Showing papers on "Static 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. >

A new theory of deadlock-free adaptive routing in wormhole networks

Abstract: The theoretical background for the design of deadlock-free adaptive routing algorithms for wormhole networks is developed. The author proposes some basic definitions and two theorems. These create the conditions to verify that an adaptive algorithm is deadlock-free, even when there are cycles in the channel dependency graph. Two design methodologies are also proposed. The first supplies algorithms with a high degree of freedom, without increasing the number of physical channels. The second methodology is intended for the design of fault-tolerant algorithms. Some examples are given to show the application of the methodologies. Simulations show the performance improvement that can be achieved by designing the routing algorithms with the new theory. >

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. >

Virtual interconnections for reconfigurable logic systems

Abstract: A compilation technique overcomes device pin limitations using virtual interconnections. Virtual interconnections overcome pin limitations by intelligently multiplexing each physical wire among multiple logical wires and pipelining these connections at the maximum clocking frequency. Virtual interconnections increase usable bandwidth and relax the absolute limits imposed on gate utilization in logic emulation systems employing Field Programmable Gate Arrays (FPGAs). A "softwire" compiler utilizes static routing and relies on minimal hardware support. The technique can be applied to any topology and FPGA device.

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. >

System for extending network resources to remote networks

Abstract: A system for interconnecting networks transparently extends the multiprotocol routing functionality of a router across a communication link to a remote LAN, while requiring a device on the remote LAN which operates independent of the higher layer protocol suites. A boundary router, having a local routing interface coupled to the first network, and a remote routing interface coupled to the communication link, provides the higher level protocol suite services for routing frames of data to terminals in the first and second networks. A routing adapter extends the remote routing interface of the boundary router transparently across the communication link to the second network.

A comparison of adaptive wormhole routing algorithms

Abstract: Improvement of message latency and network utilization in torus interconnection networks by increasing adaptivity in wormhole routing algorithms is studied. A recently proposed partially adaptive algorithm and four new fully-adaptive routing algorithms are compared with the well-known e-cube algorithm for uniform, hotspot, and local traffic patterns. Our simulations indicate that the partially adaptive north-last algorithm, which causes unbalanced traffic in the network, performs worse than the nonadaptive e-cube routing algorithm for all three traffic patterns. Another result of our study is that the performance does not necessarily improve with full-adaptivity. In particular, a commonly discussed fully-adaptive routing algorithm, which uses 2n virtual channels per physical channel of a k-ary n-cube, performs worse than e-cube for uniform and hotspot traffic patterns. The other three fully-adaptive algorithms, which give priority to messages based on distances traveled, perform much better than the e-cube and partially-adaptive algorithms for all three traffic patterns. One of the conclusions of this study is that adaptivity, full or partial, is not necessarily a benefit in wormhole routing.

Minimum crosstalk channel routing

Abstract: As technology advances, interconnection wires are placed in closer proximity and circuits operate at higher frequencies. Consequently, reduction of crosstalk between interconnection wires becomes an important consideration in VLSI design. In this paper, we study the gridded channel routing problem with the objective of satisfying crosstalk constraints for the nets. We proposed a new approach to the problem which utilizes existing channel routing algorithms and improves upon the routing results by permuting the routing tracks. The permutation problem is proven to be NP-complete. A novel mixed ILP formulation and effective procedures for reducing the number of variables and constraints in the mixed ILP formulation are then presented. The new algorithm is tested on three large benchmark circuits as well as many randomly generated circuits. The experimental results are very promising.

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.

Developing conflict-free routes for automated guided vehicles

Abstract: Automated guided vehicles AGVs are a highly sophisticated and increasingly popular type of material handling device in flexible manufacturing systems. This paper details solution methodologies for the static routing problem in which demand assignment of the AGVs are known; the focus is to obtain an implementable solution within a reasonable amount of computer time. The objective is to minimize the makespan, while routing AGVs on a bidirectional network in a conflict-free manner. This problem is solved via column generation. The master problem in this column generation procedure has the makespan and vehicle interference constraints. Columns in the master problem are routes iteratively generated for each AGV. The subproblem is a constrained shortest path problem with time-dependent costs on the edges. An improvement procedure is developed to better the solution obtained at the end of the master-subproblem interactions. Several methods of iterating between the master and subproblem are experimented with in-depth computational experiments. Our empirical results indicate that the procedure as a whole usually generates solutions that are within a few percent of a proposed bound, within reasonable computer time.

Method and system for maintaining routing between mobile workstations and selected network workstation using routing table within each router device in the network

Abstract: A method and system for maintaining a routing path between a selected workstation within a multisegment local area network and a mobile workstation wherein individual segments within the multisegment local area network are interconnected by a router device and wherein selected segments within the multisegment local area network include radio frequency transceivers adapted to provide a wireless communications link with mobile workstations. Each time communication is established between a mobile workstation and a selected workstation within the multisegment local area network via a radio frequency transceiver a routing table entry is established which identifies a segment location for the mobile workstation within a routing table associated with each router device within the multisegment local area network. A routing table entry is also established which identifies a segment location for the selected workstation within the routing table associated within each router device within the multisegment local area network in response to each attempt at establishment of communication between the selected workstation and the mobile workstation. Thereafter, all routing table entries which identify the segment location for a mobile workstation are automatically deleted in response to a termination of communications between the mobile workstation and the radio frequency transceiver. Routing path determination for communications between a mobile workstation and any workstation within the multisegment local area network may then be determined by reference to a routing table associated with each router device within a multisegment local area network without requiring the maintenance of routing path information at each workstation within the multisegment local area network.

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. >

High-Performance Routing Trees with Identified Critical Sinks

Abstract: We present two critical-sink routing tree (CSRT) constructions which exploit critical-path information that becomes available during timing-driven layout. Our CS-Steiner heuristics with "Global Slack Removal" modify traditional Steiner constructions and produce routing trees with significantly lower critical-sink delays compared with existing performance-driven methods. We also propose a new class of Elmore routing tree (ERT) constructions, which iteratively add tree edges to minimize Elmore delay. This direct optimization of Elmore delay yields trees that improve delays to identified critical sinks by up to 69% over minimum Steiner routings. ERTs also improve performance over such recent methods as [1] [6] when no critical sinks are specified.

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. >

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.

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.

Optically processed self-routing, synchronization, and contention resolution for 1-D and 2-D photonic switching architectures

Abstract: The use of optical processing to perform switch routing functions permits real-time routing of packets at high speed. The architecture of a 2*2 photonic packet switching node using optically processed fixed-directory routing, contention resolution using deflection routing, and synchronization is presented. Simplified optically processed self-routing procedures are found for banyan and lattice networks. Although lattice networks require a larger number of switching elements than banyan networks, they have a simpler interconnection field, and unlike banyan networks, the self-routing rule for lattices can avoid any internal blocking. The layout of a self-routing 2-D lattice, using 2*2 switches and a smart pixel, is described. Based on a first-arrival self-routing rule, an additional processing logic is required to perform routing. >

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. >

Area routing for analog layout

Abstract: An area router specifically tailored for the layout of analog circuits is presented. It is based on the A* algorithm, which combines the flexibility of maze routing with computational efficiency. Parasitics are controlled by means of a programmable cost function based on a set of user-defined weights. The weights can be automatically defined based on high-level electrical performance specifications and determine the net scheduling. An algorithm for symmetric routing preserves symmetries in differential architectures. Different current paths can be dealt with in each wire by means of a net partitioning procedure driven by information on the current driven by terminals. Shields can be built between critically coupled wires, in order to guarantee an effective limitation of cross-coupling. The weight-driven programmable cost function makes this router particularly suitable for a performance-driven approach to analog routing. Automatic weight definition also makes the use of the tool independent of the user's expertise. The implemented algorithms are described, and results proving the effectiveness of this approach are given. >