Showing papers on "Network topology published in 1980"

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.

Power System Observability: A Practical Algorithm Using Network Topology

Abstract: A power system is observable if the measurements made on it allow determination of bus voltage magnitude and angle at every bus of the network. This paper outlines the theoretical basis for an algorithm for determining observability. Based on this theory, an algorithm for networks containing both bus injection and line flow measurements is presented.

Deadlock Avoidance in Store-and-Forward Networks--I: Store-and-Forward Deadlock

Abstract: Store-and-forward deadlock in store-and-forward networks may be avoided by forwarding messages from buffer to buffer in accordance with a loop-free directed buffer graph which accommodates all the desired message routes. Schemes for designing such buffer graphs are presented, together with methods for using them to forward the messages in an efficient and deadlock-free manner. These methods can be implemented by a set of counters at each node. Such an implementation increases the efficiency of buffer use, and simplifies jumping between normal lowoverhead operation when deadlock is far and more careful operation when deadlock is near. The proposed deadlock avoidance mechanism works for any network topology and any finite routing algorithm.

A fundamental result concerning the topology of transistor circuits with multiple equilibria

Abstract: It is shown that a necessary and sufficient condition for a transistor network to possess more than one solution to its dc equations, for some choice of network parameter values, is that a certain simple set of connections, involving some pair of transistors, is present in the circuit's topological structure The presence of this set of connections, prescribing the presence of a certain special two-transistor substructure, referred to as a feedback structure, is thus a necessary condition that any transistor network must satisfy in order to possess the property of bistability The proof of this result is based upon a consideration of two topological properties of transistor networks possessing unique solutions to their dc equations In addition, it is shown how the amount of computation required to verify a certain well-known set of necessary and sufficient conditions which guarantees the uniqueness of solutions to the dc equations of transistor networks can be reduced by determining the location of all feedback structures

Analysis of a Two-Hop Centralized Packet Radio Network--Part I: Slotted ALOHA

Abstract: The design of packet radio systems involves a large number of design variables that interact in a very complex fashion. As this design problem in its general form is quite complex, a viable approach is to analyze some simple but typical configurations in an attempt to understand the behavior of these systems. In this paper, a two-hop centralized configuration is considered in which traffic originates at terminals, is destined to a central station, and requires for its transport the relaying of packets by store-and-forward repeaters. The through-put-delay performance is derived, and its dependence on such key system variables as the network topology, the transmission protocol, and the repeaters' storage capacities, is given. In this part, devices are assumed to be utilizing the slotted ALOHA access mode. Carrier sense multiple access is treated in Part II of this series [1].

Topological optimization of networks: A nonlinear mixed integer model employing generalized Benders decomposition

Abstract: A class of network topological optimization problems is formulated as a nonlinear mixed integer programming model, which can be used to design transportation and computer communication networks subject to a budget constraint. The approach proposed for selecting an optimal network consists in separating the continuous part of the model from the discrete part by Generalized Benders' Decomposition. One then solves a sequence of master and subproblems. The subproblems of the minimal convex cost multicommodity flow type are used to generate cutting planes for choosing potential topologies by means of the master problems. Computational techniques suited to solving the master and subproblems are suggested, and very encouraging experimental results are reported.

DNA: The Digital Network Architecture

Abstract: Recognizing the need to share resources and distribute computing among systems, computer manufacturers have been designing network components and communication subsystems as part of their hardware/software system offerings. A manufacturer's general purpose network structure must support a wide range of applications, topologies, and hardware configurations. The Digital Network Architecture (DNA), the architectural model for the DECnet family of network implementations, has been designed to meet these specific requirements and to create a communications environment among the heterogeneous computers comprising Digital's systems. This paper describes the Digital Network Architecture, including an overview of its goals and structure, and details on the interfaces and functions within that structure. The protocols implementing the functions of DNA are described, including the motivations for the specific designs, alternatives and tradeoffs, and lessons learned from the implementations. The protocol descriptions include discussions of addressing, error control, flow control, synchronization, flexibility, and performance. The paper concludes with examples of DECnet operation.

Voice Communication in Integrated Digital Voice and Data Networks

Abstract: Voice communication networks have traditionally been designed to provide either analog signal paths or fixed-rate synchronous digital connections between individual subscribers. These designs were aimed at accommodating the "streamlike" character of speech, which has traditionally been considered to flow from source to destination at a more or less constant rate. By way of contrast, interactive and computer-to-computer data transactions tend to be "bursty" in nature, and this has given rise to the development of packet-switching methods for data communications. The dichotomous nature of these two major traffic classes and the apparent conflict between the types of network services they require has resulted in the deployment of separate military communications facilities for voice and data. A challenge in the design of future systems is to achieve overall economy and flexibility in the allocation of resources via the efficient integration of both traffic types in common network facilities. This paper summarizes a number of advanced concepts for switching and flow control of combined voice and data traffic in integrated environments. Performance characteristics are described based on analysis results and computer simulation studies for both multilink terrestrial and broadcast satellite network topologies.

A locking protocol for resource coordination in distributed databases

Abstract: A locking protocol to coordinate access to a distributed database and to maintain system consistency throughout normal and abnormal conditions is presented. The proposed protocol is robust in the face of crashes of any participating site, as well as communication failures. Recovery from any number of failures during normal operation or any of the recovery stages is supported. Recovery is done in such a way that maximum forward progress is achieved by the recovery procedures. Integration of virtually any locking discipline including predicate lock methods is permitted by this protocol. The locking algorithm operates, and operates correctly, when the network is partitioned, either intentionally or by failure of communication lines. Each partition is able to continue with work local to it, and operation merges gracefully when the partitions are reconnected.A subroutine of the protocol, that assures reliable communication among sites, is shown to have better performance than two-phase commit methods. For many topologies of interest, the delay introduced by the overall protocol is not a direct function of the size of the network. The communications cost is shown to grow in a relatively slow, linear fashion with the number of sites participating in the transaction. An informal proof of the correctness of the algorithm is also presented in this paper.The algorithm has as its core a centralized locking protocol with distributed recovery procedures. A centralized controller with local appendages at each site coordinates all resource control, with requests initiated by application programs at any site. However, no site experiences undue load. Recovery is broken down into three disjoint mechanisms: for single node recovery, merge of partitions, and reconstruction of the centralized controller and tables. The disjointness of the mechanisms contributes to comprehensibility and ease of proof.The paper concludes with a proposal for an extension aimed at optimizing operation of the algorithm to adapt to highly skewed distributions of activity. The extension applies nicely to interconnected computer networks.

A Tradeoff Study of Switching Systems in Computer Communication Networks

Abstract: This paper is concerned with a comparison study of three switching techniques used in computer-based communication networks: circuit switching, message (packet) switching, and cut-through switching. Our comparison is based on the delay performance as obtained through analytic models of these techniques. For circuit switching, the model reflects the phenomenon of channel reservation through which it can be shown that when circuit switching is used, data communication networks saturate rapidly. Through numerical examples, it is shown that the boundary between the areas of relative effectiveness of these switching techniques depends very much on the network topology (more precisely the path length of communication), the message length, and the useful utilization.

Processor Interconnection Strategies

Abstract: In this paper, we describe four families of topologies for interconnecting many identical processors into a computer network. Each family extends to arbitrarily many processors while keeping the number of neighbors of any one processor fixed. These families are investigated with respect to bus load, routing algorithms, and the relation between the average interprocessor distance and the size of the network.

Simulation of a Class of Ring-Structured Networks

Abstract: This paper presents a new modular loop/ring architecture combining advantages of several earlier centralized and decentralized ring-structured loop networks while remaining simple. This is accomplished by introducing two major innovations: first, use of a separate control loop for control messages flowing between nodes and a loop controller; second, dynamically implementing partitionable segments between adjacent nodes and treating them as separate links for data transmission.

Separation axioms for interval topologies

Abstract: In Theorem 1 of this note, results of Kogan [2], Kolibiar [3], Matsushima [4] and Wolk [71 concerning interval topologies are presented under a common point of view, and further characterizations of the T2 axiom are obtained. A sufficient order-theoretical condition for regularity of interval topologies is established in Theorem 2. In lattices, this condition tuns out to be equivalent both to the T2 and to the T3 axiom. Hence, a Hausdorff interval topology of a lattice is already regular. However, an example of a poset is given where the interval topology is T2 but not T3.

Large Change Response Sensitivity of Linear Networks

Abstract: Absrmzcr-A general systematic method for determining lqe-hmge, muMiparameter sensitivity of linear networks is developed from the formal thmy of scattering in amdensed matter The method, based on matrix mdpulation, co- and unifies previous works on analog and digital networks Standard Basis Operators are intmduced as an expedient too4 wbicb aide3 in the solution of scattering matrix equations Explicit exact sensitivity formulas are developed for several types of multipammeter changes in both analog and digital networks I INTR~LXJCT~~N I N THE last decade many papers have dealt with the problem of linear network response function sensitivity to changes in network parameters Several recent works [l]-[7] have focused attention on response function change due to large-scale multiparameter changes In the area of digital networks, Temes and Cho [l] have developed a useful formula for calculating large-scale sensitivities Their method, utilizing Tellegen’s theorem for digital networks, extends the Taylor series single-parameter formula of Crochiere [5] to a multivariable sensitivity formula The motivation for the work presented here is severalfold It is shown that general linear network sensitivity functions are generated by matrix manipulation using techniques from scattering theory commonly applied in the quantum theory of condensed matter [8] The results are independent of any physical arguments, other than the assumption that the network topology is a constant No assumptions are made concerning the structure of the “shift” matrix characterizing the changed parameters of the network 4 systematic procedure, utilizing Standard Basis Operators (SBO) [9] is introduced to solve scattering matrix equations, which yields network response functions of the changed network in terms of response functions of the original network In calculating the new response functions, it is shown to be advantageous to distinguish three classes of network parameters: those associated with a single node (node parameters), those linking two nodes with one way information, or signal, transfer (unilateral bond parameters), and those linking two nodes with twoway signal transfer (bilateral bond parameters) Explicit exact sensitivity formulas are developed for parameter changes in each class, and a linear active two-port network is used as an example to illustrate the application of one of the multiparameter formulas

Computer-Aided Analysis and Design of Networks Containing Commensurate and Noncommensurate Delay Lines

Abstract: Several computer programs are described for the analysis and synthesis of networks containing transmision lines, lumped resistors, voltage sources and current sources. There are no restrictions on the topology of the networks and degenerate elements can also be included. In the noncommensurate case the transmission lines could have different delays and thus the degree of freedom for each network is doubled. State-space techniques are used to formulate the solution to the problem and the high degree of generality was achieved by using topological methods to derive the state equations. Several examples are given.

Network Theory and Filter Design

Abstract: Network Topology Network Equations Solution of Network Equations and Sinusoidal Response Network Theorems Natural Frequencies and Network Functions Multiterminal Networks State Equations Elements of Network Synthesis Approximation Insertion Loss Synthesis Active Networks and Filters Appendixes: Matrix Algebra, Laplace Transforms, Natural Frequencies, Bode Plots, Scattering Parameters, Image Parameter Filter Design Index

Signal-flow-graph analysis by decomposition method

Abstract: The paper concerns a new approach to the topological analysis of linear networks. It gives a brief description of the hierarchic decomposition method (i.e. multiple decomposition of a decomposed network) which can be applied in computer analysis of networks. It is shown that this method in computer applications considerably reduces the number of operations needed, and thus the computer time. The applications of the method to the analysis of signal-flow graphs have been pointed out. The algorithms of analysis, and some advantages of this method, are described briefly at the end of the paper.

Performance Issues in Back-End Storage Networks

Abstract: A back-end storage network allows heterogeneous mainframes and devices to share resources, unhampered by hardware compatibility requirements. This flexibility has implications for the network's performance.

Topological analysis of switched-capacitor networks

Abstract: A topological approach to the analysis of s.c. networks is presented. A graph model is chosen and explicit formulae are subsequently derived for all transfer functions in the z-domain. A corresponding topological analysis program has been constructed, giving transfer functions which are analytically dependent on z and capacitance elements.

The Time and Frequency Domain Analysis and Synthesis of Distributed and Lumped/Distributed Networks

Abstract: Using state-space techniques, a method has been developed for the computer-aided analysis and synthesis of networks containing both lumped and distributed elements. The method is very powerful as it can deal with any network topology and the same basic equations can be used in either the frequency or time domains. The method does not require the application of the Fast Fourier Transform which is not suitable for lumped/distributed networks since the frequency response is neither periodic nor monotonically decreasing. Computer-aided procedures based on this method have been developed and several examples of time and frequency domain analysis and design are given.

Critical section methods for loop plant allocation

Abstract: Allocation is the planning of current and future commitments of spare feeder capacity in the loop plant network. The purpose of allocation is to make the most efficient use of existing and future feeder facilities to reduce network operating costs and to defer capacity expansion. In this paper, new heuristic allocation algorithms are described that can be applied to multigauge feeder routes with complex topologies. Algorithms are described for both routes with high growth in customer demand and for routes with substantial customer movement but with little net growth. A combined algorithm that can be applied to routes with general growth characteristics is also described. A detailed application example is also included.

A bounded optimization algorithm for capacity assignment in computer communication networks

Abstract: An algorithm is derived here for minimizing point to point delay in a store and forward computer communication network for any of the following topologies : a single node with multiple inputs (through communication processor ports), two nodes multiply connected or a multilevel (hierarchical) network composed of many single and two node combinations of multiple connections. The constraints of (1) a given lower and upper bound on each link capacity and (2) the summation of all capacities to a specific given value, for a section of the network or the entire network, are applied to formulate the capacity equations.

遲廷을 수반하는 Network의 信賴度計算에 관한 硏究

Abstract: In a computer communication network. the reliability and transfer-delay of communication are important measures of performance. This paper describes a method of computing the reliability of a network with delay. When network elements fail, delay is defined as the length of the shortest remaining path between two specified nodes. We find the occurrence probability of events that a key node can communicate with a group of terminal nodes so that a specified delay is not exceeded. The desired events are mutually exclusive and contain a tree. Our algorithm efficiently generates all the events by noting network topology.

Learning routing applied to large scale packet–switched communication networks

Abstract: Learning routing is introduced to large-scale communication network to compensate the lack of a priori information on the network behavior. Learning routing consists of learning automaton as a learning controller placed at each network node. This learning automaton makes decision on routes for packets which are the basic unit of data to be transmitted through the network. Using learning automaton we propose two routing methods, LRI and LRI, which are basically reinforcement methods for the learning automaton. The effectiveness of these proposed methods is shown by means of simulation on a concrete network topology.

A network description language for the real time control of power systems

Abstract: The paper presents the specifications and characteristic features of a language specifically adapted for the control of large power systems. To begin with, a brief overview of the impact of computers in Energy Control Centers is presented. The use of on-line computer systems for decision making in power systems has necessitated the need for developing more specific methodology which would take into account the particularities of power systems. Our approach has been motivated by the fact that the information on the topology of a network at a given instant forms the basis of all real time control algorithms. The strategy of remote control of network topology could be an effective way of assuring security and economy in power system operations. We propose a special purpose language for describing the operations on a power system, with a view to meeting the following aims : - to construct an operational data base. Provide means of on line updating. - to provide the primitives for the automatic generation of a logically related elementary switching sequence (close/open switch) from a set of global instructions defined in the operator level language. The generation of the elementary sequence takes into account operational or legal restrictions.

Sparsity considerations in power system equivalents

Abstract: It is shown that for practical power system applications the amount of network reduction to be performed is a function of both the topology of the network and the impedance of the equivalent branches. It is also shown that it is not sufficient to consider only the topological characteristics of the network to be equivalized in deciding about the nodes that should be eliminated.

Optical Channels In Distributed Processing

Abstract: The steadily increasing number of microprocessor controlled devices such as intelligentterminals, numerically controlled machines, etc. created the need for new approaches to theproblems associated with distributing processing functions. Optical communication devicescould be used in order to develop new methods to facilitate the distribution of tasks andprograms among a large number of small and relatively slow machines. The essence of theapproach should be to find means "to pay with bandwidth and low self induced noise" forsimpler and more flexible implementation of task and program distribution. An analysis hasbeen conducted leading to the formulation of the relationship between bandwidth, protocols,and topologies. It appears that ring and common bus topologies are the most suitable forimplementation utilizing optical communication channels. An experimental fiber optic basedloop system has been designed and constructed. The current realization operates at20 Mb /sec and affords a 255 unit addressing space. The addressing space can be arbitrarilydivided into physical and functional addresses. Mechanism for controllerless operation hasbeen developed and tested. The current data rate can be increased to about 200 Mb /sec with-out major design changes. Measurement, simulation and analytical results are reported.IntroductionThe recent proliferation of microprocessor applications resulted in a growing interestin local communication networks. There usually exists a need to communicate between someor all machines in a given installation. Communication systems have to be designed whichwill enable an orderly exchange of messages between a very large number of dissimilarmachines. In addition, the thus created network will have to be able to provide for simpleaddition and deletion of machines. The limited speed of a typical microprocessor driventerminal restricts the amount of communication effort which can be assigned to any givenmachine. Hence, the interfacing procedure between a machine and the network has to requireas little computational effort on the part of the terminals as possible. In traditionalcomputor network designs, a great amount of effort was invested in communication schemeswhich maximized the channel utilization.2 The advent of optical communication systemsraises the possibility of taking a radically different approach. Namely, to try and "paywith bandwidth" for a simpler and more flexible local network. In this paper we proposesome approaches to a practical realization of the idea discussed above.In section 2 we list the required system parameters. Then we proceed to investigateseveral topologies and evaluate them in view of the established parameters. We show thatloon and common bus topologies appear to be the most suitable for satisfying the statedrequirements. Finally, we compare both approaches with regard to a fiber based implemen-

Adaptive Bifurcated Routing Algorithm with Threshold

Abstract: With cost of computation decreasing, packet switched computer communication networks are becoming increasingly cost effective. To ensure robustness, mesh type topologies are often used. However, such network configurations require efficient and effective routing algorithms.

A Distributed Computing Network for Real-Time Systems.

Abstract: : Partial interconnection, ring, and global bus topologies are examined in this document for use in a real-time distributed computing network. Message lengths and capacity allocation strategies for network links are evaluated in determining system performance based on average message delay. The data suggest a network topology for the application under study. Processor delays at each of the nine nodes in the network are introduced in a simulation model of a global bus network. Thus, link traffic and processor delays are utilized with message arrival rate, network bandwidth, and processor capacity parameters to arrive at a satisfactory computer system network for a real-time application. A methodology is developed whereby software requirements are determined in terms of the number of instructions executed. The desired system response time is established and software and hardware specifications may then be defined.