Browsing by Author "Dr. Arne Nilsson, Committee Chair"

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    Design of a Transport Layer Protocol for 4G Wireless Systems, Mobility
    (2004-06-18) Yadav, Meeta; Dr. Arne Nilsson, Committee Chair
    Mobility computing is the network-access paradigm of the future. Future network protocols will be 4G defined over an entirely packet-switched network with digital network elements, high bandwidth and built-in network security. The bandwidth provided will be 100Mbps for stationary objects and 20 Mbps while in motion. 4G wireless networks will support global roaming and service portability across multiple wireless and mobile networks, for example from a cellular network to a satellite-based network to a high-bandwidth wireless LAN. TCP Performance degrades severely on a wireless link due to higher Bit Error Rate, Mobility, Limited Capacity, Non Uniform Error Profile and frequent Disconnections. We propose a new transport layer protocol for 4G Wireless Systems, compatible with the existing TCP/ IP implementations that combines the best of the currently proposed algorithms and our own new congestion control algorithm. We designed an optimized congestion control algorithm for the wireless link that provides connection oriented, reliable data service with graceful handovers and ability to recover from frequent disconnections. The protocol deals with high bit error rate by implementing split connections with local fast retransmissions. It uses Zero Window Advertisement to accomplish smooth handover under inter-wireless cell mobility. Several other methods have been proposed to overcome TCP-over-wireless faults including split-TCP connection, triple-acknowledgements and acknowledgment caching. Each of these methods improves the efficiency of TCP by improving a single fault aspect, while our proposal combines compatible improvements into an efficient and reliable protocol.
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    Measurement Based Connection Admission Control
    (2003-09-23) Jaising, Rahul; Dr. Arne Nilsson, Committee Chair; Dr. Mihail Sichitiu, Committee Member; Dr. Mladen Vouk, Committee Member; Dr. Zsolt Haraszti, Committee Member
    We consider the problem of using the real-time measurements of the network elements for connection admission control on QoS aware networks. Our objective is to study the measurement process and determine the real-time utilization of a link, and use these measurements to determine the admission of new flows into the network, while providing statistical guarantees on the QoS ensured for the existing admitted flows. First we survey the vast amount of existing literature in the field and identify the components of a measurement-based admission control system, and the various factors which affects the performance of an algorithm. We use the ns-2 simulator to simulate some of the proposed (though not all) algorithms and test the performance of these algorithms for various arrival processes at the connection level. We use the results from these simulations to verify the performance claims of the various algorithms, and use the performance tuning parameters to find optimal performance regions. We study the buffer dynamics at the burst level and analyze the loss caused by admitting excessive flows. Our work extends from the existing literature in studying the effect of different arrival processes on the blocking probabilities of new flows and surveying an ad-hoc mix-and-match approach of the estimation technique and decision process to explore a higher performance benchmark.
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    A Network Simulator model of the DOCSIS protocol and a solution to the bandwidth-hog problem in Cable Networks.
    (2003-11-16) Shrivastav, Nitin; Dr. Jim Martin, Committee Member; Dr. Arne Nilsson, Committee Chair; Dr. Andy Rindos, Committee Member; Dr. David Thuente, Committee Co-Chair
    A number of broadband access solutions have been developed in the recent years to provide high speed Internet access to the residential users or the ?last-mile?. Some of the prominent technologies include Cable access, Digital Subscriber Loop, Integrated Services Digital Network, Satellite and Wireless. The cable broadband access is gaining widespread popularity. While several approaches to broadband access over cable have been proposed (e.g., DVB/DAVIC and IEEE 802.14), the industry is converging on the architecture developed by the Multimedia Cable Network System (MCNS) group (referred to as the Data-Over-Cable Service Interface Specification or DOCSIS standard). The DOCSIS Radio Frequency Interface specification defines the Media Access Control (MAC) layer as well as the physical communications layer. The objectives of this thesis were: Design, Implementation and Study of a Network Simulator-2 (NS-2) [1] model of the DOCSIS 2.0 MAC protocol and Design and analysis of an algorithm to solve the bandwidth-hog problem in Cable Networks. It was realized that there is a need for the support of DOCSIS protocol in a publicly available popular simulator to do research on DOCSIS. Network Simulator was chosen as it is widely used by the Internet research community for research of networking protocols and it currently lacks the support for DOCSIS. The Network Simulator implementation is conformant to the DOCSIS RF-interface specifications with support for Quality of Service features. The second part of this thesis presents a solution for congestion control in cable networks. It has been observed in cable networks that few heavy bandwidth users can cause severe congestion affecting the performance of the other users. Typically, the end user applications incorporate end-to-end congestion control for best-effort traffic (e.g. TCP congestion control). However, with the growth of the Internet, it might no longer be practical to rely on all end-nodes to use end-to-end congestion control. There is a need for the participation of the network itself in controlling the resource utilization. A solution is proposed where the central entity (known as Cable Modem Termination System) in the cable network identifies and restricts the bandwidth of selected best-effort flows in times of congestion. The flows using disproportionate bandwidth during times of congestion are restricted. As outlined in [2], this approach promotes the use of end-to-end congestion control by the end-nodes as it provides an incentive to flows responsive to congestion by not restricting them.