Showing papers on "Geographic routing published in 1983"

Cost-Performance Bounds for Multimicrocomputer Networks

Abstract: Several interconnection structures for a distributed multimicrocomputer message-passing system are compared on the basis of cost and performance. Among the structures analyzed are buses, double rings, D-dimensional toroids, trees, cube-connected cycles, and chordal rings. Network cost is defined in terms of the number of network nodes and the unit cost of communication links and their associated connections. Simple asymptotic performance bounds are derived based on the bottleneck analysis of a queueing network. In contrast to the usual assumption of uniform message routing, the technique permits the introduction of a reference locality notion to the message routing behavior of network nodes. Finally, the cost, performance, and performance/cost functions are examined as the number of network nodes becomes very large.

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.

Adaptive transmission strategies and routing in mobile radio networks.

Abstract: Local throughput in a mobile radio network is roughly defined as the rate at which packets are propagated in specified directions in local network regions. A key factor determining local throughput in an ALOHA or spatial TDMA network with randomly spaced stations is the transmission radius used by the stations. We demonstrate that allowing the transmission radius to depend on the desired direction of propagation can significantly increase local throughput. The local throughput capabilities of a radio network can be effectively used only if adequate routing strategies are employed. This is illustrated by an example based on a symmetric demand assumption for stations uniformly distributed over a disc. Suppose that the population of n stations is uniformly distributed within a circle of radius R. If n is large then in small regions the stations are distributed like a Poisson point process with intensity X satisfying n = ~ R ~ x. Assuming that the traffic demand is symmetric (i.e., uniformly distributed over all n(n-1) directed pairs of distinct stations) the mean distance between the source and destination of a packet is (see [ 4 ] , or see [ 2 ] which is a chapter from [ 4 ]) The network throughput in packet-hops for the ALOHA random access protocol can be approximated by n-where A is the area covered by a transmission and A denotes the mean of A. (If the transmission radius is always a constant r then A-is L not random and is euqal to nr2 .) Thus, if denotes the mean forward progress per successful transmission, the network end-to-end throughput in packets per time slot is where Q = L / A. C Since by equation (1.1) the end-to-end throughput is proportional to ?-I we call tl the efficiency of the transmission radius policy. The constant 17 is perhaps more meaningful than y since it does not depend on the network's global geometry and is thus a "local" measure.

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.

Address-independent routing for local networks

Abstract: A routing methodology is introduced which permits messages to be propagated throughout a network without recourse to destination or origin addresses. Two classes of networks, bidirectional trees and augmented rings, are analyzed from this point of view. An optimality property is proved for the bidirectional tree, and three types of address-independent routing strategies are derived. It is shown that augmented loops, a class of structures incorporating redundant links, may be rerouted to compensate for the failure of any single node or link.