[linux-dvb] Re: What is happening on Astra 11837 h, PID 18?

[Johannes Stezenbach <js@linuxtv.org>]

On Mon, Feb 07, 2005 at 09:16:47PM +0100, Josef Wolf wrote:
> On Sat, Feb 05, 2005 at 02:17:56AM +0100, Johannes Stezenbach wrote:
> 
> > The EIT is sliced up in segments. Read the chapter on "EIT Schedule
> > structure" in ETSI ETR-211.
> 
> I've read it, but I'm still a little bit confused.  Normally, reconstructing
> a table before all its sections (with a given version number) are received
> is illegal and would lead to a broken table.  The EIT seems to be somewhat
> special because you need to parse table contents as soon as a segment is
> complete.  Therefore segment_last_section_number is needed in order to
> decide whether you have gathered enough sections to process them.  So you
> need to look inside the contents of the sections to decide whether you can
> process them.
> 
> When does the information get valid?  When all sections of a segment with
> a given version are received?  Or when all sections of all segments with
> a given version are received?
> 
> Is the EIT the only thing that needs this sort of special handling?  Does
> this special handling apply only to table_id 0x50..0x6f or are 0x4e and
> 0x4f segmented, too?
> 
> What is this segemntation good for?

IIRC either ETR-211 or EN-300-468 state that it is segmented by time,
i.e. a segment of 16 sections covers three hours. The intention is
that low-end boxes without enough memory can set the section filters so
they just filter out the data e.g. for the next day.
The repetition rate of the sections can be different, e.g. the data
for the current and next day can be sent more often than the data for
the rest of the week.

You can also process each EIT section independently, there is no need
to collect all sections before processing. I think VDR does this.
segment_last_section_number is so you can tell when you have gathered
all available data. It depends on your app if you care about this or
if you continuously update your EPG data like VDR does (I think).

EIT current/next usually have only one section so this is irrelevant there.

Johannes