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 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 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.

The performance characteristics of a reliable broadcast protocol in a local-area network environment are analyzed. This protocol involves a source broadcasting a message to all destinations and collecting replies from these destinations. Reliability is achieved by using Send-and-Wait protocols for transmitting broadcast and reply messages. A queueing model is developed and results on the throughput and delay of the broadcast operation are obtained by approximate analysis. Numerical results showing the effect of model parameters on throughput are provided.

Broadcast addressing is the capability to send a packet from a source node to all other nodes in the network. Store-and-forward, packet-switching networks are not inherently designed to carry broadcast packets, and broadcasting has to be implemented by some sort of routing algorithm. In this paper, the source based forwarding algorithm is considered. With this algorithm, a spanning tree is defined for each node, and broadcast packets are sent along the branches of these trees. Approximation methods are presented to obtain a lower bound and estimates of the mean broadcast time. The accuracy of these methods is evaluated by comparison with simulation.