Showing papers on "Destination-Sequenced Distance Vector routing published in 1986"

Distributed asynchronous optimal routing in data networks

Abstract: In this paper we study the performance of a class of distributed optimal routing algorithms of the gradient projection type under weaker and more realistic assumptions than those considered thus far. In particular, we show convergence to an optimal routing without assuming synchronization of computation at all nodes and measurement of link lengths at all links, while taking into account the possibility of link flow transients caused by routing updates. This demonstrates the robustness of these algorithms in a realistic distributed operating environment.

Near-Optimal n-Layer Channel Routing

Abstract: In this paper we present two n-layer channel routing algorithms that guarantee successful routing of the channel for n greater than three. The first is linear and optimal given a VHV...HV assignment of layers. The second, using an HVH...VH layer assignment, is quasilinear and performs optimally on examples from the literature. Except in pathological cases, we expect the latter router to perform within one row of optimal. For comparison with published examples we implemented the second router in five and three layers. The five-layer implementation routed all examples optimally while the three-layer implementation routed the examples with the same or fewer rows than the published examples. With its n-layer capability this channel router will allow channel routing to be used when more than three layers are available. This router can also be used to evaluate the utility of additional layers.

State-dependent routing for telephone traffic: Theory and results

Abstract: In the modern telephone network, it has become feasible to consider sophisticated call-routing schemes in order to minimize network blocking --- in particular, routing schemes which select a route for a call on the basis of the network 'state' at the time of call-arrival. In this paper, we construct an analytical model for such state-dependent routing in the framework of Markov decision processes, and derive a simple state-dependent routing scheme called 'separable' routing. The performance of this routing scheme in two network designs for a metropolitan network model is compared over a range of loads, by means of call-by-call simulations of traffic flow, with that of two other schemes: the 'sequential' routing used in the Dynamic Non-Hierarchical Routing (DNHR) network, and the 'Least-Loaded Routing' (LLR) proposed for the Trunk Status Map. In one case, separable routing achieves lower network blocking than the other schemes at normal load and overloads, while, in the other case, the improvement occurs only above a certain level of overload. However, a modified version of separable routing (to be presented in a future paper) achieves better performance than the other schemes in both networks over the entire range of loads.

Computer Networks with Compact Routing Tables

Abstract: The routing problem in computer networks is traditionally solved by providing detailed routing information for all destinations at every node We consider the problem of routing messages with only a small amount of information at every node For example, for every connected N-node network a scheme can be devised such that every message can be routed within O(√N) routing decisions Improving on an observation of Santoro & Khatib [3] for trees we derive a general method of routing messages in arbitrary networks using tables of a size corresponding to the number of links at a node, while utilizing all links in the network

An optimal adaptive routing algorithm

Abstract: An adaptive routing algorithm for packet-switched networks is proposed. This algorithm updates both the estimate of external traffic input and the routing assignments at each iteration. The routing assignments determine the proportions of the traffic destined for node j to be sent from node i through the outgoing links of i . The algorithm maintains the loop freedom of the routing assignment at each iteration. It also achieves the minimum delay of the network as the limit of its successive updating procedure. The additional features of the algorithm are that it allows at any iteration some routing assignments which theoretically induce infinite delay and that it may utilize variable scaling factors to speed up the convergence.

Continuous routing and batch routing on the hypercube

Abstract: In this paper we study two related routing problems on the n-dimensional hypercube: continuous routing, referring to the infinite routing process in which one new permutation is generated every constant r time steps, and batch routing, in which n permutations axe to be routed at the same time. We show that continuous routing with suitable value of r is feasible by giving a probabilistic routing algorithm that guarantees an 0 (n) completion time for any given permutation with overwhelming probability. The proof relies heavily on a probabilistic batch routing algorithm that has an 0 (n) completion time - an improvement over Valiant's classical 2-phase probabilistic routing algorithm when routing n permutations at the same time.

Optimal routing in circuit-switched communication networks

Abstract: We consider the optimal circuit routing problem. The problem consists of accommodating a given circuit demand in an existing circuit-switched network. The objective is to find a circuit accommodation providing the maximum residual capacity over the network under the total circuit cost constraints. Practical considerations require a solution which is robust to the variations in circuit demand and cost. The objective function for the circuit routing problem is not a smooth one. In order to overcome the difficulties of nonsmooth optimization, a sequence of smooth convex optimization problems is considered. The optimal algorithm for the circuit routing problem is obtained as a limiting case of the sequence of the optimal routing strategies for the corresponding smooth optimization problems. The proof of its convergence to the optimal solution is given. This optimization algorithm is capable of efficiently handling networks with a large number of commodities. It also satisfies the above-mentioned robustness requirements. Numerical results are discussed.

An Industrial World Channel Router for Non-Rectangular Channels

Abstract: In this paper, we discuss a number of important issues that we faced designing a router in the industrial environment. We present a channel router that addresses these issues. It can route rectilinear channels with variable channel height, and it can handle channels with pre-routed buses. Pins can come in from all four sides of the channel and the sequence of the side pins is maintained after routing. Usually, it uses two routing layers and it can use a third routing layer if needed. The basic algorithm is simple but effective to give good results. It routed the Deutsch Difficult Example in density. In routing uneven channels, it routed them with the number of tracks smaller than the channel density. The number of vias used and the total wire length are comparable with the best results in the literature. The router is fully functional and has been used in routing a number of real world integrated circuits.

Optimal Rotation Problems in Channel Routing

Abstract: In the channel routing problem, a problem arising in the design of layout systems, two rows of terminals which are opposite each other, have to be connected. We study what effect the rotation of one row of terminals has on the cost measures of the routing phase. The cost measures we consider are the density, which is proportional to the width of the channel, the crossing number, which is closely related to the number of crossings between two wires in the channel, and the length of nets, which is related to the wire length needed in the routing. We present algorithms for determining the rotations which minimize each of these cost measures. The algorithms can also be used for solving optimal offset problems.

A New Routing Algorithm and Its Hardware Implementation

Abstract: Presented is a new parallel processing wire routing algorithm that can control path quality in two point connections and find a quasi-minimum Steiner tree for multi-point connections. A parallel rip-up technique for finding a candidate path which blocks an unconnected net is also presented. These routing algorithms are implemented on a two-dimensional array processor, the AAP-1. It is experimentally shown that the average AAP-1 execution time per net using the routing algorithm is 100 msec in a 256X256 grid.

Deterministic Routing to Buffered Channels

Abstract: Consider n exponential transmission channels which transmit information with different rates. Every channel has a buffer which is capable of storing an unlimited number of messages. A new message first arrives at the controller, which immediately routes it to one of the channels according to an infinite deterministic routing sequence. A cost per unit of staying time is charged in each of the channels (channel dependent cost), and the long-run average staying cost is taken as the cost criterion. For every n and a Poisson arrival process, a lower bound to the cost is found and a new routing policy, the golden ratio policy, is presented and its cost is evaluated. It is shown that for a variety of system parameters, the golden ratio routing policy has a cost close to the lower bound.

Algorithms for Global Routing

Abstract: This paper presents several algorithms for global routing, including a very fast shortest path connection algorithm based on wave propagation and diffraction, a heuristic minimum tree algorithm using 'Common Edge' analysis, an overflow control method, and global rerouting treatment. These algorithms have been implemented in C and very good experimental results have been obtained.

A provably good algorithm for the two module routing problem

Abstract: In the Mead–Conway design methodology for LSI, modules are designed and then connected by wires to form larger modules in a hierarchical fashion. It would be helpful to have a design aid that would do the routing automatically and be guaranteed of coming within some fixed percentage of the size of an optimal routing. With this goal in mind, we investigate the problem of routing two-terminal nets between two modules of the same width but possibly different heights, assuming that the sides are aligned vertically. The terminals may lie on any of the sides of either module. Wires must be routed according to the “Manhattan” reserved-layer model, in which all wires must lie on a rectilinear grid, and wires running the same direction must be separated by at least unit distance. Finding an optimal routing for this problem is NP-hard, where the measure of performance is the perimeter of the bounding box around the whole routing region. We describe an algorithm whose worst-case performance is asymptotically at most...

Routing as a flow control strategy in an integrated circuit/packet switched communications network

Abstract: This research addresses the analysis of an event-driven FORTRAN Simulation Model that simulates a special kind of Computer-Communication network. The network modeled has a circuit-switched communication subnet whose trunk lines carry both voice and data traffic simultaneously. This effort considers the viability of routing strategies as a mechanism for reducing congestion. The performance of seven alternative routing strategies are measured in terms of user-visible metrics.Based on the experimental results obtained, this research concludes that fixed routing, the technique assumed by most models, is not as effective a tool for reducing congestions as would be a strategy based on link utilization. Minimization of congestion can be realized only if the routing strategy is adjusted as workload varies. Experimental data supporting these conclusions is presented.

A routing algorithm with candidate shortest path

Abstract: An improved algorithm based on the next node routing principle is proposed in this paper. In this algorithm there is a column added to the classical routing table, in which the candidate shortest distance to the destination node is the entry. When a link fails, the new shortest path in the nodes connected directly with the failure link can be found immediately (it is just the candidate shortest path before failure). For all other nodes in which routing tables should be changed, the required number of control messages and time for convergence are also less than Tajibnapis‖ algorithm and Predecessor algorithm. The message looping problem does not exist in duplex loop networks and is radically improved in mesh networks. These statements are proved by the analysis and simulation in this paper. From the simulation results of a 30-node mesh network, when one link goes down, the total number of control messages generated during convergence with this algorithm on the average is about 30% of Tajibnapis‖ algorithm. The iterations required is 50% of Tajibnapis‖ algorithm. The memory space required and computation complexity in nodes are almost the same as the two algorithms mentioned above and the algorithm implementation is as easy as well.

Distributed control of routing in circuit-switched networks

Abstract: How should calls be routed in a circuit-switched communication network so as to minimize some overall measure of blocking? Here we show that under a simplified analytical model of a circuit-switched network there exist implicit shadow prices associated with each route and with each link of the network. These prices are defined in an essentially local manner, and can be used as a basis for distributed control of routing through the network.

A Heuristic for Manhattan Routing

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Use of toleranced ‘cost’ functions for circuit routing in complex communications networks

Abstract: A network routing algorithm is described which allows multiple routing options, from any one source to all destinations, to be defined with virtually the same computational load as the single ‘cheapest’ route to all destinations. It also presents the result in a manner well suited to further editing by the human network designer or manager. The algorithm is founded on the nature of the relevant cost functions and is supported by a discussion of the distinct types of cost functions appropriate to different applications.

TP9 - 530 OPTIMAL ROUTING IN CIRCUIT-SWITCHED COMMUNICATION NETWOFtKS

Abstract: Summarrr We consider the optimal circuit routing problem. The problem consists of accommodating a given circuit demand in an existing circuit-switched network. The objective is to find a circuit accommodation providing the maximum residual capacity over the network under the total circuit cost constraints. Practical considerations require a solution which is robust to the variations in circuit demand and cost. The objective function for the circuit routing problem is not a smooth one. In order to overcome the difficulties of nonsmooth optimization, a sequence of smooth convex optimization problems is considered. The optimal algorithm for the circuit routing problem is obtained as a limiting case of the sequence of the optimal routing strategies for the corresponding smooth optimization problems. The proof of its convergence to the optimal solution is given. This optimization algorithm is capable of efficiently handling networks with a large number of commodities. It also satisfies the abovementioned robustness requirements. Numerical results are discussed.