Robert R. Boorstyn

Large-Scale Network Topological Optimization

A cost-effective structure for a large network is a multilevel hierarchy consisting of a backbone network and a family of local access networks. The backbone network is generally a distributed network, while the local access networks are typically centralized systems. In special cases, the network may consist primarily of either centralized or distributed portions. This paper discusses topological design problems for such systems, including the concentrator location problem, the terminal assignment problem, the terminal layout problem (the constrained minimum spanning tree problem), the distributed network topological layout problem, and the backbone node location problem. Recent algorithm research, including exact and heuristic problem solutions, are described and computational experience is given. Finally, open problems in large-scale topological design are reported.

Throughput Analysis in Multihop CSMA Packet Radio Networks

In this paper, we use a Markov model to develop a product form solution to efficiently analyze the throughput of arbitrary topology multihop packet radio networks that employ a carrier sensing multiple access (CSMA) protocol with perfect capture. We consider both exponential and nonexponential packet length distributions. Our method preserves the dependence between nodes, characteristic of CSMA, and determines the joint probability that nodes are transmitting. The product form analysis provides the basis for an automated algorithm that determines the maximum throughput in networks of size up to 100 radio nodes. Numerical examples for several networks are presented. This model has led to many theoretical and practical extensions. These include determination of conditions for product form analysis to hold, extension to other access protocols, and consideration of acknowledgments.

Centralized teleprocessing network design

The problem considered is that of finding an optimal (minimum cost) design for a centralized processing network given a set of locations, traffic magnitudes between these locations, and a single common source or destination. Several heuristics, which are efficient (in terms of their execution time and memory requirements on a digital computer) and which produce seemingly good results, have already been developed and are currently accepted techniques. Some work has also been done on finding optimal solutions to this problem both as a design tool and as a means of verifying the effectiveness of proposed heuristics. We focus on this latter area. Currently known techniques for the optimal solution of this problem via integer programming have fallen short of the desired objectives as they require too much memory and running time to be able to treat problems of realistic size and complexity. We develop an improved technique which is capable of handling more realistic problems.

An Algorithm for Evaluation of Throughput in Multihop Packet Radio Networks with Complex Topologies

The problem of analyzing the thoughput of packet radio networks with realistic topologies is considered. We present an algorithm for the solution of this problem and show that both the memory requirements and running time of this algorithm in practice grow polynomially with the size of the problem. Although in theory both can grow exponentially in the worst case, we offer computational experience with the procedure and show that for realistic topologies where connectivity is related to distance, the rate of growth is quadratic in the number of links. Even for regular grids, which are pathological in their symmetry, the rate of growth is only cubic in the number of links. We thus conclude that the procedure is effective for realistic topologies with up to several hundred nodes.

A Technique for Adaptive Routing in Networks

A two-level adaptive routing scheme for packet-switched computer communication networks is proposed and investigated. The first level is quasi-static and based on the global network status. The second level is dynamic with decisions being made at each node in an attempt to obtain the savings in average delay predicted by a multiserver model of the node. Simulations confirm the predicted improvement.

Routing of voice and data in burst-switched networks

The static and centralized routing of voice and data traffic in burst switched networks is addressed. It is assumed that the routing allows random bifurcation in voice and data paths and preemptive priorities for voice requirements. A study is made of routing of voice only, by using a multicommodity flow model with linearized link losses and average network loss as a minimization objective. Solving the resulting linear program, it is observed that optimal routing strategies prefer to freeze a requirement at an early stage of its path rather than those requirements that are close to their destinations. A study is made of the voice-data interaction at the link level using an available fluid-flow model, and the combined link performance is translated as a maximum flow constraint on a link. This constraint may have undesirable effects on the voice, such as introducing routes with flow absorbing loops, and unfair freezing of some requirements. All conflicting multiple objectives and constraints are included in a linear programming formulation, and it is shown how parameters can be tuned to produce desirable voice and data paths. >

Routing in multidomain networks

Investigates the problem of management and control in a large and, for simplicity, homogeneous packet-switched network. Specifically the authors focus on routing, an important function of network management. The network consists of several individually controlled domains. Domains are interconnected via gateway links. Each domain is controlled by its own network control center, while the overall network performance is managed by an integrated network control center. Each center has only a portion of the information required for global routing. The authors investigate the impact of the reduced information available at each center on network performance (average delay in the present case). They present a general approach to designing a hierarchical algorithm for routing in multidomain networks. They propose a heuristic procedure suitable for packet-switched networks. Several numerical examples illustrate the impact of incomplete information on the network. Performance is compared with a lower bound obtained, which is not differentiating destinations in other domains. Therefore, for this bound, each domain is perceived as a single node in a simplified model of the network. >

Routing in multiple domain networks

The problem of management and control in a large and, for simplicity, homogeneous packet-switched network is investigated. In particular, routing is considered as an important function of network management. The network consists of several individually controlled domains interconnected via gateway links. Each domain is controlled by its own network control center, while the overall network performance is managed by the integrated network control center. Each center has only a portion of the information required for global routing. The impact of the reduced information available at each center on network performance is investigated. A general approach to designing a hierarchical algorithm for routing in multi-domain networks is presented. A heuristic procedure suitable for packet-switched networks is proposed. An example of the algorithm is shown. Its performance is compared against a lower bound to the network performance.<<ETX>>

A Comparison of the Performance of Protocols in Packet Radio Networks

The relative performance and merits of a number of multiple access protocols for multihop packet radio networks are compared. The effects of network size, topology, connectivity, and noise immunity are also studied.

Characterization of bursty sources and capacity estimation in high speed networks

We consider the problem of characterizing bursty sources and estimating the aggregate capacity they require. The sources are described by a mean rate, peak rate, and burst length, in a network with both loss and delay. (Only loss is considered here). We begin by presenting an efficient technique for computing loss exactly in situations where the number and diversity of sources is reasonably large. We then present computational experience using this technique, and on the basis of this experience, develop an approach for characterizing the behavior of a realistically large number of I heterogeneous bursty sources on a channel. We use this characterization to explore procedures for estimating the capacity required to achieve desired performance. The techniques are efficient and can be used in the inner loop of a network design procedure and for real time network management.