Showing papers on "Link-state routing protocol 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.

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.

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.

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. >

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.

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.

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.

Reliability and scaling issues in multicast communication

Abstract: The efficiency with which multicast communication can take place is largely determined by the network level support available for such communication. Two factors contribute to the complexity of supporting current multicast applications: the lack of reliable multicast transport mechanisms at the network level and the lack of network support for large scale multicast communication. In this paper, we examine the issues pertinent to eliminating these shortcomings. We first show that internet multicasting algorithms based on reverse path forwarding are inherently unreliable and present a source-tree-based reliable multicasting scheme. The new scheme makes use of simple inter-gateway protocols and works on top of previously developed distance vector and link state internet routing schemes. Next, to support large scale applications, we present a scheme for partial multicasting and introduce a new network level operation, called gather. The partial multicasting mechanism allows messages to be delivered to subsets of multicast destinations, while the gather operation aids gateways in selectively suppressing redundant messages, thus reducing the message complexity. Using simulations, we investigate the efficacy of our schemes in supporting a sample application based on multicast communication.

State dependent routing for multirate loss networks

Abstract: An approach to adaptive routing in multirate networks using a Markov decision theoretic framework which maintains low computational complexity while still providing quite accurate routing information is proposed. In this approach, each link is modeled as a birth-death process to reduce the state space size and a policy iteration applied to achieve better network performance. The results show that routing algorithms based on this approach yield better performance than least-load path routing (LLP) without incurring any significant increase in computational complexity. >

Shipment routing algorithms with tree constraints

Abstract: Routing shipments efficiently on less-than-truckload trucking networks represents an important subproblem of the general network design problem that arises when designing a service network. The objective of the LTL shipment routing problem is to minimize the total transportation and handling costs subject to two key constraints: (i) service between two terminals must always satisfy a given minimum frequency (measured in trailers per week) and (ii) the paths from all origins into a destination should form a tree. This second constraint reflects a practical limitation on the types of instructions that can be implemented in the field. A solution approach is developed using a shortest path based formulation with additional routing constraints imposed to refine the routing in response to minimum frequency constraints. A local improvement heuristic is presented which manipulates the routing constraints. A separate set of primal-dual algorithms are also developed which provide both upper and lower bounds. Numeri...

Requirements for deadlock-free, adaptive packet routing

Abstract: This paper studies the problem of deadlock-free packet routing in parallel and distributed architectures. We present three main results. First, we show that the standard technique of ordering the queues so that every packet always has the possibility of moving to a higher ordered queue is not necessary for deadlock-freedom. Second, we show that every deadlock-free, adaptive packet routing algorithm can be restricted, by limiting the adaptivity available, to obtain an oblivious algorithm which is also deadlock-free. Third, we show that any packet routing algorithm for a cycle or torus network which is free of deadlock and which uses only minimal length paths must require at least three queues in some node. This matches the known upper bound of three queues per node for deadlock-free, minimal packet routing on cycle and torus networks.

Method and system for correcting routing errors due to packet deflections

Abstract: A distributed and adaptive method and system are provided for correcting routing errors due to packet deflections in a dual-shuffle exchange network (DSN). The DSN includes a shuffle-exchange network (SN) and an unshuffle-exchange network (USN). A packet that cannot be routed correctly will be temporarily "deflected" to a wrong route. This deflection, or routing error, is then registered and encoded in a routing tag of the header of the packet. Using this information, an error-correcting routing algorithm is then used to correct the error at a different part of the network. The method and system can be used either as the basis of a switch architecture of a ultra high-speed local-area network or metropolitan area network. Also, the method and system can be used in circuit switching. The DSN can achieve the Shannon's lower bound N log N on switch complexity with arbitrarily small packet-loss probability.

A parallel algorithm for channel routing problems (VLSI)

Abstract: A parallel algorithm for channel routing problems is presented. The problem is to route the given interconnections between two rows of terminals on a multilayer channel where the channel area must be minimized. The current advancement of VLSI chip technology allows one to use four layers composed of two metal layers and two polysilicon layers for routing in a chip. The goal of the proposed parallel algorithm is to find the near-optimum routing solution for the given interconnections in a short time. The algorithm is applied to four-layer channel routing problems requiring n*m*2 processing elements for the n-net-m-track problem. The algorithm has three advantages over the conventional algorithms: (1) it can be easily modified for accommodating more than four-layer problems; (2) it runs both on a sequential machine and on a parallel machine with maximally n*m*2 processors; and (3) the program size is very small. The algorithm is verified by solving seven bench-mark problems. >

System for determining communication routes in a network

Abstract: A network system capable of speedily selecting an intermediate system which can provide a shortest route of data communication among various intermediate systems even if routing information is not stored on the end system side, and in which the wasteful routing information is not held on the end system side, thereby minimizing an amount of routing information stored. In the network system, each packet for broadcast communication sent from each intermediate system is imparted to an intermediate system-address extracting unit 6 via a reception unit 2 and a packet processing unit 4 in the end system. The management-address extracting unit 6 extracts addresses of the intermediate systems from the packets, and stores these addresses in the management-address storage unit 8. When the packet is transmitted from this end system, the packet processing unit 4 obtains addresses in the management-address storage unit 8 via a route request unit 9, and sends a request of routing information to the intermediate systems having these addresses via a transmission unit 10. When the respective routing information is sent from the intermediate systems to the end system in response to that request, a route selecting unit 5 determines a shortest route to the destination on the basis of each routing information. The packet processing unit 4 request the intermediate system providing the shortest route to relay the packet.

Balanced gamma network-a new candidate for broadband packet switch architectures

Abstract: The gamma network is enhanced to derive a balanced gamma network with the addition of an additional link. The performance of the proposed network is analyzed in comparison with the existing networks. The performance of replicated networks and of networks with one internal buffer are investigated. These networks are studied using two assumptions: the common assumption that each destination can accept only one packet in a given cycle and the assumption that any number of packets can be accepted by a destination. Balanced gamma networks exhibit good performance, enable simple routing schemes, and are modular. >