• Title/Summary/Keyword: Optimistic approach

Search Result 37, Processing Time 0.027 seconds

Improved ROHC Optimistic Mode for Efficient Utilization of the Resources in Mobile WiMAX (모바일 와이맥스 환경에서의 효율적인 무선링크 자원 활용을 위한 ROHC Optimistic 모드의 개선 방안)

  • Kim, Joo-Young;Woo, Hyun-Je;Lee, Mee-Jeong;Kwon, Jeong-Min
    • The KIPS Transactions:PartC
    • /
    • v.16C no.1
    • /
    • pp.57-64
    • /
    • 2009
  • In order to efficiently provide IP based Wireless Broadband services in Mobile WiMAX, schemes for more efficiently utilizing a limited bandwidth in radio links are needed. Robust Header Compression (ROHC), a standard header compression scheme proposed by IETF, Bi-directional Optimistic (O) mode provides higher compression efficiency and robustness compared with Payload Header Suppression (PHS) which is an optional header compression scheme for mobile WiMAX [1, 2]. However, if consecutive packet losses occur because of a Shadow Region of Mobile WiMAX or bit errors, header decompression failure rate of the ROHC O mode increases due to inconsistency of the compression information between the Compressor and the Decompressor. Therefore, a complementary mechanism is needed. In this paper, we propose an approach for the dynamic adjustment of an optimistic parameter, which has an effect on both the compression efficiency and the robustness, for improving the performance of ROHC O mode. We also analyze the performance of the proposed approach using an OPNET simulator.

Analysis of a Cache Management Protocol Using a Back-shifting Approach (백쉬프팅 기법을 이용한 캐쉬 유지 규약의 분석)

  • Cho Sung-Ho
    • The Journal of the Korea Contents Association
    • /
    • v.5 no.6
    • /
    • pp.49-56
    • /
    • 2005
  • To reduce server bottlenecks in client-server computing, each client may have its own cache for later reuse. The pessimistic approach for cache management protocol leads to unnecessary waits, because, it can not be commit a transaction until the transaction obtains all requested locks. In addition, optimistic approach tends to make needless aborts. This paper suggests an efficient optimistic protocol that overcomes such shortcomings. In this paper, we present a simulation-based analysis on the performance of our scheme with other well-known protocols. The analysis was executed under the Zipf workload which represents the popularity distribution on the Web. The simulation experiments show that our scheme performs as well as or better than other schemes with low overhead.

  • PDF

A Write Notification Approach for Optimistic Concurrency Control Schemes (낙관적 동시성 제어를 위한 쓰기 통지 기법)

  • SungChan Hong
    • Journal of Korea Multimedia Society
    • /
    • v.7 no.5
    • /
    • pp.633-639
    • /
    • 2004
  • The performance of optimistic concurrency control schemes which are generally used for Mobile computing is very sensitive to the transaction abort rate. Even if the abort probability can be reduced by back-shifting the timestamp from the time of requesting a commit, some transactions continuously perform unnecessary operations after the transactions accessed write-write conflicting data. In this paper, we propose an optimistic protocol that can abort the transactions during the execution phase by using the write notification approach. The proposed protocol enhances the performance of the optimistic concurrency control by reducing the unnecessary operations. In addition, we present a simulation study that compares our schemes with the timestamp based certification scheme. This study shows that our scheme outperforms the timestamp based certification scheme.

  • PDF

A Hybrid Concurrency Control without Deadlock based on Reordering (재배열 기반의 교착상태 없는 혼성 병행실행제어)

  • Cho, Sung-Ho
    • Journal of Internet Computing and Services
    • /
    • v.7 no.6
    • /
    • pp.79-86
    • /
    • 2006
  • Many of concurrency control for client-sewer database systems have been proposed and studied in the literature. However, commonly known schemes do not manage to the case of dramatic changes in data contention because the data contention of database systems is changed for each cases. In this paper, we propose o hybrid concurrency control. The proposed scheme uses a optimistic scheme for the first-run transactions and a pessimistic scheme for the second-run transactions. By pre-claiming locks in the second phase, deadlocks which ore possible in pessimistic based concurrency control are prevented in our approach. In addition, the scheme ensures at most one re-execution even if the validation in the optimistic phase fails. By a detailed simulation, this paper examines the behaviors of the Distributed Optimistic Concurrency Control and the proposed scheme. The simulation study shows our scheme outperforms Distributed Optimistic Concurrency Control in our experimental result.

  • PDF

An IP-address Auto-configuration Technique using Address Reservation for a Mobile Ad hoc Networks (모바일 애드 흑 네트워크에서의 주소 예약을 이용한 IP주소 자동 설정 기법)

  • Kim Namhoon;Ahn Soyeon;Moon Kyeongdeok;Lee Younghee
    • Journal of KIISE:Information Networking
    • /
    • v.31 no.6
    • /
    • pp.659-672
    • /
    • 2004
  • A Mobile Ad hoc Network (MANET) is a group of independent mobile computing nodes that consist of a multi-hop wireless network without a central administration or any infrastructure. Every node that wants to join a MANET must obtain an address for communication. Having a centralized DHCP server that provides addresses to nodes, we can easily and automatically obtain addresses. However, a MANET lacks any fixed infrastructure such as a DHCP server. We therefore propose a distributed address autoconfiguration approach for a MANET using a reserved address and optimistic Duplicated Address Detection (DAD). The reserved address helps to reduce the allocation latency, and the optimistic DAD guarantees the uniqueness of addresses and lessens communication overhead. We then suggest methods of handling network partition and network merging situations, and go on to evaluate our approach through simulations. The simulation result shows that our scheme guarantees the uniqueness of allocated address and considerably improves allocation latency and communication overheads.

Development of Efficient Conservative Algorithm for Distributed Simulation (분산 시뮬레이션을 위한 효율적인 보수적 알고리즘 개발)

  • 이영해
    • Journal of the Korea Society for Simulation
    • /
    • v.8 no.1
    • /
    • pp.77-88
    • /
    • 1999
  • There are two approaches to handle the Causality Error in parallel and distributed simulation. One approach is based on the conservative time synchronization and the other is the optimistic time synchronization. In this paper an efficient null message reduction method for the conservative time synchronization approach is suggested with the experimental results, which could improve performance of simulation and avoid deadlock situations.

  • PDF

Concept Analysis of Health Insensitivity using Hybrid Model (Hybrid model을 이용한 건강불감증의 개념분석)

  • 이동숙;이은옥
    • Korean Journal of Health Education and Promotion
    • /
    • v.20 no.3
    • /
    • pp.145-170
    • /
    • 2003
  • The purpose of this study was to clarity the concept of health insensitivity using Hybrid model, which consists of three phases: theoretical, empirical, and analytic. In the theoretical phase, the definitions of health insensitivity were searched in korean dictionary and examples used in the websites because the concept of health insensitivity has never been studied before. Two dimensions of health insensitivity emerged out from this investigation were cognitive and behavioral. And then a working definition of health insensitivity was established. The sub-concepts and related factors of health insensitivity were identified through the extensive reviews of the literature focusing on two dimensions of cognitive and behavioral. In the empirical phase, in order to obtain description of health insensitivity, face-to-face in-depth interviews were conducted with nine persons who are not related to professional health care. Grounded theory approach was applied to analyze these qualitative data. In the final analytic phase, theoretical results and empirical results were analyzed in the integrated way and a theoretical framework of health insensitivity was established. A refined definition of health insensitivity was that decreased health risk perception in cognitive dimension and conduction of the unhealthy behaviors in behavioral dimension. Sub-concepts of decreased health risk perception were optimistic bias and decreased general fear. Sub-concepts of unhealthy behavior were doing health threatening behavior and not doing desirable health behavior. The contact of health information was a causal condition of health insensitivity. Optimistic disposition, health locus of control, and avoidance coping style were intervening conditions of health insensitivity. Three types of health insensitivity were identified: unconcern or ignorance type, optimistic bias type, and cognitive dissonance type. Finally, The implications of these findings for further research and nursing practice are discussed.

Analysis of Optimistic Cache Protocols based on broadcasting for Mobile Computing Environments (이동 컴퓨팅 환경에서 방송기반의 낙관적 캐쉬 프로토콜들에 대한 분석)

  • Cho, Sung-Ho
    • Journal of Internet Computing and Services
    • /
    • v.6 no.5
    • /
    • pp.177-185
    • /
    • 2005
  • Caching in mobile computing environments Is an important technique that will reduce the effects such as limitation of bandwidth, restriction of resources and frequent disconnection. To reduce limitation and disconnection problems in mobile computing, a new form of caching system have been proposed based on a broadcast approach. This paper proposes a broadcast based cache protocol and examines the behaviors of the proposed scheme and well known schemes such as multiversion based scheme and Certification Reports. By a detailed simulation, we show some characteristics of different approaches to detect and resolve conflicts. We also show proposed scheme out performs other schemes with a low space and operation overhead.

  • PDF

병렬분산 환경에서의 DEVS형식론의 시뮬레이션

  • Seong, Yeong-Rak;Jung, Sung-Hun;Kon, Tag-Gon;Park, Kyu-Ho-
    • Proceedings of the Korea Society for Simulation Conference
    • /
    • 1992.10a
    • /
    • pp.5-5
    • /
    • 1992
  • The DEVS(discrete event system specification) formalism describes a discrete event system in a hierarchical, modular form. DEVSIM++ is C++ based general purpose DEVS abstract simulator which can simulate systems to be modeled by the DEVS formalism in a sequential environment. We implement P-DEVSIM++ which is a parallel version of DEVSIM++. In P-DEVSIM++, the external and internal event of models can be processed in parallel. To process in parallel, we introduce a hierarchical distributed simulation technique and some optimistic distributed simulation techniques. But in our algorithm, the rollback of a model is localized itself in contrast to the Time Warp approach. To evaluate its performance, we simulate a single bus multiprocessor architecture system with an external common memory. Simulation result shows that significant speedup is made possible with our algorithm in a parallel environment.

  • PDF

Improving Security Awareness about Smishing through Experiment on the Optimistic Bias on Risk Perception (위험인식의 낙관적 편향 실험을 통한 스미싱 보안인식 개선)

  • Kang, Ji Won;Lee, Ae Ri;Kim, Beomsoo
    • Journal of the Korea Institute of Information Security & Cryptology
    • /
    • v.26 no.2
    • /
    • pp.475-487
    • /
    • 2016
  • Recently, various risks of smartphone hacking are emerging. Smishing crime techniques become more cunning and its damage has been increasing, thereby requiring effective ways of preventing and coping with smishing. Especially, it is emphasized the need for smartphone users' security awareness and training besides technological approach. This study investigates the effective method for providing news messages in order to improve the perception of risk from smishing. This research empirically examines that the degree of optimistic bias on risk perception can vary depending on news frame, topic type, and involvement regarding smishing. Based on the findings, it identifies the factors influencing risk perception and verifies effective ways of promoting individual security awareness on smishing. The results of this study provide implications that assist in educating, campaigning and promoting information security awareness for smart device users.