>>>The content >>>sent from the IETF can be received with Real, Media Player, Quicktime, >>>IPTV, vic/vat, etc. >>> >>Most of those are not multicast--and they certainly aren't conferencing. Every single one is absolutely multicast-capable. Even better is that there are codecs that can generate a stream that all the players can receive. In other words, interoperability works well if you use the right format. >>>Also, there are plenty of (surviving) companies offering non-conferencing >>> >>I was talking about conferencing. See above, though you can certainly question their state of "survival". ;-) Also see vbrick.com. Heck, even polycom has a multicast solution. Really, there are plenty of companies that have multicast-based conferencing solutions as part of their product lines. What it seems like you miss from not doing some homework is that multicast is a working solution with working tools. Granted, it isn't widely deployed. Granted, inter-domain deployment may not be widespread at all. But you seem to miss that there is significant use of multicast... even more so inside of corporate networks (something we can't see from general monitoring). >>>>>but consider: once you start running a >>>>>multicast session over the Internet, anybody who's within the TTL range >>>>>can intercept it. >>>>> >>>Same with UDP traffic. Same with TCP traffic. >>> >>No, those can be intercepted only by tricking the routers. Multicast >>specifically permits anyone to pick up the traffic just by asking for it. First point: not necessarily. Second point: as long as you know the group address. with large volumes of multicast traffic out there you also have a nice 28 bit key, i.e. it is now infeasible for a host to join every group and expect not to be overwhelmed with large amounts of traffic. Finally, bottom line is if the content is valuable you at least need some basic protection... something like the equivalent of the club. To use content-value or privacy or anything else along these lines as a reason for not using multicast is pretty weak. -Kevin