Video Streaming in Wireless Environments Manoj Kumar C Advisor - - PowerPoint PPT Presentation

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Video Streaming in Wireless Environments

Manoj Kumar C Advisor

• Prof. Sridhar Iyer

Kanwal Rekhi School of Information Technology Indian Institute of Technology, Bombay Mumbai

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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

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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 Server Web Browser Media Player

• 1. HTTP request/response for meta file
• 3. Audio/Video file requested and sent over HTTP
• 2. Meta File

– Substantial fluctuations in delivery times of packets due to re-transmission, available bandwidth variations etc.,

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• 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)

Storage Device

Streaming Server

Audio QoS control Application−layer Protocols Transport Compressed Video Audio Compressed Compression Video Compression Raw Audio Raw Video

Internet

Video Decoder Application−layer QoS control Decoder Protocols Transport Audio (Continuous Media Distribution Services)

Client/Receiver

Synchronization Media

( Figure from Wu et al, Streaming in the Internet : Approaches and Directions)

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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

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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.,

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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),

λ = 1.22 × MT U RT T × √p (1)

• Assuming MTU and RTT constant,

λ ∝ 1 √p (2)

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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 Server Streaming

Video Compressed Rate Shaper

Internet

Base Station

MH

RTCP RTP

Source−based Rate Control

RTP/RTCP UDP/TCP

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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)

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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

1 2 3 2 1 3 2 1 3 2 1 3 2 1 3 2 1 3 2 3 1 3 1 2 3 1 T T T 2T T

Receiver Receiver Receiver Sender Sender Sender BS BS BS Router Router ( From Nitin Vaidya et al, Discriminating Congestion Losses and Wireless Losses Using Inter−arrival times at the Receiver )

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Report Correlation of Loss and Delay (RCLD)

• Based on general patterns of throughput and response time as a function
• f load
• Besides loss rate, sender reports correlation between the packet loss and

delay curve

Delay Round Trip Load Load Throughput

• 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

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Simulation Experiments

• Network Simulator

– ns from UC Berkeley (version 2.1b8a)

• Simulation Model

Cross CBR Traffic Sink Agent RTP MPEG 2 4 BW3, D3 BW4, D4 BW4, D4 BW1, D1 BW2, D2

R

1 3

BS

RTP Agent

Mobile Host Mobile Host

Traffic

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• Experiment 1

– Network set in an uncongested state so that only wireless losses occur – Simulation parameters

BW1 = BW2 = 1Mbps , D1 = D2 = 2ms BW3 = 256kbps , D3 = 10ms BW4 = 64kbps , D4 = 1ms

• Experiment 2

– Network set in a congested state using cross traffic generated from Traffic/Expo – Simulation parameters

BW1 = BW2 = 128kbps , D1 = D2 = 2ms BW3 = 80kbps , D3 = 10ms BW4 = 64kbps , D4 = 1ms 13

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Results Experiment 1

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20 40 60 80 100 120 50 100 150 200 250 300 Report Number Congestion Losses Loss Rate Max Rate

Figure 1: Original scheme without proposed modification

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50 100 150 200 250 50 100 150 200 250 300 Report Number Congestion Losses Loss Rate Max Rate

Figure 2: “Report Only Congestion Losses (ROCL)” Scheme

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20 40 60 80 100 120 140 160 180 50 100 150 200 250 300 Report Number Congestion Losses Loss Rate Max Rate

Figure 3: “Report Correlation of Loss and Delay (RCLD)” Scheme

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Results Experiment 2

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20 40 60 80 100 120 50 100 150 200 250 300 Report Number Congestion Losses Loss Rate Max Rate

Figure 4: Original scheme without proposed modification

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20 40 60 80 100 120 50 100 150 200 250 300 Report Number Congestion Losses Loss Rate Max Rate

Figure 5: “Report Only Congestion Losses (ROCL)” Scheme

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20 40 60 80 100 120 50 100 150 200 250 300 Report Number Congestion Losses Loss Rate Max Rate

Figure 6: “Report Correlation of Loss and Delay (RCLD)” Scheme

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Related Work

• Elan Amir et al proposed “Application Level Video Gateway”
• Employs split-connection approach
• Transcodes video stream from server to lower bandwidth

Wired Network

Video

Base Station

Gateway Mobile Host

• Problems

– Increase in end-end delay due to transcoding – Transcoding difficult when packets are encrypted

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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

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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.

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