1、 International Telecommunication Union ITU-T J.241TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (04/2005) SERIES J: CABLE NETWORKS AND TRANSMISSION OF TELEVISION, SOUND PROGRAMME AND OTHER MULTIMEDIA SIGNALS Measurement of the quality of service Quality of service ranking and measurement methods f
2、or digital video services delivered over broadband IP networks ITU-T Recommendation J.241 ITU-T Rec. J.241 (04/2005) i ITU-T Recommendation J.241 Quality of service ranking and measurement methods for digital video services delivered over broadband IP networks Summary This Recommendation specifies p
3、erformance requirements and objective measuring methods of QoS for the delivery of digital video services over broadband IP networks. The specified performance requirements are based on an IP QoS ranking at various levels, from “excellent“ to “out-of-service“. They rely on the objective end-to-end m
4、easurement of the values of a small number of parameters on the delivered IP streams, performed at the consumer premises equipment and relayed back to the head end. The recommended objective measurement methods and parameters are known to influence the Quality of Service delivered to the user. Sourc
5、e ITU-T Recommendation J.241 was approved on 6 April 2005 by ITU-T Study Group 9 (2005-2008) under the ITU-T Recommendation A.8 procedure. ii ITU-T Rec. J.241 (04/2005) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of telecommunication
6、s. The ITU Telecommunication Standardization Sector (ITU-T) is a permanent organ of ITU. ITU-T is responsible for studying technical, operating and tariff questions and issuing Recommendations on them with a view to standardizing telecommunications on a worldwide basis. The World Telecommunication S
7、tandardization Assembly (WTSA), which meets every four years, establishes the topics for study by the ITU-T study groups which, in turn, produce Recommendations on these topics. The approval of ITU-T Recommendations is covered by the procedure laid down in WTSA Resolution 1. In some areas of informa
8、tion technology which fall within ITU-Ts purview, the necessary standards are prepared on a collaborative basis with ISO and IEC. NOTE In this Recommendation, the expression “Administration“ is used for conciseness to indicate both a telecommunication administration and a recognized operating agency
9、. Compliance with this Recommendation is voluntary. However, the Recommendation may contain certain mandatory provisions (to ensure e.g. interoperability or applicability) and compliance with the Recommendation is achieved when all of these mandatory provisions are met. The words “shall“ or some oth
10、er obligatory language such as “must“ and the negative equivalents are used to express requirements. The use of such words does not suggest that compliance with the Recommendation is required of any party. INTELLECTUAL PROPERTY RIGHTS ITU draws attention to the possibility that the practice or imple
11、mentation of this Recommendation may involve the use of a claimed Intellectual Property Right. ITU takes no position concerning the evidence, validity or applicability of claimed Intellectual Property Rights, whether asserted by ITU members or others outside of the Recommendation development process
12、. As of the date of approval of this Recommendation, ITU had not received notice of intellectual property, protected by patents, which may be required to implement this Recommendation. However, implementors are cautioned that this may not represent the latest information and are therefore strongly u
13、rged to consult the TSB patent database. ITU 2005 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU. ITU-T Rec. J.241 (04/2005) iii CONTENTS Page 1 Scope 1 2 References. 1 3 Definitions 1 4 Abbreviations 1 5 Quali
14、ty of Service ranking and measurement methods for digital video services delivered over broadband IP Networks 2 5.1 Background. 2 5.2 Recommendation 2 Annex A System measurement model 3 Annex B End-to-end measurements . 4 B.1 Video receiver measurements. 5 B.2 Frame rate analysis. 5 Annex C IP layer
15、. 6 C.1 IP transport requirements 6 C.2 Video streaming IP service class 7 C.3 IP transport measurements . 7 C.4 IP end-to-end service availability. 8 C.5 IP network service classification 9 Appendix I Example of an IP network service classification . 9 ITU-T Rec. J.241 (04/2005) 1 ITU-T Recommendat
16、ion J.241 Quality of service ranking and measurement methods for digital video services delivered over broadband IP networks 1 Scope This Recommendation specifies performance requirements and objective measuring methods of QoS, for the delivery of digital video services over broadband IP networks. T
17、he performance requirements are based on an objective measurement of the values of a small number of parameters performed on the delivered IP streams at the consumer premises equipment. These parameters are known to influence the Quality of Service delivered to the user and they allow defining the m
18、easurements needed to evaluate the service quality degradation introduced by an IP network. The definition of a complete system model of a digital television system over an IP network, including the definition of the appropriate FEC technique to be employed, is outside the scope of this Recommendati
19、on. It is well recognized that perceived video quality is highly affected by the performance of FEC. Therefore, this Recommendation does not guarantee that the classification that it provides is sufficient for assessing the perceived quality on a TV broadcasting over IP system, since IP end-to-end n
20、etwork performance it is measured before FEC is applied. 2 References The following ITU-T Recommendations and other references contain provisions which, through reference in this text, constitute provisions of this Recommendation. At the time of publication, the editions indicated were valid. All Re
21、commendations and other references are subject to revision; users of this Recommendation are therefore encouraged to investigate the possibility of applying the most recent edition of the Recommendations and other references listed below. A list of the currently valid ITU-T Recommendations is regula
22、rly published. The reference to a document within this Recommendation does not give it, as a stand-alone document, the status of a Recommendation. ITU-T Recommendation G.1020 (2003), Performance parameter definitions for quality of speech and other voiceband applications utilizing IP networks. ITU-T
23、 Recommendation Y.1540 (2002), Internet protocol data communication service IP packet transfer and availability parameters. ITU-T Recommendation Y.1541 (2002), Network performance objectives for IP-based services. 3 Definitions This Recommendation defines the following term: 3.1 broadband IP network
24、: Access IP telecommunications network offered by ADSL, ADSL2+, VDSL, Optical Access Network, etc. 4 Abbreviations This Recommendation uses the following abbreviations: BER Bit Error Ratio CPE Customer Premises Equipment FEC Forward Error Correction IP Internet Protocol 2 ITU-T Rec. J.241 (04/2005)
25、IPER IP packet Error Ratio IPLR IP packet Loss Ratio MPEG Moving Picture Experts Group PLR Packet Loss Ratio QoS Quality of Service RTCP Real Time Control Protocol RTP Real Time Protocol SLA Service Level Agreement STB Set Top Box TCP Transmission Control Protocol UDP User Datagram Protocol VoD Vide
26、o on Demand 5 Quality of Service ranking and measurement methods for digital video services delivered over broadband IP Networks 5.1 Background Digital transport streams based on MPEG2 encoding have become the prevailing technology for augmenting the experience of digital television services, since
27、it allows combining the distribution of high quality digital television services with the opportunity for end users to enjoy real-time interaction with multimedia service platforms. As broadband fixed communication networks start to be extensively deployed in several countries, clear opportunities e
28、merge for extending this offer through transport based on IP protocols. The native shared-access and bidirectional capabilities of an IP network, in fact, offer an ideal environment for providing customers with full end-user interactivity and support for advanced services; this offers advantages ove
29、r traditional video streaming services. IP-based broadband communication networks thus provide another high-performance, bidirectional transport environment to transparently convey MPEG2-compliant video content. 5.2 Recommendation Methods for Quality of Service measurements for digital television se
30、rvices streamed in a broadband IP network should be tailored to the specific features of the transport services provided by an IP communication network. Annex A shows a conceptual block module of a system measurement model of a chain for IP transmission of television services. In this measurement mo
31、del, the Quality of Service should be measured end-to-end, namely, from the program injection point in the network, all the way to the Customer Premises Equipment (CPE). This provides readings that closely approximate the quality of service as it is delivered to the end user, and take into account t
32、he influence of the IP network on the video stream. There are two kinds of Quality of Service measurement to be taken at the video receiver. These are described in Annexes B and C. Annex B describes the recommended end-to-end measurements to be performed on the video stream after its IP packetized s
33、tructure is removed. Annex C describes the measurements to be performed on the video stream at its IP layer. ITU-T Rec. J.241 (04/2005) 3 Annex A System measurement model In its simplest form, the television services distribution model, in an IP network, consists of three parts: The Head-end: This i
34、ncludes all the devices and applications needed to produce the video signals that are sent into the network. The Transport Network: This transports the video signal to the end user CPEs. The CPE: This is an IP end point (usually an STB) that decodes the video signal and displays it on a television s
35、et normally connected to it. Explicit SLAs need to be established between the service provider and the telecommunications network operator for the transport of the video streams between the head-end and the transport network. Audio, video, data and interactive services can be delivered in the IP tra
36、nsport network if the head-end and the STBs provide the necessary compliance. All the services and standards are compatible with the TCP/IP stack; the IP network should guarantee the required performance level and it should provide some test point where it can be measured. This Recommendation assume
37、s that the quality of the input video signal that is delivered to the IP network is under the responsibility and control of the head-end. The head-end should inject the video streams in the network according to transport rules appropriate to the IP Network. These rules should define: Maximum packet
38、rate per stream; Maximum number of sustainable streams; Maximum bandwidth per stream (or packet rate for a given packet size); Transport protocol to be used; Frame size (transport layer); Packet size; Allowed inter-packet gap profile; Maximum burst size. On its side, the IP network should guarantee
39、the agreed service level for the delivery of video streams to end-users. In an IP network, Video on Demand (VoD) services are usually associated with unicast content distribution methods while television services are distributed by using IP multicast based protocols. IP transport protocol used for u
40、nicast distribution maybe UDP or TCP while multicast distribution is transported on top of UDP. The determination of the service level should be based on end-to-end measurements, which should provide information on: The quality offered to the user; The influence of the IP network on the video signal
41、. 4 ITU-T Rec. J.241 (04/2005) Figure A.1 shows the system measurement model that summarizes this approach. Figure A.1/J.241 System measurement model The following table describes the reference points A, B, C, and D shown in Figure A.1: Reference point Description A Video encoder B IP layer at head-
42、end (Raw IP data). C IP layer at CPE (Raw IP data). D Video decoder Annex B End-to-end measurements An IP network allows each CPE (STB) to also behave as a measurement end-point. This offers the valuable opportunity to have a measurement probe at each installed video CPE. Measurements and monitoring
43、 taken at the CPE are the ones closest to the users real experience of the service. Using a CPE as a measurement probe raises some point of attention since the CPE is not under the physical control of the network operator, and measurements may be affected by the users equipment (cable not well plugg
44、ed in vertical cabling issues, improper use of the home-network). The STB should have the capability to give additional information about the quality of the video signal that is being decoded. Receiver buffer fullness and frame rate are two important indicators of service availability and overall pe
45、rformance. CPEs measurements should be used to: Measure the end-to-end IP network performance; Measure the network performance at any hierarchical level or aggregation point through statistical analysis and data processing exploiting correlation among data; Estimate the video quality offered to the
46、end-user of the service; Perform dedicated test sessions using test signals for qualification and troubleshooting. ITU-T Rec. J.241 (04/2005) 5 As an example, some network operators currently perform end-to-end measurements at all the STBs available in their residential network, in order to evaluate
47、 end-to-end video service quality and network performance; STBs periodically send back frame rate and packet loss reports to provide a continuous quality feedback about the service in progress. B.1 Video receiver measurements The table below shows the parameters that should be measured at video rece
48、ivers to estimate video quality, as described in the system measurement model. These measurements can be used for all the assessments outlined above. Parameter Value Equipment Purpose Monitoring method Measurement path (Note) Video frame rate As required by the video standards STB Image quality In s
49、ervice through codec specific methods. Sampling From A to D Buffer underflows N/A STB Image quality, smooth play-out In service while playing video. Sampling Measure underflows events and percentage of service time spent by the STB in an “underflow“ state D Buffer overflows N/A STB Image quality, smooth play-out In service while playing video. Sampling Measure underflows events and percentage of service time spent by the STB in an “overflow“ state D Coding specific parameters N/A STB Image/Service quality In service while playing video
