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Nordig LCNs

Pauly83Pauly83 Posts: 2
Forum Member
in Technical #1
Hoping someone can assist with a query. I'm trying to get an understanding of the various tables in the DVB spec.

In the NIT from UK DTT the descriptor tag 0x83 defines the channel line up.

E.g.

0000: 10 43 fc 01 11 c0 fc 09

I know this translates to LCN 1 for Service ID 1043 (BBC One South) and LCN 09 for Service ID 11c0 (BBC Four)

But in the same NIT I have the following:

0000: 3c 48 fd 01 38 f0 fc b9

This means that SID 3c48 (Arise News) should have an LCN of 1. But I know that the correct LCN is actually 257.

Can anyone explain this to me?

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    chrisjrchrisjr Posts: 33,282
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    #2
    The number groups appear to be HEX, So the LCN group likely has values from 00 to ff (0 to 255 decimal). It looks like the group to the left of the LCN group could be an offset to the LCN group.

    So fc means LCNs 0 to 255 and fd is 256 to 512 and presumably you may find an fe and ff for LCNs above 513.

    I stand to be corrected on this but it looks like that.
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    GreeboGreebo Posts: 1,418
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    #3
    chrisjr wrote: »
    The number groups appear to be HEX, So the LCN group likely has values from 00 to ff (0 to 255 decimal). It looks like the group to the left of the LCN group could be an offset to the LCN group.

    So fc means LCNs 0 to 255 and fd is 256 to 512 and presumably you may find an fe and ff for LCNs above 513.

    I stand to be corrected on this but it looks like that.

    Correct - you have to mask off the top 6 bits of 0xFD01 which is 0x0101 - convert to decimal and that is LCN 257 which would be Arise News.

    Similarly 0xFCB9 is masked to 0x00B9 - LCN 185
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    chrisjrchrisjr Posts: 33,282
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    #4
    Greebo wrote: »
    Correct - you have to mask off the top 6 bits of 0xFD01 which is 0x0101 - convert to decimal and that is LCN 257 which would be Arise News.

    Similarly 0xFCB9 is masked to 0x00B9 - LCN 185
    Does beg the question, why do it that way? There must be a good reason why they didn't just use 00, 01, 02 for the first pair rather than fc, fd, fe.
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    GreeboGreebo Posts: 1,418
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    #5
    chrisjr wrote: »
    Does beg the question, why do it that way? There must be a good reason why they didn't just use 00, 01, 02 for the first pair rather than fc, fd, fe.

    I've also wondered what those 6 bits are signalling. Hopefully someone else can enlighten us.
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    chrisjrchrisjr Posts: 33,282
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    #6
    Greebo wrote: »
    I've also wondered what those 6 bits are signalling. Hopefully someone else can enlighten us.
    It's probably buried somewhere in the DTG D-Book specs for DTT. But not being a DTG member or any reason to become one I doubt I will ever get to read a D-Book :)
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    Pauly83Pauly83 Posts: 2
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    #7
    Perfect... Makes sense now.

    Realised you can pretty much tell what kind of service the channel is from the f value.

    fc= tv

    fe= radio

    ff= retune slate

    Although I guess this is just a side effect of how they arrange the channel line up rather than the explicit service descriptor (which can be found elsewhere)

    Thanks v much!
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    GreeboGreebo Posts: 1,418
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    #8
    Pauly83 wrote: »
    Although I guess this is just a side effect of how they arrange the channel line up rather than the explicit service descriptor (which can be found elsewhere)

    Yes, just a side effect -

    FC = LCN 0 to 255
    FD = LCN 256 to 511
    FE = LCN 512 to 767
    FF = LCN 768 to 799 (LCNs 800 upwards shouldn't be in the broadcast data)
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