Showing papers on "Static routing published in 1992"

The turn model for adaptive routing

Abstract: We present a model for designing wormhole routing algorithms that are deadlock free, livelock free, minimal or nonminimal, and maximally adaptive. A unique feature of this model is that it is not based on adding physical or virtual channels to network topologies (though it can be applied to networks with extra channels). Instead, the model is based on analyzing the directions in which packets can turn in a network and the cycles that the turns can form. Prohibiting just enough turns to break all of the cycles produces routing algorithms that are deadlock free, livelock free, minimal or nonminimal, and maximally adaptive for the network. In this paper, we focus on the two most common network topologies for wormhole routing, n-dimensional mesh, just a quarter of the turns must be prohibited to prevent deadlock. The remaining three quarters of the turns permit partial adaptiveness in routing. Partially adaptive routing algorithms are described for 2D meshes, n-dimensional meshes, k-ary n-cubes, and hypercubes. Simulations of partially adaptive and nonadaptive routing algorithms for 2D meshes and hypercubes show that which algorithm has the lowest latencies and highest sustainable throughput depends on the pattern of message traffic. For nonuniform traffic, partially adaptive routing algorithms perform better than non-adaptive ones.

Planar-adaptive routing: low-cost adaptive networks for multiprocessors

Abstract: Network throughput can be increased by allowing multipath, adaptive routing. Adaptive routing allows more freedom in the paths taken by messages, spreading load over physical channels more evenly. The flexibility of adaptive routing introduces new possibilities of deadlock. Previous deadlock avoidance schemes in k-ary n-cubes require an exponential number of virtual channels, independent of network size and dimension. Planar adaptive routing algorithms reduce the complexity of deadlock prevention by reducing the number of choices at each routing step. In the fault-free case, planar-adaptive networks are guaranteed to be deadlock-free. In the presence of network faults, the planar-adaptive router can be extended with misrouting to produce a working network which remains provably deadlock free and is provably livelock free. In addition, planar adaptive networks can simultaneously support both in-order and adaptive, out-of-order packet delivery.Planar-adaptive routing is of practical significance. It provides the simplest known support for deadlock-free adaptive routing in k-ary n-cubes of more than two dimensions (with k > 2). Restricting adaptivity reduces the hardware complexity, improving router speed or allowing additional performance-enhancing network features. The structure of planar-adaptive routers is amenable to efficient implementation.

The Vehicle Routing Problem with Time Windows: Minimizing Route Duration

Abstract: We investigate the implementation of edge-exchange improvement methods for the vehicle routing problem with time windows with minimization of route duration as the objective. The presence of time windows as well as the chosen objective cause verification of the feasibility and profitability of a single edge-exchange to require an amount of computing time that is linear in the number of vertices. We show how this effort can, on the average, be reduced to a constant. INFORMS Journal on Computing, ISSN 1091-9856, was published as ORSA Journal on Computing from 1989 to 1995 under ISSN 0899-1499.

Intelligent routing of special service telephone traffic

Abstract: A method and apparatus for dynamically balancing special service telephone calling traffic among a plurality of automatic call distributors and servicing agents as a function of supply and demand for such services. Data is gathered from originating and terminating switches of the telephone network, from each automatic call distributor, and from a call routing data base. The collected data is analyzed to characterize the supply and demand. A routing plan through the network is formulated so that the number of calls to each automatic call distributor is alloted as a function thereof and of the relative costs in routing to one point or another. The formulated plan is implemented for control by effecting changes in the routing data base. In the routing plan formulation, cognizance may also be taken of manpower availability for agent staffing.

Synchronization mechanism for link state packet routing

Abstract: A method of providing loop free and shortest path routing of data packets in a network having a plurality of switches, routing messages for communicating network topology information between the switches, a plurality of links connecting the switches and a plurality of channels connecting the switches to the links. The loop free routing of data packets is achieved through modifications to known link state packet (LSP) routing protocols and permits each switch to inform adjacent switches in the network of the information in the switch's database used to compute forwarding tables. A switch uses a received LSP to compute a forwarding table and informs neighboring switches on attached links of the routing change. The switch discards any subsequent data packets whose path would be affected by the changed routing information. The discarding of data packets continues until the switch receives notification from each adjacent switch affected by the changed routing information that all affected routing paths have been recalculated and the forwarding table of each affected switch has been updated. Thus, while adjacent switches temporarily contain inconsistent LSP databases and possibly inconsistent forwarding tables, the looping of data packets is prevented. Shortest path routing for data packets from a source endnode to a destination endnode is achieved by assuring that the first switch to forward the packet is on the shortest path to the packet's destination endnode. A source endnode transmits a data packet with an appropriate destination header and the determination of the actual routing path is performed transparently to endnodes. A data packet reaches its destination endnode by following the shortest path possible based on the network topology as represented in the database of the first switch that forwards it.

Multicasting for multimedia applications

Abstract: The authors investigate multicast routing for high-bandwidth delay-sensitive applications in a point-to-point network as an optimization problem. They associate an edge cost and an edge delay with each edge in the network. The problem is to construct a tree spanning the destination nodes, such that it has the least cost, and so that the delay on the path from the source to each destination is bounded. Since the problem is computationally intractable, the authors present an efficient approximation algorithm. Experimental results through simulations show that the performance of the heuristic is near optimal. >

Multihop lightwave networks: a comparison of store-and-forward and hot-potato routing

Abstract: The achievable aggregate capacity for a variant of the basic multihop approach in which minimum distance store-and-forward routing is replaced by a hot-potato routing algorithm is determined. With hot-potato routing, all packets simultaneously arriving at a given node and not intended for reception at that node are immediately placed onto the outbound links leaving that node; if two or more packets contend for the same outgoing link to achieve a minimum distance routing, then all but one will be misrouted to links which produce longer paths to the eventual destination. Attention is confined to the development of an analytical methodology for finding the probability distribution of the number of hops with hot potato routing for symmetric networks under uniform traffic load. Results show that the maximum throughput achievable with hot-potato routing can be as low as 25% of that for store-and-forward routing, and that the relative degradation increases as the number of nodes grows larger. This implies that the link speed up needed to produce a significant overall capacity advantage with hot potato should be at least a factor of 10. >

Analysis of shortest-path routing algorithms in a dynamic network environment

Abstract: In a dynamic network environment under heavy traffic load, shortest-path routing algorithms, particularly those that attempt to adapt to traffic changes, frequently exhibit oscillatory behaviors and cause performance degradation. In this paper we first examine the problems from the perspective of control theory and decision making, and then analyze the behaviors of the shortest-path routing algorithms in details.

Adaptive deadlock- and livelock-free routing with all minimal paths in Torus networks

Abstract: Luis Gravano, Gustavo D. PifarrC, Pablo E. Berman, and Jorge L. C. Sanz, Fellow, ZEEE Abstract-This paper consists of two parts. In the first part, two new algorithms for deadlock- and livelock-free wormhole routing in the torus network are presented. The first algorithm, called *-Channels, is for the n-dimensional torus network. This technique is fully-adaptive minimal, that is, all paths with a minimal number of hops from source to destination are available for routing, and needs only five virtual channels per bidirectional link, the lowest channel requirement known in the literature for fully-adaptive minimal worm-hole routing. In addition, this result also yields the lowest buffer require- ment known in the literature for packet-switched fully-adaptive minimal routing. The second algorithm, called 4-Classes, is for the bidimensional torus network. This technique is fully-adaptive minimal and requires only eight virtual channels per bidirectional link. Also, it allows for a highly parallel implementation of its associated routing node. In the second part of this paper, four worm-hole routing techniques for the two-dimensional torus are experimentally evaluate'd using a dynamic message injection model and different tr&c patterns and message lengths.

Deflection routing in hypercube networks

Abstract: An approximate analysis of the transient and steady state behavior of deflection routing in hypercube networks is presented, under a uniform traffic model. In deflection routing congestion causes packets admitted to the network to be temporarily misrouted rather than buffered or dropped. The approximations show that deflection routing performs remarkably well in hypercube networks, for small as well as large networks and for the whole range from light to heavy load. Simulations suggest that the approximations are quite accurate. >

Dynamic multi-path routing and how it compares with other dynamic routing algorithms for high speed wide area network

Abstract: In this paper we describe briefly a dynamic multi-path routing scheme that has been considered for connection oriented homogeneous high speed networks. The fundamental objective of the scheme is to bridge the gap between routing and congestion control as the network becomes congested. Because propagation delay far out shadows queueing and transmission delay in high speed networks, the proposed routing scheme works as a shortest path (minimum hop) first algorithm under light traffic conditions. However as the shortest path becomes congested, the source node uses multiple paths when and if available in order to distribute the load and reduce packet loss. The scheme is a cross between Alternate Path routing and Trunk Reservation.We compare the performance of the proposed scheme with the Shortest Path Only algorithm, the Alternate Path routing algorithm, the Random Routing algorithm, and the Trunk Reservation scheme. The throughput and packet loss performance are compared via simulations. These have been carried out concentrating on a 5 node network with varying traffic patterns, the intention being to gain insight into the strengths and weaknesses of the various schemes.

Internetworking apparatus for connecting plural network systems and communication network system composed of plural network systems mutually connected

Abstract: An internetworking apparatus which handles a scale of a network flexibly without degrading high speed operation. A router manager and a plurality of routing accelerator modules for performing routing are connected to one another through a high speed bus, and a plurality of communication ports are connected to the respective routing accelerators independently of one another. The plurality of routing accelerators can perform the routing for reception data packet at high speed. If more routing accelerators are provided, the disposal to the networks having a small scale to a large scale can be readily realized.

Routing technique for a hierarchical interprocessor-communication network between massively-parallel processors.

Abstract: A new routing process for a single-instruction-multiple-data (SIMD) multi-level hierarchical network or nodes, (N111-N113, N121-N123, N131-N133, N141-N143, N211, N212, N221, N222, N311 and N312), which are arranged in clusters and interconnected by dual, unidirectional channels, are used to send data packets including routing address information during a succession of routing cycles from transmitting ones to receiving ones of a larger number of parallel processors (e.g., 4096 processors arranged in a hierarchy of 8 cabinets, each of which contains a cluster of 8 circuits boards, with each circuit board containing a cluster of 64 processors). Each of the nodes (N111-N113, N121-N123, N131-N133, N211, N212, N221, N222, N311 and N312) includes a storage buffer having a capacity equal to one more than the number of channels at that level. This new routine process guarantees prevention of deadlock between levels and buffer overflow, and offers high-speed, low-cost interprocessor communication for SIMD computer.

Optimal routing algorithms for mesh-connected processor arrays

Abstract: We show that there is a randomizedoblivious algorithm for routing any (partial) permutation on ann ?n grid in 2n +O(logn) parallel communication steps. The queues will not grow larger than ź(logn/log logn) with high probability. We then modify this to obtain a (nonoblivious) algorithm with the same running time such that the size of the queues is bounded by a constant with high probability. For permutations withlocality, where each packet has to travel a distance at mostL, a generalization of the algorithm routes in time proportional toL with high probability. Finally, we identify a class of meshlike networks that have optimal or near-optimal diameter. These meshes have the potential of being adapted to run existing sorting and routing algorithms with corresponding reduction in their running times.

Resource pooling in queueing networks with dynamic routing

Abstract: In this paper we investigate dynamic routing in queueing networks. We show that there is a heavy traffic limiting regime in which a network model based on Brownian motion can be used to approximate and solve an optimal control problem for a queueing network with multiple customer types. Under the solution of this approximating problem the network behaves as if the service-stations of the original system are combined to form a single pooled resource. This resource pooling is a result of dynamic routing, it can be achieved by a form of shortest expected delay routing, and we find that dynamic routing can offer substantial improvements in comparison with less responsive routing strategies.

Adaptive routing in mesh-connected networks

Abstract: It is shown that wormhole routing in mesh-connected networks can be deadlock free and adaptive without the addition of channels to the basic topology. Several partially adaptive routing algorithms for 2-D and 3-D meshes are described and simulated for a variety of conditions. Simulations of policies for selecting input channels show that transmitting extra information in the header flits can reduce communication latencies at high network throughputs. Simulations of policies for selecting output channels show that avoiding turns reduces latencies at high throughputs. Unrestricted nonminimal routing is found to reduce latencies slightly at low throughputs but increase latencies significantly at high throughputs. For nonuniform traffic patterns, a partially adaptive routing algorithm performs better than a nonadaptive one. >

Routing in virtual path based ATM networks

Abstract: The issue of routing requests for virtual circuits in a virtual path (VP) based asynchronous transfer mode (ATM) network is addressed. It is supposed that the VPs are partitioned in a manner such that all the virtual circuits (VCs) making use of any given VP have the same traffic characteristics and quality of service demands. A virtual circuit request can be accepted in the network only if the specified loss and delay bounds can be guaranteed for the cells belonging to it. After suitable simplifying assumptions about the operation of the network are made, simple admission rules for virtual circuit requests are proposed. Routing policies are then proposed that try to minimize the fraction of virtual circuit requests denied. Simulations are carried out to evaluate the proposed routing policies. >

Self-timed mesh routing chip with data broadcasting

Abstract: A method and apparatus providing for data broadcasting in a two dimensional mesh of processor nodes is disclosed. In accordance with the present invention, a self-timed message routing chip is coupled to each processor node, thereby forming a two dimensional mesh of message routing chips. Broadcasting originates from a corner node, and data can broadcast through the mesh routing chips to a row, a column, or a matrix of nodes. The mesh routing chips, together, form a self-timed pipeline with each individual message routing chip having broadcasting hardware which provides for the forking of a message within that particular message routing chip. The self-timed forking of a message within individual message routing chips directly supports data broadcasting within the two dimensional mesh.

Optimal routing and buffer allocation for a class of finite capacity queueing systems

Abstract: The problem of routing jobs to K parallel queues with identical exponential servers and unequal finite buffer capacities is considered Routing decisions are taken by a controller which has buffering space available to it and may delay routing of a customer to a queue Using ideas from weak majorization, it is shown that the shorter nonfull queue delayed (SNQD) policy minimizes both the total number of customers in the system at any time and the number of customers that are rejected by that time The SNQD policy always delays routing decisions as long as all servers are busy Only when all the buffers at the controller are occupied is a customer routed to the queue with the shortest queue length that is not at capacity Moreover, it is shown that, if a fixed number of buffers is to be distributed among the K queues, then the optimal allocation scheme is the one in which the difference between the maximum and minimum queue capacities is minimized, ie becomes either 0 or 1 >

Vehicle routing with stochastic demands and restricted failures (revised edition)

Abstract: This paper considers a class of stochastic vehicle routing problems (SVRPs) with random demands, in which the number of potential failures per route is restricted either by the data or the problem constraints. These are realistic cases as it makes little sense to plan vehicle routes that systematically fail a large number of times. First, a chance constrained version of the problem is considered which can be solved to optimality by algorithms similar to those developed for the deterministic vehicle routing problem (VRP). Three classes of SVRP with recourse are then analyzed. In all cases, route failures can only occur at one of the last k customers of the planned route. Since in general, SVRPs are considerably more intractable than the deterministic VRPs, it is interesting to note that these realistic stochastic problems can be solved as a sequence of deterministic traveling salesman problems (TSPs). In particular, when k = 1 the SVRP with recourse reduces to a single TSP.

Design and implementation of MaRS: a routing testbed

Abstract: MaRS is a discrete-event simulation testbed for developing routing algorithms for wide-area computer networks. It was developed as a modiied and enhanced version of an existing simulator, NetSim. MaRS allows the user to deene a network connguration consisting of physical network, routing algorithm and workload. The user can control its simulation, log the values of selected parameters, and save, load and modify network conngurations. MaRS provides both steady-state and instantaneous performance measures to facilitate the study of the complex dynamics that arises in routing systems (due to delayed feedback). We have used MaRS to evaluate and compare several next-hop routing algorithms.

Scalable inter-domain routing architecture

Abstract: As internets grow, both in size and in the diversity of routing requirements, providing inter-domain routing that can accommodate both of these factors becomes increasingly crucial. We propose a scalable inter-domain routing architecture consisting of two major components: source-demand routing (SDR) and node routing (NR).The NR component pre-computes and installs routes that are shared by a significant number of sources. These generic routes are commonly used and warrant wide propagation. The SDR component provides on-demand computation and installation of specialized routes that are not shared by enough sources to justify computation by NR. The potentially large number of different specialized routes, combined with their sparse utilization, make them too costly to support with the NR mechanism. Together NR and SDR address the issue of scaling to global internet sizes without restricting the availability of a diverse set of routes. Routing will adapt naturally over time to changing traffic patterns and new services by shifting computation and installation of particular types of routes between the two components.To complement earlier discussions of SDR design choices [3], this paper evaluates the algorithmic design choices for the NR component in terms of scalability and functionality. In addition, we discuss mechanisms for improving the scaling properties of link-state SDR, and for integrating the two components of the architecture.

A theory of wormhole routing in parallel computers

Abstract: Virtually all theoretical work on message routing in parallel computers has dwelt on packet routing: messages are conveyed as packets, an entire packet can reside at a node of the network, and a packet is sent from the queue of one node to the queue of another node until its reaches its destination. The current trend in multicomputer architecture, however, is to use wormhole routing. In wormhole routing a message is transmitted as a contiguous stream of bits, physically occupying a sequence of nodes/edges in the network. Thus, a message resembles a worm burrowing through the network. The authors give theoretical analyses of simple wormhole routing algorithms, showing them to be nearly optimal for butterfly and mesh connected networks. The analysis requires initial random delays in injecting messages to the network. They report simulation results suggesting that the idea of random initial delays is not only useful for theoretical analysis but may actually improve the performance of wormhole routing algorithms. >

Separable routing: a scheme for state-dependent routing of circuit switched telephone traffic

Abstract: Separable routing is the first of a number of routing schemes for circuit switched telephone traffic invented at Bellcore. These routing schemes are state dependent, in the sense that, for each call attempt, a routing decision is made on the basis of the state of the network (defined in terms of the numbers of busy and idle trunks in the various trunk groups at the moment of the call attempt). In this paper, we describe separable routing and its mathematical background. Simulation results we have presented elsewhere show that the family of state-dependent routing schemes, of which separable routing is a member, is very attractive in terms of blocking rate, built-in network management features, and behavior in the presence of traffic forecast error.

Communications network class-of-service routing

Abstract: The routing of calls of different classes of services as well as the administration thereof is enhanced by associating each such class of service with a number of parameters common to such services, such that each class of service, as well as a new class of service, may be readily identified by its respective parameter values. Accordingly, the routing and administration of calls of different classes of services may be handled in a systematic, straight forward manner so that basic network capabilities may be made available to various services using an administratively defined menu like structure. In addition, such class of service advantageously partitions network bandwidth allocation, call routing priority, voice/data transport, and traffic data registers into respective classes of services.

Performance comparison of routing protocols using MaRS: distance-vector versus link-state

Abstract: There are two approaches to adaptive routing protocols for wide-area store-and-forward networks: distance-vector and link-state. Distance-vector algorithms use O(N x e) storage at each node, whereas link-state algorithms use O(N2), where N is the number of nodes in the network and e is the average degree of a node. The ARPANET started with a distance-vector algorithm (Distributed Bellman-Ford), but because of long-lived loops, changed to a link-state algorithm (SPF). We show, using a recently developed network simulator, MaRS, that a newly proposed distance-vector algorithm (ExBF) performs as well as SPF. This suggests that distance-vector algorithms are appropriate for very large wide-area networks.