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Originally Posted by jungleguy
The physical design of the network varies regionally. (or franchise to franchise)
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What kind of headend kit do they use?
Dunno
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Varies depending which headend it is.
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Are they still delivering Analogue AND Digital down to customers houses?
You can subscribe to analogue but its gonna be turned off soon.
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To some customers, in some areas analogue is already turned off.
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Is there a central "feed" to all headends for channels coming from say Sky (non regional channels)
dunno
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No.
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Is there a local feed from Local stations to your local headend?
these are tough questions
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Yes
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How do they obtain the SKY and Terrestrial Channels from? ie dish or fibre?
At a guess Its from large dishes at the head end.
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Combination of direct fibre feeds and dishes.
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Do they fibre the headend output to ALL local street cabs or just some?
The network is designed as a fibre loop, so if there is a break the services can be supplied from the other direction if that makes sense. Its fibre to all cabs then coax to the houses.
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Only nodal cabinets, and it's not a fibre ring to the cabinets it's a star network. A fibre break means bye bye node.
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What speed is their green cab fibre network? STM-1 / STM-4 / STM-16 ?
Are you doing research for BT? i hear they'll be laying cable soon?
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None of the above as far as cable TV, etc, go, it's not SDH nor is the signal travelling along the fibre digital, and the bandwidth depends on the area. Some areas use DWDM while others carry a single wavelength. The only SDH / PDH being used is to carry telco and would very rarely be above STM-1. You can get a lot of 64kbps phone calls into 155.52Mbit
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Are all green cabs the same or are some 'master' ones?
Some cabs are bigger and referred to as 'main distros'
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There are bigger cabinets which contain telco multiplexers. From the CATV point of view there are 3 kinds of cabs, nodes which terminate fibre, trunks which as they suggest are coaxial trunk amplification cabinets, and the smallest kind which are line extender cabinets which usually feed small areas such as a single street.
By small I am not referring to physical size necessarily though the biggest cabinets are telco or optical muxes.
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How many households can a green cab supply before its "overloaded"
EX NTL 80%, ex Telewest 120%.
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Ummm...
There's no real definite figure if you are referring to broadband, it depends on how much bandwidth has been allocated to that
nodal cabinet and how much usage there is. There could be anything from 250 to 2000 homes sharing a single piece of fibre.
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Is there a distance limit on the length of coax from the Green Box?
Yes but they can pull RG-11 cable which is fatter, the problem being fatter cable takes up more capacity of the ducting, so less cable can be pulled through it before it is blocked up.
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Ideally they try and avoid going over a 100m run from the tap in the cabinet to the home. As above if signal levels are low a lower resistance larger cable can be pulled.
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How do they get the right signal levels in everyones house ie near and far houses?
The tech measures it, also different taps in the cab give a different signal strength.
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What he said. There are 3 different levels of resistance in the cabinet usually from 3 different taps which supplies some level of granularity, and for finer adjustment attenuators can be used.
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What frequency range are we talking about in a cable network?
no idea
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Dealing with what you'll find on VM's network only...
On upstream it's one of the following depending on network:
5MHz - 30MHz (Cheap rubbish)
5MHz - 42MHz (DOCSIS / NTSC Systems)
5MHz - 50MHz (Extended DOCSIS / Non-NTSC)
5MHz - 65MHz (EuroDOCSIS)
On Downstream
On decent NTSC cable systems downstream spectrum starts at 50MHz.
On DOCSIS (not EuroDOCSIS) systems running the same split it starts at 50MHz.
On fully EuroDOCSIS / PAL compatible systems it starts at 88MHz.
Actually here you go, specs of the filtering hardware that might be used (diplex filters):
Code:
Passband Low port (MHz) Passband High port (MHz)
0 to 10 14 to 750
0 to 33 43 to 750
0 to 40 50 to 750
0 to 48 54 to 750
0 to 65 88 to 750
On the VM network a very few areas max out at 450 or 550MHz, most max at 750MHz and a very few at 880MHz.
Please see this link for a more generic overview:
http://en.wikipedia.org/wiki/Hybrid_fibre-coaxial
HTH.
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Re: VirginMedia Network Technical Diagrams?
