Generic RTP Payload Format guaranteeing QoS of Video communication - PowerPoint PPT Presentation

About This Presentation
Title:

Generic RTP Payload Format guaranteeing QoS of Video communication

Description:

... to recover the lost information from the correctly received packets. ... prediction frames are used to reconstruct just one picture based on the previous ... – PowerPoint PPT presentation

Number of Views:20
Avg rating:3.0/5.0
Slides: 13
Provided by: ietf
Learn more at: https://www.ietf.org
Category:

less

Transcript and Presenter's Notes

Title: Generic RTP Payload Format guaranteeing QoS of Video communication


1
Generic RTP Payload Format guaranteeing QoS of
Video communication
  • draft-bsong-fecframe-gfec-00.txt
  • Hao Qin
  • hqin_at_mail.xidian.edu.cn

2
Summary
  • Aim
  • To reduce the impact of packet loss to a video
    receiver.
  • Solution
  • Use FEC technique to recover the lost information
    from the correctly received packets.
  • Bundle maximum number of output data blocks from
    an FEC encoder into each RTP packet to maximize
    the bandwidth utilization and minimize the
    latency.

3
Unequal FEC protection
  • Different parts in the video stream may have
    different importance to the receiver.
  • reference frames are critical to a decoder to
    reconstruct following pictures.
  • prediction frames are used to reconstruct just
    one picture based on the previous reference
    frame.
  • Losses of reference frames may cause far more
    serious disasters to the video decoder because
    the video decoder may be forced into a very long
    time of interruption.
  • Data with different importance may be unequally
    protected with different FEC algorithms.

4
Interleaving
  • Many consecutive data blocks from an FEC encoder
    may be encapsulated into a single RTP packet, so
    that loss of an RTP packet means loss of many
    data blocks. This brings difficulty to an FEC
    decoder for the insufficient information to
    reconstruct the source data.
  • Interleaving should be introduced to solve this
    problem.

5
Protected by FECInterleaving
6
Protected by FEC only
  • If the data are protected by FEC only, the format
    of encapsulation is different from the format
    mentioned above. To mitigate the impact of burst
    packet loss to the FEC decoder, exactly one FEC
    block is encapsulated in one RTP packet.

7
Generic payload format for FEC
0 0 7 8 15 15 16 23 24 31
RTP Header RTP Header RTP Header RTP Header RTP Header RTP Header RTP Header RTP Header RTP Header RTP Header
R C FEC type FEC subtype FEC subtype Interleaving index Interleaving index Interleaving index Block size Block size
One or more encoded data blocks One or more encoded data blocks One or more encoded data blocks One or more encoded data blocks One or more encoded data blocks One or more encoded data blocks One or more encoded data blocks One or more encoded data blocks One or more encoded data blocks One or more encoded data blocks
8
R 3bits reserved
C 1bit interleaving indication
FEC type 4bits mapped to a particular FEC algorithm
FEC subtype 6bits mapped to the FEC algorithm parameters
Interleaving index 10bits zero-based index within an interleaving group if the interleaving algorithm is used, otherwise, the field indicates the zero-based block index within an FEC unit. The field is useful for the decoder.
Block size 8bits number of octets in a data block
9
Delay consideration and parameter determination
  • FEC and interleaving reduce the effect of
    pack losses at the cost of increasing the delay.
    Large values of N, K or U increase not only the
    ability of the receiver to be tolerant of packet
    losses, but also the delay. Tradeoff between the
    low end-to-end delay and great tolerance for
    packet losses should be made in the choice of FEC
    and
  • interleaving parameters.

10
Detecting packet losses
  • To make the FEC decoder work, the position
    and the amounts of the lost packets in their
    corresponding FEC unit need to be determined.
  • If the data are neither protected by the FEC and
    nor interleaved, the lost packet cannot be
    recovered.
  • If the data are protected by the FEC only or by
    FEC and interleaved, the decoder can detect
    packet losses by the sequence number, FEC type,
    FEC subtype and index field.

11
The process flow of the video stream
12
Thanks/Comments
Write a Comment
User Comments (0)
About PowerShow.com