Showing papers on "Equal-cost multi-path routing published in 1993"

A survey of wormhole routing techniques in direct networks

Abstract: Several research contributions and commercial ventures related to wormhole routing, a switching technique used in direct networks, are discussed. The properties of direct networks are reviewed, and the operation and characteristics of wormhole routing are discussed in detail. By its nature, wormhole routing is particularly susceptible to deadlock situations, in which two or more packets may block one another indefinitely. Several approaches to deadlock-free. routing, along with a technique that allows multiple virtual channels to share the same physical channel, are described. In addition, several open issues related to wormhole routing are discussed. >

Packet Routing in Dynamically Changing Networks: A Reinforcement Learning Approach

Abstract: This paper describes the Q-routing algorithm for packet routing, in which a reinforcement learning module is embedded into each node of a switching network. Only local communication is used by each node to keep accurate statistics on which routing decisions lead to minimal delivery times. In simple experiments involving a 36-node, irregularly connected network, Q-routing proves superior to a nonadaptive algorithm based on precomputed shortest paths and is able to route efficiently even when critical aspects of the simulation, such as the network load, are allowed to vary dynamically. The paper concludes with a discussion of the tradeoff between discovering shortcuts and maintaining stable policies.

Cyclic transfer algorithms for multivehicle routing and scheduling problems

Abstract: This paper investigates the application of a new class of neighborhood search algorithms—cyclic transfers—to multivehicle routing and scheduling problems. These algorithms exploit the two-faceted decision structure inherent to this problem class: First, assigning demands to vehicles and, second, routing each vehicle through its assigned demand stops. We describe the application of cyclic transfers to vehicle routing and scheduling problems. Then we determine the worst-case performance of these algorithms for several classes of vehicle routing and scheduling problems. Next, we develop computationally efficient methods for finding negative cost cyclic transfers. Finally, we present computational results for three diverse vehicle routing and scheduling problems, which collectively incorporate a variety of constraint and objective function structures. Our results show that cyclic transfer methods are either comparable to or better than the best published heuristic algorithms for several complex and important ...

How bad is naive multicast routing

Abstract: In previous approaches to routing multicast connections in networks, the emphasis has been on the source transmitting to a fixed set of destinations (the multicast group). There are some applications where destinations will join and leave the multicast group. Under these conditions, computing an 'optimal' spanning tree after each modification may not be the best way to proceed. An alternative is to make modest alterations to an existing spanning tree to derive a new one. An extreme, though nonoptimal, variation of this is to use minimal cost source to destination routing for each destination, effectively ignoring the existing multicast tree. The authors examine just how nonoptimal these trees are in random general topology networks and conclude that they are worse by only a small factor. The factor is reduced still further if a hierarchy is imposed on the random network to give a more realistic model. >

Neural networks for shortest path computation and routing in computer networks

Abstract: The application of neural networks to the optimum routing problem in packet-switched computer networks, where the goal is to minimize the network-wide average time delay, is addressed. Under appropriate assumptions, the optimum routing algorithm relies heavily on shortest path computations that have to be carried out in real time. For this purpose an efficient neural network shortest path algorithm that is an improved version of previously suggested Hopfield models is proposed. The general principles involved in the design of the proposed neural network are discussed in detail. Its computational power is demonstrated through computer simulations. One of the main features of the proposed model is that it will enable the routing algorithm to be implemented in real time and also to be adaptive to changes in link costs and network topology. >

Routing device utilizing an ATM switch as a multi-channel backplane in a communication network

Abstract: A data communications network providing for a multiport router and providing for use of an asynchronous transfer mode (ATM) switch or the like as a routing backplane or packet switching engine. A router front end formats ATM cells including providing routing information in the cell header. The routing information may comprise, for example, a destination port identifier in the VPI field of the cell header. The ATM switch then switches the cell from an input port, coupled with the router front end to an output port based on the routing information. The ATM switch may also translate the routing information to provide source identification information to the destination. In a described embodiment, the multiport router is used as a backplane bus in a network concentrator.

Computing approximate blocking probabilities for large loss networks with state-dependent routing

Abstract: A reduced load approximation (also referred to as an Erlang fixed point approximation) for estimating point-to-point blocking probabilities in loss networks (e.g., circuit switched networks) with state-dependent routing is considered. In this approximation scheme, the idle capacity distribution for each link in the network is approximated, assuming that these distributions are independent from link to link. This leads to a set of nonlinear fixed-point equations which can be solved by repeated substitutions. The accuracy and the computational requirements of the approximation procedure for a particular routing scheme, namely least loaded routing, is examined. Numerical results for six-node and 36-node asymmetric networks are given. A novel reduced load approximation for multirate networks with state-dependent routing is also presented. >

Fault-tolerant wormhole routing in meshes

Abstract: It is shown how to modify the routing algorithms produced by the turn model to encompass dynamic faults The authors describe how to modify the negative-first routing algorithm, which the turn model produces for n-dimensional meshes without virtual channels, to make it one-fault tolerant Simulations of the one-fault-tolerant routing algorithms in a two-dimensional mesh indicate that misrouting increases communication latencies significantly at high throughputs The conclusion is that misrouting should be used only for increasing the degree of fault tolerance, never for just increasing adaptiveness Finally, the authors describe how to modify the negative-first routing algorithm to make it (n-1)-fault tolerant for n-dimensional meshes

A Distributed Reinforcement Learning Scheme for Network Routing

Abstract: In this paper we describe a self-adjusting algorithm for packet routing, in which a reinforcement learning module is embedded into each node of a switching network. Only local communication is used to keep accurate statistics at each node on which routing policies lead to minimal delivery times. In simple experiments involving a 36-node, irregularly connected network, this learning approach proves superior to a nonadaptive algorithm based on precomputed shortest paths.

Methods and apparatus for routing packets in packet transmission networks

Abstract: A packet communications system provides for point-to-point packet routing and broadcast packet routing to limited subsets of nodes in the network, using a routing field in the packet header which is processed according to two different protocols. A third protocol is provided in which a packet can be broadcast to the limited subset even when launched from a node which is not a member of the subset. The routing field includes a first portion which contains the route labels necessary to deliver the packet to the broadcast subset. A second portion of the routing field contains the broadcast subset identifier which can then be used to deliver the packet to all of the members of the broadcast subset. Provision is made to backtrack deliver the packet to the last node identified before the broadcast subset if that last node is itself a member of the subset.

Economical payload stream routing in a multiple-ring network

Abstract: The present invention is directed to a system for routing data between rings. A routing symbol is provided, and as it crosses a bridge, the local target address of the bridge is dropped, and the local source address of the bridge node (in the far side ring) is added to the routing symbol. Fields are shifted in the routing symbol so that the value that was in a hop field becomes the local target address in the new ring. Because the routing symbol that arrives at the ultimate target has been transformed into a source node list, the return path is available to the target.

Dispersity routing in high-speed networks

Abstract: Dispersity routing distributes the data between a source and destination over several paths through the network, rather than concentrating it on a single path. Non-redundant and redundant dispersity routing techniques are described. By using dispersity routing on virtual circuits, that operate similar to the TASI circuits used in voice networks, long, bursty data sources can share channels without buffering in the network or resequencing packets. This sharing ability is demonstrated by an example that has characteristics and requirements similar to those in medical image transmission. Dispersity routing is better able to deal with unexpected network loads than conventional, single channel systems. This ability is demonstrated by allowing a rogue source to upset the expected statistical utilization of the network.

Choice of allocation granularity in multipath source routing schemes

Abstract: Multipath source routing schemes can be distinguished by their choice of allocation granularity. The schemes proposed in the literature advocate a per-connection allocation wherein all the packets of a connection are constrained to follow the same path. The authors believe that a smaller allocation granularity permits a finer control to be exerted and would result in improved performance, especially in the presence of bursty traffic sources. A simple two-node network is used to compare the performance of both allocation schemes. An analytical model is developed to compute the resequencing delay distribution for the per-packet allocation. It is observed that as the burstiness of the arrival process increases, the per-packet allocation is able to accommodate bursts in a more graceful fashion, resulting in better performance. The per-packet allocation also permits a more equitable distribution of network resources than the per-connection. >

Asynchronous transfer mode communication system

Abstract: An ATM communication system capable of minimizing the delay period and achieving high throughput without requiring setting of the corresponding virtual connection (VC) table and routing. The communication system includes a vacant virtual connection table indicating unused VC. The VC is retrieved in response to a transmission demand and set in an ATM cell as a virtual connection ID (VCI). Then, the cell is transmitted with added address information identifying the destination. An ATM switch and a routing controller determine routing from a transmitting terminal to a receiving terminal. The determined routing is stored in a routing table in the routing controller. Then, through the determined routing, data is transferred from the transmitting terminal to the receiving terminal.

A dynamic routing control based on a genetic algorithm

Abstract: It is demonstrated that dynamic routing control based on a genetic algorithm can provide flexible real-time management of the dynamic traffic changes in broadband networks. A string structure is proposed, each of whose elements represents paths between each pair of origin and destination terminal nodes, together with a new technique using the past solutions as the initial data for new searches. These techniques dramatically improve the efficiency and convergence speed of the genetic algorithm. Computer simulations show that the genetic algorithm using the proposed techniques can generate the exact solution of path arrangement and can find a routing arrangement that keeps the traffic loss-rate below a target value, even after changes in traffic. >

Sharp approximate models of deflection routing in mesh networks

Abstract: Deflection routing is a simple, decentralized, and adaptive method for routing data packets in communication networks. The focus of this work is on deflection routing in the Manhattan street network (a two-dimensional directed mesh), although the analytic approach should apply to any regular network. Two approximate performance models that give sharp estimates of the steady-state throughput and the average packet delay for packets admitted to the network are presented. The results of extensive simulation experiments are reported, which corroborate the models' predictions. The results show that deflection routing is very effective. Two measures of the merit of a network for deflection routing are its diameter and its deflection index. Networks are presented whose diameter and deflection index are near the optimal values. >

The Message Flow Model for Routing in Wormhole-Routed Networks

Abstract: In this paper, we introduce a new approach to deadlock-free routing in wormhole-routed networks called the message flow model. We first establish the necessary and sufficient condition for deadlock-free routing based on the analysis of the message flow on each channel. We then show how to use the model to prove that a given adaptive routing algorithm is deadlock-free. Finally, we use the method to de? velop new, efficient adaptive routing algorithms for 2D meshes and hypercubes.

Routing in frequency-hop packet radio networks with partial-band jamming

Abstract: Research in adaptive, decentralized routing for frequency-hop packet radio networks with mobile partial-band jamming. A routing technique called least-resistance routing (LRR) is developed, and various versions of this routing method are examined. LRR uses a quantitative assessment of the interference environment experienced by a radio's receiver to determine a resistance value for that radio. Two components for the interference environment are considered: transmissions from other radios and partial-band jamming. The resistances for each of the radios in a particular path are combined to form the path resistance, and packets are forwarded on the path with the smallest resistance. Comparisons are made between different versions of LRR and between LRR and previously developed adaptive routing techniques. It is found that LRR is an effective way for dealing with mobile jamming in a frequency-hop packet radio network. Significant increases in throughput and end-to-end probability of success are obtained with LRR. >

A direct combination of the Prim and Dijkstra constructions for improved performance-driven global routing

Abstract: Motivated by analysis of distributed RC delay in routing trees, a new tree construction is proposed for performance-driven global routing which directly trades off between Prim's minimum spanning tree algorithm and Dijkstra's shortest path tree algorithm. This direct combination of two objective functions and their corresponding optimal algorithms contrasts with the more indirect 'shallow-light' methods. The authors' method achieves routing trees which satisfy a given routing tree radius bound while using less wire than previous methods. Detailed simulations show that these wirelength savings translate into significantly improved delay over standard MST routing in both IC and multichip module (MCM) interconnect technologies. >

Adaptive Deadlock-Free Routing in Multicomputers Using Only One Extra Virtual Channel

Abstract: We present three protocols defin ing the relationship between messages and the chan nel resources requested: request-then-hold, requestthen wait, and request-then-relinquish. Based on the three protocols, we develop an adaptive deadlockfree routing algorithm called the SP routing. The SP routing uses shortest paths and is fully-adaptive, so messages can be routed via any of the shortest paths from the source to the destination. Since it is a minimal or shortest routing, the SP routing guar antees the freedom of livelocks. The SP routing is not limited to a specific network topology. The main requirement for an applicable network topology is that there exists a deterministic, minimal, deadlock-free routing algorithm. Most ex isting network topologies are equipped with such an algorithm. In this paper, we present an adaptive deadlock-free routing agorithm for n-dimensional meshes by using the SP routing. The hardware re quired by the SP routing uses only one extra virtual channel as compared to the deterministic routing.

Fast deflection routing for packets and worms

Abstract: We consider deflection routing on the n x n mesh and torus. In deflection routing a message cannot be buffered, and is therefore always moving until it reaches its destination. In addition, routing choices have to be made locally. We give a nearly optimal deterministic algorithm for the permutation routing problem for packets, the first such result for deflection routing. We extend the deterministic algorithm to the case when the messages are worms; a contiguous physical stream of bits that must follow the head of the message uninterrupted through the network. We then give an optimal randomized algorithm for permutation routing for worms of any length up to n.

Routing multipoint connections using virtual paths in an ATM network

Abstract: The point-to-multipoint routing problem is studied for an asynchronous transfer mode (ATM) network that uses virtual paths (VPs). ATM networks with asymmetric and symmetric VPs are considered, and the performance factors studied are bandwidth and establishment and switching costs. A VP with intermediate exit, where a node that performs VP switching can copy the switched packets for the local destination, is proposed and studied. Mathematical formulations of multicast routing problems are presented, and heuristics for finding a low cost multicast routing tree, based on the transshipment simplex algorithm, are developed. >

An Efficient Timing-Driven Global Routing Algorithm

Abstract: In this paper, we propose an efficient timing-driven global routing algorithm. Unlike other conventional global routing techniques, interconnection delays are modeled and included during routing and rerouting process in order to minimize the routing area as well as to satisfy timing constraint. The timing-driven global routing problem is formulated as a multiterminal, multicommodity flow problem with integer flows and additional timing constraint. Two efficient timing-driven Steiner tree approach and one Steiner tree improving approach have been used to create initial routing results and reroute trees respectively. The algorithm has been implemented and the experimental results are quite promising.

Minimax open shortest path first routing algorithms in networks supporting the SMDS service

Abstract: Two quasi-static minimax open shortest path first (OSPF) routing algorithms in networks supporting the Switched Multi-megabit Data Service (SMDS) are presented and compared. In OSPF routing, the network is modeled as a graph and each link is associated with a nonnegative arc weight. A shortest path spanning tree is calculated for each origin to carry both the individually addressed and the group addressed (multicast) traffic. The OSPF routing protocol is adopted as a major part of the default inter-switching system interface (ISSI) routing algorithm for SMDS networks where arc weights are inversely proportional to the aggregate link set capacities. The problem of choosing a set of link set metrics is considered so that the maximum link utilization factor is minimized in an SMDS network. The problem is formulated as a nonlinear mixed integer programming problem. >

Dynamic signal routing

Abstract: Data packets are delivered through a constellation of nodes to a termination unit. The node where a packet leaves the constellation is a terminal node. Each packet includes a routing code. When a node receives a packet, it examines the routing code to determine if that node might be the packet's terminal node. A table look up operation is performed using the routing code as an index to a routing table. The table identifies a link to use in routing the packet away from the node to a neighbor node. The packet is also examined to verify compatibility between packet type and a selected link. If an incompatibility exists, a substitute link is selected. When a node concludes that it might be a terminal node for a packet, it evaluates a channel identifier to determine if it is currently serving the party to whom the packet is directed.

An analytical model for wormhole routing in multicomputer interconnection networks

Abstract: The communication performance of the interconnection network is critical in a multicomputer system. Wormhole routing has been known to be more efficient than the traditional circuit switching and packet switching. To evaluate wormhole routing, a queueing-theoretic analysis is used. This paper presents a general analytical model for wormhole routing based on very basic assumptions. The model is used to evaluate the routing delays in hypercubes and meshes. Delays calculated are compared against those obtained from simulations, and these comparisons show that the model is within a reasonable accuracy. >

Unslotted deflection routing in all-optical networks

Abstract: When nodes of a communication network have identical input- and output-link capacities, it is possible to use as few as one packet buffer per link, if one is willing to deflect-or misroute-a subset of simultaneously arriving fixed-length packets from preferred to alternate output links. This scheme, known as deflection routing, can achieve very fast packet switching in regular networks and has been proposed as the basic routing and switching protocol of several all-optical networks. The performance models of deflection-routing networks that have appeared in the literature have assumed that time is slotted and packets arrive at nodes on time-slot boundaries. In practice, however, slotted operation is difficult to implement in all-optical networks. The present authors evaluate by simulation the performance of deflection routing in unslotted networks. The evaluations show a surprising degradation of throughput in unslotted deflection routing networks, compared to slotted networks, and reveal situations where severe congestion occurs. To overcome these limitations they propose the use of specific control mechanisms in unslotted networks that allow one to eliminate congestion and to improve substantially the network throughput. >

Optimal fully adaptive wormhole routing for meshes

Abstract: A deadlock-free fully adaptive routing algorithm for 2D meshes which is optimal in the number of virtual channels required and in the number of restrictions placed on the use of these virtual channels is presented. The routing algorithm imposes less than half as many routing restrictions as any previous fully adaptive routing algorithms. It is also proved that, ignoring symmetry, this routing algorithm is the only fully adaptive routing algorithm that achieves both of these goals. The implementation of the routing algorithm requires relatively simple router control logic. The new algorithm is extended, in a straightforward manner, to arbitrary dimension meshes. It needs only 4n-2 virtual channels, the minimum number of an n-dimensional mesh. All previous algorithms require an exponential number of virtual channels in the dimension of the mesh.