光纤通道区分服务优先级流量的路径分配方法

针对航空电子光纤通道网络通信任务服务要求的不同,对于硬实时偶发、硬实时周期以及软实时任务区分优先级,发展了一种优先考虑高优先级任务的端到端延迟保证路径分配方法。采用共轭网络演算分析得到流量经过级联后的端到端最坏情况延迟上限,并结合优先级得到流量的路径。共轭网络演算使级联服务曲线的min-plus卷积转化成变换域中的加法,简化了端到端服务曲线的计算。最后通过一个实例进行分析验证,说明采用上述方法得到路径分配方案可以使高优先级任务的延迟上界小于不进行区分服务的延迟上界。     

WDM网络中基于负载平衡的动态波长路由算法

在WDM网络中，路由和波长分配（RWA）算法是一个焦点问题．当前的RWA算法多是考虑路径跳数或全网拥塞程度，并没有分析各个链路的具体情况．文中提出一种WDM网络中能实现负载平衡的路由算法——最大波长跳数比值（MWHR）算法。基本思想是：根据各备选路径的跳数和其经过的各链路上的可用波长数信息。计算该路径的优先选取权值，优先选取权值最大的路径．仿真表明，该算法在保证较低的阻塞率情况下，能有效的将业务负载均衡分布在网络中的所有链路上．     

基于模糊流感知的动态优先公平调度算法

为适应网络的动态性,提高调度公平性和资源效率,流感知优先公平调度机制需要动态的多业务区分转发。与链路负载状态相关的模糊流感知能够实现路径上的一致性业务区分,而基于模糊流感知的动态优先公平调度算法通过调整优先队列负载门限在流式流和弹性流之间实现转发优先权的动态交替,在链路轻载时实现不同流间的相对公平调度,在链路重载时则强调实时业务的绝对优先权以保证其时延要求。算法公平性分析和仿真计算显示提出算法的动态区分转发通过适度增加优先业务队长能够大幅度提高弹性流的接纳率,具有较高的链路平均吞吐量和资源效率。     

基于灰色关联的ZigBee网络混合路由算法研究

ZigBee网络混合路由算法(ZigBee Routing,ZBR)中将源目的节点之间的最小跳数作为唯一的路由度量因素。但随着节点能量消耗以及节点的频繁移动,ZBR算法的这一特性会造成网络间歇性连接,从而导致网络性能下降。本文提出一种选择最优分组转发路径的ZigBee网络混合路由算法—GRA-ZBR算法。GRA-ZBR算法在目的节点选择路径时引入灰色关联算法,综合考虑节点剩余能量、链路质量、节点剩余队列长度、以及路径长度等因素。仿真结果表明：GRA-ZBR算法可以有效提高网络分组投递率,降低平均端到端时延。     

Web集群的区分服务与负载均衡策略研究

该文从区分服务和负载均衡两方面研究Web集群系统,设计并实现了一种支持区分服务的负载均衡集群模型,通过系统辨识和资源最优控制,对后端资源统一调度,动态调整每台后端节点不同优先级业务类的资源配额;同时设计了基于业务类的最大空闲节点优先的负载均衡策略以保证各个后端节点同一业务类资源被公平消耗,从而控制端到端延迟,实现比例延迟保证。经实验验证,无论采用轮询调度、最少连接数调度还是最大空闲节点优先的均衡策略,资源最优控制器均能取得良好的区分效果,扩展实验还表明,相对于轮询调度和最少连接数调度,采用最大空闲节点优先的均衡策略,能够使该集群系统在实现比例延迟保证的同时获得最大的性能优化,整体吞吐量提高了25%,平均延迟降低了33%。     

基于快速转发服务机制的端到端延时上界预测研究

以往运用确定性网络演算理论已经得到EF(Expedited Forwarding)流端到端延时上界表达式,它对实际网络的QoS控制起到了重要参考作用,但是这个表达式不够精确,而且只能描述网络状况最坏情况下的延时上界.本文改进了用确定性网络演算得到的EF流端到端延时上界,推导出更精确的延时上界表达式.同时,引入生灭模型,得到EF流端到端延时上界的概率分布表达式,能够描述不同网络状况下的延时上界.相比以往的结果,本文推导出的延时上界概率分布能够更准确地描述延时上界,具有更好的参考价值.     

基于灰色关联的ZigBee网络混合路由算法

ZigBee网络混合路由算法(ZigBee Routing,ZBR)中将源节点和目的节点之间的最小跳数作为唯一的路由度量因素.但随着节点能量消耗以及节点的频繁移动,ZBR算法的这一特性会造成网络间歇性连接,从而导致网络性能下降.提出一种选择最优分组转发路径的ZigBee网络混合路由算法(Grey Relational Algorithm based ZBR,GRA-ZBR).GRA-ZBR算法在目的节点选择路径时引入灰色关联算法,综合考虑节点剩余能量、链路质量、节点剩余队列长度以及路径长度等因素.仿真结果表明,GRA-ZBR算法可以有效提高网络分组投递率,降低平均端到端时延.     

一类基于网络服务品质要求的单播路由算法

本文提出了一类基于网络服务品质QoS（quality of service）要求的单播路由算法。首先,我们给出了基于网络分组调度机制WFQ的延迟和带宽相耦合的分析模型,从而推导出了最佳端到端通信延迟的上界。基于该模型,我们改造了传统最小跳数和最短延迟的两类路由算法以支持实时通信的服务品质要求。此外,我们还给出了两种新的服务品质路由算法,它们是多路径第k条最短延迟路由算法以及组合带宽和跳数（hop counts）的最大能量路由算法。仿真实验结果表明,四种算法尤其是后两种算法在满足用户带宽、延迟服务要求以及增加网络资源使用效率和网络吞吐率等方面各有特色。     

面向路径的无线多跳网络端-端吞吐量分析

基于802.11 DCF机制的无线多跳网络性能深受MAC层的介质访问机制和上层路由机制相互作用的影响.本文面向自组织网络路径,给出了端-端最优吞吐量的模型以及计算其上下界的方法.本文的研究更加注重无线多跳网络的实际特性:分组调度可以任意方式调度,节点的载波侦听范围大于其传输范围.研究发现路径的端到端吞吐量与路径长度、分组发送速率和分组调度策略等因素密切相关.本文还分析了其他因素对端-端带宽的影响程度.本文从面向路径的分析模拟工作中得出的一些独特结论相信将有助于上层应用程序以及路由协议的研究.     

全光网络中动态型波长路由算法的研究

分析了光路径的跳数（H）、拥挤程度（C）以及全网剩余波长总数（FW）对选路的影响,进而提出一种新型的动态波长路由算法。该算法利用网络中剩余资源的数量,动态调节选路策略,将业务分布在最短、负载最小以及剩余波长数和跳数比值最大的路径上;当有效资源减少时,增加最短路径选择的概率;当有效资源增加时,增加小负载路径的选择概率。计算机仿真结果表明,该算法的阻塞率比传统算法FAR和FPLC算法分别降低了19．1％和12．7％。     

Efficient delay based scheduling with fairness in multi-hop wireless mesh networks

Some scheduling algorithms have been designed to improve the performance of multi-hop wireless mesh networks (WMNs) recently. However the end-to-end delay is seldom considered as the complexity of multi-hop topology and open wireless shared channel. This article proposes an efficient delay based scheduling algorithm with the concept of buffer-data- hops. Considering the demand satisfaction factor (DSF), the proposed algorithm can also achieve a good fairness performance. Moreover, with the interference-based network model, the scheduling algorithm can maximize the spatial reuse, compared to those graph-based scheduling algorithms. Detailed theoretical analysis shows that the algorithm can minimize the end-to-end delay and make a fair scheduling to all the links.     

Capacity Optimization in TDMA Ad-Hoc Networks

Many scheduling techniques have been developed to solve the problem of sharing the common channel to multiple stations. TDMA has been increasingly used as a scheduling technique in ad-hoc networks. The current trend for QoS capable applications led to the deployment of numerous routing schemes that use TDMA. These schemes try to solve the problem of distributing the available slots among the wireless nodes and at the same time, to find paths within the network that fulfill some QoS related limitations, such as end-to-end delay. The exact way the slots are distributed among the transmitting nodes has an impact on the end-to-end delay and other performance parameters of the network, such as capacity. Therefore, the efficiency of the scheduling algorithms is closely related to the network topologies. In this paper, we propose two new end-to-end TDMA scheduling algorithms that try to enhance the network capacity by increasing the number of concurrent connections established in the network, without causing additional end-to-end delay. We study the efficiency of the proposed algorithms, when applied on various random topologies, and compare them in terms of end-to-end delay and network capacity.     

Performance Comparison and Analysis of IP and MPLS Networks

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GPRS中分组调度算法

主要讨论通用无线分组业务（GPRS）调度算法。首先介绍了一些常用分组调度算法，给出了GPRS中服务质量（QoS)定义和GPRS中选择分组调度算法原则，并根据对GPRS特性和三种算法性能的分析与比较，提出了一种新的基于延迟约束分组调度算法。通过仿真发现，新算法可在满足延迟要求基础上以较小复杂度获得比其余算法更高的资源利用率。     

Average waiting time assignment. II. The integrated servicesnetwork case

For pt.I see ibid., vol.38, p.2049-51 (Nov. 1990). Priority scheduling as a means of selectively controlling the average delay of the users in a virtual circuit integrated services network is investigated. Specifically, quantifying the end-to-end delay preferences of the users on an individual basis through associated delay cost functions, the selection of the scheduling strategies on the links of the network is formulated as a convex optimization problem whose objective consists of minimizing the overall delay cost. A set of optimality conditions is given for this problem, and two distributed algorithms for solving it are constructed. The first algorithm always converges to an optimal solution, while the second algorithm is approximate. However, the second algorithm requires less coordination than the first, and by appropriately selecting the parameters the solution can be brought as close to optimality as desired. With simple modifications, the algorithms also solve the problem of selecting the scheduling strategies on the links so as to minimize the lexicographic ordering of the cost vector     

Media Synchronization and QoS Packet Scheduling Algorithms for Wireless Systems

Wireless multimedia synchronization is concerned with distributed multimedia packets such as video, audio, text and graphics being played-out onto the mobile clients via a base station (BS) that services the mobile client with the multimedia packets. Our focus is on improving the Quality of Service (QoS) of the mobile client's on-time-arrival of distributed multimedia packets through network multimedia synchronization. We describe a media synchronization scheme for wireless networks, and we investigate the multimedia packet scheduling algorithms at the base station to accomplish our goal. In this paper, we extend the media synchronization algorithm by investigating four packet scheduling algorithms: First-In-First-Out (FIFO), Highest-Priority-First (PQ), Weighted Fair-Queuing (WFQ) and Round-Robin (RR). We analyze the effect of the four packet scheduling algorithms in terms of multimedia packet delivery time and the delay between concurrent multimedia data streams. We show that the play-out of multimedia units on the mobile clients by the base station plays an important role in enhancing the mobile client's quality of service in terms of intra-stream synchronization and inter-stream synchronization. Our results show that the Round-Robin (RR) packet scheduling algorithm is, by far, the best of the four packet scheduling algorithms in terms of mobile client buffer usage. We analyze the four packet scheduling algorithms and make a correlation between play-out of multimedia packets, by the base station, onto the mobile clients and wireless network multimedia synchronization. We clarify the meaning of buffer usage, buffer overflow, buffer underflow, message complexity and multimedia packet delay in terms of synchronization between distributed multimedia servers, base stations and mobile clients.     

Rate-proportional servers: a design methodology for fair queueingalgorithms

Generalized processor sharing (GPS) has been considered as an ideal scheduling discipline based on its end-to-end delay bounds and fairness properties. Until recently, emulation of GPS in a packet server has been regarded as the ideal means of designing a packet-level scheduling algorithm to obtain low delay bounds and bounded unfairness. Strict emulation of GPS, as required in the weighted fair queueing (WFQ) scheduler, however, incurs a time-complexity of O(N) where N is the number of sessions sharing the link. Efforts in the past to simplify the implementation of WFQ, such as self-clocked fair queueing (SCFQ), have resulted in degrading its isolation properties, thus affecting the delay bound. We present a methodology for the design of scheduling algorithms that provide the same end-to-end delay bound as that of WFQ and bounded unfairness without the complexity of GPS emulation. The resulting class of algorithms, called rate-proportional servers (RPSs), are based on isolating scheduler properties that give rise to ideal delay and fairness behavior. Network designers can use this methodology to construct efficient fair-queueing algorithms, balancing their fairness with implementation complexity     

Real-time multimedia scheduling policies for end-to-end delayjitter and loss guarantees across ATM satellite systems

We propose a simple first-in first-out (FIFO)-based service protocol which is appropriate for a multimedia ATM satellite system. The main area of interest is to provide real-time traffic with upper bounds on the end-to-end delay, jitter, and loss experienced at various service queues within a satellite network. Various service protocols, each based on a common underlying strategy, are developed in light of the requirements and limitations imposed at each of the satellite's subsystems. These subsystems include the uplink (UL) earth station (ES) service queue, on-board processing (OBP) queues, and the downlink (DL) ES service queue feeding into a wireline ATM network or directly to an end-user application. Numerous network simulation results demonstrate the tractability, efficiency, and versatility of the underlying service discipline. Key features of our strategy are its algorithmic and architectural simplicity, its non-ad-hoc scheduling approach, and its unified treatment of all real-time streams at all service queues. In addition, the delay and jitter bounds are uncoupled. In this way, end-to-end jitter can be tightly controlled even if medium access requires long indeterminate waiting durations     

基于统计网络演算的端到端时延上界研究

为分析融合网络端到端统计时延性能,根据最小加代数理论中的统计网络演算相关知识,提出了一种改进的统计服务曲线并应用GPS调度系统模型,然后利用网络演算理论求解串型网络节点统计时延上界。数值分析结果表明,改进的调度模型有效改善了自相关特性对时延上界所造成的影响,比未改进的模型相比统计时延上界更具有良好的紧致性,为在融合网络环境中对端到端节点延迟上界研究提供有效控制、调度和管理具有一定的参考价值。     

A new deterministic traffic model for core-stateless scheduling

Core-stateless scheduling algorithms have been proposed in the literature to overcome the scalability problem of the stateful approach. Instead of maintaining per-How information or performing per-packet How classification at core routers, packets are scheduled according to the information (time stamps) carried in their headers. They can hence provision quality of service (QoS) and achieve high scalability. In this paper, which came from our observation that it is more convenient to evaluate a packet's delay in a core-stateless network with reference to its time stamp than to the real time, we propose a new traffic model and derive its properties. Based on this model, a novel time-stamp encoding scheme, which is theoretically proven to be able to minimize the end-to-end worst case delay in a core-stateless network, is presented. With our proposed traffic model, performance analysis in core-stateless networks becomes straightforward.