No abstract

Streaming multimedia content in real-time over a wireless link is a challenging task because of the rapid fluctuations in link conditions that can occur due to movement, interference, and so on. The popular IEEE 802.11 standard includes low-level tuning parameters like the transmission rate. Standard device drivers for today's wireless products are based on gathering statistics, and consequently, adapt rather slowly to changes in conditions. To meet the strict latency requirements of streaming applications, we designed and implemented an advanced hybrid control algorithm that uses signal-strength (SNR) information to achieve fast responses. Since SNR readings are quite noisy we do not use that information to directly control the rate setting, but rather as a safeguard limiting the range of feasible settings to choose from. We report on real-time experiments involving two laptops equipped with IEEE 802.11a wireless interface cards. The results show that using SNR information greatly enhances responsiveness in comparison to statistics-based rate controllers. Finally, we will present the results of an experiment with realtime video streaming to a moving laptop in an office-like environment. Our hybrid control algorithm effectively prevented many packets losses, thereby achieving a much higher video quality than 1 the statistics based algorithm.

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Broadband Iriteniet access rising ADSL or cable niodenis provides suficienr bandwidth for real-time video streaming. If television channels could be distribrrted on die Inremet, each channel ivorrld get a world wide arrdienre. Howeimec teleiision distributiorr from a single seri'er does not scale and IP-level mrrlricasring is cornplex ai7d costly. We propose a solution based on application-level n~ulticasrirrg rising a P?P riehvork, called P2P-TV. Each peer receiivs a vid,?o streani ar7d initsf also fomard this stream to others. This pgper presents a 1 7 orcliitectrrrr for streariiing video. Oiir PZP-I'V proposal aims to solve three pmblenis rhar are cirrrenrly not iddressed in other P2P strean~ing pmposnls. rtanicly 1) 11711~-in7i:irzg the usage of 011 aioilable peer bandwidth, 2 ) rakirig nmrnl rrehi.ork coirdi1;oiis into acconrit (network a r'arenes?), arid 3 ) the Freeriding probleni. Multiple Description CO,$-ing is an ir~tegralpart of orir solution. By splitting the ifidm stream iiito snialler streanis we car7 riri1i:e all the bandwidth of a pee,: Mrrlriple .stt-eanis allow more eflcierrt aduptarion oj the rniilticast wee 10 ciirrent r7ehl'ork conditions. Bittorrenrlike bartering of conleiif is also enabled by rrsirig nrrrlriple stream.

Peer-to-peer networks (P2P) form a distributed communication infrastructure that is particularly well matched to video streaming using multiple description coding. We form M descriptions using MDC-FEC building on a scalable version of the "Dirac" video coder. The M descriptions are streamed via M different application layer multicast (ALM) trees embedded in the P2P network. Client nodes (peers in the network) receive a number of descriptions m < M that is dependent on their bandwidth. In this paper we consider the optimization of the received video qualities, taking into account the distribution of the clients' bandwidth. We propose three "fairness" criteria to define the criterion to be optimized. Numerical results illustrate the effects of the different fairness criteria and client bandwidth distributions on the rates allocated to the compressed video layers and multiple descriptions.

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The work reported here has been funded by the Delft University of Technology DIOC research programme. DIOC programmes are an initiative of the ARTD ("Advisory Council Technology T.U. Delft"), and aim at solving, in a multidisciplinary way, specific technological problems with engineering and social significance.

Collaborative storytelling using user generated audio-visual narratives is becoming a popular medium for creative social sharing, hyper-local TV, and collective awareness. Through two storytelling user experiments, we recognized that the challenges around ethics and copyrights in managing user data are far more pressing than the simple technical feasibilities of a storytelling platform. Recognizing the importance of some actual and anticipated ethical problems we attempted to address the issue in our experiments using purpose-built technical features and a specifically designed consent form as the code of conduct. The resultant platform effectively maintains the life-cycle and dependencies of the narratives and composite user stories.