一种采用流切割实现报文保序的负载均衡算法

网络链路过载或链路失效时,使用负载均衡技术可以避免网络发生拥塞。负载的分派粒度决定了负载均衡系统的均衡性能。分派粒度越细,均衡效果越理想。基于包水平粒度的负载分派可以实现理想的均衡性能,但是会造成同一TCP业务流中报文乱序;基于流水平的分派可以保证报文不乱序,但均衡效果不理想。提出了按照报文段粒度分派负载的FSLB算法。仿真实验表明,该算法可避免报文乱序并能达到较理想的均衡效果。     

缓冲交叉开关交换结构多播调度算法研究

高性能核心交换设备多播调度受到越来越多的关注·交叉开关结构下的多播调度方案或者性能较差,或者过于复杂,难于应用在高速交换场合·为此,提出一种面向多播的多输入队列缓冲交叉开关体系结构·将多播调度分解为信元分派、输入调度、输出调度3个可分布式并行执行的子问题,并设计了相应的调度算法,降低了算法复杂性·实验结果表明,交叉点缓冲区容量与输入队列数量对多播性能都具有很大的影响·在突发流量到达下,与单多播输入队列的体系结构相比,无论是采用O(1)复杂度的HA-RR-RR还是复杂度更高的调度算法,均能显著提高系统吞吐性能·     

利用直连网络实现可扩展路由器

Internet的迅速发展直接表现为用户流量的迅速增长,这就要求路由器必须提供更大的容量.传统的路由器由线卡和集中式交换网络构成.集中式交换网络只能支持有限的端口数目,而且随着端口数目的增加,调度算法也变得越来越复杂,所以交换网络正成为整个路由器的性能瓶颈.集中式交换网络还是路由器的单一失效点,无法提供令人满意的容错性能.直连网络具有良好的扩展性和容错性.其中,3-D Torus拓扑结构已被成功应用到可扩展路由器的设计当中.但是在实际应用中,3-D Torus结构受到等分带宽的约束,限制了扩展规模.介绍了一种新型的直连网络结构,称为蜂巢式结构.将对蜂巢结构作简单的改动,修改后的拓扑表现出很好的拓扑属性.基于该结构,提出了两类最短路径路由算法.其中,负载均衡的最短路径路由算法较好地利用了直连网络路径多样性的特点,针对均匀随机和Tornado两种类型的流量都表现出较低的分组延时和较高的吞吐量.另就队列长度和单节点调度算法等方面对路由算法的影响进行了讨论.蜂巢结构为可扩展路由器的设计提供了新的选择.     

一种适合于多播和单播的集成调度算法

具有输入队列结构的路由器或交换机内部交换可以工作在线路速率上，适应了高速网络交换的要求，但现有输入队列调度方案将单播和多播流量分开考虑，使用不同的交换结构和调度算法，不适合网络中多播流和单播流并存的实际情况．该文提出一种不区分多播、单播分组，遵循同一入队策略和同一调度规则的集成调度算法EOPF、(Extented Oldest Port First)．仿真实验表明EOPF算法在各种多播和单播负载组成比例下始终保持高吞吐率，并能在全单播流量下达到100％吞吐率，适合于多播、单播混合存在的网络流量。     

具有o(N2)复杂性的输入缓冲队列加权调度算法

Internet核心路由器多采用输入缓冲交换矩阵,研究输入缓冲队列的调度算法十分重要。加权调度算法具有较高的性能,但由于硬件实现困难,因此很少得到应用。提出了一种简单的加权高度算法L2QF,该算法采用串行轮询的思想,根据虚拟输出队列的长度依次为每个输入端口选择一个输出端口。L2QF算法具有LQF算法的性能,但复杂性仅为o(N^2)。由于L2QF是所有LQF算法中复杂性最低的算法,而且以叠代的方式的执行,因此易于硬件实现。     

一种抗突发分布式循环调度算法的设计与分析

输入队列因具有良好的可扩展性而广泛应用于高速交换结构和路由器中，但输入队列需要精心设计调度算法以获取较好的性能．iSLIP算法因其简单性和并行性而得到广泛的研究，但现有的iSLIP（iterative SLIP）算法在突发流量和非均匀流量下的负荷延迟性能较差．本文针对突发业务流，在基于优先级调度算法的思想上，提出了调度决策双重门限的概念，并且根据其设计出双门限循环调度算法-iADT（iterative Algorithm with Dual Thresholds）．仿真结果表明，iADT不仅在均匀流量下是稳定的，在非均匀流量和突发流量下的延迟性能均远好于现有的iSLIP算法．     

时隙间迭代的输入队列交换机Round-Robin调度算法

输入队列因具有良好的可扩展性而广泛应用于高速交换机和路由器中,但输入队列需要精心设计调度算法以获取较好的性能.Round-Robin算法因其简单性和并行性而得到广泛的研究,但现有的Round-Robin算法在突发流量和非均匀流量下的负荷-延迟性能较差.提出了调度决策在时隙间进行迭代的思想,并利用队列长度具有随机性的特点设计了能近似最大匹配的Round-Robin算法--iSLOT.仿真结果表明,iSLOT不仅在均匀流量下是稳定的,在非均匀流量和突发流量下的吞吐率及延迟性能均远好于现有的Round-Robin算法.     

面向控制网络的交换机调度机制研究

针对基于虚拟输出排队的输入队列交换机应用于控制网络所存在的诸多困难,提出了一种新的输入队列交换机结构,并根据新的结构设计了一种基于记录矩阵和需求矩阵的信元传输川页序控制方案,以解决交换机中存在的信元行为及时延的不确定性问题。交换机采用两级调度机制,链接调度提供分级服务,交换调度实现端口匹配,以适应控制网络的流量特征。     

一种支持高速IPv6转发的路由器体系结构FIS

本文提出了一种在交换网络中执行转发操作的路由器体系结构,采用多个低速且具有独立转发和交换功能的转发交换结点FSN,组成多级流水线结构,以流水的方式执行报文转发和交换。本文对FIS中实现IPv6转发的关键技术—IPv6转发表的分解、转发表到FSN结点的映射、IPv6转发引擎的设计及报文调度算法进行了深入的研究,并基于FIS体系结构提出了易于硬件实现的IPv6查找机制和基于Hash老化的报文调度算法,为下一步FIS原型系统的实现提供了切实可行的方案。     

输入缓存Clos网络中分布式正交分路路由算法

提出了一种采用输入缓存MSM结构的Clos网络,该结构适用于高速交换网络。提出了这一结构中的路由算法,该算法采用正交分路的方法来减小网络内部的冲突,引入路由优先级来提高网络内部的链路利用率,使用优先级轮转来均衡网络内部负载。针对这一路由算法,还给出了与之对应的信元调度算法。仿真表明,尽管采用共享缓存的MSM结构内部使用了很高的加速比,但是采用了正交分路的路由算法后,输入缓存MSM结构,可以获得比共享缓存MSM结构更好的时延及吞吐性能,更适合在高速大容量多端口的路由器或交换机中采用。     

Port partitioning and dynamic queueing for IP forwarding

With the increase of internet protocol (IP) packets the performance of routers became an important issue in internet/working. In this paper we examine the matching algorithm in gigabit router which has input queue with virtual output queueing. Dynamic queue scheduling is also proposed to reduce the packet delay and packet loss probability. Port partitioning is employed to reduce the computational burden of the scheduler in a switch which matches the input and output ports for fast packet switching. Each port is divided into two groups such that the matching algorithm is implemented within each pair of groups in parallel. The matching is performed by exchanging the pair of groups at every time slot. Two algorithms, maximal weight matching by port partitioning (MPP) and modified maximal weight matching by port partitioning (MMPP) are presented. In dynamic queue scheduling, a popup decision rule for each delay critical packet is made to reduce both the delay of the delay critical packet and the loss probability of loss critical packet. Computational results show that MMPP has the lowest delay and requires the least buffer size. The throughput is illustrated to be linear to the packet arrival rate, which can be achieved under highly efficient matching algorithm. The dynamic queue scheduling is illustrated to be highly effective when the occupancy of the input buffer is relatively high.Scope and purposeTo cope with the increasing internet traffic, it is necessary to improve the performance of routers. To accelerate the switching from input ports to output in the router partitioning of ports and dynamic queueing are proposed. Input and output ports are partitioned into two groups A/B and a/b, respectively. The matching for the packet switching is performed between group pairs (A, a) and (B, b) in parallel at one time slot and (A, b) and (B, a) at the next time slot. Dynamic queueing is proposed at each input port to reduce the packet delay and packet loss probability by employing the popup decision rule and applying it to each delay critical packet.The partitioning of ports is illustrated to be highly effective in view of delay, required buffer size and throughput. The dynamic queueing also demonstrates good performance when the traffic volume is high.     

基于SSOM的网络流量分类方法

针对目前基于端口号匹配和特征码识别的流量分类方法准确率低、应用范围受限等问题,提出一种基于有监督的自组织映射(SSOM)的网络流量分类方法。该方法使用已标注类别的网络流量训练集,通过改变自组织映射(SOM)训练过程中的权值调整规则,使输出层中获胜神经元的选择更容易,各类别之间划分更清晰,从而提高分类性能。实验结果表明,SSOM的分辨率及拓扑连续性均优于SOM,对网络流量分类具有更高的准确率。     

Synchronous versus asynchronous operation of a packet switch with combined input and output queueing

A single-stage non-blocking N × N packet switch with combined input and output queueing is considere. The limited queueing at the output ports partially resolves output port contention. Overflow at the output queues is prevented by employment of a backpressure mechanism and additional queueing at the input ports. This paper investigates the performance of the switch under two different modes of operation: asynchronous and synchronous or slotted. For the purpose of comparison a switch model is developed. Assuming Poisson packet arrivals, several performance measures are obtained analytically. These include the distribution of the delay through the switch, the input queue length distribution, packet losses at the inputs in the case of finite input queues, and the maximum switch throughput. The results obtained demonstrate a slight performance advantage of asynchronous over synchronous operation. However, the maximum switch throughput is the same for both modes of operation.     

Session level flow classification by packet size distribution and session grouping

Classifying traffic into specific network applications is essential for application-aware network management and it becomes more challenging because modern applications complicate their network behaviors. While port number-based classifiers work only for some well-known applications and signature-based classifiers are not applicable to encrypted packet payloads, researchers tend to classify network traffic based on behaviors observed in network applications. In this paper, a session level flow classification (SLFC) approach is proposed to classify network flows as a session, which comprises of flows in the same conversation. SLFC first classifies flows into the corresponding applications by packet size distribution (PSD) and then groups flows as sessions by port locality. With PSD, each flow is transformed into a set of points in a two-dimension space and the distances between each flow and the representatives of pre-selected applications are computed. The flow is recognized as the application having a minimum distance. Meanwhile, port locality is used to group flows as sessions because an application often uses consecutive port numbers within a session. If flows of a session are classified into different applications, an arbitration algorithm is invoked to make the correction. The evaluation shows that SLFC achieves high accuracy rates on both flow and session classifications, say 99.9% and 99.98%, respectively. When SLFC is applied to online classification, it is able to make decisions quickly by checking at most 300 packets for long-lasting flows. Based on our test data, an average of 72% of packets in long-lasting flows can be skipped without reducing the classification accuracy rates.     

Load-balanced three-stage switch

A load-balanced two-stage switch is scalable and can provide close to 100% throughput. Its major problem is that packets can be mis-sequenced when they arrive at outputs. In a recent work, the packet mis-sequencing problem is elegantly solved by a feedback-based switch architecture. In this paper, we extend the feedback-based switch from two-stage to three-stage for further cutting down average packet delay while still ensuring in-order packet delivery and close to 100% throughput. The basic idea is to use the third stage switch to map heavy flows to experience less middle-stage delays. To identity heavy flows, an adaptive traffic estimation algorithm is proposed. To ensure max-min fairness in bandwidth allocation under any inadmissible traffic pattern, an efficient fair scheduler is devised.     

Marking algorithms for service differentiation of TCP traffic

Class-based service architectures for quality-of-service (QoS) differentiation typically provide loss, throughput, and delay differentiation. However, proposals for class-based service differentiation generally do not account for the needs of TCP traffic, which are characterized by a coupling of packet losses and achievable throughput. Ignoring this coupling may result in poor service differentiation at the microflow level. This paper shows how Explicit Congestion Notification (ECN) can be used to achieve service differentiation for TCP traffic classes at the microflow level. We present a traffic-marking algorithm for routers, which, if used in conjunction with ECN, regulates the transmission rate of TCP sources in such a way that packet drops due to buffer overflows are avoided. We demonstrate how the algorithm can be integrated in a service architecture with absolute and proportional QoS guarantees. Simulation results illustrate the effectiveness of the presented algorithms at avoiding packet losses and regulating traffic for meeting service guarantees, and provide a comparison with other algorithms proposed in the literature.     

An Optimal Lower Bound for Buffer Management in Multi-Queue Switches

In the online packet buffering problem (also known as the unweighted FIFO variant of buffer management), we focus on a single network packet switching device with several input ports and one output port. This device forwards unit-size, unit-value packets from input ports to the output port. Buffers attached to input ports may accumulate incoming packets for later transmission; if they cannot accommodate all incoming packets, their excess is lost. A packet buffering algorithm has to choose from which buffers to transmit packets in order to minimize the number of lost packets and thus maximize the throughput. We present a tight lower bound of e/(e?1)≈1.582 on the competitive ratio of the throughput maximization, which holds even for fractional or randomized algorithms. This improves the previously best known lower bound of 1.4659 and matches the performance of the algorithm Random Schedule. Our result contradicts the claimed performance of the algorithm Random Permutation; we point out a flaw in its original analysis.     

一种选择性丢包机制的分析与设计

随机早期捡测算法(RED)在产生丢包时简单地丢弃到达的数据包，由于Web流占据了网络上75％左右的带宽，而Web流的特点是数据包比较少，这就使得早期丢包的效果难以体现。本文提出一种选择性丢包机制，引进一个类似公平队列的虚队列，检测发遥速率过大的流，筛选出丢包的候选链接，拥塞时丢弃候选链接在队列申的第一个连接的数据包。模拟实验结果表明，与队头丢包相比，采用选择性丢包的RED算法可进一步降低网关的丢包率，提高吞吐率，缩短Http的响应时间，提高队列的稳定性。     

使用多级交换网络进行高性能路由器设计

拓扑结构和路由算法是影响多级交换网络性能的重要因素．在比较多种多级互连拓扑属性的基础上,提出将3D Torus结构应用于大规模交换网络设计．然后针对3D Torus交换网络中报文路由面临的两个关键问题：多路径负载均衡和报文保序,提出一种基于维序的多路径路由算法DMR(dimension-order—based multi—path routing)．该算法可在保证报文顺序的同时在多条路径上平衡负载,提高交换网络吞吐率．最后通过模拟验证了算法的性能,并与维序路由和随机路由算法进行了比较．模拟结果表明,DMR算法的性能优于维序路由算法,能够达到随机路由算法性能水平,同时具有随机路由算法所不具备的报文保序特性．     

一种报文大小可变的TFRC改进算法

基于Internet的实时多媒体数据传输是一种报文发送速率固定,报文大小变化的应用。该文分析了这类应用对TFRC的影响,通过对TFRC协议的扩展,提出了一种支持报文大小可变应用的改进TFRC拥塞控制算法。这种算法在接收方采用了对报文数量进行加权的方法来计算丢失事件率以支持报文大小变化的应用。同时在网络仿真器ns2中实现了这种改进算法。仿真实验表明：这种改进算法能够支持报文大小变化,报文发送速率固定的应用,并且具有TCP友好性,与TCP相比具有较平缓的流量抖动。