Tino Hutschenreuther

Protocol support for optimized, context sensitive request/response communication over connection oriented networks

This paper describes a research project on specification and implementation of a fast, reliable and context sensitive transfer system. The design considers the behavior of various connection oriented networks and the requirements of request/response based communication schemes. First we describe the current situation. This is based on recent measurements and experiences with remote procedure call (RPC) over ATM and GSM networks. The major basis is the RPC of the OSF Distributed Computing Environment. Furthermore, we discuss different approaches and existing solutions including VMTP, IIOP, RMI, IPv6 and XTP.

Video Communication and Media Scaling System "Xnetvideo": Design and Implementation

Todays networks are characterized by heterogeneous environments. Various transmission techniques coexist and offer different bandwidths at different costs. For example, it is possible to transmit 155 Mbps and more with the Asynchronous Transfer Mode (ATM). As opposed to that, most LANs are based on Ethernet links, which allow only a 10 Mbps transfer rate. The major problem of multimedia communication systems is the lack of resource reservation protocols such as RSVP in current practical environments. Scaling of media streams is a current possibility and trade-off to meet the needs of the end user, to prevent the waste of bandwidth and to react onto phases of low available bandwidth.

QoS support for advanced RPC interactions

QoS support is necessary for nearly every communication between computers. We present an approach for supporting request response communication behavior with particular respect to an ATM LAN environment. The goal is to extend the RPC protocol with mechanisms for QoS-specification mapping and -monitoring for the effective transmission of data in such an ATM environment. As a first basis for validating our conceptual work, we present a facility to transmit multimedia data by extending the RPC pipe mechanism.

Architectural support for QoS management and abstraction: SALMON

High-performance communication protocols are being used in our lab as an experimental base for advanced distributed applications with a special focus on quality of service (QoS) characteristics. During our recent work, we recognized that QoS abstractions would prove very useful for facilitating distributed application development. As a first base, we present a management tool for inspecting and controlling QoS related characteristics on top of XTPX (eXpress Transfer Protocol Extended) and TCP/IP. Based on a classification of QoS requirements of various multimedia data streams, the design and implementation of a higher-level QoS manager tool and channel library named SALMON is then described. We finally illustrate how such an approach will be integrated with traditional client/server platforms such as the OSF Distributed Computing Environment.

Content based discarding in IP-routers

There is a growing set of UDP (user datagram protocol) based applications using inadequate congestion control algorithms or none at all (i.e., the flow does not throttle back upon receipt of congestion notification). Such UDP applications include streaming applications like packet voice and video, and also multicast bulk data transfer. Congestion avoidance algorithms in routers are not able to handle these flows adequately and this leads to an unfair distribution of bandwidth among TCP and UDP flows in times of congestion. Moreover the random dropping of IP packets in times of congestion in routers causes a decreasing goodput delivered to the receiving application because whole TCP or UDP packets are discarded at the receiver when one IP packet is missed. This leads to retransmissions when using TCP and can cause serious problems with the display of a multimedia stream when using UDP. This paper proposes a method to overcome the mentioned problems by introducing an additional header into the IPv6-header (Internet Protocol Version 6 Draft Specification, 1998) to label the dependencies of several IP packets and distinguish between different flows at the IP level. A structured description of the application data contents helps to include dependencies of the application data level. The description is mapped onto several priority levels to describe the dependencies within an ADU (application data unit). This paper also explains the way to derive ADUs from the multimedia data and the benefit that can be taken from IP-labeling inside the Internet. As a technical basis, the concepts described in the paper are validated by a simulation study.

A Framework for High Quality/Low Cost Conferencing Systems

This paper presents a framework for the development of advanced video conferencing systems with very high quality. The design and performance of the developed components like session management, real-time scheduler and a specific transport system are outlined. The core of the framework consists of a toolkit for the processing of audio and video data. It integrates capturing, compression, transmission and presentation of media streams into an object oriented class library. The specifics of audio/video hardware, preferred operation modes, compression algorithms and transport protocol properties are encapsulated. Due to the achieved abstraction level complex application software can easily be developed resulting in very short design cycles. Contrary to existing systems the developed application is regarded in its entirety. The focus on highest possible performance throughout all components is unique to our approach. Due to a number of optimisations, specific compression hardware is not required which leads to low overall system costs.

Supporting distributed applications on advanced communication networks

Distributed applications are of growing importance in many application fields such as office automation, manufacturing, telematics or information services. This paper outlines support facilities for such applications based on distributed platforms. It then discusses further requirements resulting from the use of advanced network technologies. Architectural support for such environments is presented and experiences with specific software support solutions are discussed. As an application example, workflow processing in distributed environments is used in order to illustrate the approaches. The paper concludes with an outlook to future work.

Quality of Service Abstraktionen für verteilte Multimedia-Systeme

Mit dem zunehmenden Einsatz multimedialer Anwendungen im Rechnemetzbereich wächst die Forderung nach qualitätsgerechter Medienstromübertragung. Wesentliche Probleme sind die Abbildung abstrakter Quality-of-Service (QoS)Anforderungen der Anwendung auf das Transportprotokoll sowie die Überwachung der Dienstgüte. Die Anforderungen multimedialer Ströme, die auftretenden Probleme bei der Übertragung sowie ein Ansatz für das QoS-Mapping werden in diesem Beitrag betrachtet.

Architecture and implementation for scalable transfer of live videos in multimedia applications

Todays networks are characterized by heterogeneous environments. Various transmission techniques coexist and offer different bandwidths at different costs. Because of videoconferences and similar applications becoming more and more important this paper presents the architecture of the video communication system XNetvideo which is scalable in terms of SNR (signal to noise ratio)-scaling, image size and frame rate. Xnetvideo is a tool for video transmission over IP-networks and especially ATM, that was developed at our Institute. The description of this architecture, and the discussion of implementation issues and performance results are the major topics of this contribution. Moreover a brief survey of existing tools and architectures in this area is given.