Wassim Ramadan's research while affiliated with Institut FEMTO-ST and other places

Nowadays, video data transfers account for much of the Internet bandwidth and a huge number of users use it daily. However, despite its apparent interest, video streaming is still done in a suboptimal manner. Indeed, more and more high-definition and high-quality videos are nowadays stored on Internet but they are not accessible for everybody because a high and stable bandwidth is needed to stream them; also, during videoconferencing, the highest possible quality often exceeds the available bandwidth. Hence, a lower bitrate encoding is usually chosen but it leads to lower quality and network under-utilization too. This paper presents Video Adaptation at Application Layer (VAAL), a simple and efficient method designed to use optimally network resources and to ameliorate user video experience. It involves only the application layer on the server. The main idea of VAAL is that it checks Transmission Control Protocol-friendly transport protocol buffer overflows and adapts the video bitrate accordingly; as a result, the bitrate constantly matches the network bandwidth. It can be used together with Zigzag Avoidance Algorithm (ZAAL), a novel algorithm aiming to avoid quality oscillations. Experimental results show that the video adaptation using VAAL+ZAAL performs much better compared with the currently widely used static encoding, making it a strong candidate for hard real-time video streaming.

Nowadays, video data transfers account for much of the Internet traffic and a huge number of users use this service on a daily base. Even if videos are usually stored in several bitrates on servers, the video sending rate does not take into account network conditions which are changing dynamically during transmission. Therefore, the best bitrate is not used which causes sub-optimal video quality when the video bitrate is under the available bandwidth or packet loss when it is over it. One solution is to deploy adaptive video, which adapts video parameters such as bitrate or frame resolution to network conditions. Many ideas are proposed in the literature, yet no paper provides a global view on adaptation methods in order to classify them. This article fills this gap by discussing several adaptation methods through a taxonomy of the parameters used for adaptation. We show that, in the research community, the sender generally takes the decision of adaptation whereas in the solutions supported by major current companies the receiver takes this decision. We notably suggest, without evaluation, a valuable and realistic adaptation method, gathering the advantages of the presented methods.

A high number of videos, encoded in several bi- trates, are nowadays available on Internet. A high bitrate needs a high and stable bandwidth, so a lower bitrate encoding is usually chosen and transferred, which leads to lower quality too. A solution is to adapt dynamically the current bitrate so that it al- ways matches the network bandwidth, like in a clas- sical congestion control context. When the bitrate is at the upper limit of the bandwidth, the adaptation switches constantly between a lower and a higher bitrate, causing an unpleasant oscillation (zigzag) in quality on the user machine. This paper presents a solution to avoid such oscillations. It uses an EWMA (Exponential Weighted Moving Average) value for each bitrate, which reflects its history. The evalu- ation of the algorithm shows that loss rate is much smaller, bitrate is more stable, and so received video quality is better.

This thesis deals in improving the data transfer on wireless networks and for the continuous data such as video. To improve transmission over wireless networks, we were interested in congestion control transport protocols and we also proposed a practical method for adjusting the video rate to network conditions.This thesis composes of two parts. The first part concerns the loss differentiation between congestion losses and losses on the wireless network. It is known that when there is a loss, transport protocols reduce the current sending rate (e.g. by two). However, for wireless losses, it has no interest in reducing the rate. To differentiate these losses on the data senders side, we propose a novel method that uses both the ECN (Explicit Congestion Notification) and the change of RTT of the packet following the loss. The second part proposes a novel method for video adaptation at the application layer of the sender. With the advent of high bitrate video (e.g. HD, 3D) and steadily increasing but irregular network bandwidth, video quality to the user lags. It is non-optimal (bitrate is highly smaller or larger than the available bandwidth) and not adaptable (to the dynamic conditions of the network). We propose a simple method to implement, since it requires a change only at the application layer of the sender. It adapts the bitrate of the video to the network conditions, i.e. it is a congestion control on the transmitter. Videoconferencing is an ideal case for the application of adaptation. This method works over any transport protocol with congestion control (e.g. TCP, DCCP), which also confers the property of TCP-friendliness.

A high number of videos, encoded in several bitrates, are nowadays available on Internet. A high bitrate needs a high and stable bandwidth, so a lower bitrate encoding is usually chosen and transferred, which leads to lower quality too. A solution is to adapt dynamically the current bitrate so that it always matches the network bandwidth, like in a classical congestion control context. When the bitrate is at the upper limit of the bandwidth, the adaptation switches constantly between a lower and a higher bitrate, causing an unpleasant oscillation (zigzag) in quality on the user machine. This paper presents a solution to avoid such oscillations. It uses an EWMA (Exponential Weighted Moving Average) value for each bitrate, which reflects its history. The evaluation of the algorithm shows that loss rate is much smaller, bitrate is more stable, and so received video quality is better.

One major yet unsolved problem in wired-cum-wireless networks is the classification of losses, which can be due either to wireless temporary interferences or to network congestion. The transport protocol response to losses has to be different for these two cases. If the transmission uses existing protocols like TCP, the losses will always be classified as congestion losses by the data sender, causing reduced throughput. In wired networks, ECN (Explicit Congestion Notification) can be used to control the congestion through active queue management such as RED (Random Early Detection). It can also be used to resolve the transport protocol misreaction on wireless networks. This paper proposes a loss differentiation method (EcnLD), based on ECN signaling and RTT, and applied to TCPlike. TCPlike is one of the two current congestion controls present in the new transport protocol DCCP (Datagram Congestion Control Protocol). Our results indicate that EcnLD is a good approach to optimize congestion control and therefore increase the performance of transport protocols over wireless networks.

One major yet unsolved problem in wired-cum-wireless networks is the classification of losses, which can be due either to wireless temporary interferences or to network congestion. The transport protocol response to losses has to be different for these two cases. If the transmission uses existing protocols like TCP, the losses will always be classified as congestion losses by the data sender, causing reduced throughput. In wired networks, ECN (Explicit Congestion Notification) can be used to control the congestion through active queue management such as RED (Random Early Detection). It can also be used to resolve the transport protocol misreaction on wireless networks. This paper proposes a loss differentiation method (EcnLD), based on ECN signaling and RTT, and applied to TCPlike. TCPlike is one of the two current congestion controls present in the new transport protocol DCCP (Datagram Congestion Control Protocol). Our results indicate that EcnLD is a good approach to optimize congestion control and therefore increase the performance of transport protocols over wireless networks.