Showing papers on "Link-state routing protocol 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.

The Gradient Projection Algorithm for Multiple Routing in Message-Switched Networks

Abstract: Various algorithms have been proposed for determining the routing paths designed to minimize the average overall message time delay in message-switched networks. In this paper we describe the application of the gradient projection algorithm to this problem. This algorithm is a gradient-type search procedure designed to handle constrained optimization problems, into which category the routing problem falls. Calculations of the computational complexity of this algorithm indicate that it is particularly well-suited to networks with a limited number of commodities or source-destination pairs. The algorithm is applied to a representative group of distributed-type networks, of varying complexity. Execution times for this algorithm are compared with those obtained using the flow deviation routing algorithm. These agree roughly with the results of the computational requirement calculations; i.e., this algorithm generally requires less execution time for networks with a relatively small number of commodities than does the flow deviation method. (The actual running time depends significantly on the choice of the initial flows or routing paths, however.) For those networks in which all network nodes may be expected to communicate with all other nodes, however, the flow deviation method would be expected to be superior.

Reliability of packet switching broadcast radio networks

Abstract: Packet switching broadcast radio networks are receiving considerable attention as a feasible solution for applications involving fast network deployment requirements, inaccessible physical environments, and mobile communication devices. Such networks also offer economic alternatives to traditional multiplexing schemes for local distribution. Routing algorithms which enable point-to-point packet transportation have been developed for broadcast radio networks. It appears that a routing algorithm becomes more efficient when the number of alternate paths are restricted; on the other hand, reliability considerations suggest increasing the number of alternate paths. In this paper, we study and compare the reliability of broadcast radio networks for different routing algorithms.

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.

Reduction and Solution of Large Scale Vehicle Routing Problems

Abstract: This paper discusses the General Routing Problem approach to solving large scale routing problems. The General Routing Problem on network G = N; A requires finding the minimum cost cycle that visits every node in subset Q ⊆ N and that traverses every arc in a subset R ⊆ A. Utilizing special problem characteristics and the structure of real transportation networks, large reduction in effective problem size and complexity can often be made. This permits a very effective heuristic to produce optimum and near optimum solutions quickly.

Explicit Path Routing in Communications Networks.

Abstract: Alternate path routing (APR) has been applied to telephone networks, ATM and the Internet to support load balancing and survivability. The potential benefits of APR make it appear to be an ideal candidate for the bandwidth limited and dynamic mobile ad-hoc networks (MANETs). Our investigation of APR in the MANET environment has revealed that APR can, in some circumstances, provide as much as a 40% improvements in end-to-end traffic delay. Quite often, however, the network topology and channel characteristics severely limit what APR is able to achieve. Whereas these factors can be addressed in wired networks through the deliberate addition and rearrangement of routers and cables, this level of administration contradicts the distributed and self-organizing philosophy of MANETs. This does not mean that APR cannot flourish in this environment. Proper design choices can help to realize some of APR's potential. Multiple channel systems provide better link/route isolation than single broadcast channel networks. Routing protocols that provide a thorough view of network connectivity can fully reveal whatever diversity exists in the network. Other features, like multiple full-duplex transceivers per node and tighter integration of routing with media access control and power control may extend APR's abilities even further. The diversity offered by alternate path routing may contribute to improved capacity and reduced delays. However, the use of multiple diverse routes also increases a session's exposure to interruption by link failure. This tradeoff is a particular concern in the MANET environment, where node mobility and limited transmission power conspire to make link failures a frequent occurrence. Figure 8 illustrates the tradeoff between diversity and survivability, for our ad-hoc network with a uniform node speed of 10 [m/s]. Whereas the median lifetime for a single six hop route is 2.2 seconds, a typical pair of independent six hop routes will last only one second before experiencing a failure. In practice, the drop in interruption times resulting from APR may be less significant, as route coupling and limited knowledge of the network topology make completely independent route sets somewhat of a rarity. Of course, coding techniques (i.e. minimum descriptions coding, diversity/dispersity coding) can be applied to protect the user from service interruption. However, such protection requires extra bandwidth and may counteract any performance gains that might have been achieved through load balancing. Figure 8: tradeoff between route diversity and session stability Figure 6c: average end-to-end delay of 16 kbps UDP session multiple channels, proactive …

On the probability of success in a routing process

Abstract: Lee's path search mechanism has been identified as a percolation process and the probability of a successful search is obtained analytically.

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.

On Routing and "Delta Routing": A Taxonomy and Performance Comparison of Techniques for

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 ultimab 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 in- sight 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.

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.

Routing algorithm for a three-stage connection network in presence of fanout

Abstract: In this paper, the problem of routing connections through a three-stage connection network in presence Of fanout is considered. The assignment problem is viewed as a mapping of the input terminal set onto the output terminal set. An algorithm is presented which employs mapping operations to resolve blocking conflicts systematically as they are encountered. Relationships between the parameters of a 3-stage asymmetrical connection network which will minimize the number of switches and still leave the network rearrangeable, are also presented. The results from randomly generated output full and maximal assignments show that the algorithm is optimal for carefully designed networks.