Jochen Sandvoss

Media scaling for audiovisual communication with the Heidelberg transport system

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.

Media scaling in a multimedia communication system

HeiTS, the Heidelberg Transport System, is a multimedia communication system for real-time delivery of digital audio and video. HeiTS operates on top of guaranteedperformance 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 nontransparent 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 nontransparent 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.

Network Layer Scaling: Congestion Control in Multimedia Communication with Heterogeneous Networks and Receivers

Because of the admission control schemes in computer networks, in many multimedia communication scenarios it is not possible to get guaranteed quality of service for data transmission along the entire route from sender to receiver. In such cases scaling mechanisms can be used to overcome problems caused by resource congestion. Whenever resource bottlenecks are noticed, the multimedia traffic through these resources will be reduced for a limited time. The scaling scheme described in this paper uses mechanisms in the network layer to enable short delay times between detection of overload and the reduction of multimedia traffic. Network layer scaling allows priority-controlled regulation of multimedia traffic over network resources and adaptive handling of various paths and receivers. The monitoring and scaling strategies in the network layer and a prioritization scheme for multimedia stream packets are described.

BERKOM multimedia transport system

The BERKOM MultiMedia Transport System is designed for communication between distributed multimedia applications on top of broadband ISDN networks. Its core are the ST-II protocol on the network layer and an extended version of the XTP protocol called XTP-Lit on the transport layer. ST-II provides mechanisms for fast packet forwarding, multiple target connections and bandwidth management. XTP-Lite supports negotiation of QoS parameters, rate control and flexible error handling.

XTP and multimedia

The paper analyses the requirements of multimedia communications in terms of XTP (Xpress transfer protocol). In a first step, multimedia communication requirements are described. Subsequently individual features of XTP relevant for audio and video data transfer are presented. The authors describe the multimedia requirements and provide a possible way to satisfy them using XTP. It turns out that a multimedia capable XTP requires new interpretations of existing mechanisms as well as some extensions.<<ETX>>

XTP und Multimedia

Dieser Beitrag untersucht die Eignung der in XTP (Xpress Transfer Protocol) eingesetzten Protokollfunktionalitaten zur Kommunikation von Audio- und Videodaten. Ausgehend von den Anforderungen multimedialer Anwendungen werden die vorhandenen XTP-Mechanismen kurz erlautert. Anschliesend werden fur die wichtigsten Teilaspekte des Kommunikationsprotokolls (Verbindungsmanagement, Prioritatssteuerung,Flussteuerung etc.) jeweils im Einzelnen die Anforderung von Seiten der Ubertragung kontinuierlicher Medien und mogliche Losungen im Kontext von XTP diskutiert. Es zeigt sich, das zur Unterstutzung multimedialer Kommunikationsformen sowohl geeignete Interpretationen vorhandener XTP-Protokollmechanismen wie auch Protokollerweiterungen erforderlich sind.