✬ ✩ Video Streaming in Wireless Environments Manoj Kumar C Advisor Prof. Sridhar Iyer Kanwal Rekhi School of Information Technology Indian Institute of Technology, Bombay Mumbai ✫ ✪ 1
✬ ✩ Motivation • Refers to real-time transmission of stored video • Has stringent bandwidth, delay and loss requirements • Approaches – New protocols, router scheduling disciplines – Adapt output rate of video to available bandwidth • Rate Control Schemes - employ feedback ( loss, delay etc.,) • Need to adapt rate control schemes to wireless environments • What is specific to Video Streaming ? – Application layer QoS control – Affects user-perceived presentation quality ✫ ✪ 2
✬ ✩ Architectures for Video Streaming • HTTP based Streaming – Standard web servers used to deliver video content – Guaranteed-delivery protocols (like HTTP, TCP etc.,) not optimal for continuous media Web Browser 1. HTTP request/response for meta file 2. Meta File Web Server 3. Audio/Video file requested and sent over HTTP Media Player – Substantial fluctuations in delivery times of packets due to ✫ ✪ re-transmission, available bandwidth variations etc., 3
✬ ✩ • UDP/RTP based Streaming – Streaming Server retrieves media components in a synchronous fashion – Video sent over UDP using application-layer protocols tailored for video streaming (e.g., RTP) Client/Receiver Streaming Server Media Audio Video Decoder Synchronization Decoder Storage Device Video Compression Compressed Application−layer Raw Video Application−layer Video QoS control QoS control Audio Compressed Compression Raw Audio Transport Audio Transport Protocols Protocols Internet (Continuous Media Distribution Services) ✫ ✪ ( Figure from Wu et al, Streaming in the Internet : Approaches and Directions) 4
✬ ✩ Transport Protocols (RTP/RTCP) • RTP – Provides end-end transport functions for supporting real-time applications – Functions for media streaming like ∗ sequence numbering ∗ time-stamping ∗ payload identification • RTCP – Works in conjunction with RTP – Designed to provide QoS feedback to participants ✫ ✪ 5
✬ ✩ Application-Layer QoS Control : Rate Control • Minimizes network congestion by adjusting the output rate of the video coder to estimated available bandwidth • Classified into – Source-Based Rate Control – Receiver-Based Rate Control • Source based rate control schemes may use – Probe-Based Approach Example : AIMD, MIMD Algorithms etc., – Model-Based Approach Example : TFRC, RAP Algorithms etc., ✫ ✪ 6
✬ ✩ Rate Control in Wireless Environments • Characteristics of Wireless Channels – Limited Bandwidth – High Error Rates – Burst Errors • Loss based rate control schemes may inaccurately estimate the available bandwidth • AIMD based on packet loss fraction during each interval • In TCP Friendly Rate Control (TFRC) , 1 . 22 × MT U λ = (1) RT T × √ p • Assuming MTU and RTT constant, 1 λ ∝ (2) √ p ✫ ✪ 7
✬ ✩ The Problem • During bad channel conditions, loss rate reported by receiver may be high • Sender may inaccurately assume the network to be congested and decrease the output rate • Hence, quality of video delivered to the receiver affected Storage Device Compressed Streaming Video Server Source−based Rate Shaper Rate Control RTP/RTCP UDP/TCP RTP RTCP Base Internet MH Station ✫ ✪ 8
✬ ✩ Solution Scheme(s) • Prime reasons for the problem – Inability of receiver to distinguish between congestion and wireless packet losses – Sender estimates state of network using loss rate as principal feedback parameter • Two Schemes proposed – Report Only Congestion Losses (ROCL) – Report Correlation of Loss and Delay (RCLD) ✫ ✪ 9
✬ ✩ Report Only Congestion Losses (ROCL) • Receiver enabled to report loss rate only due to congestion • Uses heuristic proposed by Saad Biaz et al to discriminate congestion and wireless losses • Heuristic based on inter -arrival times of packets at the receiver T T T Sender 3 2 1 3 2 1 3 2 1 BS Receiver Router 2T Sender 3 2 1 3 2 1 3 2 1 BS Receiver Router T Sender 3 2 1 3 1 3 1 BS Receiver 2 ( From Nitin Vaidya et al, Discriminating Congestion Losses and Wireless Losses Using Inter−arrival times at the Receiver ) ✫ ✪ 10
✬ ✩ Report Correlation of Loss and Delay (RCLD) • Based on general patterns of throughput and response time as a function of load • Besides loss rate, sender reports correlation between the packet loss and delay curve Throughput Load Round Trip Delay Load • During congestion, delay curve increases with loss curve hence will have positive correlation • If loss rate high, sender decreases rate only if correlation is positive ✫ ✪ 11
✬ ✩ Simulation Experiments • Network Simulator – ns from UC Berkeley (version 2.1b8a) • S imulation Model Mobile Host MPEG Traffic RTP Agent RTP Agent 3 1 BW4, D4 BW1, D1 BW3, D3 R BS BW2, D2 BW4, D4 2 4 CBR Sink Cross Traffic ✫ ✪ Mobile Host 12
✬ ✩ • Experiment 1 – Network set in an uncongested state so that only wireless losses occur – Simulation parameters BW 1 = BW 2 = 1 Mbps , D 1 = D 2 = 2 ms BW 3 = 256 kbps , D 3 = 10 ms BW 4 = 64 kbps , D 4 = 1 ms • Experiment 2 – Network set in a congested state using cross traffic generated from Traffic/Expo – Simulation parameters BW 1 = BW 2 = 128 kbps , D 1 = D 2 = 2 ms BW 3 = 80 kbps , D 3 = 10 ms BW 4 = 64 kbps , D 4 = 1 ms ✫ ✪ 13
✬ ✩ Results Experiment 1 ✫ ✪ 14
✬ ✩ 120 Congestion Losses Loss Rate Max Rate 100 80 60 40 20 0 0 50 100 150 200 250 300 Report Number ✫ ✪ Figure 1: Original scheme without proposed modification 15
✬ ✩ 250 Congestion Losses Loss Rate Max Rate 200 150 100 50 0 0 50 100 150 200 250 300 Report Number ✫ ✪ Figure 2: “Report Only Congestion Losses (ROCL)” Scheme 16
✬ ✩ 180 Congestion Losses Loss Rate Max Rate 160 140 120 100 80 60 40 20 0 0 50 100 150 200 250 300 Report Number ✫ ✪ Figure 3: “Report Correlation of Loss and Delay (RCLD)” Scheme 17
✬ ✩ Results Experiment 2 ✫ ✪ 18
✬ ✩ 120 Congestion Losses Loss Rate Max Rate 100 80 60 40 20 0 0 50 100 150 200 250 300 Report Number ✫ ✪ Figure 4: Original scheme without proposed modification 19
✬ ✩ 120 Congestion Losses Loss Rate Max Rate 100 80 60 40 20 0 0 50 100 150 200 250 300 Report Number ✫ ✪ Figure 5: “Report Only Congestion Losses (ROCL)” Scheme 20
✬ ✩ 120 Congestion Losses Loss Rate Max Rate 100 80 60 40 20 0 0 50 100 150 200 250 300 Report Number ✫ ✪ Figure 6: “Report Correlation of Loss and Delay (RCLD)” Scheme 21
✬ ✩ Related Work • Elan Amir et al proposed “Application Level Video Gateway” • Employs split-connection approach • Transcodes video stream from server to lower bandwidth Mobile Host Base Station Wired Network Video Gateway • Problems – Increase in end-end delay due to transcoding – Transcoding difficult when packets are encrypted ✫ ✪ 22
✬ ✩ Conclusion & Future Work • ROCL and RCLD try to decrease the output rate only in response to congestion • Simulation experiments using ROCL and RCLD show significant increase in the output rate of video during bad channel conditions • Future Work – Investigate appropriate functions to replace loss event rate p in model-based schemes – Maintain network state at the sender to aid in making adaptation decisions ✫ ✪ 23
✬ ✩ References [1] Elan Amir, Steve McCanne, and Hui Zhang. An application level video gateway. In Proc. ACM Multimedia ’95, San Francisco, CA , 1995. [2] S. Biaz and N. Vaidya. Discriminating congestion losses from wireless losses using inter -arrival times at the receiver. IEEE Symposium ASSET’99, Richardson, TX, USA , 1999. [3] Jean-Chrysostome Bolot and Thierry Turletti. A rate control mechanism for packet video in the internet. In INFOCOM (3) , pages 1216–1223, 1994. [4] Sally Floyd, Mark Handley, Jitendra Padhye, and Jorg Widmer. Equation-based congestion control for unicast applications. In SIGCOMM 2000 , pages 43–56, Stockholm, Sweden, Auguest 2000. [5] Dapeng Wu and et al. Streaming video over the internet: Approaches and directions. IEEE Transactions on Circuits and Systems for Video Technology , 11:282, 2001. ✫ ✪ 24
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