3GPP2 Evolution Workshop - 2005 Multimedia Codecs and Protocols 3GPP2 TSG-C SWG1.2.
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Transcript of 3GPP2 Evolution Workshop - 2005 Multimedia Codecs and Protocols 3GPP2 TSG-C SWG1.2.
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3GPP2 Evolution Workshop - 2005Multimedia Codecs and Protocols
3GPP2 TSG-C SWG1.2
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Multimedia in PS Domain
•Transitioning from CS to PS – Shared channels as opposed to dedicated channels– User expectation: Similar to that with dedicated
channels– Application Level Framing (ALF) in IP
– Requires special considerations for wireless hops
•Codec and transport related challenges– IP fragmentation– Jitter in packet arrival– Codecs’ view of QoS:
– Greater need for error resiliency and concealment– …
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TSG-C SWG1.2 “Multimedia Services” ToR
• Evaluation and adoption of – Visual Codecs (Video, Image, Graphics),– Audio Codecs (synthetic and natural audio)– Audio/visual synchronization methods
• Evaluation and adoption of complementary protocols– RTSP/SDP, RTP/RTCP, to support real-time, near real-time
and interactive multimedia services • Development of fileformats to support
– over the air transmission for streaming, pseudo-streaming, downloading
– associated methods for content protection
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IP Terminology
• ADU – Application Data Unit– Independently decodable data; minimum unit of error recovery– e.g. a vocoder frame, a video slice, …
• SDU – Service Data Unit– One or more ADUs, including required headers for transmission
• MTU – Maximum (size of a) Transmission Unit, in octets– e.g. 1500 octets on an Ethernet hop, 576 octets on PPP, …
• Fragmentation and Re-assembly – 1 SDU n PDU mapping, when SDU exceeds MTU on a given hop
• PDU – Protocol Data Unit– In this context, we consider physical layer frames– payload size in one physical layer frame
– Not including MAC, CRC and tail bits overhead
Observation: Significant fragmentation over cdma2000® hops
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IP Fragmentation
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“Goodput” above RTP
• From RFC2736, Best Current Practice for RTP payload design,– … relying on IP fragmentation is a bad design strategy as it significantly
increases the effective loss rate of a network and decreases goodput– … if one fragment is lost, the remaining fragments (which have used up
bottleneck bandwidth) will then need to be discarded by the receiver• Pick ADU/SDU sizes not to exceed PDU sizes• Do not concatenate SDUs (use stuffing bits)
Link Layer Packets: PDU i ... PDU n
Application Packets: SDU 2 SDU 1 ...
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What is optimal ADU size?
• One size does not fit all– Except for Constant bitrate (CBR) Channels and CBR codecs
• Most 3G networks provide multiple PDU sizes to support “Bandwidth on Demand”
• Entropy in multimedia content (video, speech, Audio, …) is not constant over a TTI
– Variable bitrate (VBR) encoding: improved compression efficiency• Examples
– cdma2000 vocoders– Channel: RS-1 and RS-2 support 4 PDU sizes in addition to dtx– Source: cdma2000 vocoders generate 4 ADU sizes, based on source characteristics– SO60: ADU = PDU; CS like efficiency in PS!
– ITU and MPEG Video codecs– VBR rate control constrained to generate ADUs of known size – Improved error resiliency when ADUs are matched to PDUs
• Significant statistical multiplexing gains when codecs are optimized to lower layers
• Challenges: Optimize 3G services, without cross-layer violations and maintain interoperability with other networks
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Jitter in Packet Arrival
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Jitter in PS networks
• Variance in the ADU inter-arrival time– SDUs queued behind cross-traffic in routers– Routing changes in end-to-end path
• De-jitter buffer – a buffer to restore constant inter-packet timing prior to decoding– Increases playout delay
20ms De-jitter bufferDe-jitter buffer DecoderDecoder
Even delivery of Even delivery of voice framesvoice frames
20ms of voice20ms of voice per frameper frame
20ms
Variable Delay, in-order delivery not Variable Delay, in-order delivery not guaranteedguaranteed
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Example: Jitter in packet arrival times
End2end Packet Delay
0
50
100
150
200
250
300
350
400
1 56 111 166 221 276 331 386 441 496 551 606 661 716 771 826 881 936 991 1046 1101
Frame Count
Del
ay (m
s)
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Example: Packet Loss due to Delay bound
0
0.5
1
1.5
2
2.5
1 168 335 502 669 836 1003 1170 1337 1504 1671 1838 2005 2172 2339 2506 2673 2840AT Index
PER
Total PERDelayed PER
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Smart Decoders
• Reduce playout delay with variable rate rendering– Speech: Signal processing tricks such as “Time Warping”– Video: Audio visual synchronization (lip-synch)
• Improved concealment techniques to mitigate packet loss– Interpolation in time and/or frequency domains
• Challenges– Develop improved objective metrics and subjective evaluation methodologies– Study and characterize the effects of such enhancements on user experience
GoodGoodErasureErasureGoodGood
Playback Time linePlayback Time line
CircuitCircuit
VoIPVoIP
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RTP Packet Loss Simulator
• SWG1.2 Simulation methodology to characterize multimedia content in cdma2000 wireless IP
Video/Audio Codec
Cdma2000/WCDMA
IP
UDP
RTP
Video/Audio Codec
Cdma2000/WCDMA
IP
UDP
RTP
MS MS or Content Server
RTP Packet Loss S/W
BitratePDU SizesError Masks
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Proposed Video Objective MetricsForeman example
Avg PSNR
[dB]STD PSNR
[dB] pDVD [%]
Bitrate [Kbps
]Clean 32.35 0.80 NA 64.69
1.5% FER : Scheme A 26.92 7.09 45.67 64.691.5% FER : Scheme B 28.98 6.11 35.67 66.601.5% FER : Scheme C 32.03 2.57 3.67 67.111.5% FER : Scheme D 31.57 3.51 8.33 67.86
•Percentage Degraded Video Duration (pDVD)•Standard deviation of PSNR (STD_PSNR)
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PSNR Traces: Foreman
Objctive Metrics comparison: Foreman QCIF 300 frames
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25
30
35
40
1 11 21 31 41 51 61 71 81 91 101 111 121 131 141 151 161 171 181 191 201 211 221 231 241 251 261 271 281 291
Frame #
PS
NR
[dB
]
Clean
1.5% FER A
1.5% FER B
1.5% FER C
1.5% FER D
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Summary
• Optimize codecs and bearer protocols to lower layers for efficient IP services
– e.g. VBR codecs and VBR channels in 3GPP2 CS voice– Rate control and RTP packetization to maximize “goodput”– Interoperability with other IP networks (cross-layer issues)
• Develop smart codecs – Improved error resiliency – Better concealment techniques– Variable rate rendering
• Develop/adopt suitable objective metrics and subjective evaluation methodologies
– Characterize user experience in realistic 3GPP2 environments