At 8:45 PM -0800 12/12/04, Kon Wilms wrote: >On Sun, 2004-12-12 at 18:02 -0500, Manfredi, Albert E wrote: >> We've been over these tradeoffs many times, and the >> upshot of it is that unicast cannot save on bandwidth >> unless the number of viewers on the network is lower >> than the number of TV channels available to choose >> from. > >Well unfortunately the writer of the article doesn't know what he is >talking about and he really *does* mean multicast. Or he is talking >about some new IPTV system that is doing something that everyone else is >not (doubtful). > >Unicast adds nothing except more pipe bandwidth and headend server load. >You can still track user operations just as easily as fully-fledged >unicast sessions by doing delayed unicast reportback and initial >requests for decryption keys et al to 'join' a session. Switching is now >intelligent enough to prune sessions even if only one person is watching >the broadcast. And you bet your bottom dollar all the channels coming as >IP contribution feeds are being multicast as the broadcast channels they >are. > >Handing out packets with continuous handshaking is so passe. :-) > >Cheers >Kon The author knew exactly what he was taking about, but he did not describe it precisely. In essence, there are two segments of the IP network that are used to get packets into the home. The first link is between the head-end and the neighborhood router. IF ANYONE in the neighborhood wants a specific channel, then the neighborhood router joins the IP multicast for that channel which is available from the router at the head end. IF NOBODY in the neighborhood is watching a specific channel, then it IS NOT carried on the link from the head-end to the neighborhood. This frees up bandwidth on both segments of the network as described above. At the neighborhood level, if multiple homes want the same channel, then the IP multicast packets are routed to multiple homes. You can think of this as a "filter" which only passes packets that are needed in the neighborhood from the head-end. This is not that different from the way the Internet works, however, it is much more manageable in a local, private, branching -ree network environment. The telcos will be even better equippend to deal with this, as they can connect your home directly to the correct channels right in the central office, if they so desire, or they can mimic what the cable guys are doing, by putting routers out in the neighborhoods. And both can also put servers into the neighborhoods to deal with on-demand packets that a re heavily used. Regards Craig ---------------------------------------------------------------------- You can UNSUBSCRIBE from the OpenDTV list in two ways: - Using the UNSUBSCRIBE command in your user configuration settings at FreeLists.org - By sending a message to: opendtv-request@xxxxxxxxxxxxx with the word unsubscribe in the subject line.