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排序方式: 共有1366条查询结果,搜索用时 15 毫秒
1.
Nguyen Quoc Dinh Author VitaeDong-Sung KimAuthor Vitae 《Computer Standards & Interfaces》2012,34(1):117-123
The International Society of Automation recently released ISA100.11a as an open standard for reliable wireless networks for industrial automation. ISA100.11a uses the TDMA scheme in the medium access layer to provide deterministic services. However, ISA100.11a adopts the CSMA-CA mechanism with priorities for retransmission from failure on dedicated links, sporadic data, and network configuration.This paper evaluates ISA100.11a CSMA-CA by simulation, considering the effects of backoff procedures and priority settings to probability of collision and successful use of slots. It's demonstrated that a high number of priority classes enable better network utilization resulting in less number of packets exceeding their lifetime. 相似文献
2.
韩新峰 《信息安全与通信保密》2007,(6):105-106
论文主要从四个方面简要介绍了网上银行所存在的安全隐患以及各种防范措施,主要采用数字加密技术、数字证书、信息隐藏、防病毒等一系列技术。 相似文献
3.
Advanced Infrared (AIr) is a proposed standard of the Infrared Data Association (IrDA) for indoor infrared LANs. AIr Medium Access Control (MAC) employs Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) techniques with Request To Send/Clear To Send (RTS/CTS) frame exchange to address the hidden station problem. A long Collision Avoidance Slot (CAS) duration, that includes the beginning of the CTS frame, is defined to cope with collisions caused from hidden stations. AIr MAC employs linear adjustment of the Contention Window (CW) size to minimize delays emerging from the long CAS duration. This paper provides a simple and accurate analytical model for the linear CW adjustment that calculates AIr throughput assuming a finite number of stations and error free channel transmissions. Validity of the model is verified by comparing analysis with simulation results. By examining the first derivative of the throughput equation, we derive the optimum CW size that maximizes throughput as a function of the network size. In the case of the AIr protocol, where a collision lasts exactly one CAS, different conclusions result for maximum throughput as compared with the corresponding conclusions for the similar IEEE 802.11 protocol. Using the proposed model, we present an extensive AIr throughput performance evaluation. The effectiveness of physical and link layer parameters on throughput performance is explored. The proposed long CAS duration combined with CW linear adjustment are proven quite effective. Linear CW adjustment combined with the long CAS duration offer an efficient collision avoidance scheme that does not suffer from collisions caused from hidden stations. 相似文献
4.
张楠 《信息技术与信息化》2005,(2):22-24
作为公钥基础设施PKI(Public Key Infrastructure)的核心实体认证机构CA(Certificate Authority),是开展电子政务的重要基础建设。本文是以威海电子政务应用系统建设为背景开发CA系统的过程中,对基于PKIX的时间戳协议TSP(Tune-Stamp Protocol)进行了研究与实现。 相似文献
5.
对采用CSMA/CA控制策略实现CATV多媒体交互通信的介质存取方法进行详尽的分析与讨论,其最重要的特点就是发送站数据无碰撞危险,由于不存在的数据包碰撞检测,从而对数据包无最小长度要求,包可以非常短,数据吞吐量可以大大增加。 相似文献
7.
一种新的移动Ad hoc网络的安全路由策略 总被引:1,自引:2,他引:1
本文从各网络节点易受攻击、俘获,各网络节点之间不可信赖的角度出发,引入了可信任第三方的信任分散策略并结合Diffie-Hellman密钥交换算法,提出了一种新的移动Adhoc网络的安全路由策略。 相似文献
8.
《Mechatronics》2015
Collaboration has been found in previous studies on the design of assembly lines to be a useful mechanism. In this study, the focus is on a collaborative assembly (CA) framework, inspired by the design principles of CCT, the Collaborative Control Theory, to improve balanceability and flexibility of assembly lines through tool sharing (TS) among idle and bottleneck workstations. TS is widely practiced in advanced assembly facilities to reduce cost and improve consistency and standardization in assembly and in assembly-and-test utilities, relying often on real time control. The framework developed here addresses the systems design aspect of Mechatronics, covering the planning, execution, and control mechanisms. Planning includes assembly line balancing (ALB) and initial TS decisions, made continually by solving a bi-objective mixed-integer program (BOMIP). A collaborative multi-agent system (CMAS) enhanced with a TS-best matching (BM) protocol is developed to execute the plan, control the process, and modify the TS decisions, considering dynamic changes in the system’s operations. Experiments show that the new CA framework significantly outperforms classic approaches (i.e., ALB without TS-BM) in terms of cycle time, utilization of tools, and balanceability. In addition, the control mechanism is proven to augment the line’s flexibility against the inherent uncertainties of assembly processes, compared to the previously developed static CA frameworks. 相似文献
9.
Sangman ChoAuthor VitaeSrinivasan RamasubramanianAuthor Vitae Onur TurkcuAuthor VitaeSuresh SubramaniamAuthor Vitae 《Ad hoc Networks》2012,10(3):373-387
Wireless infrastructure networks (WINs) provide ubiquitous connectivity to mobile nodes in metro areas. The nodes in such backbone networks are often equipped with multiple transceivers to allow for concurrent transmissions in multiple orthogonal channels. In this study, we develop an analytical model for the estimation of the delay and throughput performance of wireless infrastructure networks employing slotted ALOHA channel access and slotted Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) over multiple channels. The analytical model, which takes into account the correlation due to multi-hop transmissions, approximates the performance observed through simulations accurately. 相似文献
10.
Multiple access control (MAC) protocols play a significant role in wireless LANs. The IEEE 802.11 MAC protocol specifies two
coordination functions that are Distributed Coordination Function (DCF) and Point Coordination Function (PCF). While both
DCF and PCF are available in a wireless cell, we propose a novel access mechanism called Adaptive Coordination Function (ACF)
to support various classes of traffic. The ACF superframe comprises two periods, one TDMA period designed for real-time traffic
and followed by an adaptive period which adaptively employs DCF or PCF to support non-real-time traffic. In this paper, we
apply the theory of M/G/1 queues to analyze the performance of adaptive period in terms of queuing delay, end-to-end delay,
and saturation throughput. With our analytic model, DCF or PCF can be invoked appropriately according to the number of stations,
packet arrival rate, packet payload size, and effective channel bit rate. Analytical results are derived for an extensive
throughput and delay performance evaluation of both DCF and PCF. 相似文献