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Transport of Transport of Real-Time TrafficReal-Time Trafficover the Internetover the Internet
Transport of Transport of Real-Time TrafficReal-Time Trafficover the Internetover the Internet
Bernd GirodBernd Girod
Information Systems LaboratoryInformation Systems LaboratoryStanford UniversityStanford University
22B. Girod: Internet Real-Time Transport, September 2005
[Economist, September 2005]
THE MEANING OF FREE SPEECH
The acquisition by eBay of Skype is a helpful reminder to the world's trillion-dollar telecoms industry that all phone calls will eventually be free . . .
. . . Ultimately—perhaps by 2010—voice may become a free internet application, with operators making money from related internet applications like IPTV . . .
THE MEANING OF FREE SPEECH
The acquisition by eBay of Skype is a helpful reminder to the world's trillion-dollar telecoms industry that all phone calls will eventually be free . . .
. . . Ultimately—perhaps by 2010—voice may become a free internet application, with operators making money from related internet applications like IPTV . . .
33B. Girod: Internet Real-Time Transport, September 2005
IPTV Rollout IPTV Rollout
IPTV SBC18M householdsby 2007
IPTV SBC18M householdsby 2007
Verizon10M households
by 2009
Verizon10M households
by 2009
[IEEE Spectrum, Jan. 2005]
44B. Girod: Internet Real-Time Transport, September 2005
Why Is Real-Time Transport Hard?Why Is Real-Time Transport Hard?
Internet is a best-effort network . . .
Congestion Insufficient rate to communicatePacket loss Impairs perceptual qualityDelay Impairs interactivity of services;
Telephony: one way delay < 150 ms [ITU-T Rec.
G.114]
Delay jitter Obstructs continuous media playout
55B. Girod: Internet Real-Time Transport, September 2005
Outline of the TalkOutline of the Talk
• QoS vs. best effort
• Resource allocation for IPTV
• Rate-distortion optimized streaming
• Multi-path routing
• P2P multicasting of live video streams
66B. Girod: Internet Real-Time Transport, September 2005
1.22 MTUr
RTT p
1.22 MTUr
RTT p
How 1B Users Share the InternetHow 1B Users Share the Internet
maximum transfer
unit
roundtrip time
packetloss rate
data rate
[Mahdavi, Floyd, 1997]
[Floyd, Handley, Padhye, Widmer, 2000]
Rate r
Growing congestion
p0.0010.0001 0.10.01
TCP Throughput
77B. Girod: Internet Real-Time Transport, September 2005
QoS vs. Best EffortQoS vs. Best EffortReservation-ism
– Voice and video need guaranteed QoS (bandwidth, loss, delay)
– Implement admission control: “Busy tone” when network is full
– Best effort is fine for data applications
Best Effort-ism– Best Effort good enough for
all applications– Real-time applications can
be made adaptive to cope with any level of service
– Overprovisioning always solves the problem, and it’s cheaper than QoS guarantees
88B. Girod: Internet Real-Time Transport, September 2005
Simple Model of A Shared LinkSimple Model of A Shared Link• Link of capacity C is shared among k flows
• Fair sharing: each flow uses data rate C/k• Homogeneous flows with same utility function u(.)• Total utility
C
CU k k u
k
[Breslau, Shenker, 1998]
99B. Girod: Internet Real-Time Transport, September 2005
Rigid ApplicationsRigid Applications• Utility u=0 below of
minimum bit-rate B
• Maximum total utility U=k* is achieved by admitting at most k* flows
u
C/k
* arg maxk
C Ck k u
k B
B
1
[Breslau, Shenker, 1998]
1010B. Girod: Internet Real-Time Transport, September 2005
Rigid Applications (cont.)Rigid Applications (cont.)• Expected loss in total utility w/o admission control
• Gap U is substantial when number of admissable flows k* is small
• Gap U usually disappears with growing capacity C Overprovisioning can solve the problem!
PrC C
U kB B
[Breslau, Shenker, 1998]
1111B. Girod: Internet Real-Time Transport, September 2005
Elastic ApplicationsElastic Applications• Elastic applications: utility function u(k), such
that total utility U(k)=ku(C/k) increases with k• Example:
u(C/k)=1-aC/k
• All flows should be admitted: best effort!
C/k
u
1212B. Girod: Internet Real-Time Transport, September 2005
0 500 1000 1500 2000 2500 3000 3500 400024
26
28
30
32
34
36
38
40
42
44
Y-PS
NR
in d
B
encoding rate in kbps
mobile
foreman
Video CompressionVideo Compression• H.264 video coding for 2
different testsequences• Video is elastic application• Rate must be adapted to
network throughput• How to achieve rate control
for stored content or multicasting?
• Utility function depends on content: should use unequal rate allocation Foreman
Mobile
Goodpicturequality
Badpicturequality
1313B. Girod: Internet Real-Time Transport, September 2005
• Example: uk(rk)=1-akrk
• With rk>=0 Karush-Kuhn-Tucker conditions (“reverse water-filling”)
• Better than utility-oblivious “fair” sharing
Different Utility FunctionsDifferent Utility Functions
rk
uk
Equal-slope “Pareto condition”
Vilfredo Pareto1848-1923
1414B. Girod: Internet Real-Time Transport, September 2005
Distribution of IPTV over WLANDistribution of IPTV over WLAN
[courtesy: van Beek, 2004]
5 Mbps
2 Mbps
11 Mbps
Home MediaGateway
1515B. Girod: Internet Real-Time Transport, September 2005
Receiver
(Multi-Channel)
Transcoder
Transcoder
Transcoder
Transcoder
0
1
2
3
Decoder
Decoder
Decoder
Decoder
0
1
2
3
Controller
Video Streaming Over Shared ChannelVideo Streaming Over Shared Channel
[Kalman, van Beek, Girod 2005]
1616B. Girod: Internet Real-Time Transport, September 2005
0 10 20 30 400
2
4
6
8
10
ba
cklo
g in
fra
me
s
0 10 20 30 400
2
4
6
8
10
0 10 20 30 400
2
4
6
8
10
time in seconds
ba
cklo
g in
fra
me
s
0 10 20 30 400
2
4
6
8
10
time in seconds
Tx Backlog for 4 Video Streams Tx Backlog for 4 Video Streams 85% WLAN Utilization85% WLAN Utilization
[Kalman, van Beek, Girod 2005]
1717B. Girod: Internet Real-Time Transport, September 2005
Streaming of Stored ContentStreaming of Stored Content
DSL
Cable
wireless
Media files are already compressed:How can we nevertheless adapt to network?
100s to 1000ssimultaneousstreams
Server ClientNetwork
1818B. Girod: Internet Real-Time Transport, September 2005
Not All Packets are Equally ImportantNot All Packets are Equally Important
P PI
I
B B B P P PI
I
B B B P
A
…
…
…
A …
1919B. Girod: Internet Real-Time Transport, September 2005
PBP PI
I
B B P PI
I
B B B P
A
…
…
…
A …
Not All Packets are Equally ImportantNot All Packets are Equally Important
2020B. Girod: Internet Real-Time Transport, September 2005
Distortion-Aware Packet DroppingDistortion-Aware Packet DroppingGoodPicturequality
Badpicturequality
Percentage of Packets Retained [%]
Distortionaware
Packet droppingNo retransmissionsQCIF CarphoneI-P-P-P-P-P- . . .Oblivious
[Chakareski, Girod, ICME 2004]
2121B. Girod: Internet Real-Time Transport, September 2005
Rate-DistortionRate-DistortionOptimized (RaDiO) StreamingOptimized (RaDiO) Streaming
“Decide which packets to send (and when) to maximize picture quality while not exceeding an average rate” [2001]
Server Client
Request stream
Rate-distortionpreamble
Packetschedule
Video data
RepeatrequestRepeatrequestRepeatrequest
Network
2222B. Girod: Internet Real-Time Transport, September 2005
A Brief History of Media StreamingA Brief History of Media Streaming
1) Media streaming w/o congestion avoidance: “reckless driving” [1995]
2) TCP-friendly rate control: “Limit average rate for fair sharing with TCP” [1997]
3) Rate-distortion optimized packet scheduling (RaDiO): “Decide which packets to send (and when) to maximize picture quality while not exceeding an average rate” [2001]
4) Congestion-distortion-optimized scheduling/routing (CoDiO): “Decide which packets to send (and when) to maximize picture quality while minimizing network congestion.” [2004]
2323B. Girod: Internet Real-Time Transport, September 2005
Congestion vs. RateCongestion vs. Rate• Congestion: queuing delay that packets experience
– weighted by size of the packet– averaged over all packets in the network
• Congestion increases nonlinearly with link bit-rate
Congestion [seconds]
Rate R
max
Example: M/M/1 model
1 =
R -R
max
Example: M/M/1 model
1 =
R -R
Rmax
2424B. Girod: Internet Real-Time Transport, September 2005
Video Distortion with SelfVideo Distortion with Self CongestionCongestion
GoodPicturequality
Badpicturequality
Bit-Rate [kbps]
Self congestioncauses late loss
2525B. Girod: Internet Real-Time Transport, September 2005
Streaming with Last Hop BottleneckStreaming with Last Hop Bottleneck
Random cross traffic
Low bandwidth last hop
Video traffic
Acknowledgments
High bandwidth links
2626B. Girod: Internet Real-Time Transport, September 2005
Delay distributionDelay distribution
• Overall delay distribution
• Queue length determines delay of last hop
delay
C
2727B. Girod: Internet Real-Time Transport, September 2005
Comparison RaDiO vs. CoDiOComparison RaDiO vs. CoDiO
Simulations using H.263+
Rate : 10 fps
Sequence : Foreman (32kbps,32kbps)
Sequence length : 60s
Playout deadline : 600ms
50 %
PS
NR
[dB
]
Rate [kbps]P
SN
R [
dB]
End-to-end delay [ms]
2828B. Girod: Internet Real-Time Transport, September 2005
How To Avoid Traffic Jams?How To Avoid Traffic Jams?
• Avoid congested times . . .Congestion-aware packet
scheduling
• Avoid congested roads . . . Congestion-aware routing
2929B. Girod: Internet Real-Time Transport, September 2005
Multipath Routing for Minimum CongestionMultipath Routing for Minimum Congestion
7716kbps
25
15
718
35
222
8
23 238
69
4364 24
24
31 kbps
45
24
Mesh network, fully connected Streaming 100 kbps from Node 1 to Node 5 Random cross traffic
3030B. Girod: Internet Real-Time Transport, September 2005
Multipath Video StreamingMultipath Video Streaming
6 dB
Sequence : Foreman QCIF, 250 frames, 30 fps
Codec: H.26L TML 8.5
Playout deadline : 500 ms
Packetization : 1 frame/packet
Traffic model: CBR
No. of realizations: 400
GoodPicturequality
Badpicturequality
Bit-Rate [kbps]
3131B. Girod: Internet Real-Time Transport, September 2005
Multipath Video Streaming
1 path80 kbps, PSNR 32.5 dB
3 paths187 kbps, PSNR 36.2 dB
3232B. Girod: Internet Real-Time Transport, September 2005
Distribution of Live Streams Distribution of Live Streams via “Pseudo-Multicast”via “Pseudo-Multicast”
ExampleAOL webcast of Live 8 concert
July 2, 2005
Content delivery network
. . . . . . . . . . . . . . . . . .
Splitterservers
Mediaserver
1500 servers in 90 locations
50 Gbps
175,000 simultaneous viewers
8M unique viewers
3333B. Girod: Internet Real-Time Transport, September 2005
P2P live multicast
Content delivery network
. . . . . . . . . . . . . . . . . .
Splitterservers 1500 servers in 90 locations
50 Gbps
Distribution of Live Streams Distribution of Live Streams via “Pseudo-Multicast”via “Pseudo-Multicast”
ExampleAOL webcast of Live 8 concert
July 2, 2005
Mediaserver
175,000 simultaneous viewers
8M unique viewers
300 kbps
3434B. Girod: Internet Real-Time Transport, September 2005
P2P Multicast over 1 TreeP2P Multicast over 1 Tree
3535B. Girod: Internet Real-Time Transport, September 2005
P2P Multicast over 2 TreesP2P Multicast over 2 Trees
3636B. Girod: Internet Real-Time Transport, September 2005
P2P Ungraceful Parent LeaveP2P Ungraceful Parent Leave
3 treesParent of yellow tree is down
Hello, Yellow Tree
Parent?
Parent leave is detected
Retransmissions requested
New parent is selected
Yellow tree is recovered
3737B. Girod: Internet Real-Time Transport, September 2005
Experimental Set-upExperimental Set-up• Network/protocol simulation in ns-2
– 1000 nodes– 300 active peers – Random peer arrival/departure:
ON (5 min)/OFF (30 s) – Over-provisioned backbone– Typical access bandwidth distribution– Delay: 5 ms/link + congestion
• Video streaming– Compression H.264 at 220 kbps– 15 minute live multicast
[Setton, Noh, Girod, ACM MM 2005]
3838B. Girod: Internet Real-Time Transport, September 2005
Join and Rejoin LatenciesJoin and Rejoin Latencies
[Setton, Noh, Girod, ACM MM 2005]
3939B. Girod: Internet Real-Time Transport, September 2005
Congestion-DistortionCongestion-DistortionOptimized P2P Live StreamingOptimized P2P Live Streaming
% peersconnected to 4/4 trees
% peersconnected to 4/4 trees
[Setton, Noh, Girod, ACM MM 2005]
With CoDiO
Without CoDiO
4040B. Girod: Internet Real-Time Transport, September 2005
Congestion-distortion optimized (CoDiO) streaming
Without CoDiO
P2P Video Multicast: 64 out of 300 Peers
H.264 @ 220 kbps2 sec latency for all streams
4141B. Girod: Internet Real-Time Transport, September 2005
Concluding RemarksConcluding Remarks• Over-provisioning makes QoS superfluous• Elastic applications don’t need QoS• Joint rate control for access bottlenecks
(e.g. IPTV, WLAN)• Media-aware congestion control (e.g. CoDiO)• Multipath routing to mitigate congestion• P2P viable alternative for content delivery
networks
Client-server edge-based P2P
The EndThe EndThe EndThe Endhttp://www.stanford.edu/~bgirod/publications.htmlhttp://www.stanford.edu/~bgirod/publications.html