Abstract

Abstract
Distributed systems emerged in the last decade as a more efficient way of sharing networked resources, allowing cooperating processes to be executed in remote computers with possibly distinct architectures and operating systems. This paper presents the motivations that may lead to the usage of distributed architectures in the support of telecommunications services, particularly multimedia services. It also gives an overview of one distributed architecture, ANSA, which was used to implement a prototype of a distributed multimedia service, briefly described.

Abstract
Technical advances in communication networks and terminal equipment make possible the provision of a wide range of new and appealing telecommunication services. However, the increasing user demand and the strong market competition require that the creation of those services is efficient and fast, and that they have attractive interfaces. The complexity of networks and distributed systems, which support those services, renders the usage of formal specification languages, such as SDL, almost mandatory in their development. According to some authors, fifty percent of the total time necessary to develop applications is spent in building and testing graphical interfaces for different platforms. In this paper, an efficient methodology to create graphical interfaces for telecommunication services specified in SDL is presented.

Abstract
One of the most-used rendering algorithms in Computer Graphics is the Ray-Tracing. The ''standard'' (Whited like) Ray-Tracing(1) is a good rendering algorithm but with a drawback: the time necessary to produce an image is too large (several hours of CPU time are necessary to make a good picture of a moderately sophisticated 3D scene) and the image is only ready to be observed at the end of processing. This kind of situation is difficult to accept in systems where interactivity is the first goal. ''Increasing Realism'' In Ray-Tracing tries to avoid the problem by supplying the user with a preview of the final image. This preview can be calculated in a considerably shorter time but permits that, with some margin of error, the user can imagine (even see, sometimes) some final effects. With more processing time the image quality continues improving without loss of previous results. The user can, at any time, interrupt the session if the image does not match what he wants. Simultaneously with the above idea, it is necessary to accelerate image production. Parallelism is then justified by the need of more processing power. The aim of this text is to describe the Interactive Ray-Tracing Algorithm implementation, using a parallel architecture based on Transputers. An overview of the architecture used is presented and the main parallel processes and related problems are discussed.

Abstract
In a distributed memory MIMD parallel machine, the efficient communication between processes/processors, through messages, is an important task to be handled by the programmer. Because the number of inter-processor connections is limited, the communication between any two processors is made by passing the messages through several other processors and then, a problem of messages routing appears. For dedicated systems, special architectures can be defined simplifying the problem but, if an environment constituting a basis for general applications development is desired, the problem is more serious due to the deadlock possibility. A general router, able to avoid the problem, becomes then a very important tool for software development in parallel architectures. We have been defining a development platform, based on a network of Transputers and written in OCCAM, for image synthesis applications. This paper reports our efforts in writing different versions of routers, based on two different strategies, and justifies the choice of an efficient one to integrate in the platform.

Abstract