IEC 60728-9:2000/AMD1:2005

INTERNATIONAL IEC
STANDARD 60728-9
AMENDMENT 1
2005-06
Amendment 1
Cabled distribution systems for television
and sound signals –
Part 9:
Interfaces of cables distribution systems
for digitally modulated signals
 IEC 2005 Droits de reproduction réservés  Copyright - all rights reserved
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– 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 based 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 will
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• withdrawn,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 standard 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 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 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
tx-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 for 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 Asynchronous 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 suppliers. 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 interoperability 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 poor 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.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
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.

tx-clk rx-clk
ASI-Link
Variable
TB RB
delay
IEC  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 isochronous 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 receiver 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 function.
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 overflow.
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 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 improve
interoperability, ASI implementations need to be sub
...