基于抖动激励的VoIP终端拥塞控制机制

针对基于H．323的VoIP系统，提出了一种抖动激励式终端拥塞控制机制，将语音分组的延迟抖动参数与RTCP协议相结合，控制动态改变语音编码方式及传输分组大小，从而缓解网络拥塞，降低传输延时和丢包率。     

WiMAX拓展实时轮询调度机制分析

为了提高无线资源的利用率,使WiMAX系统更好地支持语音业务,基于IEEE 802.16e协议的QoS调度体系,提出了针对带有静默压缩语音业务的拓展实时轮询调度机制的具体实现方案.而且通过对方案中关键参数的分析,给出了一种QoS保证方法.方法根据用户时延对数据带宽分配进行补偿,并按照用户负载情况动态地调整轮询请求带宽的分配周期.使用OPNET软件进行了系统级性能评估,结果表明所提出的方法可有效地降低用户上行接入时延和上行丢包率,从而提高了通信质量.     

VoWLAN系统的MAC层改进机制

IEEE 802.11b的DCF接入方式是为无线数据业务提供接入而设计的,不能有效地支持诸如语音之类的实时业务。提出了两种改进的MAC层机制来提高无线局域网上传输语音（VoWLAN）的系统容量和有效性。分析和仿真结果表明,改进机制显著提高了系统容量,并保证了传输延迟、抖动和平均丢包率等服务质量（QoS）要求。     

基于Ip的甚高频传输系统的丢包补偿问题探讨

基于时分复用技术的SDH传输系统中,VHF信号因丢包而造成的语音信号失真现象并不明显.然而,基于IP协议的数据分组交换技术的新一代传输PTN系统,因传输过程中出现的延迟和丢包,会造成大量的音频质量恶化.PTN中采取音频丢包补偿技术对丢失语音数据包进行修复和还原是十分必要的.本文通过具体分析发现引入媒体相关前向差错纠正语音丢包补偿算法.可以较好的解决此类问题,同时兼顾了信号质量和开销间的平衡问题.     

基于QCI优先级的分组调度算法

长期演进(LTE)系统对用户同时获得的多种业务配置了服务质量(QoS)等级标识(QCI)优先级参数,从而优化了移动通信系统QoS评价体系。为此,结合M-LWDF算法,提出一种基于QCI优先级的分组调度算法。将QCI参数引入资源分配和分组调度判决机制,在用户与申请的多项业务间建立优先级关联性,实现多用户之间、单用户的多类型业务之间的联合优化调度。仿真结果表明,该算法能有效提高系统平均吞吐量,降低平均时延。     

Packets Schedule Algorithm for LTE Downlinks Based on QoS

提出一种基于服务质量(QoS)的长期演进(LTE)下行分组调度算法.根据业务的QoS对分组进行分类,提高时延敏感业务的优先级,通过分析传输流量,进行资源分配的公平性补偿.仿真实验结果表明,该算法能有效平衡吞吐量和用户公平性,且在丢包率方面性能较优.     

M-WiMAX网络中预测LWDF调度算法的稳定性分析

移动无线城域网作为4G标准无线移动网络,其无线信道具有用户依赖和时变信道的特性,具有服务质量保证机制,分组调度算法是系统保证服务质量的核心要素之一。建立一个多用户泊松到达业务流,用Markov链建模一个无线时变信道,Pre-LWDF调度算法在各个用户间调度实时业务流,这样,移动无线城域网在PMP模式下形成了一个M/G/1的排队系统。根据队列理论计算并推导出无线城域网的信道容量域和系统的稳定域,在此基础上,用李雅普诺夫漂移稳定性理论分析证明Pre-LWDF调度算法具有分组级稳定性。进一步在NS2仿真平台上搭建一个移动无线城域网仿真环境,验证Pre-LWDF调度算法的稳定性。仿真结果表明,该算法在移动无线城域网中具有分组级稳定性。     

基于改进的SOM网络模型的VoIP QoS应用研究

VoIP的服务质量（QoS,Quality of Service）评估可以采用一系列可度量的参数来描述：业务可用性、吞吐量、延迟、抖动、分组丢失率等。现有的感知语音质量评价（PESQ）很难对不同环境下的网络结构进行实时和恰当的语音等级质量分类。为了能够综合考虑几种QoS相关因素,在给出改进的自组织映射神经网络模型（ESOMNN）的基础上,利用ESOM能够对高维输入数据有效分类的特点,提出了将端到端延迟、丢包率、抖动、语音编码以及测试系统标识作为ESOMNN的输入数据,在对采样数据进行训练后可自动完成语音质量评价和映射,并能根据得到的实时变量有效地评价包含多种相关因素的QoS级别。     

移动WiMAX网络中的VoIP调度机制

移动微波存取全球互通(WiMAX)网络使用了5种调度机制来保证服务质量,其中的3种被设计用于实时性业务。但是,这3种调度机制都缺乏公平性。在资源不足的时候,通过丢弃新用户的请求来保证旧用户的服务质量(QoS)。为此,针对WiMAX中的因特网语音(VoIP)服务提出了一种基于优先权的新调度机制。该机制中,不同用户的业务请求将被赋予不同的优先权。新旧用户同时请求资源时,新用户的请求拥有更高的优先权;资源分配中心再根据优先权的高低为用户分配资源,从而在最大限度上保证了资源分配的公平性。仿真结果显示,新调度机制可以将网络中的因特网语音服务的连接数和总吞吐量分别提高15%和11%左右。     

Vo IP 的语音质量分析与控制

分析了VoIP语音质量的影响因素，通过E模型定量地描述了语音质量与端到端延迟和丢包率的关系。为了控制VoIP的语音质量，计算出VolP系统在各种情况下的语音质量极限，提出一种自适应编码和分组封装的控制策略。将该方法应用于自行开发的IP电话网关，实际测试证明能在很大程度上提高VoIP的语音质量。     

Uplink Scheduling for Supporting Real Time Voice Traffc in IEEE 802.16 Backhaul Networks

In this paper we propose simple enhancements to the bandwidth (BW) request messages in IEEE 802.16 for supporting real-time packet voice traffc. Three different BW request formats are proposed, each requiring a different amount of latency information about the buffered packets at the SS. On this basis, packet scheduling schemes are proposed for the BS to make resource allocations for real-time traffc. Our results show that the proposed BW request and scheduling schemes achieve significantly lower packet loss probability than the standard IEEE 802.16 BW request with round robin scheduling. The results further show that there is an optimum point about how much delay information the SS should report to the BS in order to best utilize the uplink resources while the SS provides satisfactory real-time performance for the voice traffc.     

地铁通信系统的RPR

地铁传输系统承载着大量的业务,在保留同步数字体系（SDH）4优势的基础上,将弹性分组环（RPR）处理功能融入其中,强化多业务传输平台（MSTP）的以太网业务处理能力,可以实现以太网带宽的统计复用、公平的带宽分配、更加严格的业务分类（Cos）和服务质量（Oos）以及更加安全的用户隔离功能,逐步成为当前城域网建设的主流技术。解决了目前地铁通信系统中IP业务的不断增长的问题。     

Incorporating packet semantics in scheduling of real-time multimedia streaming

In this work, we develop a novel packet scheduling algorithm that properly incorporates the semantics of a packet. We find that improvement in overall packet loss does not necessarily coincide with improvement in user perceivable QoS. The objective of this work is to develop a packet scheduling mechanism which can improve the user perceivable QoS. We do not focus on improving packet loss, delay, or burstiness. We develop a metric called, “Packet Significance,” that effectively quantifies the importance of a packet that properly incorporates the semantics of a packet from the perspective of compression. Packet significance elaborately incorporates inter-frame, intra-frame information dependency, and the transitive information dependency characteristics of modern compression schemes. We apply packet significance in scheduling the packet. In our context, packet scheduling consists of two technical ingredients: packet selection and interval selection. Under limited network bandwidth availability, it is desirable to transmit the subset of the packets rather than transmitting the entire set of packets. We use a greedy approach in selecting packets for transmission and use packet significance as the selection criteria. In determining the transmission interval of a packet, we incorporate the packet significance. Simulation based experiments with eight video clips were performed. We embed the decoding engine in our simulation software and examine the user perceivable QoS (PSNR). We compare the performance of the proposed algorithm with best effort scheduling scheme and one with simple QoS metric based scheduling scheme. Our Significance-Aware Scheduling scheme (SAPS) effectively incorporates the semantics of a packet and delivers best user perceivable QoS. SAPS can result in more packet loss or burstier traffic. Despite these limitations, SAPS successfully improves the overall user perceivable QoS.     

IEEE 802.11e协议HCCA机制下的QoS研究

分析了IEEE 802.11e协议HCCA信道接入机制下的简单带宽调度算法对多媒体业务的QoS支持情况,指出其不足并在其基础上进行了改进,提出了一种基于业务等级的带宽调度算法E-HCCA（Enhanced HCCA）。E-HCCA对不同优先等级业务的数据在带宽分配上采用不同的策略,在优先保证各个节点CBR业务的基础上,根据节点的VBR流量动态平均分配剩余带宽。相比较简单调度算法,E-HCCA算法更好地支持了多用户下的语音业务流和视频业务流,降低了分组时延,增加了系统吞吐率。     

基于HSDPA的增强型分组调度算法研究

从系统吞吐量、用户公平性等方面分析研究了HSDPA系统中支持非实时业务的三种经典分组调度算法RR、Max C/I和PF。针对PF算法重传时延过长问题,提出了一种结合混合自动请求重传HARQ的增强分组调度算法。该算法通过提高重传分组的优先级降低重传时延,有效地避免系统资源的浪费。MATLAB仿真结果表明,该算法在降低单用户重传时延的同时,仍能保证用户间的公平性和系统的吞吐量。     

Uplink Scheduling for Supporting Real Time Voice Traffic in IEEE 802.16 Backhaul Networks

In this paper we propose simple enhancements to the bandwidth （BW） request messages in IEEE 802.16 for supporting real-time packet voice traffic. Three different BW request formats are proposed, each requiring a different amount of latency information about the buffered packets at the SS. On this basis, packet scheduling schemes are proposed for the BS to make resource allocations for real-time traffic. Our results show that the proposed BW request and scheduling schemes achieve significantly lower packet loss probability than the standard IEEE 802.16 BW request with round robin scheduling. The results further show that there is an optimum point about how much delay information the SS should report to the BS in order to best utilize the uplink resources while the SS provides satisfactory real-time performance for the voice traffic.     

Upper-level scheduling supporting multimedia traffic in cellular data networks

Wireless data networks such as cdma2000 1x EV-DO and UMTS HSDPA use downlink scheduling that exploits channel fading to increase the system throughput. As future wireless networks will eventually support multimedia and data traffic together, we need a proper criterion for scheduling that can count various service requirements such as delay and packet loss. Although some previous approaches proposed opportunistic schedulers at the lower layer, it has not been investigated well whether they are able to meet explicit QoS defined at the upper layer. Hence, in this paper, we develop a hierarchical scheduling model that considers QoS provisioning and the time-varying channel feature separately. We focus on the upper-level QoS scheduling that supports various traffic classes in a unified manner. Supposing that a user gets some satisfaction or utility when served, we introduce a novel concept of opportunity cost, which is defined as the maximum utility loss among users incurred by serving a particular user at the current turn. We obtain each user’s net profit by subtracting the opportunity cost from its expected utility, and then select a user with the maximum profit for service. Simulation results reveal that our scheme supports various QoS classes well that are represented by delay and packet loss under various traffic loadings.     

基于IXP2400的流量控制实现

网络流量控制(TC)是为了保证网络中不同服务的需要,在确保业务可靠性、时延、时延抖动、吞吐量、包丢失率的前提下,充分利用各调度机制对网络中各种业务流的状态所进行的控制。网络处理器平台提供了高效灵活的处理机制,优化了网络包处理。基于Intel IXP2400的平台,通过对IPv4包头中ToS字段的修改及判断,更好地实现了网络流量控制。     

基于邻居信息表的移动IPv6切换研究

分析标准移动IPv6(MIPv6)的快速切换机制,提出一种基于邻居信息表的移动IPv6快速切换解决方案。通过预配置和定时更新的方法使移动节点提前获取将要进入目标有限区域的信息表——邻居信息表,从而缩短切换中过程转交地址唯一性验证时间及移动检测延迟时间,降低切换过程中的丢包率。仿真结果表明,该机制不额外占用网络资源,能够减少切换过程中的丢包率和切换延迟时间。