1、 INTERNATIONAL STANDARD IEC 60728-92000 AMENDMENT 1 2005-06Amendment 1 Cabled distribution systems for television and sound signals Part 9: Interfaces of cables distribution systems for digitally modulated signals PRICE CODE IEC 2005 Droits de reproduction rservs Copyright - all rights reserved Inte
2、rnational Electrotechnical Commission, 3, rue de Varemb, PO Box 131, CH-1211 Geneva 20, Switzerland Telephone: +41 22 919 02 11 Telefax: +41 22 919 03 00 E-mail: inmailiec.ch Web: www.iec.ch H For price, see current catalogue Commission Electrotechnique Internationale International Electrotechnical
3、Commission 2 60728-9 Amend. 1 IEC:2005(E) FOREWORD This amendment has been prepared by technical area 5: Cable networks for television signals, sound signals and interactive services of IEC technical committee 100: Audio, video and multimedia systems and equipment. The text of this amendment is base
4、d on the following documents: FDIS Report on voting 100/947/FDIS 100/977/RVD Full information on the voting for the approval of this amendment can be found in the report on voting indicated in the above table. The committee has decided that the contents of this amendment and the base publication wil
5、l remain unchanged until the maintenance result date indicated on the IEC web site under “http:/webstore.iec.ch“ in the data related to the specific publication. At this date, the publication will be reconfirmed, withdrawn, replaced by a revised edition, or amended. _ Amend the title of this standar
6、d on the cover page, the title page and on pages 3 and 6 as follows: Cable networks for television signals, sound signals and interactive services Part 9: Interfaces for CATV/SMATV headends and similar professional equipment for DVB/MPEG-2 transport streams Page 2 CONTENTS Rename the existing Annex
7、F, Annex G. Add the title of new Annex F as follows: Annex F (informative) Guidelines for the implementation and usage of the DVB Asynchronous Serial Interface (ASI) Page 6 2 Normative references Add the following new ETSI technical report: ETR 290:1997, Digital Video Broadcasting (DVB); Measurement
8、 guidelines for DVB systems Page 9 60728-9 Amend. 1 IEC:2005(E) 3 3.2 Abbreviations Add the following new abbreviations: LF low frequency NTSC national television system committee PAL phase alternation line PCR program clock reference RB receiver buffer rx-clk receiver clock TB transmission buffer t
9、x-clk transmission clock Page 17 4.4 Asynchronous Serial Interface (ASI) Replace the second paragraph by the following new text: A detailed specification of ASI is provided in Annex B. Implementation guidelines and deriving clocks from the MPEG-2 packets for ASI are provided in Annex E. Guidelines f
10、or the implementation and usage of ASI are laid down in Annex F. Page 47 Rename the existing Annex F, Annex G. Add a new Annex F as follows: 4 60728-9 Amend. 1 IEC:2005(E) Annex F (informative) Guidelines for the implementation and usage of the DVB Asynchronous Serial Interface F.1 General The DVB A
11、synchronous Serial Interface (ASI) is a very popular standard interface for conveying MPEG-2 transport streams between professional equipment. However, there are concerns over interoperability in the market place, based on system integrators experiences with available equipment from multiple supplie
12、rs. This note is intended to explain some of the causes of problems and to offer guidelines to ASI implementers that will encourage maximum interoperability. This annex addresses interoperability issues specific to ASI data transmission links, and explicitly is not concerned with general MPEG-2 inte
13、roperability issues. An example of an ASI interoperability problem is where equipment receiving an ASI data stream occasionally drops out of lock, or never achieves lock at all. An example of a problem not addressed by these guidelines is where the video and audio on the output of a decoder have poo
14、r clock stability, because of PCR clock recovery problems at some point in the end-to-end equipment chain, for example resulting in LF wander in a regenerated PAL/NTSC subcarrier. This annex contains a clause providing a description of the design issues confronting ASI equipment designers (Clause F.
15、2). This annex also contains a recommendation clause, which provides simple measures to improve interoperability between ASI equipment. There may be situations where systems will work outside these recommendations, depending on precise system and equipment implementation. F.2 ASI transmission links
16、The ASI is a uni-directional transmission link to transfer data between professional digital video equipment. Figure F.1 presents an abstract model of an ASI transmission link. The model represents signals at the Layer 1/Layer 0 interface of Figure B.1. RB rx-clk TB tx-clk Variable delay ASI-Link IE
17、C 900/05 Figure F.1 Abstract ASI transmission model 60728-9 Amend. 1 IEC:2005(E) 5 The diagram contains an ASI transmission node, where data are held in a transmission buffer TB. Data are read from this buffer at a constant rate determined by the transmission clock (tx-clk). This generates an isochr
18、onous data stream. One should keep in mind that the ASI is asynchronous. This gives implementers the freedom to deviate from isochronous data delivery. The diagram models this explicitly by including a “variable delay” function. The modified stream is transported over the ASI link to arrive at the r
19、eceiver buffer RB. Data are removed from this buffer at a constant rate, determined by the receiver clock (rx-clk). The abstract ASI delivery model is used to make sure that the isochronous output stream from the receiver buffer is similar to the isochronous input stream to the variable delay functi
20、on. A design issue in this transmission model is that bytes need to be removed from the receiver buffer at a high enough data rate. To achieve this, the receiver clock frequency needs to be equal to or greater than the transmission clock frequency. If this is not the case, the receiver buffer will o
21、verflow. It is assumed that the receiver clock is linked to the transmission clock, but is silent about how to achieve this in practice. When the receiver clock is linked to the transmission clock, the remaining design issue is to remove any aperiodicity introduced in the isochronous data stream. On
22、 the ASI link, the bytes can be displaced in time with respect to their isochronous position. This displacement can occur for a variety of reasons, for example technical convenience at the generating end of the link. The ASI specification allows for unlimited time displacement of data bytes. To impr
23、ove interoperability, ASI implementations need to be subject to certain restrictions on the data transmission. The variable delay block in the diagram models the asynchronous transmission characteristics of the ASI. The aperiodicity can be expressed as a short-term change in the transport rate. A go
24、od starting point is the definition of data rate from the DVB Measurement Group that is contained in ETR 290 rev.1. In this DVB specification, the data rate is averaged over a fixed time gate (called “window”). Each window contains a fixed number of N “time slices”. For the time slice number k, the
25、notation D krepresents the number of bytes transferred in that period of time. The average data rate (in bytes per second) is then given by the formula: T D rate ASI N n n n k k = = = 1 0 _ (B/s) where N is the integer number of time slices in the time gate window, T is the duration of the time gate
26、 window. After each measurement the time gate window is shifted by one time slice unit of time, denoted by = T/N. The rate specification permits different values for N and T. For this analysis, it is assumed that the transmission clock equals the average rate expressed by the formula. As the actual
27、rate may deviate from the average, we introduce the peak rate as the highest rate found in the N time slices. The highest rate then fills the receiver buffer more rapidly than the average rate at which data is removed from the buffer. A temporary higher rate is followed by a temporary lower rate. Th
28、e combined effect is that the receiver buffer should be empty at the end of the time gate window. An example is shown in Figure F.2. 6 60728-9 Amend. 1 IEC:2005(E) 50150 50200 50250 50300 50350 50400 1 11 21 31 41 51 61 71 81 91 100 200 300 400 500 600 1 10 19 28 37 46 55 64 73 82 91 100 0 IEC 901/0
29、5Figure F.2 Random aperiodic transport stream rate and buffer utilisation In this example, a simulated data transport is shown with an average data rate of 50 kB/s. The time gate window consists of 100 time slices. The number of bytes transferred in each time slice is shown in the left curve of Figu
30、re F.2. The rate varies from 45 kB/s to 55 kB/s. As the bytes are removed from the ASI receiver buffer at the average rate, the buffer occasionally fills with excess bytes. The number of bytes in the receiver buffer is shown in the right-hand curve. One can see that the buffer occasionally underflow
31、s. Both the buffer underflow and the relatively large buffer size should be avoided in practical situations. Another example uses a more well-behaved stream. Here each transport packet is played out with a constant delay between the Sync bytes. The packets are transmitted in a burst with a constant
32、data rate of 8 MB/s. After every packet a small gap is present where no data bytes arrive at the receiver. The data rate is much more constant, and the required receiver buffer also is much lower. 50150 50200 50250 50300 50350 50400 1 11 21 31 41 51 61 71 81 91 101 0 10 20 30 40 50 60 70 80 1 10 19
33、28 37 46 55 64 73 82 91 100 IEC 902/05Figure F.3 Deterministic aperiodic transport stream rate and buffer utilisation Figure F.3 shows that a deterministic aperiodic transport stream has a lower and more predictable buffer utilisation for approximately the same variations in transport rate. The wors
34、t case receiver buffer size occurs when all data in the peak rate time slice is transmitted in one burst at the maximum ASI link rate of 27 MB/s. In such a worst case scenario, the peak time slice transports all data and all other time slices carry no data. Both examples shown above highlight the fa
35、ct that in an ASI design careful consideration needs to be given to the properties of the delay variation of the link. The receiver buffer size, which is required to properly receive the data stream when the transmit and receive rates are linked, should be specified. Hence, this measure is used in t
36、he recommendations below. 60728-9 Amend. 1 IEC:2005(E) 7 F.3 Recommendations It is recommended that equipment manufacturers include the following information on their product data sheets: for equipment with an ASI input, the size of the ASI receiver buffer in transport packets that is available to r
37、emove ASI transmission aperiodicity should be stated; for equipment with an ASI output, the minimum ASI receiver buffer size in transport packets required to remove the ASI transmission aperiodicity it creates should be stated. To maximise equipment interoperability, it is suggested that equipment w
38、ith an ASI output should be designed to work with equipment with a small ASI receiver buffer. Additionally, an ASI input should be designed with a receiver buffer that accommodates as wide a variety of ASI outputs as possible within appropriate commercial constraints. The aperiodicity of some ASI ou
39、tput streams and the receiver buffer size they require for proper reception is illustrated in the following diagrams. The signals represented in these diagrams occur at the Layer 1/Layer 0 interface of Figure B.1. In the first two diagrams below, the ASI receiver buffer size required would be one MP
40、EG-2 transport packet. s s s s 1 transport packet period 1 transport packet period 1 transport packet period s s s s 1 transport packet period 1 transport packet period . . . s Key: MPEG sync byte MPEG transport byte(s) ASI stuffing byte(s) : K28,5 characters 1 transport packet period IEC 903/05In t
41、he following example, an ASI receiver buffer of three packets would be required to remove the ASI aperiodicity. s s s s 3 transport packet periods IEC 904/05F.4 Clarifications Note that if the equipment can accept 204-byte transport packets (optional) in addition to 188-byte transport packets (manda
42、tory), then the size of the required buffer in bytes would have to be larger than if only 188-byte transport packets are supported. 8 60728-9 Amend. 1 IEC:2005(E) In some cases, an ASI output may work with an ASI input with a smaller buffer than is specified for the output, however ASI interoperabil
43、ity under these circumstances cannot be guaranteed. In order to establish whether such inputs and outputs will interface to each other correctly, it is necessary to understand precisely the distribution of transport packet bytes and ASI stuffing bytes, and the detailed operation of the equipment. A
44、general solution for this cannot be given. Requirements for the ASI input will vary depending on the equipment function, for example a decoder may not need as flexible an ASI input as a remultiplexer. Annex G (Former annex F) Replace, in the first paragraph, 7 throw: “108 bytes” by “188 bytes”. _ IS
45、BN 2-8318-8073-4 -:HSMINB=UXU: ICS 33.040.40; 33.060.40; 35.110 Typeset and printed by the IEC Central Office GENEVA, SWITZERLAND INTERNATIONAL STANDARD IEC 60728-9 First edition 2000-11 Cabled distribution systems for television and sound signals Part 9: Interfaces of cabled distribution systems fo
46、r digitally modulated signals Systmes de distribution par cbles destins aux signaux de radiodiffusion sonore et de tlvision Partie 9: Interfaces des systmes de distribution par cbles utilisant des signaux moduls numriques Reference number IEC 60728-9:2000(E)Publicationnumbering Asfrom1January1997all
47、IECpublicationsareissuedwithadesignationinthe 60000series.Forexample,IEC341isnowreferredtoasIEC600341. Consolidatededitions TheIECisnowpublishingconsolidatedversionsofitspublications.Forexample, editionnumbers1.0,1.1and1.2refer,respectively,tothebasepublication,the basepublicationincorporatingamendm
48、ent1andthebasepublicationincorporating amendments1and2. FurtherinformationonIECpublications ThetechnicalcontentofIECpublicationsiskeptunderconstantreviewbytheIEC, thusensuringthatthecontentreflectscurrenttechnology.Informationrelatingto thispublication,includingitsvalidity,isavailableintheIECCatalogueof publications(seebelow)inadditiontoneweditions,amendmentsandcorrigenda. Informationonthesubjectsunderconsiderationandworkinprogressundertaken bythetechnicalcommitteewhichhaspreparedthispublication,aswellasthelist ofpublicationsissued,isalsoavailablefromthefollowing
