Showing papers on "Routing table published in 1988"

The landmark hierarchy: a new hierarchy for routing in very large networks

Abstract: Landmark Routing is a set of algorithms for routing in communications networks of arbitrary size. Landmark Routing is based on a new type of hierarchy, the Landmark Hierarchy. The Landmark Hierarchy exhibits path lengths and routing table sizes similar to those found in the traditional area or cluster hierarchy. The Landmark Hierarchy, however, is easier to dynamically configure using a distributed algorithm. It can therefore be used as the basis for algorithms that dynamically configure the hierarchy on the fly, thus allowing for very large, dynamic networks. This paper describes the Landmark Hierarchy, analyzes it, and compares it with the area hierarchy.

Improving gateway performance with a routing-table cache

Abstract: A way to increase gateway throughput is to reduce the routing-table lookup time per packet. A routing-table cache can be used to reduce the average lookup time per packet and the purpose of this study is to determine the best management policies for this cache as well as its measured performance. The performance results of simulated caches for a gateway at MIT are presented. These results include the probability of reference versus previous access time, cache hit ratios, and the number of packets between cache misses. A simple, conservative analysis using the presented measurements shows that current gateway routing-table lookup time could be reduced by up to 65%. >

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.

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. >

Hyperswitch network for the hypercube computer

Abstract: The performance of a parallel algorithm depends in a large part on the interconnection topology of the multicomputer system. The method presented in this paper realizes a kind of interconnection network, called a hyperswitch network, that is achieved using a mixture of static and dynamic topologies. Here, available or fault free paths need not be specified by a source because the routing header can be modified in response to congestion or faults encountered as a path is established. This method can be accomplished in a static topology such as the hypercube network if the nodes have switching elements which are capable of performing the necessary routing header revisions dynamically. Detailed simulation results show that the hyperswitch network is consistently more efficient than fixed path routing for large message traffic conditions. The simulation results also show that the hyperswitch network has equivalent latency overhead for messages with localized and antilocal destinations (i.e., less then a 25% difference between diameter 1 and 5).

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. >

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. >

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. >

Landmark hierarchy method for routing signals in a communications network

Abstract: A hierarchy of landmarks is established for the nodes in the network. Each node is assigned at least one hierarchy level designation and has a corresponding radius. An address is assigned to each of the nodes, the address including components representing landmarks wherein each landmark represented by the address component is within the radius of the landmark represented by the next lower address component. Each node maintains a routing table for routing entries to landmarks within the radii of which a node resides. A source node chooses a path toward the highest level landmark represented by the address components of a destination node until the path reaches a node within the radius of the landmark represented by the next lower level address component. This procedure is repeated for the remaining address components.

Analysis of a 3D toroidal network for a shared memory architecture

Abstract: Horizon is a shared-memory multiple-instruction-stream-multiple-data-stream architecture currently under development. A synchronized network model suitable for this architecture is described. The model is defined in terms of a topology and routing policy. A three-dimensional toroidal topology is investigated for its multiple redundant paths, memory locality, and simplicity in both routing and construction. The routing policy is based on a desperation routing scheme in which it is not guaranteed that a message will make progress on a given network cycle. This scheme requires no complex deadlock avoidance algorithms or node-to-node flow control, allowing a very simple and efficient implementation. Design considerations and preliminary performance results are discussed. >

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.

Optimal routing in a network with unreliable links

Abstract: An investigation is conducted of the routing of packets in a network in which the link error rates vary A queuing network model that incorporates the effect of the link error rates is developed and is used to find optimal routing assignments for fixed error rates Single-path and multiple-path dynamic routing algorithms that minimize the average packet delay or the failure probability of packet transmission are proposed In case the network state is not exactly known, stochastic learning automata are proposed to drive the routing process >

Connectivity biased channel construction and ordering for building-block layout

Abstract: A number of techniques are presented for the construction and ordering of routing channels for building-block layout. First, before the routing channels are defined the placement is modified such that proper routing space is assigned between the circuit blocks. Second, a channel graph is constructed on which the global routing will be performed. Finally, after the global routing a feasible routing order is assigned to the channels. In contrast to other works, the algorithms use both the geometrical data (the placement) and the topological data (the connectivity) to decide which channel structure should be chosen from the feasible set.

Performance evaluation of a hierarchical hybrid adaptive routing algorithm for large scale computer communication networks

Abstract: A hierarchical hybrid adaptive routing algorithm (HHARA) is presented for dynamic large-scale computer communication networks (LSCCN). The performance of the proposed algorithm is evaluated and compared to that of nonhierarchical routing algorithms by simulation experiments on a 50-node network model. The major evaluation criteria are reliability, communication overhead, computation overhead, and average packet delay. A fixed routing algorithm, the most recent ARPANET routing algorithm, and HHARA are compared using simulation experiments. The simulation study indicates that HHARA makes a good balance between the reduction of routing database maintenance overhead, and the global routing capability as well as the local adaptivity to the network changes. >

Simple three-layer channel routing algorithms

Abstract: In this paper we present a simple three-layer assignment algorithm for planar layouts generated by a class of layout algorithms. This class of algorithms includes simple variations of the currently best algorithms for the three layer channel routing problem (CRP). More specifically, this class includes algorithms "equivalent" to the following algorithms (i–iii) developed by Mehlhorn, Preparata and Sarrafzadeh [7].

Discretionary channel routing

Abstract: In the paper, the channel routing model is generalised to incorporate some design flexibilities into the channel routing process. The channel router then makes use of the additional flexibilities to obtain better overall routing solution (and hence more compact layouts). Specifically, the channel routing problem is generalised so that a given net is only required to connect some (not necessarily all) of the pins in that net. The generalised problem is called the discretionary channel routing problem (DCRP). Various applications of the DCRP are presented. Solution of the DCRP involves two phases: the selection phase in which the pins are selected, and the connection phase in which the selected pins are routed. Two classes of algorithms for solving the DCRP are studied. In the first class, a target router is selected and the pins are selected to enhance the performance of that router. In the second class, pins are selected according to some absolute criterion that is independent of the target router. The algorithms have been implemented and tested on various (benchmarks and randomly-generated) problems. For all the test problems, the algorithms produce results that are either nearoptimal or optimal. In particular, excellent results were obtained for all the benchmark problems. Comparisons of these methods are also given, together with recommendations for choice of method for a given situation. Finally, the results show that the additional flexibility in the DCRP model leads to substantial savings in the wiring area, thus leading to more compact layout.

On routing and performance comparison of techniques for packet-switched networks using learning automata

Abstract: Distributed adaptive routing algorithms with the ability to adaptively proportion traffic over several paths is proposed for packet-switched data networks. A learning automaton is situated at each node of the network where a routing decision must be made and directs traffic entering the node onto one of the outgoing links. Using network feedback, and automaton modifies its routing strategy to improve its link selections. This approach has the advantage over existing routing schemes of offering a simple and extremely practical feedback and updating policy. >

A survey of hierarchical routing algorithms and a new hierarchical hybrid adaptive routing algorithm for large scale computer communication networks

Abstract: A survey is presented of present algorithms, with emphasis of a proposed scheme, the hierarchical hybrid adaptive routing algorithm (HHARA). HHARA reduces the size of routing database by dynamically organizing nodes into hierarchically structured clusters so that only partial information is stored and maintained in each site. The responsibility for routing is shared by the routing hierarchy so that the algorithm can maintain the global routing optimality and the local adaptivity at the same time. In this way, the storage, maintenance, communication, and computation overheads can be reduced while the response time to local status changes is kept small. HHARA can be used with either diagram routing or virtual circuit routing. Due to its ability to adapt to the network changes, it is specially useful for dynamic networks such as large military computer communication networks. >

Optimum routing for fiber network design: model and applications

Abstract: The authors propose a model to globally optimize topology and routing for survivable fiber networks. Numerical experiments show that the integer program approach for the routing model is computationally attractive for the intra-LATA fiber-hubbed network design using the DS3 as the basic routing unit and terminal multiplexers. The experiments also provide quantitative support for arguments that the hubbing network architecture and hub routing are an appropriate alternative architecture and approximation routing model, respectively, under the projected telephone demand and fiber technology environments. It is also found that the appropriate network architecture for future broadband ISDNs is likely to be determined by DS3 demand requirement along with optimization of tradeoffs between fiber cost and route mileage cost. >

NOM-a tool for optimal design and performance evaluation of routing strategies and its application to the Telenet network

Abstract: A network optimization model (NOM) that provides a tool for performance analysis and optimal design of a broad class of routing strategies is presented. It can evaluate and optimize both static and dynamic, local and global routing strategies. The tool is applicable to both packet-switched and circuit-switched networks. NOM software is based on original modeling methods and optimization algorithms. It is user-friendly and menu-driven, and has extensive 'what if' capabilities. NOM can be used for performance evaluation of existing routing strategy and for optimal routing design for a given performance criterion. As a performance evaluation tool, for a given network topology, link and node capacities, point-to-point demand matrix, and routing strategy, NOM models the routing and computes important characteristics of network performance. As a routing optimization tool, for a given network topology, link and node capacities, point-to-point demand matrix, and performance criterion, NOM generates the optimal routing, and computes important characteristics of network performance. The current Telenet local dynamic routing strategy is compared with a set of optimal routing strategies designed for various performance criteria. >

Optimal routing in the shuffle-exchange networks for multiprocessor systems

Abstract: The authors propose the shuffle-exchange and exchange-unshuffle network and a combination routing scheme. They prove that combination routing is optimal for s/e&e/u interconnection networks in the sense that it leads to the lowest possible number of cycles through the single-stage for every pair of source and destination addresses. The authors design a systolic algorithm for calculating the parameters for carrying out combination routing. Using standard shuffle-exchange routing, the average network delay can not be less than log N even with various augmented hardware. Simulation experiments on the combination routing show that the average network delays are significantly less than log N. >