Showing papers on "Network topology published in 1988"

Topological properties of hypercubes

Abstract: The n-dimensional hypercube is a highly concurrent loosely coupled multiprocessor based on the binary n-cube topology. Machines based on the hypercube topology have been advocated as ideal parallel architectures for their powerful interconnection features. The authors examine the hypercube from the graph-theory point of view and consider those features that make its connectivity so appealing. Among other things, they propose a theoretical characterization of the n-cube as a graph and and show how to map various other topologies into a hypercube. >

ShuffleNet: an application of generalized perfect shuffles to multihop lightwave networks

Abstract: The authors propose a multihop wavelength-division-multiplexing (WDM) approach, referred to as ShuffleNet, for achieving concurrency in distributed lightwave networks. ShuffleNet can be configured with each user having as few as one fixed-wavelength transmitter and one fixed-wavelength receiver, avoiding both wavelength agility and pretransmission coordination problems. Still, the network can achieve at least 40% of the maximum efficiency possible with wavelength-agile transmitters and receivers. To transmit a packet from one user to another, however, may require routing the packet through intermediate users, each repeating the packet on a new wavelength, until the packet is finally transmitted on a wavelength that the destination user receives. For such a multihop lightwave network, the transmit and receive wavelengths must be assigned to users to provide both a path between all users and the efficient utilization of all wavelength channels. A class of assignment schemes is proposed which is based on a generalization of the perfect shuffle and achieves high efficiency for uniform traffic loads. Physically, the network may take on a variety of topologies, including a bus, tree, or star. >

The iPSC/2 direct-connect communications technology

Abstract: This paper describes the hardware architecture and protocol of the message routing system used in the iPSC®/2 concurrent computer. The Direct-Connect router was developed by Intel Scientific Computers to replace the store-and-forward message passing mechanism used in the original iPSC system. The router enhances the performance of the iPSC/2 system by reducing the message passing latency, increasing the node-to-node channel bandwidth and allowing simultaneous bi-directional message traffic between any two nodes. The new communication system has nearly equal performance between any pair of processing nodes, making the network topology more transparent to the user.The Direct-Connect router is a specialized self-contained hardware module attached to each hypercube node. The router is implemented in CMOS programmable gate-arrays with advanced CMOS buffering. Routers are connected by full-duplex bit-serial channels to form a Boolean n-cube network. The router also provides a high performance interface between the node memory bus and the network.

Comparison of resonant topologies in high-voltage DC applications

Abstract: Because of their tolerance of transformer nonidealities, resonant converters are considered to be well-suited to high-voltage applications. The series and parallel resonant topologies, as well as a newly discovered hybrid resonant topology are compared for high-voltage applications. Design criteria which incorporate transformer nonidealities are developed and used in the construction of high voltage prototypes for each topology. It is found that the parallel topology leads to the lowest peak switch current and the most ideal behavior. >

Detection and identification of topology errors in electric power systems

Abstract: A method for detecting topology errors in electric power networks is developed by providing a geometric interpretation of the measurement residuals caused by such errors. A test for single topology errors is presented that is similar to the normalized residuals test for measurement errors. This test is generalized to multiple topology errors. The concept of critical network branches (where their removal renders the network unobservable) is introduced and extended to critical-branch k-tuples. It is shown that topology errors on critical branches cannot be detected from measurement residuals. An equation is developed for a matrix whose column linear dependencies determine topology error detectability and identifiability. An example for an IEEE 14 bus network is provided. >

Designing networks with compact routing tables

Abstract: Classes of network topologies are identified in which shortest-path information can be succinctly stored at the nodes, if they are assigned suitable names. The naming allows each edge at a node to be labeled with zero or more intervals of integers, representing all nodes reachable by a shortest path via that edge. Starting with the class of outerplanar networks, a natural hierarchy of networks is established, based on the number of intervals required. The outerplanar networks are shown to be precisely the networks requiring just one interval per edge. An optimal algorithm is given for determining the labels for edges in outerplanar networks.

Automatic feedback of network topology data

Abstract: An automatic feedback mechanism in a communications network having dynamic routing. The invention detects the failure of an element in a route that is either in the process of being created or has been created and is being used. The invention provides a means for sending information as to the failure of the element back to the node originating the communication and, if the route had been established, to the destination node as well. The information sent back is used to update the network topology data base of the receiving node for subsequent route creation decisions by that node. In this way, proliferation of status messages in a communications network is avoided.

Distributed match-making

Abstract: In many distributed computing environments, processes are concurrently executed by nodes in a store- and-forward communication network. Distributed control issues as diverse as name server, mutual exclusion, and replicated data management involve making matches between such processes. We propose a formal problem called "distributed match-making" as the generic paradigm. Algorithms for distributed match-making are developed and the complexity is investigated in terms of messages and in terms of storage needed. Lower bounds on the complexity of distributed match-making are established. Optimal algorithms, or nearly optimal algorithms, are given for particular network topologies.

A topology processor that tracks network modifications

Abstract: Software considerations and test results are given for a topology processor that can track the changes in the network over time. It is expected that by knowing the changes from one cycle to the next, certain steps in the network solution can be avoided or replaced with steps requiring significantly less computation. The steps of particular interest are the ordering and factoring of the network solution matrix. In the operator training simulator, where solution time is critical, the simulation computation slows down when changes take place in the network, but the presented topology processor may provide the means to keep up with real time. In the security analysis real-time time sequence, computation can be saved in the state estimator if its tracking topology processor is used. The use of this topology processor modifies the solution of the tracking mode. For large topology changes, it is the same as the conventional tracking mode. But for the more common small topology changes, the matrices are not rebuilt and considerable computation time is saved. >

Lan communication system and medium adapter for use therewith

Abstract: A communication system, medium adapter (10) for use therewith, and methods are provided which permit standard ring network transmission media (15) to support both ring and bus communication topologies and protocols, which may be selectively adapted to differing topologies and protocols without physical modification. Means (50) are provided for permitting each medium adapter (10) to maintain a continuous ring communication path in a quiescent state, and to break the ring and establish bus communication both originating and terminating at the transmitting adapter in a transmit state. The medium adapter provided may be used with existing 802.5 token-ring dual twisted pair wiring (19), while supporting existing 802.3 CSMA/CD, 802.4 token bus, or 802.5 token-ring interface hardware, among others.

All topologies come from generalized metrics

Abstract: RALPH KOPPERMAN: I received my Ph.D. from M.I.T. in 1965, and came to The City College in 1967. SEEK is a special program for students from poor areas of the city, and I have coordinated its mathematics efforts since 1969. My research interest has always been in limits, which I first tried to study through infinitary languages (logic). I was able to publish in the field, but was not happy with the results of that research, and went into point-set topology in 1980. I was a founding member of the CCNY Seminar on General Topology and Topological Algebra in 1981, and have been involved with it ever since.

Topological constraints on basic PWM converters

Abstract: A modeling and synthesis technique is introduced for single-ended, ladder-structured, DC-DC converter topologies. Topological constraints are derived that enhance the understanding of structural properties of converter circuits and clarify the roles of inductors and capacitors in various converters using magnetic or capacitive energy storage/transfer mechanism. The exact duality relationships among the basic converter topologies are established. >

Parallel discrete event simulation using shared memory

Abstract: With traditional event-list techniques, evaluating a detailed discrete event simulation-model can often require hours or even days of computation time. By eliminating the event list and maintaining only sufficient synchronization to ensure causality, parallel simulation can potentially provide speedups that are linear in the numbers of processors. A set of shared-memory experiments using the Chandy-Misra distributed simulation algorithm, to simulate networks of queues is presented. Parameters of the study include queueing network topology and routing probabilities, number of processors, and assignment of network nodes to processors. These experiments show that Chandy-Misra distributed simulation is a questionable alternative to sequential simulation of most queuing network models. >

Dynamic networks are as fast as static networks

Abstract: An efficient simulation is given to show that dynamic networks are as fast as static ones up to a constant multiplicative factor. That is, any task can be performed in a dynamic asynchronous network essentially as fast as in a static synchronous network. The simulation protocol is based on an approach in which locality is perceived as the key to fast adaptation to changes in network topology. The heart of the simulation is a technique called a dynamic synchronizer, which achieves 'local' simulation of a global 'clock' in a dynamic asynchronous network. Using this result, improved solutions to a number of well-known problems on dynamic networks are obtained. It can also be used to improve the solution to certain static network problems. >

Hyperswitch network for the hypercube computer

Abstract: The performance of a parallel algorithm depends in a large part on the interconnection topology of the multicomputer system. The method presented in this paper realizes a kind of interconnection network, called a hyperswitch network, that is achieved using a mixture of static and dynamic topologies. Here, available or fault free paths need not be specified by a source because the routing header can be modified in response to congestion or faults encountered as a path is established. This method can be accomplished in a static topology such as the hypercube network if the nodes have switching elements which are capable of performing the necessary routing header revisions dynamically. Detailed simulation results show that the hyperswitch network is consistently more efficient than fixed path routing for large message traffic conditions. The simulation results also show that the hyperswitch network has equivalent latency overhead for messages with localized and antilocal destinations (i.e., less then a 25% difference between diameter 1 and 5).

Adaptive link assignment for a dynamic communication network

Abstract: An adaptive link assignment scheme for dynamically changing communication node topologies such as satellite networks, fleets of ships or aircraft, etc. Periodically each node in the network transmits topology information to all the nodes in the network. Then each node determines the degree of connectivity of the network. It is preferred that the network be at least triconnected, and if the network is less than that each node determines what connections it can make to improve the network connectivity. If more than one alternative is available, a choice is made based on line of sight endurance and then on traffic delay. The identification of the selected connection is then broadcast to all the nodes in the network. Each node thus receives the proposed changes from all the network nodes, and each node then resolves conflicts between the broadcast selections and determines what change it should make. Finally, the changes are implemented. The scheme emphasizes network connectivity to bring the network to a triconnected state and then emphasizes line of sight endurance and reduction of traffic delay.

Tree structured fiber optics MANs

Abstract: A fiber-optic architecture, Tree-Net, is introduced that does not require intermediate processing components and supports a large number of stations. Tree-Net is based on a tree topology, passive station taps, and implicit token protocol. The properties and performance of Tree-Net are evaluated. It is shown that the basic topology and access scheme of Tree-Net can be extended so that a family of tree-structured fiber-optic MANs (metropolitan area networks) can be defined to suit different needs, including data, voice, and video integration. >

Distributed assignment algorithms for multi-hop packet-radio networks

Abstract: Distributed dynamic channel assignment algorithms for a multihop packet radio network are introduced. The algorithms ensure conflict-free transmissions by the nodes of the network. The basic idea of the algorithms is to split the shared channel into a control segment and a transmission segment. The control segment is used to avoid conflicts among the nodes and to increase the utilization of the transmission segment. It is shown how these algorithms can be used to determine time-division multiaccess cycles with spatial reuse of the channel. >

New models and algorithms for future networks

Abstract: In future networks, transmission and switching capacity will dominate processing capacity. The authors investigate the way in which distributed algorithms should be changed in order to operate efficiently in this new environment. They introduce a class of new models for distributed algorithms which make explicit the difference between switching and processing. Based on these new models they define new message and time complexity measures which, they believe, capture the costs in many high-speed networks more accurately then traditional measures. In order to explore the consequences of the new models, they examine three problems in distributed computation. For the problem of maintaining network topology they devise a broadcast algorithm which takes O(n) messages and O(log n) time for a single broadcast in the new measure. For the problem of leader election they present a simple algorithm that uses O(n) messages and O(n) time. The third problem, distributed computation of a "globally sensitive" function, demonstrates some important features and tradeoffs in the new models and emphasizes and differences with the traditional network model. The results of the present paper influenced later research, as well as the design of IBM Networking Broadband Services (NBBS). >

On the existence of symmetric algorithms to find leaders in networks of communicating sequential processes

Abstract: We define a semantic notion of symmetry well-suited for networks of processes specified in Hoare's language CSP. Symmetric algorithms to find a leader in such networks are then studied. We show that the existence of such algorithms depends crucially on the network topology and on the use of input/output guards in processes. The election problem appears thus as a powerful criterion in assessing the expressive power of distributed programming languages like CSP.

Comparison of the square-wave and quasi-resonant topologies

Abstract: The waveforms of a square-wave DC-DC converter and a quasiresonant DC-DC converter are examined in detail and a comparison is made between the switching losses and conduction losses for each topology. Using data from commercially available semiconductor devices, conservative estimates are then given for the switching frequency at which the resonant approach becomes advantageous. The effect of an isolation transformer on this comparison is also addressed. >

Optimum design of IC power/ground nets subject to reliability constraints

Abstract: The authors formulate and solve the problem of sizing power/ground (p/g) nets in integrated circuits composed of modules, where the nets are routed as trees in the channels between the modules. Constraints are developed to maintain proper logic levels and switching speed, to prevent electromigration, and to satisfy certain design rule requirements. The objective is to minimize the area of the p/g nets subject to these constraints. An optimization technique tailored to this problem is developed. The technique solves the problem more efficiently than the steepest descent method and Newton's method. Several case studies are presented. >

Crossover minimization in directional-coupler-based photonic switching systems

Abstract: Methods of design directional-coupler-based switching networks with minimum number of crossovers are presented. Also presented is a modular construction scheme that allows large switching networks (with minimum of crossovers) to be built using identical chips containing smaller networks of the same type. The total number of crossovers and the maximum number of crossovers between an inlet-outlet pair have been analyzed in three major self-routing networks. Since many networks are based on these topologies, the results can be applied extensively to the study of many other switching networks. >

Optical interconnection using ShuffleNet multihop networks in multi-connected ring topologies

Abstract: In many applications, such as metropolitan area, campus, and local area networks, multicomputer interconnection networks, and the interconnection of cabinets, shelves, and boards, optical interconnection is increasingly favored over electrical. Recently, ShuffleNet multihop lightwave networks were proposed as a way to tap the vast bandwidth potential of optical fiber for multiuser packet communications. We consider the use of ShuffleNet multihop networks for optical interconnection, and study their implementation in ring topologies with each node connected to several other nodes of the ring (i.e., multi-connected ring topologies). To minimize fiber cabling congestion, the design procedure uses a new representation of the ShuffleNet connectivity graph and a generalization of Gray code patterns. As an example, only six fibers (without wavelength-division multiplexing) are required to interconnect 24 Network Interface Units (NIUs), providing a total network throughput of 1.47 Gb/s for an optical transmission rate of 100 Mb/s. The design also provides for easy, modular growth of multi-connected rings.

Training of a neural network for pattern classification based on an entropy measure

Abstract: A neural net model for pattern classification is introduced Unlike models in which the network topology is specified before training, in this model the network expands during training The proposed model introduces a novel type of unit (neuron) and a standard treelike feedforward network topology The simplicity of the interconnection pattern is a particular advantage over existing models Internal representations are formed by separating hyperplanes Selection of the hyperplanes and expansion of the network is based on an entropy measure which is appropriately defined The weight vectors of all units with a certain layer are determined in a single presentation of the training set >

Nonblocking photonic switch networks

Abstract: A practical algorithm is described, with examples, for deciding whether or not a given network of 2*2 photonic switches is truly unblocking. Nonblocking photonic networks with specific additional properties, e.g. planarity, short path length, are also discussed, and specific networks, which have advantages over the square networks so far fabricated, are described. It is also shown that a correspondence can be set up between classical switch networks and networks of 2*2 switches, so that the classical results on blocking can be carried over to these networks. >

The new routing algorithm for the ARPANET

Abstract: The new ARPANET routing algorithm is an improvement over the old procedure in that it uses fewer network resources, operates on more realistic estimates of network conditions, reacts faster to important network changes, and does not suffer from long-term loops or oscillations. In the new procedure, each node in the network maintains a database describing the complete network topology and the delays on all lines, and uses the database describing the network to generate a tree representing the minimum delay paths from a given root node to every other network node. Because the traffic in the network can be quite variable, each node periodically measures the delays along its outgoing lines and forwards this information to all other nodes. The delay information propagates quickly through the network so that all nodes can update their databases and continue to route traffic in a consistent and efficient manner. An extensive series of tests were conducted on the ARPANET, showing that line overhead and CPU overhead are both less than two percent, most nodes learn of an update within 100 ms, and the algorithm detects congestion and routes packets around congested areas.

A tradeoff between information and communication in broadcast protocols

Abstract: This paper concerns the message complexity of broadcast in arbitrary point-to-point communication networks. Broadcast is a task initiated by a single processor that wishes to convey a message to all processors in the network. We assume the widely accepted model of communication networks, in which each processor initially knows the identity of its neighbors, but does not know the entire network topology. Although it seems obvious that the number of messages required for broadcast in this model equals the number of links, no proof of this basic fact has been given before.