We present a cost-efficient topology design technique for optical metropolitan area networks (MANs) using WDM. The network employs a topology with a two level hierarchy. The lower level physical topology is a passive ...
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We present a cost-efficient topology design technique for optical metropolitan area networks (MANs) using WDM. The network employs a topology with a two level hierarchy. The lower level physical topology is a passive optical star interconnecting a number of electrical local area networks (LANs), while the higher level physical topology uses a wavelength routing switch (WRS) at the center for intercluster communication. Thus the number of wavelengths as well as the optical links needed for the network has been significantly reduced as compared to that of the single level (i.e., non-hierarchical) counterparts. An algorithm has been proposed for the formation of clusters based on the geographical locations of the electrical LANs. The algorithm assigns more weightage to the total link cost as compared to the number of wavelengths required. When number of wavelength is found to be at a premium as compared to the link cost, the weightage can swung towards wavelength economy at the cost of increased overhead.
The purpose of this panel is to present and discuss the key issues in distance learning from different perspectives and to envision future directions. The different views of the panelists include: professionals vs. st...
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SNMPv2 management tools for networks based on Novell NetWare and TCP/IP facilitate management of individual network workstations which allows a very detailed description of the network operation to be constructed. Usi...
There is a need for information exchange and communication between management applications that are distributed over a large system. In this situation, a fundamental problem is how the management systems should cooper...
This article argues that the mobile agent approach is well suited for sporadic communication in open distributedsystems, especially for rather ''loose '' cooperations across focal and organization of ...
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This article argues that the mobile agent approach is well suited for sporadic communication in open distributedsystems, especially for rather ''loose '' cooperations across focal and organization of boundaries. In an increasing number of cases, management of distributed business procedures reaches beyond such boundaries. This means, for most existing workflow management systems that cooperating partners are required to give up their focal autonomy. However for cases in which business partners intend to cooperate but still need To preserve their local autonomy, process participation on the basis of mobile agents represents an appropriate mechanism. This article shows how such process integration can be achieved. it also demonstrates how the Common Open Service Market (COSM) system software can be extended in order to use petri-net based process definitions that realize mobile agents in an integrated distributed system platform.
The provision of services such as credit card facilities using Intelligent Networks (IN) depends upon the ability to process real-time data. If their data is deliberately delayed during transit, these services may not...
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The provision of services such as credit card facilities using Intelligent Networks (IN) depends upon the ability to process real-time data. If their data is deliberately delayed during transit, these services may not be able to function accurately. This paper examines INs and highlights their vulnerability to network delay attacks. In particular, the nature of rear-time communications and the main approach that has been developed to determine whether received data is being sent in real-time or not is discussed. The deficiencies in this approach in terms of its ability to counteract the different forms of a network delay attack are highlighted and an alternative method which addresses these drawbacks is presented. Finally, the results achieved following the implementation and subsequent testing of the alternative approach are discussed. (C) 1997 Elsevier science B.V.
Object databases have been recognized as providing rich data modeling capabilities for the next generation applications, especially CAD/CAM, software engineering, and multimedia, The core object model consisting of ob...
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Object databases have been recognized as providing rich data modeling capabilities for the next generation applications, especially CAD/CAM, software engineering, and multimedia, The core object model consisting of objects, messages and inheritance, however, is not adequate to tackle all the requirements of these applications, Since collaborative activity is one of the key features of next-generation applications, it is essential that the basic object model be extended to support collaborative activity, We propose an object model for collaborative designing based on objects and constraint meta-objects. Each design object has an associated constraint space consisting of one or more constraint meta objects. The object/constraint meta-object separation achieves a clear distinction between design object and its associated design environment and provides a framework for supporting collaboration among members of a design team, Collaboration is modeled as dependencies among multiple constraint spaces on different nodes, and collaborative activity as design transactions satisfying local constraints and propagating constraints among interrelated constraint spaces, We propose language extensions to C++ for capturing the object/constraint meta-object paradigm. The extensions are implemented using filters, a special mechanism for capturing messages sent to an object, Our model has been applied to the case of a mechanical CAD problem.
Several international standards for asynchronous data compression are available today. In 1993 the International Telecommunication Union (ITU) started to research possible ways to compress synchronous data. Special at...
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Several international standards for asynchronous data compression are available today. In 1993 the International Telecommunication Union (ITU) started to research possible ways to compress synchronous data. Special attention was given to compatibility with previous asynchronous standards, namely V.42bis. In September 1993 a proposal for modification of the V.42bis standard to make ii applicable to synchronous data was published. In this paper a prototype of a synchronous data link layer protocol based on the ITU proposals is described. The protocol chosen is HDLC based. The V.42bis compression standard is adapted to serve the needs of a synchronous protocol. A functional model is designed followed by a performance analysis of the protocol. The analysis shows a decrease of the compression ratio due to the adaption of the compression algorithm. (C) 1997 Elsevier science B.V.
Vergence provides robot vision systems with a crucial degree of freedom: it enables fixation of points in visual space at different distances from the observer. Vergence control, therefore, affects the performance of ...
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Vergence provides robot vision systems with a crucial degree of freedom: it enables fixation of points in visual space at different distances from the observer. Vergence control, therefore, affects the performance of the stereo system as well as the results of motion estimation and tracking and, as such, must satisfy different requirements in order to be able to provide not only a stable fixation, but a stable binocular fusion, and a fast, smooth and accurate reaction to changes in the environment. To obtain this kind of performance the paper focuses specifically on the use of dynamic visual information to drive vergence control. In this context, moreover, the use of a space-variant, anthropomorphic sensor is described and some advantages in relation to vergence control are discussed to demonstrate the relevance of image plane geometry for this particular task. Expansion or contraction patterns and the temporal evolution of the degree of fusion measured in the log-polar domain are the inputs to the vergence control system and determine robust and accurate steering of the two cameras. Real-time experiments are presented to demonstrate the performance of the system covering different key situations.
Applications that cross the boundaries of different computing machines, operating systems, and programming languages are increasingly the norm. As a result, the need for what might be called bridging technologies to d...
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Applications that cross the boundaries of different computing machines, operating systems, and programming languages are increasingly the norm. As a result, the need for what might be called bridging technologies to develop software that works across heterogeneous environments has become more compelling. The Common Object Request Broker Architecture is one such technology that is both robust and commercially available. CORBA essentially describes how client applications can invoke operations on server objects using the services of an intermediary known as an Object Request Broker, or ORB. This article introduces CORBA by describing its key components. It then reviews the boundaries it helps to bridge. It concludes by comparing CORBA with a number of other bridging technologies available today.
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