Jaehong Shim

Priority inversion handling in microkernel-based Real-Time Mike

We propose a resource management model to avoid priority inversion problem that may occur when two tasks attempt to send service requests to a server task, and then the server task sends a request to another server task in a nested fashion. In this model we introduce two new concepts: job identifier inheritance and priority ceiling inheritance. We also suggest a new resource locking condition of the priority ceiling protocol for the computational model of the microkernel-based real-time system, called Mike, in which both IPC and synchronization are utilized and client/server communication model is frequently used in a nested fashion. To see the effectiveness, the proposed model has been implemented in Real-Time Mike developed previously. The implemented system shows that the resource management model efficiently prevents the priority inversion problem and avoids deadlock and multiple blocking.

Design issues on a popularity-independent video-on-demand server

In this paper, the design issues on a scaleable popularity independent video on demand (VOD) server which has been designed and implemented at Ajou University are discussed. The server with parallel architecture aims to resolve a basic performance bottleneck, which has been encountered in the design steps of many other VOD servers. The performance degradation caused by the skew in video popularity becomes minimized through the realization of server-level striping. The server-level striping increases the scalability of server: the increase in performance follows closely the increase in the number of video pumps. The communication and processing power overhead introduced by the parallel server architecture is relieved by a specially designed meshed pipeline type interconnection network. The design issues on the interconnection network and data placement policy are also addressed with empirical data. In the last part of this paper, the real-time operating system and the schedulers for the video pump are described.

A Jitter Management Policy for Monitoring System Using JPEG

We propose a jitter management policy. called S-policy, and a simple negotiation strategy for monitoring system and general multimedia applications. The proposed policy is empirically proved by a monitoring system iniplernented on the LAN network environment. The system utilizes a JPEG codec for generating and restoring variable size data. The performance is also compared with the approaches shown in the literatures.

A real-time reconfigurable entrance control system

A real-time reconfigurable entrance control system is presented in this paper. The system is designed and implemented with considering compatibility with the existing systems, reliability, expandability, and maintenance. The presented system consists of a host which manages a central database, terminals which control entrances, and terminal controllers which connect the host with terminals. To utilize the existing popular network, Ethernet is used for the network between the host and terminal controllers, while LONNET is used to connect terminal controllers and terminals. The software in each terminal controller and terminal is divided into two parts. The kernel part which is unchangeable for the normal cases is responsible for low level communication and house keeping. The application part controls peripherals. It can be replaced with a new one with aid of the kernel during initialization process or even on-line operation. With this approach, an application program can be modified without stopping the system. Another advantage is that installation and maintenance become very easy, saving the related cost.

A Heuristic Session Distribution Algorithm for Switch with Multiple Output Links

We propose a heuristic session allocation algorithm for switch with multiple output links, named SCDF (Shortest Class Delay First) algorithm. The proposed SCDF algorithm allocates a new session to an output link with the smallest estimated average packet delay among those of sessions that belong to the same class. The empirical study proves that SCDF shows the best performance comparing those of other competitive algorithms, in terms of balancing packet delay difference and maximizing throughput.

Measurement of Short-term Temporal Locality Based on Request Interarrival Time

Temporal locality of Web server references is one of the important characteristics to be considered in the design of a Web caching strategy, and it is important to measure the temporal locality exactly. Various methods to estimate the temporal locality have been proposed, however, Web server designers have still troubles in its measurement by using the tools that don`t reflect the interarrival time of document requests. In this paper, we propose a measurement tool for short-term temporal locality based on request interarrival time, and discuss the simulation results based on the flares from NLANR and NASA Web sites. The results show that the proposed tool estimates the short-term temporal locality more exactly than that based on a stack.

A Session Allocation Algorithm for Fair Bandwidth Distribution of Multiple Shared Links

In this paper, a session allocation algorithm for a switch with multiple shared links is proposed. The algorithm guarantees the reserved bandwidth to each service class and keeps the delay of sessions belonging to a service class as close as possible even if the sessionsare allocated to different shared links. To support these qualities of services, a new scheduling model for multiple shared links is defined and a session allocation algorithm to decide a shared link to be allocated to a new session on the connection establishmentis developed based on the model. The proposed heuristic algorithm allocates a session to a link including the subclass with the shortest (expected) delay that subclasses of the service class the session belongs to will experience. Simulation results verify that a switch with multiple shared links hiring the proposed algorithm provides service classes with fairer bandwidth allocation and higher throughput, and guarantees reserved bandwidth better than the switch hiring other session algorithms. It also guarantees very similarservice delay to the sessions in the same service class.

IRIS Task Scheduling Algorithm Based on Task Selection Policies

We propose a heuristic on-line scheduling algorithm for the IRIS (Increasing Reward with Increasing Service) tasks, which has low computation complexity and produces total reward approximated to that of previous on-line optimal algorithms. The previous on-line optimal algorithms for IRIS tasks perform scheduling on all tasks in a system to maximize total reward. Therefore, the complexities of these algorithms are too high to apply them to practical systems handling many tasks. The proposed algorithm doesn´t perform scheduling on all tasks in a system, but on (constant) W´s tasks selected by a predefined task selection policy. The proposed algorithm is based on task selection policies that define how to select tasks to be scheduled. We suggest two simple and intuitive selection policies and a generalized selection policy that integrates previous two selection policies. By narrowing down scheduling scope to only W´s selected tasks, the computation complexity of proposed algorithm can be reduced to O(Wn). However, simulation results for various cases show that it is closed to O(W) on the average.

A switch scheduling algorithm for periodic messages using laxity decomposition method

This paper presents a very unique and analytic method for scheduling real time messages routed through a non-blocking switch. The laxities of schedulable messages are decomposed and rearranged so that the packets to be scheduled in the next time instance are placed in the diagonal of the traffic matrix. The MLF algorithm we modified is utilized to schedule the messages. We present some examples and simulation results which show that the success rate is improved significantly regardless of the size of switch.