网络计算机上的点优势询问算法

给出了在二维网格计算机上平面点集的的点优势询问算法，并分析了算法的正确性和时间复杂性。     

关于32维Barnes—Wall格的有效译码算法

本文给出了３２维Ｂａｒｎｅｓ－Ｗａｌｌ格的一个有效的译码算法，该算法将这个格的译码问题率为在ＲＭ（２，５）＝（３２，１６，８）码的修正赋权格子图上求最短路径的问题，该算法在最坏情况下的译码时间复杂性为２２７８３次二元运算，小于Ｆｏｒｎｅｙ给出算法的最坏时间复杂性，此外，该算法结构简单易于实现。     

关于32维Barnes-Wal格的有效译码算法

本文给出了３２维Ｂａｒｎｅｓ－Ｗａｌ格的一个有效的译码算法，该算法将这个格的译码问题转化为在ＲＭ（２，５）＝（３２，１６，８）码的修正赋权格子图上求最短路径的问题，该算法在最坏情况下的译码时间复杂性为２２７８３次二元运算，小于Ｆｏｒｎｅｙ给出算法的最坏时间复杂性。此外，该算法结构简单易于实现     

一个高效的匹配协议

比较两个秘密整数是否相等这类协议称为匹配协议。目前这样的协议要么效率极低，要么不能抗击字典攻击。本文给出了一个新的匹配协议，该协议是语义安全的，不存在概率多项式时间算法区分对两个输入的猜测值。协议是高效的，可以比较两个大整数是否相等，计算复杂性和通信复杂性都为D(1)，可以验证参与者是否诚实。该协议可以用于口令认证、电子彩票、可证实加密等安全协议设计。     

一种改进的椭圆曲线算法及在电子商务中的应用

椭圆曲线公钥密码体制(ECC)具有最高的位安全强度。文章分析了ECC的优势，讨论了椭圆曲线的数学基础和离散对数问题的复杂性，并对现有的ECC数字签名算法(ECDSA)进行了改进，进一步加快了运算速度，缩短了数据传输的时间。将改进的椭圆曲线密码体制应用在电子商务中实现数字签名，取得了较好的效果。     

Golay码的快速译码

本文利用Ｇｏｌａｙ码的代数结构给出了二元（２３，１２，７）Ｇｏｌａｙ码及三元（１１，６，５）Ｇｏｌａｙ码新的译码算法。对于二元Ｇｏｌａｙ码，所提的算法的最坏时间复杂性为５３４次ｍｏｄ２加法，比已知的同类译码算法的时间复杂性都小；平均时间复杂性为２２４次ｍｏｄ２加法，比目前已知的最快的译码算法的平均时间复杂性２７９次ｍｏｄ２加法还要小。对于三元Ｇｏｌａｙ码，所提算法的最坏时间复杂性为１２３次ｍｏｄ３加法，平均时间复杂性为８５次ｍｏｄ３加法，比同类的算法都快。此外，这里给出的算法结构简单，易于实现。     

10轮3D分组密码算法的中间相遇攻击

3D密码算法是一个代换-置换网络(SPN)型结构的新分组密码。与美国高级加密标准(AES)不同的是3D密码算法采用3维状态形式。该文利用3D算法结构,构造出一个5轮中间相遇区分器,并由此给出10轮3D的新攻击。结果表明:新攻击的数据复杂度约为2128选择明文,时间复杂度约为2331.1次10轮3D加密。与已有的攻击结构相比较,新攻击有效地降低了攻击所需的数据复杂度以及时间复杂度。     

网格计算机上的凸多边形交算法

文中给出了二维网格结构的计算机上求平面上的两个凸多边形交的一个算法，并分析了算法的正确性和时间复杂性。     

基于DWR—OBS网络服务质量的研究

本文讨论了基于动态波长路由技术的光突发交换网络(DWR-OBS)中业务服务质量的关键技术,从传输时延和数据包的丢失率两个方面对DWR-OBS网的QoS进行分析,给出了数据传输时延和边缘节点的缓存容量之间定量的数学关系,详细分析了一种新的动态首选波长集(D-PWS)资源预留算法,给出了基于D-PWS预留算法的完全候选路径集(E-CPS)业务信道分配方案,用以控制DWR-OBS网络中各优先级业务的丢失率。使用OPNET Modeler对DWR-OBS网络进行仿真,并且讨论仿真结果。     

SAT问题中隐蔽集求解的改进

隐蔽集(backdoor sets)作为隐藏结构的一种,能有效地提高难求解问题的求解效率,近年来成为人们研究的热点.隐蔽集中变量的赋值能有效减少SAT问题求解的搜索分支,从而减少问题求解的时间复杂度和空间复杂度.为提高SAT问题的求解效率,提出一种求解SAT问题隐蔽集的改进算法,并给出最小隐蔽集的定义.在该算法中加入启发式,使求解出的隐蔽集变量个数较少,最后给出隐蔽集问题的总结和展望.     

A Cooperative Peer-to-Peer Repair Scheme Based on Hybrid Network Coding

Cooperative peer-to-peer (P2P) repair (CPR) is an efficient way to recover the lost packets in wireless multicast system. Using network coding in CPR can further improve the transmission efficiency. However, there will be high computational overhead for random linear network coding and high optimization complexity for XOR-based network coding when the number of multicast data packet is relatively large. With regard to this problem, we propose a hybrid network coding based cooperative P2P repair scheme (HNC-CPR) with two efficient and light-weight scheduling algorithms. The HNC-CPR scheme can reduce the computational complexity while ensuring high transmission efficiency. Finally, example analyses and simulations demonstrate the efficiency and low-complexity of HNC-CPR.     

Improved heuristics for multicast routing in wireless mesh networks

Multicast is a communication technique that allows a source to transmit data to a set of recipients in an efficient manner. Therefore, the primary objective of a multicast routing protocol would be to minimize number of transmissions to conserve bandwidth. The problem of computing multicast trees with minimal bandwidth consumption is similar to Steiner tree problem and has shown to be NP-complete. So, heuristic based algorithms are suitable to approximate such bandwidth optimal trees. This paper proposes a multicast routing protocol based on minimum number of transmission trees using an heuristic approach. The simulation results show that the proposed algorithm offers better performance over existing protocols, even in the worst-case scenario when the set of multicast receivers are sparsely distributed across the network.     

Multipath routing for video delivery over bandwidth-limited networks

The delivery of quality video service often requires high bandwidth with low delay or cost in network transmission. Current routing protocols such as those used in the Internet are mainly based on the single-path approach (e.g., the shortest-path routing). This approach cannot meet the end-to-end bandwidth requirement when the video is streamed over bandwidth-limited networks. In order to overcome this limitation, we propose multipath routing, where the video takes multiple paths to reach its destination(s), thereby increasing the aggregate throughput. We consider both unicast (point-to-point) and multicast scenarios. For unicast, we present an efficient multipath heuristic (of complexity O(|V|/sup 3/)), which achieves high bandwidth with low delay. Given a set of path lengths, we then present and prove a simple data scheduling algorithm as implemented at the server, which achieves the theoretical minimum end-to-end delay. For a network with unit-capacity links, the algorithm, when combined with disjoint-path routing, offers an exact and efficient solution to meet a bandwidth requirement with minimum delay. For multicast, we study the construction of multiple trees for layered video to satisfy the user bandwidth requirements. We propose two efficient heuristics on how such trees can be constructed so as to minimize the cost of their aggregation subject to a delay constraint.     

加权的基于多播节点的多播路由算法

在许多多播应用中,降低多播树网络费用非常重要.本文提出了加权的基于多播节点的多播路由算法（WDDMC算法）.由于改变了DDMC（Destination-Driven routing for low-cost Multicast ）算法中的指示函数,适当降低了多播节点作为中间节点的优先级,提高非多播节点作为中间节点的优先级,从而使得多播树更接近最小Steiner树.在随机网络上的仿真结果表明,WDDMC算法的多播树网络费用优于DDMC算法.该算法的复杂度与DDMC算法完全相同.     

多播路由算法MPH的时间复杂度研究

多播通信是从一个源点同时向网络中的多个成员发送分组的通信服务,一个最小代价的多播路由算法是NP完全的,在时间敏感的应用中其运行时间是一个关键问题.MPH(Minimum Path Cost Heuristic)算法是一个著名的启发式最小代价多播路由算法,本文对该算法进行了理论分析和证明,并做了广泛的仿真实验,结果表明其时间复杂度是O(m²n)而不是过去文献中所给出的O(m²n+e).     

Subgrouping‐based multicast transmission over high‐throughput satellite systems with beam cooperation

This paper investigates the multicast transmission for multicast services in high‐throughput satellite (HTS) systems. Considering the multibeam multicast feature of HTSs, cooperative transmission among beams is involved in to improve the efficiency of the multicast transmission. Since the multicast transmission rate depends on the worst user channel state, all the users experience an unreasonably low rate. In this situation, subgrouping techniques are employed to increase transmission rates of users. A subgrouping‐based multicast transmission problem aiming at maximizing the lowest transmission rate of the users is studied to guarantee fairness among users. We formulate the problem as a max–min optimization problem and propose two low‐complex subgrouping algorithms for this problem. Additionally, we also consider multicasting in a single beam and devise a two‐layer transmission scheme for it. In the performance evaluation part, besides the impact of parameters on subgrouping performance, we analyze the performance and the computational complexity of the proposed algorithms. The results indicate that the two subgrouping algorithms can achieve favorable performance with low complexity.     

Efficient routing and wavelength assignment for multicast in WDMnetworks

The next generation multimedia applications such as video conferencing and HDTV have raised tremendous challenges on the network design, both in bandwidth and service. As wavelength-division-multiplexing (WDM) networks have emerged as a promising candidate for future networks with large bandwidth, supporting efficient multicast in WDM networks becomes eminent. Different from the IP layer, the cost of multicast at the WDM layer involves not only bandwidth (wavelength) cost, but also wavelength conversion cost and light splitting cost. It is well known that the optimal multicast problem in WDM networks is NP-hard. In this paper, we develop an efficient approximation algorithm consisting of two separate but integrated steps: multicast routing and wavelength assignment. We prove that the problem of optimal wavelength assignment on a multicast tree is not NP-hard; in fact, an optimal wavelength assignment algorithm with complexity of O(NW) is presented. Simulation results have revealed that the optimal wavelength assignment beats greedy algorithms by a large margin in networks using many wavelengths on each link such as dense wavelength-division-multiplexing (DWDM) networks. Our proposed heuristic multicast routing algorithm takes into account both the cost of using wavelength on links and the cost of wavelength conversion. The resulting multicast tree is derived from the optimal lightpaths used for unicast     

Online Multicasting for Network Capacity Maximization in Energy-Constrained Ad Hoc Networks

In this paper, we present new algorithms for online multicast routing in ad hoc networks where nodes are energy-constrained. The objective is to maximize the total amount of multicast message data routed successfully over the network without any knowledge of future multicast request arrivals and generation rates. Specifically, we first propose an online algorithm for the problem based on an exponential function of energy utilization at each node. The competitive ratio of the proposed algorithm is analyzed if admission control of multicast requests is permitted. We then provide another online algorithm for the problem, which is based on minimizing transmission energy consumption for each multicast request and guaranteeing that the local network lifetime is no less than gamma times of the optimum, where gamma is constant with 0 < gammaleq 1. We finally conduct extensive experiments by simulations to analyze the performance of the proposed algorithms, in terms of network capacity, network lifetime, and transmission energy consumption for each multicast request. The experimental results clearly indicate that, for online multicast routing in ad hoc wireless networks, the network capacity is proportional to the network lifetime if the transmission energy consumption for each multicast request is at the same time minimized. This is in contrast to the implication by Kar et al. that the network lifetime is proportional to the network capacity when they considered the online unicast routing by devising an algorithm based on the exponential function of energy utilization at each node.     

Reliable Key Management and Data Delivery Method in Multicast Over Wireless IPv6 Networks

Multicast is an efficient way to reduce the required bandwidth of transmitting data simultaneously to a group of users in wireless IPv6 networks. Nevertheless, multicast suffers from two main drawbacks which can be looked from two perspectives, namely security and QoS. With regard to security, the main challenge is to provide security protection to multicast data, which can be achieved by using a secure key management process. Considering a highly dense environment where connection of users to the network is changing frequently due to join or leave operations, key updating approach may burden a network devices with a huge amount of complex encryption/decryption processes. From the QoS perspective, multicast transmission over WLAN offers a tradeoff between the transmission rate and the coverage. The transmission rate of multicast is confined by the user with the lowest data rate in the group which is called fixed base rate problem. To address the above mentioned problems, we propose and implement a lightweight key management and data delivery scheme for multicast over wireless IPv6 networks. The proposed solution is envisaged to reduce the complexity of key updating, while at the same time is able to address the fixed base rate problem. The performance evaluation (by means of analytical and test-bed implementation) of the proposed key management method indicates its efficiency in reducing communication, computation, and storage costs, while maintaining both forward and backward securities. Moreover, the proposed data delivery method is able to improve the throughput and QoS, with low packet loss and transmission delay.     

Dynamic Multicast Session Provisioning in WDM Optical Networks with Sparse Splitting Capability

In this work, we study dynamic provisioning of multicast sessions in a wavelength-routed sparse splitting capable WDM network with an arbitrary mesh topology where the network consists of nodes with full, partial, or no wavelength conversion capabilities and a node can be a tap-and-continue (TaC) node or a splitting and delivery (SaD) node. The objectives are to minimize the network resources in terms of wavelength-links used by each session and to reduce the multicast session blocking probability. The problem is to route the multicast session from each source to the members of every multicast session, and to assign an appropriate wavelength to each link used by the session. We propose an efficient online algorithm for dynamic multicast session provisioning. To evaluate the proposed algorithm, we apply the integer linear programming (ILP) optimization tool on a per multicast session basis to solve off-line the optimal routing and wavelength assignment given a multicast session and the current network topology as well as its residual network resource information. We formulate the per session multicast routing and wavelength assignment problem as an ILP. With this ILP formulation, the multicast session blocking probability or success probability can then be estimated based on solving a series of ILPs off-line. We have evaluated the effectiveness of the proposed online algorithm via simulation in terms of session blocking probability and network resources used by a session. Simulation results indicate that our proposed computationally efficient online algorithm performs well even when a fraction of the nodes are SaD nodes.