On Fri, 14 May 2010 20:00:11 -0700, Darren New wrote:

> Jim Henderson wrote:
>> Assuming the switch isn't multicast aware.  I wouldn't be surprised if
>> some were these days (but I haven't looked at it recently).
> 
> Um, no. Even so.
> 
> If you have one cable coming into the university campus, and a network
> for each building, the router is going to have to send the packets to
> each building, duplicating the packets, regardless of how "aware" anyone
> is.

Yes, but that's not a 1:1 transmission (compared to the receiving 
clients).

>> The difference between, for example,
>> using unicast to push an image down to 15 workstations on a subnet and
>> using multicast to push an image down to 15 workstations on a subnet is
>> a significant reduction in overall network traffic.
> 
> Only for that one subnet.

The router is part of the subnet, though.  It retransmits upstream if the 
TTL hasn't expired (and it's configured to do so).

> It's better than a unicast stream to each destination, yes. That doesn't
> mean IP isn't point-to-point, if you factor in the broadcast address as
> meaning "one subnet is the point."

That's a bit like saying shouting is point-to-point, though, because the 
target "point" is a group.

Jim

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