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A Rate/Quality Controlled MPEG Video Transmission System in a TCP-Friendly Internet Scenario


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Title: A Rate/Quality Controlled MPEG Video Transmission System in a TCP-Friendly Internet Scenario

A Rate/Quality Controlled MPEG Video Transmission
System in a TCP-Friendly Internet Scenario
  • Francesco Licandro, Giovanni Schembra
  • Dipartimento di Ingegneria Infomatica e delle
  • University of Catania
  • E-mail addresses (flicandro, schembra)_at_diit.unict

Presentation outline
  • Motivations and paper target
  • Background
  • TFRC TCP-friendly rate control
  • TM-5 MPEG rate control algorithm
  • The MPEG video transmission system
  • Performance analysis
  • Conclusions and future work

Paper target
  • Definition of a Video-over-IP adaptive-rate
    quality-controlled transmission system
  • Scenario BEST EFFORT Internet

Problems of Video-over-IP
  • From the user point of view
  • Available bandwidth discovery
  • Bandwidth variation
  • From the network point of view
  • TCP friendliness
  • Network utilization maximization

The idea
  • Use of
  • the TCP-friendly TFRC algorithm
  • to discover the available bandwidth
  • to be friendly with TCP sources sharing the same
    bottleneck link
  • the MPEG TM-5 rate control algorithm
  • to change the transmission rate according to the
    network congestion situation

A brief background
  • TCP-friendly TFRC algorithm
  • MPEG and TM-5

TFRC (TCP-Friendly rate control)
  • Target to control the rate of a real-time source
    in order to be friendly with TCP flows sharing
    the same bottleneck links
  • Equation-based protocol it estimates the
    throughput according to the following equation

TFRC declared objectives
  • TFRC was defined to support real-time traffic,
  • and to provide sources with a
  • rate-control algorithm to achieve
  • fairness towards TCP traffic

only the fairness aspects have been considered up
to now
no attention has been paid to real-time
sources using TFRC
TFRC protocol scheme
TFRC sender
TFRC receiver
  • TFRC receiver
  • PR calculates the loss rate
  • PR sends feedback to the TFRC sender every time
    it receives a packet
  • this allows RX to calculate the RTT and to know
    the loss rate
  • TFRC sender
  • divided into two parts TX and RX
  • this division not present in the original TFRC
  • the TFRC sender in mind of the TFRC authors was a
    GREEDY SOURCE, with always something to transmit
  • RX entity
  • applies the equation and proposes the maximum
    rate to the source
  • TX entity
  • receives from the source the packets to be
    transmitted, and the rate to apply in their

MPEG source and TM-5
  • MPEG video source is an adaptive-rate source
  • the emission rate can be tuned through the
    quantizer scale parameter (qsp), q
  • the most widely used algorithm to change the
    emission rate by varying q is the TM-5
  • The TM-5 rate control algorithm works in three
  • Target bit allocation
  • Rate control
  • Adaptive quantization

TM-5 Target bit allocation
  • This step estimates the number of bits available
    to encode the frames of the beginning GoP

TM-5 Rate control
  • It is performed macroblock by macroblock
  • It is based on the state of three virtual
    buffers, one for each kind of frame
  • Each virtual buffer is a counter having memory of
    the past
  • it is positive if credits have been accumulated
  • it is negative if debts have been accumulated
  • From the state of the virtual buffers, the
    reference value of q is set for each macroblock

TM-5 Adaptive quantization
  • This step modulates the reference value of the
    quantizer scale according to the spatial activity
    in the macroblock to be encoded

The MPEG video transmission system
  • Targets
  • the output bit rate has to follow the bandwidth
    available in the network
  • user requirements have to be met, in terms of
    encoding quality (mean PSNR and PSNR

Network Bandwidth Smoother
  • It receives the network bandwidth estimated by
    the TFRC
  • It has the aim of eliminating the high
    frequencies ofthis process
  • To this end, it uses a low-pass filter with an
    Exponential Wighted Moving Average (EWMA)

Rate/Quality MPEG Video source
Video source
Rate controller
MPEG encoder
RQ-source Rate Controller
  • Target to calculate the quantizer scale
    parameter for each macroblock, according to a
    given law
  • Input data the budget to be allocated to each
    beginning GoP
  • Three different Rate controller laws
  • rate controller using the classical
  • rate controller derived from
    , by imposing an hysteresis mechanism to
    guarantee better quality stability
  • rate controller derived from
    , by imposing the memory-less property at the
    beginning of each GoP

rate control mechanism
  • Rate controller applying an hysteresis mechanism
    to the classical TM-5
  • Hysteresis mechanism
  • divide the PSNR range in L levels, F1, F2, , FL
  • the frame quality must remain at the same PSNR
    level for at least H frames (H hysteresis
  • the frame quality can step by at most one PSNR
    level up or down if the PSNR associated to the
    quantizer scale suggested by RCTM5 does not
    belong to one of the allowed PSNR levels, the qsp
    providing the PSNR closest to the suggested one
    (at most one PSNR level up or down) will be chosen

The PROBLEM during the hysteresis period a large
number of credits or debts may be accumulated
rate control mechanism
  • Memory-less rate controller
  • Defined as an extension of the
  • Target to avoid the fact that, due to
    hysteresis, such a great number of credits or
    debts are accumulated that, when it is possible
    to change level (after H frames), the source will
    not follow the behavior required by the TFRC
  • The memory is deleted at the beginning of each GoP

Case study
360 km 2 ms
RQ source
  • Network topology
  • easy, but representing the worst case for the
    quality stability of the video source (the same
    source has to face up to congestion situation)
  • Movie
  • 90 minutes of The silence of Lambs, encoded
    with the GoP structure IBBPBB
  • Link capacity
  • 2 Mbits/s
  • Simulative approach
  • Network simulator ns-2
  • Video-trace generator for ns-2 (www.diit.unict.it/

Encoding quality levels
PSNR level F1 39.2, 49.2 dB
PSNR level F2 36.2, 39.2 dB
PSNR level F3 35.0, 36.2 dB
PSNR level F4 33.7, 35.0 dB
PSNR level F5 31.5, 33.7 dB
Rate processes
Loss process
PSNR process
Quality-level process
  • The paper defines an MPEG video transmission
    system for the best-effort Internet
  • TFRC rate control algorithm is used to discover
    the available bandwidth
  • Three TM5-like source rate controllers have been
    defined to follow the bandwidth calculated by TFRC

Peculiarities of our approach
Encoding video for transmission on the Internet
must follow a right tradeoff between
TCP-friendliness and encoding quality
Variation of encoding parameters does not provide
an infinitesimal fine tuning of the rate
TCP dynamics are deleterious for real-time video
Future works
  • TCP-friendliness evaluation
  • Introduction of channel encoding techniques (e.g.
    Forward Error Correction - FEC) to protect video
    from losses caused by the TFRC behavior (TFRC
    increases bandwidth until losses do not occur)

Support material
  • Material relating to this topic, and an extended
    version of this paper can be found at

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