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cable & dsl

Blim
Grafter
Posts: 462
Registered: 06-03-2012

cable & dsl

how come you can have more than one person per cable line with upto 300mb and dsl can only have one?
Is vdsl anything like cable?
Will cable be a thing of the past when FTTP rolls out?
My local cable company already dose FTTP but at a cost. If they went fully fibre they would no longer be classed as cable and just a alternative to BT.
2 REPLIES
kmilburn
Grafter
Posts: 902
Thanks: 2
Registered: 30-07-2007

Re: cable & dsl

For clarification,  cable is short for 'cable television',  and is a system of distributing television programs to subscribers via radio frequency (RF) signals transmitted through coaxial cables or light pulses through fiber-optic cables.
Technically, more companies are supplying cable television now, given the ability to stream TV over the internet.  Even BT can now be considered a 'cable' operator because of BT Vision.
With traditional cable network, most systems use hybrid fiber coaxial (HFC) distribution; this means the trunklines that carry the signal from the headend to local neighborhoods are optical fibre to provide greater bandwidth.
The fibre trunkline goes to several distribution hubs, from which multiple fibres fan out to carry the signal to boxes called optical nodes in local communities.
At the optical node, the light beam from the fibre is translated back to an electrical signal and carried by coaxial cable distribution lines on utility poles, from which cables branch out to subscriber residences.
This distribution pattern is similar to that now employed by BT with FTTC, but rather than coax it uses the phone line.  BT use VDSL between the cabinet and the subscriber,  cable has its equivalent, but I'm not sure what it is.
With FTTP in its purest form,  a single fibre will connect the subscriber to the distribution hub or telephone exchange,  however, this is not a cheap option.
More commonly,  the the fibre from the subscriber would connect to a local optical node on a cable network,  and BTs 'FTTP on Demand' system will connect to cabinet.
kmilburn
Grafter
Posts: 902
Thanks: 2
Registered: 30-07-2007

Re: cable & dsl

As for Speeds,  the only reason BTs FTTP is limited to 300mbps is for commercial reasons not technical ones.
Quote
Each fiber can carry many independent channels, each using a different wavelength of light (wavelength-division multiplexing). The net data rate (data rate without overhead bytes) per fiber is the per-channel data rate reduced by the FEC overhead, multiplied by the number of channels (usually up to eighty in commercial dense WDM systems as of 200Cool.
YearOrganizationEffective speedWDM channelsPer channel speed
2009Alcatel-Lucent15 Tbit/s155100 Gbit/s
2011KIT26 Tbit/s126 Tbit/s
2010NTT69.1 Tbit/s432171 Gbit/s
2011NEC101 Tbit/s370273 Gbit/s
2012NEC, Corning1.05 Petabit/s12 core fiber
While the physical limitations of electrical cable prevent speeds in excess of 10 Gigabits per second, the physical limitations of fiber optics have not yet been reached.