Multimedia Communications

Mitnehm.TV is a new approach to Mobile TV that we have developed at TZI in order to investigate possibilities for robust, personal video streaming in challenging environments, e.g., in high mobility scenarios with intermittent connectivity and varying link characterstics. Mitnehm.TV focuses on two concepts in the context of service and network convergence: session mobility for personalized media streaming between user environments (home and personal device) and robust video streaming for mobile devices.

For mobile personalized media streaming, robustness in terms of delay- and disconnection-tolerance is an important feature for successful deployment in real day-to-day scenarios. Even in the presence of seamless mobility, disconnections cannot be completely avoided, e.g., when users decide to pause and resume sessions. Also, usage scenarios with highly mobile users (e.g. in vehicles) may cause disconnections, variable link qualities and unpredictable available bandwidth. Furthermore, mobile clients may suffer from disconnections due to sparse coverage, as it is currently the case with the HSDPA coverage in 3G networks.

Usable 3G-based personalized streaming solutions must therefore take disruptions due to different factors into account. Mitnehm.TV will therefore address the issue of disconnection tolerance by developing a robust video streaming solutions that can accommodate user-generated interruptions (pausing and resuming sessions) as well as disruptions caused by incomplete coverage, varying link characteristics etc. In this context, the adaptation of content and transport protocols will also be considered as mechanisms to further enhance service quality in challenged environments.

Disruption-tolerant transport is a topic for other applications as well and has been generally addresses by the Delay-Tolerant-Networking (DTN) architecture. Those concepts are, in principle, also applicable for the transmission of video content. However, since DTN is rather aimed at asynchronous store-and-forwarding of information bundles, it is more suited to Podcast-like distribution of standalone video files, not directly at robust video streaming.

Digital Broadcast as a scalable, high-bandwidth communication technology that enables many new applications. Besides the already commercially deployed fixed digital TV broadcast services (e.g., DVB-S) terrestrial digital broadcast is now becoming available for mobile usage, e.g., as DVB-H, DMB, ISDB-T oneseg. Mobile digital broadcast can complement bi-directional mobile communication services such as 3G and WLAN and can thus form the basis for scalable mass distribution to mobile users, interactive multimedia and other applications.

In Japan, commercial operation of mobile TV (based on ISDB-T oneseg) has started in April 2006 and has initiated a successful roll-out of mobile TV based on free-reception and supported by the major mobile operators. New applications and business models are being developed and new alliances are alliances between mobile operators and content providers are being established. As part of other Japan-related activities, I am occasionally reporting on the progress of the mobile TV business in Japan and on related technical developments.

The Message Bus (Mbus) is a light-weight local coordination protocol for developing component-based distributed applications that has been developed by TZI and University College London. Mbus provides a simple and flexible message oriented communication channel for a group of components that may be distributed on multiple hosts in a local network. The Mbus transport services include useful features such as peer location, point-to-point and group communication and security. The protocol specification has been published as RFC 3259.

Mbus implementations have been developed for different programming languages and platforms, including small one-chip computers. The protocol has been applied to different application domains, e.g., for coordinating application components in decomposed multimedia conferencing applications and for providing coordination services for pervasive computing environments such as home networks. End-user releases of Mbus implementations are available at http://www.mbus.org/. SVN access to the C++ version for developers is available at https://prj.tzi.org/cgi-bin/trac.cgi/wiki/Mbus.

Internet Media Guides (IMGs) are a generalization of Electronic Program Guides (EPGs) as known from digital video broadcasting (DVB). They are independent of specific metadata formats and thus are able to support a broad range of applications, including EPG distribution for TV networks and distribution of session descriptions for Internet-based multimedia sessions. Unlike most existing approaches, the IMG framework is also completely independent of specific delivery networks for the media content described in media guides - and it is also independent of the distribution mechanisms for the media guides themselves: IMGs can be distributed in unidirectional broadcast networks, they can also retrieved over established query/response protocols such as HTTP, and they allow for asynchronous change notifications to interested subscribers.

Only recently, with the advent of digital mobile broadcasting technologies (DVB-T, H), broadcasting services for 3G networks, the introduction of video (on-demand) services for residential users, and the evolution of networked multimedia home architectures, this landscape has started to change. The largely independent deployment of these - often but not always IP-based - delivery methods has led to a split into different application areas, each of which relying on dedicated networks, transport and control protocols, and finally different approaches to describing media sessions and to distributing these descriptions to user devices. Clearly, the assumption of a single, unified, IP Multicast enabled architecture that the original SDP/SAP- and RTP-based approach to media broadcast is based on, is no longer valid. Instead, new approaches must be developed that can achieve an integration of service and content access across different networking environments.

The Internet Media Guide (IMG) framework, a current development and standardization effort in the IETF, is an important component in that respect and may be used as replacement for SDP/SAP for media broadcast applications but goes well beyond the scope of SAP/SDP. The IMG framework supports common description languages to express meta information about services (and contents), their identification, and the dissemination of such information in a standardized fashion. Peered with adequate description languages, Internet Media Guides (IMGs) \cite{img-req} \cite{img-framework}, are able to provide the necessary service description and discovery functionality that is required for today's diverse media broadcast environment and will also support the incremental conversion to an integrated IP-based infrastructure.

SDPng is a description language for both potential configurations (i.e. capabilities) of participants in multimedia conferences and for actual configurations (i.e. final specifications of parameters). Capability negotiation is the process of generating a usable set of potential configurations and finally an actual configuration from a set of potential configurations provided by each potential participant in a multimedia conference.

SDPng itself is an application-independent framework that defines a description syntax and processing rules that are applied to the capability negotiation process. The rules specify how to process two or more capability description in general in order to obtain an interworking configuration.