Multiwavelength lightwave networks for computer communication

The different approaches being considered to build high-capacity lightwave networks are described. Two kinds of lightwave network architectures are examined: broadcast-and-select networks and wavelength-routing networks. A comparison of the two shows that broadcast-and-select networks may be more suitable for local area networks (LANs) and metropolitan area networks (MANs), while wavelength-routing networks are suitable for wide area networks (WANs). The overall network may then be a combination of broadcast subnets interconnected by a point-to-point wavelength-routing network     

Reliability polynomials of computer communication networks

The expression for the overall reliability of a computer communication network (CCN) when all edges have equal probability of being up is called the reliability polynomial of the CCN. For a complicated network, the overall reliability of the CCN can be approximated by the truncated polynomial. A characterization of the reliability polynomial and its approximation are give in this paper.     

An availability evaluation for computer communication networks

Among the various availability criteria for computer communication networks, based on strictly topological considerations or taking into account also the traffic characteristics, we propose, as a network performance measure, the probability that an assigned fraction of the stability throughput can be carried out with average packet and message time delays not greater than specified values.At the aim, an algorithm for the availability analysis has been developed; given the topological and physical characteristics of the network, the external traffic statistics at the network node pairs and the routing procedure, the network availability and the average loss of throughput due to single failures of lines or switching nodes are evaluated with regard, as an example, to a simple five node network.     

Information theory and communication networks: an unconsummatedunion

Information theory has not yet had a direct impact on networking, although there are similarities in concepts and methodologies that have consistently attracted the attention of researchers from both fields. In this paper, we review several topics that are related to communication networks and that have an information-theoretic flavor, including multiaccess protocols, timing channels, effective bandwidth of bursty data sources, deterministic constraints on datastreams, queuing theory, and switching networks     

Applications of computer communications in education: an overview

Applications of computer communications can be used in many ways in education. An overview is given of a number of categories of computer communications applications in learning-related activities. Particular attention is given to a new type of system called a course-support environment. In this type of system a database is integrated with Web-based tools and applications, and used to generate a course-support environment accessed via a standard Web browser. Some examples are given. The article moves on to an overview of various issues confronting the acceptance of computer communication systems in educational settings, and indicates some of the ways in which computer communications engineers will have to deal with those issues     

Empirical prediction of overall reliability in computer communication networks

Incorporation of an overall reliability parameter in the design of reliable computer communication networks makes the computation prohibitive. A composite reliability index based on the network topological parameters has been presented [1], which is very simple to evaluate and gives computation while designing maximally reliable computer networks as compared to the techniques based on several reliability measures. In this paper, we use the tabulated results of Soi and Aggarwal [1] and develop empirical formulae which can be used for quick estimation of overall reliability of a computer network for a specified value of the link reliability.     

Kerberos: an authentication service for computer networks

When using authentication based on cryptography, an attacker listening to the network gains no information that would enable it to falsely claim another's identity. Kerberos is the most commonly used example of this type of authentication technology. The authors concentrate on authentication for real-time, interactive services that are offered on computer networks. They use the term real-time loosely to mean that a client process is waiting for a response to a query or command so that it can display the results to the user, or otherwise continue performing its intended function. This class of services includes remote login, file system reads and writes, and information retrieval for applications like Mosaic     

Overall reliability evaluation for large computer communication networks: An MHC approach

An important parameter in the topological design of computer communication networks is that of overall reliability, rather than terminal-pair reliability, as one is interested in not allowing service disruption between any pair of nodes. Exact techniques for overall reliability evaluation based on the spanning trees idea fail for networks even of reasonable size because of the enormous amount of computer time and storage required. In this paper, we present a very simple and fast method based on an m-level hierarchical clustering (MHC) for network overall reliability evaluation which gives results as good as exact techniques for realistic values of link reliability (e.g. 0.9 or more). Adaptability of a practical clustering method (i.e. complete linkage, CL) to obtain near optimal clusters for overall reliability evaluation by incorporating suggested modifications is proposed.     

Optical metropolitan DWDM networks an overview

The paper deals with the subject of how to build a core network in the current technology scenario. We start with an overview ofwhat we consider a core network, not in an abstract way but referring to real country situations, and pointing out the differentaspects conditioning its realisation – population distribution, territory shape, traffic characteristics. In the next section asummary of different network topologies is presented and briefly analysed – rings, meshes, loosely or tightly interconnected,with particular attention to the resilience aspect in case of faults. The following section is dedicated to a short presentation of thecurrent technology scenario and how it reflects on the network elements (NEs) offered on the market (OXC, OADM, PXC, etc).Finally, the question is posed: “What is the best way to implement a core network?” with the conclusion being that there is nosingle answer – each situation must be pursued on a case-by-case basis. This paper describes some important aspects of next-generation metropolitan networking, with special focus on market driversand applications, upcoming standards like GFP and GMPLS, required functionalities like optical switching and protection, and ageneric view on a next-generation platform.     

Virtual private networks: an overview with performance evaluation

Virtual private networks have gained immense popularity among commercial and defense organizations because of their capability to provide secure connectivity at lower costs. Several commercial and open source VPN products are now available that can be configured to provide VPN services with varying characteristics. This article studies some of the most popular open-source Linux-based VPN solutions (OSLVs) and compares them with respect to network performance (measured in terms of overhead, bandwidth utilization, and latency/jitter), features and functionalities (e.g., algorithm plugins and routing), and operational concerns (defined by security and scalability). Our experiments suggest that there is no single OSLV solution that excels in all considered aspects, and a combination of different VPN products and/or trade-off among desired characteristics may be required to deliver optimal performance. Our experiments also suggest that on an average, OSLVs using UDP-based tunnels have 50 percent lower overhead, 80 percent higher bandwidth utilization, and 40-60 percent lower latency/jitter than those using TCP.     

计算机通信网络中基于速率的端对端拥塞控制

运用现代控制理论和方法，在多个信源节点单个信终端节点的端对端模型基础上，考虑到信终端节点的缓冲占有量的动态稳定，设计了一类可以比较好地调节ABR信源节点发送速率的控制器，使得终端节点的缓冲占有量可以逐渐稳定。     

Cognitive radio networks for green wireless communications: an overview

As power consumption results in greenhouse gas emissions and energy costs for operators, analyzing power consumption in wireless networks and portable devices is of crutial importance. Due to environmental effects resulted from energy generation and exploitation as well as the cost of surging energy, energy-aware wireless systems attract unprecedented attention. Cognitive Radio (CR) is one of the optimal solutions that allows for energy savings on both the networks and devices. Thus, cognitive radio contributes to increase spectral and energy efficiency as well as reduction in power consumption. In addition, energy consumption of the CR technologies as intelligent technology should be considered to realize the green networks objective. In this article, we look into energy efficiency of the cognitive wireless network paradigms. Moreover, energy efficiency analysis and modelling in these systems are specifically focused on achieving green communications objectives. However, CRs by altering all elements of wireless data communications are considered in this paper, and the energy-efficient operation and energy efficiency enabler perspectives of CRs are also analyzed.

     

Radio communication via Near Vertical Incidence Skywave propagation: an overview

Near Vertical Incidence Skywave (NVIS) propagation can be used for radio communication in a large area (200 km radius) without any intermediate man-made infrastructure. It is therefore especially suited for disaster relief communication, communication in developing regions and applications where independence of local infrastructure is desired, such as military applications. NVIS communication uses frequencies between approximately 3 and 10 MHz. A comprehensive overview of NVIS research is given, covering propagation, antennas, diversity, modulation and coding. Both the bigger picture and the important details are given, as well as the relation between them.     

An overview of RF energy harvesting and information transmission in cooperative communication networks

Telecommunication Systems - Wireless energy harvesting and information transfer (WEHIT) is a new paradigm in cooperative communication networks. WEHIT enables energy constrained cooperative...     

Approximating dependability measures of computer networks: an FDDIcase study

An approximation technique is presented to evaluate the dependability of FDDI networks. This technique, based on the most likely paths to failure concept, is simple and practical. It may be applied easily to evaluate and compare the dependability of different FDDI network configurations. The effects of various network parameters on the network availability are examined. We conclude that, in order to guarantee high availability, an FDDI network backbone should be interconnected using dual-attachment concentrators. Furthermore, dual-homing configurations are required for high-availability paths between end stations and the backbone. For less stringent availability requirements, single-attachment concentrator trees with single attachment stations may suffice. We also discuss how the technique may be extended easily to more general heterogeneous networks including Token Ring and Ethernet     

Media access control for Ethernet passive optical networks: an overview

Medium access control is one of the crucial issues in the design of Ethernet passive optical networks. To ensure efficient transmission, an EPON system must employ a MAC mechanism to arbitrate access to the shared medium in order to avoid data collisions in the upstream direction and at the same time efficiently share the upstream transmission bandwidth among all ONUs. The purpose of this article is to provide a good understanding of the MAC issue, discuss the major problems involved (e.g., multiple access, bandwidth allocation, transmission scheduling, and quality of service support), and present an overview of the state-of-the-art solutions proposed thus far to the problems. It is also our purpose to motivate further studies on the problems described in this article     

Empirical relationship between communication costs and the channel bit rate for large computer networks

The primary trade-off in a large computer-communication network (CCN) is the balance between computation processing capability and communication capability. Essentially, a CCN model should utilize operational optimization (rather than mathematical optimization) allowing the user (mostly a non-programme network expert) to call upon his experience and insight in dealing with real-life networks to decide upon proper direction for modifications. We propose, in this paper, a unified approach which will hopefully allow an on-line user to make real-time modifications to CCNs to obtain operationally optimal system trade-offs in such areas as network overall reliability, communication response, computation response, and optimum channel capacities etc.