>> Does fibre optic cable use bitswap.
No.
>> Does vdsl (FTTC) use bitswap
Yes.
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Bitswap is an essential part of xDSL which uses DMT technology.
The reasons why are all explained in more detail in these sections.
What is DMT.
What is DMT modulation.
What is bit LoadingWhat is bit swappingFurther info on those pages helps slot understanding into place.
But to simplify things to the most basic of levels :-
~ DMT technology is used between the dslam and CPE (your router)
~ Without DMT, telephone cable to the home is limited to 56kbps,(dial up)
~ DMT modulation is splitting of frequencies so each subchannel can carry 'up to' 56kbps (if the bin is fully bit loaded)... and merging to provide higher bandwidth.
The downside being the higher frequencies are more subject to signal deterioration.
~ DMT modulation is why DSL needs a modem (adsl modem/router) rather than a 'standard' router used for cable broadband.
~ Without bitswapping the line would lose sync if the SNR in any of the subchannels dropped too low and became unstable.
~ Bitswapping can be performed between any of the available subchannels
Cable broadband doesnt use DMT at all.
Optical Fibre uses Frequency Division Multiplexing* or Wave Division Multiplexing.
(See
Wave Division Multiplexing (WDM)).
Although fibre can be subject to attenuation, it is minimal when compared with copper.
Co-ax is used for the entry into the home, which as snadge mentioned is better quality copper than the twisted pair... and use of amplifiers if needed to ensure against signal deterioration. - Think how ethernet doesnt need/use bitswap either. This length of co-ax only has a relatively short run.
*DSL also uses FDM to separate the upstream and downstream channels. DMT splits it into subchannels.
IIRC Bitswapping is a standard in g.DMT not just the rate adaptive products - its interleaving/FEC that doesnt occur on the traditional fixed rate products.
I
think adsl2/2+ may use a different/better bitswap algorithm as it handles SNR slightly differently.. and bit loading of min 1 bit per bin (3dB SNRM) when compared to min 2 bits (6dB SNRM) of adsl1.
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edited to add
Excellent and informative post by snadge - thank you