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Congestion Control and Adaptive Retransmission for Multimedia Streaming over Wireless Networks

Kamal Singh, Árpád Huszák, David Ros, César Viho and Jeney Gábor

IRISA/INRIA, Rennes, France BUTE, Budapest, Hungary

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Agenda

Overview Congestion control for Video Flows Adaptive retransmissions and

wireless loss estimation Results Conclusion and Future Work

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Agenda

Overview Congestion control for Video Flows Adaptive retransmissions and

wireless loss estimation Results Conclusion and Future Work

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Overview: Next Generation Wireless Network

Users of Voice, TCP, …

Video Streaming anywhere in the cell

“Hotspots” with high bandwidth

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Overview: Wireless Problems in the context of Video Streaming

Problems due to the use of IP IP doesn’t support real time streaming

requirements

Problems due to radio conditions Scarce and time varying bandwidth Congestion, wireless losses & large delay

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Overview: Video Streaming

Video Streaming

• Delay & Jitter• Bandwidth, Congestion• Packet loss

constraints

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Overview: Video Streaming …

Video Streaming

• Underflow• No Playout

• Packet losses will cause quality distortion

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Agenda

Overview Congestion control for Video Flows Adaptive retransmissions and

wireless loss estimation Results Conclusion and Future Work

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Congestion Control for Video Flows

Motivation• Variable bandwidth, delay …• Congestion, packet losses

How can applications adapt to the network conditions?

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Existing Schemes

Congestion control for video TCP: Retransmissions, rate oscillations, …

TFRC [Floyd 2000] Sending Rate is calculated by a TCP model

Better Rate Stability

TCP Friendly

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Problems: Wireless Losses

Problem: Two types of losses in wireless Networks Packet drops due to congestion Packet drops due to bad channel conditions

Node B

Router

Wireless loss

Wireless network

IP Packets IP Queue

Congestion loss

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Problems …

Inefficiency for TCP, TFRC … Cannot distinguish between these losses. Reduce their sending rate on loss.

How to distinguish Wireless losses from congestion losses? Previous Work have used Round Trip Time

variations: May not be reliable ARC [O. B. Akan et al. 04]: Sending Rate

(S) is calculated using w :

ARC: How to calculate w ?

,

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Differential dropping in the DiffServ Assured Forwarding (Green, Yellow & Red)

Video applications mark their packets

Wireless Loss Estimation (Background: DiffServ)

Drop Red packets

Drop Red + Yellow packets

Rarely drop Green packets

I B P B P

Increasing Congestion

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Wireless Loss Estimation Wireless Loss Estimation in DiffServ (WLED)

Networks: [VTC 2006]

Red packets are dropped first on congestion

Wireless loss rate (w) is correlated with green loss rate

If loss of yellow packets is not significant

Estimate w for ARC using green loss rate

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WLED: Improves link utilization

There is no change in other properties: TCP friendliness, loss rate, rate stability

But, works only with DiffServ aware applications

WLED

WLED

TFRC

TCP

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Agenda

Overview Congestion control for Video Flows Adaptive retransmissions and

wireless loss estimation Results Conclusion and Future Work

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Adaptive retransmissions and wireless loss estimation

We improved link utilization in case of wireless losses.

But, lost data still deteriorates the quality!

Solution: We integrate a scheme to retransmit the lost data.

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Adaptive retransmissions and wireless loss estimation …

Retransmission Scheme If packet has the possibility to arrive before its

deadline No congestion Enables retransmission schemes Congestion Disable retransmission

Example Scenario:

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Adaptive retransmissions and wireless loss estimation …

Depending on: Available Bandwidth shown by Congestion

Control scheme Amount of I, P and B frames in video files

Retransmit either I frames I + P frames or All frames

WLED scheme integrated

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Adaptive retransmissions and wireless loss estimation : Transport protocol

DCCP (Datagram Congestion Control Protocol) Sequence numbers Feedback/ACK vectors Useful for loss detection

Retransmissions done at the application layer

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Adaptive retransmissions and wireless loss estimation : Simulation details

NS2 Dumbbell topology with 1Mbps of link

with 40ms delay Packet losses simulated in the wireless

link Reference Video: 360kbps “Mother

and Daughter” encoded using H.264

FTP and WWW flows as background

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Agenda

Overview Congestion control for Video Flows Adaptive retransmissions and

wireless loss estimation Results Conclusion and Future Work

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Key Results

• 10 WWW users in background

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Key Results …

• Wireless loss probability 0.1 and varying WWW users

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Agenda

Overview Congestion control for Video Flows Adaptive retransmissions and

wireless loss estimation Results Conclusion and Future Work

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Conclusion and Future Work

Used a wireless loss estimation scheme integrated with a retransmission scheme Obtained better video quality

Future Work Performance of WLED + retransmission in real

network Congestion control and adaptive

retransmission for MPEG4-scalable video codec (SVC)

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Thank You !