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NADA: A Unified Congestion Control Scheme for Real-Time Media. Xiaoqing Zhu and Rong Pan Advanced Architecture & Research Cisco Systems August 2012. Agenda. Design goals System model Network node operations Sender / Receiver behavior Evaluation results Open issues. Packet loss. - PowerPoint PPT Presentation
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© 2010 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 1Cisco Confidential 1© 2011 Cisco and/or its affiliates. All rights reserved.
NADA: A Unified Congestion Control Scheme
for Real-Time Media
Xiaoqing Zhu and Rong Pan
Advanced Architecture & Research
Cisco Systems
August 2012
© 2010 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 2
Agenda
• Design goals
• System model
• Network node operations
• Sender/Receiver behavior
• Evaluation results
• Open issues
© 2010 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 3
Design Goal #1:Limit Self-Inflicted Delay
network queue network queue
Time
Congest
ion
win
dow
Siz
e
Packet loss
Time
Rate
React early
© 2010 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 4
Design Goal #2:Leverage A Suite of Feedback
Mechanisms
Delay-based ECN-based
PCN-based
none existing feature
new feature
Network Support
Perf
orm
an
ce
Existing loss-basedschemes
© 2010 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 5
Design Goal #3:Weighted Bandwidth Sharing
Relative bandwidth
Application-level priority
Bandwidth sharing among flows:
© 2010 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 6
video playout
optimal rate calculation
encoderrate control
RTCP report
video packets
network node
measure delay/marking
sender receiver
target rate
update networkcongestion notification
System Overview
rate shaping buffer
bufferlevel
© 2010 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 7
Network Node Behavior
• Queuing discipline: FIFO
• Congestion notification via:
Delay: no special operation at the queue
ECN: queue-based random marking
PCN: token-bucket-based random marking
© 2010 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 8
Queue-based ECN Marking
if :
no marking
else if :
else:
mark all packets
update: Avg. Queue OccupancyM
ark
ing P
robabili
ty
© 2010 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 9
Token-bucket-based PCN Marking
upon packet arrival:
meter packet against token bucket ;
update token level
if :
no marking
else if :
else:mark all packets
Remaining Token BucketM
ark
ing P
robabili
ty
© 2010 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 10
target rate
Sender Structure
target rate calculation
encoderrate control
video packets
rate shaping buffer
sending rate calculation
RTCP report(loss/delay/ECN/PCN)
bufferlevel
videorate
© 2010 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 11
Target Rate Calculation
• Reacting to delay: session priority
queuing delay
marking ratio
• Reacting to ECN/PCN marking:
scaling parameter
scaling parameter
© 2010 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 12
Sending Rate Calculation
• Accommodate lag in encoder reaction
• Trade-off between between network queuing and rate shaping delay
scaling parameter
encoder reaction time
© 2010 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 13
Slow-Start Rate
start time
time horizon
Time
Rate
© 2010 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 14
Receiver Behavior
• Observe instantaneous end-to-end per packet statistics:
Queuing delay:
ECN/PCN marking:
• Obtain time-smoothed estimations:
• Periodic RTCP reports (e.g., at 3% of received packets)
© 2010 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 15
Test Scenario
• Bottleneck bandwidth: 30Mbps
• Random delay measurement error for stream 6, at time t=30s
Flow ID
1 1 2 1
2 1 2 1
3 2 6 1
4 2 6 2
5 3 5 2
6 3 5 2
7 2 4 3
8 2 4 3
9 3 6 3
10 3 6 3
© 2010 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 16
Delay-Based Adaptation: Per-flow Rate
Stream 6 delay measurement error
Weighted BW sharing
© 2010 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 17
Delay-Based Adaptation: Total Rate
Fast convergence
© 2010 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 18
Delay-Based Adaptation: Bottleneck Queue
Low standing queue
© 2010 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 19
Delay-Based Adaptation: Packet Loss Ratio
No persistent losses
© 2010 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 20
Delay vs. ECN: Per-Flow RateECN-BasedDelay-Based
© 2010 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 21
Delay ECN
Delay vs. ECN: Bottleneck Queue
© 2010 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 22
ECN vs. PCN: Per-Flow RateECN PCN
Smoother streaming rates
© 2010 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 23
ECN vs. PCN: Total RateECN PCN
Slight under-utilization
No losses
© 2010 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 24
ECN PCN
ECN vs. PCN: Bottleneck Queue
Zero standing queue
© 2010 Cisco and/or its affiliates. All rights reserved. Cisco Confidential 25
Conclusions and Next Steps
• Key benefits of NADA: Fast rate adaptationWeighted bandwidth sharingCan work with a range of congestion signalsIn case of PCN: zero standing queue and smoother streaming rates
• Next steps: Future evaluations in linux-based implementationsGraceful transition between different congestion signalsCompete robustly against loss-based schemes