Showing papers on "Node (networking) published in 1977"

Large-Scale Network Topological Optimization

Abstract: A cost-effective structure for a large network is a multilevel hierarchy consisting of a backbone network and a family of local access networks. The backbone network is generally a distributed network, while the local access networks are typically centralized systems. In special cases, the network may consist primarily of either centralized or distributed portions. This paper discusses topological design problems for such systems, including the concentrator location problem, the terminal assignment problem, the terminal layout problem (the constrained minimum spanning tree problem), the distributed network topological layout problem, and the backbone node location problem. Recent algorithm research, including exact and heuristic problem solutions, are described and computational experience is given. Finally, open problems in large-scale topological design are reported.

The navigation system of the JPL robot

Abstract: The control structure of the JPL research robot and the operations of the navigation subsystem are discussed The robot functions as a network of interacting concurrent processes distributed among several computers and coordinated by a central executive The results of scene analysis are used to create a segmented terrain model in which surface regions are classified by traversibility The model is used by a path-planning algorithm, PATH, which uses tree search methods to find the optimal path to a goal In PATH, the search space is defined dynamically as a consequence of node testing Maze-solving and the use of an associative data base for context-dependent node generation are also discussed Execution of a planned path is accomplished by a feedback guidance process with automatic error recovery

A correctness proof of a topology information maintenance protocol for a distributed computer network

Abstract: In order for the nodes of a distributed computer network to communicate, each node must have information about the network's topology. Since nodes and links sometimes crash, a scheme is needed to update this information. One of the major constraints on such a topology information scheme is that it may not involve a central controller. The Topology Information Protocol that was implemented on the MERIT Computer Network is presented and explained; this protocol is quite general and could be implemented on any computer network. It is based on Baran's “Hot Potato Heuristic Routing Doctrine.” A correctness proof of this Topology Information Protocol is also presented.

Shortest route with time dependent length of edges and limited delay possibilities in nodes

Abstract: Few algorithms have been proposed for the solution of the shortest route problem with time dependent lengths of edges. These algorithms are valid only under the assumption that parking in the nodes is unlimited and any desirable delay in departure time from a given node is permitted. This paper considers the case where such an assumption is not acceptable, and presents an efficient algorithm for the solution of the shortest route problem in networks with time dependent lengths of edges and parking regulations at the nodes. Some other possible extensions are discussed.

Backtracking Algorithms for Network Reliability Analysis

Abstract: Backtracking algorithms are applied to determine various reliability measures for networks These algorithms are useful in analyzing the reliability of many data communication networks We consider an undirected network where each node and each arc may be in one of two states: operative or inoperative These states are independent random events In addition to the more usual measure of network reliability, the probability that a specified pair of nodes can communicate, we consider more global measures such as the probability that all nodes can communicate and all operative nodes can communicate

Optimal Control of Single-Server Queuing Networks and Multi-Class M/G/1 Queues with Feedback

Abstract: We consider a queuing network with Poisson arrivals at each node. At each service completion epoch, a reward is received and the serviced customer changes nodes or leaves the system according to specified probabilities. In addition, linear holding costs are incurred. The problem is to schedule the server so as to maximize the expected discounted reward over an infinite planning horizon. This model is equivalent to a single-server, multi-class queuing system with feedback of the customers. We study two cases: general service times with a non-preemptive service discipline and exponential service times with a preemptive service discipline. For each case we show that a modified static policy of priority form is optimal and we provide an algorithm for computing an optimal policy.

Finding Equivalent Network Formulations for Constrained Network Problems

Abstract: This paper describes a procedure for determining if constrained network problems i.e., network problems with additional linear constraints can be transformed into equivalent pure network problems by a linear transformation involving the node constraints and the extra constraints. These results extend procedures for problems in which the extra constraints consist of bounding certain partial sums of variables. This has proved to be an effective managerial technique for a major automobile manufacturer and a major energy modeling company.

An Efficient Procedure for Implementing a Dual Simplex Network Flow Algorithm

Abstract: This paper shows that for linear programming formulations of network flow problems, the nonzero components of rows of the basis inverse are identical. A simple algorithm for identifying these nonzero components is given along with a suggested data structure for implementation. The algorithm requires only one bit of storage for each node plus one additional bit. Finally we indicate how these ideas may be used in the development of a dual simplex code for network flow problems.

The data management machine, a classification

Abstract: There has been much interest in the use of special purpose processors as the data base management component of data processing systems. The generic terms “backend” and “data management machine” have been applied to such devices. Examination of the literature reveals a broad cross section of host to backend functional distribution and interconnection methodology. This discussion represents an attempt to examine and classify several of these backend data base management machine configurations in terms of their operational parameters and application constraints. A formal taxonomy of such systems remains yet to be performed.At least three distinct classes of data management machine (DMM) are evidenced in the literature; they are the large host backend, distributed network data node and smart peripheral. The intended classes of problem that the various authors envision amenable to solution by the DMM approach exhibit overlap while the performance envelope in which each DMM architecture would provide a technically acceptable, economically sound solution to a given user requirement set varies. Some of the papers used as source for this work contained no explicit mention of either the problem classes or performance constraints that the described configuration was to address; thus liberty has been taken in interpreting the implicit application goals of these authors.

Software Controlled Access to Distributed Data Bases

Abstract: Control of a distributed computing network requires an efficient method of allocating file resources, together with the capability of avoiding or recovering from deadlock. This paper describes alternative approaches to the deadlock problem, and examines two control schemes, one centralized and one distributed. Simulation shows that when perfect reliability is assumed, the centralized scheme is more efficient, except when traffic is primarily local in nature at each node. In practice, however, a centralized controller is often undesirable, since failure of the central node causes system paralysis. A modified control scheme is proposed, in which the centre of control can shift its location to adapt to failure of network elements. It is expected that such an adaptive controller will prove superior in performance to either of the previous alternatives.

Topological Design of Distributed Data Communication Networks Using Linear Regression Clustering

Abstract: A new network decomposition-optimization algorithm is presented and evaluated via computer simulation. The network is first partitioned into subnetworks on the basis of lines fitted via linear regression to the node locations weighted by their traffic loads. Each node is then connected via a data line of appropriate capacity to a concentrator-multiplexer. The concentrators are then regarded as nodes, and the process is repeated as often as required. The resulting singly connected network consists of a hierarchy of concentrators whose number, capacity, location, and interconnection are selected as an inherent part of the design procedure to minimize network cost. The linear regression clustering (LRC) design procedure is evaluated via computer simulation by comparing the costs and performance of the resulting networks with that which results from use of an algorithm based on the generally applicable network design approach of iterative local optimizations or "search" procedures. The data supplied to the LRC and search algorithms include randomly generated node locations and traffic matrices, and specific (realistic) cost vs. capacity schedules for data lines and concentrators. Comparisons of network costs, queuing and transmission delays, network reliability and network design costs show the LRC algorithm to be markedly superior to the search algorithm. The paper includes a brief discussion of our results, and their implications.

Analysis and simulation of message-switched loop data networks

Abstract: The loop or ring-type data networks using full duplex-communication links between the nodes have been investigated. The results presented in the paper concern two specific modes for handling the messages. These are termed ‘store and forward’ and ‘check and forward’. Both modes have been analysed using extensions of the single-server queueing theory and also simulated extensively using GPSS software.The message traffic is Poisson distributed and can arise from any node with equal probability. The destination is selected to be any other node again with equal probability. The study has also considered the performance of the two modes for traffic having priorities. One conclusion arrived at in this investigation is that the traffic with priorities can be better handled by a network which handles messages in either store and forward or check and forward mode depending on the priority of the message.

Statistical multiplexing of data and encoded voice in a transparent intelligent network

Abstract: The paper describes the work done thus far in the development of a means of statistically multiplexing data and encoded voice in a transparent and intelligent network called TI-NET. A review of previous work in packetized voice transmission in a conventional packet switched network (ARPANET) has revealed problems related to large fixed and variable transmission delays. These problems result in degradations in speech quality in the form of time scale distortion and gaps due to very late or lost packets. The paper shows that TI-NET has various features which counter the above problems, and thereby make it appear very suitable for encoded voice transmission.The paper describes a software implementation of a protocol for encoded voice transmission which takes advantage of the 60 to 65% idle time in conversations (one way) so that only active periods in speech need be transmitted; this is not possible with present frame synchronous vocoders which transmit continuously.The paper describes the present experimental TI-NET which consists of two nodes (PDP11's) joined by a 9.6 kb/s link. For convenience the protocol for encoded voice transmission has been implemented in the TI-NET nodes, and the transparent transmission of data and encoded voice has been demonstrated. With regard to packetizing synchronous messages within TI-NET, a new protocol is described (and has been implemented) for padding partially filled “minipackets” that are likely to occur at the end of most synchronous messages.In addition, the paper discusses the features of another aspect of TI-NET, i.e. satellite extension nodes, which are used to enable both local and remote regions of high data concentration to access the subnet through 12-14 GHZ satellite links. It is shown that the advantages of accessing TI-NET by satellite extension nodes (as compared to accessing a conventional packet switched network by terrestrial facilities), include lower communication costs, greater accuracy and security, and smaller entrance delay.Finally, the paper describes an experiment in which data and encoded voice was transmitted from a TI-NET node at Carleton University, Ottawa, at 9.6 kb/s in “multiuser” packets, over the Hermes (CTS) satellite to NASA AMES Research Center in California, where it was looped back and returned to the same TI-NET node.The significance of the work described in the paper is that it represents an important step in the development of a transparent and intelligent public network capable of transmitting encoded voice (at 9.6 kb/s and lower rates) and data. Such a network can serve as an integrated system for data and voice and provide cost benefits to its users through savings in bandwidth of the order of 50 to 1, by statistically multiplexing data with vocoded voice.

Central telephone exchange for decentralised digital exchanges - scans for free time division in releiving cable

Abstract: The central telephone exchange, for digital decentralised exchanges, has incoming signals passed on to the receive cable alone that is connected to the subscriber for whom the incoming information is destined. The incoming information is temporarily stored in a memory using special switches. For time multiplexed operations, synchronisation at the beginning of a time frame ensures that the sync. signals appear on the transmit cable at the same time. This is achieved by holding the sync. signals in delay lines at each node in the telephone network until they all have the same phase.

Shortest route with time dependent length of edges and limited delay possibilities in nodes.

Abstract: Few algorithms have been proposed for the solution of the shortest route problem with time dependent lengths of edges. These algorithms are valid only under the assumption that parking in the nodes is unlimited and any desirable delay in departure time from a given node is permitted. This paper considers the case where such an assumption is not acceptable, and presents an efficient algorithm for the solution of the shortest route problem in networks with time dependent lengths of edges and parking regulations at the nodes. Some other possible extensions are discussed.

A Mask Pattern Analyzer With Circuit Check Data And Logic Simulation Outputs

Abstract: A mask pattern analyzer is described which features pattern generator tape and node overlay inputs and generates [1[ a floating node report t [2] floating branch report [3] a LOOCAP direct network file and [4] a LOGCAP with review file. All standard NAND, NOR, AND-OR-INVERT, OR-AND- INVERT circuits and nearly all transmission gate logic elements are synthesized directly into LOGCAP defined devices and placed in the LOGCAP network file. Circuits for which non-standard configurations are synthesized are placed in a file for review to make sure the logic synthesized is intended and not the result of errors in the layout or the node overlay. The analyzer also features an option allowing the user to direct the formation of subnets through the node overlay. Mirroring and/or rotation of previously defined subnets in the node overlay is permitted. When the subnet options are invoked, a subnet stringlist is generated as a 5th report.

Communicating path control system

Abstract: PURPOSE:To make unnecessary for the buffer at the intermediate node and to enable the priority control between the data within the communication network, by separating the setting and data transfer of communicating path.

The Design and Data Model of the BNL Archive and Dissemination System.

Abstract: The BNL Archive and Dissemination (BNLAD) System was designed to operate on a homogeneous distributed data base in a computer network. Its primary function is to present a uniform logical and physical view of already existing sequential files of data, so that these files can be accessed at any node of a computer network where the BNLAD System is operable. The architecture of the system, based on a subset of PL/I (the host language), is presented. The Data Model, i.e. the information content of the data base as it is viewed by the users, of the BNLAD System is discussed by means of examples. 7 figs.

Dynamic Modeling and Control of Digital Communication Networks

Abstract: Communication networks for digital data transmission can be classified as either circuit switched, message switched, or packet switched. In circuit-switched networks, a direct communication link is established between two users by closing a sequence of switches at appropriate network node points. The message is then transmitted continuously as is done, for example, in the national telephone network. In a message-switched network, the complete message is routed from node to node in the network until it reaches its destination. At each node, the message is placed in a queue to await next-node routing decisions and retransmission to a neighboring mode. Because of this two-step process, message-switched networks are known as store-and- forward networks. The packet-switched network is also a member of the store-and-forward class and differs from the message-switched network in that each message is subdivided into basic units called packets before being offered as input to the network.

Dynamic response time prediction for computer networks

Abstract: If the ultimate aim of a computing network is resource sharing, then the human component as well as the technical component of networking must be fully investigated to achieve this goal. This research is a first step toward assisting the user in participating in the vast store of resources available on a network. Analytical, simulation, and statistical performance evaluation tools are employed to investigate the feasibility of a dynamic response time monitor that is capable of providing comparative response time information for users wishing to process various computing applications at some network computing node. The research clearly reveals that sufficient system data are currently obtainable, at least for the five diverse ARPA network systems studied in detail, to describe and predict the response time for network time-sharing systems as it depends on some measure of system activity or load level.

On the Maximum Average Throughput Rate for a Tandem Node Network

Abstract: The problem of regulating inputs into a tandem store-and-forward node pair with finite queue limits in order to maximize the average message completion rate is considered from the viewpoint of Markov Decision Theory. A variation of the policy iteration procedure due to Howard [3] is used to compute optimum control policies and message completion rates for various configurations of system parameters. Comparative data are provided on the performance of the optimum control law relative to simpler local control laws which require no information sharing.