[mythtv] [mythtv-commits] Ticket #1866: DVB Scanning - Remaining Issues

Rudy Zijlstra mythtv at edsons.demon.nl
Mon Aug 21 18:19:12 UTC 2006


Janne Grunau wrote:

>On Monday 21 August 2006 01:23, Rudy Zijlstra wrote:
>  
>
>>Janne Grunau wrote:
>>    
>>
>>>>Alternatively, full scan is available to find
>>>>all the transports being broadcast, which will
>>>>work even if the transports do not provide any
>>>>information about other transports, as happens
>>>>in certain countries.
>>>>        
>>>>
>>>There is no full scan for DVB-S and DVB-C. I don't think that an
>>>equivalent to the DVB-T full scan is practical for DVB-S and DVB-C.
>>>... For DVB-C we could scan the appropiate
>>>frecency tables we have already. Although it is most of the time
>>>more effort than needed.
>>>      
>>>
>>For DVB-C using the frequency tables is not a good idea. Most of the
>>European cable operators are not adhering  to any frequency table but
>>there own. Which may be different for each city.
>>    
>>
>
>How do they handle analog channels? I've have never heard something like 
>this at least for Germany. I can't remember a single complaint of a 
>analog MythTV user (may be caused by my one ignorance). 
>
>  
>
As stated, German operators are still using a 7MHz bandwidth in the 
lower frequencies

>>German cable is 
>>slowly moving to a 8MHz raster layout. This is also not covered by
>>any standard.
>>    
>>
>
>Can you name one cable provider that changed from the known frequency 
>tables to a 8 Mhz raster? It would make sense for Kabel Deutschland 
>since the use DVB-S transponders to transmit the streams from the 
>playout center to their local  
>
>  
>
I said: "moving to". And analog PAL can be transmitted in 7 or 8MHz 
bandwidth. You get a slighty better quality in 8MHz. Many Dutch 
operators do that. For Germany i expect the lower frequencies (say below 
350 to remain on 7 MHz raster), depending on how many channels they will 
keep in analog.

And they use 8MHz for their digital channels on the cable. I have their 
full layout, as well as from KBW and UM, but covered under NDA, as all 
exchanges are basically covered under NDA.

>>The best way to detect all streams on DVB-C is by a slow frequency
>>scan, with 125MHz step size (or 250MHz, depending on tuner
>>capability). yes, this takes time. It is the only way though.
>>    
>>
>
>You surely meant khz. And it's not the best way. It is maybe the only 
>  
>
I did indeed mean kHz.

>reliable way, but I would consider it as bad. This will take roughly 
>  
>
If it is not reliable, it is not good. Thus the only reliable is also - 
slow though it is - the best (if you want 1 algo to cover all).

>6400 tuning attempts (if you know the symbol rate) and is only reliable 
>  
>
Use symbolrates of 6.875 and 6.9 Any others are too rare to consider for 
normal scanning.

>if the hardware can handle offsets smaller than 75 (125) khz (I don't 
>know if this within standard tuner/frontend capabilities).
>  
>
With current tuners you can do 250kHz steps and find all. With older you 
have to use 125kHz steps. Some newer will find if you use 500kHz steps. 
It depends on the AGC capabilities.

>  
>
>>And please, please, do ignore NIT while you are doing this?? Because 
>>many cable operators do not provide a valid NIT-actual. They provide
>>many NIT-Other, but no, or no valid NIT-actual.....
>>    
>>
>
>This is something I personally don't get. I can understand that a NIT 
>becomes invalid after time if nobody maintains it. But I don't see the 
>point in transmitting a NIT_other in cable natworks. It isn't a useful 
>information at all.
>  
>
It is, if you have a different frequency layout in different area's, and 
only 1 HE. Or clearly less Head-Ends than area's. In that case the 
NIT-Other describes the area frequency layout *for a specific area*, and 
NIT-Actual is worthless. You use the network ID to select the correct 
NIT-Other for your area. If you are willing to use the NIT-Other 
information, better algo's are possible. But you need to know a bit 
about the network you are installing on. Often the NIT-Other will also 
tell you the area it is valid for, in the network description.

>Do the cable providers claim adhering the DVB spec? I.e. can you buy any 
>DVB-C STB (with the appropiate crypto system) and use it? Or have you 
>to buy or rent a STB from the provider? Are the STBs from the providers 
>standard DVB STBs?
>  
>
Euhhhh, none of the DVB-C STB on the market are pure standard..... Be 
they in retail or in direct sales. And this is true for Germany as well! 
(Please keep in mind that in Germany once you add CA, you also add the 
German "JugendSchutz" which is most definitly not DVB-C standardized.) 
Pure FTA STB for Germany are a very limited niche market, as most people 
want to be able to receive either Premiere or Arena content. To name 
only the 2 best known at the moment. Both have additional requirements... 

If you have a level-4 operator who is not affiliated with either KBW, 
KDG or UM, you can have very, very odd layouts. For German retail STB 
this leads to very exhaustive STB field testing (at least for the major 
brands, as many others simply ignore this problem (and refuse to have 
callcenters)).

>Janne
>
Rudy


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