[linux-dvb] DVB-S2 Multiple logical TS on the same frequency

Manu Abraham abraham.manu at gmail.com
Sun Oct 14 18:32:24 CEST 2007


Nico Sabbi wrote:
> Il Sunday 14 October 2007 17:06:38 Francesco Schiavarelli ha scritto:
>> I own a TT-3200 and I'm interested in receiving those kind of
>> signal. I understand that ATM is not possbile, but will it be in
>> the future? In other words it's an hardware or software/firmware
>> limitation?
>>
>> thanks,
>> Francesco
>>
> 
> aren't they transmitted on the two hyerarchical streams (that have
> been supported for years now) ?

Nope. DVB-S2 is a bit complex, additional to all that it carries the overhead of 
backward compatibility. The specification is more like the EN50221 specification, 
where you need to read it over and over again many times, in conjunction to an 
actual device specification. That said:


1) Hierarchial modulation is used only for one of the backward compatibility 
methods. Here there is a HP/LP stream.

Ref: EN302 307  v 1.1.2 Appendix F Page 55


2) This has nothing to do with MTS aka Multiple Transport Streams.

This is in fact to simply state is: SIS (Single Input Stream) /MIS (Multiple Input Streams) 
according to the ETSI specifications

Ref: EN302 307 v 1.1.2 Page 49

Not all demodulators are capable of doing this (1) and (2)

1) is not a big concern, but 2) might be when broadcasters do MTS similarly to the 
DVB-T HP/LP streams. (stated as an example, this has nothing to do with Hierarchial 
modulation HP/LP itself, in fact)

You can have MIS in 2 cases again:

1) Transport Streams

 a) When it is SIS, it is similar to our normal DVB-S transmissions
 b) When it is flagged MIS in the Baseband Header, we have Multiple Streams.
     When it is MIS, if the logical streams are scrambled, we will need to route the relevant 
     stream to the CA module, which means we have some additional job at the demuxer level.
     (this will be a bit of  headache, coupled with a CA device)

2) Generic Streams (note this need not be a MPEG2 stream at all)
    This at least we can pipe everything to userspace at least as a last resort.

Temporarily, we do not need to worry about Generic streams (Single or Multiple), since they 
aren't basically used in the broadcast profiles, _but_ MTS might be.


Manu



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