MUMF-支持单多播公平服务的调度策略

基于联合输入交叉点排队(CICQ,combined input and cross-point queuing)交换结构探讨了单多播混合调度的公平性问题,提出了能够为单多播业务提供混合公平性的CICQ理想调度模型。基于理想调度模型,提出了逼近理想调度模型的MUMF(mixed uni-and multicast fair)调度算法,MUMF调度算法采用了分级和层次化的公平调度机制,通过输入调度和交叉点调度确保单多播业务混合调度的公平性。MUMF交换机制的每个输入、输出端口可独立地进行分组交换,具有良好可扩展特性。最后,基于SPES(switching performance evaluation system)的性能仿真结果表明MUMF调度算法具有良好的时延、公平性和吞吐量性能。     

一种支持扇出分割能力的光组播调度算法研究

组播调度是影响光组播分组交换节点吞吐量的重要因素.针对“一次发送”模型下的光组播调度算法对阻塞的源组播实行全部丢弃的缺点,文章基于节点共享有限波长转换器的光分组交换结构,提出了一种支持扇出分割能力的光组播调度算法,该算法采用随机丢弃阻塞的源组播复制的方法,有效地提高了端口资源的利用率.仿真结果表明,该算法与已有算法相比...     

一种星载CICQ交换机单组播分组调度算法

以缓解联合输入交叉队列(CICQ)交换机分组调度中的组播HOL Blocking问题为目标,同时对因GEO信道问题传输失败而需要重传的分组进行补偿,提出一种新的单组播混合调度算法,即缓解组播头分组阻塞算法RMHB。该算法在交换机尽量工作于Work-Conserving的前提下,尽量缓解组播队列头分组对次分组的阻塞,在单组播分组裁决中,将分组在信道中重传的次数作为考虑的首要因素。目前尚未见到CICQ结构中在考虑GEO卫星信道状态的情况下,进行单组播混合业务分组调度的方法。     

iRGRR/PM：一种新的高速crossbar分组调度策略

iRGRR(iterative Request-Grant-based Round-Robin)算法是一种输入排队crossbar调度算法,具有硬件易实现、可扩展性强、性能优良等优点。在此基础上,该文提出一种新的高速crossbar分组调度策略iRGRR/PM(iRGRR with Packet Mode),可以更好地支持IP分组的调度,能够被应用于高速、大容量的路由器中。与iRGRR算法相比,iRGRR/PM简化了分组输出重组模块的设计,并且提高了crossbar的带宽资源利用率。文中简单分析了两种算法间的分组时延关系,并进行了详尽的仿真研究。结果表明：在相同条件下,iRGRR/PM算法具有更高的吞吐量,尤其在非均匀业务流下能获得接近100%的吞吐量;调度长分组时,iRGRR/PM算法具有更好的时延性能。     

基于TD-HSDPA系统的新型调度算法

通过对TD-HSDPA (TD-SCDMA高速下行分组接入技术)中关键技术的分析,研究了CQI(信道质量信息)的反馈时延对系统性能的影响,分析了信令开销与反馈准确性之间的联系;同时提出了一种基于TD-HSDPA系统的新型调度算法,此算法通过对调度流程和优先级计算方式的改进,能够有效地避免CQI反馈时延对于Node B(基站)快速调度器的调度效率和准确性的影响.通过对系统级仿真结果的分析,证明在系统负载持续增加的情况下,新算法能够有效地保证小区吞吐量和分组业务的延时性能.     

面向可重构服务承载网的分域混合承载组调度研究

传统网络技术体系,网络是封闭的、刚性的,无法满足未来网络大量差异化业务的规模化应用,由此提出了面向服务提供的柔性网络技术体系,该体系将传统网络中的用户业务、网络服务和网络基础设施中的紧耦合关系转变为松耦合关系,通过资源分割构建可重构服务承载网实现对业务的服务质量保证。该文分析了服务承载网映射到交换结构的需求,提出分域调度的思想。通过选择关闭部分交叉节点的方法建立了crossbar交换结构分域模型,实现了分域调度的端口分离。提出了支持可重构服务承载网构建的混合承载组调度(HCGS)算法,推导了承载组内SDRR(Smoothed Deficit Round Robin)调度、单个域内基于时间戳的输入端口调度和交叉节点输出端口调度算法,证明了HCGS具有良好的时延性能和最坏公平指数(WFI)公平性。仿真结果表明：在均匀分布的泊松业务源条件下,分域HCGS算法具有更优的时延性能,可保证业务带宽的公平性。在diagonal非均匀允许流量条件下,该算法的吞吐量可达100%。     

多用户MIMO-OFDMA系统混合业务的跨层分组调度算法

该文提出了一种针对多输入多输出-正交频分多址系统混合业务的跨层分组调度算法。该算法基于物理层的信道状况和媒体接入控制子层用户的排队时延,分别为实时业务用户和非实时业务用户的排队时延构建相应的效用函数,以保障不同业务的服务需求。仿真结果表明:该算法不但能保证实时业务的时延需要,而且能够获得很好的吞吐量,并满足公平性要求。     

一种提高PON承载IPTV鲁棒性的算法研究

结合加权轮询调度(WRR)算法,提出了一种基于IP层的前向纠错框架(FWRR),用来解决OLT端由于阻塞所导致的丢包问题。OPNET仿真结果显示,相比WRR和RR算法,FWRR机制降低了丢包率、时延和抖动,提高了PON承载IPTV组播业务的鲁棒性。     

一种光交换核心节点调度算法研究

光交换核心节点是光交换网络的核心设备,其性能的优劣直接影响网络的吞吐量、时延等重要指标。文章提出一种SWC-MSD(基于波长变换器的多播空分交换)模块的严格无阻塞光交换核心节点,在此基础上提出了三种调度算法,通过数学分析和实验仿真验证了算法的正确性。考察了这种核心节点在有无波长变换以及业务优先级不同的场景下阻塞率的变化情况,结果表明所提出的严格无阻塞光交换核心节点具有较低的阻塞率。     

一种支持HFC网中QoS业务的调度方法

为了在HFC中支持不同QoS的业务,必须仔细研究CMTS的上行业务调度算法。但是在当前最重要的标准 MCNS DOCSIS1.1中,没有规定任何针对 QoS设计的调度算法,而很多文献都是以改进的先到先服务(FCFS)为基础讨论的。该文提出了一种可支持 QoS的调度算法,通过将业务分类,按照不同类型业务的带宽占用动态分配业务的优先级,同时还考虑了回带(piggyback)对网络吞吐量的影响,给出了仿真结果,并针对典型的时延敏感业务IP Telephony提出了改善网络通道利用率的方法。     

Minimizing the Number of Multicast Transmissions in Single-Hop WDM Networks

The problem of minimizing the number of transmissions for a multicast transmission under the condition that the packet delay is minimum in single-hop wavelength division multiplexing (WDM) networks is studied in this paper. This problem is proved to be NP-complete. A heuristic multicast scheduling algorithm is proposed for this problem. Extensive simulations are performed to compare the performance of the proposed heuristic algorithm with two other multicast scheduling algorithms, namely, the greedy and no-partition scheduling algorithms. The greedy algorithm schedules as many destination nodes as possible in the earliest data slot. The no-partition algorithm schedules the destination nodes of a multicast packet to receive the packet in the same data slot without partitioning the multicast transmission into multiple unicast or multicast transmissions. Our simulation results show that (i) an algorithm which partitions a multicast transmission into multiple unicast or multicast transmissions may not always produce lower mean packet delay than the no-partition algorithm when the number of data channels in the system is limited and (ii) the proposed heuristic algorithm always produces lower mean packet delay than the greedy and the no-partition algorithms because this algorithm not only partitions a multicast transmission into multiple unicast or multicast transmissions to keep the packet delay low but also reduces the number of transmissions to conserve resources.     

Scheduling Combined Unicast and Multicast Traffic in Broadcast WDM Networks

This paper studies the performance of various strategies for scheduling a combined load of unicast and multicast traffic in a broadcast WDM network. The performance measure of interest is schedule length, which directly affects both aggregate network throughput and average packet delay. Three different scheduling strategies are presented, namely: separate scheduling of unicast and multicast traffic, treating multicast traffic as a number of unicast messages, and treating unicast traffic as multicasts of size one. A lower bound on the schedule length for each strategy is first obtained. Subsequently, the strategies are compared against each other using extensive simulation experiments in order to establish the regions of operation, in terms of a number of relevant system parameters, for which each strategy performs best. Our main conclusions are as follows. Multicast traffic can be treated as unicast traffic, by replicating all multicast packets, under very limited circumstances. On the other hand, treating unicast traffic as a special case of multicast traffic with a group of size 1, produces short schedules in most cases. Alternatively, scheduling and transmitting each traffic component separately is also a good choice.     

A high-performance input access scheme for ATM multicast switching

In this paper, we propose an input access scheme for input-queued ATM multicast switches, achieving high system throughput, low packet delay and packet loss probability. Multicast and unicast packets of each input port are separately queued. Multicast queues take priority over the unicast queues, and both types of queues are fairly served in a cyclic-priority access discipline. In particular, each unicast queue is handled on a window-service basis, and each multicast packet is switched in a one-shot scheduling manner. To evaluate the performance of the access scheme, we propose an approximate analysis based on a simplified cyclic-priority model for anN×N finite-buffer multicast switch possessing Bernoulli multicast and unicast arrivals, with window-service (for unicasting) and one-shot scheduling (for multicasting) both taken into account. Finally, we show simulation results to demonstrate the accuracy of the approximate analysis and the superiority of the scheme over existing schemes with respect to normalized system throughput, mean packet delay, and packet loss probability.An earlier version of this paper appeared in IEEE ICC'96.     

Priority differentiated multicast flow scheduling method in Ceph cloud storage network

In order to solve the problem that existing flow scheduling method is difficult to meet the different multicast scheduling requirements of multi-service flows in the Ceph cloud storage network,a service priority-based multicast flow scheduling method was tailored.First,the network status was obtained via software defined network (SDN) to support flow scheduling.Then,a multicast task was decomposed into multiple attribute decision problems for multiple unicast path selection,and a method of unicast path selection based on technique for order preference by similarity to ideal solution (TOPSIS) was proposed.The unicast path selection method was used to find the optimal unicast path set for the service flow based on the flow’s network performance requirements.Then,the multicast distribution node was determined by the maximum common sub-path among the optimal unicast path sets for construct a multicast transmission path.The experiment results show that the proposed method can reduce the transmission delay of high priority flows while reduce the redundant traffic and better balance the traffic loads compared with the existing methods.     

Designs of high-performance multicast scheduling mechanisms in WDM networks

In this article, we propose three multicast scheduling mechanisms, lookback queue access, lookback ratio access, and double check head access, for the employment in the single-star Wavelength Division Multiplexing optical network. Each of the proposed scheduling schemes consists of two phases and is executed in real time. In general, the first phase is to search for a candidate multicast packet that can be sent, without partition, to all of its intended recipients. If phase 1 fails, the second phase is then activated to partition a multicast packet into multiple transmissions in accordance with specific criteria of each individual mechanism. These algorithms are designed to mitigate the head-of-line blocking effect, while at the same time achieving excellent network throughput levels and delay performance via the partitioning procedure. Performance results reveal the distinct features of each mechanism under various scenarios. For a wider range of networking environments, we further propose an interconnected dual-star structure and enhanced multicast scheduling algorithms. These enhanced schemes aim to exploit the inter-data channels efficiently and utilize the wavelength reuse property of the intra-data channels properly. Performance results have demonstrated the merits of deploying the proposed multicast algorithms in such a dual-star structure.     

面向可重构基础网络的部分扇出组播交换阻塞率模型

传统网络采用调度前复制和扇出拷贝方式的多播交换模型不具备大规模可扩展能力。面向可重构基础网络,提出了一种部分扇出多播交换模型,该模型采用2×2布尔单元和布尔群组集线器建立基本交换结构,采用部分扇出拷贝方式和四状态分割编码实现自路由路径选择,进而推导了该模型在单多播混合业务源输入下的单播阻塞率、多播阻塞率和多播扇出率迭代过程。仿真实验表明:该模型在Bernoulli均匀业务源条件下,单播归一化负载强度为0.2时,多播阻塞率在10 10～10 2之间,多播时延总小于百纳秒量级上限,能够为到达业务提供时延上限保障。     

V2V系统中半静态资源分配算法的研究

本文主要研究在城镇场景中,基于LTE的V2V通信系统在通信过程中的资源分配算法,搭建了系统级LTE-based V2V仿真平台,对V2V系统资源分配算法进行研究。同时对比动态调度算法,主要提出了基于单播、多播的半静态调度算法。仿真结果表明,在单播和多播下的半静态资源分配算法具有资源利用率高,系统吞吐量大等优点。     

Priority-based grant-aware scheduling for low-latency switching

This paper introduces new scheduling algorithms supporting low-latency switching. The proposed grant-aware (GA) algorithm improves the average delay performance by using the grant information of previous iteration. The simulation result shows that the average delay of GA algorithm is about one-tenth of the existing algorithm in high-load condition. We also introduce two priority-based scheduling algorithms grant-aware and priority-aware (GAPA) algorithm and cyclic scheduling with the longest-queue-first (C-LQF) algorithm. In the priority-based scheduling, the scheduling priority of VoQ is determined based on its queue size. GAPA and C-LQF consider the priority only after the first iteration to prevent the starvation problem. The simulation result shows that GAPA and C-LQF scheduling achieves better performance than GA in terms of average delay, maximum delay, and hotspot throughput.     

Performance analysis of bandwidth requests under unicast, multicast and broadcast pollings in IEEE 802.16d/e

In the polling mode in IEEE 802.16d/e, one of three modes: unicast, multicast and broadcast pollings, is used to reserve bandwidth for data transmission. In the unicast polling, the BS polls each individual MS to allow to transmit a bandwidth request packet, while in the multicast and broadcast pollings, the truncated binary exponential backoff (TBEB) mechanism is adopted as a contention resolution among mobile stations (MSs) in a multicast or broadcast group. This paper investigates the delay of bandwidth requests in the unicast, multicast and broadcast pollings, by deriving the delay distribution of the unicast polling and the TBEB by means of analytical methods. We consider an error-free channel as well as an error-prone channel with i.i.d. constant packet error rate per frame. Furthermore, we find the utilization of transmission opportunity to see efficiency of the bandwidth in the TBEB. Performance evaluations are provided to show that analytical results are well-matched with simulations. By the numerical results, we can find the optimal parameters such as the initial backoff window size of the TBEB and the number of transmission opportunities (or slots) satisfying quality of service (QoS) requirement on delay and loss, and thus we can determine which scheme is better than others depending on the probability of a request arrival during one frame. Numerical examples address that the TBEB performs better than the unicast polling for light traffic loads and vice versa for heavy traffic loads. Also, it is shown that the multicast polling has better performance than the broadcast polling in the sense of shorter delay, lower loss probability and higher utilization of transmission opportunity.     

Design of multicast delivery for providing VCR functionality ininteractive video-on-demand systems

Multicast delivery is one of the solutions to reduce the cost in a large video-on-demand (VoD) system. However, multicast transmission makes much more difficult the implementation of interactive functions for individual users and introduces start-up delays for the users, which contradicts the idea of on-demand services. In this paper, we first try to explore and evaluate the performance of different multicast VoD systems. A new scheme called single-rate multicast double-rate unicast (SRMDRU) is then developed to minimize the system resources for supporting full VCR functionality in a multicast VoD system. This scheme also allows multicast systems to support true VoD services so customers can be served as soon as the system receives the requests. Computer simulations show that the multicast systems using the SRMDRU scheme perform much better than other multicast systems in terms of system blocking probabilities