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Re: Forward from Art Alison: WGLC ULE - Data Broadcast Descripto rs

Please read below.

Goldberg, Adam wrote:

Re #2 below, without discussion of PSI it will be both (1) difficult for
equipment to interoperate in that they may not be able to find the PID value
My question wrt this is, why should not someone propose a dedicated ULE Stream Table (UST) for that purpose? Even on a dedicated PID, say 0x16, and registered/reserved for that purpose? It could well serve also INT/IMT/... purposes, without having to parse other sections. Consequently, the responsibility would be there, where it should be. Although, it wold make sense if someone would take responsibility for registration and someone else for semantics? But that seems quite innovative. Would ATSC/DVB let IETF/... come up with a draft/standard for a MPEG-2 section after having only reserved a dedicate PID for that? 


in use for SNDU streams, and (2) passing through non-SNDU-aware MPEG
Transport equipment (of which none exists, I suppose) is not likely
(certainly not guaranteed).
It is very difficult to compare television equipment (what MPEG-2 still primarily is?) with network equipment. Whether a unreferenced (ghost) PID is being dropped by a multiplexer or not is probably just a configuration issue. But, in what way can an IP router can tell (MPEG-2) receivers, where (on what PID) a specific ULE Stream is available? In a carneval like statement one could argue, that MPEG-2 is like a room with 8K Ethernet plugs, guess which is the right one to connect to your local network. Of course we know, that it is physically more the opposite: one plug, where 8K networks are on it, so more the nightmare for security admins. 


I note from another response that the carriage may be specified in another
document. That seems fine, but perhaps mention should be made about it.
Yes, information about the 8K PID Networks is essential for routing/addressing/... purposes. 


In any case, 'TS Logical Channel' remains irksome to me.  I'll respond
separately to other responses.
Well, meanwhile my favourite is ULE Stream instead (thanks Gorry). It simply says what it is. 


Adam Goldberg
Director, Television Standards & Policy Development
Sharp Laboratories of America
8605 Westwood Center Drive, Suite 206
Vienna, VA  22182
+1-703-556-4406
+1-703-556-4410 fax
+1-571-276-0305 cell
Thanks for the interesting discussion, which is unfortunately a liitle bit late, yet fundamental. 

Kind regards,
Bernhard

Ass.Prof.Dr. Bernhard Collini-Nocker
Head of Multimedia Communication Group
University of Salzburg, Department of Scientific Computing
Jakob Haringer Str. 1
A-5020 Salzburg
Tel: *43 662 8044 6316
Fax: +43 662 8044 172




-----Original Message-----
From: Bernhard Collini-Nocker [mailto:bnocker@cosy.sbg.ac.at]
Sent: Monday, February 07, 2005 7:49 AM
To: ipdvb@erg.abdn.ac.uk
Cc: Goldberg, Adam; Allison, Art; Matthew Goldman
Subject: Re: Forward from Art Alison: WGLC ULE - Data Broadcast Descripto
rs

Hello,

let me try to summarize the two major points being raised and what the
discussion is about:
1. the name/definition of "TS Logical Channel" is not well received and
the name/definition of a "SNDU stream" is proposed instead
2. it is proposed to consider MPEG-2 conformance in specifying that ULE
requires a specific stream_type value for the PMT

Personally I have no objection against 1., because it is easy to change
and improves wording and naming (unless somebody has an even  better
name for it).
For 2. my concern is that mentioning stream_type may require some
additional wording about PSI/SI in general, which is likely out of scope
of the ULE draft. Even worse, in introducing a "world" besides the
encapsulation/decapsulation of ULE, this may result in further confusion
about what the MPEG-2/Section layer does in addition to and/or in
comparison to ULE/IP. Actually some difficult question may arise from
this direction, for example whether it is a wishful requirement for ULE
to support PAT/PMT/NIT/INT/... table parsing?

Any opinions, recommendations or suggestions about this?

Regards,
Bernhard

Goldberg, Adam wrote:


ARGH.  I fat-fingered 'send' before completing the email.  See below.

Adam Goldberg
Director, Television Standards & Policy Development
Sharp Laboratories of America
8605 Westwood Center Drive, Suite 206
Vienna, VA  22182
+1-703-556-4406
+1-703-556-4410 fax
+1-571-276-0305 cell





-----Original Message-----
From: Goldberg, Adam
Sent: Monday, February 07, 2005 12:42 AM
To: 'Bernhard Collini-Nocker'; Goldberg, Adam
Cc: ipdvb@erg.abdn.ac.uk; Allison, Art; Matthew Goldman
Subject: RE: Forward from Art Alison: WGLC ULE - Data Broadcast


Descripto


rs

See below...

Adam Goldberg
Director, Television Standards & Policy Development
Sharp Laboratories of America
8605 Westwood Center Drive, Suite 206
Vienna, VA  22182
+1-703-556-4406
+1-703-556-4410 fax
+1-571-276-0305 cell


Bernhard Collini-Nocker wrote:



Goldberg, Adam wrote:



I apologize for being "late to the party", but:

I do not see a particular need to define new term "TS Logical


Channel",



and



indeed doing so creates risks of ill-specification (such as those Art


points



out), as well as confusion heaped upon someone familiar with MPEG-2
Transport (as typically used in entertainment delivery).


Unfortunately the MPEG-2 standards do not provide a reasonable term for
the purpose of networking. The question is whether other terms, for
example "PID network" or "PID stream" would be better received and
understood?
The term "TS logical channel" tries to verbally visualize that the
encapsulation uses a continouos stream of transport stream packets


using


one specific packet identifier to transport subnetwork data units.


Maybe


the term "TS (virtual) circuit" better names this?


It is perhaps not well defined in 13818-1, but the term of art is
"streams".  Many people use "PID stream" which is a poor combination of
words.  I'd have no objection to defining a "SNDU Stream" as something
like "a sequence of MPEG-2 Transport Stream packets identified by a


common


PID value" (or some such).

Perhaps discussing 'virtual circuits' relative to a Transport Stream is
begging for confusion.  Use of any such words ("TS (virtual) circuit")
needs careful definition, likely requiring the above SNDU Stream
definition plus an explanation of what it means for multiple SNDU


Streams


to exist in a single Transport Stream.




Furthermore, the definition is quite wrong with respect to ATSC and


DVB



use



of "specific TS Logical Channels".  To my knowledge, this internet-


draft



is



the only document anywhere which uses such terms.  It is certainly


true



that



MPEG, DVB and ATSC define //elementary streams// identified by


stream_type



values. I suspect this is what is meant by "TS Logical Channel", but


it



is



difficult for me to tell.


I am not so sure, whether this analysis is correct. Elementary streams
are those that are transported as Packetized ES, whereas "auxillary"
data and signalling is transported as sections. Although a stream_type
in the program map section is used to reference both PESs and sections
the term elementary stream is used very vague and we tried to avoid
using it in the same vague manner.


Perhaps I overstepped with "elementary stream".

Consider the 13818-1 definition of "Packetized Elementary Stream":  "A
continuous sequence of PES packets of one elementary stream with one
stream ID may be used to construct a PES Stream." (ISO/IEC 13818-1:2000


p.


xiii)

Stuff carried as payload of Transport Stream packets are merely


'payload'.


What the draft starts to define is a new type of payload stream (that


is,


a new way to carry data in a transport stream).  The definition is not
compete.




According to, for example EN301192 v1.3.1, defines Data Piping as:
" The data broadcast service shall insert the data to be broadcast
directly in the payload of MPEG-2 TS packets."
That raises the question, how to call a continouos stream of MPEG-2 TS
packets with a certain PID?

Further the standard details that:
"The data broadcast service may use the payload_unit_start_indicator
field and the transport_priority field of the MPEG-2 Transport Stream
packets in a service private way. The use of the adaptation_field shall
be MPEG-2 compliant."
ULE uses PUSI and does not utilize the AF.

"The delivery of the bits in time through a data pipe is service


private


and is not specified in the present document."
It seems obvious that the use of the term "TS Data Pipe" would lead to
the wrong conclusion that ULE equals Data Piping. But Data Piping is


not


detailed at all, whereas ULE tries to be.


I'm not going to argue that DVB's specification is complete.  I will


argue


that ULE isn't complete.




(from the draft)
 TS Logical Channel: Transport Stream Logical Channel. In this
 document, this term identifies a channel at the MPEG-2 level [ISO-
 MPEG]. It exists at level 2 of the ISO/OSI reference model. All
 packets sent over a TS Logical Channel carry the same PID value
 (this value is unique within a specific TS Multiplex). According to
 MPEG-2, some TS Logical Channels are reserved for specific
 signalling purposes. Other standards (e.g., ATSC, DVB) also reserve
 specific TS Logical Channels.

While I'm commenting on this definition, it also seems to me that


"channel



at the MPEG-2 level" is either wrong or also ill-specified.  What's a
channel?  If you're talking about MPEG-2, it's certainly conceivable


that



the reader may associate "channel" with "[television] channel" - which


are



the subject of a large amount of ATSC and DVB systems.


The term channel is indeed problematic in the context of television,
however, network engineers might have a different understanding about
what a channel is.
According to ATIS a channel is "1. A connection between initiating and
terminating nodes of a circuit. 2. A single path provided by a
transmission medium via either (a) physical separation, such as by
multipair cable or (b) electrical separation, such as by frequency- or
time-division multiplexing. ..."


I understand that 'channel' vis-à-vis networking has a different meaning
than 'channel' vis-à-vis television.  This was my point actually, that
those familiar with MPEG transport should not be assumed to be


networking-


types (even when speaking with respect to ULE).




Additionally, it is also wrong or ill-specified to say "According to


MPEG-2



... TS Logical Channels ...".  There is no such concept defined or


used



within MPEG (unless what you really mean is elementary stream, in


which



case



what do you need this extraneous term for anyhow?).


Again, elementary stream is not exactly what is being meant:
For example EN 300468 v1.5.1 defines:
"component (ELEMENTARY Stream): one or more entities which together


make


up an event, e.g. video, audio, teletext"

and says further:
"The component descriptor identifies the type of component stream and
may be used to provide a text description of the elementary stream"

where:
"component_type: This 8-bit field specifies the type of the video,


audio


or EBU-data component. The coding of this field is specified in table


26."



Table 26 then lists all kinds of video, audio, and teletext formats,


but


unfortunately no networking formats.

At other places this standard is as innovative/creative in naming:
"event: grouping of elementary broadcast data streams with a defined
start and end time belonging to a common service, e.g. first half of a
football match, News Flash, first part of an entertainment show"
What is a "elementary broadcast data streams"? Not by guessing but by
definition?




In any case, Art is certainly correct that merely identifying a "TS


Logical



Channel" as a sequence of packets identified with a common PID value


without



identifying the PSI details is an invitation to multiplexers and
remultiplexers to drop those packets on the floor.


Oh yes, this is the real problem of defining something outside
television standardiszation bodies: one risks that ULE packets are


being


dropped.
We have discussed basically two approaches:
1. define the PSI and get an ID, or tag, or "stream_type" for ULE, or


2.


define ULE and let somebody else do the PSI work.
We have had some reasons for choice 2.


This is a very easy thing to fix and something which should be done.
Without defining a stream_type for ULE data, it is neither possible to
construct a transport stream compliant with MPEG-2 nor one that
interoperates with other ULE equipment.

ATSC maintains a 'codepoint registry', and would be happy to allocate a
stream_type value for ULE data upon request from IETF.  Furthermore, the
text to specify usage of the stream_type would be reasonably easy (and
perhaps ties in to my suggested "SNDU Stream" definition (that is,


define


it as



SNDU Stream: a sequence of MPEG-2 Transport Stream packets identified by


a


common PID value of stream_type <0xnn>.

All that then remains, I think, would be to signal when a Program


carries


SNDU Stream(s), and what it means when there are more than one SNDU


Stream


per program, or more than one Program that carries one or more SNDU


Streams.




If there remains an opportunity to repair what I believe to be errors


in



the



draft, I'm eager and willing to participate from a MPEG-2


entertainment



(which is to say, legacy use of MPEG-2 Transport) point of view.


Of course the terms in the document should not conflict with meaning in
another context. However, ambiguous terms in other documents should be
avoided as well.




[Apologies for being strident at all, to say nothing of at such an
apparently late stage - if the above is perceived as such]

Regards,
Adam Goldberg
Director, Television Standards & Policy Development
Sharp Laboratories of America
8605 Westwood Center Drive, Suite 206
Vienna, VA  22182
+1-703-556-4406
+1-703-556-4410 fax
+1-571-276-0305 cell


-----Original Message-----
From: owner-ipdvb@erg.abdn.ac.uk [mailto:owner-ipdvb@erg.abdn.ac.uk]


On



Behalf Of Gorry Fairhurst
Sent: Friday, February 04, 2005 6:56 AM
To: ipdvb@erg.abdn.ac.uk; Bernhard Collini-Nocker
Cc: AAllison@nab.org
Subject: Re: Forward from Art Alison: WGLC ULE - Data Broadcast


Descriptors



1) Done - point 1 was an edit mistake.

2) I think some text on data broadcast descriptors, stream-type,


or/and



PSI



entries would be a valuable addition.

On thinking about this, I wonder if the text about this should go at


the



end



of the Introduction (1.0) to the whole document, where people can see


it



clearly and then undesrtand that there may be something else needed


for



those
networks that rely on PSI for remultiplexing!

- Bernhard & others who understand PSI, can you work with Art to agree


the



exact wording please?

Gorry Fairhurst
(ipdvb WG Chair)

Gorry Fairhurst wrote:





WG please read and respond to this message.

The following message was received on January 22nd before WGLC, but


was



dropped because the email source address was not verified by the list
server.

The exact text of the message follows.

best wishes,

Gorry
(ipdvb WG Chair)

-----



1)




Thanks for considering my previous input...
I note that the new draft has an editorial oversight in that it


contains



two definitions of PSI. I suggest the second should be deleted.



2)




I previously made a comment about the ancillary requirements when


adding



a



TS logical channel to a TS multiplex and asserted there appeared to


be


under
specification. Perhaps it was viewed as out of scope, or perhaps I


simply



don't recognize the change that resulted.  I can not find what


stream_type



is required to be used for the ULE stream when a "TS Logical Channel"


is



added to a multiplex.


The problem here is the same as above. Without "applying" for a
"stream_type" for ULE there is no stream_type for ULE. In contrary why
should one register a stream_type value for ULE earlier than ULE is
standardized?




I suggest at least an informative note be added in Section 6 (after


the



third line which says: "These are transmitted using a single TS


Logical



Channel over a TS Multiplex.") The note should say "PSI entries to be
consistent with [ISO-MPEG] when constructing a conformant TS


Multiplex


and



means for Receivers to locate each such TS Logical Channel are


outside


the



scope of this recommendation."


Thanks, this is a very helpful suggestion for potential readers. In
addition the ipdvb-wg works on providing signalling other than PSI/SI.




Reason:
Just inserting a "TS Logical Channel" without including a
TS_Program_map_section that lists the PID and a stream_type does not
appear to me to result in a strictly MPEG-2 conformant bit stream;


and



practically
could result in the PIDs being dropped by a remultiplexer.   If the


means



for binding the inserted element into a multiplex and subsequent


discovery



is to be covered in another document, a pointer to that document


would


be



more helpful than this warning. It seems at least a warning is needed


and



preferably a pointer to where this next level of TS construction is
defined.


From an architectural point of view it is a reasonable assupmption


that


whatever is being sent in a TS multiplex should be referenced. However,
the reality is that "ghost" PIDs do occur in many services either
accidentially or for well-defined reasons.

What is the penalty for not being strictly MPEG-2 conformant/compliant?




Art Allison
Director, Advanced Engineering
NAB Science & Technology
1771 N St NW, Washington Dc 20036
202 429 5418



Regards,
Bernhard Collini-Nocker