[mythtv] DVB EIT in mythtv-eit

[Rudy Zijlstra]

Janne Grunau wrote:

>On Thursday 04 May 2006 10:40, Rudy Zijlstra wrote:
>  
>
>>Daniel Kristjansson wrote:
>>    
>>
>>>On Tue, 2006-05-02 at 00:31 +0200, Rudy Zijlstra wrote:
>>>That is, this information could be used to seed information for use
>>>during the initial EIT scan, but might not be worth the bother of
>>>implementing since we will discover this same information in a more
>>>general way during the first EIT scan anyway.
>>>      
>>>
>>I think you are forgetting an important use case: the channel scan.
>>Also, if you check the information, you will see that several NITs
>>are available. These NITs are referring to several TS.
>>    
>>
>
>You will see one NIT with table id 0x40 (actual network) and maybe 
>several other with table id 0x41 (other networks). Each NIT regardless 
>of the table id value will hold one one or more transport descriptors.
>  
>

Fine, this explains why network scanning on my cable network always fails.
The network ID i have to give the STB is 1111. The NIT which is selected 
that way has a table id of 0x41 (other network).
I guarantee though, that it is the valid NIT for my location.

This is common cable behaviour. This was recorded on Essent in the 
Netherlands.

>  
>
>>Important 1: only the TS referred to by the NIT with the correct
>>network ID will be present on the cable!
>>    
>>
>
>Cabel, satellite, terestial transmitter, something like that but it 
>doesn't depend on the network id, but the table id matters.
>
>  
>
See above. I happen to disagree. More importantly, so does my cable 
provider. (and most cable providers in EU).

For SAT there is yet another reason to scan by network ID. When you have 
payTV, you have a subscription with Premiere, C+, ...
At that point you are interested in services from them, and not from 
another. So in all cases you are interested in receiving a minority (the 
services you have a subscription on). This can be done by scanning on 
network ID.

>>Important 2: The different network layouts may (and will) overlap.
>>Leading to different TS having the same frequency. Of course, only 1
>>will actually be present (see 1).
>>    
>>
>
>We handle only the NIT with table id 0x40. So this is not a problem at 
>all.
>
>  
>
And so any scanning i do on my DVB-C tuner fails.

>>Important 3: this means you cannot tune based on SDT info. There is
>>no 1-1 mapping between SDT and NIT.
>>    
>>
>
>Of course there is. In the NIT of the actual network each transport is 
>specified by original_network_id and transport_stream_id. For every 
>combination of this two should exist only one SDT.
>
>  
>
In theory, yes. In practice: No.

>>Important 4: The same services will be referenced in different TS.
>>(from different NIT). I actuality only 1 NIT is valid, and only 1 TS
>>will actually carry the service.
>>    
>>
>
>Not a problem, we get the service information from the SDT of the actual 
>tuned transport. And there is only one SDT for each actual transport.
>
>I haven't read your previous mail (was it send directly to Daniel?). It 
>might be that your cabel provider is incompetent and does not rewrite 
>the NITs in the transport streams it provides. But please wait with 
>  
>
I am willing to forward to the provider management. Do you want his 
answer on this one?
By the way, your cable provider is most likely Telenet. As far as i know 
they do not use NIT-actual at all.

>complaints until the channel scanner is working for standard conforming 
>DVB networks.
>  
>

Some information for you: none of them (DVB-C) comply in that way....
They tend to have 1 central HE, and distribute over their complete 
territory without having Multiplexors in between. So NIT is determined 
in the HE for all possible networks they have. And they tend to have 
several network layouts.

For germany in case of private network you actually have to ignore the 
NIT in many cases. Many of those networks take a signal from SAT, 
trans-modulate to QAM and transmit without touching the NIT.

>Janne
>_______________________________________________
>  
>
Rudy