Wen-Shyang Hwang

An Evaluation Framework for More Realistic Simulations of MPEG Video Transmission

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.

A novel realistic simulation tool for video transmission over wireless network

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 two markers system for improved MPEG video delivery in a DiffServ network

The failure of legacy packet markers such as the Single Rate Three Color Marker (SRTCM) and the Two Rate Three Color Marker (TRTCM) to distinguish important and less important data renders them unsuitable for MPEG video transmission in a DiffServ network. Therefore, we propose a Two Markers System (TMS) to improve the delivery quality of MPEG video streams. We use authentic MPEG4 video traffic traces to compare the performance of the proposed TMS system with those of legacy packet markers. Results show that TMS outperforms the legacy traffic markers in terms of the quality of the delivered MPEG video streams.

A RED-FEC Mechanism for Video Transmission Over WLANs

This paper proposes a Random Early Detection Forward Error Correction (RED-FEC) mechanism to improve the quality of video delivered over Wireless Local Area Networks (WLANs). In contrast to previous FEC schemes, in which the rate determination information is fed back from the receiver side, in our proposed method, the redundancy rate is calculated directly at the wireless Access Point (AP) in accordance with the network traffic load, as indicated by the AP queue length. An analytical model is developed to predict the effective packet loss rate of a video stream delivered over a WLAN with RED-FEC protection. The numerical results show that the proposed RED-FEC mechanism consistently achieves higher recovery efficiency than a conventional FEC scheme under high and low network loading conditions.

A novel and simple beforehand bandwidth reservation (BBR) MAC protocol for OBS metro ring networks

This paper proposes a novel and simple MAC protocol called beforehand bandwidth reservation (BBR) to reserve the empty slots in the next big-slot cycle for OBS ring networks by control channel. The node architecture uses one tunable transmitter and one fixed receiver to add or drop data channels and a fixed transmitter/receiver pair to transmit and receive on the control channel. Each node possesses a dedicated channel to receive data, so it inherently occupies a priority position. Fortunately, a well-known packet scheduling approach, time-division multiplexing (TDM), can overcome this problem. In addition, the length of the big-slot cycle is studied with a view to investigating performance divergence. Finally, a multi-token protocol using the (FT W-FR W) node architecture is compared with the BBR protocol. According to simulation results, the BBR scheme using the TDM approach achieves the best bandwidth utilization (more than 95%), while the multi-token protocol achieves the worst performance based on packet distribution in the MCI backbone.

Supporting end-to-end QoS in DiffServ/MPLS networks

In MPLS networks, the higher-priority LSP (label switching path) will preempt the resource of lower-priority LSP when its bandwidth resource is limited. At the time, the lower-priority LSP is destroyed, and Its bandwidth resource is released to the higher-priority LSP. The destroyed path has to be rerouted by selecting another LSP; the new LSP maybe quickly suffer another bandwidth resource preemption again. If this scenario occurs frequently, routers would be subjected to the superfluous overload, and the quality of delivering flow can not be guaranteed. In a previous Chin et al. (see IASTED CCN 2002) had proposed a new policy to avoid the preemption because of flow priority and load balancing in the MPLS networks. In this paper, the policy supports the end-to-end QoS in DiffServ-aware MPLS networks is discussed. Moreover, many simulations are done to compare the QoS of all service levels in DiffServ which constraint-based routed (CR) scheme includes the new policy of Chin et al. The simulation results indicate that adding our policy to CR is better then the traditional CR.

Performance Evaluation of 802.11e EDCF in Infrastructure Mode with Real Audio/Video Traffic

Multimedia wireless network QoS support has become one of the most important researches in recent years. IEEE wireless 802.11e is the most hopeful among these methods. However, 802.11e experiment performance metrics are essentially network-level measures. They represent the network state, not the perceptual quality of the end user. This paper presents an application-level study on the wireless 802.11 DCF and 802.11e EDCA scheme using an NS-2 simulator

Improving the ramping up behavior of TCP slow start

This paper proposes an improvement to the TCP ramp up behavior in slow-start. Current implementations of the TCP start-up procedure may result in an exponential growth of the congestion window, which results in the transmission of an excessive number of packets. Consequently, the network becomes congested and the self-clocking mechanism of the TCP fails. By estimating the number of packets that which can be in flight in the network from the viewpoint of the TCP source, this study develops an algorithm to suppress congestion before it becomes significant. The simulation results indicate that the proposed algorithm enhances the TCP performance by establishing a smoother transmission rate at the end of the slow-start phase and reducing the number of dropped packets significantly as a result.

Burst-Aware Adaptive Forward Error Correction in Video Streaming over Wireless Networks

Video streaming over wireless networks have many challenges due to the high error rate and burst packet error characteristic. Forward error correction (FEC) is a method commonly used to handle losses in real-time communication. Conventional FEC mechanisms provide redundancy by an averaged packet loss rate and performance decreases by burst packet losses. However, the average packet loss rate cannot give any indication of burst packet loss. Hence, the conventional FEC mechanisms cannot recover original source data over wireless networks. In this paper, we propose a burst-aware adaptive FEC (BAFEC) control mechanism to overcome burst packet losses. We will therefore be able to take account of average burst packet loss length. The sender can rely on this information in order to adjust the FEC redundancy. The experimental result shows that compared to the conventional FEC mechanisms, our proposed mechanism achieved better recovery performance in terms of packet loss rate and PSNR.

A self-regulated redundancy control scheme for wireless video transmission

This paper presents a self-regulated redundancy control scheme for high-bit-rate video transmission using packet-level forward-error-correction (FEC) codes over error-prone wireless networks. The effectiveness of FEC on video is obtained by regulating its redundancy cost to balance that tradeoff of bandwidth utilization and FEC efficiency based on channel status, temporal dependency of video frames, and network congestion level. Experimental results show the proposed scheme maintains the desired quality-of-service (QoS) control over unloaded networks with the realistically measured wireless loss trace in 802.11b WLAN and over loaded networks, the adverse effect of FEC efficiency due to blindly increasing redundancy can be reduced to achieve the better video quality.