[linux-dvb] Re: TS tables doubts

["Robert Schlabbach" <robert_s@gmx.net>]

From: "Nico" <sabbi@cs.unibo.it>
> 1) read the PAT to find the list of programs ids
> 2) read the PMT to find the list of ES streams
(audio/video/teletext/subs)
> associated to a given program id
>
> Is it correct?

Yes, but this is only ISO-MPEG2.

> Now I wonder
> 3) what's the use of NIT and SDT?

Those are the extensions that DVB makes to ISO-MPEG2. It defines additional
tables and "abstracts" the information from MPEG-2. While MPEG-2 only knows
"programs" and refers to them by "program numbers", DVB calls these things
"services" and refers to them by service identifiers (SIDs). MPEG-2 has no
means to specify a transport stream (multiplex), DVB introduces the
Original Network Identifier (ONID) and the Transport Stream Identifier
(TSID) to address a stream.

So in DVB you can fully address a service with an ONID:TSID:SID triple.
ONID:TSID uniquely identifies a transport stream. The required tuning
information for each ONID:TSID is transmitted in the DVB NIT (Network
Information Tables). The services (SIDs) for each transport stream are
described in the SDTs, including e.g. broadcaster, network and channel
name. AFAIK, MPEG-2 has no means to transmit such information.

Consider MPEG-2 as only a _base_ for a digital broadcasting system, which
_needs_ to be extended to become a fully functional system. Two such
extensions are ATSC (North America) and DVB (Europe), of which DVB appears
to be the more complex and powerful one.

Regards,
--
Robert Schlabbach
e-mail: robert_s@gmx.net
Berlin, Germany



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