Tony Li wrote:

Ok, it's not clear to me that a niche application implies that the amount of traffic is insignificant. If UUnet decides to deliver live real-time CNN to all desktops in all of their customers, that IMHO might be significant.

Hmmm... Isn't that in the definition of "niche"? There always were very high-bandwidth applications (like access to supercomputers). If there's enough money in those applications, they'd merit building of separate networks. So far i see equipment, software and operational costs of multicasting by far exceeding any possible gain, for public carriers. | PS I do not see how isolated network violates "all assumptions". Well, my primary assumption was that we're talking about global Inetrnet, not about relatively small private networks.

For example, you assumed (implicitly) that arbitrary systems could become mcast sources. Clearly the UUnet model does not allow this. This makes the problem tractable.

If we don't allow arbitrary systems to be sources, then we already have the network designed for that kind of traffic - already deployed and accessible to many more customers than Internet. It's a lot cheaper to fly a bird up there than to drag T-1 to every house. BTW, how do they fix security problem with mcast packets having forged addresses? | And i fail to see why the same functionality (and a lot more) | couldn't be implemented in application-level host-based | caches/mcast servers. There's no particular reason to drag these | functions into core gateways.

Once again, if the traffic volume is significant, there would be a significant bandwidth savings.

Doing multicasting in host software allows _bigger_ bandwidth savings - because things like rate conversion and retaining of data for delayed transmission can be done closer to clients. Actually, CNN "on TV" is the perfect example - they run the same segments over and over again. Of course, to do that with significant traffic volumes one would need to have real big computers in POPs. Sounds like something somebody's building. --vadim