[opendtv] Re: (No Date: Tue, 28 Sep 2004 10:30:37 -0400

  • From: "John Willkie" <johnwillkie@xxxxxxxxxx>
  • To: <opendtv@xxxxxxxxxxxxx>
  • Date: Fri, 15 Oct 2004 09:12:11 -0700

Ron;

I agree with your issue on the location of modulation_mode in the VCT, but
only to a point.  I disagree on the other points.

If the only forms of modulation of virtual channels were 8-VSB, you would
have a good point.  However, you missed an aspect of virtual channels that
does require modulation mode:  analog transmissions during the phase in.

How would you distinguish analog from digital in a channel display without
the modulation mode? I would note that this requirement is mandatory per the
FCC and ATSC.

The modeling of the modulation_mode in PMCP is different than in plain PSIP;
it has been moved up to the transport stream layer.

Also, your unstated assumption is that only VSB transmissions will be listed
in PSIP.  This would be an artificial straight-jacket.  PSIP permits
broadcasters to list cable (and A/81 satellite) channels/program services.
Do you see any advantage in preventing this from happening?

There are issues with the Cable Virtual Channel table, which has been
discussed a bit on my PSIP list by actual people working with this.  For
example, only one current CVCT is permitted.  What if three different
modulation schemes are used in a particular station's market?  (Speaking for
EtherGuide Systems, I have ways to make this usable.)

To say that there is no need for CVCTs or even PSIP in cable is legacy
thinking, imho.  Dynamic PSIP is now mandatory in transmission.  Cable, if
only to save themselves from the listing companies, will have to adopt PSIP
reception, if only to translate to their preferred scheme.

The alternative is for them to rely on TV Guide to get OTA program listings.
In a properly configured TV station, PSIP will always be accurate and
timely.  Can't say the same -- despite best efforts -- about the listing
services.

John Willkie

-----Original Message-----
From: opendtv-bounce@xxxxxxxxxxxxx
[mailto:opendtv-bounce@xxxxxxxxxxxxx]On Behalf Of Ron Economos
Sent: Friday, October 15, 2004 4:04 AM
To: opendtv@xxxxxxxxxxxxx
Subject: [opendtv] Re: (No Date: Tue, 28 Sep 2004 10:30:37 -0400


The modulation_mode field in the VCT seems pretty goofy to me
given that ATSC is only used for OTA and never for cable.

First of all, it's a chicken and egg problem. You can't demodulate
the contents of the field unless you already have the receiver
in the correct modulation mode. It also seems self referential.
What other value but 0x04 would appear in a Terrestrial VCT?

It's a hangover from when ATSC had cable aspirations and has
no meaning in the terrestrial context. I agree with Frank, you could
send an ATSC MPEG-2 Transport stream with any modulation
scheme you prefer. At a high enough S/N ratio, even on/off
transmitter keying (Morse code).

Ron

John Willkie wrote:

> So, it's going to happen by your decree?
>
> Ah, the bugaboo of DVB Harmonization.  I've read the document several
times,
> and I've examined the ATSC code point registry as well.  DVB Harmonization
> largely came down to one thing:  don't use the PIDs reserved for DVB-SI.
If
> I'm not mistaken, the issue isn't not to use program number 1, it's the
> lowest PID assigned to the lowest program_number.  In due course, MPEG-2
> establishes the lowest PID at decimal 48.  That insures no conflict with
> DVB-SI.
>
> (For the uninitiated, in many (but not all) ATSC stations, program_number
1
> is assigned PID 16.  That is (somewhat unwisely, IMHO) hardwired in DVB-SI
> for one of the DVB-SI tables.
>
> Your argument tends to disprove your point.  If it's just a number, why is
> it so hard for broadcasters to not change a single number in their
transport
> stream?
>
> I noticed something when I demodulated my first off-air signal.  A station
> that was putting, in the section of the PAT (PID = 0), the packetid for
> PSIP.  This is outside of ATSC practice, but it's standard practice in DVB
> countries, where program_number = 0 in the PAT provides the PID of the
NIT.
>
> I've looked for a DVB document that deals with ATSC harmonization.  Still
> looking, and I have about 2+ GB of DVB documents.
>
> It's not just a number, and it takes two to tango.  ATSC has met DVB
> half-way on this, and DVB has done nothing except whine about the
> "non-standard" Americans going their own way.  'Twas ever thus.
>
> And, I need to point out the disconnection in your argument.  DVB-SI is
> mandatory.  PSIP is mandatory per the ATSC and now per the FCC.  A/58 is a
> recommendation.  You can't say that the route to solve these issues is
> broadcasters following a mere recommendation: last time I checked,
> recommendations were voluntary.
>
> That's why MPEG stepped in.  Table conflicts solved; EPG integration a
> non-issue, and nobody does anything about it.  I suspect it's another
reason
> why EchoStar does not fully support integrated 8-VSB/Dish receivers, and
why
> it's easy for DirecTV to offer same.  DirecTV uses an early version of
PSIP,
> and I can only assume that it has the same three hour blocks as does
> terrestrial and cable PSIP.
>
> John Willkie
>
> -----Original Message-----
> From: opendtv-bounce@xxxxxxxxxxxxx
> [mailto:opendtv-bounce@xxxxxxxxxxxxx]On Behalf Of Terry Harvey
> Sent: Thursday, October 14, 2004 9:39 PM
> To: opendtv@xxxxxxxxxxxxx; opendtv@xxxxxxxxxxxxx
> Subject: [opendtv] Re: (No Date: Tue, 28 Sep 2004 10:30:37 -0400
>
> The modulation mode in PSIP is simply a number: if needed a 'COFDM'
> modulation mode number could have been included under the modulation
> mode.  The modulation mode is therefore a non-issue. I feel the issue is
to
> ensure that there are no conflicts is the PSIP/ DVB-SI schemes.
>
> Recall that ATSC A/58 from 1996 is the "ATSC/DVB Harmonization"
> recommendation. Note that it was the basis to provide some sort of harmony
> to minimize table conflicts between ATSC and DVB. Also note that many ATSC
> broadcasters still ignore the recommendation in A/58 not to use 'Program
1'
> in A/58.
>
> Terry Harvey
>
> At 07:41 PM 10/14/2004 -0700, John Willkie wrote:
>
> >For each virtual channel emitted in the 8-VSB, there is a modulation mode
> >parameter.  There are provisions in A/65 for analog and digital services,
> >and NTSC and 8/16 VSB modulation.  In ATSC A/81 (satellite ATSC) there
are
> >provisions for a variety of modulation modes.  No provision for COFDM.
> >
> >You asserted that COFDM could have been permitted without any change in
> >PSIP. I challenged that.
> >
> >The problem is symmetrical: there is no provision in DVB-SI for NTSC or
> 8/16
> >VSB.
> >
> >So, they both don't recognize the other.  To make COFDM useful in TV sets
> >that also support VSB, there has to be common ground in the metadata
> >schemes, beyond MPEG-2 SI (PAT) and PSI (PMTs).  I also am unaware of any
> >way at the MPEG-2 level to signal modulation mode -- that's effectively
> >"user private" with the users being DVB and ATSC.
>
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