Greedy pebbling for proof space compression

International Journal on Software Tools for Technology Transfer - Automated reasoning tools for the verification and synthesis of software often produce proofs to allow independent certification of...     

Two dynamic programming algorithms for which interpreted pebbling helps

We consider extensions of one-person and two-person pebble games that take into account the types of the gates of the circuits on which the games are played. A simple relationship is established between the extended games and the corresponding original games. This is useful in showing that the extended games allow more efficient pebbling than the original games on certain natural circuits for problems such as context-free language recognition and transitive closure of directed graphs.     

Bandwidth packing

We model a server that allocates varying amounts of bandwidth to “customers” during service. Customers could be computer jobs with demands for storage bandwidth or they could be calls with demands for transmission bandwidth on a network link. Service times are constants, each normalized to 1 time unit, and the system operates in discrete time, with packing (scheduling) decisions made only at integer times. Demands for bandwidths are for fractions of the total available and are limited to the discrete set {1/k, 2/k, …, 1} wherek is a given parameter. More than one customer can be served at a time, but the total bandwidth allocated to the customers in service must be at most the total available. Customers arrive ink flows and join a queue. Thejth flow has rate λ _j and contains just those customers with bandwidth demandsj/k. We study the performance of the two packing algorithms First Fit and Best Fit, both allocating bandwidth by a greedy rule, the first scanning the queue in arrival order and the second scanning the queue in decreasing order of bandwidth demand. We determine necessary and sufficient conditions for stability of the system under the two packing rules. The average total bandwidth demand of the arrivals in a time slot must be less than 1 for stability under any packing rule, i.e., the condition $$\rho {\text{ : = }}\sum\limits_i {\lambda i\left( {i/k} \right)} {\text{< 1}}$$ must hold. We prove that if the arrival rates λ₁, …, λ _k?1 are symmetric, i.e., λ _i =λ _k?i for alli, 1 ≤i ≤k ? 1, theρ<1 is also sufficient for stability under both rules. Our Best Fit result strengthens an earlier result confined to Poisson flows and equal rates λ₁=…=λ _{k ? 1}, and does so using a far simper proof. Our First Fit result is completely new. The work here extends earlier results on bandwidth packing in multimedia communication systems, on storage allocation in computer systems, and on message transmission along slotted communication channels. It is not surprising thatρ<1 is sufficient under Best Fit, since in a congested system, Best Fit tends to serve two complementary (matched) customers in each time slot, with bandwidth demands beingi/k and (k ? i)/k for somei, 1 ≤i ≤k ? 1. It is not so obvious, however, thatρ<1 is also sufficient under First Fit. Interestingly, when the system becomes congested, First Fit exhibits a “self-organizing” property whereby an ordering of the queue by time of arrival becomes approximately the same as an ordering by decreasing bandwidth demand.     

Efficient pebbling for list traversal synopses with application to program rollback

We show how to support efficient back traversal in a unidirectional list, using small memory and with essentially no slowdown in forward steps. Using O(lgn)$O(lgn)$ memory for a list of size n$n$, the i$i$’th back-step from the farthest point reached so far takes O(lgi)$O(lgi)$ time in the worst case, while the overhead per forward step is at most ?$?$ for arbitrary small constant ?>0$?>0$. An arbitrary sequence of forward and back steps is allowed. A full trade-off between memory usage and time per back-step is presented: k$k$ vs. kn^1/k$k{n}^{1/k}$ and vice versa. Our algorithms are based on a novel pebbling technique which moves pebbles on a virtual binary, or n^1/k$n^{1/k}$-ary, tree that can only be traversed in a pre-order fashion.     

基于RED的带宽分配算法

实现带宽资源的分配对于QoS控制来说是非常重要的。常见的带宽分配算法如WFQ、DRR等分组调度算法存在着诸如计算复杂度高、需在路由器进行每流状态的管理等不足。该文在前人的基础上,提出了一种基于RED的带宽分配算法,避免了上述问题,从而提高了算法的可扩展性。     

HSDPA,更高效地利用带宽

随着范围广泛的全新高速数据服务的不断涌现,人们对用户体验的更高追求导致了对更高带宽的需求,在移动通信领域更是如此。高速下行分组接入(HSDPA)技术是现有W-CDMA系统高成本效益的升级,可以提供媲美当今无线局域网的性能,同时拥有移动性和无所不在的覆盖能力所带来的额外优势     

Internet带宽分配的公平性研究

依据带宽分配的公平性原则可以实现网络资源的合理分配和利用,从而提高网络的服务质量。根据一广域网模型,介绍了带宽分配的最大－最小公平性和比例公平性,并采用效用函数方法设计了一种带宽分配的最优速率迭代算法。     

一种端到端可用带宽的测量方法

重点研究了网络端到端可用带宽的测量方法,分析了IGI和PTR算法的原理和局限性,将算法从单跳模式扩展到多跳网络,利用延时变更的概念,分析了探针包序列间隔变化与背罱流量的关系,以此估计背罱流量,并运用“相等区间”的方法确定最佳测量点,提高了可用带宽测量的准确性。     

Bandwidth compression of noisy images

The effect of additive noise on Discrete Fourier Transform of pictorial data (2DFT) must be considered in several important problems such as filtering, enhancement and bandwidth compression. This paper investigates the statistical properties of the corrupted 2DFT coefficients, and the error involved in reconstruction when a subset of these coefficients is employed for the purpose. The latter being often the case, the present analysis provides a rational basis for frequency selection and filter specification. Application of an F-test quantifies the reliability of filtering or bandwidth compression.     

一种基于多主体的网络带宽分配方案

本文介绍了一种基于多主体在多个用户和网络供应商之间进行自动并实时地进行交互协商达成带宽分配的方案。在此基础上，借鉴近年来对多主体间协作机制的研究，进一步提出了具体的设计方法以及实现的技术细节。最后，探讨了这一方案在应用上的适用特点和局限性。     

带宽整合技术的研究与应用

通信网络中带宽整合的基本原理及其实现机制。分析了网络协议栈不同层带宽整合方案的应用价值。     

Approximating the Bandwidth of Caterpillars

A caterpillar is a tree in which all vertices of degree three or more lie on one path, called the backbone. We present a polynomial time algorithm that produces a linear arrangement of the vertices of a caterpillar with bandwidth at most O(log n/log log n) times the local density of the caterpillar, where the local density is a well known lower bound on the bandwidth. This result is best possible in the sense that there are caterpillars whose bandwidth is larger than their local density by a factor of Ω(log n/log log n). The previous best approximation ratio for the bandwidth of caterpillars was O(log n). We show that any further improvement in the approximation ratio would require using linear arrangements that do not respect the order of the vertices of the backbone. We also show how to obtain a (1+ε) approximation for the bandwidth of caterpillars in time . This result generalizes to trees, planar graphs, and any family of graphs with treewidth .     

DPI带宽管理技术的研究与应用

DPI检测技术是一种基于应用层的流量检测和控制技术,它能深入检查信息包流,准确地识别网络的业务类型,并通过特征库的匹配,有效识别P2P应用。DPI应用识别技术使网络运行变得透明,实现网络的智能化管理,保证网络资源的合理分配。     

自适应带宽均值移动算法及目标跟踪

首先提出了一种经典均值移动算法的推广算法,即自适应带宽均值移动算法,进而提出了基于自适应带宽均值移动的二维视频目标跟踪算法（ABMSOT）.前者提出了在带宽自适应情况下均值移动算法求取局部极值的框架步骤,后者可实时跟踪目标的位置、大小和方向.在ABMSOT算法中,目标模型和候选模型采用自适应带宽核函数加权特征直方图描述,目标模型和候选模型的相似性采用Bhattacharyya系数度量;通过迭代两步法搜索到目标最有可能的位置、大小和方向.第一步执行一次均值移动迭代搜索目标位置,第二步计算出最能描述目标区域大小和方向的带宽矩阵.从理论上证明了两个算法的收敛性,并通过实验证明了ABMSOT算法能实时跟踪目标的位置、大小和方向.     

调频脉冲串相参合成研究与FPGA硬件实现

介绍了利用调频脉冲串合成宽带信号的原理,进行了合成宽带信号的仿真。给出了基于FPGA的调频脉冲串产生的硬件实现电路。利用该电路得到了中频信号的测量波形,通过后处理将3个30MHz带宽的子脉冲合成了等效带宽90MHz的信号。验证了用调频脉冲串合成宽带信号来提高雷达距离分辨率方法的正确性和有效性,及其工程可行性。     

多种网络带宽测量算法及其比较

网络环境的复杂性造成测量网络带宽面临巨大困难。文章对现有的网络带宽测量算法进行了分类介绍,并对各种算法优缺点从滤波算法、时间分辨率、对网络交通影响、隐藏瓶颈、链接的多通道识别、可用带宽测量、带宽变化适用性的角度进行了比较。     

DiffServ网络的拥塞控制和带宽保证

该文对DiffServ网络的拥塞控制和带宽保证的机制进行了分析和综述,包括TCP拥塞控制机制和路由器缓冲管理算法RED及RIO。研究表明DiffServ网络的拥塞控制和带宽保证的影响因素包括RTT、TCP/UDP相互作用等,解决方案包括对TCP拥塞控制机制的改进和对路由器流量调节器的改进。     

局域网带宽测试工具的设计与实现

为了实现负载均衡的性能测试,分析网络参数对网络带宽的影响,开发了基于SOCKET编程的带宽测试工具。该工具能测试出服务器与不同客户端之间的极限带宽、能在客户端将当前带宽用实时曲线的形式表现出来、能对影响带宽的各项网络参数进行手动设置。