Computer communications

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.

An Evaluation Framework for More Realistic Simulations of MPEG Video Transmission

The performance evaluation of video transport mechanisms becomes increasingly important as encoded video accounts for growing portions of the network traffic. Compared to the widely studied MPEG-4 encoded video, the recently adopted H.264 video coding standards include novel mechanisms, such as hierarchical B frame prediction structures and highly efficient quality scalable coding, that have important implications for network transport. This tutorial introduces a trace-based evaluation methodology for the network transport of H.264 encoded video. We first give an overview of H.264 video coding, and then present the trace structures for capturing the characteristics of H.264 encoded video. We give an overview of the typical video traffic and quality characteristics of H.264 encoded video. Finally, we explain how to account for the H.264 specific coding mechanisms, such as hierarchical B frames, in networking studies.

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Video Transport Evaluation With H.264 Video Traces

Vehicular ad hoc networks (VANETs) are an extreme case of mobile ad hoc networks (MANETs). High speed and frequent network topology changes are the main characteristics of vehicular networks. These characteristics lead to special issues and challenges in the network design, especially at the medium access control (MAC) layer. In this paper, we provide a comprehensive evaluation of mobility impact on the IEEE 802.11p MAC performance. The study evaluates basic performance metrics such as packet delivery ratio, throughput, and delay. An unfairness problem due to the relative speed is identified for both broadcast and unicast scenarios. We propose two dynamic contention window mechanisms to alleviate network performance degradation due to high mobility. The first scheme provides dynamic level of service priority via adaptation to the number of neighboring nodes, while the second scheme provides service priority based on node relative speed. Extensive simulation results demonstrate a significant impact of mobility on the IEEE 802.11p MAC performance, the unfairness problem in the vehicle-to-vehicle (V2V) communications, and the effectiveness of the proposed MAC schemes.

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Mobility impact in IEEE 802.11p infrastructureless vehicular networks

Vehicu lar ad-hoc networks (VANETs) technology has emerged as an important research area over the last few years. Being ad-hoc in nature, VA NET is a type of networks that is created from the concept of establishing a network of cars for a specific need or situation. VA NETs have now been established as reliable networks that vehicles use for co mmunication purpose on highways or urban environments. Along with the benefits, there arise a large number of challenges in VANET such as provisioning of QoS, h igh connectivity and bandwidth and security to vehicle and individual privacy. This article presents state-of-the-art of VANET and discusses the related issues. Network architecture, signal modeling and propagation mechanis m, mobility modeling, routing protocols and network security are discussed in detail. Main findings of this paper are that an efficient and robust VANET is one wh ich satisfies all design parameters such as QoS, minimu m latency, low BER and high PDR. So me key research areas and challenges in VANET are presented at the end of the paper.

/pdf/vehicular-ad-hoc-networks-vanets-an-overview-and-challenges-z05s5jwcn3.pdf

Vehicular Ad-Hoc Networks (VANETs): An Overview and Challenges

According to the latest version of the IEEE 802.11 standard, the backoff parameters of its collision avoidance mechanism are far from optimal, especially in a heavy load or error-prone WLAN environment. This strategy has a high collision probability and channel utilization is degraded in bursty arrivals or congested scenarios. Besides, the standard backoff mechanism may treat noise corruption as packet collisions. In this paper, we identify the relationship between backoff parameters, contention level, and channel BER in order to propose a simple, but yet well-performing distributed algorithm that allows a station to dynamically adjust its contention window size based on turn-around-time measurement of channel status. In addition to theoretical analysis, simulations are conducted to evaluate its performance. The proposed scheme works very well in providing a substantial performance improvement in heavy loaded and error-prone WLAN environments.

Contention window optimization for ieee 802.11 DCF access control

The objective of this paper is to present a novel realistic simulation tool-set for evaluating video delivered quality over wireless network. This tool-set integrates EvalVid and NS-2. With the integration, researchers can easily analyze their designed mechanisms, such as network protocols or QoS control schemes in a realistic simulation environment. We used a case study about video transmission over wireless network to demonstrate the simulation with the tool-set. From the results, we found that the quality of video transmission with burst packet errors is superior to the random distributed packet errors in the same packet error rate. In addition, in the same packet error rate, unicast transmission leads to better video delivered quality than multicast transmission because of retransmission. Also, using the tool-set researchers can assess video quality not only with the evaluation metrics, but also with real video sequences. In brief, researchers who utilize our proposed QoS assessment framework will be benefited in verifying their designs regarding video transmission over wireless network.

A novel realistic simulation tool for video transmission over wireless network

myEvalSVC: an Integrated Simulation Framework for Evaluation of H.264/SVC Transmission

The purpose of this paper is to study the packet loss effect on MPEG video transmission quality in wireless networks. First, we consider the distribution of packet losses in wireless network, including distributed and burst packet losses. Besides, we also discuss the additional packet drops by the play-out buffer at the received end, and the effect of the transmission packet size on the video delivered quality. From the results, we find that the effect of burst packet losses on the video delivered quality is less than distributed packet losses in the same packet loss rate. Moreover, the smaller size of the play-out buffer leads to more packet drops and worse video quality. Finally, if there is no video recovery for video transmission, the video delivered quality of the larger packet size will be better than smaller packet size.

Chih-Heng Ke

Papers

An Evaluation Framework for More Realistic Simulations of MPEG Video Transmission

Contention window optimization for ieee 802.11 DCF access control

A novel realistic simulation tool for video transmission over wireless network

myEvalSVC: an Integrated Simulation Framework for Evaluation of H.264/SVC Transmission

The Packet Loss Effect on MPEG Video Transmission in Wireless Networks