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Originally Posted by SMHarman
The old unvandalised Iron/Steel types are BT methings. NTL has the huge green three door 5ft tall cabs, the double door 3x3 cabs and the lift off top / front 1.5x2 cabs.
Lots of doors the 5ft tall ones with three doors? They will be around all areas. It's the NTL equivilant of a telephone exchange (so if you don't have Caller ID in your area, that is the box they have to install the hardware in (as you can see there are lots more of these than BT exchanges), also amplifiers to get the signal for TV distributed in the local area, batteries to power the phone exchange in the event of a power cut (as telco is an emergency service or something). Cable modem equipment (is this where the UBRs are?). It's the termination of the NTL backbone into the local cables.
Others with full knowledge of the NTL network will be better placed to elaborate on this though.
The two smaller cabs are very similar for content, one just holds more than the other, nothing powered in there, just lots of terminations.
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The big cabs are mux cabs aka nodal cabs.They are the termination point for the fibre. The muxs (multiplexers) turn the light into electric (as well as compressing all the signals etc.) from here on in it is twisted copper pairs to the home, via a DP/ DA cabs. It's not an exchange but it is fed from the exchange/headend/hub/switch. UBRs are kept at the headend etc not within the nodal cabs. It does have batteries in case of a power cut. I'm not sure of the life of them but its around a few days.
The fibre that terminates on the nodal cab is local ring fibre, the main ntl backbone fibre terminates at the headend/switch.
Generally speaking the nodal cab is telco only and they are usually accompanied by the main CATV cab, you will find two or sometimes three cabs sitting right next to each other. They usually feed an area of up to 500 homes.