Showing papers on "Routing table published in 1983"

Minimum-Via Topological Routing

Abstract: A new approach to the two-dimensional routing utilizing two layers is proposed. It consists of two major steps, topological routing and geometrical mapping. This paper describes the topological routing algorithm in detail. Based on a circle graph representation of the net intersection information of the routing problem, a maximal set of nets that can be routed without vias are selected. The layer assignments for the selected nets are determined by a global analysis so that the total number of vias needed is minimum. The layer assignment problem turns out to be a maximum-cut problem on an edge-weighted graph and we developed a greedy algorithm for it. According to the layer assignments, the detailed topological routes are then generated.

River Routing: Methodology and Analysis

Abstract: The problem of river routing across a channel is only a special case of more general routing configurations Both its methodological and combinatorial characteristics can be extended in useful ways which will be explored in this paper The two characteristics that we generalize here are planarity and grouping Planarity means that the connections are realizable in one layer; ie the interconnection pattern of the nets is planar Grouping means that the connections are made in order, that is to say that the routing of net i+l is adjacent, conceptually and preferably physically, to the routing of net I

Single Row Routing

Abstract: The automated design of multilayer printed circuit boards is of great importance in the physical design of complex electronic systems. Wire routing is a crucial step in the design process. In this paper, the single row routing problem is considered. First, we discuss the relevance of single row routing in the context of the general routing problem. Then, we show that relaxing the restriction that backward moves are not allowed can result in smaller street congestions when there are at least four tracks in each street. Next, we obtain an O((2k)!kn log k) algorithm to determine whether or not an instance involving n nodes can be laid out (without backward moves) when only k tracks per street are available. With the additional restriction that wires are not permitted to cross streets, an efficient (O(n2)) algorithm is obtained. This restricted problem is shown to be related to a furnace assignment problem.

Issues in routing for large and dynamic networks

Abstract: The routing function is necessary in computer communication networks in order to create the appearance of complete connectivity in an environment of sparse physical links. The purpose of this dissertation is to examine ways of providing the routing function in large networks or networks which are characterized by frequent topological changes or both. The focus is on distributed routing algorithms because of their failsafe property. Two new event driven distributed route table update algorithms, A and B, are introduced and proven correct. Algorithm A requires less buffer space to store route tables than other event driven algorithms. Algorithm B, a variation of algorithm A, allows each node to maintain a source tree, i.e. a tree rooted at the node and containing the shortest path to all possible destinations in the network. The source tree may be used to implement source routing, i.e. the whole path from source to destination is determined at the source. Transient route table looping is also studied for algorithms A, B, as well as other algorithms in the literature. Hierarchical routing has been suggested in the literature as a means to reduce the size of the route tables when networks become very large. Reduction of the table size may also reduce the communication cost incurred during the update of the route tables. A possible effect of the shrinking of the route tables is that the resulting paths are not optimal. A classification of hierarchical routing schemes is introduced. The trade-off between between route table reduction and path length increase is studied in detail for two classes of schemes. Alternate policies for routing in the absence of necessary information are suggested and evaluated. In order to implement hierarchical routing it is necessary to partition the network into clusters. The network partitioning problem is abstracted to a graph partitioning problem which is shown to be NP complete. A new heuristic procedure, V3.2, is developed which is compared to the agglomerative method, a procedure suggested in the literature. V3.2 is shown to perform considerably better computationally as well as in terms of desired properties of the partitions. The comparison is performed by simulation experiments. An algorithm is developed to randomly generate connected networks suitable to be used in the simulations.

Dynamic Routing and Call Repacking in Circuit-Switched Networks

Abstract: The performance of three dynamic routing techniques for small circuit-switched networks is compared by simulation with three static routing techniques and with a repacking technique for calls in progress. It is found that dynamic routing algorithms improve network performance by increasing the number of paths available for call connection over what would otherwise be available to a corresponding static routing. It is also shown that call repacking increases the amount of carried traffic significantly, and that this improvement is obtained by a different mechanism than for dynamic routing. The possibility of combining the two techniques is also investigated, and general characteristics of good dynamic routing techniques are presented.

Analysis of routing table update activity after resource failure in a distributed computer network

Abstract: In a distributed computer network each node participates in the routing process, making routing decisions based on information about network topology which is stored in tables in the node. To maintain the accuracy of these tables without interrupting the functionality of the network, they must be dynamically updated whenever there is a topology change in the network. The purpose of this paper is to analyze update activity required by a topology information maintenance scheme which has been implemented on the three-node MERIT Computer Network in Michigan. The main theorem gives upper and lower bounds on the number of update messages required after failure of a single network resource, either a node or a link.

Defining routing tables for SNA networks

Abstract: This paper addresses three basic problems associated with the definition process for the routing tables of IBM'S Systems Network Architecture (SNA). The paper then introduces a program called the Routing Table Generator (RTG) and describes how these problems were solved with RTG. Also discussed are some approaches on how to use RTG in managing routing tables for growing networks.

On the structure of decentralized dynamic routing strategies

Abstract: The problem of dynamic routing in data communication networks is considered. A model is introduced which takes into proper account the decentralization of the information about the network status. The problem is thus considered in a team-theory framework and the structure of the optimal strategies is derived.

Adaptive Routing for Damaged Networks

Abstract: This paper proposes and examines adaptive routing algorithms for communication networks that are subject to damage. These algorithms route calls through the network when the network configuration is not fully known, and adaptively reorder the routing tables as they gather more information about the network configuration. (The path that a call follows in the network is determined by routing tables. When a call reaches a node, a routing table is consulted to find the next node to attempt.) We concentrate on learning mechanisms that reorder the routing tables in real-time. For example, the success-to-top mechanism moves the table entry that led to a successful connection of a call to the top of the routing table. Success-to-top leaves the relative order of the other entries in the routing table unchanged. Other possible schemes include failure-to-bottom (entries that lead to unsuccessful connection attempts are placed on the bottom of the list), and success-up-one (in which the successful entry is moved up by one in the routing table). Markov chain models are described for success-to-top and failure-to-bottom schemes. Analytical expressions for the steady-state probabilities are used to form measures for these two strategies. We compare these measures for a wide selection of blocking probabilities. Further, a simulation model is used to evaluate the merits of all three (and more) schemes. The simulation provides network measurements not available from the analytical model. The simulation also examines information sharing mechanisms in which a single call is used to change the routing tables at many nodes.

A new probabilistic routing algorithm for packet-switched computer networks

Abstract: A probabilistic method is proposed for message routing in packet-switched computer networks with distributed control. The routing table associated with each node consists of path entries, instead of branch entries as found in most routing schemes. Packets are assigned with different paths on a probabilistic basis. The path selection is entirely processed at the source node. The routing table is updated dynamically with change of packet-generating rates at all nodes. We introduce a new quantitative measure, path capacity, to model each path as an M/M/1 queue. With the path capacities, routing tables are updated frequently to achieve balanced minimum delays among all paths. The update overhead is a constant, independent of the size of the network. Both analytical and simulation results are presented and compared with the new ARPANET routing method under various traffic conditions. This probabilistic, path-directed routing algorithm performs significantly better than the new ARPANET routing method under moderate and heavy traffic conditions. Under very light traffic conditions, the two methods have almost equal performance. This method can be applied to improve packet routing in any computer communications networks with distributed control.

Optimal Routing in the Cube-Connected Cycles Interconnection Network

Abstract: An optimal message routing algorithm for thc cube-connected cycles processor interconnection network is described, and the average:- message path length is derived assuming a uniform message routing distribution. The optimal algorithm is comparetl to one preViously proposed and is shown to have significanlly shorter average path length.

Routing table update epoch in packet-switching networks

Abstract: A computer communication network must be capable of managing its resources efficiently using a routing procedure, flow control, and buffer management techniques. A general network simulator has been developed as a tool in evaluating the many possible combinations of such techniques. It can also be used in evaluating existing strategies in operating networks and investigating new techniques. In this paper the simulator has been used to investigate several strategies of determining an optimum routing table epoch.