> I've already sent Scott a lengthy reply off-list. For the benefit of
> others, I will simply say that I know the guy at his computer shop
> is wrong. It stands to reason, DSL runs over the phone line and
> you do not share a phone line with your neighbor ... (well, at least
> not anywhere DSL is available <g>). The 'location on the line' stuff
> is hooey, too.
>
> Randall
Randall, as usual, is correct.
But for simplicity, and to give a better illustration of how the
infrastructure is laid out, I will add my bit. DSL networks are setup the
same, architecturally, as phone networks (as Randall mentioned). This forms
what some people call star topology. Imagine a wire wheel, with each spoke
representing a different DSL line. The hub in the center, collecting each
of the spokes. The hub in this case is the central switching office of your
telephone company. Once at the CO (Central Office) the data all comes
together, so in a sense it is shared... but only much much further down the
line where heavy peer usage isn't really a problem.
Cable networks can be imagined as the inner tube on a wire wheel. The inner
tube house all the air molecules in one giant ring. If there was a breeze
in the inner tube, all the air would flow one direction around the inner
tube in circles. Cable networks are laid out in loop form primarily because
the coaxial cable in most neighbourhoods is not bi-directional, the majority
of the data can only flow in one primary direction. If anyone is familiar
with the old IBM Token Ring networks, it is a similar concept. Basically
one house is connected to the other, connected to the other, connected to
the other... until both ends of the ring meet back at the cable company's
equipment.
Both architectures are subject to slow downs when major internet faults
occur. DSL networks are inherently more redundant, since a break in one
line doesn't have any major effect on the others. When peer traffic is
higher (such as when all your neighbours stay in during a snow storm and
browse the internet for hours) the cable network is prone to much more
slowing than the DSL network. Security wise, the layout of cable networks
also works against the user as your 15 year old neighbour can sniff around
your packets if he wished (more an issue 3 years ago, than it is now).
Enforcement of bandwidth limits (how heavily you use your account
essentially) is more dominant on cable networks, as companies like Comcast
try to keep the network as speedy as possible. It is less important with
DSL networks, as no one else is infringing on the total capacity of your
single DSL connection. This is one of the reasons cable companies assign
IPs dynamically (randomly), so that it becomes more difficult to run
unauthorized internet services from your home. DSL providers typically
provide you with one or more static IPs, and if you wish you can run your
own web or mail server (depending on your User Agreement). Generally,
bandwidth conservation is less of a concern for the companies who sell DSL
than for cable, and it is this reason that most (if not all) cable companies
are heavy enforcers of their limits and user agreements.
There may be a few discrepancies in my over-simplified examples, but hey it
is like 1AM here and Monaco GP practice is on in 6 hours... and I just might
not sleep since I don't feel like it.
Cheers,
Kai
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