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Haitao Zheng and Jill Boyce

IEEE Transaction on Multimedia

Leif 9/10/01

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

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

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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.

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Introduction (2/3) UDP: no retransmission (delay), CRC Reliable UDP(RUDP):

Retransmission and CRC (header and payload) UDP Lite:

no retransmission, CRC (head only)

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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.

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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) Type1:LTU Error Indicator

(For FEC decoders that require erasure indicator)

Error indicators contain the starting and ending location of the erroneous frame.

Type2:Reformatted 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

FER

GP

ER

Fig. 5.

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LVPCG

PE

R

FER Fig. 6.

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Internet-to-wireless, VPC

Fig. 7.

GP

ER

FER

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Internet-to-wireless, LVPC

Fig. 8.

GP

ER

FER

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CUDP, VPC, LVPC

Fig. 9.

GP

ER

FER

18Fig. 10.

PSNR for Internet + Wireless with VPC

PS

NR

FER

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PSNR for Internet + Wireless with VPC

Fig. 11.

PS

NR

Congestion Packed Loss Rate

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PSNR for Internet + Wireless with VPC

Fig. 12.

PS

NR

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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.

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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.