The Effects of Contention among Stations on Video Streaming Applications over Wireless Local Area Networks: an Experimental Approach (original) (raw)
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The bursty nature of video streaming applications is due to the frame-based structure of video and this has an important impact on the resource requirements of the WLAN, affecting its ability to provide Quality of Service (QoS) particularly under heavily loaded conditions. For video streaming applications, packet loss and packets dropped due to excessive delay are the primary factors that affect the received video quality. In this paper, we analyse the effects of contention on the performance and behaviour of video streaming applications over IEEE 802.11b WLANs. We show that as contention levels increase, the packet delay increases significantly, despite the total offered load in the network remaining the same. The increased delay is shown to be related to the MAC mechanism used in the IEEE 802.11 standard. We also show that the characteristics of the video content significantly affect the degree to which the stream is affected by contention.
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IEEE International Conference on Wireless and Mobile Computing, Networking and Communications, 2006. (WiMob'2006), 2006
The performance of video streaming over WLAN networks is not only influenced by the state of the network but also by the encoding configuration parameters of the video stream, such as the video content being streamed, how the video is encoded and how it is transmitted. In this paper, we analyse the unique delay characteristic of video streaming applications in a WLAN environment. We show that the "burstiness" of video is due to the frame-based nature of encoded video. We show how each video frame is transmitted as a burst of packets that is queued at the Access Point causing the delay to exhibit a sawtooth-like characteristic over time that is related to the frame rate and frame structure of the encoded video. To our knowledge, this sawtooth-like characteristic of video streaming over WLAN has not been previously reported on. In this paper, not only do we consider the end-to-end delay, but more importantly we consider the total delay required to transmit the entire video frame. We present experimental results for VBR and CBR video streams and calculate the upper bounds on video encoding parameters for streaming realtime interactive video over a WLAN.
2006 IEEE 17th International Symposium on Personal, Indoor and Mobile Radio Communications, 2006
The bursty nature of video streaming applications is due to the frame-based structure of video and this has an important impact on the resource requirements of the WLAN, affecting its ability to provide Quality of Service (QoS) particularly under heavily loaded conditions. In this paper we analyse this bursty behaviour in depth. We show how each video frame is queued at the AP causing the packet delay to vary in a sawtooth manner that is related to the frame rate, the number of packets per video frame, and the packet size. We infer the maximum background traffic load that can be supported so that it does not negatively impact on the video streaming application. We demonstrate that there is a critical threshold load value above which the AP can no longer reliably support the video stream and compare it to the threshold load values calculated through analysis. Using this knowledge, the AP can employ resource allocation mechanisms to regulate the incoming traffic to the AP transmission queue so that QoS can be provided for streaming applications.
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This paper presents efficient mechanisms for delaysensitive transmission of video over IEEE 802.11a/e Wireless Local Area Networks (WLANs). Transmitting video over WLANs in real time is very challenging due to the time-varying wireless channel and video content characteristics. This paper provides a comprehensive view of how to adapt the quality of service signaling, IEEE 802.11e parameters and cross-layer design to optimize the video quality at the receiver. We propose an integrated system view of admission control and scheduling for both contention and poll-based access of IEEE 802.11e Medium Access Control (MAC) protocol and outline the merits of each approach for video transmission. We also show the benefits of using a cross-layer optimization by sharing the Application, MAC, and Physical layer parameters of the Open Systems Interconnection stack to enhance the video quality. We will show through analysis and simulation that controlling the contention-based access in IEEE 802.11e is simple to realize in real products and how different cross-layer strategies used in poll-based access lead to a larger number of stations being simultaneously admitted and/or a higher video quality for the admitted stations. Finally, we introduce a new concept called time fairness, which is critical in enhancing the video performance when different transmitter-receiver pairs deploy different cross-layer strategies.
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Real-time multimedia streaming applications require a strict bounded end-to-end delay and are considered to be bursty as each video frame is typically transmitted as a burst of packets. In this paper we show how the distribution of video frame sizes can be used to efficiently dimension the IEEE 802.11e TXOP limit parameter to efficiently deal with this burstiness in order to enhance the transmission of real-time video streaming services. Through experimental investigation, we show that by using the mean video frame size to dimension the TXOP limit parameter, the transmission delay for the video frame is reduced by 67% under heavily loaded conditions. Other techniques investigated in this paper include applying the TXOP facility separately to each of the constituent I, P, and B video frame types.
Experimental Comparison of Wired Versus Wireless Video Streaming over IEEE 802.11b WLANs
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In this paper the performance of streaming MPEG-4 video with a video server located on the wired network streaming to wireless clients is compared with the performance of a video server located in the wireless network streaming to wireless video clients. We experimentally investigate the performance for a number of concurrent video streams with varying video frame sizes, frame rates and packetisation schemes. The performance is measured in terms of the key parameters of bit rate, loss rate and mean delay. We show how that there is a trade-off for these parameters for a wired and wireless located server. We show that a wired located server is susceptible to high loss rates when there are a number of concurrent video streams whilst the wireless located server has greater reliability in terms of loss rate but incurs greater delays due to having to compete to access to the medium.
Analytical Modeling for Delay-Sensitive Video Over WLAN
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Delay-sensitive video transmission over IEEE 802.11 wireless local area networks (WLANs) is analyzed in a cross-layer optimization framework. The effect of delay constraint on the quality of received packets is studied by analyzing “expired-time packet discard rate”. Three analytical models are examined and it is shown that M/M/1 model is quite an adequate model for analyzing delay-limited applications such as live video transmission over WLAN. The optimal MAC retry limit corresponding to the minimum “total packet loss rate” is derived by exploiting both mathematical analysis and NS-2 simulations. We have shown that there is an interaction between "packet overflow drop" and "expired-time packet discard" processes in the queue. Subsequently, by introducing the concept of virtual buffer size, we will obtain the optimal buffer size in order to avoid "packet overflow drop". We finally introduced a simple and yet effective real-time algorithm for retry-limit adaptation over IEEE 802.11 MAC in order to maintain a loss protection for delay-critical video traffic transmission, and showed that the average link-layer throughput can be improved by using our adaptive scheme.
Implementation Issues for a Video Streaming Server in Ieee 802.11 e Wlans
Recent years have seen a proliferation of real-time multimedia traffic over a more and more heterogeneous Internet. Video streaming at high, consistent quality over wireless links proves to be a difficult task. Several optimization techniques have been proposed and studied, mostly through theoretical analysis and simulation. This article describes the implementation of a cross-layer H.264 video streaming server and the evaluation of its performance in IEEE 802.11e WLANs. Measurements present the benefits of employing several key cross-layer mechanisms which aim to improve the video transmission quality over wireless links. A cross-layer signaling solution is implemented, which addresses important QoS issues between user-space and the kernel traffic control and device driver components. Network support for efficient multiqueue transmission is enabled in the Linux network driver. In addition, the paper discusses the implementation of an enhanced scheduling scheme for the receive-side, in order to provide prioritization of video streams over elastic traffic, and also for better control of latency and improved throughput for multimedia flows.