Questions about HFC WDM and broadcast/narrowcast |

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Questions about HFC WDM and broadcast/narrowcast

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Questions about HFC WDM and broadcast/narrowcast

Hi all,

I'm working on some calculation software but need more understanding on (DOCSIS) signals with respect to optical WDM and narrow-/broadcasting. If've Googled blisters on my fingers but could not find a reasonable to-the-point explanation, so hopefully there's an expert among you who can help me a bit further. Some questions I have (lot of questions, but I'm describing architectures I can think of but may be never used in practice):

1) In the HFC network, do only legacy analog signals and DOCSIS exist? Or is, for example, within an optical WDM architecture analog/DOCSIS on one optical wavelength sometimes combined with (for example) WAN signals on another optical wavelength?
2) Does the entire signal for a consumer originate from a single optical wavelength in WDM or in other words: in a WDM structure are optical beams always modulated with the entire spectrum for a certain group of consumers? Or is it the case that analog signals are modulated onto one optical wavelength, DOCSIS onto other optical wavelengths and that after optical detection the analog signals are combined with one or more optical wavelength DOCSIS payloads in the electrical RF domain using a simple combiner (narrow-/broadcasting combining?)? This then means that the combined modulating spectra for different optical wavelengths can not have overlapping frequencies and thus are sub-efficient?
3) If the above described combining takes place, the payloads of how many optical beams are generally combined? Only 2? Or more...
4) Is it possible to do the above combining by leading two different optical wavelengths to a single optical detector instead of RF-combining after optical detection?
5) Is it possible in an HFC network using WDM that analog signals (or DOCSIS) may be modulated onto one optical wavelength, WAN (non-DOCSIS) on another wavelength and that at an optical node the WAN-data is converted to DOCSIS and then combined with the already available analog signals/DOCSIS from another optical wavelength?
6) I can imagine that DOCSIS for digital TV could be regarded as broadcast (in the sense as 'for everybody'), and DOCSIS for internet as narrowcast (in the sense as 'for a small group only') and that a WDM architecture is build up like that: one wavelength with digital TV and many other wavelengths with internet DOCSIS, and at each optical node for a group of consumers the digital TV is combined with one optical wavelength having internet DOCSIS payload. Or is it different?

Sorry for the large amount of questions....