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Originally Posted by Tristan
The answer is by using the "localness" of cable. For the greater part of its journey, all data travels around on fibre-optic connections. It's only in the last few hundred metres -- at the local cabinet level -- that this is transfered to coaxial (copper) cable and into your house. If you can then send different data to different street cabinets, then you can re-use the same frequencies on the coax cable in different areas. I beleive this is already done with cable modem connections.
Any questions, please ask. Hope this is of some use,
Tristan
PS: Usual disclaimers apply. I don't work for NTL, Telewest, the On Demand Group, Sky, Homechoice, KIT, or anybody else for that matter. I have no qualifications in the subject. I could be completely, massively wrong.
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Thats a very good description Tristan, I don't work for ntl either but would just like to add that the VOD kit feeding the Nodal cabinets will be located in the current "Hubsites" The VOD streams will probably use DWDM technology to combine with the existing Analogue/Digital Tv and cable modem downstream. The current TV and cable modem services are fed to an optical transmitter (DFB) to feed generally 4 nodes in a ring of 8, the output of the DFB in the original architecture fed a 4 way optical splitter, the DWDM diplexer to add in the VOD service would be located between the DFB and optical splitter. It is likely they will follow a similar route as they did with cable modems, ie: use the existing architecture and further split down nodal areas as and when demand for the service increased. (The 4 way optical split could become a 2 way, and double up on DFB's for existing services etc or use a 2 way split to feed a 4 way with 2 DWDM's) The optical receiver at the node location has a photodiode that converts the RF modulated optical signal back to RF, because this is a wideband device it has the capability of accepting the different wavelenghts and demodulating them to their original frequencies.
Sorry if thats a bit boring, I thought there may be some who were interested in how that part of the network works. Most people appreciate what goes on in the headend and at local distribution level, but theres not usually much mentioned about the bits in between.