In-Network Adaptation of Scalable Video Content
Supervisor(s) and Committee member(s): Hermann Hellwagner (1. rapporteur), Carsten Griwodz (2. rapporteur)
This thesis investigates mechanisms and applications for in-network adaptation of scalable video bit streams based on the recent H.264/Scalable Video Coding (SVC) standard. In-network adaptation refers to the adaptation of a video stream by a network element during the stream’s transport through the network. The advantages of performing adaptation directly in the network are the availability of local monitoring data and a higher responsiveness according to the current networking conditions. In contrast to previous work in this field, this thesis focuses on the feasibility and realization of in-network adaptation on existing home router platforms. In this context this thesis addresses the following six research objectives. Initially, the relevant transport mechanisms for H.264/SVC and their implications on in-network adaptation (1) were analysed. In the context of this work three different Linux-based router platforms which cover a representative range of residential router devices were used as a basis for further studies and evaluations. In general these platforms can be characterized by rather modest processing capabilities and networking performance. The hardware limitations were identified and quantified in evaluations (2) using both different benchmarks and real network traffic. The offered processing power and memory throughput are roughly 10 to 100 times lower than those of a modern desktop PC. Although their application-layer networking performance is not that low, all platforms fail in fully utilizing their nominal link capacities of 100 and 1000 Mbps, respectively. Based on the known limitations the thesis proposes a stateful, packet-based adaptation mechanism for adapting scalable video bit streams (3). The approach utilizes the RTP payload format for H.264/SVC and represents a light-weight approach for in-network adaptation on the application layer. It further meets the important requirements towards a media-aware network element (MANE) to be signaling aware and to operate statefully. The mechanism was integrated in a proxy service which was deployed on all of the three platforms to prove its feasibility. Experimental evaluations with different video bit streams in standard-definition quality demonstrate the scalability of the approach (4). The results indicate that the proxy service is able to adapt up to 16 concurrent video streams depending on the platform and video bit stream. On two of the three evaluated platforms the proposed approach even allows to handle and to adapt video streams in high-definition quality at bit rates around 15 Mbps. In addition to the proposed H.264/SVC-specific adaptation mechanism, also the applicability of generic metadata-driven adaptation on home router platforms was investigated. In particular, a proof-of-concept study of an XML-metadata-driven approach based on the MPEG-21 generic Bitstream Syntax Description (gBSD) was conducted on the platforms (5). In contrast to former evaluations that have been done on PC-based platforms, the obtained results indicate that the use of this generic adaptation cannot be recommended on such resource limited network devices. The benefits of using in-network adaptation on home router platforms are finally demonstrated in the context of high-definition streaming over IEEE 802.11 wireless networks (6). Monitoring information regarding the queueing delay, which is obviously available exclusively on the router, is used to control the adaptation of the video according to the varying throughput of the wireless link. This allows to react timely to changing conditions particularly in the case of mobile clients.
Multimedia Communication (MMC)
The research group "Multimedia Communication (MMC)" was founded and is being led by Prof. Hermann Hellwagner. In addition, the group currently has three research assistants, five project staff members, and three administrative and technical staff members.
The research activities of the group are in the areas of
- Multimedia communication and QoS provisioning
- Adaptation of multimedia content w.r.t. network, device, and usage contexts
- Use of Scalable Video Coding (SVC) technology in networks and P2P systems
- Adaptive multimedia applications, e.g., IPTV
- Standardization within ISO/IEC MPEG
- Multimedia in disaster management
The focus of the MMC group is clearly on adaptive delivery of audio-visual contents, taking into account, for instance, fluctuating network and environmental conditions that can occur when users are on the move. In particular, the group is currently investigating the use of Scalable Video Coding (SVC) technology in such networks. The group actively participates in several international and national research projects on all levels, ranging from basic research to application-oriented projects and direct cooperation with industry. In teaching, the MMC group covers the technical courses of the Informatics study programme such as Computer Organization, Operating Systems, Computer Networks, Servers and Clusters, Internet QoS, and Multimedia Coding.