Traditional routing metrics designed for wireless networks are application agnostic. In this paper, we consider a wireless network where the application flows consist of video traffic. From a user perspective, reducing the level of video distortion is critical. We ask the question “Should the routing policies change if the end-to-end video distortion is to be minimized?” Popular link-quality-based routing metrics (such as ETX) do not account for dependence (in terms of congestion) across the links of a path; as a result, they can because video flows to converge onto a few paths and, thus, cause high video distortion. To account for the evolution of the video frame loss process, we construct an analytical framework to, first, understand and, second, assess the impact of the wireless network on video distortion. The framework allows us to formulate a routing policy for minimizing distortion, based on which we design a protocol for routing video traffic. We find via simulations and tested experiments that our protocol is efficient in reducing video distortion and minimizing the user experience degradation.
With the advent of smart phones, video traffic has become very popular in wireless networks. In tactical networks or disaster recovery, one can envision the transfer of video clips to facilitate mission management. From a user perspective, maintaining a good quality of the transferred video is critical. The video quality is affected by: 1) the distortion due to compression at the source, and 2) the distortion due to both wireless channel induced errors and interference. Video encoding standards, like MPEG-4 [1] or H.264/AVC, define groups of I-, P-, and B-type frames that provide different levels of encoding and, thus, protection against transmission losses. In particular, the different levels of encoding refer to: 1) either information encoded independently, in the case of I-frames, or 2) encoding relative to the information encoded within other frames, as is the case for P- and B-frames.
This Group of Pictures (GOP) allows for the mapping of frame losses into a distortion metric that can be used to assess the application-level performance of video transmissions. One of the critical functionalities that is often neglected, but affects the end-to-end quality of a video flow, is routing. Typical routing protocols, designed for wireless multihop settings, are application-agnostic and do not account for correlation of losses on the links that compose a route from a source to a destination node. Furthermore, since flows are considered independently, they can converge onto certain links that then become heavily loaded (thereby increasing video distortion), while others are significantly underutilized. The decisions made by such routing protocols are based on only network (and not application) parameters.
Our thesis is that the user-perceived video quality can be significantly improved by accounting for application requirements, and specifically the video distortion experienced by a flow, end-to-end. Typically, the schemes used to encode a video clip can accommodate a certain number of packet losses per frame. However, if the number of lost packets in a frame exceeds a certain threshold, the frame cannot be decoded correctly. A frame loss will result in some amount of distortion. The value of distortion at a hop along the path from the source to the destination depends on the positions of the unrecoverable video frames (simply referred to as frames) in the GOP, at that hop. As one of our main contributions, we construct an analytical model to characterize the dynamic behavior of the process that describes the evolution of frame losses in the GOP (instead of just focusing on a network quality metric such as the packet-loss probability) as video is delivered on an end-to-end path. Specifically, with our model, we capture how the choice of path for an end-to-end flow affects the performance of a flow in terms of video distortion.
Our model is built based on a multilayer approach in the packet-loss probability on a link is mapped to the probability of a frame loss in the GOP. The frame-loss probability is then directly associated with the video distortion metric. By using the above mapping from the network-specific property (i.e., packet-loss probability) to the application-specific quality metric (i.e., video distortion), we pose the problem of routing as an optimization problem where the objective is to find the path from the source to the destination that minimizes the end-to-end distortion. In our formulation, we explicitly take into account the history of losses in the GOP along the path. This is in stark contrast with traditional routing metrics (such as the total expected transmission count (ETX) wherein the links are treated independently.
Our solution to the problem is based on a dynamic programming approach that effectively captures the evolution of the frame-loss process. We then design a practical routing protocol, based on the above solution, to minimize routing distortion. In a nutshell, since the loss of the longer I-frames that carry fine-grained information affects the distortion metric more, our approach ensures that these frames are carried on the paths that experience the least congestion; the latter frames in a GOP are sent out on relatively more congested paths. Our routing scheme is optimized for transferring video clips on wireless networks with minimum video distortion. Since optimizing for video streaming is not an objective of our scheme, constraints relating to time (such as jitter) are not directly taken into account in the design.
TITLE: AN EVALUATION FRAMEWORK FOR MORE REALISTIC SIMULATIONS OF MPEG VIDEO TRANSMISSION
PUBLICATION: J. Inf. Sci. Eng., vol. 24, no. 2, pp. 425–440, Mar. 2008.
AUTHORS: C.-H. Ke, C.-K. Shieh, W.-S. Hwang, and A. Ziviani
EXPLANATION:
We present a novel and complete tool-set for evaluating the delivery quality of MPEG video transmissions in simulations of a network environment. This tool-set is based on the EvalVid framework. We extend the connecting interfaces of EvalVid to replace its simple error simulation model by a more general network simulator like NS2. With this combination, researchers and practitioners in general can analyze through simulation the performance of real video streams, i.e. taking into account the video semantics, under a large range of network scenarios. To demonstrate the usefulness of our new tool-set, we point out that it enables the investigation of the relationship between two popular objective metrics for Quality of Service (QoS) assessment of video quality delivery: the PSNR (Peak Signal to Noise Ratio) and the fraction of decodable frames. The results show that the fraction of decodable frames reflects well the behavior of the PSNR metric, while being less time-consuming. Therefore, the fraction of decodable frames can be an alternative metric to objectively assess through simulations the delivery quality of transmission in a network of publicly available video trace files.
TITLE: MULTIPATH ROUTING OVER WIRELESS MESH NETWORKS FOR MULTIPLE DESCRIPTION VIDEO TRANSMISSION
PUBLICATION: IEEE J. Sel. Areas Commun., vol. 28, no. 3, pp. 321–331, Apr. 2010.
AUTHORS: B. Rong, Y. Qian, K. Lu, R. Qingyang, and M. Kadoch
EXPLANATION:
In the past few years, wireless mesh networks (WMNs) have drawn significant attention from academia and industry as a fast, easy, and inexpensive solution for broadband wireless access. In WMNs, it is important to support video communications in an efficient way. To address this issue, this paper studies the multipath routing for multiple description (MD) video delivery over IEEE 802.11 based WMN. Specifically, we first design a framework to transmit MD video over WMNs through multiple paths; we then investigate the technical challenges encountered. In our proposed framework, multipath routing relies on the maximally disjoint paths to achieve good traffic engineering performance. However, video applications usually have strict delay requirements, which make it difficult to find multiple qualified paths with the least joints. To overcome this problem, we develop an enhanced version of Guaranteed-Rate (GR) packet scheduling algorithm, namely virtual reserved rate GR (VRR-GR), to shorten the packet delay of video communications in multiservice network environment. Simulation study shows that our proposed approach can reduce the latency of video delivery and achieve desirable traffic engineering performance in multipath routing environment.
TITLE: PERFORMANCE EVALUATION OF H.264/SVC VIDEO STREAMING OVER MOBILE WIMAX
PUBLICATION: Comput. Netw., vol. 55, no. 15, pp. 3578–3591, Oct. 2011.
AUTHORS: D. Migliorini, E. Mingozzi, and C. Vallati
EXPLANATION:
Mobile broadband wireless networks, such as mobile WiMAX, have been designed to support several features like, e.g., Quality of Service (QoS) or enhanced data protection mechanisms, in order to provide true access to real-time multimedia applications like Voice over IP or Video on Demand. On the other hand, recently defined video coding schemes, like H.264 scalable video coding (H.264/SVC), are evolving in order to better adapt to such mobile environments with heterogeneous clients and time-varying available capacity. In this work we assess the performance of H.264/SVC video streaming over mobile WiMAX under realistic network conditions. To this aim, we make use of specific metrics, like PSNR (Peak Signal to Noise Ratio) or MOS (Mean Opinion Score), which are related to the quality of experience as perceived by the end user. Simulation results show that the performance is sensitive to the different available H.264/SVC encoding options, which respond differently to the loss of data in the network. On the other hand, if aggressive error recovery based on WiMAX data protection mechanisms is used, this might lead to unacceptable latencies in the video play out, especially for those mobiles with poor wireless channel characteristics.
EXISTING SYSTEM:
Existing methods in WMNs, it is important to support video communications in an efficient way. To address this issue, this paper studies the single path routing for multiple description (MD) video delivery over IEEE 802.11 based WMN. Specifically, we first design a framework to transmit MD video over WMNs through single paths; we then investigate the technical challenges encountered framework, multipath routing relies on the maximally disjoint paths to achieve good traffic engineering performance.
However, video applications usually have strict delay requirements, which make it difficult to find multiple qualified paths with the least joints an enhanced version of Guaranteed-Rate (GR) packet scheduling algorithm, namely virtual reserved rate GR (VRR-GR), to shorten the packet delay of video communications in multiservice network environment. Simulation study shows that existing approach can reduce the latency of video delivery and achieve desirable traffic engineering performance in single path routing environment.
DISADVANTAGES:
PROPOSED SYSTEM:
In this paper, our thesis is that the user-perceived video quality can be significantly improved by accounting for application requirements, and specifically the video distortion experienced by a flow, end-to-end. Typically, the schemes used to encode a video clip can accommodate a certain number of packet losses per frame. However, if the number of lost packets in a frame exceeds a certain threshold, the frame cannot be decoded correctly. A frame loss will result in some amount of distortion. The value of distortion at a hop along the path from the source to the destination depends on the positions of the unrecoverable video frames (simply referred to as frames) in the GOP, at that hop. As one of our main contributions, we construct an analytical model to characterize the dynamic behavior of the process that describes the evolution of frame losses in the GOP (instead of just focusing on a network quality metric such as the packet-loss probability) as video is delivered on an end-to-end path.
Specifically, with our model, we capture how the choice of path for an end-to-end flow affects the performance of a flow in terms of video distortion. Our model is built based on a multilayer approach as shown in Fig. 1. The packet-loss probability on a link is mapped to the probability of a frame loss in the GOP. The frame-loss probability is then directly associated with the video distortion metric. By using the above mapping from the network-specific property (i.e., packet-loss probability) to the application-specific quality metric (i.e., video distortion), we pose the problem of routing as an optimization problem where the objective is to find the path from the source to the destination that minimizes the end-to-end distortion.
ADVANTAGES:
Developing an analytical framework to capture the impact of routing on video distortion as our primary contribution, we develop an analytical framework that captures the impact of routing on the end-to-end video quality in terms of distortion.
Specifically, the framework facilitates the computation of routes that are optimal in terms of achieving the minimum distortion. The model takes into account the joint impact of the PHY and MAC layers and the application semantics on the video quality.
Design of a practical routing protocol for distortion-resilient video delivery: Based on our analysis, we design a practical routing protocol for a network that primarily carries wireless video. The practical protocol allows a source to collect distortion information on the links in the network and distribute traffic across the different paths in accordance to: 1) the distortion, and 2) the position of a frame in the GOP.
Evaluations via extensive experiments: We demonstrate via extensive simulations and real testbed experiments on a multihop 802.11a testbed that our protocol is extremely effective in reducing the end-to-end video distortion and keeping the user experience degradation to a minimum rate.
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