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

Manu Abraham abraham.manu at gmail.com
Mon Oct 15 01:49:29 CEST 2007


Johannes Stezenbach wrote:
> On Sun, Oct 14, 2007, Manu Abraham wrote:
>> 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.
> 
> ACK -- see old posting:
> http://article.gmane.org/gmane.linux.drivers.dvb/26040
> 
> However, contrary to what is written there I believe the demod
> recognizes SIS vs. MIS and dis/enables the stream filter automatically.
> I guess if you fail to set the correct ISI for MIS, you get no
> output (or the wrong one). For SIS the stream id filter is irrelevant,
> you can set it to any value.


If the demod was to filter Multiple streams automatically, it will mean 
something like choosing all the options in a multiple choice question, 
where you are supposed to choose one. 

I can't see anyway how the demod can select the streams that which 
you are interested in, without the user telling it what you want.


> 
> IMHO all you need is to add an u8 input_stream_identifier
> to struct dvbs2_params. You take the value and write it
> in a demod register -- done.
> 
> You can get the input_stream_identifier (ISI) from the
> S2 satellite delivery system descriptor, see EN 300 468.

yep

> 
> (In the worst case the demod wouldn't en/disable the stream id
> filter automatically, so you'd need to read SIS/MIS flags
> from a register after tuning and do it manually -- but that's
> all internal to the driver and not in the API. I think.)
> 
> (BTW, ARIB has a similar feature, transport_stream_id, see
> http://linuxtv.org/cgi-bin/viewcvs.cgi/dvb-kernel-v4/linux/include/linux/dvb/frontend.h?rev=1.20.2.2&only_with_tag=ARIB_extension&view=auto
> )
> 
> I'm very confident the output of the demod is a single TS in all
> cases, and this has nothing to do with the demux.

Maybe, not very sure on that. Also the specifications additionally adds this:

5.2 SDTV and HDTV broadcasting with differentiated channel protection

The DVB-S2 system may deliver broadcasting services over multiple Transport Streams, 
providing differentiated error protection per multiplex (VCM mode) (see note). A typical 
application is broadcasting of a highly protected multiplex for SDTV, and of a less 
protected multiplex for HDTV. Figure 17 shows an example configuration at the transmitting
side. Assuming to transmit 27,5 Mbaud and to use 8PSK 3/4 and QPSK 2/3, 40 Mbit/s 
would be available for two HDTV programmes and 12 Mbit/s for two-three SDTV programmes.

Regards,
Manu




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