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

Manu Abraham abraham.manu at gmail.com
Mon May 22 14:04:42 CEST 2006


Klaus Schmidinger wrote:
> Johannes Stezenbach wrote:
>> ...
>> I also say it again: I am deeply dissatisfied that none
>> of the people you mentioned at the bottom of
>> http://linuxtv.org/pipermail/linux-dvb/2006-May/010076.html
>> seem to care enough to participate in the discussion.
>> (Not to mention that app developers also don't
>> seem to care -- after all these are the ones who'll have
>> to deal with the new API.)
>>
>> Maybe we should just put the API change off for now. :-(
>
> Well, as an application developer (VDR) I'd like to be able to
> support DVB-S2, but I guess my knowledge about all this is too
> limited to understand what this heated debate is all about.
>
> I always thought that DVB-S2 is just "DVB-S with a new modulation",


When i first heard about DVB-S2 , that is what i too thought. But as i 
went ahead, somebody asked me to do a driver since somebody else was 
busy. While i started it one of the vendors gave me fill go ahead flag 
on it. I then went  to read some specs and lo, it is not DVB-S + 
8PSK/16APSK/32APSK

DVB-S2 has quite a lot of features. I think, this even caused the ATSC 
guys to shelve off ATSC over satellite.

* It has variable slopes. (Nyquist Rolloff rates)

This eventually affects lot of stuff, since a larger falloff, helps in 
wastage of transmitted RF power, thus saving energy, quite useful in 
portable equipment.

* DVB-S suffers from climatic changes

DVB-S2 supports additionally quite a lot of things to make things better

* Physical layer Scrambling (helps to improve data integrity)
* Multiple streams
* Many more advanced features that it supports more than a MPEG2 TS
* some of the features allow it work in bad climatic conditions as well
* Saves bandwdth, not just because of H.264, but because of the sharper 
filter slope, below a certain value the bandwidth is useless, it just 
occupies bandwidth that which is not useful



> so I would expect a new driver version that supports DVB-S2 to
> just implement that new modulation and still call it "DVB-S".
> This "...2" thing is IMHO just to make things clear to customers,
> so they know that their old boxes can't handle it. From an application's
> point of view it's still DVB-S, just with another modulation.
>

For people who just want to watch HD on the HP stream and _if_ you are 
lucky, most probably you can use DVB-S + additional modulations

The reason being, you need to tell it to select the stream that which 
you are interested in

> I wouldn't even mind if the old and new driver weren't binary
> compatible. I'd just write into the release notes of VDR that
> as of version soandso VDR requires driver version XXX.
>
> But then a again, what do I know...

Well, just making yourself small does not help in any way.


Manu




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