[mythtv] DVB-C service description tables

Karl Dietz dekarl at spaetfruehstuecken.org
Fri Apr 14 08:12:12 UTC 2017

Hi Roger,

On 14.04.2017 09:28, Roger James wrote:
> I knew that messing with this would come back to bite me. There is a
> hack in DVBStreamdata to handle the misuse of the the Service
> Description (other) table to transmit the data for the actual (currently
> tuned) stream. I need to improve the handling of this in my new SI code.
> To help me do this, can anyone explain to me why some cable providers
> feel the need to break the DVB spec in this way, or point me at any info
> about it.

They don't violate or hack anything. There are things in the spec from
the dark ages of digital data transmission to get away with the most
primitive equipment possible.

Its perfectly valid to push a pack of network information tables down
the satellite link for DVB-S and various DVB-C networks.
Then the local cable headends just convert the bitstream from the DVB-S
modulation to DVB-C modulation and send it to the customers unmodified.
A random DVB-C NIT will be marked active, all others as other. The cable
operator send their customers the correct network_id when they book the
service so they can configure their TV sets.

I have to look where this mode of operation is documented, IIRC some
technical recommendation or network/device implementers guide.
A quick search over collected standards didn't highlight anything. I
must have been using the wrong search terms.


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