Nicola Cranley

University College Dublin, Dublin, Leinster, Ireland

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Publications (21)2.06 Total impact

  • Source
    N. Cranley, M. Davis
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    ABSTRACT: 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.lie 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.
    Global Telecommunications Conference, 2007. GLOBECOM '07. IEEE; 12/2007
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    Nicola Cranley, Mark Davis
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    ABSTRACT: In this paper we perform an experimental investigation of using video frame differentiation in conjunction with the TXOP facility to enhance the transmission of parallel multimedia streaming sessions in IEEE 802.11e. The delay constraints associated with the audio and video streams that comprise a multimedia session pose the greatest challenge since real-time multimedia is particularly sensitive to delay as the packets require a strict bounded end-to-end delay. Video streaming applications are considered to be bursty. This burstiness is due to the frame rate of video, the intrinsic hierarchical structure of the constituent video frame types, and the different compression ratios for the different video frame types. The TXOP facility is particularly suited to efficiently deal with this burstiness since it can be used to reserve bandwidth for the duration of the packet burst associated with a packetised video frame. Through experimental investigation, we show that there is a significant performance improvement for video streaming applications under heavily loaded conditions by differentiating between the constituent video frame types. The results show that video frame differentiation reduces the mean loss rate by 12% and increases the mean PSNR by 13.1dB.
    Personal, Indoor and Mobile Radio Communications, 2007. PIMRC 2007. IEEE 18th International Symposium on; 10/2007
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    Nicola Cranley, Philip Perry, Liam Murphy
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    ABSTRACT: Most adaptive delivery mechanisms for streaming multimedia content do not explicitly consider user-perceived quality when making adaptation decisions. We show that an optimal adaptation trajectory (OAT) through the set of possible encodings exists, and that it indicates how to adapt encoding quality in response to changes in network conditions in order to maximise user-perceived quality. The OAT is related to the characteristics of the content, in terms of spatial and temporal complexity. We describe a method to automatically determine the OAT in response to the time-varying characteristics of the content. In this way, as the characteristics of the content change over time, the system can dynamically and intelligently adjust the adaptation process in order to maximise the user-perceived quality. The OAT can be used with any sender-based transmission adaptation policy. We demonstrate content-based adaptation using the OAT in a practical system using two different adaptation algorithms. Furthermore, we show how this form of adaptation can result in differing adaptation behaviour not only as a result of the dynamics of the content but also as a result of the adaptation algorithm being used. Finally, we show how increased feedback frequency does not necessarily improve the behaviour of the adaptation algorithm being used.
    Journal of Network and Computer Applications 08/2007; · 1.47 Impact Factor
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    N. Cranley, T. Debnath, M. Davis
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    ABSTRACT: In this paper we perform an experimental investigation of the IEEE 802.11e TXOP facility to enhance the transmission of parallel multimedia streaming sessions through efficient bandwidth reservation and explicitly consider both the audio and video streams. The delay constraints associated with the audio and video streams that comprise a multimedia session pose the greatest challenge since real-time multimedia is particularly sensitive to delay as the packets require a strict bounded end-to-end delay. We show how the TXOPLimit parameter can be efficiently dimensioned to reduce the transmission delay for the video frames. Due to its frame-based nature, video applications are considered to be bursty as each video frame is typically transmitted as a burst of packets. The size of the burst is related to the size of the video frame and the number of packets required to transmit the video frame. The TXOP facility is particularly suited to efficiently deal with this burstiness since it can be used to reserve bandwidth for the duration of the packet burst. Through experimental investigation, we show that there is a significant performance improvement for the video streams by using the TXOPLimit parameter however there is no such improvement for the audio streams. We show that over-dimensioning the TXOPLimit parameter can cause the video stream to seize too much bandwidth which results in a deterioration in performance for the other competing traffic streams. This deterioration becomes more prominent as the number of parallel multimedia streams increases. We show that there is a performance improvement to all traffic streams by providing differentiated service to the constituent I, P, and B video frame types in conjunction with the TXOP facility.
    Communications, 2007. ICC '07. IEEE International Conference on; 07/2007
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    G.-M. Muntean, N. Cranley
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    ABSTRACT: For multimedia streaming over wireless networks, there is a trade-off between the capacity of the wireless links and the end-user perceived-quality, which can be affected by the compression scheme used, content characteristics and adaptation algorithm (if any). In this paper, this trade-off is investigated for streaming various motion content multimedia over an IEEE 802.11b-based wireless-home area network using the quality-oriented adaptation scheme (QOAS). QOAS performance is compared to that of a non-adaptive scheme when using MPEG-2 and MPEG-4 encoding in terms of average end-user perceived quality, number of streaming sessions concurrently supported, loss rate, delay, jitter and total throughput. Simulation results show that by using QOAS and MPEG-4 encoded streams a much higher number of concurrent streams are supported at an average quality above "good" level on the ITU-T five-point quality scale in comparison with other situations. In this case all the other streaming performance parameters were also significantly better.
    Vehicular Technology Conference, 2007. VTC2007-Spring. IEEE 65th; 05/2007
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    N. Cranley, M. Davis
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    ABSTRACT: 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
    Personal, Indoor and Mobile Radio Communications, 2006 IEEE 17th International Symposium on; 10/2006
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    Tanmoy Debnath, Nicola Cranley, Mark Davis
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    ABSTRACT: 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 performance in terms of a low loss rate but incurs greater delays due to having to compete with more stations in order to access to the medium
    Irish Signals and Systems Conference, 2006. IET; 07/2006
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    N. Cranley, M. Davis
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    ABSTRACT: 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 analyze 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 real-time interactive video over a WLAN
    Wireless and Mobile Computing, Networking and Communications, 2006. (WiMob'2006). IEEE International Conference on; 07/2006
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    Nicola Cranley, Philip Perry, Liam Murphy
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    ABSTRACT: In general, video quality adaptation and video quality evaluation are distinct activities. Most adaptive delivery mechanisms for streaming multimedia content do not explicitly consider user-perceived quality when making adaptation decisions. Equally, video quality evaluation techniques are not designed to evaluate instantaneous quality where the quality is changing over time. We propose that an Optimal Adaptation Trajectory (OAT) through the set of possible encoding exists, and that it indicates how to adapt encoding quality in response to changes in network conditions in order to maximize user-perceived quality. The subjective and objective tests carried out to find such trajectories for a number of different MPEG-4 video clips are described. Experimental subjective testing results are presented that demonstrate the dynamic nature of user perception with adapting multimedia. The results demonstrate that adaptation using the OAT out-performs conventional adaptation strategies in which only a single aspect of the video quality is adapted. In contrast, the OAT provides a mechanism to adapt multiple aspects of the video quality thereby giving better user-perceived quality in both the short and long term.
    International Journal of Human-Computer Studies. 01/2006;
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    Nicola Cranley
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    ABSTRACT: There is an increasing demand for streaming video applications over both the fixed Internet and wireless IP networks. The fluctuating bandwidth and time-varying delays of best-effort networks makes providing good quality streaming a challenge. Many adaptive video delivery mechanisms have been proposed over recent years; however, most do not explicitly consider user-perceived quality when making adaptations, nor do they define what quality is. This chapter describes research that proposes that an optimal adaptation trajectory through the set of possible encodings exists, and indicates how to adapt transmission in response to changes in network conditions in order to maximize user-perceived quality.
    01/2006;
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    Nicola Cranley, Philip Perry, Liam Murphy
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    ABSTRACT: Most adaptive delivery mechanisms for streaming multimedia content do not explicitly consider user-perceived quality when making adaptations. We propose that an op- timal adaptation trajectory through the set of possible encodings exists and that it indicates how to adapt encoding quality in response to changes in network conditions to maximize user-perceived quality. Such an optimum adapta- tion trajectory can be used with any transmission adaptation policy. We describe the subjective tests we carried out to find such trajectories for a number of different MPEG-4 video clips and indicate how this knowledge could be used in the operation of a practical system.
    Multimedia Systems 08/2005; 10:392-401. · 0.60 Impact Factor
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    N. Cranley, M. Davis
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    ABSTRACT: Video streaming has a large impact on the resource requirements of the WLAN. However, there are many variables involved in video streaming, such as the video content being streamed, how the video is encoded and how it is sent. This makes the role of radio resource management extremely difficult. In this paper we investigate the effect that video encoding configurations has on the network resource requirements for unicast video streaming in a WLAN environment. We compare the network resource requirements of several content types encoded at various encoding configurations with varying I-frame frequencies, target encoding bit rates and hint track settings. We present two key findings. We show that by halving the hint track MTU values, the access requirements of the WLAN are increased by 20%. Furthermore, we show how the I-frame frequency of the encoded file relates to the resource requirements of the WLAN.
    Wireless Networks, Communications and Mobile Computing, 2005 International Conference on; 07/2005
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    Nicola Cranley, Mark Davis
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    ABSTRACT: There is an increasing demand for multimedia streaming applications over WLAN networks. MPEG-4 and H.264 are compression standards targeted at high-quality streamed multimedia services over wireless best-effort IP networks. However, the dynamic nature of wireless networks in terms of fluctuating bandwidth and time-varying delays makes it difficult to provide good quality streaming under such constraints. Multimedia streaming applications are a demanding and challenging service to deliver over wireless networks. There is a trade-off between the capacity of the wireless network and the quality of the multimedia streaming application. In this paper we investigate the effect the background traffic load has on unicast streaming video sessions. We show that above a certain load value, the video streaming session is slowly starved of bandwidth. The load value at which this occurs depends on the characteristics of the background traffic load in terms of packet rates and the number of sources contributing to the load.
    WMuNeP'05 - Proceedings of the First ACM Workshop on Wireless Multimedia Networking and Performance Modeling, Montreal, Quebec, Canada, October 13, 2005; 01/2005
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    N. Cranley, L. Murphy, P. Perry
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    ABSTRACT: Many adaptive delivery mechanisms have been devised for streaming multimedia over best-effort IP networks, such as the Internet. Most of these adaptive schemes do not consider the user's perception of quality when making adaptations. We describe a perceptual quality adaptation algorithm (PQA) and prototype system architecture that uses knowledge of user perceived quality to make adaptation decisions using an optimum adaptation trajectory. This optimum adaptation trajectory indicates how encoding quality should be adapted (upgraded/downgraded) with respect to user perceived quality in response to rapidly fluctuating network conditions. We present simulation results that demonstrate the behavior of a perceptual quality adaptation algorithm.
    Personal, Indoor and Mobile Radio Communications, 2004. PIMRC 2004. 15th IEEE International Symposium on; 10/2004
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    Nicola Cranley, Liam Murphy, Philip Perry
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    ABSTRACT: Most adaptive delivery mechanisms for streaming multimedia con- tent do not explicitly consider user-perceived quality when making adaptations. We show that an Optimal Adaptation Trajectory (OAT) through the set of pos- sible encodings exists, and that it indicates how to adapt encoding quality in re- sponse to changes in network conditions in order to maximize user-perceived quality. The OAT is related to the characteristics of the content, in terms of spa- tial and temporal complexity. We describe an objective method to automati- cally determine the OAT in response to the time-varying characteristics of the content. The OAT can be used with any transmission adaptation policy. We demonstrate content-based adaptation using the OAT in a practical system, and show how this form of adaptation can result in differing adaptation behaviour.
    Management of Multimedia Networks and Services: 7th IFIP/IEEE International Conference, MMNS 2004, San Diego, CA, USA, October 2004, Proceedings; 01/2004
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    Nicola Cranley, Liam Murphy, Philip Perry
    [Show abstract] [Hide abstract]
    ABSTRACT: Many adaptive delivery mechanisms have been devised for streaming multimedia over best-effort IP networks. Most of these adaptive schemes do not consider the user's perception of quality when making adaptations. We propose that an optimum adaptation trajectory exists which indicates how encoding quality should be adapted (upgraded/downgraded) with respect to user perceived quality in response to network conditions. This optimum adaptation trajectory can be used with any transmission adaptation policy. We describe a system architecture that uses knowledge of user perceived quality to make adaptation decisions and give an example of how this knowledge can be used to complement the sender-based adaptation algorithm, LDA.
    Network and Operating System Support for Digital Audio and Video, 13th International Workshop, NOSSDAV 2003, Monterey, CA, USA, June 1-3, 2003, Proceedings; 01/2003
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    N. Cranley, L. Murphy
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    ABSTRACT: Currently multimedia is either downloaded before viewing, or streamed over a network. However, the problem of streaming real-time or near real-time applications with a specified quality of service (QoS) over the Internet is still unsolved. The Real-time Transport Protocol (RTP) can be used to facilitate streaming, but also has the potential to support QoS. By gathering network statistics during the session and defining different QoS levels, we propose to adapt multimedia streaming to a fluctuating network load and/or client requests, thereby providing adaptive QoS. We describe the simple server and client applications we have implemented to illustrate this adaptation process
    Communications, 2001. ICC 2001. IEEE International Conference on; 02/2001
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    Nicola Cranley, Ludovic Fiard, Liam Murphy
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    ABSTRACT: this paper, an alternative approach using a protocol stack comprising a Real-time Transport Protocol (RTP) layer over a User Datagram Protocol (UDP)/Internet Protocol (IP) layer is described. Firstly we provide a brief description of MPEG/MPEG-4 and RTP/RTCP, followed by a description of the system implemented and plans for its future development.
    06/2000;
  • Nicola Cranley, Tanmoy Debnath, Mark Davis
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    ABSTRACT: 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.
  • Source
    Michael Searles, Nicola Cranley, Liam Murphy
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    ABSTRACT: Currently multimedia is either downloaded before viewing, or streamed over a network. However, streaming real-time or near real-time applications with a specified Quality of Service (QoS) over best-effort IP networks is not yet a solved problem. The Real-time Transport Protocol (RTP) can be used to facilitate streaming, but also has the potential to support QoS. Multicast transmissions are currently quite static and inflexible as all users receive the same treatment and it is only the network behaviour which differentiates between their perceived QoS. By gathering network statistics during the session and defining different customer groups, we propose to adapt multicast multimedia streaming to a fluctuating network load and/or client requests, thereby providing adaptive QoS.

Publication Stats

160 Citations
2.06 Total Impact Points

Institutions

  • 2003–2007
    • University College Dublin
      • School of Computer Science and Informatics
      Dublin, Leinster, Ireland
  • 2001–2007
    • Dublin City University
      • School of Electronic Engineering
      Dublin, L, Ireland
  • 2005–2006
    • Dublin Institute of Technology
      • Department of Electronic Engineering
      Dublin, L, Ireland