Seung-Jae Han

The paper presents an integrated software fault injection environment (DOCTOR) which is capable of (1) generating synthetic workloads under which system dependability is evaluated, (2) injecting various types of faults with different options, and (3) collecting performance and dependability data. A comprehensive graphical user interface is also provided. The software implemented fault-injection tools supports three types of faults: memory faults, CPU faults, and communication faults. Each inject

Since real-time applications usually require not only timeliness but also fault-tolerance, it is essential to incorporate fault-tolerance into real-time communication services that are indispensable to distributed real-time applications. The techniques for failure recovery in datagram communication are not adequate for real-time communication, because they cannot provide recovery-delay guarantees. To ensure fast recovery of a real-time channel from network component failures, we need to reserve

Many applications require communication services with guaranteed timeliness and fault tolerance at an acceptable level of overhead. We present a scheme for restoring real-time channels, each with guaranteed timeliness, from component failures in multihop networks. To ensure fast/guaranteed recovery, backup channels are set up a priori, in addition to each primary channel. That is, a dependable real-time connection consists of a primary channel and one or more backup channels. If a primary channe

For many applications it is important to provide communication services with guaranteed timeliness and fault-tolerance at an acceptable level of overhead. In this paper, we present a scheme for restoring real-time channels, each with guaranteed timeliness, from component failures in multi-hop networks. To ensure fast/guaranteed recovery, backup channels are set up a priori in addition to each primary channel. That is, a dependable real-time connection consists of a primary channel and one or mor

Positioning based on long-term evolution (LTE) signals has been introduced as an alternative positioning method when Global Positioning System (GPS) is unavailable. One option for positioning based on LTE signals is to utilize received signal strength (RSS) measurements. There is a relationship between the distance from user equipment (UE) to an LTE base station (BS) and the measured LTE RSS. In this paper, we analyzed the aforementioned relationship and developed an application that can measure

For many applications it is important to provide communication services with guaranteed timeliness and fault-tolerance at an acceptable level of overhead. In this paper, we present a scheme for restoring real-time channels, each with guaranteed timeliness, from component failures in multi-hop networks. To ensure fast/guaranteed recovery, backup channels are set up a priori in addition to each primary channel . That is, a dependable real-time connection consists of a primary channel and one or mo

Physical layer capture is one of the basic causes of throughput unfairness in IEEE 802.11 Wireless LANs. While papers have analyzed the impact of capture on the overall throughput of a single 802.11 cell, we are unaware of any analysis of the relative unfairness among users as result of capture. Since this unfairness is related to the relative location of users, we call this as spatial unfairness. We provide, to the best of our knowledge, the first such analysis that characterizes the relative t

An effective failure-detection scheme is essential for reliable communication services. Most computer network rely on behavior-based detection schemes: each node uses heartbeats to detect the failure of its neighbor nodes, and the transport protocol (like TCP) achieves reliable communication by acknowledgment/retransmission. In this paper, we experimentally evaluate the effectiveness of such behavior-based detection schemes in real-time communication. Specifically, we measure and analyze the cov

Effective detection of failures is essential for reliable communication services. Traditionally, non-real-time computer networks have relied on behavior-based techniques for detecting communication failures. That is, each node uses heartbeats to detect the failure of its neighbors and the end-to-end transport protocol (e.g., TCP) achieves reliable communication by acknowledgment/retransmission. Recently, there has been a growing demand for reliable "real-time" communication, but little research