[PATCH] Re: [linux-dvb] [PATCH] Multi protocol support (stage #1)

Johannes Stezenbach js at linuxtv.org
Thu May 25 23:22:20 CEST 2006


On Thu, May 25, 2006, christophpfister at bluemail.ch wrote:
> >On Thu, May 25, 2006, christophpfister at bluemail.ch wrote:
> >> >On Tue, May 23, 2006, christophpfister at bluemail.ch wrote:

your quoting is broken :-(

> >- hierarchical modulation: one DVB-S and one DVB-S2 signal are
> >  combined via a hierarchical mapper; the DVB-S2 signal
> >  is _SIS_ (note that the hierarchical mapper is located *after*
> >  PL header insertion); a DVB-S receiver will only see the
> >  DVB-S stream; a DVB-S2 receiver will see the DVB-S2 stream,
> >  however to do so it needs to be set in a special BC mode
> >  (because of the "asymmetric 8PSK constellation");
> >  again our API would use DVBFE_DELSYS_DVBS vs. DVBFE_DELSYS_DVBS2
> >  to select HP vs. LP stream, but also needs the obc_mode flag.
> 
> That's not quite correct. While a DVB-S device receives only the HP stream,
> a DVB-S2 device receives *both* streams.
> So the most used mode is MIS. The stream_id is used in this case to select
> either the lp or the hp stream.

I'm looking at EN 302 307 figure F.1. It shows that the HP stream
is a DVB-S stream of I/Q-bits (outer & inner coding, not yet
spectrum shaped and modulated) according to EN 300 421, thus it
cannot have a stream_id.

Please explain why you think hierarchical BC mode uses
MIS and stream_ids to select HP/LP. It contradicts
my understanding of the standard.

The frame structure of DVB-S2 is totally different than
DVB-S, so a DVB-S2 demodulator will not be able to demodulate
a DVB-S stream. E.g. STB0899 contains two completely
seperate demodulators for DVB-S and DVB-S2 mode.

Thus I think one uses DVBFE_DELSYS_DVBS vs. DVBFE_DELSYS_DVBS2
to select the HP or LP stream.


> >> >- NBC-BS == "normative broadcast mode"?
> >>
> >> Yes.
> >
> >After sleeping it over, I think NBC-BS and
> >"normative broadcast mode" are not equivalent.
> >DVB-S2 NBC-BS has mandatory and optional parts
> >(EN 302 307 table 1), and "normative broadcast mode"
> >means "the mandatory parts of NBC-BS only".
> >
> >I.e. MIS is optional and thus nor part of
> >"normative broadcast mode". Thus what EN 300 468
> >means to say is: "If you only use the mandatory parts
> >of NBC-BS you don't need the S2 descriptor".
> 
> NBC-BS doesn't need the S2 descriptor (as explained earlier).
> But still NBC-BS == "normative broadcast mode", e.g. because the backward
> compatible mode isn't the same as normative broadcast mode.

It really a bummer that EN 300 468 uses the term
"normative broadcast mode" without defining it,
but I am now convinced that "normative broadcast mode (NBC-BS)"
means "those parts of NBC-BS which are mandatory",
i.e. "normative broadcast mode" means a subset of NBC-BS.

Look at EN 302 307 table 1.

E.g. MIS is NBC-BS, but not part of "normative broadcast mode"
since MIS is an *optional* feature of NBC-BS.


Johannes



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