their participation in the multihop routing topology. By reducing the node density near the routing paths, the overhearing waste can be reduced, and the extremely unbalanced energy usage among sensor nodes is also alleviated, which results in a longer system lifetime. The unbalanced energy usage problem is further addressed at the application level, where we propose Zone-Repartitioning (Z-R) for load balancing in data-centric storage systems. Z-R reduces the workload of certain hot-spots by distributing their communication load to other nodes when the event frequency of certain areas is much higher than the others.
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    Identity-Based Cryptography: Feasibility & Applications in Next Generation Sensor Networks
    (2007-11-11) Kampanakis, Panagiotis T.; Michael Devetsikiotis, Committee Chair; Peng Ning, Committee Co-Chair; Mihail Sichitiu, Committee Member
    Elliptic Curve Cryptography (ECC) has been a very interesting research field for many applications, especially in sensor networks. The main reason for this is the restrictions on resources posed by sensor motes. ECC alleviates these restrictions by using small prime fields. At the same time, the evolution of hardware technology has built new, sophisticated motes with more capabilities which open new ways for sensor network applications. In our work, we are extending the TinyECC package, initially written by An Liu, which provides elliptic curve cryptography functionality on sensor motes running TinyOS. We extend this package by porting it to new powerful motes, called Imote2s by Intel. We also further implement Bilinear Pairing which is the most important part of Identity-Based Cryptography. Furthermore, we evaluate and prove the feasibility of using pairing on next generation sensor motes. There are various ways that Bilinear Pairing could be used in Identity-Based cryptosystems, so in this way we insert Identity-Based Cryptography in the area of security for sensor networks. Additionally, we propose a scheme that can establish keys on sensor networks using Identity-Based Cryptography. We believe that our study will open the way and motivate further research in the field and contribute in providing more robust and secure sensor networks.
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    Measurements and Analysis of the Performance Characteristics of SIP Proxy Servers.
    (2010-06-11) Subramanian, Sureshkumar; Rudra Dutta, Committee Chair; Mihail Sichitiu, Committee Member; Georgios Rouskas, Committee Member; Khaled Abdel Harfoush, Committee Member
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    Mobile Ad-hoc Networks: Mobility-induced Metrics, Performance Analysis, and System Design
    (2009-12-04) Cai, Han; Do Young Eun, Committee Chair; Michael Devetsikiotis, Committee Member; Mihail Sichitiu, Committee Member; Min Kang, Committee Member
    Mobile Ad-hoc Network (MANET), a type of self-configuring wireless ad-hoc network, comprises of mobile elements equipped with wireless communication devices. The mobility pattern of mobile nodes and the packet forwarding strategy crucially decide MANET performance. The node mobility leads to time-varying network topology. Conventional routing schemes fails due to the infeasibility to set up the end-toend path before data transmission. The mobility pattern affects system performance through mobility-induced metrics such as contact time and inter-meeting time. These metrics are critical in determining the MANET performance, as well as choosing various scheduling/forwarding algorithms. In this dissertation, we study the effect of mobility patterns on the MANET performance through the mobility-induced metrics, e.g., inter-meeting time. The intermeeting time is typically assumed to be exponentially distributed in MANET performance studies. However, recent empirical results disclose clear power-law behavior of inter-meeting time distribution. This outright discrepancy potentially undermines our understanding of the performance tradeoffs in MANET obtained under the assumed inter-meeting time with exponential distribution, and thus calls for further study on the power-law (or more generally, non-exponential) inter-meeting time including its fundamental cause, mobility modeling, and its effect. We first prove that the finite/infinite domain with respect to the time scale of interest critically decides the exponential/power-law tail of the inter-meeting time distribution. We then show a convex ordering relationship among inter-meeting times of various mobility models indexed by their degrees of correlation, which is in good agreement with the ordering of network performance under a set of mobility patterns whose inter-meeting time distributions have power-law ‘head’ followed by exponential ‘tail’. Finally, we analyze various characteristics of the relative mobility of a random pair of nodes in MANET to show that they produce inter-meeting time with different aging properties. The aging property allows us to establish for the first time that the approach based on exponential inter-meeting time assumption can always underestimate or over-estimate the actual system performance, under stochastic mobility patterns with specific aging properties. Our results also provide theoretic guidelines on how to exploit the memory structure toward better design of protocols under general mobility.
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    Performance Evaluation and Protection Management for Wireless Networks
    (2009-08-07) Agarwal, Avesh Kumar; Arne Nilsson, Committee Member; Carla D Savage, Committee Member; Wenye Wang, Committee Chair; David Thuente, Committee Member; Mihail Sichitiu, Committee Member
    Wireless networks are more vulnerable to attacks compared with wired networks due to their open and shared medium. A number of security mechanisms are available for providing different levels of protection, but with a side effect that is performance degradation. Given a wide range of real-time and non real-time applications, there is a critical demand for providing better performance in wireless networks. Motivated by this demand and the limitations of current research, we devote this dissertation to performance evaluation, and protection management in wireless networks. In this dissertation, we first study the performance impact of security mechanisms at different networking layers in wireless LANs, on a testbed with IP mobility support. One of the important observations is that statically configured security mechanisms may not be used to achieve a satisfactory performance. Motivated by the results of our first study, we propose a Self-TunEd Performance and Protection (STEP2) management framework, which is a generalized architecture for balancing the protection strength and performance for wireless clients based on network and user requirements. By implementing STEP2 in a wireless LAN testbed, we demonstrate the benefits of STEP2 such as significant reduction in delay and packet losses in various scenarios. With the growing deployment of multi-hop networks, we next extend our research to wireless mesh networks. Specifically, we investigate the performance impact of attacks in wireless mesh networks (WMNs). We study path-based denial of service (DoS) attacks as they are easy to carry out and can cause significant performance degradation. The measurements obtained in a wireless mesh testbed demonstrate the interaction between a set of factors, such as link qualities, physical diversity, packet size and rate, and the intensity of path-based DoS attacks. We believe that the comprehensive results in this dissertation will shed new lights on the performance analysis of secure wireless networks.
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    Practical Fair Queuing Schedulers: Simplification through Quantization
    (2009-06-30) Dwekat, Zyad; Mladen Vouk, Committee Chair; George Rouskas, Committee Co-Chair; Mihail Sichitiu, Committee Member; Michael Devetsikiotis, Committee Member
    Many packet scheduling schemes have been proposed, but most of them suffer from one of two extremes. A scheduling scheme may have simple implementation with low fairness qualities, or it may have good fairness qualities but high complexity. Our goal in this research is to design a frame work of schedulers that has both the desired qualities of fairness and simple implementation. We began our research by conducting a survey of the scheduling techniques and associated analysis models proposed during the last decade. Then, in the first part of this thesis we present a suite of packet fair queuing schedulers with low complexity and good fairness and delay properties. Our designs employ the concept of quantization by exploiting two widely-observed characteristics of the Internet, namely that service providers offer some type of tiered service with a small number of service levels, and that a small number of packet sizes dominate. Taken together, these two observations permit us to design a good fair queuing algorithm in a manner that packet sorting operations only need to consider a small, fixed number of packets, independent of the number of flows, and hence can be performed in constant time. Specifically, the scheduler we present is equivalent to WF2Q, with the additional advantage that the virtual time function can be computed in O(1) time. Our tiered-service schedulers operate under assumptions that are valid under a wide range of practical scenarios, and combine provable good performance with amenability to hardware implementation in high-speed routers. In the second part of this thesis, we use quantization of virtual time to design a novel packet scheduler called Worst-Case Bin Sort Queuing (WBSQ). WBSQ has constant complexity, and can be utilized in a simple hardware implementation. The WBSQ scheduler uses two methods of quantization. First, WBSQ exploits quantization of virtual time in a manner similar to the bin sorting idea in BSFQ [1] scheduler. In addition, WBSQ simplifies the system virtual time implementation of WF2Q+ [2]. Worst-Case Bin Sort Queuing has good worst-case fairness and delay properties that are demonstrated through both analytical results and simulations.
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    Providing Bandwidth on Demand Services using Optical Network Design and the SILO Network Architecture.
    (2010-06-25) Iyer, Mohan; Rudra Dutta, Committee Chair; Georgios Rouskas, Committee Chair; Mihail Sichitiu, Committee Member; David Thuente, Committee Member