This thesis work researches the theory and application of systems performing omnidirectional, non-direct path optical data communication (ONP systems). Such systems are characterized by 1) the communication involves a local, usually circular area; 2) Obstacles are allowed between a transmitter and the receivers. This is in contrast to the point-to-point and line-of-sight communications performed by almost all existing infrared data communication or transmission systems. The elimination of the point-to-point limitation makes ONP systems suitable for optical local area networking. The feasibility of ONP systems employing infrared LEDs and silicon photo detectors has been analyzed and the performance of such systems predicted. The analysis shows that indoor ONP systems are both feasible and practical. Only a few LEDs are required to cover the entire area of a large room. Efforts have been made in finding rules for optimal design of the ONP systems. A set of design criteria and curves have been established. The theoretical analysis has been verified in a successful experiment done with OptoNet, an ONP infrared datalink for local area networks. This experimental system consists of two identical communication units employing FSK modulation and microprocessor controllers. The experiment has demonstrated that the ONP optical data communications can be realized by relatively simple electronic hardware. / Graduation date: 1991

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We consider the problem of designing enterprise network security systems which are easy to manage, robust and flexible. This problem is challenging. Today, most approaches rely on host security, middleboxes, and complex interactions between many protocols. To solve this problem, we explore how new programmable networking paradigms can facilitate fine-grained network control. We present Resonance, a system for securing enterprise networks , where the network elements themselves en- force dynamic access control policies through state changes based on both flow-level information and real-time alerts. Resonance uses programmable switches to manipulate traffic at lower layers; these switches take actions (e.g., dropping or redirecting traffic) to enforce high-level security policies based on input from both higher-level security boxes and distributed monitoring and inference systems. Using our approach, administrators can create security applications by first identifying a state machine to represent different policy changes and then, translating these states into actual network policies. Earlier approaches in this direction (e.g., Ethane, Sane) have remained low-level requiring policies to be written in languages which are too detailed and are difficult for regular users and administrators to comprehend. As a result, significant effort is needed to package policies, events and network devices into a high-level application. Resonance abstracts out all the details through its state-machine based policy specification framework and presents security functions which are close to the end system and hence, more tractable. To demonstrate how well Resonance can be applied to existing systems, we consider two use cases. First relates to "Network Admission Control" problem. Georgia Tech dormitories currently use a system called START (Scanning Technology for Automated Registration, Repair, and Response Tasks) to authenticate and secure new hosts entering the network [23]. START uses a VLAN-based approach to isolate new hosts from authenticated hosts, along with a series of network device interactions. VLANs are notoriously difficult to use, requiring much hand-holding and manual configuration. Our interactions with the dorm network administrators have revealed that this existing system is not only difficult to manage and scale but also inflexible, allowing only coarse-grained access control. We implemented START by expressing its functions in the Resonance framework. The current system is deployed across three buildings in Georgia Tech with both wired as well as wireless connectivities. We present an evaluation of our system's scalability and performance. We consider dynamic rate limiting as the second use case for Resonance. We show how a network policy that relies on rate limiting and traffic shaping can easily be implemented using only a few state transitions. We plan to expand our deployment to more users and buildings and support more complex policies as an extension to our ongoing work. Main contributions of this thesis include design and implementation of a flexible access control model, evaluation studies of our system's scalability and performance, and a campus-wide testbed setup with a working version of Resonance running. Our preliminary evaluations suggest that Resonance is scalable and can be potentially deployed in production networks. Our work can provide a good platform for more advanced and powerful security techniques for enterprise networks.

Thesis (M.S.)--University of Florida, 2001. / Title from first page of PDF file. Document formatted into pages; contains xiii, 90 p.; also contains graphics. Vita. Includes bibliographical references (p. 85-89).

Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 349-382). Available also in a digital version from Dissertation Abstracts.

Thesis (Ph. D.)--Rutgers University, 2008. / "Graduate Program in Computer Science." Includes bibliographical references (p. 113-121).

Thesis (M.S.)--Worcester Polytechnic Institute. / Keywords: fair active queue management; RED; CSFQ; DRR; round trip time. Includes bibliographical references (p. 53-55).

Thesis (Ph. D.)--University of Texas at Austin, 1998. / Includes bibliographical references (leaves 145-154). Available also in a digital version from Dissertation Abstracts.

Thesis (M.S.)--Worcester Polytechnic Institute. / Keywords: Loss; TFRC; AIMD; TCP. Includes bibliographical references (p. 147-155).

Thesis (M.S.)--University of Wyoming, 2008. / Title from PDF title page (viewed on June 27, 2009). Includes bibliographical references (p. 59-60).