is no longer too young to be usable: the first RFCs were published in 2006, and a stable and quite complete Linux implementation exists. DCCP over UDP has also recently been specified to address network traversal problems. But how good is the service provided to applications by this protocol? This paper identifies some deficiencies of the current implementation—the lack of transparency in the API with regard to packet loss, the coarse granularity of the lookup table used to calculate the TFRC equation, and the lack of history discounting in CCID-3—and demonstrates that they can significantly impair the performance of typical DCCP use cases such as live video streaming. Solutions are proposed to tackle all these problems, and it is shown that they considerably improve the performance and the flexibility of applications. I.

This work proposes a quality-oriented, real-time capable prioritization technique for media units of H.264/AVC video streams. The derivation of estimates is based on the analysis of the macroblock partitioning, the spatial extents of temporal dependencies, and the length and strength of prediction chains existing among macroblocks, thus incorporating the expected impact of error propagation. It is demonstrated how the prioritization scheme can be beneficially integrated into live streaming systems which are characterized by tight timing constraints, with the focus on content-aware selective automatic repeat request mechanisms. Additionally, it is shown how potentially limited feedback can be used to adapt the estimation process to leverage prediction preciseness. The approach is compared against existing techniques in terms of practicability and efficiency, and tested under independent and bursty loss conditions in a wired and a wireless test setup. Moreover, the performance is examined when low-latency and constant bitrate video settings are enforced by using x264's novel encoding feature periodic-intra-refresh. Results of both experiments and simulations indicate that the proposed technique outperforms all reference techniques in nearly all test cases, and that the video quality can be further improved by incorporating receiver feedback.

We present a novel mechanism for estimating the perceptual importance of network packets constituting a video stream. We explain how this information can be used to extend existing rateless coding schemes and present first results demonstrating the expected increase in perceptual quality.

Over the past years, several schemes have been proposed to estimate the perceptual distortion in video quality caused by packet loss. Some of them are intuitively designed and do not correlate well with actual distortion values in most real-world scenarios. Others simulate decoders' error concealment measures and use the quality degradation of reconstructed regions as basis for calculating importance estimates. However, such techniques do not take error propagation in the temporal domain into account and are computationally expensive, especially when estimates cannot be derived in parallel to, or as side-product of the video encoding process. We therefore propose a novel approach which targets all previously mentioned problems and inspects dependencies between media units at the level of macroblocks. We show how our scheme can be applied to live video streaming systems using rateless codes for error protection and identify pitfalls which have to be considered. Test results indicate that the proposed unequal error protection scheme considerably outperforms previous approaches, independent of the resolution of the test sequences.