Showing papers on "Link-state routing protocol published in 1981"

Complexity of vehicle routing and scheduling problems

Abstract: The complexity of a class of vehicle routing and scheduling problems is investigated. We review known NP-hardness results and compile the results on the worst-case performance of approximation algorithms. Some directions for future research are suggested. The presentation is based on two discussion sessions during the Workshop to Investigate Future Directions in Routing and Scheduling of Vehicles and Crews, held at the University of Maryland at College Park, June 4–6, 1979.

Design and optimization of networks with dynamic routing

Abstract: The growth of electronic switching systems and the high-capacity interoffice signaling network provide an opportunity to extend telephone network routing rules beyond the conventional hierarchy. Network models are described that illustrate the savings inherent in designing networks for dynamic, nonhierarchical routing. An algorithm for engineering such networks is discussed, and the comparative advantages of various path-routing and progressive-routing techniques are illustrated. A particularly simple implementation of dynamic routing called two-link dynamic routing with crankback is discussed and is shown to yield benefits comparable to much more complicated routing schemes. The efficient solution of embedded linear programming (LP) routing problems is an essential ingredient for the practicality of the design algorithm We introduce an efficient heuristic optimization method for solution of the LP routing problems, which greatly improves computational speed with minimal loss of accuracy. We also project computational requirements for a 200-node design problem, which is the estimated size of the intercity Bell System dynamic routing network in the 1990s.

A generalized assignment heuristic for vehicle routing

Abstract: Abstract : We consider a common variant of the vehicle routing problem in which a vehicle fleet delivers products stored at a central depot to satisfy customer orders. Each vehicle has a fixed capacity, and each order uses a fixed portion of vehicle capacity. The routing decision involves determining which of the demands will be satisfied by each vehicle and what route each vehicle will follow in servicing its assigned demand in order to minimize total delivery cost. We present a heuristic for this problem in which an assignment of customers to vehicles is obtained by solving a generalized assignment problem with an objective function that approximates delivery cost. This heuristic has many attractive features. It has outperformed the best existing heuristics on a sample of standard test problems. It will always find a feasible solution if one exists, something no other existing heuristic can guarantee. It can be easily adapted to accommodate many additional problem complexities. By parametrically varying the number of vehicles in the fleet, our method can be used to optimally solve the problem of finding the minimum size fleet that can feasibly service the specified demand.

Provably Good Channel Routing Algorithms

Abstract: In this paper we present three new two-layer channel routing algorithms that are provably good in that they never require more than 2d-1 horizontal tracks where d is the channel density, when each net connects just two terminals. To achieve this result, we use a slightly relaxed (but still realistic) wiring model in which wires may run on top of each other for short distances as long as they are on different layers. Two of our algorithms will never use such a “parallel run” of length greater than 2d-1 and our third algorithm will require overlap only at jog points or cross points. Since in this wiring model at least d/2 horizontal tracks are required, these algorithms produce a routing requiring no more than four times the best possible number of horizontal tracks. The second algorithm also has the property that it uses uses at most 4n contacts, where n is the number of nets being connected.

Advances in Verifiable Fail-Safe Routing Procedures

Abstract: Two new versions of a distributed protocol for establishing and maintaining loop-free routing tables for communication networks with changing topology are presented. The protocols here possess significant advantages over previous versions in terms of complexity of the node algorithm and of the validation procedure, as well as the communication and storage needs. In addition, we present a procedure for establishing new and disrupted calls in a virtual or physical circuit-switched network, and for canceling existing calls, such that each call is loop-free and is established according to the routing tables provided by the protocol.

A Technique for Adaptive Routing in Networks

Abstract: A two-level adaptive routing scheme for packet-switched computer communication networks is proposed and investigated. The first level is quasi-static and based on the global network status. The second level is dynamic with decisions being made at each node in an attempt to obtain the savings in average delay predicted by a multiserver model of the node. Simulations confirm the predicted improvement.

Optimal Routing in Rectilinear Channels

Abstract: Programs for integrated circuit layout typically have two phases: placement and routing. The router should produce as efficient a layout as possible, but of course the quality of the routing depends heavily on the quality of the placement. On the other hand, the placement procedure would like to know how good a routing it can expect without actually routing the wires. This paper presents fast algorithms for optimal routing and for accurately estimating the area cost of such routings without actually laying them out.

A Failsafe Distributed Protocol for Minimum Delay Routing

Abstract: Previous distributed routing protocols in data-communication networks that achieve minimum average delay are extended to take into consideration topological changes in the network.

Modeling and analysis of flow controlled packet switching networks

Abstract: Packet switching networks with flow controlled virtual channels are modeled by closed multi-chain queueing networks. The tree convolution algorithm for an exact analysis of such models is discussed. The algorithm is very efficient when routing chains have sparseness and locality properties that are typical of communication network models. The accuracy of an approximate model of equivalent open chains was investigated. An optimal routing criterion for adding a virtual channel (with a window size of one) to an existing network is explored.

TWIGY A Topological Algorithm Based Routing System

Abstract: A two-level approach to routing is described, in which a multi-layer printed circuit board routing problem is broken down into a set of single-layer ones. A topological transformation is then applied to accomplish single-layer routing. A solution found for each layer by a search in this new domain is then translated back into physical space by means of a deterministic drawing algorithm. The algorithms are independent of specific technological parameters, affording their use on a variety of board routing grids, pad diameters and wire sizes.

A distributed minimum hop routing algorithm

Abstract: A two-part distributed algorithm for minimum hop routing in message-switched networks subject to end-to-end average message delay constraints is developed. The first part of the algorithm provides for unconstrained minimum hop routing, while the second corrects this routing to satisfy the delay constraints. Both parts are implemented nodewise via low-order linear programs wherein the information exchange required for each node to carry out its computations involves only adjacent neighbor nodes. The algorithm is illustrated via an example of an 8- node, 14-link network with 7 commodities, and directions for future research to enhance present results are indicated.

Aiming at a General Routing Strategy

Abstract: A general method for automatic routing, based on a channel splitting approach, is presented. A weighted graph depicting multilayer partitions and allowing expected channel occupancy estimation is introduced. Problems and algorithms related to the detailed routing phase are briefly reviewed.

A Preprocessor for Channel Routing

Abstract: This paper presents a "preprocessor" which separates a channel routing problem into two subproblems. One is a specialized channel routing problem where no two nodes of two different nets are of the same y-grid position. The other is a problem of connecting pairs of nodes where each pair of nodes has a path reserved for it. The use of a "preprocessor" in channel routing [5] is justified by the comparison of routing results.

A Responsive Distributed Routing Algorithm for Computer Networks.

Abstract: A new distributed algorithm is presented for dynamically determining weighted shortest paths used for message routing in computer networks. The major features of the algorithm are that the paths defined do not form transient loops when weights change and the number of steps required to find new shortest paths when network links fail is less than for previous algorithms. Specifically, the worst case recovery time is proportional to the largest number of hops h in any of the weighted shortest paths. For previous loop-free distributed algorithms this recovery time is proportional to h2.

Adaptive routing in large communication networks: Probabilistic study

Abstract: A network model is presented and conditions for stochastic stability of the network system are given. For adaptation algorithms which change the routing probabilities slowly (small stepsize), expressions for steady-state variances are derived; usimg these, guidelines for the selection of algorithm parameters are discussed.

Routing in Networks

Abstract: : This report is concerned with routing protocols in networks. The major result is a low bound for any oblivious routing strategy where the route of a packet depends only on the source and destination of the packet. We show that for any oblivious routing protocol for a network of n processors in which the maximum number of processors directly connected to any processor is d, there exists a permutation that requires time (sq. root of n) d (to the 3/2). For specific networks such as an n-cube we give an oblivious routing algorithm whose performance is close to this lower bound. (Author)