Showing papers on "Geographic routing published in 1992"

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.

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.

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.

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.

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. >

Direction order priority routing of packets between nodes in a networked system

Abstract: A method of routing messages within an n-dimensional network topology. Two directions are associated with each dimension in the n-dimensional network, for a total of 2n directions. A direction order is assigned which prioritizes the order in which a packet is routed across the 2n possible directions. Such an approach provides deadlock-free, fault tolerant wormhole routing in networks without wrap-around channels. For networks with wrap-around channels, the above method of wormhole routing is enhanced by placing a first direction from each of the n dimensions within a first group of directions. The second direction from each dimension is placed within a second group of directions. A packet to be routed from a source node to a destination node is routed in all relevant directions in the first group of directions in any order before being routed in the second group of directions. If, while traveling in a direction within the first group of directions, the packet is routed across a wrap-around channel, all further routing in that direction must be completed before moving in another direction. Routing then proceeds, if necessary, in the other directions of that first group of directions. Likewise, if, while traveling in a direction within the second group of directions, the packet is routed across a wrap-around channel, all further routing in that direction must be completed before moving in another of the second group of directions. A free hop mechanism is also taught for increase flexibility.

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.

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...

Minimum-expected-delay alternate routing

Abstract: The authors consider the problem of finding a routing strategy that minimizes the expected delay from every source to a single destination in a network in which each link fails and recovers according to a Markov chain. It is assumed that each node knows the current state of its own outgoing links and the state-transition probabilities for every link of the network. It is shown that the general problem is #P-complete, and two special cases are considered: case 1 assumes the network is a directed acyclic graph oriented toward the destination, and case 2 assumes that the link states are independent from slot to slot. For each case, it is proved that the optimal routing strategy has a simple state-independent representation. An efficient algorithm is presented for finding the optimal strategy.

Information routing and reliability issues in distributed sensor networks

Abstract: Communication issues and problems in information routing in distributed sensor networks (DSNs) are considered. Two important communication constraints, viz., the delay constraint and the reliability constraint, are identified, and their impact on information routing is discussed. It is shown that the maximum end-to-end delay in a network depends on the diameter of the network, and efficient distributed algorithms are presented to determine the diameter of asynchronous networks. A distributed algorithm that determines the diameter of an asynchronous tree network when an arbitrary node in the network initiates the algorithm is introduced. An efficient algorithm for determining the diameter when multiple nodes initiate the algorithm is presented. An algorithm to determine the diameter of arbitrary networks is presented, and its message complexity is shown. Effects of link/node failures on network delay are studied, and important network structure design criterion are discussed. The distributed, dynamic routing algorithms are reviewed, and their adaptation to DSN environments is discussed. >

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. >

Rooted routing in linear lightwave networks

Abstract: The authors propose a new scheme for optical signal routing within linear lightwave network (LLN) subnets. They study the synchronization problem that exists in these subnets which prevents efficient implementation of time division multiple access schemes for sharing a common broadcast medium. A solution for this problem is proposed, based on a new optical agent signal routing scheme, called rooted routing. The impact of the rooted routing on power losses is analyzed, and an approach for optimizing the power losses in LLNs with rooted routing is presented. It is shown that when the link and excess losses are small, the optimal power budget is close to that when the original, shortest path routing scheme is used. It is also shown that the power budget in LLNs with rooted routing can be significantly improved using a single optical amplifier. >

A New Label-Based Source Routing for Multi-ring Networks

Abstract: This paper presents a new source routing technique for ring and multi-ring networks, which uses short address labels. The main objectives for having this new method are that in case of one or more failures a frame will be guaranteed: (1) to be removed from the ring-termination property, and (2) to be copied at most once and only by its destinations-safety property. The scheme is based on dividing the label address space of each ring into subspaces, such that the address subspaces are physically disjoint. More specifically, each ring, in a multi-ring network, is divided into two or more parts such that adjacent address subspaces are disjoint. The route of each frame is described by a sequence of short address labels in the frame's header. The current route of a frame is determined by the first address label in its header, and it can be used for routing over at most one subspace of the ring. >

Reliable broadcast of routing information using diffusing computations

Abstract: A distributed algorithm called T-DA is presented. It allows the routing nodes, of a computer network or internet to maintain the correct view of the topology, even when link costs change or the topology changes due to failures or additions of nodes or links. T-DA eliminates the need for flooding by implementing a routing algorithm based on distance vectors to broadcast link-state information reliably over spanning trees that have the shortest distances to the sources of the link-state updates. T-DA eliminates the need for auxiliary information by asking each node to trust the link states reported by the neighbor closest to the source of such information. >

Connection-based communication in dynamic networks

Abstract: We analyze and improve the fault tolerance of practical, efficient end to end communication schemes. We concentrate on connection-based source routing schemes, used in most existing wide-area networks, e.g. in SNA/APPN. These schemes are composed of three components: a topology update protocol, a route selection algorithm and a connection protocol. The topology update protocol maintains an approximate ion of the network topology at every processor. The route selection algorithm in the source processor uses the topology approximation to select the ‘best’ route to the destination. The connection protocol sends messages along this route. We make the following contributions: Explicitly expressing the high efficiency possible with connection-based schemes. This efficiency is well appreciated in practice, but has not been analyzed formally so far. Roughly speaking, both communication and time complexities are in the order of the shortest route from source to destination which is up for ‘long enough’. ●IBM T.J. Watson, Yorktown Heights, NY 10598. Email: amir@ watson .ibm.com Permission to copy without fee all or part of this material is granted provided that the copies are not made or distributed for direct commercial advantage, the ACM copyright notice and the title of the publication and its date appear, and notice is given that copying is by permission of the Association for Computing Machinery. To copy otherwise, or to republish, requires a fee and/or specific permission. PoDC ‘92-81921B.C. a 1992 ACM 0-89781 .496.1 /92/0008 /0013 . ..$1 .SO ●

Design, implementation and evaluation of a deadlock-free routing algorithm for concurrent computers

Abstract: This paper describes the design, the implementation, and the performance results of a routing algorithm which provides deadlock-free communication in a tightly coupled message-passing concurrent computer. The algorithm is adaptive, isolated and uses the store-and-forward technique. It allows message communication between two processes regardless of where they are physically located on the network. The routing algorithm has many positive characteristics including provable deadlock freedom, guaranteed message arrival, and automatic local congestion reduction. It can be used as a basis for the design of high-level communication primitives. An Occam implementation on a network of inmos Transputers is discussed. The experimental results show that the routing algorithm is effective to support process to process communication on a concurrent computer.

Routing algorithms for double loop networks

Abstract: We give a new routing algorithm for double loop networks with n nodes which requires O(log n) time for preprocessing and constant processing time at each node on the route. A simple modification of the algorithm works for the case of a single fault (either node or link). The routing is always through a shortest path and the only information needed by a node to process is the address of the destination.

LIBRA: a distributed routing algorithm for large internets

Abstract: The loop-identification-and-blocking routing algorithm (LIBRA) is introduced for the distributed maintenance of routing information in large internets. According to LIBRA, each node maintains a routing table; each entry in this table contains the length of and next node in the chosen path to each destination, and a path label. Update messages contain a list of updates; each such update specifies the destination node, the length of the selected path, and its path label. A path label consists of a list of node identifiers used to identify and block a loop before it is used for routing. LIBRA is shown to converge in a finite time after an arbitrary sequence of link-cost or topological changes and to be loop-free at every instant, with no need for internodal coordination spanning more than one hop, or the specification or computation of complete paths from source to destination. LIBRA's performance is shown to be better than the performance of other routing algorithms previously proposed or currently used in network and internet routing protocols. >

Routing strategies for fast networks

Abstract: The authors examine routing strategies for fast packet switching networks based on flooding and predefined routes. The concern is to get both efficient routing and an even balanced use of network resources. They present efficient algorithms for assigning weights to edges in a controlled flooding scheme but show that the flooding scheme is not likely to yield a balanced use of the resources. Efficient algorithms are presented for choosing routes along breadth-first search trees and shortest paths. It is shown that in both cases a balanced use of network resources can be guaranteed. >

Congestion Control in High Speed Networks via Alternate Path Routing

Abstract: This paper presents a congestion control scheme based on alternate path routing. In the scheme, if a node encounters congestion or loses its preferred neighbor on its primary path to a destination, it sends data packets to that destination over precomputed alternate paths. The scheme ensures that data packets do not travel in loops and limits the spread of congestion to neighboring nodes. Simulations of the scheme show that alternate path routing reduces the number of dropped packets, achieves a more uniform link utilization and alleviates congestion in networks under light to moderate loading. When using alternate path routing, it is observed that the loss ratio closely follows the load ratio which is not true when using shortest path routing.

The use of artificial neural networks for optimal message routing

Abstract: The authors investigate the possibility of using an artificial neural network as an adaptive message router to provide optimal or near-optimal routing paths. Two different neural network architectures are implemented and tested against a network simulator to ascertain if their performance is adequate to allow them to be used as routing controllers in a network. A network simulator was written to investigate the performance of the JEB net of Jensen, Eshera, and Barash (1990) and the Hopfield net in routing messages. The results obtained using the enhanced JEB network show that the problem of optimal message routing can successfully by solved through the application of neural networks. >

Distributed fault-tolerant routing in Kautz networks

Abstract: For a Kautz network with faulty components the authors propose a distributed fault-tolerant routing scheme, called DFTR, in which each nonfaulty node knows no more than the condition of its links and adjacent nodes. They construct rooted tree for a given destination in the Kautz network, and use it to develop DFTR such that a faulty component will never be encountered more than once. In DFTR, each node attempts to route a message via the shortest path. If a node on the path detects a faulty node at the next hop, a best alternative path for routing the message around the faulty component is to be obtained. A best alternative path is first generated by the reduced concatenation of this node and the destination, and then is checked to make sure that it does not contain any of encountered faulty nodes. If it does a new alternative path is generated as before. The authors invent an efficient approach in the checking step to reduce computational time. With slight modification, DFTR may adapt to de Bruijn networks as well. >

Performance evaluation of the Manhattan street network with input buffers

Abstract: Simulation results for an 8*8 Manhattan street network with input buffers are presented. Performance data are presented for four different routing strategies, with six local traffic rates, and thirteen input buffer sizes. It is shown that a routing strategy based on packet age yields the best performance. The effect of input buffer size on blocking probability is emphasized. >

Simulation based performance study of a dynamic routing algorithm

Abstract: This paper discusses a new distributed, dynamic routing approach for communication networks. At each node, the best available route to the destination is selected and the message is forwarded to the next node on that route. The best route is evaluated at the new node again. The choice of the best mute is based on a parameter K, defined in the paper. This parameter is calculated for every path based on the characteristics of the path, such as - the number of hops, the speeds of the links, the load on the links, reliability of links etc. The method guarantees that as long as the network is connected the message will be delivered to the destination using the best available path. This approach does not have the counting to infinity problem and is loop-free. A comparative study of this scheme with some of the existing schemes is also included to demonstrate its generality and effectiveness.

Optimal routing in communication networks with delay variations

Abstract: The authors address the problem of optimal routing in packet switched networks. Optimality is discussed in terms of end-to-end delay. The variance of delay as well as its mean value are taken into account. Achieving optimal routing is necessary for multimedia networks to fully support real-time services. A network is modeled as a weighted graph with its link weights representing link delays. It is assumed that the delay statistics conform to a normal distribution. In the course of analysis, it is shown that this type of routing optimization problem can be formulated as a process of searching for a specific point in a coordinate system defined by the mean and variance of the end-to-end delay. An efficient algorithm is presented for finding the optimal point in this coordinate system. >