一种公平服务的动态轮询调度算法

调度策略是核心路由交换设备性能的重要保证.针对联合输入交叉节点排队(combined input and cross-point queuing,简称CICQ)交换结构现有调度策略在复杂度或性能方面存在的缺陷,深入探讨了CICQ交换结构调度策略设计的基本准则,并提出了CICQ下虚拟通道的概念.基于基本准则和虚拟通道概念,提出一种简单、高效和公平服务的动态轮询调度策略——FDR(fair service and dynamic round robin).其算法复杂度为O(1),具有良好的可扩展性;并依据虚拟通道的状态为其分配调度份额,具有良好的动态实时性能,能够适应流量负载非均衡的网络环境.SPES(switching performance evaluation systcm)仿真结果表明,该算法具有良好的时延、吞吐量和抗突发性能.     

混合优化的CICQ交换结构调度算法

联合输入端和交叉点排队（CICQ）的Crossbar是一种性能优于传统结构的交换结构,对CICQ交换结构的特点进行了讨论并提出一种新的混合优化调度（HOPS）算法,算法在输入端调度时采取混合优化的策略,首先尽力保证系统的吞吐率性能,然后根据长队列优先的原则优化系统的时延性能。算法以轮询调度为基础,最多只在输入端进行一次比较操作,其算法复杂度仅为O(1),实现简单。通过流体模型证明该算法对满足强大数定律的许可输入流量能够达到100%的吞吐率性能。仿真结果进一步表明HOPS调度算法在各种流量模型下都能稳定运行,且具有良好的时延和吞吐率性能。     

在CICQ交换结构下实现分布式的输入排队DRR分组公平调度

传统的基于crossbar的输入排队交换结构在提供良好的QoS方面存在很大的不足,而CICQ(combined input and crosspoint buffered queuing)交换结构与传统的交换结构比,不但能在各种输入流下提供接近输出排队的吞吐率,而且能提供良好的QoS支持。基于CICQ结构,提出了在输入排队条件下实现基于流的分布式DRR分组公平调度算法的方案,并通过仿真验证了这一方案的有效性。     

CICQ交换机中一类服务可保障的调度策略研究

具备QoS保障能力的快速调度算法是高速交换机的首选.基于EPFTS(Ethernet-oriented physical frame timeslot switching)和CICQ(combined input-crosspoint-queued)交换技术的特点,提出了一类新的调度策略——TRWFS(timeslot reservation weighted fair scheduling).为确保各端口对上保障业务的预留带宽,TRWFS以各端口对上保障业务预留时槽数为调度权重,以优先调度保障业务和平衡各保障业务的盈余时槽(surplus timeslot,定义为现实系统和理想系统之间的服务差额)为业务调度准则.基于该调度策略进一步提出了两种实现算法——TRWFS_Ⅰ和TRWFS_Ⅱ,总体上使实现TRWFS的时间复杂度降至O(1).性能分析和仿真实验结果均表明两种调度算法都达到了服务保障的设计目标,仿真实验结果还表明CICQ排队方式下与其他调度算法相比,TRWFS和轮询调度综合的调度机制具有交叉缓存容量要求更低的优点.     

高性能交换与调度仿真平台的设计与实现

仿真实验已成为交换结构和调度策略性能评价的重要手段,而目前存在的交换结构与调度策略的仿真软件在可继承性与可扩展性方面还存在缺陷.基于Crossbar交换结构,建立数学模型,引入系统级设计方法,采用面向对象技术,设计并实现了用于研究交换结构和调度策略的仿真平台——SPES(switching performance evaluation system).该平台集成了输入排队、输出排队、联合输入输出排队、联合输入交叉点排队等多种交换结构以及相应调度策略.设计上实现了业务流、交换结构和调度策略三者之间的分离,具有良好的可继承、可扩展特性.用户通过与仿真平台之间的简单交互,完成模块的添加与仿真环境参数的配置,在支持变长业务、区分服务质量模型和多交换平面仿真方面具有良好的特性.通过简单扩展。该平台还可以实现网络级性能仿真.最后给出了基于该平台,在CICQ(combined input and crosspoint queuing)交换结构下,对所提出的支持DiffServ模型的分布式调度策略DS(DiffServ supporting algorithm)在不同业务流模型下的性能测试结果,并与输入、输出排队交换结构进行了比较,展示了DS良好的性能,验证了仿真平台的合理性.     

卫星CICQ交换系统调度算法研究

联合输入交叉点排队(CICQ)交换结构由于在交叉点引入少量缓存,可以将输入端口和输出端口进行有效隔离,降低调度算法的复杂度,并适用于大容量交换。为此,研究基于交叉点缓存的各种调度算法和基于CICQ的交换结构,提出一种基于流量控制的FCSA算法,通过OPNET仿真分析表明该算法在均匀分布和突发业务源的情况下具有较好的时延性能,并且复杂度低,吞吐量大。将该算法应用于星载交换机,结果表明,该算法可以满足星载交换机多业务突发传输的特点,易于硬件实施。     

一种支持DiffServ模型的全分布式调度算法

调度算法设计对于网络路由设备实现区分服务(DiffServ)模型的单跳行为(per hop behavior,简称PHB)至关重要.现有支持DiffServ模型的调度算法普遍基于输出排队(output queued,简称OQ)或是输入排队(input queued,简称IQ)交换结构进行设计,均无法在高速环境下提供高性能的调度.基于联合输入/交叉节点排队(combinedinput-crosspoint-queued,简称CICQ)交换结构提出一种支持DiffServ模型的全分布式调度算法DDSS (distributed DiffServ supporting scheduling),并通过理论分析对其公平性进行了验证.DDSS算法采用基于预约带宽的逐级流量控制机制实现所有预约带宽在快速转发(expedited forwarding,简称EF)业务与确保转发(assured forwarding,简称AF)业务之间的分配,采用优先级调度机制为EF业务提供低延迟服务,算法复杂度为O(log N).仿真结果表明,DDSS算法具有良好的时延性能和公平特性,与现有算法相比,能够更好地支持DiffServ模型.     

在CICQ交换结构下PGPS调度算法的实现

基于CICQ结构提出了在输入排队结构下实现基于流的PGPS分组公平调度算法的方案,该结构在可管理的输入流下可提供接近100％的吞吐率。     

CICQ的高性能LQF_DRR调度算法

通过研究4种经典的CICQ调度算法,提出一种高性能的LQF_DRR交换调度算法。该算法在输入端采用最长队列优先调度策略,在输出端采用DRR调度机制,通过输入端与输出端的相互配合,优先服务异常队列,以减小交换结构输入端长队列对算法性能的影响。仿真结果证明该算法在各种流量下都有良好的时延性能和稳定性。     

基于交叉点缓存状态的CICQ调度算法

针对现有的联合输入交叉点排队(CICQ)调度算法在设计时未充分利用交叉点缓存状态信息的问题,提出一种CICQ状态堆调度算法。该算法分布式地运行于CICQ结构的各个输入端口和输出端口。仿真结果表明,在均匀或非均匀流量模型下,基于该算法的CICQ结构都能获得与输出排队结构相当的性能,且具有较高的时延。     

Achieving fair service with a hybrid scheduling scheme for CICQ switches

Providing performance guarantees for arriving traffic flows has become an important measure for today’s routing and switching systems. However, none of current scheduling algorithms built on CICQ (combined input and cross-point buffered) switches can provide flow level performance guarantees. Aiming at meeting this requirement, the feasibility of implementing flow level scheduling is discussed thoroughly. Then, based on the discussion, it comes up with a hybrid and stratified fair scheduling (HSFS) scheme, which is hierarchical and hybrid, for CICQ switches. With HSFS, each input port and output port can schedule variable length packets independently with a complexity of O(1). Theoretical analysis show that HSFS can provide delay bound, service rate and fair performance guarantees without speedup. Finally, we implement HSFS in SPES (switch performance evaluation system) to verify the analytical results.     

一种支持DiffServ模型的CICQ调度策略

结合大规模接入汇聚路由器需要对不同汇聚业务流进行不同的处理这一实际需求，基于CICQ交换结构，该文给出了一种支持DiffServ模型的调度策略(DS)，该算法以“节点行为”方式对业务流进行调度。和以往算法相比，DS采取了分布式的控制策略，并且具有较低的时间复杂度，工程上更易实现。仿真结果表明，DS不仅能够为EF和AF业务提供带宽保证，而且具有良好的时延性能。     

On the Integration of Unicast and Multicast Cell Scheduling in Buffered Crossbar Switches

Internet traffic is a mixture of unicast and multicast flows. Integrated schedulers capable of dealing with both traffic types have been designed mainly for Input Queued (IQ) buffer-less crossbar switches. Combined Input and crossbar queued (CICQ) switches, on the other hand, are known to have better performance than their buffer-less predecessors due to their potential in simplifying the scheduling and improving the switching performance. The design of integrated schedulers in CICQ switches has thus far been neglected. In this paper, we propose a novel CICQ architecture that supports both unicast and multicast traffic along with its appropriate scheduling. In particular, we propose an integrated round-robin-based scheduler that efficiently services both unicast and multicast traffic simultaneously. Our scheme, named multicast and unicast round robin scheduling (MURS), has been shown to outperform all existing schemes under various traffic patterns. Simulation results suggested that we can trade the size of the internal buffers for the number of input multicast queues. We further propose a hardware implementation of our algorithm for a 16 times 16 buffered crossbar switch. The implementation results suggest that MURS can run at 20 Gbps line rate and a clock cycle time of 2.8 ns, reaching an aggregate switching bandwidth of 320 Gbps.     

CICQ交换的流控实现机制和交叉点缓存容量分析

传统的基于crossbar的输入排队交换结构在提供良好的QOS方面存在很大的不足，而CICQ（combined input and crosspoint buffered queuing）交换结构与传统的交换结构相比，不但能在各种输入流下提供接近输出排队的吞吐率，而且能提供良好的QoS支持。文章分析了CICQ结构的流控实现机制，讨论了基于信用的流控机制的开销和实现方案，对crosspoint缓存容鼍作了分析，给出了在各种存储器写入条件下，保持交换结构100％吞吐率所需的最小缓存容量。     

Bandwidth guaranteed multicast scheduling for virtual output queued packet switches

Multicast enables efficient data transmission from one source to multiple destinations, and has been playing an important role in Internet multimedia applications. Although several multicast scheduling schemes for packet switches have been proposed in the literature, they usually aim to achieve only short multicast latency and high throughput without considering bandwidth guarantees. However, fair bandwidth allocation is critical for the quality of service (QoS) of the network, and is necessary to support multicast applications requiring guaranteed performance services, such as online audio and video streaming. This paper addresses the issue of bandwidth guaranteed multicast scheduling on virtual output queued (VOQ) switches. We propose the Credit based Multicast Fair scheduling (CMF) algorithm, which aims at achieving not only short multicast latency but also fair bandwidth allocation. CMF uses a credit based strategy to guarantee the reserved bandwidth of an input port on each output port of the switch. It keeps track of the difference between the reserved bandwidth and actually received bandwidth, and minimizes the difference to ensure fairness. Moreover, in order to fully utilize the multicast capability provided by the switch, CMF lets a multicast packet simultaneously send transmission requests to multiple output ports. In this way, a multicast packet has more chances to be delivered to multiple destination output ports in the same time slot and thus to achieve short multicast latency. Extensive simulations are conducted to evaluate the performance of CMF, and the results demonstrate that CMF achieves the two design goals: fair bandwidth allocation and short multicast latency.     

基于CICQ的动态重路由交换机制

针对现有路由交换机制存在计算复杂度过高以及端口争用问题,提出基于联合输入交叉节点排队交换结构的动态重路由交换机制。该机制依据互联网在路由拓扑层的路径多样化特点,在转发层为每个分组维护多个可选输出端口,并根据交换系统拥塞度实施分组动态重路由,从而实现网络流量的实时动态均衡。仿真结果表明,以该机制为构件的网络交换系统能获得良好的性能保障。