An Improved UDP Protocol for Video Transmission Over Internet-to-Wireless Networks

1
An Improved UDP Protocol for Video Transmission
Over Internet-to-Wireless Networks
Haitao Zheng and Jill Boyce
IEEE Transaction on Multimedia
Leif 9/10/01
2
Outline

• Introduction
• Improved UDP Design
• Packet Coding Design
• Analytical Performance
• Conclusion
• Further Work

3
Introduction (1/3)

• Packet video will become a signification portion
  of emerging and further wireless/Internet
  traffic.
• Network congestion and wireless channel error
  yield tremendous packet loss and degraded video
  quality.
• Most Internet-based real-time multimedia services
  employ UDP.

4
Introduction (2/3)

• UDP no retransmission (delay), CRC
• Reliable UDP(RUDP)
• Retransmission and CRC (header and payload)
• UDP Lite
• no retransmission, CRC (head only)

5
Introduction (3/3)

• Employing forward error correction (FEC) code to
  the application packets can mitigate channel
  unreliability and improve media quality.
• eg. Reed-Solomon (RS) codes.
• (n, k) RS codeword the encoder chooses k
  packets and generates n k parity packets. It
  can correct n k erasures.

6
Improved UDP Design (1/3)

• New interface between RLP and PPP, PPP and IP, IP
  and UDP, so that certain information can be
  exchanged in both directions.
• The improved UDP should apply CRC to the packet
  header only and forward the packet payload to the
  application.

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Improved UDP Design (2/3)

• Type1LTU Error Indicator
• (For FEC decoders that require erasure indicator)
• Error indicators contain the starting and
  ending location of the erroneous frame.
• Type2Reformatted Packet
• (For FEC decoders that can recognize erasures)

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Improved UDP Design (3/3)

• Complete UDP (CUDP) captures the error-free
  frames and the location of erroneous frames.
• When combined with FEC coding, CUDP turns
  erroneous frames into erasure frames so that the
  other error-free frames can be utilized to
  recover the loss.

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Packet Coding Design (1/3)

• Vertical Packet Coding (VPC)
• The FEC encoder takes one data unit from each of
  k packets and generates (n - k) parity units
  (additional packets). It can recover (n - k)
  erasure packets.
• eg. fig. 3. (a)
• MDS code (n, k) (7, 4) It can recover 7 4
  3 erasure packets.
• VPC provides transparent Internet-to-Wireless
  communications. The UDP within the Internet
  remains unchanged.

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Packet Coding Design (2/3)

• Long Vertical Packet Coding (LVPC)
• For a fixed ratio (n - k)/n, the MDS codes
  achieve better error/erasure correction
  efficiency as n increases.
• MDS code (n, k) value? ? burst error resiliency ?
• X/L MDS (nL, kL) L column number
• eg. Fig. 3. (b)
• L m 7 (nL, kL) (49, 28)
• 49 28 21
• If the decoder fails, all the erasures can not be
  recovered.

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Packet Coding Design (3/3)
Fig. 3.
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Analytical Performance Error Model

• Two states, good (G), and bad (B)
• Transmission probability between the two states
  PGB and PBG present the error model.

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VPC
GPER
FER
Fig. 5.
14
LVPC
GPER
FER
Fig. 6.
15
Internet-to-wireless, VPC
GPER
Fig. 7.
FER
16
Internet-to-wireless, LVPC
GPER
FER
Fig. 8.
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CUDP, VPC, LVPC
GPER
Fig. 9.
FER
18
PSNR for Internet Wireless with VPC
PSNR
Fig. 10.
FER
19
PSNR for Internet Wireless with VPC
PSNR
Congestion Packed Loss Rate
Fig. 11.
20
PSNR for Internet Wireless with VPC
PSNR
Fig. 12.
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Conclusion (1/2)

• CUDP provides great flexibility for applications
  to utilize the instantaneous physical/link layer
  performance report. The media decoder has the
  right to decide whether to use or discard the
  packet.
• CUDP outperforms the other two protocols.
  However, as the congestion packet loss rate
  grows, the advantage of CUDP shrinks.

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Conclusion (2/2)

• Using CUDP, the received video maintains good
  quality.

23
Further Work

• Could the proposed system be applied to other
  packet video/audio/image?
• Taking into account of the delay due to RLP
  layer
• And the packet loss due to real-time scheduling
  within wireless networks.