异质性网络多媒体通信的多播路由算法

在网络中提供数字化音、视频等实时业务的多媒体多播通信是当前的研究热点。运用分层编码技术,可将信源的媒体信息分成子媒体层进行传输;各信宿可根据用户各自需求或接入网络的限制接收不同编码信息,从而可以满足用户的异质性要求和网络的异质性条件。研究了两种时延、带宽受限低代价的多播路由算法,这些算法充分考虑了异质性网络环境和实时媒体流的时延受限要求,比传统的多点广播算法更适于在异质性网络下的实时通信。     

基于遗传操作的带度约束的多播路由算法

利用SPH和GA这两种算法的优点,提出了一种快速的多播路由树的生成算法,算法使用SPH的基本思想,采用遗传操作而不是遗传算法,克服了已有算法的不足。仿真结果显示,算法性能良好。     

求解有度约束多播路由问题的分布式算法

在应用多播(multicast)时,有效的多播路由是关键.现有的多播路由算法一般假定每个节点都支持multicast,但在实际网络中,某些节点并不支持多播,而为了保证网络速度,需限制进行多播所要复制信息的数量.为此,采用度约束来表示每个节点的多播能力,提出了一种有度约束的分布式多播路由算法.算法的复杂度和所需传递信息的数量都低于已有的同类算法.     

带度约束的最小直径应用层多播路由问题的启发式遗传算法

由于IP多播难以在因特网环境中配置,应用层多播作为IP多播的一种替代方案得到越来越多的研究。从网络设计的角度来看,应用层多播在网络代价模型及路由策略方面与传统的IP多播有很大区别。本文研究了带度约束的最小直径应用层网络多播路由问题,提出了解决该问题的启发式遗传算法。通过大量仿真实验,我们对比分析了两种贪婪算法法和遗传算法的性能。实验显示,启发式遗传算法具有较好的性能。     

网格环境中带度约束的多播资源查找算法

网格计算的前提是资源查找。本文分析研究了几种适应某些网格资源模型的现有资源查找算法及其时间和空间复杂度。针对有多播特征的网格环境中的资源查找,基于多播功能,同时赋予资源节点不同权值,构造带度的多播网格资源模型,提出带度约束的多播资源查找算法。与现有算法相比,此算法能更有效实现多播网格环境中资源的快速查找。     

带度约束的组播路由算法

在多媒体通信网的实际应用中 ,组播 (multicasting)技术日益重要 ,但由于节点处理信息的能力不同 ,有些节点并不具备组播能力 ,同时为保证网络负载平衡 ,有些节点的组播能力应有所限制 ,用节点的度约束来表示每个节点应具备的组播能力 ,研究在网络节点具有不同度约束情况下的组播路由问题 ,提出了一种解决这个问题的简单有效的启发式算法 ,该算法对实验的大多数网络能够找到解     

多约束QoS动态多播路由算法

YAM和QoSMIC是支持QoS动态多播路由算法,允许多播组成员动态地加入/退出,同时为接收方提供多个可选择的多播接入路径,以满足不同应用的QoS需求。该文在分析这些算法的基础上,研讨了具有延迟、延迟抖动、带宽和代价等多约束QoS的多播路由问题,描述了一种适应于研究QoS多播路由的网络模型,提出了一种具有多约束QoS的动态多播路由算法(MQDMR),MQDMR试图有效地减少生成多约束QoS的多播树的开销。在MQDMR中,一个多播组成员能动态地加入/退出一个多播会晤,且不干扰现有的多播树。仿真实验结果表明,MQDMR比YAM和QoSMIC具有较小的延时和较少的代价。     

基于遗传算法的带度约束组播路由算法

本文提出了一种基于遗传算法的带度约束的组播路由算法DCMST_on_GA,算法首先将原图转化为一个动态结构表,然后用一个二维数组表示一棵组播树,遗传操作直接作用在这样的个体上,算法采用比例选择算子和保留最佳个体的策略。本算法编码简洁,有效地解决了遗传算法解决组播树问题的编码和解码的难点,加快了全局搜索速度。     

基于遗传算法的有矢量约束的多播路由计算

针对QoS参数(带宽(bandwidth)、时延(delay)、丢包率(packet loss)等)的多样性，提出了利用遗传算法(GA)解决带有多维约束的多播路由路径的生成算法GAVCMR．该算法把各种约束结合起来，提出了矢量约束的概念；GAVCMR突破了遗传算法(GA)传统观念上的限制，对各种约束参数赋予了更为清晰的实际含义，根据参数的实际物理含义，在进化的不同阶段灵活调整各参数的大小，加快了算法的收敛速度，并在一定程度上避免算法终止在局部最优．在矢量约束下生成的多播树能够适应各种QoS参数的要求，仿真结果证明了算法的有效性．     

基于多QoS约束的多播路由算法研究

论文讨论了具有延迟、带宽和低代价等多QoS约束的多播路由算法,提出了适应于研究QoS多播路由的网络模型,并给出了一种具有多QoS约束的动态多播路由算法,分析了算法的复杂度。仿真实验证明,该算法是稳定有效的。它能够在满足多约束的情况下,使多播树的代价优化。     

一种非完全组播网络中的算法可选组播框架

提出了一种新型实用的算法可选组播框架-FMPN（Flexible Multicasting on Partial-multicast Networks），该框架能够在非完全组播网络中实现组播功能，并且可以根据不同的业务和数据类型采用算法可选的组播机制，以达到系统整体最优的组播传输性能．FMPN有三个主要的特点：（1）算法可选组播机制，根据不同的应用需求来灵活地选择组播算法．并且通过IP隧道使得在路由器不支持的情况下也可以使用组播．（2）数据分类，通过对应用类型与数据的分析来调用合适的组播算法．（3）分层传输为可伸缩性码流提供各自独立的组播信道．实验表明，FMPN多媒体传输的系统整体性能高于当前常用的反向路径组播（RPM）、生成树（SpT）等组播算法，特别适合于实时多媒体应用．     

一种求解度约束最小生成树问题的优化算法

为求解大规模结点度约束最小生成树问题,提出一种带有嫁接和剪接算子操作的优化算法.通过借鉴花草果树种植技术,建立一种以基本遗传算子为基础、带有加速和调节算子作为激励的进化计算体系;嫁接以一种贪婪的思想加速搜索,按收益最大化原则进行剪接.对可能陷入局部极值引起冲突的现象及冲突检测的方法进行分析,并提出了冲突的若干解决方法.针对DCMST问题求解中的复杂性,提出了几种有效的嫁接和剪接的策略,并对算法的收敛性和计算复杂度进行了分析.通过该算法对结点数为50~500之间的Euclidean问题和按均匀随机方式产生的non-Euclidean度约束最小生成树问题进行求解.与现有文献的实验结果对比表明,该方法在求解最好解的精度和收敛速度上均有一定的优势.     

Complexity and Approximations for Multimessage Multicasting

We consider multimessage multicasting over thenprocessor complete (or fully connected) static network (MM_C). First we present a linear time algorithm that constructs for every degreedproblem instance a communication schedule with total communication time at mostd², wheredis the maximum number of messages that each processor may send or receive. Then we present degreedproblem instances such that all their communication schedules have total communication time at leastd². We observe that our lower bound applies when the fan-out (maximum number of processors receiving any given message) is huge, and thus the number of processors is also huge. Since this environment is not likely to arise in the near future, we turn our attention to the study of important subproblems that are likely to arise in practice. We show that when each message has fan-outk=1 theMM_Cproblem corresponds to the makespan openshop preemptive scheduling problem which can be solved in polynomial time and show that fork?2 our problem is NP-complete and remains NP-complete even when forwarding is allowed. We present an algorithm to generate a communication schedule with total communication time 2d−1 for any degreedproblem instance with fan-outk=2. Our main result is anO(q·d·e) time algorithm, wheree?nd(the input length), with an approximation bound ofqd+k^1/q(d−1), for any integerqsuch thatk>q?2. Our algorithms are centralized and require all the communication information ahead of time. Applications where all of this information is readily available include iterative algorithms for solving linear equations, and most dynamic programming procedures. The Meiko CS-2 machine and computer systems with processors communicating via dynamic permutation networks whose basic switches can act as data replicators (e.g.,nbynBenes network with 2 by 2 switches that can also act as data replicators) will also benefit from our results at the expense of doubling the number of communication phases.     

Deadlock-Free Multicasting in Irregular Networks Using Prefix Routing

A deadlock-free multicast scheme called prefix multicasting in irregular networks (i.e., networks with irregular topology) is studied. In prefix routing, a compact routing table is associated with each node (processor). Basically, each outgoing channel of a node is assigned a special label and an outgoing channel is selected if its label is a prefix of the label of the destination node. Node and channel labelling in an irregular network is based on a pre-defined spanning tree which may or may not be minimum. The routing process follows a two-phase process of going up and then down along the spanning tree, with a possible cross channel between two branches of the tree between two phases. It is shown that the proposed routing scheme is deadlock- and livelock-free. The approach is extended to multicasting in which the multicast packet is first forwarded up the tree to the longest common prefix (LCP) of destinations in the multicast. The packet is then treated as a multi-head worm that can split at branches of the spanning tree as the packet is sent down the tree.     

一种精确的支持多播的MIN性能分析模型

使用分析模型对MIN的性能进行预测能够取得较好的精度,效率远高于模拟模型。本文深入分析了MIN交换单元输入端口状态之间的转换关系和相邻端口状态的相关性,对输入端口状态进行了重新定义,使用概率论和排队论的方法建立了一个精确的、支持多播的MIN性能分析模型。本文在端口状态转换中使用了条件概率,更加准确地反映了MIN执行行报文交换的实际操作过程。实验结果显示,使用本模型可以将延迟误差控制在10％以内,具有较高的精度。     

Simple Algorithms for Multimessage Multicasting with Forwarding

We consider multimessage multicasting over the n processor complete (or fully connected) static network when the forwarding of messages is allowed. We present an efficient algorithm that constructs for every degree d problem instance a communication schedule with total communication time at most 2d , where d is the maximum number of messages that each processor may send (or receive). Our algorithm consists of two phases. In the first phase a set of communications are scheduled to be carried out in d time periods in such a way that the resulting problem is a multimessage unicasting problem of degree d . In the second phase we generate a communication schedule for this problem by reducing it to the Makespan Openshop Preemptive Scheduling problem which can be solved in polynomial time. The final schedule is the concatenation of the communication schedules for each of these two phases. For 2 ≤ l ≤ d , we present an algorithm to generate a communication schedule with total communication time at most \lfloor ( 2 - 1/l ) d \rfloor +1 , for problem instances where each processor needs to send messages to at most ld destinations. We also discuss multimessage multicasting for dynamic networks. Received September 22, 1997; revised August 29, 1998.     

基于多路播送的视频会议系统及其实现

该文简要介绍了多路播送的机理,对Windows95平台上基于多路播送的视频会议系统实现的关键技术进行了讨论。