1、 ATIS-0800041 IMPLEMENTERS GUIDE TO QOS METRICS ATIS is the leading technical planning and standards development organization committed to the rapid development of global, market-driven standards for the information, entertainment and communications industry. More than 250 companies actively formula
2、te standards in ATIS 20 Committees, covering issues including: IPTV, Service Oriented Networks, Home Networking, Energy Efficiency, IP-Based and Wireless Technologies, Quality of Service, Billing and Operational Support. In addition, numerous Incubators, Focus and Exploratory Groups address emerging
3、 industry priorities including “Green”, IP Downloadable Security, Next Generation Carrier Interconnect, IPv6 and Convergence. ATIS is the North American Organizational Partner for the 3rd Generation Partnership Project (3GPP), a member and major U.S. contributor to the International Telecommunicatio
4、n Union (ITU) Radio and Telecommunications Sectors, and a member of the Inter-American Telecommunication Commission (CITEL). For more information, please visit . Notice of Disclaimer Measurement Guidelines for DVB Systems, May 2001. Broadband Forum5: 26 TR-98, DSLHomeTMGateway Device Version 1.1 Dat
5、a Model for TR-069, September 2005. 27 TR-126, Triple-Play Services Quality of Experience (QoE) Requirements, December 2006. 28 TR-135, Data Model for a TR-069 enabled STB, Issue 1, December 2007. ISO/IEC6: 29 ISO/IEC 13818-1: Information Technology Generic coding of moving pictures and associated a
6、udio information: Systems, 2007. 30 ISO/IEC 13818-2: Information Technology Generic coding of moving pictures and associated audio information: Video, 2000. 31 ISO/IEC 13818-3: Information Technology Generic coding of moving pictures and associated audio information: Audio, 1998. 32 ISO/IEC 13818-4:
7、 Information Technology Generic coding of moving pictures and associated audio information: Conformance testing, 2004. 33 ISO/IEC 13818-9: Information Technology Generic coding of moving pictures and associated audio information: Extension for real-time interface for systems decoders, 1996. SCTE7: 3
8、4 SCTE 142, Recommended Practice for Transport Stream Verification, 2009. TeleManagement Forum8: 35 GB 938 R2.0, Best Practice: Video over IP SLA Management, October 2008. 4This document is available from the European Telecommunications Standards Institute (ETSI). 5These documents are available from
9、 the Broadband Forum. 6These documents are available from the International Organization for Standardization (ISO). 7This document is available at the Society for Cable Telecommunications Engineers (SCTE). . 8This document is available from the TeleManagement Forum. ATIS-0800041 4 TIA9: 36 TIA-921-A
10、, Network Model for Evaluating Multimedia Transmission Performance Over Internet Protocol, June 2008. 3 DEFINITIONS, ACRONYMS, transaction indicators, such as channel change delay; audio indicators; and multimedia indicators. 3.1.4 Quality of Service (QoS) Metrics: Measures of technical performance.
11、 Includes network QoS metrics, such as packet loss and application; and QoS metrics, such as CoD server errors. 3.2 Acronyms rather they are representative of important metrics in each of the four layers. If all of the metric values are within acceptable ranges for a given network, the QoE related t
12、o network performance will be acceptable. The actual thresholds for the various parameters that indicate acceptable performance levels needs to be “tuned” to a given network. The equipment and devices involved in end-to-end service delivery are typically not capable of analyzing all the layers of th
13、e IP stack necessary for measuring all the metrics within the four layers of the quality model. Some nodes provide simple traffic awareness (for example, RTP packet metrics), whereas other nodes and equipment provide awareness of the IPTV video application itself. The four-ATIS-0800041 10 layer qual
14、ity model is extended here to encompass a “network segment-focused” mapping model for critical QoS metrics. The diagram below outlines the mapping of the four quality layers to a virtual network model including segments: headend, network (or hub and video serving offices), access, and ITF (or premis
15、es networks up to the ITF). Figure 2: IP Video Network Segment Focus Quality Model A simplified view of the ATIS IIF quality layers that may be used at different measurement points is presented in Figure 3 below. More detailed specification of quality layers and measurement points are contained in A
16、TIS-0800004 2 and ATIS-0800008 4. Table 2 below provides some examples of important metrics and process settings that apply in each of the four network segments. ATIS-0800041 11 Table 2: Examples of Metrics in the Four Network Segments IPTV Quality Layers IP Video Network Segments HE Core/Metro Acce
17、ss Premise Content Compression: type, GOP, CBR/VBR. DPI analysis. Video MOS, Audio MOS, AV-MOS. Media stream PCR jitter, PSI data, Error Indicator. PCR jitter, PSI errors. PCR jitter, PSI errors, PID map analysis. PCR jitter, PSI errors, PID map analysis. Transmission Packet jitter; Loss rates, Dist
18、ance/Period analysis. Packet jitter; Loss rates, Distance/Period analysis. Packet jitter; Loss rates, Distance/Period analysis. Transaction IGMP Latency. IGMP Latency. Figure 3 presents a simplified view of quality layers and associated measurement points and shows examples of implementing network e
19、lements. Figure 3: Quality Layers and Measurement Points 4.3 Headend Quality Focus The HE receives content (typically broadcast video programming) from various sources, including land lines, satellite downlinks, and terrestrial/off-air links. Programming is then aggregated for further processing in
20、the HE, which typically includes decoding, combining, encoding, trans-coding, trans-rating, and preparation for distribution. Such items as the Group of Picture (GOP) size, compression technologies used, the particular encoders used, and the various target user profiles supported (for example, high
21、or standard definition) are implemented. These items establish the quality of the programming prior to it entering the distribution network. ATIS-0800041 12 One critical component in this context is the performance of the encoders, as their output forms the compressed content and creates the MPEG-2
22、TS. As mentioned, the Program Clock Rate (PCR) timing is critical for proper decoder performance. Excessive PCR jitter may be the result of a failing encoder. A Program Specific Information (PSI) data error condition may be the result of an improper encoder setup, where scrambling of the PSI table d
23、ata is on when it should be off. Error Indicator settings indicate problems with the input to an encoder. The accuracy of the encoding clock should be ensured to avoid problems. The stability of the encoder clock should be ensured to maintain PCR jitter below the design limit. The subjective quality
24、 of the content should be monitored prior to injection into the IPTV delivery system. This can be achieved using equipment that implements a validated Perceptual Quality Measurements (PQM) model. Thus, in the HE, the quality focus is on the content and video stream layers. Transport and transaction
25、quality would not be applicable. 4.4 Distribution Network Quality Focus In the distribution network core/metro/VHO QoS (see Figure 3) the focus is primarily the transport layer quality. Packet loss and jitter are the most critical metrics. Packet loss analysis should include period and distance anal
26、ysis with thresholds for maximum period and minimum distance tuned to a given network architecture. Re-transmission for lost packet recovery and packet-based Forward Error Correction (FEC) techniques all have limitations regarding these two metrics. The jitter should be maintained to limits such tha
27、t the ITF can still extract adequate timing information to remain synchronized with the encoder. In addition, content quality is a focus in those cases where local content is inserted into a program flow. Local content insertion is typically accomplished in hub offices. This process interrupts the n
28、ormal program, such as a broadcast service channel, and inserts such items as advertising, weather, and news. In this case, content quality again becomes an issue. In addition, if the insertion splicing process is not accomplished correctly, it could potentially affect video stream quality, resultin
29、g in excessive PCR jitter, packet loss, or a program gap. Furthermore, the subjective quality of the content should be monitored prior to injection into the IPTV delivery system. This can be achieved using equipment that implements a validated PQM model. 4.5 Access Quality Focus The access network s
30、egments involve video stream, transport, and transaction quality layers, with an emphasis on transport quality. Various access network technologies may be employed, such as fiber-to-the home, various Digital Subscriber Loop technologies (xDSL), and wireless. Many of these technologies are susceptibl
31、e to noise impairments, which may cause packet loss events. Distance and period analysis is important, but correlation with the physical layer performance of the access technology for example, VDSL is critical when conducting a root cause investigation. At this network segment, it becomes critical t
32、o identify and separate network performance issues from content issues. Transaction quality also becomes a focus, because the accumulated effects of the distribution networks are visible and the effects of edge aggregation activities are present. However, packet loss metrics are primarily the focus.
33、 ATIS-0800041 13 4.6 Premises Quality Focus In the premises network segment, including the ITF, the accumulated effects of the entire distribution network are visible after all error correction. The quality layer focus includes all four layers, but experience shows that the most significant issues o
34、ccur at the transport quality layer in the form of packet loss. All metrics listed in the four-layer quality model remain critical as their measurement in this network segment allows QoS metric values to most closely indicate the actual impact on QoE. For example, when packet loss events exceed the
35、distance and period thresholds set for a given network architecture, subscribers see impairments. It becomes possible to determine whether transaction latencies fall within acceptable limits. Performing root-cause analysis will point to either a source or network performance issue. A Mean Opinion Sc
36、ore (MOS) analysis more closely represents the actual QoE, because all the accumulated impact of the distribution network is visible using the MOS analysis algorithms in this network segment. A test point at the ITF includes impairments introduced by the in-home distribution network that remain invi
37、sible, as opposed to a test point at the entrance to the home that would not show effects of the in-home distribution technology. 4.7 Linear (Broadcast) IPTV Measurement Points Figure 4 below indicates various reference measurement points applicable to Linear (broadcast) service. This figure is base
38、d upon ATIS-0800004 2, Figure 10, and ATIS-800008 4, Figure 4. ATIS-0800041 14 ContentProviderAccessNetworkCustomerDomainServiceProviderVideoHeadEndCoreVideoHubOffice-VideoServingOfficeMetroSTBRes Gateway and ). Higher-layer metrics may be instrumented at these points as discussed in Table 3 below.
39、Profile naming convention: Q = Quality profile, the number 1-4 = a focus on the network segments to facilitate instrumentation. The four network segments are: Segment 1: Headend; Segment 2: Core Metro; Segment 3: Access Network; Segment 4: Premise. The specific metrics are grouped into two groups: a
40、 = advanced and b = basic, allowing for further flexibility in instrumentation. Table 3: Profile Definitions Profile Name Q1a Q1b Q2a Q2b Q3a Q3b Q4a Q4b Content-Basic Metrics X X X X Content-Advanced Metrics X X Media Stream- Basic Metrics X X X X X X X X Media Stream- Advanced Metrics X X X X Tran
41、smission-Basic metrics X X X X X X Transmission-Advanced Metrics X X X Transaction-Basic Metrics X X X X Transaction-Advanced Metrics X X Metric groups are defined in Table 4. The quality profiles are content, media stream, transmission, and transaction. 5.1 Profile Q1b and Q1a Description Profile Q
42、1b focuses upon the egress quality at the Video Head End or at a local content insertion point such as a Video Hub Office. Instrumentation would typically be at test points 3 and 5 and includes basic metrics for both content metrics and media stream metrics as defined in Table 4 below. This profile
43、will monitor PCR performance and catch a PSI problem such as a table scrambling left on incorrectly. Establishing the quality of the media stream before it enters the distribution network is critical. ATIS-0800041 16 Profile Q1a expands this egress quality focus to include the advanced metrics for m
44、ore in-depth analysis and quality monitoring. This advanced profile may have more applicability at the egress of a local program insertion location and test access point than at the output of the headend. 5.2 Profile Q2a and Q2b Description Profiles Q2a and Q2b focus on the backbone distribution (co
45、re/metro/VHO QoS) network segments, where the focus is upon transport, assuming that the content has been monitored up-stream and transaction quality does not really apply. Media stream quality is included since local program insertion activities will affect the media stream quality layer. Instrumen
46、tation would typically be at test points A1, B, B1,C, and C1. 5.3 Profile Q3a and Q3b Description Profiles Q3a and Q3b focus on media stream and transmission quality and add transaction quality applicable to the edge and access network segments. In the access network, transmission issues may be most
47、 dominant, but a service provisioning test includes transaction performance validation as well. Instrumentation would typically be at test points C1, D, D1,and E. 5.4 Profile Q4a and Q4b Description Profiles Q4a and Q4b focus on all four quality layers appropriate at the premise where the accumulate
48、d impacts of all network segments come together. Test points at the entrance to the premise E and at the ITF F are applicable. Test point F can isolate the effects of the in-home distribution network as well. 5.5 Metric Groups The metrics in Table 4 are a sampling of metrics contained and defined in
49、 ATIS-0800008, QoS Metrics for Linear Broadcast IPTV. This was done in order to simplify instrumentation and provide focus for the most essential metrics. In-depth trouble-shooting may involve all of the metrics in ATIS-0800008. Metric group naming convention: C = content, MS = media stream, TM = transmission, and TA = transaction. ATIS-0800041 17 Table 4: Metric Groups Metrics, Table 2 C-Basic C-Advanced MS Basic MS Advanced TM Basic TM Advanced TA Basic TA Advanced 1-RTP loss rate before Pkt EC 14-PPDV X 2- RTP los
