The problem of managing telephone network resources for private virtual networks is discussed. Implementing a real-time resource counter on a distributed system is investigated. A correctness condition is developed for a real-time resource counter, and several approaches to implementing it are described. The various approaches are evaluated on a model that accounts for load-dependent message-processing delays, using both analytic and simulation techniques. The results of the performance studies also suggest heuristics for configuring a resource counter on a distributed system. A very simple approach, in which requests that cannot be satisfied locally are randomly forwarded to other processors, works well over a wide range of loads and system sizes. Unless a very large number of processors is required to handle the requests for resources or heavy overloads are expected, this may be the best algorithm.>

The authors present an adaptive control strategy for circuit-switched networks in which calls are permitted to wait for a limited time to be carried on a low-cost preferred route. The strategy uses network resources more efficiently than other conventional approaches, exhibiting lower blocking of calls under overload conditions. The proposed strategy is also adaptive in that, when there is little network congestion, there is no penalty for the policy, in contrast to other schemes in which improved performance under overload is achieved at the cost of degraded performance at lower bounds. The authors analyze an exactly solvable model and present simulation results for a more general network.>

The authors address the topic of how to meet a real-time constraint as the load on a distributed system increases, without increasing the capacity of the individual processors. The application studied is a real-time resource counter with a probabilistic correctness criterion, and is motivated by the problem of implementing resource management in the telephone network. They introduce a model that combines distributed computing, real-time constraints, probabilistic correctness, and large system size; to the authors' knowledge, no previous work addresses this combination.>

The problem of routing in a circuit-switched network with different classes of traffic is examined. The authors consider the case of two priority classes, assuming that a relatively small fraction of traffic comprises the high-priority class requiring a better grade of service, with the rest being treated as lower priority normal traffic. These high-priority calls might be used to provide a premium service with lower blocking probability, or to implement services in which failure is expensive to the network such as a multiparty conference call. The authors identify several routing schemes that give preference to high-priority calls, either by explicitly reserving capacity or by allowing more resource sharing. The performance of these schemes is studied in terms of blocking probabilities for the two classes, protection of priority traffic against overload of normal traffic, and adaptability to variations in offered priority traffic. The authors compare the schemes by the different total revenues they earn and discuss the implementation complexity. They find that some resource-sharing schemes display good performance, having the potential to provide low blocking for priority calls with minimal impact on the remaining normal traffic.>

The essence of the basic control decisions implicit in load-sharing and routing algorithms is captured in a simple model of heterogeneous queue control. The authors solve for the optimal control policy and investigate the performance of previously proposed policies in a tractable limit of this model. Using their understanding of this solvable limit, the authors propose heuristic policies for the general model. Simulation data for these policies suggest that they perform well over a wide range of system parameters.>

The authors consider the problem of job placement in load-sharing algorithms for large heterogeneous distributed computing environments. They present simulation results using a simple model; the results indicate that, under heavy loads, the usual policy of placing jobs where they will incur the shortest expected delay leads to inefficient system performance. Thus, purely greedy policies are not sufficient; the authors identify a simple threshold algorithm that does significantly better. The authors introduce a novel adaptive algorithm having a performance much closer to optimal.

As a simple example of a large heterogeneous queueing system, we consider a single queue with many servers with differing service rates. In the limit of infinitely many servers, we identify a queue control policy that minimizes the average system delay. When there are only two possible server speeds, we can analyze the convergence of this policy to optimality. Based on this result, we propose policies for large but finite systems with a general distribution of server speeds.

The evolutionary trend toward a database-driven public communications network has motivated research into database architectures capable of executing thousands of transactions per second. In this paper we introduce the Datacycle architecture, an attempt to exploit the enormous transmission bandwidth of optical systems to permit the implementation of high throughput multiprocessor database systems. The architecture has the potential for unlimited query throughput, simplified data management, rapid execution of complex queries, and efficient concurrency control. We describe the logical operation of the architecture and discuss implementation issues in the context of a prototype system currently under construction.