Multimedia applications handling audio and video data have to obey time characteristics of these media types. Besides a basic functionality to express time relations, correctness with respect to time constraints requires mechanisms which lead to favoured processing of multimedia operations. CPU scheduling techniques based on the experience from real-time operating systems offer a solution and provide multimedia applications with the ability to meet time-related quality of service requirements. This paper discusses mechanisms to express time in multimedia systems and describes an implementation of a CPU scheduler designed to run under IBM's UNIX derivate AIX. The evaluation of the implementation based on measurements shows that the scheduler is able to support the time requirements of multimedia applications and that such mechanisms are indeed necessary since otherwise deadline violations occur.

HeiTS, the Heidelberg Transport System, is a multimedia communication system for real-time delivery of digital audio and video.HeiTS operates on top of guaranteed-performance networks that apply resource reservation techniques.To make HeiTS also work with networks for which no reservation scheme can be realized (for example, Ethernet or existing internetworks), we implement an extension to HeiTS which performs media scaling at the transport level: The media encoding is modified according to the bandwidth available in the underlying networks.Both transparent and non-transparent scaling methods are examined.HeiTS lends itself to implement transparent temporal and spatial scaling of media streams.At the HeiTS interface, functions are provided which report information on the available resource bandwidth to the application so that non-transparent scaling methods may be used, too.Both a continuous and discrete scaling solution for HeiTS are presented.The continuous solution uses feedback messages to adjust the data flow.The discrete solution also exploits the multipoint network connection mechanism of HeiTS.Whereas the first method is more flexible, the second technique is better suited for multicast scenarios.The combination of resource reservation and media scaling seems to be particularly well-suited to meet the varying demands of distributed multimedia applications.

As some object-oriented computing systems support the object type buffer by hardware, it is reasonable to base their free storage management on a set of buffers, each containing free storage blocks of a specific length. Then memory space can normally be allocated and deallocated by simple buffer read and write operations. More complex routines have to be executed only when a buffer full or buffer empty exception is raised. Their task is to clear a buffer position or to insert a storage descriptor into the buffer, respectively. An algorithm that handles such exceptions by splitting and recombination of free blocks and relocation of objects is described. The algorithm is tuned by a set of parameters that specify the amount of descriptors the buffers may hold immediately after exception handling. As a consequence, each buffer receives a moderate number of descriptors, so that the probability of further exceptions is reduced. Moreover, the parameters control the tradeoff between relocation costs and resulting storage fragmentation. The performance of the algorithm is evaluated by an analytical and a simulation model, and methods to find optimal parameter values are described.>