Thomas Plagemann

Challenges and techniques for video streaming over mobile ad hoc networks

Developments in mobile devices and wireless networking provide the technical platform for video streaming over mobile ad hoc networks (MANETs). However, efforts to realize video streaming over MANETs have met many challenges, which are addressed by several different techniques. Examples include cross-layer optimization, caching and replication, and packet prioritization. Cross-layer optimization typically leverages multiple description video coding and multipath routing to provide the receiver(s) sufficient video quality. Caching and replication add tolerance to disruptions and partitioning. In this paper, we identify the challenges of realizing video streaming over MANETs, and analyze and classify the proposed techniques. Since 65 % of the identified involve cross-layering design, we study the distribution of joint optimization and parameter exchanges. Due to the importance and complexity of evaluating the techniques, we analyze the common methods, indicating that the research domain suffers from a problem of comparability.

Operating system support for multimedia systems

Distributed multimedia applications will be an important part of tomorrows application mix and require appropriate operating system (OS) support. Neither hard real-time solutions nor best-effort solutions are directly well suited for this support. One reason is the co-existence of real-time and best effort requirements in future systems. Another reason is that the requirements of multimedia applications are not easily predictable, like variable bit rate coded video data and user interactivity. In this article, we present a survey of new developments in OS support for (distributed) multimedia systems, which include: (1) development of new CPU and disk scheduling mechanisms that combine real-time and best effort in integrated solutions; (2) provision of mechanisms to dynamically adapt resource reservations to current needs; (3) establishment of new system abstractions for resource ownership to account more accurate resource consumption; (4) development of new file system structures; (5) introduction of memory management mechanisms that utilize knowledge about application behavior; (6) reduction of major performance bottlenecks, like copy operations in I/O subsystems; and (7) user-level control of resources including communication.

From content distribution networks to content networks - issues and challenges

Due to the technical developments in electronics the amount of digital content is continuously increasing. In order to make digital content respectively multimedia content available to potentially large and geographically distributed consumer populations, Content Distribution Networks (CDNs) are used. The main task of current CDNs is the efficient delivery and increased availability of content to the consumer. This area has been subject to research for several years. Modern CDN solutions aim to additionally automate the CDN management. Furthermore, modern applications do not just perform retrieval or access operations on content, but also create content, modify content, actively place content at appropriate locations of the infrastructure, etc. If these operations are also supported by the distribution infrastructure, we call the infrastructure Content Networks (CN) instead of CDN. In order to solve the major challenges of future CNs, researchers from different communities have to collaborate, based on a common terminology. It is the aim of this paper, to contribute to such a terminology, to summarize the state-of-the-art, and to highlight and discuss some grand challenges for CNs that we have identified. Our conception of these challenges is supported by the answers to a questionnaire we received from many leading European research groups in the field.

A model for dynamic configuration of light-weight protocols

This paper discusses the configuration of light-weight protocols. As opposed to other proposals which introduce a predetermined protocol hierarchy, the configuration is dynamic in the sense that an application can specify requirements of the underlying services and the configuration of a protocol is done with respect to these requirements. The approach discussed in this paper introduces a model for the configuration of protocols comprising of three layers: application, end-to-end communications, and transport infrastructure layer. The dynamic configuration takes place in the end-to-end communications layer. The emphasis of the paper is on the description of the model, a notation for the description of application requirements, and the configuration of protocol entities. The approach is particularly well-suited to make use of any progress in implementations of protocol functions.<<ETX>>

Modules as building blocks for protocol configuration

Da CaPo provides an environment for the dynamic configuration of protocols. Configuration is done with respect to application requirements, properties of the offered network services, and the available resources in the end systems. The goal of the configuration is to provide a service with minimal necessary functionality for each request, i.e., to diminish protocol complexity and so to increase protocol performance. Modules serve as basic building blocks for the protocol configuration. Common software engineering principles like encapsulation and information hiding as well as a unified module interface allow the unconstrained configuration of modules to protocols. The Da CaPo runtime environment links modules to protocols in one UNIX process and realizes an efficient data transport inside the end systems because performance reducing operations like data copying or process switches are minimized.<<ETX>>

Towards middleware services for mobile ad-hoc network applications

Mobile ad-hoc networks are typically very dynamic networks in terms of available communication partners, network resources, connectivity, etc. Furthermore, the end-user devices are very heterogeneous, ranging from high-end laptops to low-end PDAs and mobile phones. Traditionally, middleware is used to abstract from this heterogeneity and to enable the application programmer to focus on application issues. We propose to develop middleware services that additionally provide services for information sharing in mobile ad-hoc networks, because the possibility to share information is mission critical for many mobile ad-hoc network applications.

Data sharing in mobile ad-hoc networks - a study of replication and performance in the MIDAS data space

The dynamic nature of mobile ad-hoc networks (MANETs) can easily lead to data being inaccessible due to constant route changes and network partitions. One method often used for increasing reliability and availability of data is replication. However, replication comes with costs, those of transferring and storing data and keeping track of consistency between replicas. For that reason, we have identified the core factors impacting the resulting network traffic. We have performed experimental studies with a real world prototype of a distributed data management system for MANETs, called MIDAS data space. Furthermore, we have done an extensive simulation study showing where table replicas should be placed in the network, in order to minimise network traffic generated by access to the databases and by the synchronisation data. The results of the experiments are consistent and show that by using clustering techniques we can achieve close-to-optimal traffic by placing replicas on approximately 10% of nodes.

Using Data Stream Management Systems for traffic analysis: A case study

Many traffic analysis tasks are solved with tools that are developed in an ad-hoc, incremental, and cumbersome way instead of seeking systematic solutions that are easy to reuse and understand. The huge amount of data that has to be managed and analyzed together with the fact that many different analysis tasks are performed over a small set of different network trace formats, motivates us to study whether Data Stream Management Systems (DSMSs) might be useful to develop traffic analysis tools. We have performed an ex-perimental study to analyze the advantages and limitations of using DSMS in practice. We study how simple and complex analysis tasks can be solved with TelegraphCQ, a public domain DSMS, and present a preliminary performance analysis.

Q-L/MRP: a buffer management mechanism for QoS support in a multimedia DBMS

Multimedia database systems (MMDBSs) have to be capable of efficiently handing time-dependent and time-independent data, and of supporting quality of service (QoS). To support continuous playout of time-dependent data, reservations of the resource-limited disk I/O bandwidth and network bandwidth have to be combined with appropriate buffer management. Based on the special requirements of the DEDICATION (DatabasE support for DIstance eduCATION) pre-study, i.e. building a cheap prototype system for asynchronous distance education, we have designed the buffer management mechanism Q-L/MRP (QoS-Least/Most Relevant for Presentation). Q-L/MRP is a buffer preloading and page replacement mechanism for multimedia applications with heterogeneous QoS requirements. Q-L/MRP extends L/MRP with two features: (1) it supports multiple concurrent users, and (2) it supports QoS with a dynamic prefetching daemon. This daemon is able to dynamically adapt to the changes in network and disk I/O load. Furthermore, QoS requirements from the users, such as the frame rate, are mapped into the buffer mechanism. A performance analysis shows that Q-L/MRP is very suitable for the special environment in DEDICATION and outperforms other buffer management mechanisms. Since we have implemented Q-L/MRP in software only, it is also suitable for other multimedia applications on other systems with different hardware configurations and workloads.

A Data Sharing Facility for Mobile Ad-Hoc Emergency and Rescue Applications

Efficient information sharing is very important for emergency and rescue operations. Mobile ad-hoc Networks (MANETs) are often the only network environment for such operations. We have developed the MIDAS data space (MDS) to transparently share information among rescue applications in such environments. To achieve the required level of availability for important information, MDS performs optimistic replication. The problems caused by optimistic replication, like consistency management, are not solved by standard solutions; instead we employ tailor-made solutions for emergency and rescue applications.