Stephen Gordon Batsell

Algorithm for minimum end-to-end delay paths

We consider the transmission of a message of size r from a source to a destination with the minimum end-to-end delay over a computer network where bandwidth can be reserved and guaranteed on the links. Different paths will be required for different intervals of values for r. We propose a polynomial-time algorithm that computes a table that maps all intervals for r to the corresponding paths that minimize the end-to-end delay.

Reservation CSMA/CA for multimedia traffic over mobile ad-hoc networks

This paper describes the design and performance of a medium access control protocol (called reservation CSMA/CA) for multimedia traffic over mobile ad-hoc networks. The reservation CSMA/CA protocol is based on a hierarchical approach consisting of two sublayers. The lower sublayer of the MAC protocol provides a fundamental access method using CSMA/CA to support asynchronous data traffic over mobile ad-hoc networks. The upper sublayer is designed to support real-time periodic traffic by making a slot reservation with the three-way handshake prior to actual data transmission. The proposed protocol has been validated using a software emulator which was carried out with the UNIX implementation. The simulation results show that the reservation CSMA/CA offers higher throughput for real-time periodic traffic compared to the IEEE 802.11 standard, while providing deterministic delay performance.

Protocol for dynamic ad-hoc networks using distributed spanning trees

A dynamic ad-hoc network consists of a collection of mobile hosts with frequently changing network topology. We propose a distributed algorithm that adapts to the topology by utilizing spanning trees in the regions where the topology is stable, and resorting to an intelligent flooding-like approach in highly dynamic regions of the network. Routing is performed using the spanning trees based a hold-and-forward or shuttling mechanisms. We introduce the notion of connectivity-through-time and the parameter holding-time as new fundamental concepts that can be used by ad-hoc routing algorithms. For various network connectivity scenarios we evaluate the impact of these concepts on the performance of ad-hoc routing algorithms. Using simulation, we study the throughput, reachability and message–reachability ratio of the proposed schemes under various connection/disconnection rates and holding times.

Position Statement: Methodology to Support Dependable Survivable Cyber-Secure Infrastructures

Information systems now form the backbone of nearly every government and private system. Increasingly these systems are networked together allowing for distributed operations, sharing of databases, and redundant capability. Ensuring these networks are secure, robust, and reliable is critical for the strategic and economic well being of the Nation. This paper argues in favor of a biologically inspired approach to creating survivable cyber-secure infrastructures (SCI). Our discussion employs the power transmission grid.

On update algorithms for quickest paths

The quickest path problem deals with the transmission of a message of size @s from a source to a destination with the minimum end-to-end delay over a network with bandwidth and delay constraints on the links. The path-table that maps all intervals for @s to the corresponding quickest paths can be computed in O(m^2+mnlogn) time, where n and m are the number of nodes and links of the network, respectively. We propose linear-time algorithms that update the path-table after a increase or decrease bandwidth of a link or a path, respectively.

On routing algorithms with end-to-end delay guarantees

We consider the transmission of a message of size r from a source to a destination over a computer network with n nodes and m links. There are three sources of delays: (a) propagation delays along the links, (b) delays due to bandwidth availability on the links, and (c) queuing delays at the intermediate nodes. First, we consider that the delays on various links and nodes are given as functions of the message size. If the delay in (b) is a non-increasing function of the bandwidth, we propose O(m/sup 2/+mn log n) time algorithm to compute a path with the minimum end-to-end delay for any given message size r. We then consider that the queuing delay in (c) is a random variable correlated with the message size according to an unknown distribution. At each node, the measurements of queuing delays and message sizes are available. We propose two algorithms to compute paths whose delays are close to optimal delays with a high probability, irrespective of the distribution of the delays.

Fusing intrusion data for detection and containment

Fusing information from diverse detectors remains a challenge in the field of intrusion detection. We apply data fusion techniques to fuse alerts generated by different detectors that signal the potential presence of an intrusion. Data fusion has been shown to result in a decrease in false positives while achieving an improved level of detection. By combining detections from fusers on distributed hosts, a system can also detect and track the spread of an intrusion. We proceed to analyze the response time requirements of such a distributed containment system by including an explicit containment parameter in the spreading formulation.

Feasibility of telemammography as biomedical application for breast imaging

Mammographic screening is an important tool in the early detection of breast cancer. The migration of mammography from the current mode of x-ray mammography using a film screen image detector and display to a digital technology provides an opportunity to improve access and performance of breast cancer screening. The sheer size and volume of the typical screening exam, the need to have previous screening data readily available, and the need to view other breast imaging data together to provide a common consensus and to plan treatment, make telemammography an ideal application for breast imaging. For telemammography to be a viable option, it must overcome the technical challenges related to transmission, archiving, management, processing and retrieval of large data sets. Researchers from the University of Pennsylvania, the University of Chicago and Lockheed Martin Energy Systems/Oak Ridge National Laboratory have developed a framework for transmission of large-scale medical images over high-speed networks, leveraged existing high-speed networks between research and medical facilities; tested the feasibility of point-to-point transmission of mammographic images in a near-real time environment; evaluated network performance and transmission scenarios; and investigated the impact of image preprocessing on an experimental computer-aided diagnosis system. Results of the initial study are reported here.