robertj@tekgen.bv.tek.com (Robert Jaquiss) (05/13/91)
Index Number: 15518
This article is reprinted with the permission of Linda Helgerson,
President of CD-ROM ENDuser, Disc Magazine, and CE-ROM End User.
It is intended for the use in the CBFB magazine. Any other
reprinting must be authorized by Ms. Helgerson.
DDP: A Standard for Compact Disc Mastering Interchange
by Doug Carson
There are identifiable and predictable progressions in the
development and maturing of virtually any new business or
industry. One fairly predictable aspect of growth is the conflict
between flexibility and stability. New businesses or industries
tend to be very flexible, which is their unique strength. Newer
industries are often characterized by the use of various
proprietary "standards" or, at the other extreme, no recognizable
standards at all. Older, established entities tend to be fairly
stable, but sometimes are seen as inflexible. Somewhere in the
middle ground is something I call stable flexibility in which a
workable balance has been achieved. Stable flexibility is simply
the addition of the proper amount of structure into the business
or industry "system."
The CD-ROM industry, taken as a whole, is somewhere between
the initial flexibility of new industries and stable flexibility.
This has both good and bad connotations. Things are not yet so
rigid that new CD formats or applications cannot be explored. Yet
things are not yet stable enough to allow new applications to be
developed and produced as smoothly as they should. The CD-ROM
industry needs to continue to move towards stable flexibility by
adopting the structure of appropriate standards.
As anyone who has been involved with the creation of a
compact disc information or entertainment product knows, the
first time through can be quite an educational process. It is
only in the actual doing that one discovers what is real and what
is not, what hardware, software and standards exist and are
adequate and which are insufficient. This discovering process can
be frustrating, to say the least.
The Goal is Interchangeability
Figure 1 should be here -- somewhere!!
Figure 1 shows a typical progression that data goes through
before the end user actually uses it. The left of the diagram
shows three sets of dependent items dealing with the actual
database structure, file system used on the compact disc and
presentation of data for compact disc mastering. In an ideal
world, there would be standards for all three, at a minimum, and
thus perfect and total interchangeability would be achieved at
all the various levels from the developer to the user. In
practice, with the exception of CD-I, there are not yet enough
standards to make this a reality.
What is Interchangeable and What is Not
The first dependent item deals with the structure and
retrieval of the information on the compact disc. Information
that is indexed with one vendor's building program typically is
not accessible with retrieval software from another. The
technical issues involved in creating proper interchange
mechanisms are very complex. In addition, there are so many
different software packages already available to create compact
disc data that a standard may not be possible.
The second dependent item deals with file level
interchangeability. The ISO 9660 file interchange format provides
an excellent mechanism for data file interchange between various
CPU systems. The establishment and acceptance of this standard
was responsible for significant growth in the CD-ROM industry.
For applications that will use CD-I, there is a different file
interchange standard utilized. The important thing to remember is
that for a given compact disc technology, i.e., CD-ROM or CD-I,
as long as both the developers and the users agree on what the
interchange format will be, bottlenecks due to the lack of a
standard will not occur.
The last dependent item on the diagram deals with
presentation of data for mastering and replication which is the
focus of discussion here. Currently, the most widely used
transfer media is several reels of 1/2-inch ANSI labeled tape
which is sufficient for a good number of the current text type
CD-ROM applications. However, there are several developments and
trends in the compact disc industry that are severely taxing the
capability of ANSI labeled 1/2-inch tape. Applications which
change the "MODE" of data storage on one disc are good examples.
Figure 2 shows the various modes of storage currently specified
for compact disc.
Figure 2 is somewhere here!!!
Simple CD vs Complex CD
The default mode for CD-ROM is mode 1. When a compact disc
only contains one mode of data, then it is referred to as a
"Simple CD," even though the application may be quite complex.
Examples of simple CD include text databases, text with digital
page images and even the audio disc. CD-I, CD-XA and CD-ROM discs
with an audio track are all considered "Complex CD" because they
contain more than one mode of data. "Complex" refers more to the
file interchange and mastering level than to the application
level. In fact, when proper standards are accepted, the "Complex"
nature of a mixed mode CD will be entirely transparent to both
the developer and the user.
The Problem With ANSI Labeled Nine-Track Tape
As mentioned, nine-track tape is insufficient for complex CD
use. To better understand why, one must understand the makeup of
a mixed mode disc. Figure 3 shows an example of a hypothetical
mixed-mode four-track CD-ROM.
Figure 3 is here somewhere!!!
For CD-ROM, logical sector 0 is at physical sector 150, due
to the 150 sectors of pause required at the beginning of the
disc. Additional information is added between tracks where mode
changes occur, in the form of pauses and gaps. The amount and
content of these pause and gap areas is determined by what mode
you are coming from and what mode you are going to. Assuming that
each track contains 1,000 sectors, it is seen that track 3 begins
not at sector 2000 but at sector 2675. Imagine the rude awakening
of discovering this after investing in the first disc production.
To make matters worse, the Red, Yellow and Green book only
specify minimums for gaps and pauses, not maximums.
ANSI labeled nine-track tape is designed to contain and
describe only the contents of the actual CD tracks, not any pause
and gap areas. This is one of the major shortcomings of using
this media without a higher level standard. Another problem
concerns CD-I and CD-XA. Typically, one tape record is made to
equal one CD sector so a record size of 2048 is used to store
mode 1 CD data. Most mastering facilities will master any 2048-
byte record tape as mode 1 data, which is the CD-ROM default.
Both CD-I and CD-XA use different sector types that are randomly
interleaved in a single track, i.e., some sectors contain 2056
and others 2332 bytes. The problem then is how to present this
data on tape. Because record size cannot change in a tape file,
the smaller sector is padded out to the same size as the larger
sector and this now becomes the record size. However, which
records contain padded sectors and which bytes are padded? The
problems continue to grow. These types of issues and problems
necessitate the formation of standards for the industry.
The Proprietary and Non Existent Standard Traps
Imagine a situation where the major players in the industry
did not cooperate and each implemented its own proprietary
protocol between CD development stations and mastering equipment.
The industry would look like the puzzle shown in Figure 4, with
only certain workstations able to supply data to certain
mastering facilities. It would be a real shame if mastering
facilities had to turn away CD-XA business simply because its
equipment did not handle a specific proprietary format -- and
this is becoming a problem.
Figure 4 goes here somewhere!!!!
The other extreme is no protocol whatsoever, and this gets
very expensive for everybody. About the only way to create
workable complex CDs is for developers to own fairly expensive
writable CD equipment on which they could create a single working
copy and then send this for re-mastering and replication. While
this sounds nice, it does come at a fairly hefty price which
cannot always be justified for CD-ROM. Today it is entirely
possible to completely build and simulate even the most complex
CD using only hard disk and software. This not only saves the
developers tens of thousands of dollars, but time. With the
acceptance of a workable protocol, this will become the preferred
method of compact disc development as shown in Figure 5. Any disc
developed on any workstation can be mastered by any mastering
facility.
Figure 5 goes here!!!!!
The Solution is DDP
DDP (Disc Description Protocol) is the proposed interchange
standard between compact disc workstations and mastering
facilities. The drafting and refining of this proposal has been
under development for more than a year by an international group
of companies including Philips, 3M, PDO, Nimbus, ODM, Elektroson,
OMI, Meridian and DCA.
Very simply, DDP allows a developer to describe exactly
where data is stored on the interchange media, what processing
needs to be done prior to mastering and finally where the data is
to be placed on the compact disc, including pauses and gaps. The
proposal covers both direct access media such as WORM or MO media
as well as sequential access media such as nine-track or 8mm
tape.
Brief Overview of DDP
Figures 6 + 7 go somewhere around here!!!!!!!
DDP consists of four types of DDP information in addition to
the user-supplied track data. Two types, DDPID and DDPMS, are
required, while the DDP subcode and text information are
optional. Examples for both direct access and sequential access
media are shown in Figures 6 and 7 respectively. The function of
DDPID is to uniquely identify both the data set and the DDP
protocol as well as locate the DDPMS information. The real
functionality of DDP is contained in the DDPMS Packets or map
packets. These packets contain information about the input data
as well as the target compact disc. Information contained in
these packets includes:
n Whether input data is main channel, subcode or text;
n Where input data is located on input media;
n Name of input data file;
n How many CD sectors are contained in input data;
n How the data is stored on the input media;
n Where input data is to be placed on CD;
n What type of subcode data, if any is present;
n What mode of data is to be placed on the CD;
n Whether input data is already scrambled;
n Length of any gaps or pauses included in data;
n Track and index for data; and
n ISRC number for track.
As can be seen in Figures 6 and 7, the DDP information is
stored as a "burst" of information prior to the data that is to
be placed in each track. Labeled tape implementations will
utilize two small files at the beginning of the tape set (DDPID
and DDPMS), with the data files being stored thereafter. For
direct access media, the DDPID is located in sector 0 which
points to the DDPMS at any location. This allows DDP to be
written on a WORM disc even after data files have already been
written.
What DDP Does For Developers
There are three main benefits of DDP that should be the
focus of the CD-ROM industry:
1) It is flexible, yet stable. Any compact disc format, CD
Audio, CD-ROM, CD-I, CD-XA, CD-G and even proprietary
formats can be described by DDP. This ensures that DDP will
not have to be constantly changed and that new compact disc
formats will be supported.
2) Once a mastering facility implements DDP in its process
environment, it is automatically able to make all formats of
compact discs which can be described by DDP. Even when new
formats are announced, DDP-equipped facilities will be ready
to master them.
3) DDP will allow high performance workstations based upon
removable media such as WORM or MO discs to be developed and
put into general use. These workstations will not be bound
by hard disk capacity restrictions or by upload and download
times to backup or restore a project. This means more time
and money available to the developer to do the things he or
she wants to do -- be creative.
Summary
Standards are critical to the health of any industry and CD-
ROM is no exception. We have all seen the growth that came about
in "Simple CD" applications with the acceptance of the ISO 9660
file interchange standard. Without this standard, we would still
be required to purchase proprietary host adaptor cards and only
specific CD-ROM readers for our applications. Due in part to the
ISO 9660 standard, developers have had quite a bit of freedom in
choosing which CD-ROM reader and PC their applications will
utilize. In fact, most developers are not even concerned with
trivial items such as this anymore. I trust that the industry
participants who have participated in the growth of the "Simple
CD" industry will participate in the standards required to make
the "Complex CD" industry reach its potential. DDP is a key piece
of the structure that will allow the entire CD industry to
continue to mature toward stable flexibility.
Doug Carson is President of DCA Inc. The proposed standard, DDP
1.00, appears in toto on disc/in/DISC and is courtesy of DCA Inc,
317 West Broadway, Cushing, OK 74023, TEL 918/225-0346, FAX
918/225-7050. Members of the DDP Committee include Doug Carson,
DCA Inc.; Wink Saville, Meridian Data Inc.; Bjorn Bluthgen,
Polygram; Jim Fricks, PDO; John Nairn, Reference Technology; Jeff
Uitenbroek, 3M Company; Jerry Lee, 3M Company; and Parke
Lightbown, The Library Corporation.