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NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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Adaptive Playout
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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You are Here
Network
Encoder
Sender
Middlebox
Receiver
Decoder
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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How to recv and play?
open socketwhile not done
if socket is readable read packet from socketremove RTP headerdecodeplay back
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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What’s Wrong?
packet orderingpacket lossnext packet arrive in-time?
Especially bad for audio applications
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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Overview
Network
RTP Classifier
Decode
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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Packet Buffer
Sorted by sequence numberWhen ADU is complete, send to
decoder
RTP Classifier
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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Playout Buffer
Stored decoded data in playout order
Post-processing/Mixing may happen
Decode
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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Why Buffer?
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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Sending Packets
Time
Packet
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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Receiving Packets
Time
Packet
t1t0
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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With Jitter
Time
Packet
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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With Jitter
Time
Packet
t2t0
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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What causes Jitter?
Network delay = Transmission Delay (fixed) +
Propagation Delay (fixed) +Queuing Delay (variable)
Delay jitter is caused by variable queuing delay
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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Delay Jitter
Time
TransitTime
small jitter
large jitter
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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Spike
Time
TransitTime
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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Today’s Question
How big is the playout buffer?When to play back?
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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Types of Applications
Non-interactive Buffer can be large
Interactive As small as possible
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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Types of Applications
Video Frames are discrete (easier
problem)
Audio Samples are “continuous”
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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Naive Answer
How big is a buffer? Fixed at a small value, to reduce
latency
When to playback? Playback as soon as possible, to
reduce latency
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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Client Buffer Management
Bandwidth Smoothing for Non-interactive Applications
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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Multi-Threshold Flow Control
R. Zimmermann, K. Fu, M. Jahangiri, C. ShahabiMTAP 2006
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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Video-on-Demand (VoD)
High-quality playback requiredBuffer can be largeEncoding may be VBR for high
visual qualityPlayback time may be very long
(2+ hours)
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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Two Approaches (1)
Server-controlled Pre-compute transmission schedule Piece-wise linear approximation:
compute a number of constant-rate segments
Different optimization criteria Minimize: # of rate changes, #
utilization of client buffer, peak rate, etc.
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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Two Approaches (2)
Client-controlled Client adaptively informs server Advantages:
No rate history necessary (VBR) Can adjust to network conditions Works easily with interactive
commands such as FF, FR, Pause
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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Robust Stream Delivery
Smoothing of VBR media traffic has the following quality benefits: Better resource utilization (less
bursty) More streams with the same
network capacity
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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Objectives
Multi-Threshold Flow Control(MTFC) algorithm objectives: Online operation Content independence Minimizing feedback
control signaling Rate smoothing
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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Example
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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MTFC Buffer Management
Multiple Thresholds: goal is middle of buffer
Send rateadjustcommandto serverwheneverthresholdis crossed
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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How to Set Thresholds?
Simple: equi-distant m: number of thresholds Overflow and underflow thresholds
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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How to Calculate Sending Rate?
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Threshold Spacing StrategiesLinear vs. arithmetic vs. geometric
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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Threshold Spacing StrategiesGeometric and arithmetic spacing:
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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Sending Rate Computation
Relevant factors: Target buffer level (i.e., 50%): THN
Current buffer level: bwobsv
Predicted duration to reach target level Data consumed during predicted duration
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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MTFC Results
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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MTFC Results: # of Thresholds
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MTFC Results: # of Thresholds
NumberOf
RateChanges
8MB 16MB 32MB
0
1020
30
40
50
60
708090
100
3 5 9 17
Number of Thresholds
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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A Brief Introduction to Audio Conferencing
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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Audio Conferencing
Live, interactive application Latency is important
Typically each packet contains20-30ms of audio
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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Silence Suppression
Silence Detection If no sound, no need to send
Talkspurt Consecutive audio packets
(between silence) Hundreds of ms
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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Recall: RTP Header
marker bit: depends on payload e.g. beginning of frame
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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RTP and Talkspurt
First packet of a talkspurt will have marker bit set to 1
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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RTP and Talkspurt
Deduce talkspurt from sequence number and timestamp
240
120
360
5190
SeqNoTimeStamp
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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Consequences of Talkspurt
Opportunity to adjust playout delay if jitter is large, increase delay if jitter is small, decrease delay
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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Fixed Playout Delay
SEND
RECV
PLAY
Talkspurt 1Talkspurt 2
Time
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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Adaptive Playout Delay
SEND
RECV
PLAY
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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Adaptive Playout Delay
SEND
RECV
PLAY
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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Trade-Off
Latency vs. Packet Loss
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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Latency vs Loss-Rate
LossRate
Latency
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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Latency vs Loss-Rate
LossRate
Latency
• Note: Late packets are considered lost
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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Adaptive Playout Mechanisms for Packetized Audio Applications in WAN
R. Ramjee, J. Kurose, D. Towsley, H. SchulzrinneINFOCOM 1994
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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Variables and Notations
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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Variables and Notations
Tsend(i)
Tplay(i)
Tbuf(i)
Tarrive(i)
Tdelay(i)
Tnet(i)
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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1st Packet in Talkspurt
We can estimate as
Mean and variation of the end-to-end delay.
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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How to estimate Vnet(i)
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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How to estimate Enet(i)
Method 1: Jacobson’s Method
(Delay estimate as in RFC 793, TCP re-transmit timer.)
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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Spike
Arrival Time
Tnet
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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Problems
Described algorithm does not react to spike fast enough.
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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How to estimate Enet(i)
Ramjee’s Method:
SPIKE NORMAL
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Ramjee’s Idea
SPIKE NORMAL
if Tnet(i) suddenly increases
if “slope” is small enough
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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In Spike ModeSPIKE
i
Tnet
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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In Normal ModeNORMAL
i
Tnet
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Evaluations
Delay
LossRate
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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Evaluations
Delay
LossRate
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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Problems with Ramjee’s Method
Time
TransitTime
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Packet Audio Playout Delay Adjustment: Performance Bounds and Algorithms
S. Moon, J. Kurose, D. TowsleyMultimedia Systems 1998
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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Recall Previous Methods
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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How to Set Tdelay(i)
Moon’s Method
Collect statistics on packets that have arrived.
Find t such that q% of last w packets have Tnet(i) < t.
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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Example (w =50, q = 90%)num of packets
delay
1 2 3 4 5 6 7 8 9 10 11 12
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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Setting Tdelay(i)
NORMAL SPIKE
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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Setting Tdelay(i)
Time
TransitTime
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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Performance Bound
Given a trace of packets, and a loss rate, find the minimum average playout delay.
Use Dynamic Programming
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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A Packet Trace
k
M talkspurts
1,k 2,k 3,k j,k nk,k
Tnet 13 15 10 …
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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More Notations
M: Number of Talkspurt
Npacket(k) or nk
Number of packets in talkspurt kNtotal
Total number of packets
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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Definition
minimum average playout delay for choosing i packets to be played out from k-th talkspurt
k
M talkspurts
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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How to find
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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Definition
minimum average playout delay for choosing i packets to be played out from k-th to M-th talkspurt
k
M talkspurts
M..
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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Base Case
D(k, 0) =
D(M, i) =
minimum average playout delay forchoosing i packets to be played out from k-th to M-th talkspurt
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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Recursive Case
k.. M..
1,k 2,k 3,k nk,k..
j
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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Performance Bound
Given a trace of M talkspurts and n packets, and a loss rate e, find the minimum average playout delay.
Answer: Minimum possible average playout delay is D(1, (1-e)n)
minimum average playout delay forchoosing i packets to be played out from k-th to M-th talkspurt
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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Evaluations
LossRate
Delay
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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Summary
Playout Adjustment for Audio Conferencing
Weighted Average Methods vs. Statistical Methods
An Analysis of Minimum Playout Delay
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Practical Complications
Clock DriftsRoute Change
NUS.SOC.CS5248-2015Roger Zimmermann (based in part on slides by Ooi Wei Tsang)
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Advanced Techniques
Speed-up Playback