Junguk L. Kim

An efficient protocol for checkpointing recovery in distributed systems

The authors present an efficient synchronized checkpointing protocol that exploits the dependency relation between processes in distributed systems. In this protocol, a process takes a checkpoint when it knows that all processes on which it computationally depends took their checkpoints, hence the process need not always wait for the decision made by the checkpointing coordinator as in the conventional synchronized protocols. As a result, the checkpointing coordination time is substantially reduced and the possibility of total abort of the checkpointing coordination is reduced. >

Performance analysis of distributed deadlock detection algorithms

The paper presents a probabilistic performance analysis of a deadlock detection algorithm in distributed systems. Although there has been extensive study on deadlock detection algorithms in distributed systems, little attention has been paid to the study of the performance of these algorithms. Most work on performance study has been achieved through simulation but not through an analytic model. Min (1990), to the best of our knowledge, made the sole attempt to evaluate the performance of distributed deadlock detection algorithms analytically. Being different from Mins, our analytic approach takes the time-dependent behavior of each process into consideration rather than simply taking the mean-value estimation. Furthermore, the relation among the times when deadlocked processes become blocked is studied, which enhances the accuracy of the analysis. We measure performance metrics such as duration of deadlock, the number of algorithm invocations, and the mean waiting time of a blocked process. It is shown that the analytic estimates are nearly consistent with simulation results.This paper presents a probabilistic performance analysis of a deadlock detection algorithm in distributed systems. Although there has been extensive study on deadlock detection algorithms in distri...

The areawide real-time traffic control (ARTC) system: a new traffic control concept

A traffic control system, called areawide real-time traffic control (ARTC), that addresses frequent occurrences of congestion and provides areawide traffic progression is presented. The signal controllers in ARTC are interconnected through a computer network. By exchanging traffic flow information among the signal controllers, ARTC provides a new concept in areawide traffic control. With a global view of the traffic in the area, ARTC anticipates congestion. Simulation results of the ARTC prototype control algorithm over a linear road topology are also presented, and the results show significant improvement over an optimized fixed time control. The signal controllers and the computer network are designed to support the real-time communication requirements and a sufficient level of fault tolerance. >

An efficient distributed deadlock detection algorithm

We propose a distributed deadlock detection algorithm which detects cycles made of back edges in a distributed search tree. Our algorithm detects the deadlocks in which the initiator of the algorithm is directly or indirectly involved, while most of the proposed deadlock detection algorithms only detect the cycles in which the initiator is directly involved. Our algorithm is a reduced version of the one proposed previously, which resolves all deadlocks reachable from the initiator in a single execution by propagating the probe messages to the nodes in the search tree and having each node resolve deadlocks in its subtree with collected information on dependency between its subtree nodes. Our algorithm substantially reduces the message overhead of the previous algorithm. We compare the performance of our algorithm with others through extensive simulation. It is found that our algorithm detects deadlocks as fast as the previous algorithm with much fewer messages. The simulation results show that our algorithm outperforms other algorithms considerably in major performance measures.

A Distributed Election Protocol for Unreliable Networks

This paper presents a broadcast-based election protocol for distributed systems implemented on unreliable networks. The protocol is highly robust, tolerating failures such as message loss and network partitioning. Our protocol is different from others in that it effectively detects events that may possibly make the election results inconsistent, aborts the election, and causes the nodes to execute another election round. When the election completes, there is guaranteed to be agreement on a single leader. When the network is partitioned, groups with a consistent view and a single leader are formed in each partition. Compared to other broadcast-based election protocols, which use a group-merging mechanism to fix the problem of several groups independently electing different leaders, the number of election rounds needed to arrive at a single leader is on average considerably fewer.

An All-sharing Load-balancing Scheme on the CSMA/CD Network and Its Analysis

This paper analyzes a load-balancing scheme, called All-Sharing Load Balancing (ASLB), which evenly distributes the load of the system among all nodes on a CSMA/CD local area network in a collision-free manner for each load-balancing activity. A nobel analytical model is presented to evaluate performance of the ASLB scheme and its effect on the normal communication message transmissions and vice versa. The evaluation also takes into a account the tradeoff between system response time and message delay. Our analysis shows that ASLB can achieve good performance in both system response time and message transmission delay. Our analysis techniques are applicable to various distributed algorithms involved with interprocess coordination

The advanced distributed ramp metering system (ARMS)

Ramp metering is an important technique to effectively utilize the freeway capacity by regulating the traffic flow of freeway entrance ramps. In this extended abstract, we discuss the outline of the free flow control algorithm of the Advanced distributed Ramp Metering System, ARMS, for the real-time control of freeway ramp metering systems. ARMS consists of three levels of control algorithms integrated together for free flow control, breakdown prediction, and congestion resolution. Based on a free flow traffic model, the free flow control algorithm takes into account of the congestion risk when it tries to maximize the traffic throughput. The breakdown prediction algorithm can make prediction on the possibility of imminent congestion caused by flow breakdown, and the congestion resolution algorithm is to resolve the congestion if it actually occurs. The ARMS has a modular architecture so that it can be scaled for incremental implementation. To control freeway traffic, a system wide optimization objective is first defined for a target area. Then, ramp metering decisions are made by the entrance ramp controllers within the target area after their traffic data are exchanged.<<ETX>>

An all-sharing load balancing protocol in distributed systems on the CSMA/CD local area network

A protocol for dynamic load balancing in distributed systems on the CSMA/CD local area network is presented. Using the protocol, the workload is evenly distributed throughout the system when load-balancing activity is triggered, and effective load distribution is accomplished through transmission of load-balancing messages in a collision-free manner. Analytical and simulation results are presented to show the efficiency of the protocol.<<ETX>>

Integration of a relational database with multimedia data

We propose a method for integrating a preexisting conventional database system with a multimedia server in a multidatabase environment. In the multidatabase environment, changes to the preexisting database system are not allowed because such changes are too expensive. For the integration, high-level semantic description of multimedia data is modeled using the enhanced entity-relationship (EER) model to support content-based retrieval of multimedia data. The EER design is translated into a schema of the preexisting database system and then the translated schema is integrated with the preexisting database schema. The content description can be used to locate pertinent multimedia data, and the identifiers are used to access the multimedia data stored in the multimedia server. However, with only a simple schema representation of the semantic description of multimedia data, high levels of recall and precision of queries may not be obtained because conventional database systems provide only exact matching answers to the query. Thus, we extended the conventional query processing mechanism by providing a modified cooperative query answering mechanism.

Management of flexible transactions using semantics in multidatabase systems

We propose a multidatabase transaction management scheme using the flexible transaction model. In our approach, global subtransactions can be committed unilaterally at local sites before the global commit. Since such executions may not guarantee the traditional atomicity requirement of global transactions, a new correctness criterion is proposed. We also present a semantics-based concurrency control scheme and a commit protocol which ensure the proposed correctness criterion without requiring local DBMSs to provide prepare-to-commit operations.