Showing papers on "Network planning and design published in 1979"

Continuous equilibrium network design models

Abstract: It is known that the network design problem with the assumption of user optimal flows can be modeled as a 0–1 mixed integer programming problem. Instead, we formulate the network design problem with continuous investment variables subject to equilibrium assignment as a nonlinear optimization problem. We show that this optimization problem is equivalent to an unconstrained problem which we solve by direct search techniques. For convex investment cost functions, the performance of both Powell's method and the method of Hooke and Jeeves is approximately the same with respect to computational requirements for a 24 node, 76 arc network. For the case of concave investment functions, Hooke and Jeeves was superior. The solution to the concave continuous model was very similar to that of the 0–1 model. Furthermore, the required solution time was far less than that required by the corresponding discrete model of the same network. The advantages and disadvantages of the continuous approach as well as the computational requirements are discussed.

Formulating and solving the network design problem by decomposition

Abstract: The optimal transportation network design problem is formulated as a convex nonlinear programming problem and a solution method based on standard traffic assignment algorithms is presented. The technique can deal with network improvements which introduce new links, which increase the capacity of existing links, or which decrease the free-flow (uncongested) travel time on existing links (with or without simultaneously increasing link capacity). Preliminary computational experience with the method demonstrates that it is capable of solving very large problems with reasonable amounts of computer time.

Comparative Discussion of Circuit- vs. Packet-Switched Voice

Abstract: Various other studies have already indicated potential advantage of packet-switching over tradiational circuit-switching concepts for voice communications. This paper explores the robustness of such comparisons for a range of network architectures. In particular, it is demonstrated that network sizing as related to the number of voice channels traversing a particular transmission link, and network topology with respect to the number of tandem links utilized in an end-to-end connection can have significant effects on the system performance. Estimates for end-to-end delay and the efficiency of trunk utilization are developed as a function of network topology to provide the insight necessary to identify network design limitations. A number of packet-switching design approaches, ranging from a pure datagram to a circuit-switching-like mode, are also discussed together with their effects on overall performance.

Some basic considerations in the design of hydrologic data networks

Abstract: Two preeminent considerations of data network design are the random nature of the hydrologic phenomena and the uses that will be made of the data. Information distilled from the data is usually measured in a parametric statistical sense, although the data user is more concerned with the integrated measure of information—what impact does the lack of perfect hydrologic information have on the ensuing decisions? Two facets of the network, the efficiency of the data collection and the effectiveness of the resulting information, must be integrated to achieve a complete network design.

An efficient dual approach to the urban road network design problem

Abstract: In this paper we present a computationally efficient technique for determining the optimal design of an urban road network. The procedure involves the assignment of network flows and the determination of improved link parameter values so that congestion is minimized subject to a budget constraint. The resulting problem is a very large nonconvex minimization program. It is shown that by dualizing with respect to a single constraint the resulting dual objective function can be evaluated by solving a traffic assignment problem. Since the dual objective function is a concave function of one variable, effective one-dimensional search techniques based on subgradients can be utilized to solve the dual (and thus the primal network design) problem. Since this network design problem reduces to solving several traffic assignment problems, it should be efficient for realistically large networks. Computational results for several problems with up to 553 constraints and 1,862 variables are reported.

Statistical considerations in network design

Abstract: Following some general remarks on the importance and unimportance of optimization in spatial network design, we take up, in modest detail, how one might exploit spatial autocorrelations and covariateinformation. We point out that spatial autocorrelations themselves require care in their estimation andthen proceed with two illustrations to show how probabilistic error calculations are made for mappingproblems using network station data. One illustration uses a quantitative mapping variable, and the otheruses a qualitative mapping variable.

Dimensionality problems in water quality network design

Abstract: Dimensionality problems in design of water quality networks arise from the multiple variables measured, which may be generated by different physical, chemical, and biological processes, and from the multiple spatial and temporal dimensions of the processes generating the measurements. The problem is further complicated by the range of objectives which a network may be required to meet. The designer is almost inevitably constrained by budget considerations to employ the same network to measure an array of variables, often for more than one objective. These considerations serve to pose serious difficulties in arriving at an analytical formulation of the problem, far less to solve it, with the result that almost all existing water quality networks have been designed on an ad hoc basis. Although no one approach is likely to be universally applicable, several techniques have been employed in particular situations. Included are state estimation, time series analysis, probability theory, and the theory of regionalized variables. Several promising applications of these techniques to water quality network design are reviewed, and suggestions for future research directions are advanced.

Delay related issues in integrated voice and data transmission: A review and some experimental work

Abstract: This paper focuses on network delays as they apply to voice transmission. First the nature of the problem is discussed and this is followed by a review of circuit, packet and hybrid switching. The concept of introducing delay to resolve contention in speech interpolation is also noted, and when applied to both voice and data messages, forms a basis for a relatively new and so-called “transparent” approach to network design. The second part of the paper deals with experimental work. First, external link considerations involving subnet access by frame synchronous vocoders is discussed, and an experimental software interface is described which exploits the 60 to 65% idle time in voice calls. Secondly, based on the simulation of variable network delays, first indications are that with 180 ms “hangover”, the perceptable threshold of variable delay is about 200 ms average. Finally, suggestions for further works on performance analysis and subjective testing are made.

Application of optimal subset selection to problems of design and scheduling in urban transportation networks

Abstract: The paper describes some possibilities for modifying the optimal network algorithm developed by Boyce, Farhi and Weischedel in a way that makes it applicable to some practical problems of network planning. The modifications, which have been tested with respect to their effect on the efficiency of the algorithm, include the introduction of asymmetrical demand structures, the integration of an existing network, the lexico-minimization of a dynamic objective function, and the consideration of constraints related to interdependencies between candidate links. Two small network problems and one medium-sized problem (61 nodes, 104 links, 16 candidates) have been computed; the results support the hypothesis that the algorithm may be applied to produce approximate solutions to problems of practical dimensions within a reasonable range of time.

Network design for a fully automatic wide area radiotelephone service

Abstract: The paper describes the design of a fully automatic wide-area radiotelephone system using a decentralized building block approach. The building blocks are implemented using firmware-based micro-processor techniques. Reliable high speed digital signalling is used over the radio path for call set up and control. The way in which calls are automatically routed to roaming mobiles without special subscriber dialled routing digits is explained. Other areas covered include numbering plan, usage sensitive billing and arrangements for interfacing manual switchboards for operator handled calls. Details of offered traffic measured on a pilot automatic system, operated in Vancouver for the last two years, are also included.

Shannon’s information theory in hydrologic network design and estimation

Abstract: The hydrologic basin and i t s data c o l l e c t i o n network i s treated as a communication system. The s p a t i a l and temporal c h a r a c t e r i s t i c s of the hydrologic events throughout the basin are represented as a message source and t h i s message i s transmitted by the network stations to a data base. A measure of the basin information transmitted by the hydrologic network i s derived using Shannon's multivariate information. An optimum network s t a t i o n s e l e c t i o n c r i t e r i o n , based on Shannon's methodology, i s established and i s shown to be independent of the estimation of the events at ungauged l o c a t i o n s . M u l t i v a r i a t e information transmission f o r the hydrologic network i s i n i t i a l l y computed using the di s c r e t e entropy concept. The computat i o n of the mu l t i v a r i a t e entropy i s then extended to the case of va r i a b l e s represented by continuous d i s t r i b u t i o n s . B i v a r i a t e and multivariate forms of the normal and lognormal d i s t r i b u t i o n s and the b i v a r i a t e form of gamma, extreme value and exponential p r o b a b i l i t y density functions are considered. Computational requirements are substantial when dealing with large numbers of g r i d points i n the basin representation, and i n the combina t o r i a l search for optimum networks. Computational aids are developed which reduce the computational load to a p r a c t i c a l l e v e l . The performance of optimal information transmission networks i s compared with networks designed by e x i s t i n g methods. The a b i l i t y of Shannon's theory to cope with the multivariate nature of the output from a network i s shown to provide network designs with generally superior estimation performance. Although the optimal information transmission c r i t e r i o n avoids the necessity of specifying the estimators for events at ungauged locati o n s , the c r i t e r i o n can also be applied to the determination of optimal estimators. The a p p l i c a b i l i t y of the information transmission c r i t e r i o n i n determining optimal estimation parameters i s demonstrated for simple and multiple l i n e a r regression and Kalman f i l t e r estimation. Information transmission c r i t e r i o n i s applied to design the l e a s t cost network where a choice of instrument p r e c i s i o n e x i s t s .