• Journal of the Korea Institute of Information and Communication Engineering
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• v.12 no.12
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• pp.2179-2187
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• 2008

The P2P technology has been widely used to distribute files efficiently, and its use in streaming is rapidly increasing. P2P streaming has issues about startup-delay, scalability, and real-time playback, however, what affects these factors has not been researched sufficiently. This paper suggests a buffering model for progressive download within mesh-based P2P system, which corresponds to downloading and playing the content at the same time. It is used to analyze PDF(Playback Deadline First), Rarest algorithms which are block-selection strategies of P2P streaming and proposes a mixed selection of them. The mixed block selection strategy dynamically performs different strategies based on whether the blocks to be played are received or not. In consequence, it enhances the QoS of streaming in a single peer point of view, as well as improving block distributions in an overlay network.

• The KIPS Transactions:PartA
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• v.8A no.4
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• pp.319-330
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• 2001

In virtual memory system, when a process attempts to access a page that is not resident in memory, the system generates and handles a page fault that causes unpredictable delay. So virtual memory system is not appropriate for the real-time system, because it can increase the deadline miss ratio of real-time task. In multimedia system, virtual memory system may degrade the QoS(quality of service) of multimedia application. Furthermore, in general-purpose operating system, whenever a new task is dynamically loaded, virtual memory system suffers from extensive page fault that cause transient overloading state. In this paper, we present efficient overloading control mechanism called RBPFH (Rate-Based Page Fault Handling). A significant feature of the RBPFH algorithm is page fault dispersion that keeps page fault ratio from exceeding available bound by monitoring current system resources. Furthermore, whenever the amount of available system resource is changed, the RBPFH algorithm dynamically adjusts the page fault handling rate. The RBPFH algorithm is implemented in the Linux operating system and its performance measured. The results demonstrate RBPFH\`s superior performance in supporting multimedia applications. Experiment result shows that RBPFH could achieve 10%∼20% reduction in deadline miss ratio and 50%∼60% reduction in average delay.

• The Transactions of the Korea Information Processing Society
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• v.7 no.6
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• pp.1753-1765
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• 2000

As the areas of computer application are expanded, real-time application environments that must process as many transactions as possible within their deadlines, such as a stock transaction systems, ATM switching systems etc, have been increased recently. The reason why the conventional database systems can't process soft real-time applications is the lack of prediction and poor performance on processing transaction's deadline. If transactions want to access data stored at the secondary storage, they can not satisfy requirements of real-time applications because of the disk delay time. This paper designs a main-memory database prototype systems to be suitable to real-time applications and then this system can produce rapid results without disk i/o as all of the information are loaded in main memory database. In thesis proposed the improved techniques with respect to logging, checkpointing, and recovering in our environment. In order to improve the performance of the system, a) the frequency of log analysis and redo processing is reduced by the proposed redo technique at system failure, b) database consistency is maintained by improved fuzzy checkpointing. The performance model is proposed which consists of two parts. The first part evaluates log processing time for recovery and compares with other research activities. The second part examines checkpointing behavior.

• Journal of Computing Science and Engineering
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• v.4 no.3
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• pp.189-206
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• 2010

It is generally accepted that dynamic voltage scaling (DVS) is one of the most effective techniques of energy minimization for real-time applications in embedded system design. The effectiveness comes from the fact that the amount of energy consumption is quadractically proportional to the voltage applied to the processor. The penalty is the execution delay, which is linearly and inversely proportional to the voltage. According to the granularity of tasks to which voltage scaling is applied, the DVS problem is divided into two subproblems: inter-task DVS problem, in which the determination of the voltage is carried out on a task-by-task basis and the voltage assigned to the task is unchanged during the whole execution of the task, and intra-task DVS problem, in which the operating voltage of a task is dynamically adjusted according to the execution behavior to reflect the changes of the required number of cycles to finish the task before the deadline. Frequent voltage transitions may cause an adverse effect on energy minimization due to the increase of the overhead of transition time and energy. In addition, DVS needs to be carefully applied so that the dynamically varying chip temperature should not exceed a certain threshold because a drastic increase of chip temperature is highly likely to cause system function failure. This paper reviews representative works on the theoretical solutions to DVS problems regarding inter-task DVS, intra-task DVS, voltage transition, and thermal-aware DVS.

• Journal of the Korean Operations Research and Management Science Society
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• v.28 no.2
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• pp.75-89
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• 2003

Media Access Control (MAC) Protocol in IEEE 802.11 Wireless LAN standard supports two types of services, synchronous and asynchronous. Synchronous real-time traffic is served by Point Coordination Function (PCF) that implements polling access method. Asynchronous nonreal-time traffic is provided by Distributed Coordination Function (DCF) based on Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) protocol. Since real-time traffic is sensitive to delay, and nonreal-time traffic to error and throughput, proper traffic scheduling algorithm needs to be designed. But it is known that the standard IEEE 802.11 scheme is insufficient to serve real-time traffic. In this paper, real-time traffic scheduling and admission control algorithm is proposed. To satisfy the deadline violation probability of the real time traffic the downlink traffic is scheduled before the uplink by Earliest Due Date (EDD) rule. Admission of real-time connection is controlled to satisfy the minimum throughput of nonreal-time traffic which is estimated by exponential smoothing. Simulation is performed to have proper system capacity that satisfies the Quality of Service (QoS) requirement. Tradeoff between real-time and nonreal-time stations is demonstrated. The admission control and the EDD with downlink-first scheduling are illustrated to be effective for the real-time traffic in the wireless LAN.

• International Journal of Computer Science & Network Security
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• v.22 no.3
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• pp.163-172
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• 2022

The interconnection of an enormous number of devices into the Internet at a massive scale is a consequence of the Internet of Things (IoT). As a result, tasks offloading from these IoT devices to remote cloud data centers become expensive and inefficient as their number and amount of its emitted data increase exponentially. It is also a challenge to optimize IoT device energy consumption while meeting its application time deadline and data delivery constraints. Consequently, Fog Computing was proposed to support efficient IoT tasks processing as it has a feature of lower service delay, being adjacent to IoT nodes. However, cloud task offloading is still performed frequently as Fog computing has less resources compared to remote cloud. Thus, optimized schemes are required to correctly characterize and distribute IoT devices tasks offloading in a hybrid IoT, Fog, and cloud paradigm. In this paper, we present a detailed survey and classification of of recently published research articles that address the energy efficiency of task offloading schemes in IoT-Fog-Cloud paradigm. Moreover, we also developed a taxonomy for the classification of these schemes and provided a comparative study of different schemes: by identifying achieved advantage and disadvantage of each scheme, as well its related drawbacks and limitations. Moreover, we also state open research issues in the development of energy efficient, scalable, optimized task offloading schemes for Fog computing.

• Journal of KIISE
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• v.44 no.2
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• pp.115-123
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• 2017

A message processor is server software that receives non-realtime messages as well as realtime messages from clients that need to be processed within a deadline. With the recent advances of micro-processor technologies and Linux, the message processor is often implemented in Linux-based multi-core servers and it is important to use cores efficiently to maximize the performance of system in multi-core environments. Numerous research efforts on a real-time scheduler for the efficient utilization of the multi-core environments have been conducted. Typically, though, they have been conducted theoretically or via simulation, making a subsequent real-system application difficult. Moreover, many Linux-based real-time schedulers can only be used in a specific Linux version, or the Linux source code needs to be modified. This paper presents the design of a Linux-based message processor for multi-core environments that maps the threads to the cores at user level. The message processor is implemented through a modification of the traditional RM algorithm that consolidates the real-time messages into certain cores using a first-fit-based bin-packing algorithm; this minimizes the response-time delay of the non-real-time messages, while guaranteeing the violation rate of the real-time messages. To compare the performances, the message processor was implemented using the two multi-core-scheduling algorithms GSN-EDF and P-FP, which are provided by the LITMUS framework. The benchmarking results show that the response-time delay of non-real-time messages in the proposed system was improved up to a maximum of 17% to 18%.

• Journal of Institute of Control, Robotics and Systems
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• v.16 no.4
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• pp.403-410
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• 2010

The switched Ethernet has many features for real-time communications such as providing traffic isolation, large bandwidth, and full-duplex links, and so on. The switched Ethernet, however, cannot guarantee the timely delivery of a real-time message because message delay increases when collisions occurs at the output ports and message loss can even occur due to the overflow at the output buffer. Recently, many research efforts have been done to use the switched Ethernet as an industrial control network. In the industrial control network, sensors periodically sense the physical environment and transmit the sensed data to an actuator, and the periodic messages from sensors to actuators have typically real-time requirements such that those messages must be transmitted within their deadlines. This paper first suggests a feasible condition for EDF (Earliest Deadline First)-based scheduling of periodic messages on a synchronized switched Ethernet and a message scheduling algorithm which satisfies the proposed feasible condition. Pedreiras, et al. [10] suggested a feasible condition for message scheduling on the Ethernet (shared media Ethernet), but there has been no research result on the scheduling condition on the switched Ethernet until now. We compared the real-time message scheduling capacity between the Ethernet and the switched Ethernet by simulation. The simulation result shows that the message scheduling capacity of the Ethernet has almost remained constant as the number of nodes on the network increases, but, in the case of the switched Ethernet, the message scheduling capacity has increased linearly according to the number of nodes on the network.

• The KIPS Transactions:PartA
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• v.13A no.5 s.102
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• pp.405-412
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• 2006

Real-time operating systems have been used in various computing environments, where a job must be completed in its deadline, with various conditions, such as effective scheduling policies, the minimum of an interrupt delay, and the solutions of priority inversion problems, that should be perfectly satisfied to design and develop optimal real-time operating systems. Up to now, in order to solve priority inversion problems among several those conditions. There have been two representative protocols: basic priority inheritance protocol and priority ceiling emulation protocol. However, these protocols cannot solve complicated priority inversion problems. In this paper, we design a protocol, called recursive priority inheritance (RPI), protocol that effectively solves the complicated priority inversion problems. Our proposed protocol is also implemented in the Linux kernel and is compared with other existing protocols in the aspect of qualitative analysis.

• The KIPS Transactions:PartA
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• v.9A no.1
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• pp.9-18
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• 2002

In this paper, we propose scalable scheduling techniques based on EDF to efficiently integrate hard real-time and multimedia soft real-time tasks in the distributed real-time multimedia database system. Hard tasks are guarangteed based on worst case execution times, whereas multimedia soft tasks are served based on mean execution times. This paper describes a served-based scheme for partitioning the CPU bandwidth among different task classes that coexist in the same system. To handle the problem of class overloads characterized by varying number of tasks and varying task arrival rates, thus scheme shows how to adjust the fraction of the CPU bandwidth assigned to each class. This scheme fixes the maximum time that each hard task can execute in the period of the server, whereas it can dynamically change the bandwidth reserved to each multimedia task. The proposed method is capable of minimizing the mean tardiness of multimedia tasks, without jeopardizing the schedulability of the hard tasks. The performance of this scheduling method is compared with that of similar mechanisms through simulation experiments.