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ITU-T Study Group 9 (Study Period 2005-2008) |
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Question 2/9 - Measurement and control of the Quality of Service (QoS) for television transmission on contribution and distribution networks |
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1 Motivation
ITU-T has adopted several Recommendations for the transmission of digital television signals for contribution, primary distribution and secondary distribution applications. However, a number of issues related to the measurement, monitoring and control of digital and mixed analogue-digital television transmission chains still remain to be solved.
- ITU-R has recommended methods for the subjective assessment of picture quality (see for instance Recommendation BT.500-11). There is a need to confirm that those subjective assessment methods are equally applicable to the case of television transmission on digital or mixed analogue-digital chains.
- In the digital domain, ITU-R SG 6 and ITU-T SG 12 and SG 9 have been also studying together, in a Video Quality Experts Group, the identification of appropriate parameters and algorithms that are representative of digital picture quality, as well as the correlation of the objective measurement of those parameters to the subjective picture quality. This
work has resulted in Recommendations J.143 and J.144.
- Concerning the measurement of the overall Quality of Service (QoS), in the analogue world there is a direct relationship between network impairments and the QoS of television transmission. This is not the case for digital transmission networks. Furthermore, there is a need to identify the group of parameters that can provide objective measurement of the overall QoS and continuous in-service monitoring and control of it along the transmission chain for digital and for mixed analogue-digital television transmission.
- Concerning transmission of digital signals, MPEG-2 Transport Streams may be subject to
degradation in signal quality (particularly jitter) after transport over telecommunication networks.
This degradation may be caused by inherent effects of telecommunication networks such as stuffing
jitter in PDH networks, stuffing jitter and pointer actions in SDH networks, or cell delay variation
in ATM-based networks. In order to ensure reliable limits for these effects on MPEG-2 Transport
Streams, enabling safe operation of terminals and equipment at the end of the chain
(e.g. modulators for digital television transmitters if using SFN networks), standardized templates
for maximum permitted signal deviations are required.
- For some objective video quality models to operate effectively, the source and processed
video sequences need to be aligned in the spatial and temporal dimensions. (In some cases
such video registration can be treated separately from objective perceptual video quality
assessment). Furthermore, in order to test processed video sequences to see if they meet
validation test requirements (e.g., maximum spatial and temporal shifts), reliable methods
to measure video registration are required. Therefore, it would be helpful and necessary to
develop methods for video registration.
- Sometimes there is also a need for calibration methods in order to identify any
modifications introduced into the video signals (e.g. gain and offset).
2 Question
- Are the methods recommended or studied by ITU-R Study Group 6 for subjective assessment of digital picture quality also applicable to the area of activity of Study Group 9?
- If they are not, should any different or additional methods for picture quality assessment be recommended by Study Group 9, as specifically applicable to impairments introduced by digital or mixed analogue-digital television transmission chains?
- How should the methods developed by ITU-R SG 6, or extended by SG 9, for subjective assessment be applied to digital or mixed analogue-digital transmission chains?
- Which parameters and algorithms are representative of digital picture quality and how does the objective measurement of them correlate to subjective picture quality? (This work is to be carried out in cooperation with the Video Quality Experts Group.)
- How should the objective measurement of impairments introduced by digital or mixed analogue-digital transmission networks be carried out?
- Which network parameters should be used to provide objective measurement of the overall QoS and should be the basis for continuous in-service monitoring along the transmission chain both for digital and for mixed analogue-digital television transmission?
- Which network parameters can be dynamically adjusted for the supervision and control of the overall QoS in digital television transmission networks and how can such supervision and control be implemented in operation?
- What are the appropriate jitter/wander values for MPEG-Transport Streams demapped from telecommunication networks and what parameter tolerances need to be specified?
- What methods can be used for video registration of source and processed sequences for
use in objective video quality assessment?
- What methods can be used for video calibration?
- What are the necessary test materials and test signals
required for video registration and calibration?
- What trade-offs are inherent in different registration and
calibration methods with respect to such factors as speed, accuracy and
complexity and what are the effects on accuracy when limited information
is available for video registration and calibration?
3 Tasks
A new draft Recommendation should be ready before the end of 2005. Others should be ready before the end of 2006.
An up-to-date status of work under this Question is contained in the SG 9 Work Programme.
4 Relationships
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Recommendations: J-series, P-series, ITU-R BT-series
- Questions: 14/9
- Study groups: ITU-T Study Groups 12, 13, 15 and 16 and ITU-R SG 6.
Part of the work will be performed in cooperation with the Video Quality Experts Group
- Standardization bodies: ISO/IEC
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