1、 INTERNATIONAL TELECOMMUNICATION UNION ITU-T J.133TELECOMMUNICATION STANDARDIZATION SECTOR OF ITU (07/2002) SERIES J: CABLE NETWORKS AND TRANSMISSION OF TELEVISION, SOUND PROGRAMME AND OTHER MULTIMEDIA SIGNALS Transport of MPEG-2 signals on packetised networks Measurement of MPEG-2 transport streams
2、 in networks ITU-T Recommendation J.133 ITU-T J-SERIES RECOMMENDATIONS CABLE NETWORKS AND TRANSMISSION OF TELEVISION, SOUND PROGRAMME AND OTHER MULTIMEDIA SIGNALS General Recommendations J.1J.9 General specifications for analogue sound-programme transmission J.10J.19 Performance characteristics of a
3、nalogue sound-programme circuits J.20J.29 Equipment and lines used for analogue sound-programme circuits J.30J.39 Digital encoders for analogue sound-programme signals J.40J.49 Digital transmission of sound-programme signals J.50J.59 Circuits for analogue television transmission J.60J.69 Analogue te
4、levision transmission over metallic lines and interconnection with radio-relay links J.70J.79 Digital transmission of television signals J.80J.89 Ancillary digital services for television transmission J.90J.99 Operational requirements and methods for television transmission J.100J.109 Interactive sy
5、stems for digital television distribution J.110J.129 Transport of MPEG-2 signals on packetised networks J.130J.139 Measurement of the quality of service J.140J.149 Digital television distribution through local subscriber networks J.150J.159 IPCablecom J.160J.179 Miscellaneous J.180J.199 Application
6、for Interactive Digital Television J.200J.209 For further details, please refer to the list of ITU-T Recommendations. ITU-T Rec. J.133 (07/2002) i ITU-T Recommendation J.133 Measurement of MPEG-2 transport streams in networks Summary MPEG-2 Transport Streams that are transmitted over any real networ
7、ks are exposed to certain effects caused by the network components which are not ideally transparent. One of the predominant effects is the acquisition of jitter in relation to the PCR values and their position in the TS. This Recommendation specifies measurements that enable determination of this j
8、itter. Source ITU-T Recommendation J.133 was prepared by ITU-T Study Group 9 (2001-2004) and approved under the WTSA Resolution 1 procedure on 29 July 2002. ii ITU-T Rec. J.133 (07/2002) FOREWORD The International Telecommunication Union (ITU) is the United Nations specialized agency in the field of
9、 telecommunications. 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 T
10、elecommunication Standardization 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 som
11、e areas of information 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 recognize
12、d operating agency. INTELLECTUAL PROPERTY RIGHTS ITU draws attention to the possibility that the practice or implementation 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 Intelle
13、ctual Property Rights, whether asserted by ITU members or others outside of the Recommendation development process. 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. H
14、owever, implementors are cautioned that this may not represent the latest information and are therefore strongly urged to consult the TSB patent database. ITU 2002 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without the prior written permission of ITU
15、. ITU-T Rec. J.133 (07/2002) iii CONTENTS Page 1 Scope 1 2 References. 1 2.1 Normative references 1 2.2 Informative references 1 3 Abbreviations and acronyms 1 4 System clock and PCR measurements 1 4.1 Reference model for system clock and PCR measurements 1 4.2 Measurement descriptions 3 4.3 Program
16、 Clock Reference Frequency Offset (PCR_FO) 3 4.4 Program Clock Reference Drift Rate (PCR_DR) 4 4.5 Program Clock Reference Overall Jitter (PCR_OJ) 4 4.6 Program Clock Reference Accuracy (PCR_AC) 5 Appendix I PCR-related measurements 6 I.1 Introduction 6 I.2 Limits 6 I.3 Equations 7 I.4 Mask . 8 I.5
17、Break frequencies . 9 I.6 Further implicit limitations. 10 I.7 Measurement procedures 11 I.7.1 PCR_Accuracy (PCR_AC) 13 I.7.2 PCR_drift_rate (PCR_DR). 14 I.7.3 PCR_frequency_offset (PCR_FO) . 14 I.7.4 PCR_overall_jitter measurement 15 I.8 Considerations on performing PCR measurements 15 I.9 Choice o
18、f filters in PCR measurement . 17 I.9.1 Why is there a choice? 17 I.9.2 Higher demarcation frequencies. 18 I.9.3 Lower demarcation frequencies . 18 ITU-T Rec. J.133 (07/2002) 1 ITU-T Recommendation J.133 Measurement of MPEG-2 transport streams in networks 1 Scope A MPEG-2 Transport Stream that is tr
19、ansmitted over any real network is exposed to certain effects caused by the network components which are not ideally transparent. One of the predominant effects is the acquisition of jitter in relation to the PCR values and their position in the TS. The four measurement parameters defined in the fol
20、lowing describe the various jitter components which can be differentiated by demarcation frequencies. 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 publicati
21、on, the editions indicated were valid. All Recommendations 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 cu
22、rrently valid ITU-T Recommendations is regularly published. The reference to a document within this Recommendation does not give it, as a stand-alone document, the status of a Recommendation. 2.1 Normative references 1 ITU-T Recommendation H.222.0 (2000) | ISO/IEC 13818-1: 2000, Information technolo
23、gy Generic coding of moving pictures and associated audio information: Systems. 2 ETSI TR 101 290 V1.2.1 (2001), Digital Video Broadcasting (DVB); Measurement guidelines for DVB systems. 2.2 Informative references 3 ISO/IEC 13818-9:1996, Information technology Generic coding of moving pictures and a
24、ssociated audio information Part 9: Extension for real time interface for systems decoders. 3 Abbreviations and acronyms This Recommendation uses the following abbreviation: PCR Program Clock Reference 4 System clock and PCR measurements 4.1 Reference model for system clock and PCR measurements This
25、 clause presents a reference model (see Figure 1) for any source of a Transport Stream (TS) concerning the generation of PCR values and delivery delays. It models all the timing effects visible at the TS interface point. It is not intended to represent all the mechanisms by which these timing effect
26、s could arise in real systems. 2 ITU-T Rec. J.133 (07/2002) J.133_F01PCR counterPCR inaccuracy sourceMp,i+ABCReference clockf = 27 MHz + fdev(t)Np,iD + JiDelivery timingdelayFigure 1/J.133 Reference model Reference points are indicated by dashed lines. This is a model of an encoder/multiplexer (up t
27、o reference point B) and a physical delivery mechanism or communications network (between reference points B and C). The components of the model to the left of reference point B are specific to a single PCR packet identifier (PID). The components of the model to the right of reference point B relate
28、 to the whole Transport Stream. Measuring equipment can usually only access the TS at reference point C. The model consists of a system clock frequency oscillator with a nominal frequency of 27 MHz, but whose actual frequency deviates from this by a function fdev (p,t). This function depends on the
29、time (t) and is specific to a single PCR PID (p). The “Frequency Offset PCR_FO“ measures the value of fdev(p,t). The “Drift Rate PCR_DR“ is the rate of change with time of fdev(p,t). The system clock frequency oscillator drives a PCR counter which generates an idealized PCR count, Np,i. p refers to
30、the specific PCR PID p, and i refers to the bit position in the Transport Stream. To this is added a value from a PCR inaccuracy source, Mp,i, to create the PCR value seen in the stream, Pp,i. The simple relationship between these values is: ipipipMNP,+=(1) Mp,i represents the “Accuracy PCR_AC“. The
31、 physical delivery mechanism or communications network beyond point B introduces a variable delay between the departure time Tiand the arrival time Ui of bits: iiiJDTU +=(2) In the case of a PCR, Uiis the time of arrival of the last bit of the last byte containing the PCR base (see 2.4.3.5 of ITU-T
32、Rec. H.222.0 | ISO/IEC13818-1 1). D is a constant representing the mean delay through the communications network. Jirepresents the jitter in the network delay and its mean value over all time is defined to be zero. Ji+ Mp,iis measured as the “Overall Jitter PCR_OJ“. In the common case where the Tran
33、sport Stream is constant bitrate, at reference point B, the Transport Stream is being transmitted at a constant bitrate Rnom. It is important to note that in this reference model this bitrate is accurate and constant; there is no error contribution from varying bitrate. This gives us an additional e
34、quation for the departure time of packets: ITU-T Rec. J.133 (07/2002) 3 nomiRiTT +=0(3) T0is a constant representing the time of departure of the zeroth bit. Combining equations (2) and (3) we have for the arrival time: inomiJDRiTU +=0(4) 4.2 Measurement descriptions The following measurements requi
35、re a demarcation frequency for delimiting the range of drift rate and jitter frequencies of the timing variations of PCRs and/or TSs. The demarcation frequency used should be chosen from the Table 1 and indicated with the measurement results. A description of the derivation of the demarcation freque
36、ncies is included in Appendix I. Table 1/J.133 Profile Demarcation frequency Comments MGF1 10 mHz This profile is provided to give the total coverage of frequency components included in the timing impairments of PCR-related measurements. This profile provides the most accurate results in accordance
37、with the limits specified in 2.4.2.1 of ITU-T Rec. H.222.0 | ISO/IEC 13818-1. If jitter or drift-rate measurements are found out of specification when using other profiles, it is suggested to use this one for better accuracy. MGF2 100 mHz This profile is accounting for intermediate benefits between
38、the profiles MGF1 and MGF3, by giving reasonable measurement response as well as reasonable account for low frequency components of the timing impairments. MGF3 1 Hz This profile provides faster measurement response by taking in account only the highest frequency components of the timing impairments
39、. This profile is expected to be sufficient in many applications. MGF4 Manufacturer- defined This profile will provide any benefit that the manufacturer may consider as useful when it is designed and implemented in a measurement instrument. The demarcation frequency has to be supplied with the measu
40、rement result. Optionally any other data that the manufacturer may consider to be relevant may be supplied. For testing against ISO/IEC 13818-9 (25 ms jitter limit) a demarcation frequency of 2 mHz is required. A filter for such demarcation may be implemented under this MGF4 profile. 4.3 Program Clo
41、ck Reference Frequency Offset (PCR_FO) Definition PCR_FO is defined as the difference between the program clock frequency and the nominal clock Frequency (measured against a reference which is neither PCR- nor TS-derived). 4 ITU-T Rec. J.133 (07/2002) The units for the parameter PCR_FO should be in
42、Hz according to: Measured Frequency Nominal Frequency or in ppm expressed as: Measured Frequency (in Hz) Nominal Frequency (in Hz) Nominal Frequency (in MHz) Purpose The original frequency of the clock used in the digital video format before compression (program clock) is transmitted to the final re
43、ceiver in form of numerical values in the PCR fields. The tolerance as specified by ITU-T Rec. H.222.0 | ISO/IEC 13818-1 1 is 810 Hz or 30 ppm. Interface For example, at interface G in Figure I.8. Method Refer to Appendix I for a description of a measurement method. 4.4 Program Clock Reference Drift
44、 Rate (PCR_DR) Definition PCR_DR is defined as the first derivative of the frequency and is measured on the low frequency components of the difference between the program clock frequency and the nominal clock frequency (measured against a reference which is not PCR derived, neither TS derived). The
45、format of the parameter PCR_DR should be in mHz/s ( 27 MHz) or ppm/hour. Purpose The measurement is designed to verify that the frequency drift, if any, of the program clock frequency is below the limits set by ITU-T Rec. H.222.0 | ISO/IEC 13818-1 1. This limit is effective only for the low frequenc
46、y components of the variations as indicated by the demarcation frequency described in Appendix I. The tolerance as specified by ITU-T Rec. H.222.0 | ISO/IEC 13818-1 1 is 75 mHz/s 27 MHz or 10 ppm/hour. Interface For example, at interface H in Figure I.8. Method Refer to Appendix I for a description
47、of a measurement method. 4.5 Program Clock Reference Overall Jitter (PCR_OJ) Definition PCR_OJ is defined as the instantaneous measurement of the high frequency components of the difference between when a PCR should have arrived at a measurement point (based upon previous PCR values, its own value a
48、nd a reference which is neither PCR- nor TS-derived) and when it did arrive. The format of the parameter PCR_OJ should be in nanoseconds. ITU-T Rec. J.133 (07/2002) 5 Purpose The PCR_OJ measurement is designed to account for all cumulative errors affecting the PCR values during program stream genera
49、tion, multiplexing, transmission, etc. All these effects appear as jitter at the receiver but they are a combination of PCR inaccuracies and jitter in the transmission. This value can be compared against the maximum error specification by ITU-T Rec. H.222.0 | ISO/IEC 13818-1 1 for PCR Accuracy of 500 ns only if the jitter in the transmission is assumed to be zero. Interface For example, at interface J in Figure I.8. Method Refer to Appendix I for a description of a measurement method. 4.6 Program Clock Reference A
