On-the-fly coding for real-time applications

Abstract

Although ironically it does not offer any real-time guarantee, Internet is a popular solution to support multimedia time-constrained applications (e.g. VoIP, Video Conferencing, ...). Following this trend, this paper focuses on the performance of these applications by studying the benefit of using a novel reliability concept which aims at significantly improving the performance of these time constrained applications over lossy best-effort networks. This reliability mechanism emerged from several recent works from both network and coding theories. Its principle is to integrate feedbacks in an on-the fly coding scheme in order to optimize the trade-off "packet decoding delay" vs "throughput". We present the first evaluations of this mechanism for VoIP and video-conferencing applications for various erasure channels. Compared to classic block-based erasure codes, the results show significant gains in terms of quality observed by the user for both applications.

When on-the-fly erasure code makes late video decoding happen

“…Indeed, with Tetrys [13], the decoding process can be performed as soon as the number of redundancy packets received since the first unrecovered loss matches the number of missing source data packets.…”

“…For the late video decoding, it results that after the reception of R1,8, the video frames F2 and F3 can be re-decoded without error and the user will perceive F4 and F5 error free. Further details such as Tetrys' acknowledgments scheme, complexity and decoding delay can be found in [13].…”

“…The downside of these block-based erasure codes is that it requires complex probing of n and k as it trades off throughput and delay for residual loss rate. Recently, a novel erasure coding approach that prevents such complex configuration has been proposed in [12,6,13]. Tetrys [6,13] that belongs to the class of on-the-fly codes, has the advantage to be systematic 2 .…”

“…Recently, a novel erasure coding approach that prevents such complex configuration has been proposed in [12,6,13]. Tetrys [6,13] that belongs to the class of on-the-fly codes, has the advantage to be systematic 2 . Tetrys uniformly distributes the 2 An erasure code is said to be systematic if source packets appear unaltered in the encoded output.…”

“…As a result, some repair packets among the data packets and it recovers all lost packets within a small delay independent of the RTT. As a result, it has been shown in [13] that Tetrys significantly outperforms other erasure codes in the context of video transmission. Despite its performance, lost packets that are not recovered on time by Tetrys are considered as lost by the video decoder and these packets will impair the Quality of Experience (QoE).…”