NETWORK LAYER FEEDBACK ENABLED ADAPTIVE APPLICATION-LEVEL REROUTE

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NETWORK LAYER FEEDBACK ENABLED ADAPTIVE
APPLICATION-LEVEL REROUTE

• by
• Liping Guo
• Gouri Landge

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Agenda

• Motivation
• Proposed NLFEALR-scheme
• A simple simulation system
• Realization of NLFEALR MDC-PD
• Results Comparison
• Conclusion
• QA

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Motivation

• Undesirable network condition
• Two major causes for packet-loss over the
  Internet Congestion Link/node failure.
• Link/node failure happens due to faulty
  equipment, router misconfigurations, and fiber
  cuts
• Long transient period for link failure single
  domain-tens of seconds inter-domain-several
  minutes.
• What if nothing is done for the transient period?

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Say 2 second-long transient period
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Motivation (cont.)

• How to deal with it?
• Multiple Description Coding (MDC) with path
  diversity (MDC-PD)
• creates independently decodable representations
  of the video and transmitting them on different
  routs.
• Tradeoff between compression performance and
  error resilience
• What if link failure happens only infrequently?
  Overprotection ! ! !

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Motivation (cont.)

• Goal avoid overprotection and achieve
  efficient use of the network resources.
• How? Adaptive reroute on the fly
• Fast link failure feedback is essential!!!
• Good news Network Layer Feedback System (NLFS)
  proposed in
• R. Keralapura, C. N. Chuah, M. van der Schaar,
  C. Tillier, an B. Pesquet-Popsecu, Adaptive
  Multiple Descriptions Scalable Video Coding Using
  Network Layer Feedback.

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Network Layer Feedback System (NLFS) R.
Keralapura et al.

• Video server needs to register with the nearest
  Overlay Broker before starting a video session.
• Synergy Layer is created on top of the IP layer
  and deployed in every router in various domains
  to provide feedback.
• Link failure info (e.g. IP addr of failed node)
  is passed to the server through the overlay
  broker.
• The maximum feedback delay is approximately 0.26
  second.

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Adaptive Application-level Reroute The idea
0.26s
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Adaptive Application-level Reroute

• (1) Routing components
• - Routing table-like structure is maintained by
  each media server it contains info about all
  possible backup paths.
• - Loose Source Record Route (LSRR) is used to
  do reroute.
• (2) Rate adaptation component
• The focus of our project !

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Rate adaptation component
A simple video streaming system
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Rate adaptation component How did
we look at the problem?

• Assume playback starts after 2 second buffering
• Once play back starts, buffer enters equilibrium
  status the number of frames in the buffer is
  constant (avg)
• Link failure breaks the buffers equilibrium
  status in worst case, buffer could be overplayed
  to empty severe video quality degradation at the
  receiver side.
• Find a way to let the play out buffer recover its
  equilibrium status fast
• How? Send more with less quality

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Rate adaptation component
High quality to low quality switch
Synchronization control _at_ server
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Rate adaptation component What bit rate to
switch to?

• Toc buffer over-consume time includes failure
  feedback delay (max 0.26s), routing process time
  (Tp), and 1/2 RTT.

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Rate adaptation component
Lets do the math!

• Noc number of over consumed frames during Toc
  (s).
• Rn newly adapted streaming bitrate. (kbps)
• Bn available bandwidth of the chosen backup
  path.
• Rp play rate at the receiver side.
• Qn quality of the newly adapted video stream.
  (kbpf)
• Rn Rp Qn
• Assume refill buffer overrun portion within 1
  second
• (2) Qn Bn / (Rp 1s Noc)
• (3) Noc Rp Toc
• (4) Toc 0.26s Tp ½ RTT

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Rate adaptation component
An example bitrate switch table
Server maintains the bitrate switch table
Quality of video (consumption rate in bits)
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A simple simulation system
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A simple simulation system An
example packet description in a hinting file

• PACKET_NUM20
• 6
• TRANSMIT_SUCCESS
• 1
• IDENTIFICATION_TAGS
• Type GOPnum Fr_Typ Tlev Pos Res
  Ch Chunk SubChunk
• 0 1 0 4 0 0 0 0 2
• DEPENDENCIES
• 4 5
• PACKET_SIZE
• 762
• IN_STREAM_POS
• 2000

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Simulation System

• Assumptions
• Link Bandwidth 768 kbps
• Average Link Failure Feedback Delay 0.26 Sec
• Routing process time 0.04 Sec
• Round trip time (RTT) 150 m Sec
• Video Playback Rate 30 Frames/Sec
• Buffering time 2s 30f/s 60 frames
• Input
• 288 Frames of Akiyo Sequence at cif resolution

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Realization of Rate Adaptation

• Assumption
• Available Bandwidth of Backup Path 768 kbps
• The Over Consumed Frames Refilled in 1 Sec
• Toc Tfb Tp ½ RTT
• 0.26s 0.04s ½(0.15s) 0.38s
• Noc Rp Toc 30fps 0.38s 11 frames
• Qn Bn / (Rp 1 Noc)
• 768kbps/(3011) frames 18.73 kbpf
• Rn Rp Qn 30 fps 18.73kbpf 562 (kbps)

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Realization of Rate Adaptation (cont.)

• PSNR at 562 kbps is calculated while decoding
• To illustrate the effect of the quality
  adaptation, we simply replace the PSNR values of
  affected 41 frames, with new PSNR.
• Feature can be added to the codec to be able to
  decode bit stream with switched bit rate. In
  fact, this will be needed at the receiver side,
  to use Rate Adaptation.

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Realization of MDC-PD

• Codec generated Hinting File
• The packet attributes
• The status of packet transmission as seen by the
  receiver.
• Attributes
• Texture or Motion Vector
• I Frame or H Frame
• Sub chunk, the packet dependency
• Transmission Status
• Success or Fail

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Realization of MDC-PD (cont.)

• Multiple Independently Decodable Descriptions
• Redundant information along with each description
  
• Error Resilience but lower quality
• To achieve unequal protection
• Prioritize packets by assigning different weights
  based on their attributes
• Put most significant packets in all descriptions
• Discard least significant ones to maintain BW

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Realization of MDC-PD (cont.)

• Weight Assignment
• I-Frame (Intra-coded Frame) 400
• spatial redundancy within the frame
• Independent of any other frame
• Referenced by several other inter-coded frames
• Loss can cause catastrophe to the decoded video
• H-Frame (Inter-coded Frame) 100
• Temporal redundancy among neighboring frames
• Motion vector information
• Dependent on I frame and other H frames

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Realization of MDC-PD (cont.)

• Weight Assignment (cont.)
• Temporal Level 80 to 10
• I Frames and H Frames are further classified
  based on their temporal level.
• Temporal levels 4 through 1 are assigned weights
  80, 40, 20 and 10.
• Sub Chunk Number variable
• Sub chunk number indicates the packet dependency.
  
• Higher sub chunk number, lower significance

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Realization of MDC-PD (cont.)

• If cumulative weight of a packet is greater than
  the high threshold, add the packet to both
  descriptions
• Equal number of packets with weight less than the
  low threshold is discarded.
• Packets with weight between the higher and low
  thresholds are evenly distributed between the two
  descriptions such that both the streams can be
  decoded independently.

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RESULTS ANALYSIS
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RESULTS ANALYSIS (cont)

• Both MDC-PD and our application-level reroute
  scheme improve video performance in the event of
  link failure.
• Under normal condition MDC performance is about
  1dB below the performance of Feedback Method due
  to Redundancy.
• MDC experiences the lower PSNR for the entire
  duration of the transient period
• Using feedback enabled reroute method, the lower
  PSNR is experienced only for a short duration
  which is independent of the transient period

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CONCLUSIONS

• MDC-PD provides good error resiliency
• But has drawback of overprotection when network
  conditions are fairly stable
• Feedback enabled application-level reroute scheme
  can be used as complementary solution for
  bandwidth efficiency

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