Showing papers on "Network topology published in 1993"

A generalized processor sharing approach to flow control in integrated services networks: the multiple node case

Abstract: Worst-case bounds on delay and backlog are derived for leaky bucket constrained sessions in arbitrary topology networks of generalized processor sharing (GPS) servers. The inherent flexibility of the service discipline is exploited to analyze broad classes of networks. When only a subset of the sessions are leaky bucket constrained, we give succinct per-session bounds that are independent of the behavior of the other sessions and also of the network topology. However, these bounds are only shown to hold for each session that is guaranteed a backlog clearing rate that exceeds the token arrival rate of its leaky bucket. A much broader class of networks, called consistent relative session treatment (CRST) networks is analyzed for the case in which all of the sessions are leaky bucket constrained. First, an algorithm is presented that characterizes the internal traffic in terms of average rate and burstiness, and it is shown that all CRST networks are stable. Next, a method is presented that yields bounds on session delay and backlog given this internal traffic characterization. The links of a route are treated collectively, yielding tighter bounds than those that result from adding the worst-case delays (backlogs) at each of the links in the route. The bounds on delay and backlog for each session are efficiently computed from a universal service curve, and it is shown that these bounds are achieved by "staggered" greedy regimes when an independent sessions relaxation holds. Propagation delay is also incorporated into the model. Finally, the analysis of arbitrary topology GPS networks is related to Packet GPS networks (PGPS). The PGPS scheme was first proposed by Demers, Shenker and Keshav (1991) under the name of weighted fair queueing. For small packet sizes, the behavior of the two schemes is seen to be virtually identical, and the effectiveness of PGPS in guaranteeing worst-case session delay is demonstrated under certain assignments. >

Multiwavelength lightwave networks for computer communication

Abstract: 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. >

Genetic algorithms as an approach to configuration and topology design

Abstract: The genetic algorithm, a search and optimization technique based on the theory of natural selection, is applied to problems of structural topology design. An overview of the genetic algorithm will first describe the genetics-based representations and operators used in a typical genetic algorithm search. Then, a review of previous research in structural optimization is provided. A discretized design representation, and methods for mapping genetic algorithm “chromosomes” into this representation, is then detailed. Several examples of genetic algorithm-based structural topology optimization are provided: we address the optimization of cantilevered plate topologies, and we investigate methods for optimizing finely-discretized design domains. The genetic algorithm’s ability to find families of highly-fit designs is also examined. Finally, a description of potential future work in genetic algorithm-based structural topology optimization is offered.

Selecting and locating graphical icon objects to define and configure the workstations in data processing networks

Abstract: A system and method for configuring communication and database networks in a user friendly graphical environment and automatically generating related configuration files. In a preferred practice, the user defines multiple network workstation nodes using icons, specifies the resources associated with each icon, defines connections between icons using specified protocol constraints, validates the network so defined, and generates the associated configuration files for the respective workstation nodes. The workstations have requester/server capability for communication and database network operation. The configuration files for the respective workstations in the network are preferably distributed and installed using the network resources. The network topology information so created can be stored, retrieved and modified as necessary to suit the needs of an evolving network.

Artificial neural-network based feeder reconfiguration for loss reduction in distribution systems

Abstract: Strategies are proposed to reconfigure the feeder in distribution systems by using artificial neural networks (ANNs) with mapping ability. ANNs determine the appropriate system topology that reduces the power loss according to the variation of load pattern. The control strategy can be easily obtained on the basis of the system topology which is provided by ANNs. ANNs are designed in two groups. The first group estimates the proper load level from the load data of each zone. The second determines the appropriate system topology from the input load level. Several programs with the training set builder are developed for the design, the training, and the accuracy test of artificial neural networks. The performance of neural networks designed is evaluated on the test distribution system. Neural networks are implemented in FORTRAN language and trained on a 386 PC. >

Topology control for multihop packet radio networks

Abstract: A distributed topology-control algorithm has been developed for each node in a packet radio network (PRN) to control its transmitting power and logical neighbors for a reliable high-throughput topology. The algorithm first constructs a planar triangulation from locations of all nodes as a starting topology. Then, the minimum angles of all triangles in the planar triangulation are maximized by means of edge switching to improve connectivity and throughput. The resulting triangulation at this stage, the Delaunay triangulation, can be determined locally at each node. The topology is modified by negotiating among neighbors to satisfy a design requirement on the nodal degree parameter. Simulations show that the final topology is degree-bounded, has a rather regular and uniform structure, and has throughput and reliability that are greater than that of a number of alternative topologies. >

Telecommunications Network Design Algorithms

Abstract: Overview of networking analysis of loss and delay in networks modelling networks as graphs fundamental graph algorithms centralized network design routing algorithms mesh topology optimization network reliability.

Neural networks for shortest path computation and routing in computer networks

Abstract: The application of neural networks to the optimum routing problem in packet-switched computer networks, where the goal is to minimize the network-wide average time delay, is addressed. Under appropriate assumptions, the optimum routing algorithm relies heavily on shortest path computations that have to be carried out in real time. For this purpose an efficient neural network shortest path algorithm that is an improved version of previously suggested Hopfield models is proposed. The general principles involved in the design of the proposed neural network are discussed in detail. Its computational power is demonstrated through computer simulations. One of the main features of the proposed model is that it will enable the routing algorithm to be implemented in real time and also to be adaptive to changes in link costs and network topology. >

Method and apparatus for optimizing computer networks

Abstract: An optimization method collects data regarding network topology and traffic flow and creates a network model. The model is analyzed using optimization rules and network performance objectives to determine the optimal configuration of the network according to the network performance objectives. An optimization rule for positioning a shared central resource on the network identifies the communication paths between all clients of the resource and assigns a cost value to the traffic flowing between the clients and the resource. This is repeated for each potential resource position in the network. The position having the lowest traffic cost is the optimal position for the resource. An optimization rule for partitioning network segments determines all possible partitions at the hubs of a segment and scores the performance of each possible partition, according to network performance goals. The hub partition having the lowest score is the optimal hub for partitioning the network segment.

Distributed code assignments for CDMA packet radio networks

Abstract: Code-division multi-access (CDMA) techniques allow many users to transmit simultaneously in the same band without substantial interference by using approximately orthogonal (low cross-correlation) spread-spectrum waveforms. Two-phase algorithms have been devised to assign and reassign spread-spectrum codes to transmitters, to receivers and to pairs of stations in a large dynamic packet radio network in polynomial times. The purpose of the code assignments is to spatially reuse spreading codes to reduce the possibility of packet collisions and to react dynamically to topological changes. These two-phase algorithms minimize the time complexity in the first phase and minimize the number of control packets needed to be exchanged in the second phase. Therefore, they can start the network operation in a short time, then switch to the second phase with the goal of adapting to topological changes. A pairwise code-assignment scheme is proposed to assign codes to edges. Simulations based on well-controlled topologies (sparse topologies) show that the scheme requires much fewer codes than transmitter-based code assignment, while maintaining similar throughput performance. >

Tracking mobile users in wireless communications networks

Abstract: Tracking strategies for mobile wireless networks are studied. A cellular architecture in which base stations that are interconnected by a wired network communicate with mobile units via wireless links is assumed. The cost of utilizing the wireless links for the actual tracking of mobile users is considered. A tracking strategy in which a subset of all base stations is selected and designed as reporting centers is proposed. Mobile users transmit update messages only upon entering cells of reporting centers, while every search for a mobile user is restricted to the vicinity of the reporting center to which the user last reported. It is shown that, for an arbitrary topology of the cellular network (represented by the mobility graph), finding an optimal set of reporting centers is an NP-complete problem. Optimal and near-optimal solutions for important special cases of the mobility graph are presented. >

Topological optimization of a communication network subject to a reliability constraint

Abstract: Network topological optimization with a reliability constraint is considered. The objective is to find the topological layout of links, at a minimal cost, under the constraint that the network reliability is not less than a given level of system reliability. A decomposition method, based on branch and bound, is used for solving the problem. In order to speed up the procedure, an upper bound on system reliability, in terms of node degrees, is applied. A numerical example illustrates the effectiveness of the method. >

Multiwavelength survivable ring network architectures

Abstract: A new architecture for implementing unidirectional and bidirectional self-healing interoffice ring networks using wavelength division multiplexing (WDM) technology for growth is proposed. The working ring uses all-optical drop-and-add multiplexers at each office and the protection path uses optical amplifiers and optical switches. The use of WDM technology, combined with all-optical drop-and-add multiplexers, accommodates growth to a network capacity of more than 1 Tb/s. >

Classical wave propagation in periodic structures: Cermet versus network topology.

Abstract: We have investigated classical waves propagating in periodic binary composites. For electromagnetic waves the network topology, in which the low-velocity material forms a continuous network, is more favorable for the appearance of gaps. In contrast, for scalar and elastic waves the cermet topology, in which the low-velocity material consists of isolated inclusions surrounded by the high-velocity host material, is more favorable.

Lightnets: Topologies for High-speed Optical Networks

Abstract: An inherent problem of conventional point to point WAN architectures is that they cannot translate optical transmis- sion bandwidth into comparable user available throughput due to the limiting electronic processing speed of the switching nodes. This paper presents a solution to WDM based WAN networks that addresses this limitation. The proposed Lightnet architecture trades the ample bandwidth obtained by using multiple wave- length for a reduction in the number of processing stages and a simplification of each switching stage, leading to substantially increased throughputs. The principle of the Lightnet architecture is the construction and use of a virtual topology network in the wavelength domain, embedded in the original network. This paper studies the em- bedding of virtual networks whose topologies are regular, using algorithms which provide bounds on the number of wavelengths, switch sizes, and average number of switching stages per packet transmission. Algorithms for the embedding of alternative regu- lar topologies are presented and their performance is evaluated. It is shown that compared to conventional network architectures, the Lightnets offer substantial performance gains in terms of increased throughput and smaller buffering requirements.

Parallax: a tool for parallel program scheduling

Abstract: Parallax, a scheduling tool that incorporates seven traditional and nontraditional scheduling heuristics and lets developers compare their performance for real applications on real parallel machines, is discussed. Of the seven heuristics, two simple ones consider only task execution time, two consider both task execution and message-passing delay times, two use task duplication to reduce communication delay, and one considers communication delays, task execution time, and target machine characteristics such as interconnection network topology and overhead due to message-passing and process creation. Two examples of parallel applications of Parallax are described. >

Network integrated construction system, method of installing network connection machines, and method of setting network parameters

Abstract: Parameters representing types of machines to be connected to a network, connection types thereof to the network, and operation modes thereof in the network system are set from an information processing apparatus. The obtained parameters are written as parameter files on a recording medium. In each network machine, a network system is automatically constructed by referencing the files. Consequently, the parameter setting operations for the installation of the machine are simplified and there is achieved automation of operations in each network machine.

Making transmission schedules immune to topology changes in multi-hop packet radio networks

Abstract: A time-slot allocation algorithm called PRS which schedules transmissions independently of the network topology changes is presented. This makes it suitable for scheduling the transmissions in time division multiple access (TDMA) or code division multiple access (CDMA) systems with frequently and unpredictably changing topology. The algorithm guarantees correct operation under any frequency of change, and to the best of the authors' knowledge, it is the only solution for robust scheduled access when no continuous update is feasible and a guaranteed delay is required even under heavy loads. >

Method and apparatus for transforming an arbitrary topology collection of nodes into an acyclic directed graph

Abstract: A system and method are described which take an arbitrarily assembled collection of nodes on a bus or network and imposes an optimized hierarchical tree structure where there is only one root node. Nodes having both parent and child nodes are considered branch nodes while nodes having only parent nodes are leaf nodes. Loops or cycles in the physical topology are resolved into a logical topology that is acyclic and directed. A signaling scheme is developed in which nodes, via on board communications hardware, signal all connected nodes and respond accordingly until hierarchical relationships are established. Cycles are resolved by intelligently breaking links to yield an acyclic graph. Direction is established by each node recognizing its parent/child status with respect to connected nodes until a single node is established as a root node.

Connection establishment in high-speed networks

Abstract: Protocols for establishing, maintaining, and terminating connections in packet-switched networks have been studied, and numerous standards have been developed to address this problem. The authors reexamine connection establishment in the context of a high-speed packet network, introduce a protocol for connection establishment/takedown that is appropriate for such a network, and explain its advantages over previously proposed protocols. The main features of the proposed protocol are: fast bandwidth reservation in order to avoid as much as possible reservation conflicts, guaranteed release of the reserved bandwidth even under modal and link failures, and soft recovery from processor failures, which allows the maintenance of existing connections under processor failure provided the switch and links do not fail. The underlying model that is used is the PARIS/plaNET network, but the protocol can be adapted to other fast packet networking architectures as well. >

Error correction and channel restoration apparatus for T1 digital links

Abstract: Apparatus, operating in a digital communication system, for interconnecting a primary or a secondary network to an output port. The primary and secondary networks are redundant networks having point-to-point topologies (125, 130) or point-to-multi-point topologies (210, 215). When connected in a point-to-point network topology that supports extended superframe format (ESF), the apparatus functions as an error correction switch and; when connected in a point-to-multi-point network topology, the apparatus functions as a DS1/0 protection switch. In its receiver aspect, the apparatus stores frames of digital data received from each of two redundant networks, inspects certain error codes contained in the received data and, in response to these error codes, selects the digital data originating from one of the networks that does not exhibit an error code. The data selection process uses a time-slot interchanging (TSI) technique. The selected data is subsequently transferred to downstream digital signal processing equipment. In its transmitter aspect, the apparatus transmits replicated versions of digital data supplied by digital transmission equipment onto both redundant networks.

Design of robust cellular neural networks

Abstract: Shows how to systematically design an inputless cellular neural network (CNN), which processes only the information present in the initial state, with prescribed stable and unstable outputs while simultaneously maximizing its robustness with respect to changes of its parameters. This is achieved by combining a generalization of previous results on CNN design with a design centering algorithm based on linear programming. The design process is highly efficient with small numbers of cells, and it can be precisely and flexible controlled. Many kinds of implementation-related constraints may be introduced, including bounded parameters and arbitrary topological restrictions. A nonrigorous but effective practical guideline for shaping the basins of attraction of stable outputs is recommended. A simple example is given and thoroughly discussed. >

Distributed computing with high-speed optical networks

Abstract: An environment that uses wavelength division multiplexing techniques and optical switching and processing to provide large bandwidths, short delays, and multiple data streams for distributed processing is described. The focus is on the interrelationship between application needs and network services. The system level, a conceptual layer designed to bridge the gap between application requirements and underlying high-speed network services, is proposed. The system level is a logical view of the physical network represented by a virtual topology projected onto the physical network. Embedding this virtual topology introduces many new problems and performance tradeoffs into the design of the network. A few of these problems are outlined, and some initial research efforts in this area are discussed. The physical network level, the collection of optical fiber links interconnecting the nodes in the network, and the application level, a logical view of an application's computational topology and representation of the application's communication and computing requirements, are also described. >

Economic single-phase to three-phase converter topologies for fixed and variable frequency output

Abstract: Several component-minimized circuit topologies for single-phase to three-phase conversion are proposed. The topologies employ fewer semiconductor devices and generate high-quality output voltages. Suitable modification to achieve active input current shaping is illustrated in detail. Analysis and simulation of the proposed schemes are carried out to show the high-performance features. Suitable guidelines for the selection of filter components and for facilitating circuit design are presented. Selected results are verified experimentally on laboratory prototype converters. >

Classification of radar targets using synthetic neural networks

Abstract: Radar target classification performance of neural networks is evaluated. Time-domain and frequency-domain target features are considered. The sensitivity of the neural network algorithm to changes in network topology and training noise level is examined. The problem of classifying radar targets at unknown aspect angles is considered. The performance of the neural network algorithms is compared with that of decision-theoretic classifiers. Neural networks can be effectively used as radar target classification algorithms with an expected performance within 10 dB (worst case) of the optimum classifier. >

Topologies for wavelength-routing all-optical networks

Abstract: Three regular meshed topologies are compared in light of their possible use for the implementation of large all-optical wavelength-routing communication networks (or interconnection systems). These systems provide all source-destination pairs with end-to-end transparent channels that are identified through a wavelength and a physical path. The considered topologies are the K-dimensional bidirectional square lattice, the twin shuffle, and the de Bruijn graph. The comparison is based on the maximum and average distance between source and destination (number of traversed nodes), on the degree of connectivity for each node (number of input and output fibers), and on the minimum number of wavelengths in the WDM comb necessary to discriminate all source-destination pairs. >

Adaptive Deadlock-Free Routing in Multicomputers Using Only One Extra Virtual Channel

Abstract: We present three protocols defin ing the relationship between messages and the chan nel resources requested: request-then-hold, requestthen wait, and request-then-relinquish. Based on the three protocols, we develop an adaptive deadlockfree routing algorithm called the SP routing. The SP routing uses shortest paths and is fully-adaptive, so messages can be routed via any of the shortest paths from the source to the destination. Since it is a minimal or shortest routing, the SP routing guar antees the freedom of livelocks. The SP routing is not limited to a specific network topology. The main requirement for an applicable network topology is that there exists a deterministic, minimal, deadlock-free routing algorithm. Most ex isting network topologies are equipped with such an algorithm. In this paper, we present an adaptive deadlock-free routing agorithm for n-dimensional meshes by using the SP routing. The hardware re quired by the SP routing uses only one extra virtual channel as compared to the deterministic routing.

GANNET: a genetic algorithm for searching topology and weight spaces in neural network design. The first step in finding a neural network solution

Abstract: Neural networks have recently generated a great amount of interest. However, designing and training these networks are very difficult tasks, requiring much trial and error, and the standard layered network architectures do not map naturally into hardware. This dissertation presents a novel genetic algorithm which is used to design the topology and find the link weights for a layered, feedforward neural network. Since the algorithm will respect given fan-in and fan-out limits for each node, the networks will easily map into hardware. The topologies are not limited either in the number of layers or in the number of nodes per layer, and two transfer functions are available (sigmoid and Gaussian). A robust, global search is conducted by the genetic algorithm over both the link weight and topology spaces, after which a local search strategy (such as back propagation) can be used to quickly find the desired link weights. Thus, both the genetic algorithm and back propagation can be used to their greatest advantage: the global search of the GA can find the approximate area of a solution, and the back propagation can then quickly find the local optimum.

Design and performance analysis of the algorithms for channel allocation in cellular networks

Abstract: The authors consider the problem of dynamic channel allocation in cellular networks. Each cell can use any channel, subject to the interference constraints. Channel allocation algorithms are executed by the network switch in a centralized way. The authors show how to design and use objective functions aimed at proper channel allocation and improvement of network performance. As a figure of merit of network performance, they consider the blocking probability in the network as a whole, and the maximum blocking probability in any particular cell of the network ("hot-spot" in the network). They designed three specific channel allocation policies, based on three different objective functions. Compared with two other benchmark policies, the approach shows significant improvement. Performance analysis of various channel allocation policies is virtually impossible without simulations, which are prohibitively time-consuming in the case of small blocking probabilities. The authors propose an original approximate method based on a short simulation and an analytic approximation. The method exhibits good accuracy and significant improvement in efficiency. >

Telecommunications network topological design and capacity expansion: Formulations and algorithms

Abstract: This paper formulates the network topology and capacity expansion problem in a telecommunications network and suggests a family of heuristics and a dual-based lower bounding procedure for solving it. They include schemes exploiting special subproblem structures, decomposition of the problem using Lagrangian relaxation, and a global search strategy. Carefully designed experiments show that the procedure generates solutions within forty percent of the lower bound in most cases. To evaluate the solution quality more accurately, additional experiments have been performed, using a random search strategy for the topological variables with capacity expansion optimized. It is shown that the global heuristic solutions dominate solutions that use the random search strategy for topological variables. Following the computational experiments, a tighter formulation is suggested which can improve the lower bounds. The paper concludes with a discussion of further research areas.