Protocol implementation for Universe

The communications protocols used on the Universe network and the implementor's experiences with them are described. By examining ‘lightweight’ and ‘heavyweight’ protocols, the paper examines the problems of protocols for mixed networks.     

Reference models for a fast packet based network

Two possible architectural reference models are described for a network based on the fast packet switching concept. This is known as an asynchronous time division network. The first model is based on the outband principle, since signalling and data information are transmitted over different logical channels. The second model provides a complete integration at all levels of signalling and data information. It is therefore called the inband model. A comparison of both the inband and outband reference models is also given.     

An index-split Bloom filter for deep packet inspection

Deep packet inspection(DPI)scans both packet headers and payloads to search for predefined signatures.As link rates and traffc volumes of Internet are constantly growing,DPI is facing the high performance challenge of how to achieve line-speed packet processing with limited embedded memory.The recent trie bitmap content analyzer(TriBiCa)suffers from high update overhead and many false positive memory accesses,while the shared-node fast hash table(SFHT)suffers from high update overhead and large memory requi...     

Protocol for packet/circuit switch interworking

Packet and circuit network integration and interworking issues are discussed, and a method for realization of interworking with existing digital circuit switched networks is proposed. The method is based on the use of time division multiplex transmission media, digital and analogue access and the use of a new protocol. It is concluded that the benefits of interworking can be achieved with minimal disruption to the circuit switched network.     

Performance analysis of structured peer-to-peer overlays for mobile networks

Distributed Hash Table (DHT) based Peer-to-Peer (P2P) overlays have been widely researched and deployed in many applications such as file sharing, IP telephony, content distribution and media streaming applications. However, their deployment has largely been restricted to fixed, wired networks. This is due to the fact that supporting P2P overlays on wireless networks such as the public mobile data network is more challenging due to constraints in terms of data transmissions on cellular networks, limited battery power of the handsets and increased levels of node churn. However, the proliferation of smartphones makes the use of P2P applications on mobile handsets very desirable. In this article, we have analysed and evaluated the performance and efficiency of five popular DHT based structured P2P overlays (Chord, Pastry, Kademlia, Broose and EpiChord) under conditions as commonly experienced in public mobile data networks. Our results show that the conditions in mobile networks, including a high churn rate and the relatively low bandwidth availability is best matched by Kademlia and EpiChord. These overlays exhibit a high lookup success ratio and low hop count while consuming a moderate amount of bandwidth. These characteristics make these two overlays suitable candidates for use in mobile networks.     

A university computer network for South Africa?

The Council for Scientific and Industrial Research in Pretoria has recently extended their network linking CSIR sites within South Africa to include a number of teaching universities. Developments for the network system include alternative traffic routing, port hunting and access to the national Post Office network and its international X.25 packet-switching service. The eventual aim of the CSIR network is to achieve a unified packet-switching system operating under international protocols, and offering resource-sharing facilities to the scientific research and academic community throughout South Africa.     

A proactive low-overhead file replication scheme for structured P2P content delivery networks

File replication is a widely used technique for high performance in peer-to-peer content delivery networks. A file replication technique should be efficient and at the same time facilitates efficient file consistency maintenance. However, most traditional methods do not consider nodes’ available capacity and physical location in file replication, leading to high overhead for both file replication and consistency maintenance. This paper presents a proactive low-overhead file replication scheme, namely Plover. By making file replicas among physically close nodes based on nodes’ available capacities, Plover not only achieves high efficiency in file replication but also supports low-cost and timely consistency maintenance. It also includes an efficient file query redirection algorithm for load balancing between replica nodes. Theoretical analysis and simulation results demonstrate the effectiveness of Plover in comparison with other file replication schemes. It dramatically reduces the overhead of both file replication and consistency maintenance compared to other schemes. In addition, it yields significant improvements in reduction of overloaded nodes.     

多类型混合运算的面向对象设计与实现

针对多种数据类型的混合运算问题进行了研究。讨论了面向过程的解决方案和两种可能的面向对象解决方案及不足。依据敏捷设计原则,提出了一种双层函数指针数组（虚表）的面向对象新方案。分析表明,该设计具备开放封闭性,解决了灵活性、可重用性、可维护性和效率问题。     

基于虚拟位置的无线传感器网络环路由协议

无线传感器网络中节点的能源和处理能力受限,难以提供大规模的、以数据为中心的服务。为了解决以上问题,提出了一个基于虚拟位置的环路由协议。此协议使用分布式哈希表管理数据。虚拟位置概念的引入减少了冗余的路由信息并优化了路由的路径,从而减轻了节点的负担并提升了数据传送的效率。根据仿真结果以及与相关协议的对比,证明了此协议的有效性和可扩展性。     

一种面向无线Ad Hoc网络的新型分布式哈希表

为了在无线ad hoc网络上构建各种应用系统,有必要提供一种高效的数据共享机制,使得网络中各节点之间能够方便地进行协同和交互。该文将分布式哈希表(DHT)的基本思想与无线ad hoc网络中的基于地理位置的路由技术结合起来,提出了一种新型的面向无线ad hoc网络的数据共享方案——基于位置的DHT(LDHT)。与传统的DHT方案相比,LDHT不是通过逻辑上的覆盖网络来实现,而是直接基于网络的物理拓扑结构来构建,有效地消除了传统DHT方案的拓扑结构不匹配问题,提高了在无线ad hoc网络中进行数据共享的效率。     

面向大规模网络的基于政策的访问控制框架

研究防火墙(或过滤路由器)应用于传输网络中的管理问题与吞吐量问题.一方面,手工配置分布在各个接入点的大量防火墙,无法满足开放的、动态的网络环境的安全管理需求;另一方面,大量过滤规则的顺序查找导致了防火墙吞吐量下降.针对一个典型的传输网络和它的安全政策需求,提出了一种基于政策的访问控制框架(PACF),该框架基于3个层次的访问控制政策的抽象:组织访问控制政策(OACP)、全局访问控制政策(GACP)和本地访问控制政策(LACP).根据OACP,GACP从入侵监测系统和搜索引擎产生,作为LACP自动地、动态地分配到各防火墙中,由防火墙实施LACP.描述了GACP的分配算法和LACP的实施算法,提出了一种基于散列表的过滤规则查找算法.PACF能够大量减轻管理员的安全管理工作,在描述的安全政策需求下,基于散列表的规则查找算法能够将传统顺序查找算法的时间复杂度从O(N)降低到O(1),从而提高了防火墙的吞吐量.     

一种基于哈希链表的高效概念漂移连续属性处理算法

本文重点研究了数据流挖掘中存在概念漂移情形的连续属性处理算法。数据流是一种增量、在线、实时的数据模型。VFDT是数据流挖掘中数据呈稳态分布情形下最成功的算法之一;CVFDT是有效解决数据流挖掘中概念漂移问题的算法之一。基于CVFDT,本文提出了有效地解决数据流挖掘中存在概念漂移情形的连续属性处理问题的扩展哈希表算法HashCVFDT。该算法在属性值插入、查找和删除时具有哈希表的快速性,而在选取每个连续属性的最优化划分节点时解决了哈希表不能有序输出的缺点。     

一种新的基于广义细胞自动机的网络快速包交换优化方法

实时优化求解快速包交换问题(FPS)是提高网络性能的重要手段．基于梯度下降法等数学规划方法,不能并行地实时地优化求解FPS问题,而基于Hopfield型神经网络和细胞神经网络的优化方法中,都只有单一粒度的细胞动力学方程和单一粒度细胞之间的相互作用,不仅收敛到平衡点的过程长,而且神经网络参数的选择和修正十分困难．该文提出一种新的具有多粒度宏细胞的广义细胞自动机模型和方法,广义细胞自动机中的小粒度宏细胞聚合成可以独立演化的大粒度宏细胞,通过多粒度群体的不同程度群体智能的相互作用,能够比目前其他方法更快更有效地分布并行地优化求解FPS问题和其它类似的复杂的网络优化问题．     

An X.25-compatible protocol for packet voice communications

Developments in packet-switched networks have generated interest in how to integrate voice and data traffic in such networks. The paper deals with a proposed communications protocol for voice transmission within X.25 packet-switched networks. Basic protocol procedures for handling voice communications are examined, and possible formats for the identified types of voice frame and packet fitting for current CCITT standards governing packet data communications are presented.     

Analytical forms for most likely matrices derived from incomplete information

Consider a rectangular matrix describing some type of communication or transportation between a set of origins and a set of destinations, or a classification of objects by two attributes. The problem is to infer the entries of the matrix from limited information in the form of constraints, generally the sums of the elements over various subsets of the matrix, such as rows, columns, etc., or from bounds on these sums, down to individual elements. Such problems are routinely addressed by applying the maximum entropy method to compute the matrix numerically, but in this article we derive analytical, closed-form solutions. For the most complicated cases we consider the solution depends on the root of a non-linear equation, for which we provide an analytical approximation in the form of a power series. Some of our solutions extend to 3-dimensional matrices. Besides being valid for matrices of arbitrary size, the analytical solutions exhibit many of the appealing properties of maximum entropy, such as precise use of the available data, intuitive behaviour with respect to changes in the constraints, and logical consistency.     

Exponential stabilisation for time-varying delay system with actuator faults: an average dwell time method

The issue of exponential stabilisation for a class of special time-varying delay switched systems resulting from actuator faults is considered in this article. The time-varying delay is assumed to belong to an interval and can be a slow or fast time-varying function. A hybrid state feedback strategy is redesigned to guarantee the system stable since the original controller is unavailable for some actuators failures. A class of switching laws incorporating the average dwell time method is proposed so that the special switched system with interval time-varying delay is exponentially stable. New delay-range-dependent stabilisation conditions using state feedback controllers are formulated in terms of linear matrix inequalities (LMIs) by choosing appropriate Lyapunov–Krasovskii functional without neglecting some useful knowledge on system states. Parameterised characterisations of the controllers are given in terms of the feasibility solutions to the LMIs. Two numeral examples are given to demonstrate the applicability and the effectiveness of the proposed method.