Showing papers on "Multipath routing published in 1989"

A unified approach to loop-free routing using distance vectors or link states

Abstract: We present a unified approach for the dynamic computation of shortest paths in a computer network using either distance vectors or link states. We describe a distributed algorithm that provides loop-free paths at every instant and extends or improves algorithms introduced previously by Chandy and Misra, Jaffe and Moss, Merlin and Segall, and the author. Our approach treats the problem of distributed shortest-path routing as one of diffusing computations, which was first proposed by Dijkstra and Scholten. We verify the loop-freedom of the new algorithm, and also demonstrate that it converges to the correct routing entries a finite time after an arbitrary sequence of topological changes. We analyze the complexity of the new algorithm when distance vectors and link states are used, and show that using distance vectors is better insofar as routing overhead is concerned.

Compact distributed data structures for adaptive routing

Abstract: In designing a routing scheme for a communication network it is desirable to use as short as possible paths for routing messages, while keeping the routing information stored in the processors' local memory as succinct as possible. The efficiency of a routing scheme is measured in terms of its stretch factor - the maximum ratio between the cost of a route computed by the scheme and that of a cheapest path connecting the same pair of vertices.This paper presents a family of adaptive routing schemes for general networks. The hierarchical schemes H Sk (for every fixed k ≥ 1) guarantee a stretch factor of O (k2 · 3k) and require storing at most O (knk log n) bits of routing information per vertex. The new important features, that make the schemes appropriate for adaptive use, are applicability to networks with arbitrary edge costs;name-independence, i.e., usage of original names;a balanced distribution of the memory;an efficient on-line distributed preprocessing.

High Performance Communications In Processor Networks

Abstract: In order to provide an arbitrary and fully dynamic connectivity in a network of processors, transport mechanisms must be implemented, which provide the propagation of data from processor to processor, based on addresses contained within a packet of data. Such data transport mechanisms must satisfy a number of requirements - deadlock and livelock freedom, good hot-spot performance, high throughput and low latency. This paper proposes a solution to these problems, which allows deadlock free, adaptive, high throughput packet routing to be implemented on networks of processors. Examples are given which illustrate the technique for 2-D array and toroidal networks. An implementation of this scheme on arrays of transputers is described. The scheme also serves as a basis for a very low latency routing strategy named the mad postman, a detailed implementation of which is described here as well.

Expanders might be practical: fast algorithms for routing around faults on multibutterflies

Abstract: Simple deterministic O(log N)-step algorithms for routing packets on a multibutterfly are described. The algorithms are shown to be robust against faults, even in the worst case, and to be efficient from a practical point of view. As a consequence, the multibutterfly is shown to be an excellent candidate for a high-bandwidth, low-diameter switching network underlying a distributed-memory machine. >

An adaptive hierarchical routing protocol

Abstract: An adaptive hierarchical routing protocol based on the extension of the new Arpanet scheme is proposed and its simulated performance is presented. The protocol can adapt to rapidly changing environments and works for arbitrarily large networks. A number of existing schemes as well as the proposed scheme are simulated under many different environments and clustering structures. The proposed protocol is found to be superior to the other protocols tested in many different types of network traffic and topological configurations. The results indicate that intercluster links must be reliable, because (1) the failure of these links can significantly degrade the routing performance, even though the protocol does not degrade as badly as the existing scheme and (2) hierarchical routing protocols usually prefer small clusters, which means that there will be many intercluster links. The tradeoff between two conflicting performance criteria, response speed and communication overhead, is shown. >

An optimal shortest-path routing policy for network computers with regular mesh-connected topologies

Abstract: A probabilistic routing policy, the Z/sup 2/ (zigzag) routing policy, is presented within the class of nonadaptive, shortest-path routing policies for regular mesh-connected topologies such as n-dimensional toroids and hypercubes. The focus of the research is routing in networks of computers in a distributed computing environment, where constituent subcomputers are organized in a mesh-connected topology and communication among individual computers takes places by some form of message exchange. The authors prove the optimality of this policy with respect to two criteria: (1) maximizing the probability of reaching the destination from a given source without delays at intermediate nodes; and (2) minimizing the expected lifetime of a message. >

Compact distributed data structures for adaptive routing

Abstract: In designing a routing scheme for a communication network it is desirable to use as short as possible paths for routing messages, while keeping the routing information stored in the processors' local memory as succinct as possible. The efficiency of a routing scheme is measured in terms of its stretch factor - the maximum ratio between the cost of a route computed by the scheme and that of a cheapest path connecting the same pair of vertices.This paper presents a family of adaptive routing schemes for general networks. The hierarchical schemes H Sk (for every fixed k ≥ 1) guarantee a stretch factor of O (k2 · 3k) and require storing at most O (knk log n) bits of routing information per vertex. The new important features, that make the schemes appropriate for adaptive use, are applicability to networks with arbitrary edge costs;name-independence, i.e., usage of original names;a balanced distribution of the memory;an efficient on-line distributed preprocessing.

Randomized Routing on Fat-Trees

Abstract: Fat-trees are a class of routing networks for hardwareefficient parallel computation. This paper presents a randomized algorithm for routing messages on a fat-tree. The quality of the algorithm is measured in terms of the load factor of a set of messages to be routed, which is a lower bound on the time required to deliver the messages. We show that if a set of messages has load factor λ = Ω(lg n lg lg n) on a fat-tree with n processors, the number of delivery cycles (routing attempts) that the algorithm requires is O(λ) with probability 1-O(1/n). The best previous bound was O(λ lg n) for the off-line problem where switch settings can be determined in advance. In a VLSI-like model where hardware cost is equated with physical volume, we use the routing algorithm to demonstrate that fat-trees are universal routing networks in the sense that any routing network can be efficiently simulated by a fat-tree of comparable hardware cost.

DTR: A Defect-Tolerant Routing Algorithm

Abstract: A new channel routing algorithm called DTR (Defect-Tolerant Routing) is investigated. This algorithm minimizes the total area and simultaneously maximizes the performance by reducing the critical area which can potentially be the source of logical faults caused by the bridging effects of spot defects. Experimental results show DTR produces less critical area than Yoshimura & Kuh's algorithm [1].

Robust design and planning of a worldwide intelligent network

Abstract: The authors describe the structure of the worldwide intelligent network (WIN), describe methods for its design and planning, investigate the adequacy of decentralized control for problem-free worldwide call completion, explore the feasibility of adaptive routing and control concepts, discuss network robustness/reliability objectives, and describe a strategy for achieving these objectives for all cooperating international carriers. Several decentralized adaptive routing policies that are particularly attractive in the WIN environment and network performance improvements that can be achieved with the introduction of flexible routing capabilities are characterized. It is shown by example that network integration coupled with flexible routing and bandwidth allocation for preferential treatment of new services provides an effective approach for robust and economical new service provisioning. >

Optimal routing in circuit switched communication networks

Abstract: Consideration is given to the optimal circuit routing problem in an existing circuit-switched network. The objective is to find circuit routing which accommodates a given circuit demand while maximizing the residual capacity of the network. In addition, the cost of accommodating the circuit demand should not exceed a given amount. Practical considerations require that a solution be robust to the variations in circuit demand and cost. The objective function for the optimal circuit routing problem is not a smooth one. In order to overcome the difficulties of nonsmooth optimization, the objective function is approximated by smooth concave functions. The optimization algorithm for the circuit routing problem is obtained as a limiting case of the sequence of optimal routing strategies for the corresponding smooth convex optimization problems, and the proof of its convergence to the optimal solution is given. An approach to calculating the optimal multicommodity flow is presented. The optimization algorithm efficiently handles networks with a large number of commodities, satisfies the robustness requirements, and can be used to solve circuit routing problems for large networks. >

Security issues in policy routing

Abstract: Most routing protocols, including proposed policy routing protocols, focus on environments where detection of an attack after it has taken place is sufficient. The authors explore the design of policy routing mechanisms for sensitive environments where more aggressive preventative measures are mandated. In particular, they detail the design of four secure protocol versions that prevent abuse by cryptographic checks of data integrity. They analyze and compare these schemes in terms of their prepacket processing overhead. It is concluded that preventative security is feasible, although the overhead cost is quite high. Consequently, it is critical that prevention-based schemes coexist with detection-based schemes. >

A new responsive distributed shortest-path rounting algorithm

Abstract: Distributed shortest-path routing algorithms based on the Ford-Fulkerson method are simple to implement but they suffer from the cost-dependent looping problem: when link costs increase, routing table loops may form and convergence to correct paths may be too slow, depending on link costs. This problem can be eliminated if constraints are imposed on the order in which routing tables are updated at different nodes but the resulting internode protocols tend to be relatively complex. Furthermore, update constraints may restrict a node's ability to obtain alternate paths quickly in an environment where topology changes are frequent. In this paper, a new distributed shortest-path routing scheme based on the Ford-Fulkerson method is presented. Under the new scheme, each node uses partial topology information to eliminate the cost-dependent looping problem. No update constraints are imposed and no assumptions are made regarding link costs. In the worst case, the new scheme responds to link cost changes in O(D) update steps, where D is the diameter of the network after the occurrence of the changes.

A new approach to sea-of-gates global routing

Abstract: The authors integrate the concepts and techniques of two existing complementary approaches, namely, the rerouting approach and the top-down hierarchical approach based on linear assignment. This combines and enhances the advantages of the two approaches and results in a fast and high-quality router which can handle large sea-of-gates designs. In addition, it solves the problems of routing interdependence and routing resource estimation which heretofore have not been well addressed yet. The method has been implemented and successfully tested on three real gate-arrays chips: Primary 1, Primary 2, and a channelless industrial example with 100 K gates. >

Pin assignment with global routing

Abstract: An algorithm is presented which combines the pin assignment step and the global routing step in the physical design of VLSI circuits. The algorithm is based on two key theorems: the channel pin arrangement theorem and the finite interval decomposition theorem. These two theorems enable the author to deal successfully with the high complexity resulting from combining the pin assignment and global routing steps. According to these two theorems, the author need only generate a coarse pin assignment and global routing topology. The exact pin locations and global solution can later be determined optimally and by a linear time algorithm. The author implemented a pin assignment and global routing package named BeauticianGR based on the proposed algorithm. >

Convergence of gradient projection routing methods in an asynchronous stochastic quasi-static virtual circuit network

Abstract: The convergence of the gradient projection algorithms for optimal routing in virtual circuit data networks proposed by D.P. Bertsekas (1982) is studied. The routing model explicitly takes into account stochastic generation and termination of virtual circuits, distributed asynchronous routing updates, inaccurate flow measurement, and delays in forwarding control packets. The problem of assigning paths for incoming sessions (or virtual circuits) to implement the gradient projection algorithms is also studied. A metering rule based on deficiency in a desired number of virtual circuits is proposed and analyzed. It is shown that the proposed metering rule is better than a randomized rule in some sense. The gradient projection routing algorithms implemented either by the metering rule or the randomized rule are shown to converge to a neighborhood of a long-term optimal routing. >

Wiretap: an experimental multiple-path routing algorithm

Abstract: This paper introduces Wiretap, an experimental routing algorithm which computes maximum-likelihood diversity routes for packet-radio stations sharing a common broadcast channel, but with some stations hidden from others. The wiretapper observes the paths (source routes) used by other stations sending traffic on the channel and, using a heuristic set of factors and weights, constructs speculative paths for its own traffic. The algorithm is presented as an example of maximum-likelihood routing and database management techniques useful for richly connected networks of mobile stations. Of particular interest are the mechanisms to compute, select, rank and cache a potentially large number of speculative routes when only limited computational resources are available.A prototype implementation has been constructed and tested for the AX.25 packet-radio channel now in widespread use in the amateur-radio community. Its design is similar in many respects to the SPF algorithm used in the ARPANET and NSFNET backbone networks, and is in fact a variation of the Viterbi algorithm, which constructs maximum-likelihood paths on a graph according to a weighted sum of factors assigned to the nodes and edges.

Insensitivity with age-dependent routing

Abstract: The theory of insensitivity is extended to include processes where some of the routing probabilities of the process are made dependent upon the length of time the generally distributed variables have been alive. Examples of such systems are given, including networks of queues with age-dependent routing. PARTIAL BALANCE; PRODUCT-FORM QUEUEING NETWORKS; AGE-DEPENDENT ROUTING

An efficient near-optimal algorithm for the joint traffic and trunk routing problem in self-planning networks

Abstract: The configuration and routing problem (or the joint trunk and traffic routing problem) is first formulated as a mixed integer nonlinear minimization problem. Then certain properties are proved about the problem structure. These properties lead to an efficient algorithm that determines near-optimal configurations and routing assignments. A lower bound is also computed in order to evaluate the quality of the solution. The algorithm was coded and tested on several networks. Present computational experiments clearly show that the performance of a self-planning network is always better than that of the same network without the trunk routing capability. The reduction in average packet delay is as much as 67%. >

Dynamic routing in the AT&T network-improved service quality at lower cost

Abstract: The introduction of dynamic nonhierarchical routing (DNHR) into the AT&T switched network was completed in 1987. It has resulted in a marked improvement in AT&T network connection availability while simultaneously reducing network costs. The concept of dynamic routing and its implementation in the network over a several-year period by a multiorganizational team with AT&T are described. Dynamic routing has dramatically improved network service and robustness, particularly in responding to abnormal traffic or failure conditions. DNHR performance, systems engineering and development, and operation are discussed. >

Routing using a pyramid data structure

Abstract: A general-purpose routing algorithm is proposed. Ideas behind both the maze-running algorithm and the hierarchical routing algorithm are combined into a hybrid routing algorithm. The new algorithm demonstrates a speed compatible to a hierarchical router and produces routings with quality equivalent to that by a maze router. Hybrid routing is based on the maze-running method with a third search dimension added. The extra search space is built by recursively constructing a hierarchy of coarser grid meshes. A user-given parameter can turn this algorithm into a pure maze router, a pure hierarchical router, or a wide spectrum of hybrid routers with different speed/quality characteristics between the extremes. With this approach, it is possible to handle easily a routing of large size, such as those encountered in the sea-of-gate layout. >

Deadlock-free message routing in multicomputer networks

Abstract: The execution of a concurrent computation by a network of processors requires a routing algorithm that is deadlock free. Many routing algorithms proposed for processor networks have the potential of deadlock due to the cyclic topology of the network. In this paper we first formalize the concept of message routing. Next, we show a method by which a deadlock-free routing algorithm can be constructed out of a given routing algorithm. Finally the method is illustrated by constructing deadlock-free routing algorithms for cartesian product processor networks.

Routing in general junctions

Abstract: A junction is a union of channels. The L-, S-, T-, and X-shaped junction routing problems arise while generating a feasible routing order of channels for the building-block layout strategy. The authors present lower and upper bounds on the widths of the channels of general junctions. In addition to the trivial lower bounds provided by the channel densities, they establish nontrivial existential lower bounds by properly arranging nets which require excessive number (i.e. more than the density) of crossings at a set of chosen cuts. To establish the upper bounds the authors first develop a router for the L-junction, and then they show how to use this router for routing general junctions. For the two-terminal net L-, S-, T-, and X-junction routing problems, the authors' routers generate solutions matching the lower bounds; hence, they are optimal. For the three-terminal net case, their router generates solutions matching the existential lower bound for the L-junction. All lower bounds are valid for both the knock-knee and the Manhattan routing models, while the upper bounds are only valid for the knock-knee routing model. However, all the routing solutions are three-layer wireable. >

Autonomous routing scheme for large scale network based on neural processing

Abstract: The authors discuss an autonomous routing scheme (called Holonic Routing) for large-scale networks that uses the principle of neural networks. In this scheme each node computes the optimal route whenever it tries to transmit a packet; thus the network can always maintain a balanced load, providing maximum transmission capacity in response to changes in traffic and topology. Because the routing procedure is packet by packet, even if a failure occurs in transit the packet will automatically be routed to avoid failed parts. Thus, a reliable nonstop network can be easily constructed using this scheme. The scheme is especially suitable for multimedia networks where large capacity and high reliability are needed. >

Compact Distributed Data Structures for Adaptive Routing (Extended Abstract)

Abstract: A color photographic element having special chromatic effects is disclosed, the element comprising a support and three emulsion layers. Special chromatic effects are obtained by particular combinations of the sensitizers and couplers contained in the emulsion layers, the combinations being different from conventional.

A routing architecture for very large networks undergoing rapid reconfiguration

Abstract: A routing architecture is described for very large communications networks with greater than 10,000 routing nodes and 100,000 end nodes. This architecture, called the Traveler Architecture, is designed to be independent of network configuration and to be robust even under conditions of rapid reconfiguration. Traveler is an extension of the ISO routing protocols. The Traveler architecture is designed to work with traffic characteristic of existing large networks, such as the Internet. While Traveler does not require a particular routing algorithm, it is designed to work in conjunction with families of distributed routing algorithms. Because Traveler is based on the paradigm of a human traveler, it attempts to use non-deterministic and heuristic methods rather than purely algorithmic methods to determine high quality routes between two points. Traveler builds on the Landmark and Area routing architectures.

MSE routing algorithm comparison

Abstract: The US Army's Mobile Subscriber Equipment (MSE) communications system uses a flood search algorithm for routing calls. This procedure automatically finds alternate paths to the call destination during the search and requires only a directory of local subscribers to be maintained at each node. Recently, it was suggested that two other routing methods, restricted flood search and hybrid routing, would reduce call delay while retaining some of the alternate routing features of the flood search. In the present work the three algorithms are compared in terms of the MSE backbone switching network's connectivity, throughput, grade of service, and routing delay. These measures are computed as functions of node and link reliabilities to observe the network performance under possible outage conditions in the battlefield environment. It is concluded that the flood search gives the most reliable performance in all aspects under network outages. >