移动Ad Hoc网络中一种分布式QoS保证的多址接入协议

基于随机竞争和冲突解决的思想,本文为多跳移动Ad Hoc网络提出了一种分布式服务质量(QoS)保证的多址接入(QMA)协议.该协议中,节点在发送业务分组前利用预报突发进行竞争接入,节点根据业务分组时延情况和最早失效优先原则确定预报突发的长度,所发预报突发能持续到最后的节点优先获得接入.同时,具有实时业务的节点可以按照其优先级在更早的竞争微时隙中开始发送预报突发,而有非实时业务的节点只能在前面竞争微时隙空闲的情况下,才能在后面的微时隙开始发送预报突发,因此发送实时业务的节点可以比发送非实时业务的节点更优先接入信道,从而在移动Ad Hoc网络中实现了对多媒体业务的QoS保证.最后利用OPNET仿真评估了QMA协议的多址性能,并与IEEE 802.11e协议的性能做了比较,结果表明QMA协议可以提供较高的吞吐量和较低的实时业务时延.     

TR069协议在IPTV终端管理系统中的研究与应用

根据目前IPTV业务和互动需求,设计一套实时有效的IPTV终端管理系统具有极大的现实意义.详细分析了TR069协议及其关键技术,着重对IPTV机顶盒进行研究,实现了TR069协议在IPTV机顶盒终端管理业务中的应用.测试结果显示,所设计的IPTV机顶盒终端管理系统能够满足IPTV终端管理的实时性、有效性需求.     

基于竞争终端个数和跳数的802.11Mesh网络公平性优化机制

设计了一种基于竞争终端个数和跳数的公平性优化机制通过调整MeshAP的协议参数来改善不同跳数间竞争终端的公平性,同时,根据同一MeshAP下竞争终端的个数,按照预先设定的区间,动态调整其下各终端的协议参数,从而在改善系统传输性能的同时,进一步优化不同跳数间竞争终端的公平性.给出了这一机制的详细实现步骤,并利用ns2,对这一新的机制在各种场景下进行了大量的仿真实验.相关实验结果验证了这一优化机制不仅算法简单,系统开销小,适合于复杂多变的无线环境,而且能够根据竞争终端个数动态对无线系统中不同跳数下的竞争终端的公平性进行整体的优化.     

BR-TDMA:一种移动自组织网络的新型MAC协议

该文提出了一种新的、用于支持同步网络的MAC协议:BR-TDMA。该协议采用分布式控制,支持分组突发业 务和资源预留的实时业务,对网络规模不敏感,较好地解决了隐藏、暴露终端等问题。通过仿真,对该协议的性能进行了分 析、比较。     

接入网关处实时业务流的识别与防火墙策略

实时业务流的识别可以方便我们统计实时业务的流量，并为实时业务质量测量和监控打下基础。目前支持实时业务的协议有很多，例如H323协议和SIP协议。H.323协议是基于分组交换网络视频会议的端对端通信标准，为适应IP语音通信，H.323进行了改进，由于其标准复杂而严格，产品之间不存在兼容问题。SIP协议需要其终端包含用户代     

APON接人系统的一个介质访问控制协议

作为共享介质的接入网络,APON需要介质访问控制协议用于协调各终端对介质的存取.本文提出了一个符合ITU-T建议的MAC协议,采用了时延分优先级,对高优先级的实时业务按照的均匀间隔的原则分配带宽,低优先级业务的带宽按次序循环分配.上行帧长度根据处于连接的用户数动态变化,各终端的带宽申请时隙由系统动态分配.最后给出了由该协议确定的网络性能的计算机仿真结果.     

面向实时业务的认知无线网络 MAC 层频谱接入方案

摘 要：为满足认知无线网络中宽带业务实时传输的需求,提出低延迟的MAC层频谱接入方案,包括频谱感知调度与信道接入竞争两部分。在频谱感知阶段,认知用户选取最佳可用信道数实现感知与传输的延迟最小化;在信道接入竞争阶段,协议考虑频谱资源动态变化的特点,通过设计数据帧格式以及邻居节点协同侦听机制,减小信道冲突与“聋终端”的影响。理论与实验结果表明,与传统的认知无线网络MAC层协议相比,提出的接入方案数据传输延迟更短,同时在授权信道空闲率较大时吞吐量性能略优。     

基于接入控制机制的无线局域网MAC协议

本文对IEEE 802.11无线局域网点协调功能的改进协议(MPCF)的性能进行深入的研究.MPCF基于接入控制和链式轮询机制.根据业务特点,MPCF协议分别为实时业务和非实时业务提供不同的服务策略:实时业务采用ACK应答方式,非实时业务采用无ACK应答方式,从而引入接入控制机制,更好地保证实时业务的服务质量.为了提高网络吞吐量,MPCF协议采用链式轮询机制.本文给出MPCF吞吐量的分析模型.仿真结果表明:MPCF协议的性能优于PCF协议,而且理论分析结果与仿真结果基本吻合.     

一种视频监控系统中心跳机制的实现方法

为了提高视频监控系统的安全性和可靠性,通过分析现阶段的实时视频传输协议,提出了一种流媒体服务器与终端播放器间心跳机制的实现方法。该方法在实时流协议(RTSP)连接建立过程的基础上做了修改,保持原有的硬件部分不变,重构实时传输协议(RTP)数据包头部字段,增加含有终端信息的字段。结果表明,普通的实现RTSP的终端不能正确访问流媒体服务器,增加了流媒体服务器与终端间通讯的安全性和可靠性,提高了视频监控系统的整体性能。     

无冲突NC-IPRMA协议下的数据--话音综合

提出了一个面向微蜂窝通信的支持数据─话音综合业务的无冲突分组预约多址协议─—NC-IPRMA协议,通过M／M／N／／M．排队模型分析了NC-IPRMA协议的话音子系统性能,通过系统仿真分析了数据一话音综合性能。研究结果表明,在支持数据─话音综合业务方面,NC-IPRMA协议比PRMA和IPRMA协议更高效,这包括更高的信道利用率,更短的数据分组时延和更大的话音终端容量。由于采用排队等待方式接入时隙信道,NC-IPRMA协议彻底消除了以竞争方式接入信道的PRMA协议（及其各种改进方案）存在的重负荷下的不稳定问题。     

Contention-Aware Performance Analysis of Mobility-Assisted Routing

A large body of work has theoretically analyzed the performance of mobility-assisted routing schemes for intermittently connected mobile networks. But the vast majority of these prior studies have ignored wireless contention. Recent papers have shown through simulations that ignoring contention leads to inaccurate and misleading results, even for sparse networks. In this paper, we analyze the performance of routing schemes under contention. First, we introduce a mathematical framework to model contention. This framework can be used to analyze any routing scheme with any mobility and channel model. Then, we use this framework to compute the expected delays for different representative mobility-assisted routing schemes under random direction, random waypoint and community-based mobility models. Finally, we use these delay expressions to optimize the design of routing schemes while demonstrating that designing and optimizing routing schemes using analytical expressions which ignore contention can lead to suboptimal or even erroneous behavior.     

Priority-based service differentiation scheme for IEEE 802.15.4 sensor networks

In sensor networks, data packets transmitted by different devices in home networking and industrial applications maintain different levels of importance. In this paper, we propose two mechanisms for IEEE 802.15.4 sensor networks to provide multi-level differentiated services which are required by each and every device. Mathematical model based on the discrete-time Markov chain is presented and is analyzed to measure the performance of the proposed mechanisms. Numerical results show the effects of the variation of contention window size and backoff exponent for service differentiation on 802.15.4 sensor networks. From the results, we derive that contention window size is more affective than backoff exponent on the saturation throughput while backoff exponent is more affective than contention window size on the average delay of every device. Simulation results are given to verify the accuracy of the numerical model.     

有限负载下802.11 DCF的性能分析及优化

利用三维马尔可夫链和M/G/1/K队列建立了有限负载下DCF机制的性能模型,分析了终端数量、传输负载、二进制指数回退机制及MAC层有限队列对系统性能的影响.基于该模型,推导了有限负载下最大化吞吐量的最优最小竞争窗口的闭式解.仿真结果表明,模型能够有效地预测有限负载下DCF的性能,根据传输负载调整最小竞争窗口大小能够获得最大化吞吐量.     

Performance modeling and analysis of IEEE 802.11 DCF based fair channel access for vehicle-to-roadside communication in a non-saturated state

This paper considers the fair access problem in vehicular ad hoc networks and develops analytical models for analyzing the performance of an IEEE 802.11 distributed coordination function based fair channel access protocol in a non-saturated state. We first derive the relationship between the transmission probability and the minimum contention window size of a vehicle, and the relationship between the velocity and the minimum contention window size of a vehicle in a non-saturated state. Based on the analytical model, the minimum contention window size of a vehicle for a given velocity can be determined in order to achieve fair access among different vehicles. Moreover, an analytical model is also developed for analyzing the throughput performance of the fair channel access protocol in a non-saturated state. The effectiveness of the analytical models is justified through simulation results.

     

A Game-Theoretic Framework for Medium Access Control

In this paper, we generalize the random access game model, and show that it provides a general gametheoretic framework for designing contention based medium access control. We extend the random access game model to the network with multiple contention measure signals, study the design of random access games, and analyze different distributed algorithms achieving their equilibria. As examples, a series of utility functions is proposed for games achieving the maximum throughput in a network of homogeneous nodes. In a network with n traffic classes, an N-signal game model is proposed which achieves the maximum throughput under the fairness constraint among different traffic classes. In addition, the convergence of different dynamic algorithms such as best response, gradient play and Jacobi play under propagation delay and estimation error is established. Simulation results show that game model based protocols can achieve superior performance over the standard IEEE 802.11 DCF, and comparable performance as existing protocols with the best performance in literature.     

Performance modeling of multiprocessor implementations of protocols

Two major performance bottlenecks in multiprocessor execution of protocols are contention for shared memory and for locks. Locks are used to protect shared messages and/or shared protocol state in a memory shared by competing processors. Mutual exclusion by locking can be costly, in terms of both lock contention and memory contention, if the parallel protocol code frequently accesses shared state and data. This paper presents a queueing network model for performance predictions of shared-memory multiprocessor protocol executions. Predictions from this model are compared to performance measurements from a multiprocessor implementation of two commonly used communication protocol stacks, transmission control protocol/Internet protocol (TCP/IP)/Ethernet and user datagram protocol/Internet protocol (UDP/IP)/Ethernet. These stacks are implemented on a parallelized version of the x-kernel protocol environment from the University of Arizona. A “processor-per-message” paradigm is used to partition the load among the processors. The measured speedups for the parallel implementations relative to the sequential ones are more than 11 times for UDP (using 20 processors) and three times for TCP (using five processors) on a sequent symmetry. We show that the model accurately captures the effects of lock and memory contention in our shared-memory multiprocessor and predicts the performance with a discrepancy of less than 10%     

Analysis of packet networks having contention-based reservation with application to GPRS

We develop a model to quantify the performance of message transmission systems in which users must reserve transmission resources via a contention mechanism prior to transmission. Our work is motivated by a desire to understand the performance characteristics of systems such as the general packet radio service (GPRS), where the single forward link of the wireless access system is organized as a sequence of frames, each of which has first a contention period and then a service period. There are a fixed number of fixed-length contention slots in each contention period. Each contending customer chooses at random the slot in which to contend, and success is determined by a capture model. A contender who fails waits for the next contention period, then again chooses at random the slot in which to contend; this process is repeated until the contender is successful. Customers who have contended successfully are served during the service period, which has a prescribed number of fixed-length slots, on a first-come-first-served (FCFS) basis, with the required number of service units being drawn independently from a general discrete distribution having finite support. We model the system as a Markov renewal process embedded at service departure times. We solve the model and then compute the equilibrium distributions of the number of customers in the system at arbitrary points in time and at customer arrival times. Finally, we give a numerical example in which we demonstrate the usefulness of our results in understanding the behavior of GPRS.     

Performance analysis and optimization of best‐effort service in IEEE 802.16 networks

The IEEE 802.16‐based WiMAX technology has great potential for the fourth‐generation mobile networks. Some of its service classes use the contention‐based broadcast polling mechanism to request resources. In this paper, we investigate the performance experienced by these services when the network is unsaturated. In particular, we model each subscriber station as an M/G/1 queue where the service time is determined by the parameters of the network configuration and the binary exponential backoff contention resolution algorithm. We develop a fixed‐point analysis to derive analytical expressions for network throughput and packet access delay. The accuracy of the analytical model is validated by comparing it with simulation over a wide range of operating conditions. The implications of various different parameter configurations on the performance are investigated using the analytical model. Moreover, we show that the model can be degenerated to the saturated condition. The utility of both the unsaturated and saturated models is further demonstrated by finding the optimal set of parameter values that maximize the network throughput. Copyright © 2011 John Wiley & Sons, Ltd.     

A Minimum Interference Cross-Layer Routing Protocol for Mobile Ad Hoc Networks

In mobile ad hoc networks (MANETs), channel contention and packet collision can seriously affect the performance of routing protocols, which will eventually affect the performance of the whole network. Besides, the arbitrary mobility of nodes makes contention and collision ever-changing and more complex. Thus, it is imperative to analyze the problem of contention and collision so as to build appropriate routes in MANETs. In this paper, by respectively predicting the durations of the contention and collision at every hop along the route, a minimum interference cross-layer routing protocol (MI-CLR) is proposed based on Random Waypoint (RWP) model. The new protocol classifies the interference in the network into two types; the first type of interference can only affect channel contention, while the other affects both channel contention and packet collision. Via taking the two types of interference together into account, we propose a new routing metric to build routes which guarantees that the established routes will not break frequently while having the minimum interference. Simulation results show that the MI-CLR protocol can significantly improve the network performance such as the average end-to-end delay, the packet loss ratio, the routing overhead and the throughput.     

A renewal theory based performance and configuration framework of the IEEE 802.11ah RAW mechanism

IEEE 802.11ah is a new Wi-Fi standard for sub-1Ghz communications, aiming to address the challenges of the Internet of Things (IoT). Significant changes in the legacy 802.11 standards have been proposed to improve the network performance in high contention scenarios, the most important of which is the Restricted Access Window (RAW) mechanism. This mechanism promises to increase the throughput and energy efficiency by dividing stations into different groups. Under this scheme, only the stations belonging to the same group may access the channel, which reduces the collision probability in dense scenarios. However, the standard does not define the RAW grouping strategy. In this paper, we develop a new mathematical model based on the renewal theory, which allows for tracking the number of transmissions within the limited RAW slot contention period defined by the standard. We then analyze and evaluate the performance of RAW mechanism. We also introduce a grouping scheme to organize the stations and channel access time into different groups within the RAW. Furthermore, we propose an algorithm to derive the RAW configuration parameters of a throughput maximizing grouping scheme. We additionally explore the impact of channel errors on the contention within the time-limited RAW slot and the overall RAW optimal configuration. The presented analytical framework can be applied to many other Wi-Fi standards that integrate periodic channel reservations. Extensive simulations using the MATLAB software validate the analytical model and prove the effectiveness of the proposed RAW configuration scheme.