Abel Weinrib

The datacycle architecture for very high throughput database systems

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.

Using distributed topology update and preplanned configurations to achieve trunk network survivability

The authors present a new approach for trunk network survivability. This modular approach is intended for a telephone trunk network consisting of high-bandwidth fiber-optic links connected through reconfigurable digital cross-connect nodes. It works for both node and link failures. This approach comprises a distributed protocol with two parts. First, the surviving digital cross-connect nodes are caused to converge to an agreement on the topology (i.e., what is up and what is down). Second, based on the agreed topology and on a precomputed plan for that topology, the digital cross-connect nodes are reconfigured to restore as much call-carrying capacity as possible. The modularity of this approach comes from separating the problem of devising a distributed fault-tolerant protocol to determine what the failure is from the problem of designing a network reconfiguration for that failure. >

Managing Shared Ephemeral Teleconferencing State: Policy and Mechanism

In recent years there has been dramatic progress on the enabling technologies for workstation-based multimedia teleconferencing applications. We expect that such applications will soon become an important component of many future social and business interactions. Teleconferencing applications have aspects of their state, such as membership, types of media being used, and encryption, that are under joint control. Much of this state is ephemeral, in that it is of importance only for the duration of a session, and does not have importance outside of the session itself. In this paper we focus on the specification and realization of policies for managing this shared ephemeral teleconferencing state. We first define a broad family of policies which has three dimensions: initiation, voting, and consistency. We then present a mechanism that implements this family of policies for two different communication models.

A symptotic analysis of large heterogeneous queueing systems

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.

An object-oriented interface for a distributed connection manager

Connection management (CM) is the part of the network software architecture for broadband networks that allows for the abstraction and control of multimedia, multiparty connections over heterogeneous communication networks. Network control is accomplished by controlling the switching facilities and allocating transmission and special resources (e.g. multicasters, signal converters and signal combiners). This paper proposes an interface to CM that assumes that both CM and CM clients may be distributed. The CM interface is based on several requirements which call for a simple, flexible, extensible transaction-based interface. The proposed solution uses an object-oriented approach to model a directed graph. The CM interface transport model contains object classes that model the components of a directed graph and are used to represent the network resources and the connectivity among them. An additional object class satisfies the transaction requirements of the interface.<<ETX>>

Limited waiting: an adaptive overload-control strategy for circuit switched networks

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. >

Routing in a circuit-switched network with priority classes

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.<<ETX>>

Enhancing the Touring Machine API to Support Integrated Digital Transport

The current version of the Touring Machine software platform for multimedia communications uses analog transport of voice and video media streams. The next iterations of system design will, among other enhancements, support digital (packet-switched) transport of all media streams, placing new requirements on the system. This paper describes proposed changes to the Touring Machine Application Programming Interface in support of integrated digital transport. We identify new abstractions in two areas: network access control and specification of transport topology. These new abstractions will provide flexible control of multiple streams sharing the underlying integrated transport (for instance, separate packet-video streams each being displayed in separate windows on a multimedia workstation) and will support heterogeneous terminal equipment and networks by transparently converting media-stream formats within the network.

Distributed implementation of real-time resource counters

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.<<ETX>>