On Mon, 17 May 2010 12:15:13 -0700, Darren New wrote:

> Jim Henderson wrote:
>> What do you mean by "2-way broadcast"?
> 
> Well, FM radio would be a one-way broadcast. Coax ethernet would be a
> two-way broadcast.

OIC what you're saying, that the filtering is applied by the receiving 
end (either filtered by software or hardware).

>> Yes, but from a standpoint of multicast, there again, you get some
>> savings (and increased scalability).  I imagine (but don't know for
>> sure) that cable uses some sort of multicast scheme
> 
> Well, look, there really isn't something that's a multicast physical
> layer. 

Maybe Sirius radio?  Dunno, you might be right on that.

> Either the bandwidth is scaled per user, or it isn't. If we're
> all talking at the same frequency on a coax cable (say like old
> ethernet) and I'm transmiting, it's a broadcast, regardless of the
> destination address.
> 
> AFAIK, cable systems run fiber to a box in each neighborhood, and then
> have a tree of cables coming out from there, all carrying the same
> signal.

Would have to find someone who works for a cableco to confirm, 
obviously.  (Or a good article describing the technology)

>> all people who are watching channel 657 are likely part of a multicast
>> group of some sort,
> 
> Sure. And all people watching channel 657 are also receiving channel
> 652. They're just not tuning it. Just like FM radio.  (And I was talking
> about IP over cable, actually, not TV per se. :-)

That implies a pretty enormous total bandwidth on the coax cable coming 
into your house, then.  If you figure 40 SD channels and 40 HD channels, 
for example, that several megabits of digital broadcast being sent out to 
be filtered.

I was using cable TV as an example because it's data being sent over a 
network.  Data is data is data is data, after all. :-)

Jim

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