Showing papers on "Routing table published in 1979"

A Failsafe Distributed Routing Protocol

Abstract: An algorithm for constructing and adaptively maintaining routing tables in communication networks is presented. The algorithm can be employed in message as well as circuit switching networks, uses distributed computation, provides routing tables that are loop-free for each destination at all times, adapts to changes in network flows, and is completely failsafe. The latter means that after arbitrary failures and additions, the network recovers in finite time in the sense of providing routing paths between all physically connected nodes. For each destination, the routes are independently updated by an update cycle triggered by the destination.

Routing and flow control in systems network architecture

Abstract: Systems Network Architecture (SNA) has been enhanced to include features that address the topological, routing, congestion, reliability, and availability problems of networks. An important aspect of this new release of SNA is that it allows multiple active routes between network nodes. Multiple routing permits sessions between network users to use alternate routes in case of unexpected or planned route disruptions. In this paper, the multiple routing architecture of SNA is described. An unrestricted data flow into the network can cause long delays and buffer depletion. Network congestion can be avoided by employing flow control mechanisms at both the local (node) and global (network) levels. This paper focuses on global flow control and describes the adaptive trafic-pacing "window" size algorithm that is the basis of the global flow control in SNA.

An overview of the new routing algorithm for the ARPANET

Abstract: The original routing algorithm of the ARPANET, in service for over a decade, has recently been removed from the ARPANET and replaced with a new and different algorithm. Although the new algorithm, like the old, is a distributed, adaptive routing algorithm, it is not similar to the old in any other important respect. In the new algorithm, each node maintains a data base describing the delay on each network line. A shortest-path computation is run in each node which explicitly computes the minimum-delay paths (based on the delay entries in the data base) from that node to all other nodes in the network. The average delay on each network line is measured periodically by the nodes attached to the lines. These measured delays are broadcast to all network nodes, so that all nodes use the same data base for performing their shortest-path computations. The new routing algorithm was extensively tested on the ARPANET before being released. This paper describes the algorithm and summarizes the results of these tests.

Optimal Distributed Routing for Virtual Line-Switched Data Networks

Abstract: An algorithm that provides minimum delay routing in a data communication network using virtual line-switching is presented. The algorithm uses distributed computation in the sense that the nodes of the network update their information in an orderly fashion based on messages received from their neighbors. Receipt of these messages also triggers the various steps of the update and rerouting, so that these operations are performed in appropriate sequencing. For stationary input requirements and fixed topology the algorithm reduces network delay at each step and provides loop-free routing in the network. The method also provides an algorithm for quasi-static routing, when the input flows are slowly changing.

Global Router

Abstract: The paper describes a new router which develops all connections simultaneously. Routes do not exist as lines, but rather as connected irregularly shaped areas which grow and retract in an amoeba-like manner. It is as if some routes are being rerouted, but it is all done at once. Because the cell map is scanned sequentially, the data handling and storage is vastly simplified.

The Minimum Width Routing of a 2-Row 2-Layer Polycell-Layout

Abstract: This paper presents a new routing principle that leads to an algorithm to realize the minimum width of the 2-layer channel area between two rows of terminals to be interconnected. Besides the theoretical results, practically applicable routing algorithms based on our principle are developed.

A decentralized algorithm for optimal routing in data-communication networks

Abstract: The goal coordination technique of optimization theory for large-scale systems is used to develop a decentralized algorithm for optimal routing in data-communication networks. The algorithm is in two parts of which the first solves the optimal flow assignment problem and the second provides the corresponding optimal routing. All calculations are distributed among the nodes and require information only from adjacent nodes. The results are illustrated via an example and problems for future research are indicated.

Failsafe distributed optimal routing in data-communication networks

Abstract: : Iterative protocols for adaptive routing in line and message switched data communication networks are presented in this thesis. Distributed computation is used in the sense that each node in the network bases all its decisions on control messages received only from its neighbors. Thus, each node in the network determines individually onto which of its outgoing links to send the flow, addressed to a specific destination. The control messages exchanged between neighbors contain information about network connectivity, network congestion and link failures. Loop-free routing for each destination is maintained in the network at all times. Generally, prevention of loops results in saving resources and reduction in delay. In addition, loop-free routing establishes a partial ordering on the set of nodes of the network. The latter property is extensively utilized throughout this work. failsafe and deadlock-free operation of the protocols is guaranteed, meaning that after arbitrary failures and additions of links and nodes, the network recovers in finite time. Recovery means that routing paths are provided between all connected nodes. For stationary input traffic statistics and fixed topology the protocols are optimal. they reduce network delay at each iteration and minimum average delay over all routing assignments is obtained in steady-state.

A Routing Algorithm Using the Nearest-Neighbor Concept

Abstract: The design of routes for delivery or assembly of goods or people and the associated problem of vehicle scheduling is a relatively new problem to be tackled by operations researchers although it has vexed decision makers in the business world since the invention of the delivery vehicle. The salient feature of the problem is that of finding the leastcost paths emanating from and terminating at a warehouse or depot over which one or more vehicles are to traverse in serving each of n customers. This is by no means a trivial problem given the service-oriented nature of today's economy, the congestion on highways and streets, and the present energy situation. Further, it is not easily resolved with traditional techniques of the operations researcher because of its "combinatorial" nature (see Hallberg and Kriebel). The first researchers to tackle this problem appear to have been Garvin, Crandall, John, and Spellman. Their approach, however, relied on the use of linear programming which is not known to be particularly efficient (if feasible at all even with modern-sized computers) at solving "combinatorial" problems. They were able to generate optimal solutions, but only for routing problems of a size that had no practical significance. This work spurred others to investigate the problem and led to the work of Clarke and Wright, who developed a simple but effective heuristic approach that has proven in a variety of applications to yield "good," although not necessarily "optimal," solutions to routing problems of a practical size.' In a recent application, we have isolated problems having certain unique characteristics for which the Clarke-Wright technique will often produce unacceptable (and clearly nonoptimal) results. While several authors have suggested modifications to improve upon the Clarke-Wright technique (see the review articles by Turner, Ghare, and Fourds, and by Golden, Magnanti, and Nguyen), none have dealt with the specific problem encountered here. In this paper we describe the nature of these u iquely structured problems, and outline a modification of the Clarke-Wright method which mainains the integrity of the basic procedure, ensures better (more nearly optimal) solutions for the class of problems described, and ensures no worse solutions for routing problems that do not have the structure of those described here.

A simulation model for network routing

Abstract: The simulation program described in this paper was devised as a vehicle for the study of communication network routing procedures. It was designed to model the behavior of a wide range of network topologies and routing disciplines. An event driven simulation approach was chosen to minimize program development time and complexity.GASP-IV was selected as the simulation language. The determining factor in choosing the language was the clean interface it presents to FORTRAN. The use of GASP-IV permits utilizing the full power of FORTRAN in describing complex routing algorithms while simultaneously relieving the programmer of the responsibility for such essential housekeeping functions as enqueuing and dequeuing messages, file manipulation and event sequencing.As an application of this simulator, a loop-free distributed adaptive routing algorithm is proposed and analyzed. Simulation results are presented and the effect of the algorithm on overall network performance is examined. In addition to a loop-free property, the algorithm is shown to provide a partial solution to the single path routing problem. Furthermore, a modification to the algorithm is given which precludes message loss, and is shown to be superior in performance to current update algorithms (PUA).