Showing papers on "Routing table published in 1976"

A “DOGLEG” channel router

Abstract: This paper presents an algorithm for interconnecting two sets of terminals across an intervening channel. It is assumed that the routing is done on two distinct levels with all horizontal paths being assigned to one level and all vertical paths to the other. Connections between the levels are made through contact windows. A single net may result in many horizontal and vertical segments. Experimental results indicate that this algorithm is very successful in routing channels that contain severe constraints. Usually, the routing is accomplished within one track of the mathematical lower bound. The routing algorithm presented here was developed as part of LTX, a computer-aided design system for integrated circuit layout and was implemented on an HP-2100 minicomputer. A typical channel (300 terminals, 100 nets) can be routed in less than 5 seconds. Routing results are presented both for polycell chips under development at Bell Laboratories and for examples that exist in the published literature. For the latter, reductions of 10% in the wiring area were typical.

Method for building-up of routing addresses in a digital telecommunication network

Abstract: In a digital telecommunication network containing bearer channels between switching nodes, the method of building-up a routing address consisting of routing words that are associated with the switching nodes and via which the transmission of information packets is effected in accordance with the routing address contained in each packet, and for their storage in the region of a called subscriber, dispatching a build-up packet from the first calling subscriber which contains the location-independent call number of the called second subscriber, each switching node retransmitting to other switching nodes connected to it at least the first of several successively received build-up packets having the same call number and whose routing address does not exceed a specific length and adding to each build-up packet retransmitted a routing word associated with the bearer channel connected to it and forming a part of the travel path of the build-up packet, the called subscriber designated by the call number or the switching node connected directly to the called subscriber receiving at least one build-up packet intended for it and storing ar least one of the routing addresses built-up by the build-up packet received.

On Routing and "Delta Routing": A Taxonomy and Performance Comparison of Techniques for Packet-Switched Networks

Abstract: An inherent capability of packet-switched networks is the speed at which they can be reconfigured; various dynamic or adaptive routing techniques have been conceived to exploit this capability. In this study, existing techniques are described and an "ultra-dynamic" technique, delta routing, is invented. Several promising techniques are then selected for comparison with one another and with a network's ultimate carrying capacity. The goal is to shed light on the questions if and when one should use which kind of adaptive routing. First, a taxonomy of routing strategies is presented. In addition to delta routing, random, proportional, shortest path, and shortest path fixed-for-session duration are selected for comparison and their mechanisms described. The delay and efficiency performance of the five techniques are then compared with one another and with ideal behavior via simulations. These have been carried out concentrating on four very small networks, each with very different characteristics with the intention of gaining insight into the strengths and weaknesses of the various techniques. A ten-node network has also been simulated. The results favor delta routing which is most effective in highly interconnected network enviroments.

On quadratic adaptive routing algorithms

Abstract: Two analytic models of a store-and-forward communications network are constructed, one to find the optimal message routing and the other to illustrate the equilibrium (stationary state) maintained by an adaptive routing algorithm. These models show that adaptive routing does not satisfy the necessary conditions for an optimal routing. Adaptive routing tends to overuse the direct path and underuse alternate routes because it does not consider the impact of its current routing decision on the future state of the network. The form of the optimality conditions suggests that a modification of the adaptive algorithm will result in optimality. The modification requires the substitution of a quadratic bias term instead of a linear one in the routing table maintained at each network node. Simulation results are presented which confirm the theoretical analysis for a simple network.

Effects of a Priority Discipline in Routing for Packet-Switched Networks

Abstract: This paper addresses itself to some comparisons of adaptive routing algorithms in store-and-forward Communication nets. The intent here is to demonstrate how some relatively simple add-ons to already existing adaptive algorithms can decrease the average message delay and increase message throughput in the network. The overview of many existing routing algorithms is intended to point out that, although an algorithm may be adaptive, it is not necessarily good in terms of the performance measures addressed in this paper. The basic objective of this study is to assess the effects of endogenous priority assignment to messages that have reached some specified aging threshold while in the network and to note the effects of Such priority assignment on network performance. The performance measures are average message delay, throughput, and number of messages undelivered. The routing techniques are demonstrated via simulation on an 8node highly connected network and a 19-node Advanced Research Projects Agency (ARPA) network. The routing algorithms are applied with and without network element destruction on the selected networks.

Local optimization of routing tables for data networks

Abstract: Data communication networks generally contain routing tables at each of the nodes of the network. We consider the routing tables at a given node to specify the fraction of traffic for each destination that should travel over each of the outgoing links from the given node. An iteration algorithm is presented which, when applied at each node using update information from adjoining nodes, converges to the routing tables that minimize average delay in the network for stationary input statistics. The algorithm has the property that the traffic to each destination is guaranteed to be loop free at each iteration of the algorithm. Several kinds of loop freedom and their implications are discussed.

Optimal routing strategies in a class of networks

Abstract: For networks with given topology and fixed one-way link capacities the problem of the dynamic minimization of the average message delay over priority disciplines and routing procedures at each node is studied. It is assumed that a controller is available at each node and that a strategy is to be found for traffic direction on the basis of varying information patterns, such as the sizes of the queues in the different incoming and outgoing links, with or without the Poisson and exponential statistics assumptions.