改进型GEO卫星BTDAMA MAC协议时延性能分析

比较了采用不同调度策略的宽带GEO卫星网络突发目标按需分配协议,提出了采用纯按需分配与预约按需分配相结合的BTDAMA-HD协议。采用具有自相似特性的Pareto ON/OFF信源进行计算机仿真,对纯按需分配(BTDAMA-PD)与BTDAMA-HD协议进行了比较。仿真结果表明,BTDAMA-HD具有更好的时延/吞吐量性能。     

车路互联网的底层协议-802．11p标准

详细地描述了车路互联网系统的底层协议-802．11p标准。将802．11p与传统无线局域网技术进行对比,分析了802．11p在媒体接入控制层（MAC）与物理层（PHY）所做的修改,并从物理层参数、PP—DU帧结构,以及接人优先级等多方面指出了802．11p能在高速移动环境下建立稳定通信链路的原因。其次,还对802．11p所采用的频段、信道、发射功率以及频谱掩模进行分析;最后提出了802．11p在仿真方面所面临的挑战,并且在Simulink上建立了一套动态仿真系统,对标准进行仿真验证。     

Analytical modeling of bidirectional multi‐channel IEEE 802.11 MAC protocols

This paper presents an analytical approach to model the bi‐directional multi‐channel IEEE 802.11 MAC protocols (Bi‐MCMAC) for ad hoc networks. Extensive simulation work has been done for the performance evaluation of IEEE 802.11 MAC protocols. Since simulation has several limitations, this work is primarily based on the analytical approach. The objective of this paper is to show analytically the performance advantages of Bi‐MCMAC protocol over the classical IEEE 802.11 MAC protocol. The distributed coordination function (DCF) mode of medium access control (MAC) is considered in the modeling. Two different channel scheduling strategies, namely, random channel selection and fastest channel first selection strategy are also presented in the presence of multiple channels with different transmission rates. M/G/1 queue is used to model the protocols, and stochastic reward nets (SRNs) are employed as a modeling technique as it readily captures the synchronization between events in the DCF mode of access. The average system throughput, mean delay, and server utilization of each MAC protocol are evaluated using the SRN formalism. We also validate our analytical model by comparison with simulation results. The results obtained through the analytical modeling approach illustrate the performance advantages of Bi‐MCMAC protocols with the fastest channel first scheduling strategy over the classical IEEE 802.11 protocol for TCP traffic in wireless ad hoc networks. Copyright © 2010 John Wiley & Sons, Ltd.     

Analysis and enhancement of multi‐channel MAC protocol for ad hoc networks

In this paper, an analytical model is proposed to calculate the network throughput of dedicated control channel protocols that are designed to schedule multiple packets to be transmitted on different data channels simultaneously. Based on the analytical model, a scheme by tuning the initial contention window size is proposed to maximize the network throughput. We also present a novel multi‐channel MAC protocol for single‐hop scenario. Simulation results show that the proposed model is capable of modeling the behaviors of dedicated control channel protocols accurately. Furthermore, the proposed scheme can reduce the cost of collisions and enhance the network throughput up to 22% for 1 kB packet size and 80 nodes. Compared with other dedicated control channel protocols, the proposed protocol can schedule more control packets and use multiple channels more efficiently. Copyright © 2010 John Wiley & Sons, Ltd.     

一种虚拟机系统下关于多级安全的强制访问控制框架II:实现

This paper is a continuation of our last paper [1] which describes the theory of Virt-BLP model. Based on Virt-BLP model, this paper implements a mandatory access control (MAC) framework applicable to multi-level security (MLS) in Xen. The Virt-BLP model is the theoretical basis of this MAC framework, and this MAC framework is the implementation of Virt-BLP model. Our last paper focuses on Virt-BLP model, while this paper concentrates on the design and implementation of MAC framework. For there is no MAC framework applicable to MLS in virtual machine system at present, our MAC framework fills the blank by applying Virt-BLP model to Xen, which is better than current researches to guarantee the security of communication between virtual machines (VMs). The experimental results show that our MAC framework is effective to manage the communication between VMs.     

无线自组网竞争类MAC协议分析及研究

无线自组织网络是一种无基础设施的移动网络,并且每个节点的业务多以突发业务为主,因此信道资源分配适用于采用竞争方式。本文在对无线自组网各种典型竞争类MAC协议进行分析及探讨的基础上,采用Opnet仿真建模环境,创建出各协议的状态分析模型,并在此基础上对各协议的性能优劣进行了比较总结。论文对无线自组网各协议仿真建模研究及选择高效适用的MAC技术方案具有实际参考价值。     

一种生成VLAN帧的模块的设计

VLAN(Virtual LocalArea Network)是一种通过将局域网的设备逻辑地而不是物理地划分为一个个网段,从而实现虚拟工作组的新兴技术。不同的VLAN内部的广播和单播流量都不会转发到其他VLAN中,从而有助于控制流量、减少设备投资、简化网络管理、提高网络的安全性。本文介绍了一种VLAN帧的生成模块的设计方案,其中包括VLAN插入、剥离、MAC地址的更新与还原以及重写FCS位等。通过对大量相关资料的分析,最后用Verilog-HDL语言成功地对电路进行了设计。     

Cyclone V FPGA在高带宽存储接口中的应用

文中详细地分析了Altera公司Cyclone V FPGA器件的硬核存储控制器底层架构和外部接口,并在此基础上对Controller和PHY进行了功能仿真。仿真结果表明硬核存储控制器和PHY配合工作时的功能与设计预期相符,性能优良,适合于在当前FPGA的外部存储带宽需求日益增长的场合下应用。     

一种虚拟路由冗余协议负载均衡技术实现机制

标准VRRP（虚拟路由器冗余协议）解决在配置默认网关环境下消除网络单点故障问题,其协议自身不够灵活,即虚拟路由器中只有主设备进行流量转发,其他备用设备均作为备份不进行流量转发,无法负载分担,不能最大程度提高带宽和设备利用率。针对该局限,在此基于与某公司的合作项目,论述了一种虚拟路由冗余协议负载均衡实现机制,在标准VRRP协议分析研究基础上引入虚拟转发器和转发状态机,实现一个虚拟IP对应多个虚拟MAC的机制,无需配置多个备份组就能同时实现路由冗余备份和流量负载均衡,使局域网内用户能够通过每台虚拟转发器与外界通信,极大地提高资源利用率,最后以实验验证了设计可行性。     

一种基于消息缓存的多跳协作机制*

提出一种基于消息缓存的多跳协作机制(ICC机制),该机制不需要依靠准确的网络状态信息和复杂的协作节点选择算法,而是通过利用RTS/CTS交互消息获得相隔两跳的节点MAC地址,并在数据帧中添加下两跳的节点MAC地址,使得相隔两跳的节点可靠的接收到节点发送的信号,并对接收到的信号进行合并,从而获得分集为2的增益。