• Journal of Advanced Navigation Technology
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• v.14 no.6
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• pp.865-873
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• 2010

In this paper, a novel schedulability criteria is developed to provide handover calls with Quality of Service (QoS) guarantees in terms of both minimum available bandwidth, maximum tolerated packet delay, and other additive QoS constraints as required by the real-time mobile traffic. This requires prediction of the handover time using mobility trends on the mobile station, which is used as input to this work. After the handover time and the QoS are negotiated, the destination base station makes attempts to give priority to handover calls over new calls, and pre-reserves resources that will have more chance of being available during the actual handover.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.6B
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• pp.533-543
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• 2003

Recently, according to the rapid increase of Web users, various kinds of Web applications have been being developed. Hence, Web QoS(Quality of Service) becomes a critical issue in the Web services, such as e-commerce, Web hosting, etc. Nevertheless, most Web servers currently process various requests from Web users on a FIFO basis, which can not provide differentiated QoS. This paper presents two approaches to provide differentiated Web QoS. The first is the kernel-level approach, which is adding a real-time scheduling processor to the operating system kernel to maintain the priority of user requests determined by the scheduling processor of Web server. The second is the load-balancing approach, which uses If-level masquerading and tunneling technology to improve reliability and response speed upon user requests.

• The KIPS Transactions:PartA
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• v.18A no.6
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• pp.255-264
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• 2011

A sensor network is a special network that makes physical data sensed by sensor nodes and manages the data. The sensor network is a technology that can apply to many parts of field. It is very important to transmit the data to a user at real-time. The core of the sensor network is a sensor node and small operating system that works in the node. TinyOS developed by UC Berkeley is a sensor network operating system that used many parts of field. It is event-driven and component-based operating system. Basically, it uses non-preemptive scheduler. If an urgent task needs to be executed right away while another task is running, the urgent one must wait until another one is finished. Because of that property, it is hard to guarantee real-time requirement in TinyOS. According to recent study, Priority Level Scheduler, which can let one task preempt another task, was proposed in order to have fast response in TinyOS. It has restrictively 5 priorities, so a higher priority task can preempt a lower priority task. Therefore, this paper suggests Preemptive EDF(Earliest Deadline First) Scheduler that guarantees a real-time requirement and reduces average respond time of user tasks in TinyOS.

• Journal of the Institute of Electronics and Information Engineers
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• v.54 no.2
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• pp.16-27
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• 2017

IEEE 802.15.6 standard, a Wireless Body Area Network, aims to transfer not only medical data but also non-medical data, such as physical activity, streaming, multimedia game, living information, and entertainment. Services which transfer those data have very various data rates, intervals and frequencies of continuous access to a medium. Therefore, an efficient anti-collision operations and medium assigning operation have to be carried out when multiple nodes with different data rates are accessing shared medium. IEEE 802.15.6 standard for CSMA/CA medium access control method distributes access to the shared medium, transmits a control packet to avoid collision and checks status of the channel. This method is energy inefficient and causes overhead. These disadvantages conflict with the low power, low cost calculation requirement of wireless body area network, shall minimize such overhead for efficient wireless body area network operations. Therefore, in this paper, we propose a medium access scheduling scheme, which adjusts the time interval for accessing to the shared transmission medium according to the amount of data for generating respective sensor node, and a priority control algorithm, which temporarily adjusts the priority of the sensor node that causes transmission concession due to the data priority until next successful transmission to ensure fairness.

• The KIPS Transactions:PartA
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• v.9A no.4
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• pp.503-510
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• 2002

In this paper, a general purpose embedded computer system is designed and implemented. The most crucial points of the system are extensibility and flexibility. The hardware of the developed system is composed of three modules and the software provides hardware independent application program interfaces. Moreover, uC/OS-II, a well-known open realtime kernel. is extended and ported onto the system. The extended uC/OS-II supports that multiple processes can have the same priority and such processes are scheduled in a round-robin manner.

• Journal of the Institute of Electronics and Information Engineers
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• v.50 no.8
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• pp.143-150
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• 2013

Solid-state disks (SSDs) have been widely used by high-performance personal computers or servers due to its good characteristics and performance. The NAND flash-based SSDs, which take large portion of the whole NAND flash market, are the major type of SSDs. They usually integrate a cache buffer which is built from DRAM and uses the write-back policy for better performance. Unfortunately, the policy makes existing scheduling methods less effective at the I/F level of SSDs Therefore, in this paper, we propose a scheduling method for the I/F with consideration of the cache buffer. The proposed method considers the hit/miss status of cache buffer and gives higher priority to the read requests. As a result, the requests whose data is hit on the cache buffer can be handled in advance and the read requests which have larger effects on the whole system performance than write requests experience shorter latency. The experimental results show that the proposed scheduling method improves read latency by 26%.

• Proceedings of the Korean Information Science Society Conference
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• 2003.04a
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• pp.202-204
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• 2003

경성 실시간 시스템(Hard Real-Time System)어서는 주기 태스크들의 엄격한 마감시간(Deadline) 보장이 시스템의 성능을 좌우한다. 본 논문에서는 CPU의 이용률(Utilization)이 높아 비율단조 정책으로는 마감시간을 보장 할 수 없는 주기 태스크들을 위해 확장된 스케줄 가능성 검사를 통해 수행할 태스크들의 공통 주기(L.C.M : Least Common Multiple)내에서 EDF(Earliest-Deadline First) 정책을 기반으로 마감시간 보장 수행패턴(Feasible Pattern)을 찾고, 이를 참조하여 우선순위를 고려하지 않고 태스크들을 강제 수행할 수 있게 하는 비율단조 기반의 스케쥴링 기법을 제안한다. EDF를 기반으로 생성된 패턴은 EDF 정책의 특성에 따라 CPU의 이용률을 100% 까지 가능하게 하며 패턴을 참조하여 강제 수행함으로써 EDF 정책이 갖는 실행시간 스케쥴링 오버헤드를 없앨 수 있다.

• Journal of KIISE:Information Networking
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• v.32 no.2
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• pp.254-260
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• 2005

In the guaranteed service, a real-time scheduling algorithm must achieve both high level of network utilization and scalable implementation. Here, network utilization indicates the number of admitted real-time sessions. Unfortunately, existing scheduling algorithms either are lack of scalable implementation or can achieve low network utilization. For example, scheduling algorithms based on time-stamps have the problem of O(log N) scheduling complexity where N is the number of sessions. On the contrary, round-robin algorithms require O(1) complexity. but can achieve just a low level of network utilization. In this paper, we propose a scheduling algorithm that can achieve high network utilization without losing scalability. The proposed algorithm is a Hierarchical Round-Robin (H-RR) algorithm that utilizes multiple rounds with different interval sizes. It provides latency bounds similar to those by Packet-by-Packet Generalized Processor Sharing (PGPS) algorithm using a sorted-Priority queue. However, H-RR requires a constant time for implementation.

• Proceedings of the Korean Information Science Society Conference
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• 1998.10a
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• pp.287-289
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• 1998

실시간 스케줄러는 대역폭, 필요 버퍼량 등과 같은 네트워크 자원을 효율적으로 이용하면서 한정된 통신지연(bounded delay)을 제공해야 한다. 최근 이러한 제한 조건을 만족시키기 위해서 많은 스케줄링 방법론이 제시되었다. 그중EDF 스케줄링 방법론이 최적의 성능을 갖는 것으로 알려져있다. 그러나 EDF스케줄링 방법론은 "sort"나 "search"와 같은 연산작업을 수행함으로서, 과다한 오버헤드를 발생시킨다. Rotating Priority Queues(RPQ) 스케줄러는 EDF 연산 작업 없이 EDF스케줄러에 근접한 성능을 갖는 스케줄러이다. 그러나 RPQ스케줄러는 과다한 버퍼량을 필요로 한다. 본 논문에서는 이러한 문제저？ㄹ 해결하기위해서 Multiple Rotating Priority Queues(MRPQ)스케줄러를 제시한다. MRPQ스케줄러는"blick queue"라는 새로운 개념을 이용하여 회전 우선 순위 queue를 다중 계츨으로 구성한다. 이렇게 구성된 MRPQ 스케줄러는 RPQ스케줄러에서 필요한 버퍼량의 반정도의 버퍼량만을 사용하여 RPQ스케줄러와 동일한 동작을 수행한다. 또한 MRPQ스케줄러는 RPQ스케줄러와 동일한 최대 지연시간을 제공한다.러는 RPQ스케줄러와 동일한 최대 지연시간을 제공한다.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.10 no.9
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• pp.1551-1557
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• 2006

Since subscribers, who pay the same communication fees, have a strong desire to take similar services with the other users, it is an important issue to provide fairness among those subscribers wherever they are located. Therefore, in this paper we propose a QoS packet scheduler that can provide fairness among wireless LAN terminals and evaluate its performance using computer simulation. The key idea of this scheduler is to reduce the CW value of the wireless LAN terminal that has failed in sending its packets due to channel transmission error in order to offer the wireless MM terminal a higher transmission priority which is the idea of service compensation. We evaluate its performance using NS-2 network simulator, compare its numerical results to those of IEEE 802.11e without this scheme, and conclude that this scheme can reduce throughput difference between similar wireless LAN terminals.