IPTV Video Quality: QoS and QoE — February 2007
Multimedia Research Group (MRG, Inc), February 2007, Pages: 137
As IPTV operators confront increased competition from cable and satellite, they are discovering that video quality can be a crucial differentiating factor that attracts and keeps customers. Yet IPTV operators have also found that there are many parts of the systems where video quality and packet-flow can be compromised, causing major impact on consumers’ Quality of Experience (QoE).
This report report addresses how to acquire and maintain the highest video quality throughout the IPTV distribution network and in the home using both MPEG-4 AVC and MPEG-2 technologies. It provides both operational and technical insight into how to design, test, operate and monitor an IPTV network for the sake of achieving the highest quality SDTV (Standard Definition TV) and HDTV (High Definition TV) using a bandwidth-budget that is shared with other triple-play services. The report also focuses on large, medium and small IPTV systems, and reveals answers to Quality of Service (QoS) and Quality of Experience (QoE) issues in the planning, development and operational stages of IPTV services.
“This is a seminal work,” states Len Feldman, MRG Director of IPTV Analysis. “It tackles a problem for IPTV that has not previously been approached; and it brings a new level of operational simplicity to the complexities of an IPTV ecosystem.” The IPTV domains examined include: Acquisition/ingest, processing, storage, control, distribution, edge, and customer premises. The report also digs deeply into the MPEG-4 and MPEG-2 architectures as a means to demonstrate how packet restoration, fast-channel-change and other issues are accomplished; and at what cost for SDTV (Standard Definition TV), HDTV (High Definition TV), and for shared triple-play services. It also presents both operational and technical tools on how to design, test, operate and monitor a quality-centric IPTV network.
“No other available IPTV report goes into this depth or breadth on video quality,” states Gary Schultz, President, MRG. “This is both a business report and a technical report allowing IPTV operators to gain maximum value from their IPTV system investment from the first day of operation."
Over 20 companies contributed to this report and numerous service providers, including Alcatel-Lucent, Amino, AT&T, Cisco/ Scientific Atlanta, Harmonic, Harris, Modulus, Motorola, Tandberg, Optibase, Siemens/Myrio, Spirient, Thomson, Verimatrix, Widevine, and others.
1 Executive Summary
1.1 Purpose
1.2 Situation
1.3 IPTV Observation Relating to Quality
1.4 Key Recommendations
2 Overview of Video and Video Quality
2.1 IPTV Market and Technology Situation
2.1.1 The Drive for Video Quality
2.1.2 Issues Interfering with Scaleable Deployment of IPTV
2.2 Video Content Challenges Are Increasing
2.3 Definitions: IPTV, Video Quality, Video Quality of Service and Quality of Experience
2.3.1 Video Quality (VQ)
2.3.2 Video Quality of Service (V-QoS)
2.3.3 Quality of Experience (QoE)
2.3.4 Non-Video Factors Affecting Quality of Experience
3 IPTV Architecture and Reference Model
3.1 IPTV Domains
3.2 End-to-End IPTV Ecosystem Architecture
3.3 ISO/OSI Communications Reference Model as Relates to IPTV
4 The IPTV Delivery Ecosystem and Video Quality
4.1 Content Development and Production Domain
4.2 Acquisition Domain
4.2.1 Characteristics of the Acquisition Domain
4.2.2 Types of Source Content
4.2.3 Variables that Affect Video Quality in the Acquisition Domain
4.3 Content Processing Domain
4.3.1 Characteristics of the Content Processing Domain
4.3.2 Video Encoding and Compression
4.3.3 Bandwidth Conservation Techniques Associated with Video Encoding
4.3.4 Variables that Affect Video Quality in the Content Processing Domain
4.4 Storage Domain
4.4.1 Characteristics of the Storage Domain
4.4.2 Variables Affecting Video Quality in the Storage Domain
4.5 Control Domain
4.5.1 Characteristics of the Control Domain
4.5.2 Variables Affecting Video Quality in the Control Domain
4.6 Distribution Domain
4.6.1 Characteristics of the Distribution Domain
4.6.2 Variables Affecting Video Quality in the Distribution Domain
4.7 Network Edge and Access Domain
4.7.1 Characteristics of the Network Edge and Access Domain
4.7.2 Variables Affecting Video Quality in the Edge and Access Domain
4.8 Customer Premises Domain
4.8.1 VQ and QoE Impact at the Customer Premises Domain
4.9 IPTV Concerns that Span Multiple Domains
4.9.1 Video Characteristics and Functionalities Occurring Across Multiple Domains
4.9.2 V-QoS and QoE Strategies and Techniques Used Across Multiple Domains
5 Test and Measurement for VQ, V-QoS and QoE
5.1 Video Quality Measurement
5.1.1 Video Signal Parameters
5.2 Transport and Video Quality-of-Service Measurements
5.3 Quality of Experience: Measurement of Interactivity
5.4 Quality of Experience: Holistic View
5.4.1 Comparing Video Input with Video Output
5.5 IPTV QoE: Qualitative and Perceptual Measurements
5.6 Test and Measurement Across the IPTV Ecosystem
6 Conclusions
6.1 Complex Ecosystem to Deliver MPEG-4 Video
6.2 Quality of Experience (QoE) is Both Measurable and Subjective
6.3 Data Errors Occurring in the Network Have Major Effect on V-QoS
6.4 The Choice of MPEG Transport Method Has an Effect on QoE
6.5 Standards for QoE
7 Recommendations for Maximizing Video Quality
7.1 Summary of Recommendations
7.2 Acquisition Recommendations
7.2.1 Be Prepared for Stringent Ingest Requirements From Video Programmers
7.2.2 Begin Testing Before the Encoder
7.2.3 Pre-Process Video Content into a Common Format
7.2.4 Digital Transport and Backhaul
7.3 Headend Design Recommendations
7.3.1 Establish the Video Service Lineup First
7.4 Video Encoding Recommendations
7.4.1 For Distribution, Encode to the MEG-4 AVC/H.264 Format
7.4.2 Establish Parameters for Video Content Errors
7.4.3 Carefully Evaluate the Options for Transcoding
7.4.4 Smoothing the Video Stream
7.5 Network Design Recommendations
7.5.1 Service Level Agreements
7.5.2 Design the Network to Accommodate HDTV, End-to-End
7.5.3 Establish Bandwidth Budgets
7.5.4 Remember to Budget for Non-Video Traffic
7.5.5 Additional Network Considerations that Impact VQ & V-QoS
7.6 Test and Measurement Recommendations
7.6.1 Deploy with a Full-Time Test and Measurement System
7.6.2 Recommended Placement of Test and Measurement Systems
7.6.3 Test for Impairments at the Physical Layer
7.6.4 Testing to Rigid Technical Standards is Not Enough
7.6.5 Perform Anecdotal Consumer Testing
7.7 CPE Recommendations
7.7.1 Operators Must Follow the STB Recommendations of Their Software Suppliers
7.7.2 Policy Management at the Set-top Box Level
7.7.3 Correcting MPEG Video Errors in the Set-top Box
7.7.4 Minimizing the Effect of Network Errors in the Set-top Box
7.7.5 Network Termination Device
7.8 Quality of Service Recommendations
7.9 Quality of Experience Recommendations
7.9.1 Channel Change Times
7.9.2 Synchronization of Audio and Video
7.9.3 Prioritization of Service Traffic
7.9.4 MPEG Transport Streams
7.9.5 Implement Policies that Mitigate Network Issues Resulting from Oversubscription
7.9.6 Content Recommendations
7.10 Recommendations that Impact Multiple IPTV Domains
7.10.1 Implement Redundancy
7.10.2 Consider Established IPTV Architecture Reference Standards
7.10.3 Balance the Need for Standards Against the Virtues of Proprietary Solutions
8 Appendix 1: IP Communications Concepts Which Relate to Video Applications
8.1 ISO/OSI Basic Reference Model
8.2 IP Networking Standards
8.2.1 IGMP
8.2.2 RTSP
8.2.3 RTP
8.2.4 RTCP (Real-Time Transport Control Protocol)
8.2.5 UDP
9 Appendix 2: Video and Video Communications Standards
9.1 MPEG Video
9.1.1 MPEG Video Stream Structure
9.1.2 MPEG-2
9.1.3 MPEG-4
9.1.4 Other Video Standards
9.1.5 VC-1
9.1.6 MPEG-7 and MPEG-21
9.2 MPEG Transport
9.2.1 Approaches to MPEG Transport
9.2.2 Advocacy for MPEG-2 Transport
9.2.3 MPEG-2 Transport Steam Encapsulation
10 Appendix 5: IPTV Vendors
10.1 Video Networking Suppliers
10.2 Headend and Encoder Suppliers
10.3 IPTV Middleware Suppliers
10.4 Content Protection (Encryption, Watermarking) Suppliers
10.5 IPTV Network Suppliers
10.6 Test and Measurement
10.7 Professional Services
11 Appendix 6: Glossary of Terms
12 Index of Companies
Table of Figures
Figure 1-1: Domains Acquisition, Storage, Control and Distribution
Figure 1-2: Makeup of MPEG Video – Key to Controlling Packet Loss & Jitter
Figure 1-3: Comparison of MPEG-2 vs. MPEG-4 Video Quality
Figure 1-4: Comparing MPEG-2 and MPEG-4 Over DSL
Figure 1-5: Potential Sample Points Across The IPTV Ecosystem
Figure 3-1: Domains 1-5: Acquisition, Processing Storage, Control and Distribution
Figure 3-2: Domains 5-7: IPTV Distribution, Network Edge & Access and Customer Premises
Figure 3-3: IPTV Set-top Box Architectural Diagram
Figure 3-4: Hypothetical Tier-1 Operator with National (Super) Headend, Regional and Local Video Facilities
Figure 4-1: Example of Colors that are Outside of Established Color Parameters
Figure 4-2: Comparison of MPEG-2 vs. MPEG-4 Video Quality
Figure 4-3: Constant Bit-Rate Encoding
Figure 4-4: Illustration of How CF-CBR Limits Bandwidth Requirements
Figure 4-5: Aggregated Content Bundled Using CF-CBR
Figure 4-6: Embedding of Watermarks During Video Encoding
Figure 4-7: Application of Watermarks in the IPTV Ecosystem
Figure 4-8: Encrypted vs. Unencrypted Video
Figure 4-9: 1-D FEC Examples That Can Be Corrected
Figure 4-10: 1-D Example That Cannot Be Corrected
Figure 4-11: 2-D FEC Examples That Can Be Corrected
Figure 4-12: 2-D FEC Examples That Can Be Corrected
Figure 5-1: Holistic View of IPTV QoE
Figure 5-2: Potential Sample Points Across The IPTV Ecosystem
Figure 7-1: Comparing MPEG-2 and MPEG-4 Over DSL
Figure 7-2: Comparison of DSL Ability to Accommodate MPEG-2 and MPEG-4 Video
Figure 8-1: OSI ISO 7-Layer Basic Reference Model
Figure 9-1: Model for MPEG-2 Systems
Figure 9-2: Structure of MPEG Video
Figure 9-3: Data Loss Propagation in MPEG-2 Video Streams
Figure 9-4: Minimal MPEG-2 Transport Stream
Table of Tables
Table 3-1: Mapping the 7-Layer OSI Basic Reference Model to Video
Table 4-1: Home Network QoS Support
Table 8-1: ISO/OSI Model – Definitions and Functions of Each Layer In The Model
1.1 Purpose
This report is about IPTV video quality and the quality of the IPTV experience. To frame the discussion, this report provides three separate but nested definitions relating to video quality that are of highest relevance to the business success of an IPTV service provider:
Video Quality (VQ), which refers to the video content itself.
Video Quality of Service (V-QoS), which refers to the error-free video delivery from the operator’s facilities to the customer premises over the broadband wide-area network.
Quality of Experience (QoE), refers to the overall IPTV user experience, including application responsiveness, functionality, usability and the service context that surrounds it. Unlike VQ and V-QoS, which are each subject to measurement and conformance to specific metrics, QoE is ensured by using a combination of objective, testable criteria and subjective, anecdotal criteria that reflect the performance of the entire IPTV delivery ecosystem.
Only by ensuring high levels of all three, can IPTV service providers begin to capture new subscribers and keep them loyal. Because MPEG-2 and MPEG-4 AVC are similar technologies, this report includes information for both MPEG-2 and MPEG-4 AVC operations. However, the emphasis in this report is on MPEG-4 AVC, since most (if not all) new IPTV systems are forecasted to use MEG-4 AVC from 2007 forward.
1.2 Situation
Telcos are fighting an uphill and increasingly fierce battle against incumbent competitors, so VQ/V-QoS and QoE are key considerations. To deliver video services, they must not only engineer their networks more deliberately and monitor them more carefully than ever before, they also must quickly come up to speed with unfamiliar IPTV infrastructure, such as the headend, TV-enabling software and CPE.
Complicating matters is the fact that many crucial IPTV infrastructure and service-enabling elements are immature and have yet to be proven in scaled production deployments, which creates the risk of unexpected problems that affect VQ and QoE but don’t necessarily have quick fixes. We specifically make reference to IPTV middleware and interactive television applications.
1.3 IPTV Observations Relating to Quality
Because the IPTV ecosystem is complex, this report breaks it up into seven domains, which are identified in Section 3 and discussed in detail in Section 4. The complexity of this ecosystem makes it very expensive to implement. To minimize capital equipment and software costs at deployment, IPTV operators assume an oversubscription model – deploying enough equipment to serve under average conditions with statistically-determined peaks, as opposed to being designed for full-time peak capacity.
The underprovisioning associated with the oversubscription model forces operators to balance video quality against costly and scarce infrastructure resources while striving to attract consumers from competing options and keep them loyal. IPTV delivery has inherent sensitive dependencies between video encoding (compression), the bit-rates available for the delivery of aggregate and individual streams, the method of video transport, and the decoding of video.
Delivery errors attributable to the network are responsible for a majority of V-QoS and QoE issues. Unlike data, V-QoS parameters must go beyond the traditional datacomm parameters such as cyclical redundancy checking, to accommodate long sessions and a mix of different types of content.
Figure 1-2: Makeup of MPEG Video — Key to Controlling Packet Loss & Jitter
Source: Swiss Federal Institute of Technology
An MPEG-2 video stream is a hierarchically structured sequence of pictures (see Figure 1-2). The sequence is composed of several pictures. Each picture is in turn composed of slices, which are series of macroblocks.
Each macroblock (16 x 16 pixels) contains four blocks (4 x 4 pixels) of luminance samples and two, four or eight blocks of chrominance samples, depending on the chrominance format.
The MPEG-4 standard was also developed by the MPEG organization, and is similar to MPEG-2 in that it also uses I-, B- and P-Frames to form GoPs that are packetized and encapsulated for delivery over an IP network.
Finally, the architectural standards, test metrics and implementation best practices that impact IPTV video quality are either in the process of being adapted from non-IPTV digital television standards; or are still in the proposal stage and therefore still fluid; or they are lacking altogether. Fortunately, MPEG video content reflects well-defined standards for the structure and packaging of the digital video content itself.
However, operators should not be lulled into having a false sense of security by the current standards and proposals. Metrics for network-related QoS errors such as jitter and packet loss, and for QoE issues such as latency, are much more stringent for IPTV than many of the existing standards allow. Some existing standards, in fact, were established for IP voice, not video, and don’t take TV basics like channel change into account.
Alcatel-Lucent,
Amino,
AT&T,
Cisco/ Scientific Atlanta,
Harmonic,
Harris,
Modulus,
Motorola,
Tandberg,
Optibase,
Siemens/Myrio,
Spirient,
Thomson,
Verimatrix,
Widevine
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