Showing papers on "Link-state routing protocol published in 1988"

Survey Paper—Time Window Constrained Routing and Scheduling Problems

Abstract: We have witnessed recently the development of a fast growing body of research focused on vehicle routing and scheduling problem structures with time window constraints. It is the aim of this paper to survey the significant advances made for the following classes of routing problems with time windows: the single and multiple traveling salesman problem, the shortest path problem, the minimum spanning tree problem, the generic vehicle routing problem, the pickup and delivery problem including the dial-a-ride problem, the multiperiod vehicle routing problem and the shoreline problem. Having surveyed the state-of-the-art in this area, we then offer some perspectives on future research.

Designing networks with compact routing tables

Abstract: Classes of network topologies are identified in which shortest-path information can be succinctly stored at the nodes, if they are assigned suitable names. The naming allows each edge at a node to be labeled with zero or more intervals of integers, representing all nodes reachable by a shortest path via that edge. Starting with the class of outerplanar networks, a natural hierarchy of networks is established, based on the number of intervals required. The outerplanar networks are shown to be precisely the networks requiring just one interval per edge. An optimal algorithm is given for determining the labels for edges in outerplanar networks.

The probabilistic vehicle routing problem

Abstract: The probabilistic vehicle routing problem (PVRP) is a natural probabilistic variation of the classical vehicle routing problem (VRP), in which demands are probabilistic. The goal is to determine an a priori route of minimal expected total length, which corresponds to the expected total length of the route plus the expected value of the extra distance that might be required because demand on the route may occasionally exceed the capacity of the vehicle and force it to go back to the depot before continuing on its route. In this paper we analyze the PVRP using a variety of theoretical approaches. We find closed-form expressions and algorithms to compute the expected length of an a priori route under various probabilistic assumptions. Based on these expressions we find upper and lower bounds for the PVRP and the VRP re-optimization strategy, in which we find the optimal route at every instance. We propose heuristics and analyze their worst-case performance. Moreover, we perform probabilistic analysis for the case that customer locations are random in the unit square and succeed in proving some sharp asymptotic theorems for the PVRP and the VRP re-optimization strategy, in which we find the optimal route at every instance. We further propose some asymptotically optimal algorithms. It is quite surprising to find that the PVRP and the strategy of re-optimization are asymptotically equivalent in terms of performance. Our results suggest that the PVRP is a strong and useful alternative to the strategy of re-optimization in capacitated routing problems.

A tradeoff between space and efficiency for routing tables

Abstract: Two conflicting goals play a crucial role in the design of routing schemes for communication networks. A routing scheme should use as short as possible paths for routing messages in the network, 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 length of a route computed by the scheme and that of a shortest path connecting the same pair of vertices.Most previous work has concentrated on finding good routing schemes (with a small fixed stretch factor) for special classes of network topologies. In this work we study the problem for general networks, and look at the entire range of possible stretch factors. The results exhibit a tradeoff between the efficiency of a routing scheme and its space requirements. We present almost tight upper and lower bounds for this tradeoff. Specifically, we prove that any routing scheme for general n-vertex networks that achieves a stretch factor k ≥ 1 must use a total of O(n1+1/2k+4) bits of routing information in the networks. This lower bound is complemented by a family H(k) of hierarchical routing schemes (for every fixed k ≥ 1), which guarantee a stretch factor of O(k), require storing a total of O(n1+1/k) bits of routing information in the network and name the vertices with O(log2n)-bit names.

Hypercube message routing in the presence of faults

Abstract: We discuss the problem of routing messages on hypercubes which have faulty processors and/or communication links. We are motivated by the belief that simple algorithms, operating under simple assumptions, can ensure high probabilities of successful message routing. In this paper, we consider the basic problem of routing a single message from an arbitrary source to an arbitrary destination. In our study, a fault is assumed to render the processor or link non-functional for purposes of communicating messages. As such, we may also consider communications hot spots as node faults, and our results also apply to routing in congested hypercubes.A framework for the analysis of fault tolerant routing schemes on a hypercube is presented. This framework includes differing routing schemes, routing information models and fault distribution models. The a priori probabilities of successful routing of a single, indivisible message under each of our possible sets of assumptions are calculated. Using random routing, under the one-step local information routing model, we show that the a priori probability of successful message routing is high even for an exceedingly large number of faults. We also analyze the behavior of sidetracking, a routing method which combines the concepts of local information and randomization. Using sidetracking, and in the one-step local information routing model, a message will be routed forward using random routing. If the message reaches a blocked processor (no non-faulty neighbors along a minimal path to the destination) it will be sent to a non-faulty neighbor, chosen uniformly at random from the set of non-faulty neighbors. We use simulation experiments to determine the performance of this routing scheme, analyzing the probability of successful routing and the expected path length of a routed message. The empirical performance of the sidetracking algorithms indicates strongly that, in the limit as the cube dimension grows larger and for a fixed probability of node failure, the probability of successful message routing is 100%.

Over-the-cell channel routing

Abstract: A common approach to the over-the-cell channel routing problem is to divide the problem into three steps: (1) routing over the cells; (2) choosing net segments; and (3) routing within the channel. It is shown that the first step can be reduced to the problem and finding a maximum independent set of a circle graph, and thus can be solved optimally in quadratic time. Also, it is shown that to determine an optimal choice of net segments in the second step is NP-hard in general, and an efficient heuristic algorithm for this step is presented. The third step can be carried out using a conventional channel router. On the basis of these theoretical results, an over-the-cell channel router that produces solutions which are better than the optimal two-layer channel routing solutions for all test examples is designed. The over-the-cell channel router also outperforms the over-the-cell channel router described by Y. Shiraishi and Y. Sakemi (ibid., vol.CAD-6, no.3, p.462-71, 1987). In particular, for Deutsch's difficult example, the solution yields a saving of 10.5% in channel routing area when compared with the optimal two-layer channel routing solution, and a saving of 15% in channel routing area when compared with the routing solution produced by the over-the-cell channel router. >

Communication system for sending an identical routing tree to all connected nodes to establish a shortest route and transmitting messages thereafter

Abstract: The communications network includes a plurality of interconnected nodes and communication links between nodes. Computing apparatus in provided for determining a shortest path from a starting node to a destination node. The computing apparatus is adapted so that each node forms a routing tree having nodes with indentities, branches with weights, and a distinguished node called a root. The routing tree is the estimated shortest path to all of the nodes and each node communicates its routing tree to each adjacent node. Upon receipt of a routing tree by a reference node from an adjacent node, the reference node stores the routing tree and produces a large tree having roots and branches by placing the reference node as the root of the large tree and creating branches from the reference node to the roots of the routing trees of the adjacent nodes. The lengths of the branches are equal to the lengths of the links from the reference node to the adjacent nodes. A breadth first search of the large tree is performed to determine a connected subset of the large tree where each node identity appears only once. The connected subset forms the new routing tree for the reference node. If the new routing tree differs from the previous routing tree, the new routing tree is broadcast to all adjacent nodes and the procedure is repeated until no new tree differs from a previous tree, thereby defining a final routing tree. The final routing tree includes the shortest path from the reference node to all connected nodes.

Vehicle routing and scheduling problems with time window constraints: efficient implementations of solution improvement procedures. vehicle routing: methods and studies. studies in management science and systems - volume 16

Abstract: A number of heuristic algorithms have been proposed for the vehicle routing and scheduling problem with time window constraints. These algorithms include both route construction and route improvement procedures. This paper extends branch exchange solution improvement procedures, well known from the standard vehicle routing literature, to vehicle routing and scheduling problems with time window constraints. We focus on efficient implementations of these procedures and present extensive computational results. The methods presented are completely robust in that significant reductions in running time are achieved without any degradation in the quality of the solution. (Author/TRRL)

Addressing, bridging, and source routing (LAN interconnection)

Abstract: The concept of source routing for the interconnection of local networks is described. An architectural framework is provided to emphasize the principal advantages inherent with such a bridging mechanism. Motivation for this form of routing is shown to be a consequence of the address structure within the local network standards that have been adopted by IEEE, the European Computer Manufacturers Association (ECMA), and the International Organization for Standardization (ISO). As with many internetworking protocols, the use of a qualified address structure allows a more efficient routing mechanism. The physical address of a station, although not explicitly present in each transmitted frame, is implied by its attachment to a specific segment of the local network. This subtle point relative to local network addressing provides the foundation for the incorporation of source routing protocols. >

A new algorithm for standard cell global routing

Abstract: The algorithm considers all of the interconnection nets in parallel. This produces superior results, since information about all of the nets is available throughout the global routing process. The global routing is formulated as finding the optimal spanning forest (a generalization of optimal spanning trees) on a graph that contains all of the interconnection information. The results of several theorems allow many nonoptimal connections to be pruned before the process begins. This approach successfully solves the net-ordering and congestion-prediction problems from which other approaches suffer. The algorithm was implemented as part of the DATools systems. The benchmarks from the Physical Design Workshop are used as part of the comparison suite. The algorithm achieves up to 11% area reduction compared to the previous global routing package used in the DATools systems and up to 17% reduction in the total channel density compared to the Timberwolf 4.2 package. In no case does the algorithm do worse than its competitors. >

A new approach to three- or four-layer channel routing

Abstract: An approach to the three-layer or four-layer channel-routing problem is presented. A general technique that transforms a two-layer routing solution systematically into a three-layer routing solution is developed. The proposed router performs well in comparison with other three-layer channel routers proposed thus far. In particular, it provides a ten-track optimal solution for the famous Deutsch's difficult example, whereas other well-known three-layer channel routers required 11 or more tracks. The approach is extended to four-layer channel routing. Given any two-layer channel-routing solution without an unrestricted dogleg that uses w tracks, the router can obtain a four-layer routing solution using no more than w/2 tracks. A theoretical upper bound d/2+2 for arbitrary four-layer channel routing problems is also given. >

On the Evaluation of Telecommunications Network Reliability Using Routing Models

Abstract: A reliability measure that takes into account routing and rerouting policies after failures as well as the capacity of the network to satisfy its demand is proposed. The measure, based on the evaluation of the lost call traffic, needs resolution of a routing model for the states of perfect functioning as well as the most probable failure states. A type of routing model useful for network planning is also proposed. The model is closer to reality and easier to implement than the other classical multicommodity formulations. A convex-simplex implementation with a reoptimization feature explicitly adapted to the proposed model is used. >

Codar: a congestion-directed general area router

Abstract: A general area router that integrates the phases of global routing and detailed routing has been developed. The global phase coarsely places the nets based on the congestion of the routing region, and the detailed phase modifies the course wiring to find legal positions for all wire segments. Both phases use the same grid space of routing tracks with two or more levels of interconnect. With this integrated data structure, the router can alternate between global and detailed routing operations, both of which use rip-up and reroute techniques. This integration has resulted in a router that can solve difficult problems not solvable by other programs while exhibiting runtimes that grow only moderately with the size of the routing problem. >

The new routing algorithm for the ARPANET

Abstract: The new ARPANET routing algorithm is an improvement over the old procedure in that it uses fewer network resources, operates on more realistic estimates of network conditions, reacts faster to important network changes, and does not suffer from long-term loops or oscillations. In the new procedure, each node in the network maintains a database describing the complete network topology and the delays on all lines, and uses the database describing the network to generate a tree representing the minimum delay paths from a given root node to every other network node. Because the traffic in the network can be quite variable, each node periodically measures the delays along its outgoing lines and forwards this information to all other nodes. The delay information propagates quickly through the network so that all nodes can update their databases and continue to route traffic in a consistent and efficient manner. An extensive series of tests were conducted on the ARPANET, showing that line overhead and CPU overhead are both less than two percent, most nodes learn of an update within 100 ms, and the algorithm detects congestion and routes packets around congested areas.

Optimal routing algorithms for mesh-connected processor arrays (extended abstract)

Abstract: We show that there is a randomized oblivious algorithm for routing any (partial) permutation on an n × n grid in 2n+O (log n) parallel communication steps. The queues will not grow larger than Θ(log n) with high probability. We then modify this to obtain a (non-oblivious) algorithm with the same running time such that the size of the queues is bounded by a constant with high probability. For permutations with locality, where each packet has to travel distance at most L in either the horizontal or the vertical direction, a generalization of the algorithm routes in time 3L+o(L), while the queue size remains bounded by Θ(log n) with high probability. Finally, we show that for a general class of oblivious deterministic routing strategies, Ω(n 2) time is required if we want to have constant size queues.

Source routing bridge implementation (LANs)

Abstract: Source routing is a bridging technique where the bridge makes a routing decision based on the contents of the media access control (MAC) frame header of the frame. This header consists of a routing information field, which immediately follows the source address field in the frame. The routing information field describes the path across one or more bridges to the ring containing the destination station. With source routing bridges, the source and destination addresses of the frame on the media are the MAC addresses of the originating and target stations, respectively. The operation of a source routing bridge is examined. An implementation example using the TMS380 token-ring-adapter chipset is presented. >

Adaptive packet routing in a hypercube

Abstract: All commercial hypercubes use fixed-path routing for packet switching. However, it has long been known that adaptive routing reduces packet delay by sending packets via less congested areas. Moreover, the hypercube topology contains many alternative, equal-length paths, suggesting the desirability of adaptive routing. Noting the importance of a communication system and the efficiency of adaptive routing, we investigate the effect of packet routing on communication latency and message throughput in a hypercube. As a feasibility study of adaptive routing, we selected four representative adaptive routing methods for testing on the Intel IPSC: NRCC routing, shortest queue, delta, and hybrid weighted routing. In NRCC routing, a single node, the network routing control center (NRCC), collects network status information and distributes routing tables to all other nodes. In contrast, shortest queue routing is fully distributed; each node selects the link with the shortest queue of outgoing messages that is the part of a shortest path to the destination node. Delta and hybrid weighted routing are hybrid schemes, combining centralized NRCC routing and distributed shortest queue routing. Extensive simulation studies and implementation confirm the superiority of adaptive routing to the fixed-path routing in commercial hypercubes. This result holds for a variety of traffic models, including high temporal locality and traffic surges.

Multi-pads, single layer power net routing in VLSI circuits

Abstract: An algorithm is presented for obtaining a planar routing of two power nets in building-block layout. In contrast to other works, more than one pad for each of the power nets is allowed. First, conditions are established to guarantee a planar routing. The algorithm consists of three parts, a top-down terminal clustering, a bottom-up topological path routing, and a wire-width calculation procedure. Because of the hierarchical nature of the algorithm, it is inherently fast. >

Decentralized adaptive routing for virtual circuit networks using stochastic learning automata

Abstract: The problem of routing virtual circuits according to dynamical probabilities in virtual-circuit packet-switched networks is considered. Queueing network models are introduced and performance measures are defined. A decentralized asynchronous adaptive routing methodology based on learning automata theory is presented. Every node in the network has a stochastic learning automaton as a router for every destination node. The routing probabilities that are assigned to the network paths are updated asynchronously on the basis of current network conditions. A learning algorithm suitable for routing is used. Some initial simulation experiments, for a simple network, show convergence to optimal routing. >

Packet forwarding

Abstract: A packet network is viewed as consisting of two major interacting layers: a lower layer responsible for the determination of a set of paths that can be used to carry packet flows, and an upper layer responsible for actually sending the flows over these paths, on a per-packet basis. A systematic review is provided of the various techniques that can be used to perform the actual packet-by-packet routing operation at the upper layer, called the packet forwarding function. The function components of a routing system and its characteristics (responsiveness to changes in network state and degree of centralization) are discussed. Five routing techniques are then examined, namely source, directory, destination, global-path, and channel-link-path routing. >

Permutation Channel Routing

Abstract: Most of the channel routing algorithms in the literature [Deut76, YoKu82, RiFi82, BuPe83, ReSS85] including the simulated annealing channel routers studied in Chapter 4 assume a model in which the pins on the two sides of the channel are fixed (both physically and logically.) Other models that reflect less stringent physical constraints have also been studied. In [GoCW83], it was assumed that only the relative ordering of the pins is fixed. The pins are allowed to “shift” horizontally. This model captures the possibility of expanding or contracting the dimensions of a cell. In [LeLi83] and [Leon86a], the discretionary channel routing problem in which only some of the pins in a given net need to be interconnected was studied. This model captures the possibility of having physically equivalent pins or duplicated pins in a cell. As expected, such flexibilities lead to better routing results, namely, fewer tracks are required for interconnection.

Smoothed perturbation analysis algorithm for a G/G/1 routing problem

Abstract: The smoothed perturbation analysis (SPA) algorithm is proposed for estimating the derivative of the mean delay with respect to the routing probability for a routing problem in data-communication networks. The algorithm requires minimum knowledge about the system and is very suitable for on-line optimization of clata-conimunication networks. It is shown that the SPA algorithm is unbiased.

Comparison of two bridge routing approaches

Abstract: Two routing algorithms proposed for a bridged LAN environment are examined. One is based on creating a spanning tree topology; the other takes a source routing approach. The features of the running environment and the functional requirements of bridge routing are identified, and the two approaches are compared. >

Integrating bridges and routers in a large internetwork

Abstract: A review is presented of the principal functional characteristics of routers and bridges, particularly as they relate to the construction of large-scale internetworks. The discussion of bridges covers filtering performance, forwarding performance, packet latency, adaptability, internetwork topology, network management, security transparency, and multiway and fault-tolerant bridges. The discussion of routers covers network layer protocols, internetwork size, static versus dynamic routing, routing information updates, network management, routing optimizations, session survivability, contamination containment, routing optimization, and load sharing. >

Spatial reuse through dynamic power and routing control in common-channel random-access packet radio networks

Abstract: Topologies of common-channel packet radio networks (PRNETs) are difficult to optimize because some of the links between multiple pairs of packet radio units are not independent. Previous analysis has shown that designing the topology to provide spatial reuse of the common-channel will improve the network throughput and delay performance in general. Unfortunately, the complexity of the link interactions has impeded the design of protocols that can be implemented in operational networks. This dissertation discusses how to optimize the topologies of common-channel random-acess PRNETs through dynamic power control at the link layer and routing at the network layer. Methods of implementing dynamic power control at the link layer on an individual packet-by-packet transmission basis are presented. These methods should be implementable at the link layer of any packet radio with dynamic per-packet power control capability. A new routing protocol, called Least Interference Routing (LIR), is defined which is designed specifically to operate in common-channel random-access PRNETs. The goal of LIR is to minimize the destructive interference caused along each route within the network, thus improving the spatial reuse of the common-channel. The LIR protocol calculates the potential destructive interference along each link, creates the network routing tables that minimize the potential destructive interference along an entire route, and specifies the per-packet transmission power. The implementation flexibility of each of these operations allows LIR to be implemented in a variety of radios and radio networks. Myopic one-hop and network multiple-hop simulations indicate that dynamic power control and/or LIR improve end-to-end PRNET performance over no power control or other routing strategies, such as minimum hop routing.